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Training manual

Inductive Sensors

Training manual

2

You will find further information, data sheets, prices etc. at: www.ifm-electronic.com

Training manual Inductive proximity switches (March 2003)C:\lokal\s100e.doc 10.01.07 11:55

Guarantee note

This manual was written with the utmost care. However, we cannot assume any guarantee for the contents.

Since errors cannot be avoided despite all efforts we appreciate your comments.

We reserve the right to make technical alterations to the products so that the contents of the training manual maydiffer in this respect.

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Contents

1 Introduction 5

1.1 Proximity switches in industrial processes 5

1.2 Notation 7

1.3 On the contents 7

2 Basics 9

2.1 Electromagnetic induction 9

3 Features of inductive proximity switches 12

3.1 Comparison 123.1.1Limitation 12

3.1.2Mechanical and electronic switches 13

3.2 Technology and operating principle 15

3.2.1Basic inductive sensor 15

3.2.2Signal generation 19

3.2.3Evaluation 21

3.3 Practical use 23

3.3.1Operating distance 23

3.3.2Hysteresis 28

3.3.3Correction factors 30

3.3.4Switching times and switching frequency 34

3.3.5Notes on practical use 39

3.4 Mounting instructions 413.4.1Flush / Non flush 41

3.4.2Mutual interference 44

3.4.3Mechanical stability 46

3.5 Technology and operating principle K1, K0 48

3.5.1Designations 48

3.5.2Conventional inductive sensor 48

3.5.3Sensor with K = 1 51

3.5.4Sensor with K = 0 54

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4 Inductive proximity switches of ifm 56

4.1 Mechanical properties 56

4.1.1Structure in general 56

4.1.2Chronological development 56

4.1.3Modular technology 60

4.1.4Application of the efectorm 62

4.1.5Production of the efectorm 63

4.2 Designs 63

4.3 Electrical data 65

4.3.1 Important parameters 65

4.3.2Overview 67

4.4 Switches with special features 68

4.4.1Use in hazardous areas 68

4.4.2Switch for quarter-turn actuators 69

4.4.3Units with mounting aid 70

4.4.4quadronorm units 72

4.4.5Non polarised units 73

4.4.6Self-monitoring systems 73

4.4.7Weld-field immune units 74

4.4.8Units with increased operating distance 77

4.4.9Units for overflush mounting 78

4.4.10 Special correction factors, K1, K0 80

4.5 Criteria for practical use 82

5 Application examples 85

Annex 90

Technical glossary 91

Type key 96

Production code 98

Index 99

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1 Introduction

1.1 Proximity switches in industrial processes

What for? Automated production processes require sensors for supplyinginformation. They provide signals about positions, limits, levels or serve aspulse pick-ups. Without reliable sensors even the best controller is notable to control processes.

In general, all these sensors consist of two parts: The first registers thechange in the physical conditions (basic sensor), the second converts thesignals of the basic sensor into electrical output signals (signalprocessing).

In general, a distinction is made between binary sensors which provide adefined high-low signal and analogue sensors which are preferably usedfor temperature, distance, pressure, force measurement, etc. The sensorsupplies an analogue signal which is further analysed for measurementand control.

Figure 1: Structure of a sensor

Sensor The figure shows the general diagram which basically applies to everysensor. The sensors only differ in some details, e.g. individualcomponents are not used or cannot be used separately. Sometimes thebasic sensor is also called just sensor. In this case it must be seen from thecontext whether the whole unit or the basic sensor is meant. Some unitsconsist of separate components, e.g. NAMUR sensors or often alsotemperature sensors. Here the transducer is connected to a separateevaluation unit or amplifier.

Intelligent In Figure 1 the characteristic feature of the intelligent sensor is itscommunication capability. But this term is also used in a different sense.A sensor which only supplies the binary information  object detected or  object not detected

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is in general not called intelligent. But a sensor which is able to supplyadditional information, e.g.  object reliably detected or  object unreliably detectedis considered to be intelligent.

Binary and digital In order to avoid misunderstandings the difference is briefly explained.Binary means "two states" (on/off). An analogue signal which can haveany value within certain limits is often digitized today so that it can beprocessed in electronic controllers. This is done using an A/D converter(analogue to digital). It divides the analogue signal into steps. Thenumber of steps results from the number of the bits used. Whereas onebit can only take two values, 8 bits can take 256 and 10 bits 1024. This isalso called resolution. Less than 8 bits are seldom used because theresolution would then be too coarse. More than 12 bits are also seldomused because it does not make sense if the resolution is much higherthan the measurement accuracy.Encoders are an exception. They provide digital signals straight away (seetraining manual encoders).

This text mainly deals with binary sensors as replacement for mechanicalswitches. It provides information about the operating principle, featuresand criteria for using inductive sensors. Furthermore it presents typicalapplications and suitable types to make it easier for the user to select theright unit for his application. Many names are used for inductive sensors:Proximity switch, initiator, inductive sensor, non-contact position sensor.In addition, manufacturer-specific names are also used, e.g. efector(registered trademark of ifm electronic gmbh). The term proximity switch,however, is standardised and used in the following text.

In industrial applications mainly one system has been tried and tested:Inductive proximity switches. These sensors are suitable for the non-contact detection of a wide range of different conductive materials.

ifm has produced non-contact proximity switches for over 30 years. Theyare used in all industrial applications. What makes these units and inparticular the efectors so successful?

The inductive sensor withstands interference best (see training manualphotoelectric sensors). With the experience of the past decades the unitshave been improved. For more than 20 years ifm has granted a 5-yearwarranty for standard units. Due to its high reliability the inductiveproximity switch has virtually replaced the mechanical switch. Moreover,new applications come up again and again where a high degree ofautomation was inconceivable in the past.

Next generation When the electronic proximity switch was launched it was simply seen asa replacement for the mechanical switch which has now been replaced.This means different types were developed, produced and sold to theuser who contacted the manufacturer if the sensor needed additionalfeatures in his application. After many years of experience with the unitsanother point of view can be taken. The first question now is: Whatfeatures does a sensor need for a certain application?

Are there any examples? In the food industry for example the following conditions must be takeninto account:

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  Temperature shocks (cooled fruit juice � hot cleaning liquid)  New cleaning agents (are to creep into all crannies to remove build-

up, residues, i.e.: high demands on ingress resistance)  Aggressive media (fruit juice also contains acids!)e.g. in metalworking  Coolants (surface wetting increasingly improved, i.e. there are also

high demands on ingress resistance, moreover the medium can reactwith the sensor materials)

To fulfil such requirements, the efectorm was developed as a newgeneration. It is described in section 4.1 how the above-mentionedconditions (temperature, ingress resistance, materials) are met.

1.2 Notation

For a better understanding a few notations are explained to makereading the text and finding information easier.

Keywords Keywords which refer to the topic to be dealt with in the followingsection are given in the left margin.

What does FAQ mean? This stands for Frequently Asked Questions. This term is also used formodern electronic media. Almost everybody starting to cope with a newtask asks the same questions. Sometimes FAQs instead of keywordsprecede a section. To differentiate them from simple keywords, they arewritten in italics.

( 4) A figure in round brackets in the left margin refers to a formula used inthe text, e.g. see (4). Of course these formulas do not need to be learntby heart. They are meant to make understanding of the subject easierbecause a formula similar to an illustration describes a relation morebriefly and clearly than many words.

1.3 On the contents

Basic information about inductive proximity switches is found in thismanual. Important terms and relations are explained, state-of-the-arttechnology and technical data of ifm units are presented. This results inthe following structure.

1. Introduction The introduction is followed by the chapter:

2. Basics Here the physical basics that are useful for a better understanding of theoperating principle and features are briefly presented. A few basic termsare explained.

3. Features of the inductive proximity switchesHere the limitation to binary sensors is discussed. Other more complexsystems in practical use are presented. Then comes a general overview ofdifferent sensing systems to make the correct classification of inductiveproximity switches and the decision where they can be used and wherenot easier. The knowledge of their features, advantages anddisadvantages enables successful use.

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4. ifm units Here the data of ifm sensors are listed and explained. The mechanicalstructure, electrical features and use are described. Special units arepresented.

5. Applications A few applications with illustrations are briefly described.

Annex This manual is intended to help you with your self-study. Thereforeimportant terms are briefly explained again in the technical glossary. Thepoints which are important for the ifm units are presented in detail in thechapters preceding the glossary. The index helps to look them up. Thetype key and code for the production date are also explained.

Much success! With this basic information everybody should be able to benefit from thisproduct and to use the efector 100 successfully.

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2 Basics

Do I have to know this? Many operators use inductive sensors successfully without knowing thesebasics. In the following chapters several notes on practical applicationsare given. The basic knowledge helps to structure such information. Thismakes more sense than learning a dozen rules by heart. Understandingthe operating principle also makes the selection of the switches and theirapplication easier. Some basic knowledge is necessary to be a competentpartner. The physical basics are outlined in this chapter. This description is not toolong and theoretical. Only essential information is provided.

In the following section a few basic terms are explained which will thenbe used without any further explanation in 3.2. Those who are familiarwith these basic terms can skip this chapter or come back to it if needed.

2.1 Electromagnetic induction

Flux If magnetic field lines penetrate a surface, this is referred to as magneticflux . Figure 2 is only a simplified representation. It is assumed that themagnetic field is homogenous (identical over the whole surface) and thedirection is everywhere perpendicular to the surface.

Figure 2: Magnetic flux

( 1) = B A

[ ] = 1 Wb = 1 Weber =1 Vs, magnetic flux[B] = 1 T = 1 Tesla = 1 Vsm-2 magnetic flux density, magnetic induction[A] = 1 m3 , area

It may be confusing that the quantity B itself is sometimes referred to asmagnetic induction. This should not be mixed up with the phenomenonof induction.

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Faraday The following relation was first discovered and described by the Englishphysicist Faraday. It is therefore called Faraday's law. It is one of thebasics in electrical engineering. Important applications are for examplegenerators, transformers and eddy current brakes. However, the sensordoes not brake objects, but its operating principle is also based on eddycurrents.

Figure 3: Eddy currents

( 2) U = - / t

[U] = 1 V, electrical voltage[ ] = 1 Wb = 1 Weber =1 Vs, magnetic flux[t] = 1 s, time

The rate of change of the magnetic flux is essential. This also explains theimportance of the alternating current. A transformer for example canonly be used with alternating current. The greater the change of the fluxwithin a time interval, i.e. the faster it changes, the greater is the inducedvoltage. It is always present even in vacuum but can of course onlygenerate a current if there are mobile charge carriers. So an eddy currentcan be created in the surface of Figure 3 if it is imagined as a thin plate ofconductive material. From this important conclusions can be drawn forpractical use:

  Conductivity is decisive  Magnetizability can be another effect

Energy If electric current flows through a conductor, heat is generated (apartfrom superconductors). Where does it come from? This can for examplebe explained with the generator. Work must be performed permanentlyif energy is to be supplied permanently. If much energy is taken from atransformer on its secondary side, e.g. in case of a short circuit, it mustbe supplied by the primary side. If on the primary side the current islimited, the voltage goes down to the short-circuit voltage. This effect is

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also used for the inductive sensor (see 3.2) even if the energy volume isso small that the heat generated by the eddy currents is virtually notmeasurable.

Lenz This name refers to a definition of the negative sign in ( 2) and is knownas Lenz's Law. It states that the effect of induction is always opposite toits cause. With this in mind it is easy to understand the next section.

Skin effect The skin effect occurs for example for eddy currents generated in aconductive plate (see Figure 3). If the surface and directions remainconstant, the voltage can only be induced by the change in the magneticflux density B according to ( 2). Eddy currents are then generated in theconductor. But current-carrying conductors also have a magnetic field.This means a magnetic flux density is part of eddy currents. How is this"induced" B related to the one generated? The answer is given by Lenz'sLaw: It is opposite. So the magnetic field is weakened, i.e. preventedfrom penetrating the conductor. It remains at the surface, i.e. in the skin.This also explains that high-frequency currents do not flow withinconductors but at their surface. This has also an effect on the detectionof thin foils by means of inductive proximity switches (see 3.2).

Where are the fluids? It is easy to understand what is the flux of water flowing through a tube.It is for instance the amount of volume per time. But what means the fluxof a magnetic field and what is flowing there? In a magnetic field there isno real flow. But for electromagnetic (and also for gravitational) fieldsapply the same relations, rules, equations etc. as for real fluids. Because itis easier to understand real fluids , they can be used as a model also formagnetic fields. This is the reason why the same expressions, for instanceflux, are used. The advantage is, that you have to understand only oncethe basic concepts. Then you may apply this knowlwdge to manydifferent cases, as fluids or magnetic fields etc.

Is this all? These basics are sufficient to understand inductive proximity switches.The rest "only" refers to technical matters. Again it's the little things thatcause big problems! Much know-how acquired during decades is neededto build a sensor operating on this principle which withstandsinterference best (see training manual photoelectric sensors).

Knowledge of the basics is no end in itself but facilitates understandingof the sensor characteristics which are important for practical use. Thisfor example concerns the detection of thin foils, small or irregularlyshaped objects, detection of objects with different conductivity, etc.

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3 Features of inductive proximity switches

3.1 Comparison

3.1.1 Limitation

Position sensor This sensor belongs to the group of position sensors. Photoelectric orcapacitive sensors also belong to this group. Criteria to select the suitableposition sensor are given in the training manual photoelectric sensors,criteria to select an inductive proximity switch in the following sections(e.g. 3.3.5). Another group are the fluid sensors. There is no cleardistinction between these groups, they overlap. Capacitive sensors withbinary output for example are often used for level monitoring of fluids.But as a position is detected after all they can still be considered to beposition sensors.

Alternatives The criteria to select a position sensor for a certain application aredescribed in the above-mentioned documentation. Measuring systems forlengths and distances are no real alternative to inductive proximityswitches because the task to be performed is different. The onlyalternative to the inductive sensor as binary sensor (this point is treatedfarther below) is the mechanical position switch. This is detailed in 3.1.2.

Binary In general, the inductive proximity switch is used as a binary positionsensor (see 1.1). The external evaluation of the analogue signal of thetransducer only makes sense in special cases. To be able to use this signalfor distance measurement, very restrictive conditions must be taken intoaccount. It must for example be ensured that the detected objects arevery similar. Furthermore the object must approach the sensor in alwaysthe same way, i.e. mechanical guidance must be accurate (see 3.3.2 andFigure 21). ifm supplies no inductive proximity switch with an analogueoutput as standard unit.

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3.1.2 Mechanical and electronic switches

Figure 4: Schematic representation of a mechanical switch

The following figure shows an example of a mechanical limit switch.

Figure 5: Mechanical limit switch

If an inductive sensor is compared with a mechanical limit switch, themechanical limit switch has the following features:

  For actuation a switching force is required, mechanical contact isnecessary

  Only low switching frequencies can be achieved  Calculation of angle of approach and travel (switch-on graph)

necessary  Wear of the mechanically moved parts  Change of the switch points due to wear  Transfer resistance of the contacts changes  Life is limited due to the number of switching cycles  Contact bouncing leads to undefined signals  Due to the contact resistance a certain minimum current is required

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  High susceptibility to dirt and moisture  Even slight dirt leads to corrosion  Completely different designs or sensing elements (rolls, plungers,

levers, etc.) are necessary for different applications (e. g. approachfrom front or side)

The proximity switch which converts without contact the approach ofobjects into switching signals has the following features:

  The movement of the objects to be sensed is not impeded  Short response and switching times  High switching frequencies  No wear, no change of the switch points  Life not limited due to the number of switching cycles  No failure due to dirty or corroded contacts  No contact bouncing due to the electronic, i.e. non-contact output

(transistor, thyristor, triac)  Signals are suitable for further processing in electronic circuits  No need to calculate the travel (switch-on graph)  Only one design for different movements

Figure 6: Replacement for different designs

  Very small designs feasible  Insensitive to moisture, dust, oil, etc..

The following figures show the difference in the switching response:

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Ideal switchno delay

Proximity switchswitches in the µs range

Mechanical switchhigh delay

switches in the ms rangealso contact bouncing

Figure 7: Switching delays

It is obvious which of the two types comes closest to the ideal switchingresponse (i.e. low-high change without delay). The non-contact proximityswitch (efector) performs this task almost perfectly and provides thesignal which can be evaluated more easily and more reliably.

When comparing all features it can be clearly seen that the inductiveswitch only has advantages over the mechanical limit switch. So usingnon-contact sensors is a benefit for the user, which increases theoperational reliability of his installation and reduces the operating costthus improving competitiveness.

3.2 Technology and operating principle

3.2.1 Basic inductive sensor

Electromagnetic field / Resonant circuit An LC oscillator generates an alternating electromagnetic field with afrequency between 100 kHz and 1 MHz. Here the magnetic field isimportant, any air-core inductor can be used to generate it.

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ï î í ì

1 Ferrite core2 Coil3 Housing4 Magnetic field

Figure 8: Field of an inductive sensor

Below the sensor is built up step by step: from the coil to the sensor.

î

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Figure 9: Field of a coil

Coil with core It can be seen that the field is generated symmetrically to the coil withoutany preferred direction. In practice, however, no air-core inductor is usedbut attempts are made to give the magnetic field a preferred direction bymeans of a highly permeable ferrite material. By integrating the coil intoa ferrite core the magnetic field of the coil concentrates on the area infront of the sensor, i.e. in this area the sensor becomes particularlysensitive. The field distribution is similar to that of a lifting magnet withthe only difference that for a lifting magnet a static field is generated.

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1 Coil2 Ferrite core

Figure 10: Coil with core

Screen If coil and ferrite core are additionally surrounded by a metal screen, themagnetic field is exclusively limited to the area in front of the sensor.Thus such a sensor can be completely surrounded by metal on its sideswhich does not affect its switching response. These sensors are suitablefor flush installation (see 3.4.1).

1 Coil2 Ferrite core with outer metal ring3 Housing

Figure 11: Coil with screen

If an electrically conductive material passes through this alternatingmagnetic field, eddy currents are induced in the material in accordancewith the law of inductance which draw energy from the LC oscillator ofthe sensor.

This system can be compared with a transformer. The primary winding isrepresented by the coil, the secondary winding and the load by theelectrically conductive object. Primary coil and secondary coil are coupledvia the field, i.e. in principle this is an air-core transformer.

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Figure 12: Block diagram

The amount of the eddy current losses depends on several factors:

  Distance and position of the object in front of the proximity switch  Dimensions of the object and its outer shape  Electrical conductivity and permeability.

This means: For the binary sensor the distance where it changes itsswitching state depends on all these factors (cf. 3.4.1). Thereforeproximity switches are normally designed as binary sensors. An analogueoutput signal is less suitable, for example, for distance measurement.

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3.2.2 Signal generation

Figure 13: Schematic representation oscillator circuit

Oscillator circuit As can be seen on the diagram the eddy current losses can be taken intoaccount by changing the resistance R2 in the oscillator circuit. If theobject is brought so close that the equation

( 3)4

3

2

1

RR

RR

is no longer valid, the operational amplifier can no longer supply theenergy required to maintain the oscillation, so the oscillation isattenuated (damped) or breaks down. So the circuit represents afunctional inductive sensor which converts the two states  object outside the critical distance = oscillator oscillates with a large

amplitude and  object within the critical distance = oscillator oscillates with a small

amplitude or not at allinto an easily evaluable electrical signal.

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1 Proximity switch not damped2 Proximity switch damped

Figure 14: Damping (trigger stage)

What does "damped" mean? You often hear: "The sensor is damped". This is easier to understandwith the information given above.

Other evaluation methods are also possible. So the change in inductanceor the quality factor of the oscillator circuit can be measured in adifferent manner. But so far the method described above has proven tobe the best choice. But to obtain special features, other methods are alsoapplied, see 3.5.

Resistance characteristics In the following figure the energy consumption of the detected object isrepresented as an apparent change in resistance in the oscillator.As can be easily seen, this relation is clearly non linear. This confirms thatan inductive proximity switch is of only limited use for providing a signalwhich is proportional to distance. It is therefore mainly used as a binaryswitch.

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Figure 15: Resistance characteristics

Operating principle As the energy loss caused by the object is determined using an oscillator,the operating principle can be described as follows: Inductive proximityswitches take advantage of the physical effect of the change in thequality factor in a resonant circuit caused by eddy current losses inmaterials of good electrical conductivity.

3.2.3 Evaluation

First, the information contained in the oscillation amplitude must beconverted into a switching signal. This is done by rectifying andsmoothing the oscillation (demodulation). This signal is transferred to aSchmitt-Trigger stage. So only one of the two possible switching states"current flows" or "current does not flow" can be taken.

Signal processing / output stage The basic sensor which belongs to the oscillator circuit is followed byfurther stages which evaluate the signal. They are shown in the followingblock diagram. A comparison with the training manual capacitiveproximity switches clearly shows that inductive and capacitive sensorshave a similar electronic structure. The differences are as follows: type ofbasic sensor, type of oscillation and setting option for capacitive units.Only for a few special inductive sensors (large designs) the sensitivity isadjustable. The new generation of capacitive sensors operates on anotherprinciple, and so sensitivity is adjustable as standard.

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Figure 16: Block diagram

Clear condition If an object is exactly located at this switch point or if it approaches thispoint slowly ("creepingly"), the switching output may constantly changebetween the two states, which would result in output chattering. This isprevented by a clearly defined hysteresis which is generated electronically(see 3.3.2).

Time response Furthermore it must be ensured by a corresponding circuit that at poweron no wrong switching signal is produced, a power-on pulse suppressionmust be available. The time which elapses between power on and sensorreadiness for operation is called power-on delay time and lies in themillisecond range. Occasionally, this leads to confusion. The power-ondelay time is not the same as the switching time (see 3.3.4 or Figure 24).The latter is much shorter. Another quantity is the response time, i.e. thetime which elapses between presence of the object and switching of theoutput. It depends on the switching frequency (see 3.3.4) and is alsoshorter.

Figure 17: Power-on delay time

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Switching function For many units the switching function normally open or normally closedcan be selected. For former units this was also called programming evenif just a wire link had to be cut open.

Output To switch the output, solid-state switches like transistors and thyristorsare now widely accepted in the market. They have clear advantages overmechanical switches as regards lifetime, number of reliable switchingoperations, switching frequency, and bounce-free switching.

The few disadvantages, i.e. leakage current in the switched-off state,voltage drop in the switched state and higher sensitivity as regardsovervoltage and overcurrents (see training manual connectiontechnology) can normally be tolerated or more or less avoided by meansof suitable protective measures.

The block diagrams represent the general principle. Some types havespecial features, e.g. a second LED as mounting aid or setting option via apotentiometer.

3.3 Practical use

3.3.1 Operating distance

What does this mean? At first sight the answer seems quite easy. But on closer examination itbecomes obvious that this term is of prime importance for correctunderstanding. Inductive proximity switches operate without contact. Theobject to be detected only has to come close to the sensor. But whatdoes close mean? The distance where a proximity switch can reliablydetect an object is called operating distance. It depends on  the type and design of the sensor  the specific characteristics of the individual switch  external conditions  shape, dimensions and material characteristics of the objects to be

detected.

Rated operating distance (sn) A characteristic distance, i.e. the rated operating distance, is allocated toeach type and indicated on the type label. For inductive sensors itdepends on the coil, shape and dimensions of the ferrite core and thestructure of the sensing head, i.e. the basic sensor. As a rule of thumb, itcan be said that the longer the operating distance, the larger are theexternal dimensions of the sensor. The values are between 1 and 60 mm.For special types this can also be 100 mm. Instead of this designationwhich is laid down in the standard (IEC 60947-5-2) ifm uses the termnominal sensing range sn.

What does "rated" mean? This means that this quantity cannot be considered to be an absolutevalue but must be interpreted. How is the effective operating distancerelated to the rated operating distance? In other words: What does theoperating distance depend on? There are several influences.Different units of one and the same type cannot be completely identical.This means there are individual variations. Moreover, the sensor isexposed to changing environmental conditions, e.g. temperaturevariations, fluctuations of the operating voltage, etc. Objects near thesensor but which are not detected, e.g. stationary machine parts, can

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also influence the operating distance (cf. 3.4.1). Finally, the characteristicsof the objects must be taken into account. The effect of these influencesis explained below.

Standard To obtain comparable measurement results for the operating distance astandard measurement method is prescribed for inductive proximityswitches. This measurement method is defined in IEC 60947-5-2,formerly in the European standard EN 50010. It defines a standard squaretarget which is 1 mm thick. The side length a of the target must at leastcorrespond to the diameter of the sensing face or be three times therated operating distance of the sensor, if this value is higher The materialprescribed for the target plate is mild steel.

sn Rated operating distancesr Effective operating distancesu Usable operating distancesa Assured operating distance (switched on reliably!)A Sensing facea = d Diameter of the sensing face ora = 3 x sn if this value is higherTarget material: mild steel 1 mm thick

Figure 18: Standard measurement method for the operating distance

This measurement, however, only results in the operating distance of atypical individual switch under defined environmental conditions.Therefore fixed limit values are prescribed in the standard which all unitsof the manufacturer must meet in case of changing environmentalconditions and individual variations.

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Individual variations The rated operating distance sn which is indicated in the data sheet andon the type label is a reference value which does not considermanufacturing tolerances or variations due to temperature influences andvoltage fluctuations. The effective operating distance s r is more useful. Ittakes the component and manufacturing tolerances into account. Theeffective operating distance is determined at the rated operating voltageand an operating temperature of 23°C. It can deviate from the ratedoperating distance up to 10%. This covers the typical individualvariations. For high quality sensors this is not fully utilised. For theproduction of the efectors the component tolerances are kept to aminimum by precisely adapting every finished circuit to the operatingdistance. In practice, it is an advantage if sr is slightly below sn. For anefector with sn of 10 mm sr is approx. 9.8 mm.

Environmental influences In case of voltage and temperature variations the operating distance ofevery proximity switch may vary max. 10% from its effective operatingdistance over its whole guaranteed temperature and voltage rangespecified in the data sheet. This also applies when the mountinginstructions are adhered to. If this is not possible, the tolerance range of10% can shift upward or downward. As every electronic componentchanges its characteristics with temperature, it is difficult to meet thisrequirement. The flush mountable type (see 3.4.1) has the highestrequirements. To fulfil these requirements, thorough selection of thecomponents and optimisation of the circuit design are required.

Usable operating distance su The operating distance thus obtained is called usable operating distancesu. It is between 0.9 and 1.1 of the effective operating distance. Whenconsidering all individual switches and operating conditions the usableoperating distance is 0.81 to 1.21 of the rated operating distance. Theminimum value of 0.81 of sn is important and interesting for the user. Arated operating distance of e.g. 10 mm would lead to an operatingdistance of 8.1 mm under extremely poor conditions. This is theminimum achievable operating distance sa. (assured operating distance).At this distance every proximity switch must operate reliably (referred tothe standard target).

Maximum value The maximum value of 1.21 of the rated operating distance is importantto avoid interference caused by remote objects. An object which isfarther away damps the oscillation a little, see the point "predamping"below. It can be clearly seen that such an object can influence theoperating distance by taking the hysteresis of max. 0.2 of the effectiveoperating distance into account (see 3.3.2). So every proximity switchmust switch off reliably at 1.43 of the rated operating distance.

Temperature variations How is the operating distance changed by external influences, e.g.temperature variations? No general rule can be given. The influencedepends on the design, rating of the circuit, characteristics of thecomponents, etc. In most cases the operating distance increases. This canlead to problems if as a result of this remote objects are detected whichare not within the range according to the standard. The output can thenswitch and stay in this state. Even if the sensor is operated outside thespecified range, e.g. at -40°C or at 100°C, it is not destroyed straightaway. But the switch point will shift. Frequent sharp temperaturevariations have a more negative effect on the sensor life. Due to thedifferent thermal expansion this can lead to mechanical tensions betweenthe different materials used for the circuit. The new efectorm switches

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(see 4.1.3) withstand even sharp temperature shocks much better. Thetest method for this feature is described in 4.1.4.

How precise is the sensor? The wide range of the allowed tolerances of0,81 sn < s < 1,21 sn

does not mean that the inductive proximity switch is inaccurate becausethe operating distance varies much.First, no individual sensor can cover the whole tolerance range. Fortemperature variations in the specified range for example a change of theoperating distance of 10% as defined in the standard occurs. Only if thesensor is replaced by another unit of the same type, individual variationsmust be taken into account. This means that if high accuracy is importantthe sensor may have to be readjusted. But in practice, such problemsseldom occur because the achievable accuracy is limited by otherinfluences, e.g. mechanical deformation, vibrations, etc.

Example For a better understanding a switch with a rated operating distance of 10mm is to be looked at. sr has been determined to be 9 mm. This meansdue to external influences, e.g. temperature or voltage fluctuations in thepermissible range the switch point may vary between 8.1 and 9.9 mm. Ifthis sensor is replaced by another unit of the same type, e.g. sr = 11 mm,the switch point can then vary between 9.9 and 12.1 mm. If the object(assumed to be of an easily detectable material with sufficient areasurface) is typically at a distance of 5 mm, no problems are expected dueto individual variations. This is an example of a general rule.

Rule of thumb As a rule of thumb the distance of the object (assumed to be of an easilydetectable material with sufficient area surface) is roughly half the ratedoperating distance. This distance is for example used when the switchingfrequency is determined (see 3.3.3).

Rules Here is a summary of the points which are of special importance forpractical use:  The sensor should be placed so that the object to be detected is

within the assured operating distance, i.e. 0...0.81 of sn. ifm providesunits with an additional set-up LED which signals that the object iswithin this range.

  If the sensor directly controls the movement of the object (e.g.switching off the motor), lateral approach must be preferred as dueto the switch-on/switch-off graph (see 3.3.2) the tolerance range issmaller (the risk of mechanical damage is also lower, see 3.4.3).

  Damping from the front is mainly used to detect presence of theobject, e.g. workpiece in a device or closed chuck, etc. Withmechanical devices like limit stops the assured operating distance canbe set.

Repeatability R This term and the measurement method are also defined in the standard.In accordance with IEC 60947-5-2 sr is measured for a voltage in therated voltage range for a period of 8 h. The operating temperature is 23±5°C. With this test the effect of intrinsic heating is determined.

What does this mean? In practice, it is interesting to know how the switch point varies if thesensor is approached several times by one and the same object in thesame way. It is not quite correct to call this repeatability because themeaning of this term is defined in the standard (see above). Nevertheless,the term is used in this sense, sometimes the term reproducibility is used.

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It is important that the value is much better if the conditions only changeslightly, e.g. in case of directly successive measurements. Under idealconditions in the laboratory a very high repeatability in the µm range canbe achieved.

Predamping What are the effects if other detectable objects, e.g. the metal wall of astationary enclosure or build-up of metal swarf, are close to the sensor?In such a case the efector is predamped. This means that the oscillationamplitude has already been slightly reduced by these objects but is stillabove the switching threshold. As a result of this only a little additionalinfluence is necessary, e.g. a remote or small object so that the outputswitches. Thus the sensor has become more "sensitive", the operatingdistance has increased. If possible, this should be avoided because therewill be a higher risk of malfunction (cf. 3.4). In some cases a new typecan be used which "selectively" only reacts to ferromagnetic materialsand is immune to aluminium chips (see 3.3.3).

Clear space To avoid predamping it is important to know how far an object may beaway, e.g. from an opposite wall of an enclosure so that the sensorfunction is not affected. In Figure 38 it can be seen that a distance of 3 xsn is recommended.

�Reliably off� What has already been discussed under "maximum value" above ispointed out again because of its importance for applications. Especially inconnection with predamping switching off may pose a problem.Switching on is not critical here. If the above rule of thumb (half the ratedoperating distance) is applied, the sensor reliably switches on if it ispredamped. In adverse cases, however, switching off may then no longerbe ensured. Here the hysteresis, see 3.3.2, must also be considered. Thesensor must only switch off at 1.43 of the rated operating distance. Ifsensitivity has been increased due to predamping, it can happen that itdoes not switch off at all.

Increased operating distance It can be clearly seen with predamping that a greater sensitivity of thesensor is not always an advantage. It can become more susceptible tointerference. In practice this means that the permissible temperaturerange would have to be limited because otherwise the temperaturewould inadmissibly influence the operating distance. In the standard IEC60947-5-2 certain designs are allocated certain (minimum) operatingdistances. With many years of experience it is now possible to makereliable inductive proximity switches which achieve much better operatingdistance values than stated in the standard without any restriction of thetemperature range (see 4.4.8). They are called units with increasedoperating distance.

Operating distance reduction This term is closely related to the increased operating distance. As theoperating distance increases the operating distance reduction alsoincreases. The unit may then no longer operate reliably. One requirementfor the development of units with increased operating distance is tominimise the operating distance reduction. These units are described in4.4.8. The term is explained in the following section.

What does it mean? To answer this question some mounting information is necessary (see3.4).For non-flush mountable units there must be a defined clear space in thesurrounding area. The influence of predamping thus avoided is thereason for the longer operating distance compared to flush mountableunits of the same design.

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Flush mountable units can be mounted flush, e.g. with a metal surface.They are shielded as much as possible from their environment. For thesame design the flush mountable unit has approx. half the ratedoperating distance of the non-flush mountable unit. In this operatingdistance predamping by the environment has already been taken intoaccount.If a flush mountable sensor is not mounted flush, it is not predamped. Itsoperating distance is normally reduced compared to flush mounting. Thiseffect is called operating distance reduction.

3.3.2 Hysteresis

Context This subject is often treated in combination with the operating distance.But for the sake of clarity it is described separately in this section.

Is a hysteresis requested? The hysteresis is the difference between the distance at which the outputswitches when the object approaches and the distance at which theoutput switches back again when the object moves away. If an object islocated precisely at the switch point, the switching output may constantlychange between the two states ON and OFF. This is prevented by aclearly defined hysteresis which is generated electronically. The differencebetween switch-on point and switch-off point integrated into the circuitresults in a range of 1 � 20% of the operating distance in which theobject to be detected must move so that the proximity switch switcheson and off reliably.

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Figure 19: Hysteresis

The hysteresis is also important for other sensors, e.g. pressure andtemperature sensors. Here a freely adjustable hysteresis is an advantagebecause easy control functions can thus be implemented.

Lateral approach If the object does not approach the proximity switch axially but radially,i.e. from the side, the exact switch-on and switch-off points depend onthe shape of the electromagnetic field. The manufacturers indicateswitch-on graphs in their data sheets which normally correspond to thefollowing figure. As can be easily seen, the required deviation betweenswitch-on and switch-off points is reduced considerably if the objectapproaches radially. As repeatability is also improved, this should be thepreferred direction of actuation, e.g. for positioning tasks. Moreover,mechanical damage of the sensor is avoided (see 3.4.3).

This switch-on graph, also called hysteresis graph, supplies furtherinformation about accuracy. In areas where the switch-on graph is fartheraway from the switch-off graph, i.e. in the limit area where the object isjust still detected, accuracy is lower. Finally it also depends on the design.The smaller the design, i.e. the shorter the operating distance, the higheris the achievable (absolute) repeatability.

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Figure 20: Hysteresis graph

Half the rated operating distance This is also confirmed by the above-mentioned rule of thumb (see 3.3.1).This distance is a good compromise between the extreme cases too close(low hysteresis, i.e. possible output chattering and risk of mechanicaldamage) and too far away (low accuracy).

3.3.3 Correction factors

Do you have to know more? In practice, the object is of course seldom a standard target (see 3.3.1).The objects can be larger, smaller, irregularly shaped and consist ofdifferent materials. The rated operating distance must then be multipliedwith correction factors to determine the actual operating distance. Thisvirtually is a change in scale. The tolerances of the standard, e.g. ± 10%for temperature variations are maintained. For the hysteresis graph aswell (see Figure 20) the values change accordingly. How these factors aredetermined is described below.

In practice, the type of approach does not always correspond to thatdefined in the standard. But it has an effect on the operating distance.This can hardly be considered by means of a correction factor. In case ofdoubt the user should always carry out a test in his application. Figure 21shows what happens if there is no precise mechanical guiding whichensures that the object always approaches in the same way. This exampleconfirms that the inductive sensor is normally not suitable for distancemeasurement (see 3.1.1).

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Figure 21: Approach of an object

Side length If a smaller or non-square target is used instead of the standard target(see Figure 18) to IEC 60947-5-2, the operating distance must becorrected by a factor. For square targets which differ from the standarddimensions this factor is shown in the figure below. The typical graph ofthis correction factor is indicated which shows the shorter operatingdistance for much smaller targets and the virtually constant operatingdistance for longer sides.

Figure 22: Correction factor side length

Rule of thumb Another rule of thumb says that the operating distance corresponds tothe rated operating distance if the object is not smaller than the sensingface of the sensor (see 3.2.1). Only if the dimensions are much smaller,objects are no longer detected.

Shape factor For other shapes, e.g. if metal balls are detected, the factor can no longerbe specified in general. With the ball the operating distance is reduced alittle. The value, however, depends on the radius of the ball. For objectswhich are shaped even more irregularly the operating distance can onlybe estimated from experience and should be determined by carrying outtests on site.

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Material If instead of the material defined in the standard (mild steel) anothermaterial is used for the target, the operating distance must also becorrected. For inductive proximity switches this correction factor directlydepends on the electrical conductivity of the material as this determinesthe level of the eddy current losses (exception: ferromagnetic materials,see below).

Is good conductivity an advantage? It can be seen from the following figure that the correction factor for amaterial which is a good conductor such as copper or aluminium leads toa shorter operating distance. Conversely, the electrical conductivity ofgraphite and ferromagnetism of iron cause greater losses in the oscillatorcircuit so that the achievable operating distances are longer. Thesurprising consequence is that the better the conductivity of the material,the worse it is detected.

Figure 23: Correction factor material

The continuous line represents the values to be expected theoretically fordifferent diamagnetic or paramagnetic materials. The indicatedmeasurement points show the actually measured values. It can be seenthat the maximum correction factor is achieved for a conductivity ofapprox. 104 - 105 1/ m. It is approx. 1. A still poorer conductivity resultsagain in shorter operating distances. Thus substances like water with aconductivity of approx. 100 to 10-2 1/ m or other substances which arepoor conductors cannot be detected. In case of iron there is a point nearthe graph maximum because iron is a ferromagnetic material. Since thisferromagnetism limits the penetration depth of the sensor field to a fewmicrometres, the conductivity of the substance is apparently reduced.From this results the good detectability of iron, steel and alloys containingiron. If, however, the ferromagnetism of the alloy is weaker, theoperating distance is reduced considerably. For stainless steel thecorrection factor is approx. 0.7.

K = 1 (see 3.5 and 4.4.10) Occasionally the dependence of the operating distance on the material isnot desired in applications because it is a possible source of interferencefor the detection of different materials. Inductive proximity switches havebeen developed which more or less compensate for this dependence onthe material by means of different methods. At ifm these units are

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referred to as K = 1 units (K stands for correction factor). This means thatfor these switches the correction factor is virtually always 1, i.e. isconstant. But this feature is not often needed in applications. Sheet metalworking is taken as an example. To position the sheets correctly, theirposition is monitored using inductive proximity switches. But it willhappen very seldom that in one and the same installation using the samemethods copper, iron and aluminium sheets are worked alternately. Itmust also be said that it is very difficult to optimise a special feature, heredependence on the material, without deteriorating other features, e.g.immunity to interference such as temperature variations.

K = 0 (see 3.5 and 4.4.10) This does not mean that the sensor detects nothing at all. What is meantis a sensor which detects selectively. It is also required in practice that asensor for example only detects a target of iron sheet but is immune toaluminium chips which may deposit on its sensing face. So the correctionfactor refers to non-ferrous metals.

Material thickness In the standard IEC 60947-5-2 the thickness of the target for inductiveproximity switches is specified with 1 mm. If, however, a dampingmaterial like thin metal foils is used, the operating distance may be longerthan would have to be expected after having applied the materialcorrection factor. This is due to the different depth of penetration of thesensor field into the material � the so-called skin effect (see 2.1).

The depth of penetration of the magnetic field is typical of the skineffect. It depends on the oscillator frequency. Strictly speaking, the fieldintensity does not reach a sharply defined cut-off but rather falls away to1/e. This is a limit for the thickness of the foil.

In the following table the limit thickness of different electricallyconductive materials is indicated for an oscillator frequency of 100 kHz.Below this limit thickness a longer operating distance must be expected.

Material [mm] at100 kHz

Iron(electrical sheet)

ca.0,02

Silver 0,2Copper 0,2Aluminium 0,3Zinc 0,4Brass 0,4Lead 0,7

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3.3.4 Switching times and switching frequency

ms The time which elapses when an object to be detected moves into themagnetic field and switching of the output of the proximity switch is ingeneral only a few milliseconds. The switching times are much shorterthan for mechanical limit switches, which is important as these sensorsare used in modern, fast running machines.

Dependence The switching time depends on several factors. On the one hand, itdepends on the energy stored in the oscillator circuit which in turn isdetermined by inductance, capacitance and the quality factor of theoscillator circuit, the oscillator frequency and type of oscillator. On theother hand, it mainly depends on the level of the eddy current losses inthe circuit. As already mentioned, they depend on the object size,material and distance from the sensing face. In general, the time fordamping proximity switches (design specific) is between 0.2 and 2 msand for undamping between 0.3 and 3 ms.

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Figure 24: Schematic representation of damping and undamping

Damping and undamping time If oscillation breaks down, the undamping time, i.e. the time theoscillator takes to oscillate again at its full amplitude is longer than thedamping time. For units made in the past the typical ratio ofdamping/undamping time was 1:2. For more recent switches theoscillation does not break down completely, which reduces theundamping time. Nowadays the time ratio of most units is 1:1. Deviationsare more frequent for larger designs.

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Figure 25: Oscillation and output in the past

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Figure 26: Oscillation and output at present

The switching time has a major influence on the maximum switchingfrequency and maximum switching speed at which an object can pass thesensor so that it is reliably detected. To achieve comparable results for themaximum switching frequencies despite all these factors a measurementmethod to determine the switching frequency is described in IEC 60947-5-2 which defines that targets (see 3.3.1) with the side length a and fixedon a disc at a distance of 2 a pass a proximity switch at half the ratedoperating distance. The switching frequency thus determined is normallyspecified in the data sheets of the proximity switch manufacturers.The switching time must not be confused with the power-on delay timewhich is much higher (see 3.2.3).

Mark-to-space ratio 1 The mechanical mark-to-space ratio of 1:2 results in a damping andundamping ratio of approx. 1:1. This is so because the output switchesshortly after the leading edge of the target enters the active zone (seeFigure 27). It does not switch off until the trailing edge of the targetleaves the active zone.

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1 Mild steel target2 Disc of non magnetic and non conductive material

Figure 27: Standard measurement method of the switching frequency

Switching cam Inductive proximity switches are frequently used as pulse generators, e.g.for monitoring rotational speeds (see training manual ecomat 200). To doso, a plastic disc is fitted with one (or several) screws. It is placed onto theaxis to be monitored. The screw head serves as the switching cam. Forhigh rotational speeds it is not sufficient to consider the switchingfrequency. One example:The rotational speed is 60,000 rpm. The calculated pulse frequency is 1kHz. Most standard sensors have switching frequencies of 1 kHz.Seemingly the application should function. But if the screw head has aslightly smaller diameter than the sensing face, it may not stay longenough in front of the sensor to damp it reliably.

Figure 28: Rotational speed monitoring

What has to be done? The switching cam must be made longer. It should at least be as long asthe target. A sheet strip with a max. length of. 1/3 to 1/2 of thecircumference can be fixed on the plastic disc. See "mark-to-space 2"below.

Disc with a hole This is even more difficult if instead of the switching cam on a plastic disca hole is used in a metal disc to generate pulses. Here a slot would haveto be used instead of a hole.

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Figure 29: Rotational speed monitoring using a disc with hole

But the example also shows that this is only important in case of veryhigh rotational speeds.

Mark-to-space 2 The mark-to-space ratio should be optimised for several reasons. Even ifthe rotational speed is not extremely high and the switching cam isreliably detected, reliable processing of the pulses in an externalevaluation electronics is not ensured. One example:The rotational speed is 600 rpm. The calculated signal frequency is 10 Hz.Can the signals be evaluated by a plc?There are mainly two features of a plc which limit the signal frequencythe plc is able to process. To answer the question they must be known.

Limit frequency The low-pass filter at the input has a limit frequency of 25 Hz (thiscomponent is normally used to protect the standard plc inputs againstspurious peaks). So the signals can be reliably detected by the hardware.

Cycle time The cycle time is 20 ms (i.e. long program or slow plc). Thus the cyclefrequency is 50 Hz. This is much above the signal frequency.Seemingly, the question can be answered with yes. But in practiceproblems occur again and again. It results from the above values that onerevolution takes 100 ms. If the diameter of the switching cam is 1/10 ofthe circumference (probably smaller), the estimated signal length is 10ms. This is half the cycle time. Thus the signals cannot be reliablydetected!

Consequence If the signal frequency is above the cycle frequency, the signals cannot beevaluated. But this does not mean that a lower signal frequency issufficient for evaluation. The mark-to-space ratio must be taken intoaccount.

What has to be done? There are several options:  Connect a counter  Use fast plc inputs  Make the switching cam longerThe last option is of course the easiest and cheapest one. The optimummark-to-space ratio is 1:1 to ensure that the two signal states 1 and 0can be detected with the same reliability.

1:1 Whenever pulses are unreliably evaluated or counted, the mark-to-spaceratio should first be optimised to 1:1.

The following figures show again the problem. Direct detection of theteeth of a toothed wheel to monitor rotational speed by evaluating thepulses is represented, which is not unusual in practice.

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Figure 30: Toothed wheel 1

Figure 30 shows the normal case. For this sensor type there should be noproblem when objects, here teeth, and gaps have the same length. Forlarger designs this can be difficult because the gap is not deep enough.The mechanical mark-to-space ratio is closer to 1:1 than to 1:2 as definedin the standard for the measurement method. For higher rotationalspeeds the undamping time may not be sufficient. It would then bebetter to have a larger, i.e. deeper and wider gap.

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If the gaps are relatively large as shown in Figure 31, there is a higher riskof assessing the application incorrectly if only the frequency is taken intoaccount. It must be additionally checked whether the damping time issufficient.

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Figure 32: Toothed wheel 3

Figure 32 shows the opposite case of Figure 31. The same considerationmust be made. The undamping time is critical here.

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Figure 33 shows a better arrangement than Figure 32. Here the usermust determine the maximum detectable rotational speed from thespecified dimensions. To do so, the catalogue must be consulted.

3.3.5 Notes on practical use

In this chapter some points are added and other points detailed aboveare only briefly mentioned.

First it can be said that the inductive proximity switch is simple anduncomplicated. This is confirmed by the enormous number of switchesused without specialists. Most explanations and notes in this text arehardly needed in practice. But even with an uncomplicated unit mistakescan be made. Moreover, there are marginal applications. This manualhelps to find solutions, especially for more difficult applications when thesensor does not react as expected.

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Material of the object An inductive sensor can detect all materials which are good electricalconductors. Its function is neither limited to magnetic materials normetals, it can also detect, for example, graphite.

Movement of the object Due to the high-frequency electromagnetic alternating field generated bythe inductive sensor it can detect objects regardless of whether they aremoving or not.

Shape of the object The best target for an inductive sensor is a object with a flat surface asonly there a sufficient amount of eddy currents can be formed. Individualobjects small in relation to the sensor, e.g. pieces of swarf from amachining process, marks or burrs on the surface of the workpiece donot affect the function until they are present in large numbers. Sodistance measurement is no point measurement but is integrated over agiven surface area. The number of steel balls which can be placed on thesensing face without affecting the switch is a useful criterion forassessing the operational reliability of inductive switches.

Interaction on the object An inductive sensor can be operated with only a few microwatts ofelectrical energy. This has the advantage that its high-frequency fieldcauses no radio interference and no measurable heat in the object. Asthe sensor has no magnetic effect either, it is virtually free of interaction.By the way, it generates no electrosmog either.

Selection The following example briefly describes the selection of a suitableinductive proximity switch for an application.An aluminium sheet strip which is 4 cm long and 3 cm high is to bedetected at a distance of 4 mm.Detection at half the operating distance is optimum. So s should be 8mm. The correction factor of aluminium is 0.4. Therefore the ratedoperating distance should be 20 mm (= 8 mm / 0.4).There are units type M30 with sn = 22 mm which can be used here

Alternatives In our example the material aluminium is critical. To achieve the requiredoperating distance for this correction factor a unit with increasedoperating distance must be selected. The M30 design corresponds to theheight of 3 cm. A larger design with a longer operating distance is notmore reliable here because the object would then be smaller than thesensing face. For a smaller type, e.g. M18 the maximum operatingdistance sn is 12 mm. Multiplication with the correction factor 0.4 resultsin 4.8 mm for sn Al. Calculating the assured operating distance, i.e. 81%of 4.8 mm, leads to 3.89 mm. This would no longer be reliable for thisapplication.

Improvement It would make selection much easier if the aluminium sheet could bereplaced by steel sheet.

How do I find these values? In the past this sometimes required some search in the catalogue. Theelectronic catalogue (www.ifm-electronic.com) is an advantage. Anautomatic selector finds suitable units using defined criteria.

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3.4 Mounting instructions

3.4.1 Flush / Non flush

This is an important criterion for the practical use of the switches. Theflush/non flush feature is determined by the design of the unit andindicated in the data sheet and on the type label.

f / nf The international designation f (for flush mountable) and nf (for non-flush mountable) is used (and no longer b and nb).

What is the background? Inductive proximity switches operate with an electromagnetic field whichis radiated from the sensor. It is almost inevitable that this field does notonly interfere with the object to be detected but also with other objectsnear the switch. To ensure the correct function of a proximity switch thearea around the sensing face must be kept clear of detectable materials.For inductive proximity switches no materials which are good electricalconductors are allowed in this area.

Clear space for nf The clear space for mounting non-flush inductive proximity switches isdefined in EN 60947-5-2.

ï

d Diameter of the proximity switchs Rated operating distance1 Clear space

Figure 34: Non-flush mounting, cylindrical

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1 Clear space

Figure 35: Clear space cylindrical non flush

Figure 35 shows the switch and clear space around the sensing face. Athreaded metal type can be seen here. The metal housing is mountedflush in metal, only the plastic sleeve is located in the clear space.Obviously, it must be 2 x sn in the clear space.

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Feature for f Wherever the clear space shown above cannot be adhered to flushmountable units must be used. The sensing face of the proximityswitches can be mounted flush in metal. For these switches theelectromagnetic field is screened to such a degree that only a negligibleamount escapes at the side of the sensing face. Thus these types areimmune to interference from the side. But the disadvantage of thisscreen is that the operating distance of flush mountable proximityswitches is shorter than for the corresponding non-flush mountabletypes. Depending on the type the operating distance reduction can be upto 50% of the rated operating distance. This is one of the reasons whyunits with increased operating distance have been developed (see 4.4.8).

Figure 37: Flush mounting cylindrical

1: Clear space

Figure 38: Clear space cylindrical flush

Operating distance reduction If a non-flush mountable unit � this is indicated on the type label � ismounted flush in metal, it must be assumed that no defined signal isprovided or the output is constantly switched. What happens in theopposite case, i.e. a flush mountable unit is mounted non flush? This isdefinitely done in practice. If for example both types are needed, theflush mountable switch is chosen (provided the operating distance issufficient) to have fewer types in stock as spare parts. In this case it mustbe assumed that the operating distance is slightly shorter becausepredamping is reduced. This difference is called operating distancereduction. To use these switches without problem the operating distancereduction should be as small as possible. This point is very critical,especially for units with increased operating distance (cf. switch forspecific applications). For standard efectors the operating distancereduction is normally not greater than 5% (see 4.4.8). However, the

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permissible tolerances defined in the standard EN 60547-5-2 must not beexceeded.

If all these requirements are fulfilled, the flush mountable sensor is themore universal choice because the user does not have to take the (lateral)clear space into account. Moreover units with metal housing are moreresistant to mechanical influence.

Quasi flush A term which is sometimes found in this context is "quasi flushmountable". These are units with a smaller permissible clear space thanindicated above. It is in the mm range. However, this term is notstandardised but manufacturer-specific. So the user must follow themanufacturer's instructions diligently. He cannot rely on the usualmeaning of flush, i.e. sensing face is mounted flush with a metal surface.This is why ifm only supplies flush or non-flush mountable sensors.

Overflush Especially for switches used for monitoring transport processes it canhappen that a heavy object hits the sensor thus damaging itmechanically. Here it would be an advantage if the sensor could not onlybe mounted flush but recessed in metal or be fitted with a protrudingprotective metal cover. For this application a unit was developed. Specialmounting instructions must be adhered to (see 4.4.9). This is also amanufacturer-specific term. As this does not restrict but exceed thestandard this designation is more acceptable than quasi flush.

Predamping If it cannot be avoided at all that the sensor is influenced by an object inits vicinity, this is called predamping. This term is explained in 3.3.1. Toavoid predamping the clear space in Figure 35, Figure 36 and Figure 38must be adhered to. If for an nf switch this clear space is not adheredto, predamping increases inadmissibly. So it is possible that the unitswitches immediately without object or that it switches once and thenremains in this state.

3.4.2 Mutual interference

If in a plant several proximity switches of the same type are to beoperated close to each other, certain minimum distances between theunits must be adhered to. The minimum distances given in the followingFigure 39 represent a rule of thumb.

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A: Sensing faceSn: Rated operating distanced: Diameter of the sensing face

Figure 39: Mutual interference cylindrical

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A: Sensing faceSn: Rated operating distanced: Diameter of the sensing face

Figure 40: Mutual interference rectangular

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It can be seen from Figure 40 that in this context there is virtually nodifference between rectangular and cylindrical designs.

Offset frequencies The range of mutual interference also depends on the randomproduction-related difference in oscillator frequencies So interferencecan often only be noticed with certain specific damping conditions orafter replacement of a switch. If the minimum distances indicated in thefigure cannot be adhered to, it is possible to use ifm switches with anoscillator frequency that has been changed by a certain amount.

3.4.3 Mechanical stability

In an environment with high vibration the proximity switch must becarefully fixed. Although many threaded types look like bolts, thetightening torque for the nuts is limited. Only the fixing elementssupplied or recommended by the manufacturer should be used. This isespecially so for units with a smooth sleeve which must on no account befixed using a grub screw.

If the tightening torque for the nuts specified by the manufacturer seemsinsufficient, metal threaded units can be used. For small types with plasticthread rubber washers are recommended to improve fixing. Proximityswitches should be mounted in places where they are protected againstmechanical damage as much as possible. In case of need, they can becovered. Glass or ceramics is suitable for protecting the sensing faceagainst sharp-edged or hot chips. For direct use in pneumatic orhydraulic systems there are special versions which can withstand apressure on the sensing face of max. 300 bar.

The standard connection cable of proximity switches is only suitable forslight mechanical stress. If the operating conditions require a strongercable, a conduit is necessary for strengthening. As an alternative, a switchwith terminal chamber can be used. The cable must be laid so that noforces can be transferred to the housing. If the cable must be movedconstantly, using a conduit is also recommended (see the followingfigure).

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Figure 41: Mounting and direction of movement

Direction of movement The type of mounting shown at the top is not recommended as there isthe risk of mechanical destruction. The switch should on no account beused as a "limit stop".

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3.5 Technology and operating principle K1, K0

Overview In this chapter the operating principle of these special types is describedin detail. In addition to new information, the following sections partlyrepeat what has already been described in 3.2, 3.3 and 3.4. The readerswho would like to skip these sections can continue with 3.5.3. Thefeatures of these special types which are important for practical use aredescribed in 4.4.10.

3.5.1 Designations

K = 0, K = 1 The abbreviation of this designation is K0, K1. It stands for the feature ofthe new switch families which makes it easier to use inductive proximityswitches under special operating conditions.

In short, these are inductive proximity switches which react  only to ferromagnetic materials (in short K0, in general referred to as

K = 0) and  to any (conductive) materials without different correction factors (in

short K1, in general referred to as K = 1).

Correction factor To remind you: For the conventional inductive sensor the correctionfactor for the material has to be taken into account. In the standard IEC60947-5-2 which defines the measurement method to determine therated operating distance the target material (in addition to otherparameters) is also prescribed, i.e. mild steel. To determine the operatingdistance for an aluminium target (Al) the standardised value for mild steelis multiplied with the correction factor for aluminium which is approx.0.4, i.e. the operating distance is reduced by 60%. This explains therequirement for an inductive proximity switch which detects all(conductive) materials at the same distance, thus having a constantcorrection factor (K = 1 or in short K1).

3.5.2 Conventional inductive sensor

K 1 First the conventional type is treated again. In short, it is referred to as K 1. Its operating principle can be explained in several ways. These are

simplified models to make understanding easier. Depending on theaspect to be illustrated they can be different.  Damping of the oscillation due to eddy current losses in the target  Change in the quality factor in a resonant circuit. This is often

described with a representative circuit diagram where the resistancewhich stands for the losses is connected in parallel to the coil.

  As an alternative, a series connection can also be used for therepresentative circuit diagram (figure 42). These two representationsare equivalent. For a given frequency the corresponding values canbe easily converted.

For a better understanding of the difference between K 1 and K1 theseries connection is used for the representative circuit diagram for K 1.The letter T for the designations in the following figures meanstransmitter.

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Figure 42: Representative circuit diagram series connection

For K 1 the change in resistance is evaluated.

Switching frequency The switching frequency of the sensor depends on the oscillatorfrequency. A higher oscillator frequency cannot be implemented easilyfor the conventional switch. As the change in the quality factor isevaluated the oscillator circuit operates in the range of its maximumquality factor. For higher frequencies the quality factor decreases becausethe AC resistance increases considerably. This is easier to implement for K= 1, see 3.5.3.

Resistance characteristics The Figure 43 shows the graph of R = Rcu + RAC represented as afunction of s, which is the distance of the target of Fe (iron, no stainlesssteel). sr is the distance at which the sensor switches. Only the qualitativegraph is shown. The axes are without units of dimension. T stands fortransmitter.

L InductanceRCu Resistance material (Cu)RAC AC resistance

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RT Resistance for the transmitterRT Limit value of the resistanceFe Iron (ferromagnetic material)E SensitivityRTCu Resistance of the coil (copper)s Distance of the targetsr Effective operating distance

Figure 43: Resistance and distance

It can be seen from the graph in Figure 43 that the total resistance Rasymptotically moves to a limit value R . The longer the distance, thesmaller is the change in resistance. For the switch point however(effective operating distance sr) the value is approx. 5% above the limitvalue. This 5%, the signal deviation for Fe, is also called sensitivity and isa tried and tested value. The graph for another material, e.g. aluminium,is not represented here. It would be difficult to see this graph because itwould virtually overlap with the line for RT . The following table indicatestypical approx. values for the differences:

Al Fe RT 0 % + 5 %...10

LT - 0,4 % - 0, 2 %

The table shows that it is difficult to detect an aluminium target via theresistance. It can now be understood more easily that an aluminiumtarget is only detected at a much shorter distance (see 3.5.1, correctionfactor). A sensor with sr = 10 mm on a standardised mild steel target onlyswitches on an aluminium target at 4 mm.

If the goal, however, is that the sensor switches on all materials at thesame operating distance, it can be seen from the table that the change ininductance L is more suitable. On the one hand, inductance depends lesson the material. On the other hand, it is much lower, i.e. more difficult toevaluate.

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3.5.3 Sensor with K = 1

Here the change of inductance is evaluated. It is related to the change ofthe permeability µr. To remind you:

( 4) L = µ0µr n2 A / l

L [Henry] Inductanceµ0 [1,2566 10-6 Vs/Am] Magnetic field constantµr Permeability numberA[m2] Areal[m] Length

( 4) is the formula for the inductance of a coil. µ r is also called relativepermeability. This number describes the property of a material, i.e. thereaction of a material in the magnetic field. This subject is not furtheraddressed here. Permeability is described in more detail in the trainingmanual magnetic sensors, cylinder switches. ( 1) only illustrates howinductance is related to permeability. µr is no absolute constant butdepends on the frequency, for example for alternating fields.

Figure 44 shows (again in a qualitative manner) the relation between µ r

and the frequency f.

Figure 44: Permeability and frequency

Figure 44 shows the clear difference between Fe (iron and ferromagneticmaterials) and the virtually constant value for Al (aluminium) for lowerfrequencies. This difference is reduced for higher frequencies. This inshort is the difference between K0 and K1.

Frequency evaluation There are different options to evaluate the change in inductance. Oneoption would be the evaluation of the change of the oscillator frequencywhich is caused by the change in inductance. But for K0 and K1 thismethod was not applied. But as this technology is used for units whichare available on the market, it is briefly explained below.  CounterTo determine the frequency, pulses can be counted. The requiredcomponents, however, are overdimensioned for a standard sensor asregards volume and price.  Reference resonant circuit

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To compare the frequency with that of a reference resonant circuit, itscomponents must meet special requirements. It is difficult to obtainprecise and temperature stable capacitors. So it is natural to chooseanother option using the available know-how concerning coils.

For the ifm sensor the change in the coupling of two oscillators isevaluated. The coupling factor describes the change in inductancebetween the two coils LT and LR in another way.

(CF) coupling factor

Figure 45: Coupled coils

T and R The coil of the left oscillator which is excited to oscillate can beconsidered to be a transmitter (T), the coil of the right high-ohmic circuitto be a receiver (R). The two oscillators are coupled via the magnetic field.

Coupling factor The coupling factor CF is a characteristic value for the coupling intensity.It depends for example on the position and arrangement of the coils.Furthermore on external influences, e.g. presence or absence of a target.This relation becomes clearer when one imagines the target to bebetween the coils similar to a slot switch. The extent of the change in thecoupling factor depends on the material of the target. A parameter forthis is the permeability µr.

Material It can be seen from the above graph (Figure 44) that for high frequenciesthe change of the coupling factor is independent of the material. Thismeans that this arrangement (for high frequencies!) reacts to every targetin the same way. This is just the requested feature for the K1 sensor.

Now the remaining task "only" is to develop a unit which makes use ofthis effect and can be easily made in large volumes at low cost.

Signal deviation This task is difficult because the signal deviation is so small. If the voltageat the receiver coil is identified as UR, the resulting typical value is

UR/ UR 0,3 %

This value is called basic sensitivity. A direct evaluation would be verycomplex. One option to solve this task consists of measuring thedifference between two values. In the representative circuit diagram infigure 46 this can be shown with 2 coils being connected in series on thereceiver side. If the direction of rotation of the windings is reversed, thesign of the voltage of the 2nd receiver changes. The voltage across thetwo coils is then the difference of the individual voltages. External

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influences, like temperature or magnetic fields, are more or lesscompensated for by forming the difference. The first receiver isinfluenced by the target as in Figure 47. A suitable arrangement of thecoils ensures that the second coil is virtually not affected by the target. Itserves as a reference to compensate for interference which has the sameeffect on both coils.

Figure 46: Generation of the differential signal

The following formula applies to this arrangement:

(UR2 + UR1)/( UR2 + UR1) 10 %

Such a value can now be easily evaluated. The coil arrangement must beselected so that the above-mentioned properties result. How this isimplemented is schematically shown in Figure 47 and Figure 50.

T Transmitter coilR1, R2 Receiver coils- - - Housing (for K = 0 incl. stainless steel sensing face)

Figure 47: Structure of the sensor

The operating principle is now explained in more detail. In Figure 47 thedesignations T for transmitter and R for receiver are used. R1 reacts tothe target, i.e. is sensitive, R2 is virtually insensitive.

Precision For production maximum precision of the carrier and winding of the coilsis of prime importance to keep individual variations to a minimum. Thecarrier consists of a special plastic which was mainly selected because ofits mechanical properties. With this plastic precise injection-mouldedparts can be made with a high repeatability. No ferrite was chosen

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because otherwise the transmitter coil would be virtually shielded fromthe target.

Evaluation For evaluation another trick is also used. The voltages at the transmitterand receiver circuit are further processed by a multiplicator (x in Figure48). This has the effect of an additional compensation of interference.The result is integrated ( in Figure 48) and then transferred to a stagetriggering the switching output.

Figure 48: Evaluation of the signal difference

3.5.4 Sensor with K = 0

Selective The special feature of this sensor is its selectivity. This and further featuresare briefly described below.

Less interference The reason for developing this sensor was the following requirement: Thesensor is to reliably detect a target of ferromagnetic material, e.g. mildsteel. It is not to be interfered with by aluminium chips even if they areon the sensor.

Same principle To fulfil this requirement no fundamental new considerations anddevelopments are necessary. Looking at the graph in Figure 44 where µr

is represented as a function of the frequency shows that for lowerfrequencies µr of iron increases substantially. This is the characteristicfeature of ferromagnetic material. If the sensor works at lowerfrequencies, this effect can be evaluated easily. The coils can be arrangedin the same way as for K1. Differences are the much lower oscillatorfrequency and the evaluation which is carried out by a further oscillatorwhich either starts to oscillate or where the oscillation breaks down.

Figure 49: Cross-section through K0

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Figure 49shows a cross-section through such a sensor. Figure 50 showsthe decisive component, the coil system and the implementation of theschematic representation in Figure 47.

Figure 50: Coil system

pcb It can be seen that a special PCB is used. For this PCB the connectionbetween sensor (coil) and the circuit can be established more easily. Forthis reason a combination of a flexible film and special PCB is alreadyused and will be increasingly used in the future.

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4 Inductive proximity switches of ifm

4.1 Mechanical properties

4.1.1 Structure in general

Main groups A distinction can be made between main groups which consist of thefollowing components:  Housing  Basic sensor  Circuit  ConnectionBut as these components are in relation with each other, they are nottreated separately.

Structure of an efector The figure shows the schematic structure of an inductive proximityswitch. The technical implementation resulted in different variants whichwere modified considerably with time. For a correct understanding of thecurrent situation it is useful to know the progress of development. Anoverview is given in the following table.

ï î í

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Figure 51: Structure of an inductive proximity switch

4.1.2 Chronological development

Step Housing Circuit1 plastic potted PCB2 plastic and/or

metal pottedPCB

3 plastic and/ormetal potted

filmtechnology

4 plastic and/ormetal modular

filmtechnologymodular

Explanation The individual points in the table are briefly explained below.

Time As the transition between the variants was fluid, a classification in stepsand not in years was made.

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Potting In the past filling cavities with a potting compound, e.g. cast resin was aconsiderable progress. ifm was granted patents on this. Thanks to thismethod it was possible for the first time to use electronic units undersevere operating conditions. With time the following disadvantagesbecame obvious:+ Protection against moisture and dust+ Mechanical fixing of the components- Resistance to temperature shocks- Heat dissipation- Resistance to coolants and cleaning agents- Separation of the componentsDue to the different thermal expansion of the components temperatureshocks lead to mechanical tension which can destroy the unit in theworst case.As the chemical components of the above-mentioned substances havebeen continuously developed problems have increased recently.For the disposal of old units it is more economical to separate thecomponents as toxic substances may only be contained in electroniccomponents. This requires a high level of input for potted units.

Compound The potting compound was changed several times for different reasons.For some mixtures for example forming of health-damaging vapoursduring curing was reduced. Resistance to coolants was improved.However, potting must always be monitored carefully and cannot be fullyautomated. This depends on the change in volume (contraction) duringcuring. Forming of air bubbles which prevent the complete filling of thecavities is critical. For low viscosity media this does not happen often. Butduring potting the compound can leak through the sleeve.

Metal in step 2 The reason for using metal sleeves is their improved resistance tomechanical stress.

Film technology (step 3) Using this technology has major advantages.+ Mounting+ Design+ Time+ Quality (fewer faulty circuits)This is why film technology is preferred to conventional PCBs which areoften still manufactured manually.Due to the flexible film it is easier to make the small designs required bythe market.The fully automatic placement of components on the film results insubstantial time saving. Furthermore the circuits can be modified moreeasily.

SMD For film technology the designations SMD (surface mount device) andSMT (surface mount technology) are often used. These terms indicatethat the components and the conductor tracks are on the same side.

ifm ifm pioneered in film technology which was introduced for theproduction of standard sensors Only sensors with a circuit onconventional PCBs are found on the market except special technologiesthat are only important for special units.

Figure 51 is relatively "neutral". The schematically shown componentscan be conventional PCB mounted or SMD devices. The film as well ismounted on a carrier. For cylindrical designs it is rolled up, but this

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cannot be clearly seen in the cross-section. In film technology the screenis applied on the film as a closed layer of conductive material. If the film isthen rolled up, the screen surrounds the circuit. No modular sensor canbe seen in the figure because for modular technology another method isused to seal the housing. This is described in chapter 4.1.3.

More details The explanation of the table is now finished. Modular technology istreated in the next chapter. Some information which was not given in thetable for the sake of clarity is now provided below.

Hybrid For efectors as well additive technologies for special units (miniaturedesigns) are used where the semiconductors are directly bonded onto the(ceramic) carrier and resistors are applied using the screen printingmethod (hybrid technology).

Trend towards integration To reduce the number of components and to implement additionalfunctions special integrated circuits are increasingly used. These ICs aremade by semiconductor manufacturers according to ifm's specifications.

Basic sensor The basic sensor consists of an oscillator circuit with a coil in a ferrite core(see 3.2.1). For the sake of clarity it was not included in the table above.The basic sensor remained more or less unchanged. Only for special units(electromagnetic field immune and K = 1 or 0) combinations of severalcoils are used.

Figure 52: Sensor for non-flush and flush mounting

Flush mountable sensors are also available without a metal ring as shownin Figure 53. For these sensors the metal housing has the function of thering, i.e. lateral screening.

Connection Connection technology has hardly been changed. With time only thepreference for a technology has changed.

Connector units There is a trend towards connector units because for the maintenance ofautomated installations, e.g. replacement of a broken cable, time is amajor cost factor. A connection with a failed seal as a possible source offailure is accepted. But the seal can only fail if the coupling nut isfastened insufficiently or too tight (risk of mechanical damage). Here theuniversal connector with M12 thread is the preferred choice.For small designs including cylinder switches (magnetic switches) and forweight reduction, e.g. for use on the arm of a robot, connectors with M8thread are more and more often used.

Food industry To fulfil the special requirements of this industry optimised units can besupplied. They have gold-plated contacts and a high-grade stainless steelhousing. For connection a high-grade stainless steel nut should also be

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used for the cable plug. The connector housing should be made of PVCbecause this material features the best resistance to water and cleaningagents.

Tightening torque In general it is not necessary to use a key with an adjustable maximumtightening torque for mounting. It should go without saying that morecare must be taken with plastic threads than with metal threads. For unitswith terminal chamber the cable gland must be tightened sufficiently toensure the protection rating (see training manual protection ratings).

Housing materials In industrial processes inductive proximity switches are exposed toenvironmental influences like heat, cold, dust, vibration, moisture,aggressive liquids, vapours, etc. Therefore they must be incorporated intoresistant housings.

In general the housing material is a glass-fibre reinforced plastic whichhas a good chemical resistance and insulation capacity. To improve thehousing stability with regard to fixing metal sleeves are often used forthreaded units.

PBTP The housing plastic normally used by ifm is a cadmium-freepolybutyleneterephthalate (PBTP) which is for example produced by Bayerunder the trade name Pocan.

Metal In the past ifm used nickel-plated brass for standard cylindrical units.Nowadays Optalloy is used for coating. This is an allow of copper, tin andzink which is also known as white bronze.For special units the designs are also available with a high-grade stainlesssteel sleeve, e.g. for the food industry.

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4.1.3 Modular technology

efectorm In 2000 the new generation of inductive proximity switches waspresented under the name efectorm. This was preceded by a lengthydevelopment process.

The existing generation has already featured a high noise immunity andoperational reliability under severe conditions. But some of the pointsmentioned above (see 4.1.2) could not be further optimized using thistechnology.

Structure Special features of the modular sensor are described below. Abefore/after comparison is made.

Circuit The circuit design has remained unchanged except for its modularstructure. This enables reduction of the variety of circuits to a fewmodules.

Before Several circuit variants are available for one switch type with a givenoperating distance, for example pnp, npn, AC/DC variants. The numberof variants can be double as high for units with cable or plug connection.

After The generation of signals, i.e. the generation of oscillations, theevaluation of the amplitude, etc. are the same for every unit. For themodular sensor only one module is used for this. For the output circuit(pnp, etc.) there is a separate module for each variant. This module isthen connected to the plug or cable module.

Figure 53: Sensor module

Housing The following information refers to metal housings. Before The circuit is placed onto a carrier, the coil with its core is also applied to

this carrier. For the finished unit it is incorporated in a plastic sleeve whichis surrounded by the actual housing (plastic or metal). The cavities arepotted with cast resin. For the most part, the individual processing stepscan only be carried out manually. In case of temperature fluctuations themetal sleeve and other components expand differently. If due to specialenvironmental conditions the sensing face must be protected with aspecial material, this requires the production of another complete unit.

After Part of the circuit is placed onto a mechanical carrier which is directlyinserted into the metal sleeve. The ends of the metal sleeve are sealedwith O-rings. The sensing face can consist of different materials such asPEEK, ceramics, etc. depending on the application requirements. Thiseliminates the need for a complex development and production of specialunits. With the technology used so far it was hardly possible to make asensing face of ceramics. At the other end the connection � cable or plug

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� is attached. These ends are the only components that are still potted toensure optimum sealing and mechanical stability. Assembly is fullyautomated. The seal test as well can be automated easily and reliably.

Figure 54: Modular technology housing

Ingress resistance This feature has also been improved Before Even in the past a unit with a failed seal seldom went through the quality

tests unnoticed. This was achieved by thorough monitoring of theproduction process. Testing every unit was more difficult with theconventional technology.

After As the efector m is not potted, the seal test can be carried out by asimple pressure test. This test is integrated in the automated productionprocess. Every efector m is released for sale only after passing the sealtest. This was one of the major reasons why the development of thistechnology required such a high level of input. The units now complywith the higher protection rating IP 69K and not only with the IP67requirements (see training manual protection ratings).

There are of course technical developments which are not only useful formodular units. But as they are the latest generation, they are the first tobenefit from this.

Electrical connection More information about the electrical properties and their importance forthe application is given in 4.3. General information about importance andfeatures of 2 and 3-wire units can be found in the training manualconnection technology.

Before Units made in the tried and tested quadronorm technology also have alow leakage current as 2-wire units which normally is < 0.4 to 0.6 mA. Atleast with regard to this current value easy connection to electroniccontrollers is ensured without the need of additional components. Butthe plc standard type 1 additionally requires a minimum load current. Thisrequirement could not always be fulfilled with the quadronorm units.Moreover, there are 3-wire units with a negligible leakage current..

After For the 2-wire units the leakage current is < 0.5 mA. There is a newvariant for the 3-wire units. They are referred to as 3/2-wire units. Thismeans that they can be connected either as 2 or 3-wire units. Thusstorage of spare parts is simplified even more. As these units additionallyhave a 2nd LED (set-up LED), the maximum leakage current is 0.6 mA forthe 2 and 3-wire operation due to the higher current need. With aleakage current of 0.5 mA and a minimum load current of 2 mA thenew 2-wire units comply with the plc specification without restriction.

Labelling Electrical units must be fitted with a label. Before So far most units have been fitted with a type label (for very small designs

also at the cable). With time the label could get dirty or come loose undersevere conditions. Replacing a failed unit which cannot be identifiedtakes of course longer.

After The units have a permanently legible laser type label. Even if anaggressive cleaning agent must be used due to soiling, the label remains

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legible. Thanks to the high degree of automation this could be achievedvery easily and reliably for the efectorm.

2 advantages The advantages can be summed up as follows:  Application  ProductionThey are explained in the following section.

4.1.4 Application of the efectorm

Mechanics The mechanical properties have been further optimised.In the past the protective circuitry was also rated to such a degree thatelectrical interference, overload, short circuit, reverse polarity, etc. couldhardly destroy the unit. Mechanical damage is the major cause of failureof efectors. As a further protection against damage, units with increasedoperating distance, especially those with an LED indicating the certainrange can be used.

Temperature resistance Some units are subjected to a 1000-hour test. During this test thetemperature specified in the data sheet cyclically goes up and downwithin the specified limits at an interval of 2 hours. At the limit values thetemperature is maintained for 1 hour. The production release is givenonly after this test has been passed. Such tests which normally exceed therequirements of users and standards have been carried out by ifm foryears. They ensure that the units withstand harsh operating conditions.

Temperature shocks Especially for applications in the food industry the efector can come incontact with boiling water (100°C) and then with icy water (0°C). Inaccordance with the standard for environmental tests (EN 60068-2-14 N L

test) resistance to temperature shocks is tested using the 2-bath method.The medium used is water. One measurement cycle consists of 15 to 60min. at 100°C and 15 to 60 min. at 0°C. The efector m has also passedthis test. The test was stopped after the switch withstood over 50 cycles.

Media Due to the modular design the material with suitable properties forcritical media can be selected easily. The sleeve is made of high-gradestainless steel. The material for the sensing face is decisive.

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Medium Sensing faceOilsCoolants

LCPCeramics

Hot metal chips CeramicsCleaning agentsfood

PEEK

Gold-plated contacts protect against corrosion.

Identification Permanently legible laser type label.

4.1.5 Production of the efectorm

Modularity With a few modules a wide range of different units can be made. Thisconcerns mechanics and electronics:  Material of the sensing face (LCP, ceramics, PEEK)  Circuit (pnp-npn, 2-wire, 3-wire)In the long term it is conceivable that a unit is made and deliveredimmediately after receipt of the order.

Automation The degree of automation could be increased considerably compared tothe technology used so far.

Test In addition to the circuit tests already carried out every unit is now alsotested for ingress resistance.

4.2 Designs

ifm's standard range covers rectangular and cylindrical designs commonlyused in industry, cf. IEC60947-5-2.

Rectangular This design is mainly used for:  units with a long operating distanceThe long operating distance, for standard units up to 60 mm, is achievedby means of big coils. They are incorporated on the flat side, e.g. 120 x80 mm² (see table below).  Units based on standard dimensionsFor the formerly common mechanical position switches (see 3.1.2)standard dimensions were usual. A machine can be designed more easilywith threaded holes being made right from the start for fixing the switchwithout the need of knowing the exact type.The housing is normally made of plastic (Pocan).

Cylindrical and smooth The very first efector generation was made in this design which is stillused today. These switches can be easily mounted and correctlypositioned using a clamp. Normally, the clamp is supplied with the unit. Ifthe clamp is replaced, care should be taken that it is replaced by theoriginal clamp to avoid mechanical damage (squeezing). The housing isnormally made of plastic (Pocan).

Cylindrical and threaded This design is also frequently used. The units can be fixed with an anglebracket (available as accessory) or via a mounting hole with screw andcounternut.

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Another accessory is a special mounting sleeve for M8, M12, M18 andM30 units. It enables quick replacement of a failed unit without havingto readjust the new part.This design is typical of flush mountable units (see 3.4.1). The housing ismade of plastic or metal. The efectorm belongs to this last group. .

The following table gives an overview. It does not indicate all dimensions.In particular threaded designs are often supplied with short housings sothat the large number of types which only differ in length are not listedfor the sake of clarity.

Design Dimensions in mm Material52 x 8 x 8 metal

rectangular

27,8 × 16 × 10,240 × 26 × 1240 x 40 x 6660 × 36 × 10

121,3 × 40,5 × 40,590× 60 × 40

120 × 80 × 30105 × 80 × 39,2

plastic

4 × 304 x 45

6,5 x 356,5 x 496,5 × 3511 x 6018 x 70

metal

smooth

11 x 5420 × 77,420 × 9234 × 82

plasticcylindrical

threaded

M5 × 0,5M8 × 1

M12 × 1M18 x 1M30 ×

plasticor

metal

For the cylindrical designs diameters or thread dimensions and length areindicated. The length refers to the housing, i.e. up to where the cable orthe threaded block starts.

I would like to know more! More details, scale drawings, information on permitted tolerances of thedimensions, etc. can be found in the catalogue or atwww.ifm-electronic.com.The requested design can be quickly and easily found using the selectorof the dynamic product search.For the overview of the designs the attached type key (page 96) ishelpful.

Is this all? In addition to this basic product line ifm offers a wide selection of moreswitches: Designs compatible with mechanical switches (e.g.microswitches to DIN 41635, encapsulated limit switches to DIN 43694),designs according to the international CENELEC standards as well as ahigh number of application-oriented and custom-made special designs.

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There are also new inductive sensors for use with special switchingamplifiers for safety-related applications. Details can be found in thetraining manual safety technology.

Below are 2 examples of further types which are also available on themarket.

.Application-oriented designs cover slot and ring sensors even if these twotypes are no proximity switches in the conventional sense.

Due to the special shape of the sensing field slot sensors are preferablyused where a high repeatability is required. Ring sensors can detect smallobjects like balls, needles, nuts, etc. without problems.

Connection 3 variants are available: Cable The cable is firmly connected to the unit. So the fault source of a

connector with failed seal due to incorrect mounting is excluded. Connector These quick-disconnect units are increasingly used. A fault by reversing

the wires is excluded even for first mounting. Due to the increasingimportance a connector brochure is available. Moreover standardconnectors or connectors with special features, e.g. for the food industry,are recommended for proximity switches with plug connection in thecatalogues, brochures and on the internet (see above).

Terminal chamber Another variant are special units with terminal chamber where the usercan choose the cable to connect. Sealing of the terminal chamber isachieved by a cable gland through which the cable is passed. There arecylindrical designs where the cable runs in direction of the longitudinalaxis or, where space is at a premium, is angled by 90° by rotating thepatented end part.

4.3 Electrical data

There are several electrical data which are common to all electronic,binary position sensors (cf. 3.1.1), e.g. inductive and capacitive proximityswitches, photoelectric sensors, etc. Therefore they are detailed in thetraining manual connection technology. Only important points andspecial features are indicated below without a detailed explanation of thetechnical terms.

Interface directive The IEC 61131-2, the current plc standard, defines requirements for unitsfor connection to plcs. The electrical data have thus become even moreimportant.

4.3.1 Important parameters

The connection technology is important for every sensor, so it isseparately treated in the respective training manuals. Here only someimportant points are summed up.

Connection technology Binary switches are available in 2-wire, 3-wire and (for special cases) 4-wire technology. For 3 and 4-wire switches the operating voltage isapplied between +UB and 0 V and the load is switched via a signal wire.For 2-wire switches the operating voltage is the voltage commonlyavailable for connecting the proximity switch and the load in series. A

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special case are the modular sensors with types which can either be usedas 2 or 3-wire units. The following points have to be taken into account:  Voltage drop and leakage current for 2-wire unitsVoltage drop reduces the voltage applied to the load.For former units the leakage current of a few mA could lead to uncertainswitching states, e.g. when connected to electronic controllers type 1 (formechanical switches). For more recent units, especially the quadronormunits, the leakage current was reduced to typically 0.4 to 0.6 mA. For the2-wire modular units it is 0.5 mA, the voltage drop is 2.5 V and theminimum load current 2 mA. These technical data correspond to the plcstandard type 1. As the wiring complexity is substantially reduced thecurrent 2-wire switches are a low-cost alternative to the 3-wire units(unless a fieldbus system like AS-interface is used anyway).  Series and parallel connectionFor state-of-the-art technology electronic positions sensors are directlyconnected to plc inputs and then logically combined via the program. Soseries and parallel connection is hardly important any more. But if itcannot be avoided, some special points have to be taken into account,see the training manual connection technology. They concern again theleakage current and voltage drop for 2-wire units and for 3-wire unitspossible effects on the power-on delay time.

Voltage supply The voltage range in which the units operate reliably and not the nominalvoltage is important for practical use. It is specified in the data sheets andon the type label. The standards for the CE marking define the degree ofthe conducted interference the unit has to withstand, see trainingmanual CE marking.

Residual ripple Note for DC voltage that the residual ripple does not exceed the limitvalues. It is not sufficient to check the root-mean-square value. If a powersupply of inadequate quality is used so that no sufficiently smoothedvoltage is provided, a reliable function is no longer ensured.

¬

Ë

Figure 55: DC current supply and residual ripple

If the residual ripple falls below the limit value of the operating voltage ofthe proximity switch, a smoothing capacitor must be used. A rule ofthumb for this is: 1000 µF per 1 A current intensity.

Protective circuitry Depending on the design and type the units are fitted with differentprotective components. They protect against  overload  short circuit  reverse polarity  conducted interference

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4.3.2 Overview

The following overview shows the tree structure of the "family" ofinductive proximity switches. DC and AC should be terms which areknown. UC stands for universal current or dual voltage. Such units can beconnected to DC or AC within the specified range.

The figure is in preparation. For information see Figure 64...

The * refers to units with short-circuit protection

It can be seen that the current rating for solid-state outputs is betweenapprox. 100 and 400 mA depending on the design.

A nominal voltage of 24 V DC is now more or less used as controlvoltage. Other voltages are used in special industries or countries.

quadronorm quadronorm units (see 4.4.4) are something special. They operate in bothpolarities.

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4.4 Switches with special features

4.4.1 Use in hazardous areas

Note As this is important for many binary position sensors and fluid sensors(see 4.3), this subject is also treated separately in the training manualATEX. In this manual the terms, designations, in particular marking of theunits, standards, etc. are detailed. In this section the term ATEX is brieflyexplained. It stands for a directive of the EU which is now in force.Former terms, e.g. Ex units, NAMUR units, are still often used. Somedefinitions and designations have been changed. An example for experts:The former zone 10 is now called zone 20.

Important! The sensor manufacturer can have his units tested and approved bynotified bodies. Due to the wide range of applications ifm gives no adviceas to which unit is allowed for a specific application. Every user isresponsible for knowing and correctly applying the standards andregulations which are valid for his application, e.g. ATEX 100a and ATEX118a.

The use in hazardous areas in the chemical industry, paint sprayingcabins, in mill or tanks is the oldest application area for proximityswitches. As only very small voltages are allowed in these areas problemsoften occur with mechanical switches. In proximity switches, however, nosparks, arcs or inadmissibly high temperatures are formed duringoperation. In the past many versions could be directly used in hazardousareas. This is no longer so with the ATEX directive.

This has briefly described the requirements for the unit. On no account isa spark allowed which can trigger an explosion, e.g. in case ofmechanical destruction of a unit, short circuit through a componentwhich stores electrical energy, i.e. a coil or capacitor. For less hazardousareas as well (zone 2, the exact definition is given in the ATEX trainingmanual) every electrical apparatus must be clearly identified as beingsuitable for use in hazardous areas even if it has already met therequirements as standard unit. In areas with a higher risk of explosion therequirements can for example be fulfilled by mounting the sensorseparately from the switching amplifier. For these so-called NAMURsensors (see training manual ATEX) there are maximum values for currentand voltage which must be strictly adhered to. Power is only switched inthe switching amplifier which must be located outside the hazardousarea, e.g. in an encapsulated control cabinet. Rules must also be appliedto the cables which connect the sensor and amplifier.

As a special feature for the zone and group classification the inductiveand capacitive values of the units caused by sensors and cables are takeninto account for the ia IIc area (see training manual ATEX).

Note for the connection of different external energy stores to the controlcircuit: As the energy content of the control circuit is changed by thecable and the sensor (e.g. cable capacitances) compliance with the valuesindicated on the type label is absolutely required. Therefore generalinformation about the maximum admissible cable length cannot begiven.

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Use of efectors in ATEX areas Only approved and marked sensors are allowed for use in hazardousareas. The former generation of these sensors supplied an analogueoutput signal which was evaluated by the switching amplifier. Today abinary output signal is provided. To do so, more components than in thepast are integrated in the sensor. The circuit must of course still complywith the strict specifications.

ATEX switching amplifier The switching amplifiers with an electrically isolated output stagegenerate binary information from the signals of the intrinsically safe unitsin the hazardous areas.The amplifiers can be triggered by all conventional switching elements:  Mechanical contacts  Proximity switches to DIN 19 234

NV 0100 The amplifier has a blue type label and terminal strips in different coloursfor the sensor side (blue) as intrinsically safe circuit and for the powersupply side (black). The operating voltage for the control side (sensor) is8.2 V DC. The corresponding 2-wire DC efectors also have a blue cable toidentify them for use in ATEX areas (blue = note ATEX area).

4.4.2 Switch for quarter-turn actuators

IND With the IND switch for quarter-turn actuators it is possible to monitorthe open and closed position of quarter-turn actuators for valves inaccordance with the standard interface VDI / VDE 3845.3.1 withouthaving to mount and wire two separate switches � as usual so far.Installation input and related cost are thus considerably reduced. Themechanical design of the IND and the connector in combination with adisc with switching cams available as accessory eliminate the need ofmounting and wiring in an additional terminal box. The switch can bedirectly mounted onto the quarter-turn actuator via two long holes withstandardised spacing.

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Figure 56: IND

AS-i The introduction of this system (see catalogue) opened up newapplications for this sensor or its modified versions. As positionmonitoring and valve triggering are combined in one unit quarter-turnactuators can be controlled at low cost. This is an example that thissystem enables implementation of new units with a high integrationdensity.

4.4.3 Units with mounting aid

efectors with a two-colour LED function meet the requirements for asimple, non-polarised connection and an optical mounting and settingaid. A red and green (or yellow) LED indicate the position of the object tobe detected in the sensing zone. As soon as the object is detected bothLEDs light. When coming close to a value below 80% of the ratedoperating distance only the switching LED lights and indicates a safemounting distance. In addition, the units feature a long operatingdistance for flush and non-flush mounting.

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Figure 57: Function diagram two-colour LED

AS-i For some types of photoelectric sensors another switching output hasbeen brought out to signal an uncertain switching state. This is alsocalled failure warning and can for example be used to remove soilingbefore problems occur. This option is also conceivable for inductiveproximity switches but has not been implemented so far. The extra workinvolved when two outputs per sensor must be connected to thecontroller is for example a reason not to do so. Therefore the uncertainswitching state of these sensors is only indicated via the LED which servesas a mounting aid. However, this is different with the intelligent sensors.They are direct participants of the AS-i system (see catalogue) and haveup to 4 data bits. In addition to the uncertain switching state it is alsopossible to monitor readiness for operation.

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4.4.4 quadronorm units

Leakage current For the 2-wire switches of the former generations the leakage currentcould be some mA. Thus a reliable signal processing, e.g. by plc inputs,was no longer guaranteed.

Polarity For solid-state DC outputs polarity must be taken into account. In manycountries and industries pnp switching sensors are commonly used. Byimporting controlgear or exporting complete installations to countrieswhere the other polarity is common, the different polarities are a possiblesource of failure, in particular if a failed sensor must be replaced. In Japanfor example npn units are still frequently found.

Normally open / normally closed Often two units are needed which only differ in their switching functionand are otherwise completely identical. This doubles storage of spareparts. Moreover, replacement of a failed unit is a possible fault source.Especially for units with terminal chamber the switching function can bedetermined by selection of the terminals. But this is not possible withstandard units.

The goal of the development of the quadronorm units was to improvethe above-mentioned points. They have the following features:  Leakage current normally 0.4 to 0.6 mA  Automatic recognition and adaptation to the polarity  Switching function is inverted by reversing the wires.

Core colours For the colour marking of the wires a new approach had to be pursuedas the usual colours, e.g. BN für L+ could not be used (cf. 4.3.2).

Figure 58: Wiring diagram quadronorm

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4.4.5 Non polarised units

They are special quadronorm units. Non-polarised connection means thatthe function of the unit, e.g. normally open, is maintained no matter howthe switch is connected. This function comes closest to the mechanicalswitch.

The two black wires are typical of efectors with non-polarisedconnection. They show that connection in either way is possible.

Ô õ

Ô ó¾µ

¾µ

Figure 59: Wiring diagram non polarised

This avoids the only mistake which can be made when connectingquadronorm units, i.e. undesired inversion of the switching function byreversing the two wires.

4.4.6 Self-monitoring systems

Safety for machines and equipment According to a statistical analysis 90% of all faults in a plant are causedby peripheral equipment, i.e. sensors (e.g. electronic proximity switches)and actuators (e.g. solenoid valves).

This is easily understood when taking into account that these units andtheir cables are often exposed to extreme environmental conditions.Failures caused by wire break, short circuit or mechanical damage cannotbe excluded. An unnoticed failure of a sensor or actuator may lead todestruction of machinery, damage to products or even danger foroperators.

Safety of people? No! In principle, self-monitoring systems indirectly also concern the safety ofpeople. However, this subject is treated by safety technology. Units whichare allowed for use in applications where the safety of people must beensured are subject to strict rules, standards and regulations. Specialapprovals are required as for ATEX units. These units are thereforetreated separately in the training manuals ATEX and safety technology.As indicated above, this is about safety of machines and equipment.

Past A combination of sensors, called s efectors, with the control monitorF400 were supplied in the past. They are now no longer available but stillused.

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Current solution: AS-i These units were not taken from the product line because theapplications do not exist any more. An optimum protection of machineryand valuable production equipment is always important. But today thereare alternatives to such units.The intelligent AS-i sensors (see catalogue) described above (see 4.4.3)are such an alternative. Moreover there are also units which are used forthe safety of people. But this is also treated separately for AS-i (see thetraining manual safety technology).

4.4.7 Weld-field immune units

Use in welding equipment with high constant and alternating fields.Inductive proximity switches are used in welding lines (see IEC 60947-5-2,annex E), for example:  for welding robots in the immediate vicinity of the welding tongs or

welding electrodes to monitor their position during welding;  to monitor the position of the chuck;  to detect the parts to be welded in the tool, e.g. metal sheets;  for the automatic control and positioning of the tool during the

different welding operations.

Influence of the magnetic field During welding a welding current of 8 to 30 kA flows depending on the  characteristics of the material,  thickness of the metal sheets,  intended use of the parts for cars (e.g. sheets for the body shell

whose surface characteristics must not be negatively affected),  wear of the welding electrodes.

Why? The magnetic field thus generated can interfere with inductive proximityswitches in the immediate vicinity  by a magnetic saturation of the ferrite core when they are not

switched,  by induced voltages within the electronics when they are switched or

not.

Position in the magnetic field The position of the proximity switch in the magnetic field plays animportant role with the axial position being the most unfavourable due tothe high magnetic field intensity.

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1: Conductor with welding current I2: Sensor in the radial field3: Sensor in the axial field

Figure 60: Position in the magnetic field

Welding current and distance from the conductorThe application of weld-field immune inductive sensors depends on thelevel of the welding current I and the distance r from the conductorwhere the welding current flows.

The graph of the magnetic inductance B in dependence on the distance rof the current-carrying conductor is shown in the following figure.

Figure 61: Magnetic field and distance from the conductor

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Equation Reference values for sensor mounting are calculated with the magneticinductance equation.

( 5)r

IB

Iã 200

B[mT]: Magnetic inductanceI[A]: Current intensityr[mm]: Distance

The electromagnetic-field immune efectors of ifm electronic, also calledweld-field immune efectors, can be used at close range to weldingelectrodes in alternating and constant fields. For example M12 and M18efectors were tested successfully in an alternating field with a weldingcurrent of 21 kA and a distance of 30 mm between the sensor andconductor where the welding current flows. These operating conditionscorrespond to a magnetic inductance B = 140 mT.

To compare: At a distance of 1 mm from a conductor where a current ofI = 1 A flows B is 0.2 mT. The Earth's magnetic field is in the range of0.01 mT.

How? The magnetic field immunity was achieved using  a special oscillator  a new coil structure.  an air-core inductor

To protect the electromagnetic-field immune inductive efectors againstweld spatter they were fitted with an anti-adhesive and temperature-resistant sensing face. The coating contains no silicone as silicone breaksdown the paint surface tension, which can cause flemishes in carpaintwork. For the more recent units PTFE is used.

Depending on the application, PTFE (teflon) caps can be ordered asaccessories for M12, M18 and M30 switches to provide additionalprotection against mechanical damage. Sockets with irradiated cables arealso available as accessories which are particularly suitable forapplications in welding lines.

Special features of the electromagnetic-field immune switches:  Electromagnetic-field immune (weld-field immune) for 50 Hz and

1000 Hz welding  Insensitive to predamping (flush mountable units)  Coil structure: 1 and 2-coil technology  Sensing face protected against mechanical damage  Sensing face of PTFE (teflon) or with anti-adhesive (safecoat) coating,

heat-resistant  Design for the automotive industry, length 60 mm, incl. plug  High switching frequency  Designs M12 f/nf, M18 f, M30 f and rectangular with universal US-

100 plug.

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4.4.8 Units with increased operating distance

In industrial applications units with increased operating distance are moreand more often used. This is so because the installation conditions inplants no longer correspond to IEC 60947-5-2, i.e.  the required clear space for mounting non flush units in metal is no

longer available,  smaller designs or smaller targets are used,  the division into flush and non-flush mountable switches is to be

eliminated to reduce mounting, servicing and storage of spare parts.

To comply with these customers' requests ifm developed units withincreased operating distance. Important requirements for the units are asfollows:  Small operating distance reduction, i.e. the difference of the

operating distance of flush units when mounted flush and non flush,see 3.3.1.

  Sufficient excess gain to avoid uncontrolled switching for exampledue to conductive dust and high temperatures

  Compliance with the installation conditions according to IEC 60947-5-2 for flush and non-flush mounting of inductive proximity switches

  At least the same correction factors as for units with normaloperating distance, i.e.:

  Longer operating distance for materials other than mild steel  Series production, i.e. cost-optimised volume-limited sensor

technology

How is this achieved? Operating distance and quality factor of the oscillator circuit are in directrelation, i.e. the better the quality, the higher the attainable operatingdistance. The quality factor is improved by changing the followingparameters:  Core material and geometry  Coil wire  Magnetic field distribution (development of a sandwich sensor)  Oscillator frequency  Use of NTC networks for temperature compensation

Mounting flush units non flush results in an operating distance reduction,especially for large designs (M18, M30), see 3.3.1 and the followingFigure 62:

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Figure 62: Operating distance reduction

  Normally ifm units have an operating distance reduction below 10%,see graph 1 and graph 2

  If the operating distance reduction for an increased operatingdistance is only insufficiently compensated for, large designs have ahigher operating distance reduction, see graph 3 and graph 4

  or even switch on permanently, see graph 5

The following table indicates some typical values for increased operatingdistances of ifm units.

flush mountable non-flush mountablealt neu alt neu

M8 1 2 (+ 100 %) 2 4 (+ 100 %)M12 2 4 (+ 100 %) 4 7 (+ 75 %)M18 5 8 (+ 60 %) 8 12 (+ 50 %)M30 10 15 (+ 50 %) 15 22 (+ 47 %)

All indications are for sn [mm]. "Old" means according to IEC 60947-5-2,"new" stands for the increased value.

4.4.9 Units for overflush mounting

In 3.4.1 the term overflush has already been explained. For monitoringtransport processes, in particular when moving heavy objects, longoperating distances as achieved with rectangular units, are required. Sucha unit is overflush mountable. Figure 63 shows the clear space to beadhered to. The unit can be recessed by a maximum of 5 mm. To do so,a lateral clear space of 3 to 4 mm must be adhered to.

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Figure 63: IDC overflush mounting

In 3.4.1 the term overflush has already been explained. For monitoringtransport processes, in particular when moving heavy objects, longoperating distances as achieved with rectangular units, are required. Sucha unit is overflush mountable. Figure 63 shows the clear space to beadhered to. The unit can be recessed by a maximum of 5 mm. To do so,a lateral clear space of 3 to 4 mm must be adhered to.

Overview of inductive units Due to the wide selection of types and variants an overview can nolonger be given in a simple table. Here the screen representation of theselector is shown as an example. Note that when working with theselector not every combination of features is possible. It is recommendedto get familiar with the selector because you can then obtain a goodoverview of the variety of switches.

Figure 64: Overview of inductive switches in the selector

There is one special feature for the large rectangular units: the sensitivity,i.e. the operating distance is adjustable with a potentiometer. For theother units it is fixed.

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4.4.10 Special correction factors, K1, K0

K = 1 The operating principle was detailed in 3.5. Below the special features ofthis type which are important for the user are described.

Features In principle, this sensor behaves like a conventional inductive proximityswitch. But for special applications certain features must be taken intoaccount. The switch-on graph is much narrower than with theconventional type. The coil arrangement has a certain sensing directionwhich has a higher effect with this type.

The broken line in Figure 65 shows the switch-on graph for theconventional sensor (not to be confused with the hysteresis graph, Figure20), the unbroken line the graph of the K1 sensor. For the sake ofillustration the figure is a little exaggerated.

K1- - - - - Conventional sensor

Figure 65: Switch-on graphs

Narrow objects If stacks of sheets, e.g. transformer sheets, are detected, the selectedposition should be transverse to the layers (horizontal arrow in Figure 66).The other position (vertical arrow) is unfavourable. It is known that thelayers of transformer sheets are electrically isolated to minimize eddycurrent losses. But for K1 this can have the effect that the individualsheet directly opposite the sensor (lower position in Figure 66) which"sees" the sensor from the edge has too small dimensions, i.e. is toonarrow to be detected. Due to the sensing direction detection of thesheets positioned on the side is especially poor.

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Figure 66: Detection of transformer sheets

Which designs? The following information refers to the new cylindrical designs.

Frequency The K1 sensor has a higher switching frequency due to the higherfrequency of the oscillator.

Temperature To be on the safe side, the maximum value of the temperature range isspecified with 70°C for the K1 sensor.

Welding current Due to the operating principle the K1 sensor is weld-field(electromagnetic-field) immune without additional measures beingrequired.

Predamping In practice, problems can arise due to predamping, especially for the non-flush mountable conventional type. The influence of predamping is muchsmaller for K1 (all the more so for K0, see 3.5.4). So it functions morereliably.

Small objects However, the disadvantage of low susceptibility to predamping is that thesensor does not detect small objects as reliably as the conventionalsensor.

K = 0 The features of the K0 sensor are more or less the same as for the K1sensor except for the switching frequency.

Operating distance reduction Compared to the conventional sensor, the opposite effect of predampingis a remarkable feature. In case of predamping the operating distance canbecome even smaller. Due to this effect a sensing face of high-gradestainless steel can be used.

Area of applications In metalworking applications proximity switches are directly exposed toharsh environmental conditions. The "ferrous-only" efectorm ingress-resistant design incorporates high-quality materials such as Viton O-ringsor a stainless steel sensing face. They guarantee long life.

Ferrous-only The new efectorm ferrous only switches only detect ferrous metals.Aluminium chips which build up on the sensing face during the processand lead to incorrect switching of conventional sensors are ignored dueto this principle.

Absolutely ingress-resistant The sensor is resistant to oil and coolants due to the special design,additional seals as well as the use of a stainless steel cover as sensing

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face. This results in a long life. These efectorm units have the protectionratings IP68 and IP67 (see training manual protection ratings).

Robust The full metal housing of the K0 sensor is for example more resistant toabrasion than standard sensors. Due to the laser type label units can stillbe identified afters years.

Features  Aluminium chip immune, therefore no malfunction caused by

aluminium chips.  IP68, IP67. Absolutely reliable in permanent contact with oil and

coolants.  High vibration and shock resistance.  Robust design with stainless steel sensing face and reinforced

housing.  Permanently legible laser type label.

Units The first type with K = 1 was rectangular. The new generation also coversthreaded housings.

Rectangular IMC (see catalogue, type IM5067)

Thread IFK (M 12), IGK (M 18), IIK (M30)

K = 0 Designs: IF and IG (see catalogue, types IFC211 and IGC211).

4.5 Criteria for practical use

Overview Most of the following points have already been discussed in detail andare again briefly summed up below.

Since sensors in production processes are normally mounted at exposedmachine locations, they are directly subjected to harsh environmentalconditions like heat, cold, shock, vibration, dust, moisture, chemicallyaggressive liquids, etc. Therefore they must be protected againstmalfunction caused by such harsh operating conditions. The data sheetscontain information about applications and environmental conditionswhere the units can be used without problem.

Operating temperature This indicates the temperature of the medium surrounding the proximityswitch. The specified permissible temperature range is often �25°C to+80°C. Within these limits the switch is allowed to be operated as longas desired. Temperatures which are slightly above or below these limitsfor a short time are normally tolerated by the switches. This means thatthe switch is not destroyed but the operating distance can be outside thepermissible range within this time. Special units are available for othertemperature ranges.Resistance to temperature shocks and high temperature fluctuationswithin a short time is much better for the modular units.

Shock and vibration resistance Proximity switches have no moving parts. They are thus extremelyresistant to shocks or vibrations. A standard value for the maximumshock resistance is 30 times the gravitational acceleration (30 g). Areference value for the maximum vibration resistance is a frequency of upto 55 Hz with an amplitude of 1 mm. Furthermore the efectorm units for

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mobile use have been specially developed to withstand increased shocksand vibrations in mobile applications. The features of these units aremuch above the standard requirements.

Foreign bodies and dust Inductive proximity switches are in no way influenced by build-up ofelectrically non conductive materials. Smaller conductive particles likemetal chips do not lead to eddy current losses that are so high that theycan influence the switch.To identify ingress resistance of electrical apparatus (see training manualprotection ratings) an internationally standardised combination of figuresis used by the proximity switch manufacturers to indicate ingressresistance of their units, e.g. IP 67. IP stands for "internationalprotection". The first figure indicates protection against contact with liveparts and ingress of solid foreign objects. 6 means protection againstingress of fine dust and complete protection against contact with liveparts. The second figure refers to the protection against ingress of water.

Moisture and water The function of inductive proximity switches is not directly influenced bywater, moisture, mist and vapours. Their function is only restricted in caseof long-term exposure.To be on the safe side, it is however important to know how well aproximity switch is protected against ingress of water. This is shown bythe second figure of the IP rating. 7 for example means that a proximityswitch is protected against ingress of water so that it can be placed in 1m water depth for half an hour without water penetrating in harmfulquantities.As a rule proximity switches are offered with the protection ratings IP65and IP67 according to the requirements of the standard. In general, unitswith potted cable have the protection rating IP67. For units with terminalchamber or connector IP65 is specified. But they can also be often usedunder conditions where IP67 is required. This protection rating isindicated because incorrect mounting, e.g. incorrect placing of seals, canresult in another protection rating.For the modular units ingress resistance has been improved even more.

Chemical influence Whenever solid, liquid or gaseous chemical substances can interfere withthe operation of a proximity switch it must be carefully checked whetherhousing and cable sufficiently withstand this substance. The commonplastic housings of glass fibre reinforced material or the units withadditional metal sheath are in most cases a good option for use in achemical environment. For especially difficult applications specialhousings of corrosion-resistant stainless steel or PTFE sleeves are availableas accessories.In particular the continued development of additives for cleaning agentsor coolants in the chemical industry place increasing demands on theunits. They are fulfilled best by the modular units.

Electromagnetic influence In applications for proximity switches, i.e. in industrial environments,various high-energy electromagnetic disturbances occur caused e.g. byradio transmitters, switching operations in the mains, switch-off ofinductive loads or lightning strikes. Such electromagnetic interference canbe picked up by the sensing field or the connection cable. Due to thedimensions of the sensor which are small compared to the length ofradio waves the risk of influence of such periodic interference is very low.Abrupt and short disturbances can be filtered by suitable circuitcomponents so that the noise immunity of proximity switches is high.

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Interference can also be picked by the cable. When the cable has notbeen laid favourably, it can happen that the cable to the proximity switchacts as an antenna for radio waves or numerous abrupt disturbances canbe picked up by cables with a high noise component laid in parallel. Inparticular the further development of frequency inverters leads toincreased requirements. In special cases using interference-suppressionfilters can help.Limit values for immunity to this interference are defined in the EMCdirective (see training manual CE marking). The units must pass a numberof tests to be allowed to carry the compulsory CE mark. Here immunity todefined interference is tested.The requirements for units for mobile use (road traffic) are much higherthan laid down in the EMC law (CE marking). ifm offers units (with e1approval) for this area as well.

Other influences Compared to other sensor types the function of inductive proximityswitches cannot be disturbed by sound and light. The only interference towhich a proximity switch is not immune is intensive X-ray radiation orradioactivity. Strong magnetic fields close to the proximity switch, e.g.for electrical welding equipment can affect the function of inductiveproximity switches. For this application ifm offers so-called weld-fieldimmune special versions.

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5 Application examples

Proximity switches are mainly used as position switches as an alternativeto mechanical position switches. Mechanical switches are cheaper butsubjected to wear. If they fail, complete plant sections, conveyor belts,etc. can be brought to a standstill for hours. Therefore it makes sense touse non-contact and wear-free electronic proximity switches instead ofmechanical switches for these applications.

Proximity switches are also a good choice for rotational speedmonitoring. High switching frequencies must be achieved and a largenumber of switching cycles are required for a correct function of themonitoring system. Moreover a clearly defined switching signal isimportant for an exact evaluation. Proximity switches with a highswitching frequency and solid-state output are an excellent choice toprovide clearly defined output signals (see 3.3.4).

Hazardous areas in the chemical industry, mills or tanks are the oldest ofall applications for proximity switches. Since in this area only very smallvoltages are allowed, proximity switches with additional safety areavailable for such applications. Many types of proximity switches hold anATEX approval for use in hazardous areas. These switch types arestandardised in the DIN 19 234 and are frequently referred to as NAMURswitches.

For applications where failure of a proximity switch, e.g. due tomechanical damage is not acceptable, many manufacturers supply self-monitoring systems where the proximity switch itself is continuouslymonitored for its function.

This is only a short overview of the universal suitability of inductiveproximity switches. The user comes across many tasks which are notobvious at first sight during the design stage of his installation. So sooneror later the knowledge alone of the function and features of inductiveproximity switches helps to solve application problems.

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Figure 67: Robot arm

The two possible end positions of the robot arm are monitored withoutcontact by inductive proximity switches.

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Figure 68: Pipe production

For the pipe production the inductive proximity switch monitors thesupply of new pipes for further processing.

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Figure 69: Rotational speed monitoring

Inductive proximity switches used for rotational speed monitoring of amachine (see 3.3.4). The proximity switch detects the teeth of thetoothed wheel without contact. Mounting additional targets or switchingcams is not necessary.

Figure 70: Car washer

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Inductive proximity switches with increased operating distance used in anautomatic car washer. The increased operating distance ensures reliabledetection even in case of mechanical tolerances

Figure 71: Welding robot

Electromagnetic field immune efectors monitor the end position, e.g. onwelding robots close to the welding electrodes.

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Figure 72: Conveyor

Inductive efectors monitor the position on automatic transport systemsand conveyors, e.g. in the automotive industry.

Figure 73: Elevator

efectors used to monitor an elevator. In combination with speed andskew monitors the sensors signal misalignment of the conveyor andmonitor the rotational speed of the drive.

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Appendix

Advantages In general it can be assumed that efectors do not only meet the specifieddata, but are on the safe side. Standards are complied with and evenexceeded. IP 67 means that the unit operates correctly in 1 m waterdepth for 30 min. There are applications where efectors operatecontinuously without problem in deep water. Values above or below thespecified temperature range of e.g. �25° C to +80°C are possible withincertain limits (cf. 3.3.1). Modular units are distinguished by their highresistance to temperature shocks.Further advantages:  Product availability  Reliability (5-year warranty for standard units)  Service (large sales force)  Compliance with special requests (custom-made units)  Use of film and modular technology

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Technical glossary

Active zone / sensing zone The active zone is the area over the sensing face in which the proximityswitch reacts to the approach of the damping material, e.g. changes itsswitching status.

Assured operating distance (sa) The assured operating distance is the distance from the sensing facewhere a proximity switch operates reliably under given temperature andvoltage conditions (see operating distance). It is the minimum value ofthe usable operating distance.

Cable material PVC In order to avoid cable break PVC cables must not be moved if the

temperature falls below -5° C.

Correction factor If the shape, material or thickness of the target is different from thestandard target, operating distances other than the standard operatingdistance result. They can be calculated using correction factors which arespecified in the technical data sheet. The following factors must also betaken into account:

Shape factor If instead of the standard target, a smaller or non square target is used orif the target is not flat, the operating distance must be corrected with ashape factor.

Material factor If instead of the target material defined in the standard, e.g. FE360 to ISO630, another target material is used, the operating distance must becorrected with a material factor. For inductive sensors it depends on theconductivity and the permeability of the material.For K1 units it is constant ( = 1), K0 units only detect steel (ferromagneticmaterials).

Material thickness factor If a target is used with a thickness below the penetration depth of thesensing field (e.g. metal foil), the operating distance must be correctedwith a material thickness factor. For inductive switches this factor is ingeneral greater than 1, i.e. the conductivity of the material seems to beless than normal as part of the magnetic field emerges behind the metalfoil due to the skin effect. This leads to a longer operating distance.For capacitive switches this factor is normally below 1.

Current rating/peak Switch-on and switch-off capacity under usual/unusual conditions.The peak current rating is the maximum current which may flow for ashort time at the moment of switch-on without destroying the proximityswitch.Especially AC units are rated so that they can be operated with six timesthe nominal current for a short time due to the high inrush currents ofmany AC loads (pilot lamps, contactors...) (also see utilization categories).

Effective operating distance sr The effective operating distance of a proximity switch is the operatingdistance measured at rated voltage and room temperature (23 ±5°C). Itmust lie between 90 % and 110 % of the rated operating distance (seeoperating distance).

Flush mounting The sensing face can be mounted flush with the surface of the dampingmaterial.

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Housing materials Metal housing Aluminium

Stainless steel *Steel sheet galvanisedBrass with Optalloy (nickel-free)*PTFE coated brass (safecoating)**: Inductive unitsStainless steels (rust-free stainless steel and acid-resistant high-gradestainless steel):Stainless steel: 303S22 (X10CrNiS 189)

304S15 (X2CrNiMo)High-grade steel: 316S12 (X2CrNiMo 17132)

316S12 (X2CrNiMo 18143)320S31 (X6CrNiMoTi 17122)

Plastic housing PBTP (polybutyleneterephtalate) The housing is largely resistant to aliphatic and aromatic hydrocarbons,

oils, greases, hydraulic fluids, fuels; no stress cracking when exposed toair.The housing is not resistant to hot water, hot steam, acetone,halocarbons, concentrated acids and alkalis.

Modified PPO The housing is largely resistant to diluted mineral acids, weak alkalis,some alcohols, oils and greases depending on the additives.

Chemically resistant fluoroplastics: PTFE (polytetrafluoroetylene)LCP, PEEK, PEI, PA, mod. PC

The resistance of plastics depends on the environmental and operatingconditions. Therefore certain properties or the suitability for a certainapplication cannot be guaranteed.For frequent or permanent exposure to chemicals it is recommended totest all housing materials prior to use.

The chemical resistance of the cast resin used for potting is comparableto that of the plastics for the efector housings. For unpotted efectorm

units protection against contact with the medium other than the housingmaterials has been further improved due to the design..

Hysteresis The hysteresis is the difference between switch-on and switch-off pointof the proximity switch. It is indicated in percent referred to the switch-onpoint measured under the same conditions and serves to preventuncontrolled switching of the proximity switch when the target is nearthe switch point ("output chattering").

Leakage current in 2-wire units The leakage current is the current which flows through 2-wire units whenthe output is blocked in order to supply the electronics with current. Theleakage current also flows through the load.

Measurement of the operating distance The operating distance is determined according to EN 60947-5-2.

NAMUR NAMUR stands for Normenarbeitsgemeinschaft für Meß- undRegeltechnik (standardisation group for metrology) in the chemicalindustry. A NAMUR switch is a special version of a 2-wire DC unit to DN19234 suitable for use in hazardous areas (today ATEX, see trainingmanual).

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No-load current for 3-wire units The no-load current is the intrinsic current consumption of the proximityswitch when it is not switched.A very low leakage current of about 0.1 µA flows through the outputtransistor when the output is not switched (open collector).

Nominal operating distance See rated operating distance.

Non-flush mounting A proximity switch is non-flush mountable when a specified free zonearound its sensing face is necessary in order to maintain itscharacteristics.

Normally closed Principle of normally closed operation. If an object is in the area of theactive zone, the output is blocked (see output function).

Normally open Principle of normally open operation. If an object is in the area of theactive zone, the output is switched.

Operating distance The operating distance of a proximity switch is the distance at which anobject approaching the sensing face axially causes the output to changeits state (see correction factors and measurement...).Also see rated operating distance, usable operating distance, effectiveoperating distance and assured operating distance.

Operating temperature range The temperature range specifies the temperatures at which proximityswitches can be used.Common ranges for ifm efectors:Standard units -25...80° CUnits with special features (e.g. increased operating distance)-25...70 °C 0...100 °C-40...85 °C

Operating voltage The voltage range (around the nominal voltage) in which the proximityswitch operates reliably. For DC units the minimum and maximum values,including the residual ripple, must be adhered to.

Output function Normally open Object within the active zone � output switched / high signal Normally closed Object within the active zone � output blocked / low signal Programmable Normally closed or normally open selectable Complementary Normally open and normally closed output functions are available

simultaneously.

Overload protection The output of a proximity switch is protected against overload if anycurrents between nominal load current and short-circuit current can flowcontinuously without damage.

Passing speed If the proximity switch is damped and undamped by one single targetwhich moves through the active zone at high speed, there is a maximumpassing speed at which a reliable switching signal is just provided.

Power-on delay time The time the proximity switch needs to be ready for operation afterpower on. It depends on the switch type and is in the ms range (5 ms toover 200 ms depending on the type). Within this time the internal voltagesupply must stabilise and the oscillator must start to oscillate. Theoutput is not active.

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Programming For some efector types the output function can be programmed to benormally open or normally closed. Depending on the efector type theoutput function is programmed via a wire link, a jumper or pinconnection.

Protection rating See the training manual protection ratings. IP 65 Complete protection against contact with live parts. Protection against

the ingress of dust. Protection against water jets. IP 67 Complete protection against contact with live parts. Protection against

the ingress of dust. Protection against the ingress of water whensubmerged in 1 m depth for 30 minutes.

Rated impulse withstand voltage Uimp This is the voltage reference for clearance rating.

Rated insulation voltage Ui This is the voltage reference for the dielectric voltage tests and creepagedistances. For units with protection class II the voltage of the adjacentmains supply is considered to be Ui, 250 V AC.

Rated operating current The rated operating current (continuous current rating) indicates thecurrent at which a proximity switch can be continuously operated (alsosee current rating/peak).

Rated operating distance (sn) The rated operating distance is a value which does not take into accountindividual variations and changes due to external influence liketemperature and voltage (also see operating distance).

Repeatability (reproducibility) The difference between two operating distance measurements carriedout for 8 hours under standardised conditions is called repeatability andspecified in percent referred to the effective operating distance. Thedifference between two random measurements must not exceed 10% ofthe effective operating distance.

Reverse polarity protection A switch is protected against reverse polarity if the wire connection to theterminals can be reversed without damage to the switch. As a rule 3-wireswitches which are protected against reverse polarity must be short-circuit protected because otherwise reversing the output and groundconnection (0 V) would destroy the unit.

Sensing face The sensing face is the face on the proximity switch where theelectromagnetic field is generated.

Sensing zone see Active zone

Short-circuit protection The output of a proximity switch is short-circuit protected according toVDE 0160 if it withstands a short circuit of the load or a short to groundat the output permanently without damage and if it is ready foroperation again without any switching after the short circuit has beenremoved.In the event of a short circuit the output transistor is blockedimmediately. After rectification of the short circuit the unit is ready againfor operation immediately. Reversing the connection wires does notdestroy the units. Short-circuit protected units are normally protectedagainst overload and reverse polarity.

Smallest operating current in 2-wire unitsThis is the current which must at least flow in the switched state toensure reliable operation of the proximity switch (sometimes also calledminimum load current).

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Switching delay The switching delay is the time which elapses between moving the targetinto the active zone and switching of the output. The switching delays fordamping and undamping can differ considerably. For ifm efectors thesetimes (depending on the type) are normally 0.2 to 2 ms for damping and0.3 to 3 ms for undamping. For units with F-IC a ratio of 1:1 for thesetwo times can be achieved.

Switching frequency The switching frequency is the limit frequency at which each periodicdamping and undamping operation of the proximity switch is just reliablyconverted into a switching signal. Since the attainable switchingfrequency depends on several factors, a standard measurementarrangement is defined in EN 60947-5-2 to obtain values for comparison.The switching frequencies in real applications are often much higher.If the proximity switch is operated with a high inductive load (contactor,relay, solenoid valve) for a longer period and high switching frequency,additional protective measures must be taken to reduce the switchingovervoltage (e.g. free-wheeling diodes).

Temperature / switch point drift Switch point drift is the shifting of the switch point caused by a changeof the operating temperature.

Types of mounting When inductive proximity switches are mounted, a distinction is madebetween flush and non-flush mounting.

Flush mounting (f) The sensing face can be mounted flush with the surface of the dampingmaterial.

Non-flush mounting (nf) The sensing face must be surrounded by a clear space (see mountinginstructions).When proximity switches are mounted side by side or opposite eachother defined minimum distances depending on the design must beadhered to.

Usable operating distance su The usable operating distance is measured within the permissibleoperating voltage and operating temperature ranges according to EN60947-5-2. It must lie between 90 % and 110 % of the effectiveoperating distance (see operating distance).

Utilization category The categories are listed and explained in the following table accordingto EN 60947-5-2.

Utilization categories for switching elementsCategory Typical applicationsAC-12 Control of resistive and solid-state loadsAlternating currentAC-140 Control of small electromagnetic loads with

holding current < 0.2 A; e.g. contactor relays

DC-12 Control of resistive and solid-state loadsDirect currentDC-13 Control of electromagnets

Category AC -140 applies to AC/DC efectors, category DC -13 to 2 and3-wire DC efectors and category DC-12 to NAMUR types.

Voltage drop (on-state voltage) As the switching output of the proximity switch is equipped with a solid-state component (transistor, thyristor, triac), a (small) voltage drop occursin series to the load in the switched state. In two-wire technology thevoltage drop also serves to supply the electronics of the proximity switchwith energy. The amount of the voltage drop depends on the type andlies between 2.5 V (DC) and 6.5 V (AC/DC).

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Type key

Pos. Designation Contents

1 Sensing principle inductive2 Type 1 = cylindrical, smooth plastic housing 100mm

2 = cylindrical, smooth plastic housing 164mm3 = rectangular housing 8 x 8 x 40mm (old, now = L)6 = special unit (Still)A = cylindrical, smooth plastic housing 20mmB = cylindrical, smooth plastic housing 34mmC = rectangular plastic housing 90 x 60 x 40mmD = rectangular plastic housing 120 x 80 x 30mmDC = rectangular plastic housing 92 x 80 x 40mmDE = rectangular plastic housing 105 x 80 x 40mmE = cylindrical housing M8 x 1F = cylindrical housing M12 x 1G = cylindrical housing M18 x 1I = cylindrical housing M30 x 1.5J = rectangular plastic housing 27 x 25 x 10.5mm and further special unitsL = rectangular housing 8 x 8 x 40mmM = rectangular plastic housing 120 x 40 x 40mmMC= rectangular plastic housing 66 x 40 x 40mmN = rectangular plastic housing 40 x 26 x 12mmND = rectangular plastic housing 40 x 26 x 26mmNS = power clamp switchO = rectangular plastic housing 26 x 26 x 70mmQ = rectangular plastic housing 30 x 28 x 15mm (cable) rectangular plastic housing 30 x 28 x 24mm (plug)R = high-pressure special typeS = rectangular plastic housing 28 x 16 x 10mmT = cylindrical, smooth housing 6.5mmV = rectangular plastic housing 118 x 40 x 40mm rectangular plastic housing 118 x 55 x 55W = rectangular plastic housing 60 x 36 x 10mmZ = cylindrical, smooth housing 4mmY = cylindrical housing M5 x 0.59 = special type

3 Design of housing � = standard / plastic housing A = standard / metal housing B = short body / metal thread C = short body / plastic thread D = dual sensor (IND) E = housing with terminal chamber G = smooth housing K = intermediate length / metal thread W = cube

4 Connection system 2 = two-wire system3 = three-wire system4 = four-wire systemC = 2/3-wire system (modular technology)

5-7 Sensing range in mm

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8 Additional designations � = standardB = flush installation (for extended sensing range)D = 2 separate output stages (IND)P = 2 distance-related outputsS = s-efectorR = series connection possibleU = electromagnetic-field immuneZ = temperature-resistant

9 Switching function A = normally open for two-wire units and for three-wire NPN units normally closed for three-wire PNP units normaly open for 2/3-wire modular technologyB = normally closed for two-wire units and for three-wire NPN units normally open for three-wire PNP units normaly closed for 2/3-wire modular technologyC = complementary outputD = analog outputE = NO and NC (independent, not complementary)F = output function programmableV = voltage outputN = NAMUR sensors (positions 10-12 not used)S = safety switch (positions 10-12 not used)asi = asi sensors (position 12 not used)

10 Output B = semiconductor output for AC and AC / DC unitsN = semiconductor output negative switchingP = semiconductor output positive switchingR = semiconductor output positive or negative switchingS = 2/3-wire modular technology (3-wire PNP; 2-wire PNP/NPN)T = 2/3-wire modular technology (3-wire NPN; 2-wire PNP/NPN)

11 Short-circuit protection K = with short-circuit protectionL = latchingO = without short-circuit protection

12 Supply voltage A = choice of AC or DC voltage (AC / DC)G = DC voltageW = AC voltage

13 Slash14 Options 2LEDs = 2 LED's

SL = earth wireV2A = V2A metal housingV4A = V4A metal housingMS = metal conduit attachmentUP = non-polarised outputSC = safecoatedF = frequency offsetxm = cable x m longSF = increased noise immunityAC = with AC connector (only with ... / xm - JAPAN)DC = with DC connector (only with ... / xm - JAPAN)T2 = dual sensor T2M = modular technologyK0 = Ferrous onlyK1 = no correction factorxD = ATEX approved for x category DustxG = ATEX approved for x category GasxxV = with Ub=xxV

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Production code

d:\dokumente und einstellungen\dezeyegu\eigene dateien\lokalab05-04\materiallevele\originale\prodcode-e.docThis copy was printed on 03.06.04 enclosure to EA SIT-015

Explanation production code The coding is indicated on the type and box labels of our products or on an alternative type oflabelling, e.g. 'direct laser labelling' as it is used with the units in modular technology.

The coding covers information about Legend 'production site'

production site production month special designation

(meaning registered in the production site)

production status

E ifm ecomatic, KressbronnK ifm prover, Kressbronn (from 1/3/2000)P (bought-in products)S ifm syntronT ifm Tettnang (parent plant)U ifm USA (efector inc.)W ifm SwedenF ifm France

Current production code:

Standard coding Direct laser labelling(conventional units) (modular units)

Example: SA8 made byifm Syntron inOctober (A) 1998

- no special designation -

Example: 9903 made in 1999,in March (03)

AA first production status (AA)

T AB in the parent plantifm Tettnang ;second prod. status (AB)

- no special designation -

Old coding (until September 1995)

spec.des.

prod. site(see

legend)

prod.month(hex.)1...9,A,B,C

Prod. year(last pos.)

prod. statusAA...ZZ spec.

des.prod. site

(see legend)

prod. month(dec.) 01...12

prod. year(last two pos.)

prod. statusAA...ZZ

spec.des.

prod year(last pos.)

prod. month(dec.) 01...12

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Index

#

............................................................................33

2

2-wire units........................................................61, 66

3

3/2-wire units...........................................................613-wire units........................................................61, 66

A

AC ...........................................................................67active zone...............................................................91advantages ..............................................................90aggressive media........................................................7Al ................................................................48, 50, 51alternating current ...................................................95aluminium chips.......................................................54analogue....................................................5, 6, 12, 18angle bracket ...........................................................63angle of approach....................................................13application examples................................................85AS-i..............................................................70, 71, 74assured operating distance.................................25, 91ATEX............................................................68, 69, 85axially.......................................................................29

B

b ............................................................................41basic inductive sensor...............................................15basic sensor ...............................................................5basics ...................................................................7, 11binary ..................................................5, 6, 12, 18, 20block diagram ..........................................................21blue cable ................................................................69

C

cable ........................................................................65cable gland ..............................................................65cable length .............................................................68cable material ..........................................................91car washer ...............................................................88carrier ......................................................................53category...................................................................95CE marking ........................................................66, 84ceramics.............................................................60, 63change in the quality factor .....................................48change of the switch point ......................................13chemical influence ...................................................83cleaning agents........................................7, 57, 63, 83clear space ...................................................27, 41, 78coil.....................................................................16, 58coil system ...............................................................55

complementary ........................................................93conductivity .............................................................10conduit ....................................................................46connection...............................................................58connection cable......................................................46connection technology.......................................61, 65connector.................................................................65connector units ........................................................58contact bouncing ...............................................13, 14contact resistance ....................................................13continuous current rating.........................................94coolants ...................................................7, 57, 63, 83core colours .............................................................72correction factor ........... 30, 31, 32, 33, 40, 48, 77, 91corrosion..................................................................14cost..........................................................................69counted pulses.........................................................37coupling factor.........................................................52cross-section ............................................................55curing ......................................................................57current ...............................................................93, 94current rating.....................................................67, 91cycle frequency ........................................................37cycle time.................................................................37cylindrical and smooth .............................................63cylindrical and threaded ...........................................63

D

damped .............................................................19, 20damping ..................................................................34DC ...........................................................................67degree of automation ..............................................63depth of penetration................................................33design ................................................................14, 63difference.................................................................53digital.........................................................................6dimensions...............................................................18direct current ...........................................................95direction of movement.............................................47dirt...........................................................................14disc with a hole........................................................36distance ...................................................................18distance measurement .............................................18dust .............................................................14, 57, 83

E

eddy current ............................................................18eddy currents ...............................................10, 11, 17edge ........................................................................80efector .......................................................................6efectorm .........................................................7, 60, 64effective operating distance .........................25, 50, 91electrical conductivity .........................................18, 32electrical data...........................................................65

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Training manual

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electrically conductive material .................................17electromagnetic induction..........................................9electromagnetic influence ........................................83electronic catalogue .................................................40electronic circuits......................................................14elevator ....................................................................89EMC law ..................................................................84energy......................................................................10environmental influences..........................................25evaluation ................................................................54excess gain...............................................................77

F

f .......................................................... 41, 43, 45, 95failure warning.........................................................71FAQ............................................................................7Faraday's law ...........................................................10Fe.............................................................................50ferrite core ........................................................ 16, 58ferromagnetic ............................................. 32, 48, 51field..........................................................................16film technology ........................................................57fixing elements.........................................................46flush................................................ 17, 28, 43, 77, 95flush mountable .......................................................41flush mounting.........................................................91food.........................................................................63food industry....................................................... 6, 58for non-flush mountable ..........................................41formula ......................................................................7frequency.......................................................... 15, 54

G

gold-plated contacts.......................................... 58, 63graphite ............................................................ 32, 40guarantee ..................................................................2

H

half the rated operating distance....................... 30, 35hazardous areas ................................................ 68, 85heat dissipation ........................................................57high-grade stainless steel................................... 58, 62hot metal chips ........................................................63housing....................................................... 53, 56, 60housing material ......................................................59housing materials .............................................. 59, 92hybrid technology ....................................................58hysteresis .............................................. 22, 28, 29, 92

I

ICs............................................................................58IDC...........................................................................79IEC 60947-5-2..........................................................24ifm ...................................................................... 6, 57increased operating distance ....................... 27, 40, 77IND...........................................................................69individual variations..................................................25inductive load...........................................................95

information ............................................................... 2ingress resistance .......................................... 7, 61, 63ingress-resistant ...................................................... 81installation input ..................................................... 69intelligent sensor ....................................................... 5interaction............................................................... 40interference............................................................... 6IP ............................................................................ 94IP 67........................................................................ 83IP 69K ..................................................................... 61iron ......................................................................... 32is K0........................................................................ 48

K

K 1 ....................................................................... 48K = 0................................................................. 33, 48K = 1................................................................. 32, 48K1 ........................................................................... 48

L

label ........................................................................ 61laser type label .................................................. 61, 63lateral approach ...................................................... 29LC oscillator............................................................. 15leakage current ..................................... 61, 66, 72, 92Lenz's Law............................................................... 11life time............................................................. 13, 14limit for the thickness .............................................. 33limit frequency ........................................................ 37

M

M12.................................................................. 58, 64M18 ........................................................................ 64M30 ........................................................................ 64M8 .................................................................... 58, 64magnetic field immune............................................ 74magnetic flux ............................................................ 9magnetic-field immune ........................................... 76magnetizability ........................................................ 10mark-to-space ratio ........................................... 35, 37material....................................................... 32, 40, 48material factor......................................................... 91material thickness.................................................... 33material thickness factor.......................................... 91measurement ............................................................ 5mechanical limit switch ........................................... 13mechanical stability ................................................. 46metal....................................................................... 59metal foil........................................................... 33, 91metal housing ......................................................... 92metal ring................................................................ 58metal sleeve ............................................................ 57mild steel........................................................... 24, 48minimum distances ................................................. 44minimum load current............................................. 94mist......................................................................... 83modular technology ................................................ 60moisture...................................................... 14, 57, 83

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mounting.................................................................95mounting aid ...........................................................70mounting instructions ........................................41, 44mounting sleeve.......................................................64movement ...............................................................40multiplicator.............................................................54mutual interference..................................................44

N

NAMUR ...................................................................92narrow objects .........................................................80nb ............................................................................41nf ................................................................41, 45, 95no-load current ........................................................93nominal operating distance......................................93nominal voltage .......................................................66non-contact output..................................................14non-flush .........................................41, 43, 77, 93, 95non-flush mountable................................................27non-polarised...........................................................73normally closed ............................................23, 72, 93normally open..............................................23, 72, 93notation.....................................................................7npn..........................................................................72NV 0100 ..................................................................69

O

offset frequencies ....................................................46oil ............................................................................14oils ...........................................................................63on-state voltage .......................................................95operating distance23, 33, 40, 43, 79, 81, 91, 93, 94,

95operating distance reduction............27, 28, 43, 77, 81operating temperature .............................................95operating temperature range ...................................93operating voltage.....................................................93operational reliability..........................................15, 40Optalloy ...................................................................92O-ring ......................................................................60oscillator circuit ........................................................19oscillator frequency ......................................49, 51, 54output .........................................................21, 23, 67output function........................................................93overflush............................................................44, 78overload...................................................................66overload protection..................................................93

P

parallel connection...................................................66passing speed ..........................................................93PBTP ..................................................................59, 92pcb ..........................................................................55peak ........................................................................91PEEK ..................................................................60, 63penetration depth ....................................................91permeability .......................................................18, 51pipe production .......................................................86

plastic housing ........................................................92plc............................................................................37pnp..........................................................................72Pocan.......................................................................63point measurement..................................................40polaritiy....................................................................67polarity.....................................................................72position....................................................................18position sensor.........................................................12potting.....................................................................57power-on delay time ....................................22, 66, 93PPO..........................................................................92precise .....................................................................26precision ..................................................................53predamping .................................................27, 44, 81Production code.......................................................98programmable .........................................................93programming...........................................................94protection ................................................................94protection rating ....................................59, 61, 83, 94protective circuitry....................................................66proximity switch...................................................6, 14PTFE .........................................................................76PVC....................................................................59, 91

Q

quadronorm.......................................................67, 72quarter-turn actuator ...............................................69quasi flush................................................................44

R

radially .....................................................................29rated impulse withstand voltage ..............................94rated insulation voltage............................................94rated operating current ............................................94rated operating distance ..................23, 40, 43, 48, 94readiness for operation ............................................71receiver ..............................................................52, 53rectangular...............................................................63reference resonant circuit.........................................52reliably detected.........................................................6repeatability .................................................26, 29, 94representative circuit diagram ..................................48reproducibility ..........................................................94residual ripple ..........................................................66resistance characteristics ....................................20, 49resolution...................................................................6response times .........................................................14reverse polarity.........................................................66reverse polarity protection........................................94robot arm.................................................................86room temperature....................................................91rotational speed ........................ 36, 37, 39, 85, 87, 89rule of thumb...............................................26, 30, 31rules.........................................................................26

S

sa ......................................................................25, 91

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Training manual

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safe mounting distance ............................................70safecoat ...................................................................76safety of people .......................................................73safety technology .....................................................73scale drawings..........................................................64screen ......................................................... 17, 43, 58seal test....................................................................61selector ............................................................. 40, 79sensing elements......................................................14sensing face .......................................... 46, 60, 91, 94sensitivity .................................................... 50, 52, 53sensor ........................................................................5sensor module..........................................................60serial connection ......................................................66series connection......................................................48setting aid ................................................................70shape .................................................... 18, 31, 40, 91shock resistance .......................................................82short circuit ..............................................................66short-circuit protection ...................................... 67, 94short-circuit voltage..................................................10side length ........................................................ 24, 31signal deviation ........................................................52signal frequency .......................................................37skew monitor ...........................................................89skin effect ................................................................11small objects ............................................................81SMD.........................................................................57smoothing capacitor.................................................66SMT .........................................................................57sn ...................................................................... 25, 94sr ...................................................................... 25, 91stainless steel ...........................................................32standard...................................................................24standard dimensions ................................................63standard square target .............................................24su ...................................................................... 25, 95switch off reliably .....................................................25switch point .............................................................50switch point drift......................................................95switching amplifier ............................................ 68, 69switching cam ................................................... 36, 37switching cycles................................................. 13, 14switching delay ........................................................95switching force.........................................................13switching frequency .................. 13, 14, 35, 49, 81, 95switching function............................................. 23, 72switching response...................................................14switching speed .......................................................35switching time................................................... 14, 34

switch-on graph .................................... 13, 14, 29, 80switch-on graphs..................................................... 29

T

target ................................................................ 24, 48temperature .................................... 25, 62, 81, 82, 95temperature range .................................................. 93temperature shocks..................................... 57, 62, 82temperature variations ............................................ 25terminal chamber .................................................... 65Tesla.......................................................................... 9test.......................................................................... 63thickness ................................................................. 33thin foils .................................................................. 11tightening torque .............................................. 46, 59time response.......................................................... 22toothed wheel......................................................... 37transfer resistance ................................................... 13transformer ............................................................. 17transmitter .................................................. 49, 52, 53transport processes ................................................. 78travel................................................................. 13, 14trigger stage...................................................... 20, 54type key ............................................................ 64, 96types of mounting................................................... 95

U

UC .......................................................................... 67uncertain switching state......................................... 71undamping.............................................................. 34universal current...................................................... 67unreliably detected.................................................... 6usable operating distance.................................. 25, 95utilization category.................................................. 95

V

valves ...................................................................... 69vapours ................................................................... 83vibration resistance.................................................. 82voltage drop...................................................... 66, 95voltage supply ......................................................... 66

W

warranty.................................................................... 6water ...................................................................... 83wear.................................................................. 13, 14weld spatter ............................................................ 76weld-field immune ................................ 74, 75, 76, 81welding robot ......................................................... 88