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What is an RTD?Resistance Temperature Detectors (RTDs) aretemperature sensors that contain a resistor thatchanges resistance value as its temperature changes.They have been used for many years to measuretemperature in laboratory and industrial processes,

and have developed a reputation for accuracy,repeatability, and stability.

Why use an RTD instead of a thermocoupleor thermistor sensor?Each type of temperature sensor has a particularset of conditions for which it is best suited. RTDsoffer several advantages:

A wide temperature range (-50 to 500C forthin-film and -200 to 850C for wire-wound)

Good accuracy (better than thermocouples) Good interchangeability Long-term stability

With a temperature range up to 850C, RTDs can

be used in all but the highest-temperature industrialprocesses. When made using metals such asplatinum, they are very stable and are not affectedby corrosion or oxidation.

Other materials such as nickel, copper, and nickel-ironalloy have also been used for RTDs. However, thesematerials are not commonly used since they havelower temperature capabilities and are not as stable orrepeatable as platinum.

RTD standardsThere are two standards for platinum RTDs:the European standard (also known as theDIN or IEC standard) and the American standard.

The European standard, also known as theDIN or IEC standard, is considered the world-widestandard for platinum RTDs. This standard,DIN/IEC 60751 (or simply IEC751), requires theRTD to have an electrical resistance of 100.00 at 0C and a temperature coefficient of resistance(TCR) of 0.00385 //C between 0 and 100C.

There are three resistance tolerances for Thin FilmRTDs specified in IEC60751:

Class AA (Formerly 1/3B) = (0.1+0.0017*t)C or100.00 0.04 at 0C

Class A = (0.15+0.002*t)C or 100.00 0.06 at 0C

Class B = (0.3+0.005*t)C or 100.00 0.12 at 0C

Also, one special class not included in DIN/IEC60751:

Class 1/10B = 1/10 (0.3+0.005*t)C or100.00 0.012 at 0C

The combination of resistance tolerance andtemperature coefficient define the resistance vs.temperature characteristics for the RTD sensor.The larger the element tolerance, the more thesensor will deviate from a generalized curve, and themore variation there will be from sensor to sensor(interchangeability). This is important to users whoneed to change or replace sensors and want tominimize interchangeability errors.

Section Z contains a resistance vs. temperature curvefrom -200 to 850C with resistance values given forevery degree Celsius. The following interchangeabilitytable shows how the tolerance and temperaturecoefficient affect the indicated temperature of the

sensor in degrees Celsius (Note: each tolerance classhas its own temperature range):

At Omega, our standard RTD product offering isbased on the European or IEC standard, and it isdesignated with an E in the model number.

Example: PR-10-2-100-1/4-6-EThe American standard, used mostly in NorthAmerica, has a resistance of 100.00 0.10 at 0Cand a temperature coefficient of resistance (TCR) of0.00392 //C nominal (between 0 and 100C).Section Z also includes a resistance vs. temperaturecurve from -100 to 457C, with resistance valuesgiven every one degree Celsius. At Omega, weprovide the American standard as an option anddesignate it with an A in the model number.

Example: PR-10-2-100-1/4-6-A

Other resistance value optionsRTD elements can also be purchased withresistances of 200, 500, and 1000 at 0C. TheseRTDs have the same temperature coefficients aspreviously described, but because of their higherresistances at 0C, they provide more resistancechange per degree, allowing for greater resolution.

What are RTD Sensors?Why Use Them? How Do They Work?

Element Interchangeability in C

Temp Class Class Class AA ClassC B A (13 B) 110 DIN

-196 1.28

-100 0.80 0.35

-50 0.55 0.25 0.18

-30 0.45 0.21 0.15

0 0.30 0.15 0.10 0.03

100 0.80 0.35 0.27 0.08

150 1.05 0.45 0.35 200 1.30 0.55 0.43

250 1.55 0.65 0.52

300 1.80 0.75

400 2.30 0.95

450 2.55 1.05

500 2.80

600 3.30

Tolerance Class Temperature Ranges

Class Wire Wound Thin Film

AA -50 to 250C 0 to 150C

A -100 to 450C -30 to 300C

B -196 to 600C -50 to 500C110B 0 to 100C 0 to 100C


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OMEGAs Class 10 Clean Room

For years Omega has been a leader in the manufactureand sale of thermal, pressure, load, flow, and other

sensing products and instrumentation. As part of ourcontinuing commitment to our customers, OEM andend user alike, Omega has invested in world-classmanufacturing facilities such as our Class 10 cleanrooms, our industry-leading mineral insulated cableproduction facility, and customized assembly andmolding processes.

RTD Element ConstructionPlatinum RTD elements are available in two types ofconstructions: thin film and wire wound.

Thin FilmThin-film RTD elements are produced by depositing athin layer of platinum onto a substrate. A pattern isthen created that provides an electrical circuit that istrimmed to provide a specific resistance. Lead wiresare then attached and the element and the assemblycoated to protect the platinum film and wire connections.

This investment provides us with a substantialadvantage in developing innovative products for ourcustomers. These advanced capabilities, along withour experienced technical, application, and customerservice professionals, are at your disposal indeveloping the best solution for your specificmeasurement and control needs.

Thin film elements are available in the Europeanstandard (0.00385 //C), and in a special version,used primarily in the appliance industry, that has atemperature coefficient of 0.00375 //C. Thin filmelements are not available in the American standard.

Wire WoundRTD elements also come in wire-wound constructions.

There are two types of wire-wound elements: those withcoils of wire packaged inside a ceramic or glass tube(the most commonly used wire-wound construction),and those wound around a glass or ceramic core andcovered with additional glass or ceramic material (usedin more specialized applications).

OMEGAs F2020, 100 , Class A thin-film element, see page C-1

Did you know that a Class 10 Clean Room can have no more thanten 0.5 micron particles per cubic foot of volume? Hospitaloperating rooms are Class 10,000, which means they can have10,000 particles per cubic foot. For a sense of scale, consider thatthe human hair is approximately 0.002 to 0.003" in diameter(or 51 to 77 microns).

Preparing to run another batch of elements

Substrates ready for processing

Did You Know That OMEGA Has theCapability Of Producing RTD, Pressure, Force,and Other Sensing Products in Our OwnNorth American Class 10 Clean Rooms?

Typical wire-wound RTD element


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RED

BLACK

RED

2 WIRE 3 WIRE

4 WIRE 2 WIRE WITH

COMPENSATING LOOPOMEGA HISTORICAL COLOUR CODES

RED

REDRED REDRED

WHITE WHITEWHITE

BLUE

IEC/ASTM COLOUR CODES

4 WIRE2 WIRE WITH

COMPENSATING LOOP

BLUEWHITE3 WIRE

WHITE

BLACKBLACK

BLACK BLACK

BLACK

BLACK

RED REDRED

RED RED

2 WIRE

Probe ConstructionOnce the RTD element is selected, the wiring andpackaging requirements need to be determined.There are a number of ways to wire the sensors,along with an unlimited number of probe or sensor

constructions to choose from.Wiring ArrangementIn order to measure temperature, the RTD elementmust be connected to some sort of monitoring orcontrol equipment. Since the temperaturemeasurement is based on the element resistance,any other resistance (lead wire resistance,connections, etc.) added to the circuit will result inmeasurement error.

The four basic wiring methods are shown below.

Sensors using the 4-wire construction are found inlaboratories and other applications where very precisemeasurements are needed. The fourth wire allowsthe measuring equipment to factor out all of the leadwire and other unwanted resistance from themeasurement circuit.

In the 2-wire with loop construction, the sensorresistance measurement includes the lead wireresistance. The loop resistance is then used to factorout the lead resistance.

The 2-wire construction is typically used only with high-resistance sensors, when lead lengths will be very short,or when tight measurement accuracy is not required.

Wire MaterialsWhen specifying the lead wire materials, careshould be taken to select the right lead wires forthe temperature and environment the sensor will beexposed to in service. When selecting lead wires,temperature is by far the primary consideration,however, physical properties such as abrasionresistance and water repelling characteristicscan also be important. Below is a table listing thecapabilities of the three most popular constructions:

ConfigurationOnce the RTD element, wire arrangement, and wireconstruction are selected, the physical constructionof the sensor needs to be considered. The final sensorconfiguration will depend upon the application.

Measuring the temperature of a liquid, a surface,or a gas stream requires different sensor configurations.

Lead Wire Materials

Temperature Abrasion WaterInsulation Range Resistance Submersion

PVC -40 to 105C Excellent Good

PFA -267 to 260C Good Excellent

Fiberglass -73 to 482C Poor Poor

Except for the 2-wire configuration, each of the abovewiring arrangements allows the monitoring or controlequipment to factor out the unwanted lead wireresistance and other resistances that occur in the circuit.

Sensors using the 3-wire construction are the mostcommon design, found in industrial process andmonitoring applications. The lead wire resistance isfactored out as long as all of the lead wires have thesame resistance; otherwise, errors can result.

TX92 transmitter, $188, shown actual size (see page N-39).

450-APT, $315,(see page L-51) withPR-11 style sensor,$66 (see page C-80), shownsmaller than actual size.

F3105 element. 3-conductor, PFA insulated cable.

RTD-2-F3105-36-T without epoxy potting over connection, $45, shown smaller than actual size (see page C-112).


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Liquid MeasurementsProbe-type sensor styles are normally used formeasuring liquids. They can be as simple as ourgeneral purpose PR-10 and PR-11 constructions,or as involved as our PR-12, 14, 18, or 19withconnection heads and transmitters. A popular choiceis the quick-disconnect sensor. This can be used asis, with compression fittings for flexible installation, orwith our PRS plastic handle for a handheld probe.

When measuring the temperature of harshenvironments such as plating baths or highlypressurized systems, sensors can be coated witha material like PFA PTFE, or they can be housedin a thermowell to protect the sensor from extremeconditions. Speak to our application engineersif you have any special measurement challenges.

Air and Gas Stream Measurements

Air and gas stream measurements are a challengebecause the rate of transfer of temperature from thefluid to the sensor is slower than for liquids. Therefore,sensors specifically designed for use in air or gas placethe sensing element as close to the media as possible.

OMEGAs RTD-805 and806 sensors allow thesensing element to benearly in direct contactwith the air stream. With ahousing design containingslots that allow the air toflow past the element,this construction is verypopular in measuring air temperature in laboratories,clean rooms, and other locations.

When the situation requires a little more protection forthe sensor, an option is to use a design similar to theRTD-860. This designhas a small diameterprobe with a flangefor mounting. Theconfiguration will be alittle slower to respond tochanges in the air stream,but it will provideimproved protection forthe sensor.

Surface Temperature MeasurementsSurface measurements can be one of the mostdifficult to make accurately. There are a wide varietyof styles to choose from, depending on how you wantto attach the sensor, how sensitive to changes intemperature the sensor has to be, and whether theinstallation will be permanent.

The most accurate and fastest-responding surfaceRTD is our SA1-RTD sensor. When applied toa surface, it becomesvirtually a part of thesurface it is measuring.

Surface sensors can alsobe bolted, screwed,glued, or cemented intoplace. The RTD-830 hasa pre-machined hole inthe housing to allow foreasy installation with a #4screw. The RTD-850 hasa housing with threadedtip that allows it to beinstalled into a standard#8-32 threaded hole. ThisRTD is handy formeasuring the

temperature ofheat sinks or structureswhere screw holes mayalready exist.

Element andWire Assemblies

Finally, if a simple RTD sensor with element and leadsis all you need, or you would like to build up your ownsensor, there are a wide variety of element and cableconfigurations to choose from. Our element and wireassemblies can also be cemented directly to astructure. These sensors can be manufactured withany of OMEGAs RTD elements and can includePFA, fiberglass, or bare lead wires to suit yourapplication. Standard configurations are sold ineconomical 5-packs, so you can keep a few handyfor those unanticipated tests. If you dont see thecombination you need in this handbook, just ask oneof our application engineers.

The information in this section is but a summaryof the technical information and applicationsexperience OMEGA can provide to support yourmeasurement and testing needs. We encourageyou to call our application engineers to tap into thesevast resources. If the product you need is not on theshelf, in most cases we can turn it around quickly tomeet your needs.

PRS/HDX Handle Probes,$95, see page C-55.

RTD-805, $86,see page C-105.

RTD-860, $83,see page C-102.

PR-17, $90,see page C-88.



SA1-RTD, $50,see page C-107.


RTD-2-F3105-36-T-B, $82 per 5 pack, see page C-64.

RTD-830, $64,see page C-104.

RTD-809, $83,see page C-106.

RTD-2-F3105-36-T-OTP, $52,see page C-110.

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