SENSOR SELECTION GUIDE1 Sensor Selection Guide 1. INTRODUCTION T he detection of hazardous gases has always been a complex subject, making the choice of an appropriate gas monitor-ing

SENSORSELECTION

GUIDE

SENSORSELECTION

GUIDETOXIC AND COMBUSTIBLE GAS MONITORS

(Includes gas listings with TLV-TWA, STEL, IDLH, LEL, and UEL for most gases)

INTERNATIONALSENSOR TECHNOLOGY

The Leader In Gas Detection Since 1972

3 Whatney, Irvine, California 92618-2836 • Telephone 949-452-9000 • FAX: 949-452-9009 • TLX: 4722070

Sensor Selection Guide

TABLEOF

CONTENTS

1. Introduction.................................................................................. 12. Solid State Sensors .................................................................... 1

2.1 General2.2 Principle of Operation2.3 Characteristics

3. Catalytic Bead Sensors .............................................................. 23.1 General3.2 Principle of Operation3.3 Characteristics

4. Electrochemical Sensors............................................................ 34.1 General4.2 Principle of Operation4.3 Characteristics

5. Sensor Selection ........................................................................ 45.1 Combustible Gas Monitoring5.2 Toxic Gas Monitoring

5.2.1 Carbon Monoxide5.2.2 Hydrogen Sul�de5.2.3 Chlorine/Hydrogen Chlorine5.2.4 Ammonia

6. Sensor Installation Notes .......................................................... 67. Definitions 68. Solid State Sensor Gas Data...................................................... 79. Product Data................................................................................ 9

9.1 Stationary Instruments9.1.1 Transmitters

SM954-20 IQ

9.1.2 Conventional SystemsMP Series

9.2 Portable Instruments9.2.1 Single Gas

IQ250/IQ3509.2.2 Multi-Gas

IQ1000IQ200

1


1. INTRODUCTION

The detection of hazardous gases hasalways been a complex subject, makingthe choice of an appropriate gas monitor-

ing instrument a difficult task. InternationalSensor Technology (IST) has been providing gasdetection equipment to customers worldwidesince 1972. Through this experience we havecompiled this guide which will provide you withsome insight into the various sensing methodsused for gas detection and provide you withinformation about the different instrumentsavailable to you. It will help you to make aninformed decision concerning which sensor typeand which instrument is best suited to your par-ticular application.

Discussion of sensing methods will focus on thefollowing three sensor types: Solid State,Electrochemical, and Catalytic Bead. These arethe most suitable and widely used sensors forambient air monitoring, and all three of thesetypes are available from IST. It should be notedthat instruments utilizing these sensors are notintended for use as analytical laboratory devices.The readings provided by these sensors shouldbe used primarily as indicators of whether anarea is safe or not, much like a smoke detector.While these sensors are much more refined thansmoke detectors, they are nonetheless subject toerroneous readings from interference gases andlack of periodic calibration, among other things.However, as long as these limitations are under-stood, the sensors will provide meaningful dataand are a valuable tool for ambient air monitor-ing. Instruments using these sensors willrespond quickly in the presence of gas, enablingalarms to be triggered and allowing personnel totake appropriate action. In addition, they aregenerally easy to use, require little maintenance,and are economically priced.

To date, no gas sensors exist which are 100%selective to a single gas. Achieving selectivityrequires the use of an analytical instrument.Various analytical techniques have beenemployed for gas detection and find use in cer-tain applications. Examples of such instruments

include Fourier Transform Infrared (FTIR) analyzers, Gas Chromatographs, and MassSpectrometers. These instruments can providefairly accurate and selective gas readings.However, they are generally very expensive and,in addition, many suffer from limitations suchas high maintenance, slow response time, largesize, and difficulty of use, making them imprac-tical for use as ambient air monitors. As ambi-ent air monitors, they are typically used only asa last resort for applications in which a suitablesensor is not available.

2. SOLID STATE SENSORS

2.1 GENERAL

Solid state sensors were introduced in the 1970’sand represented a major breakthrough in thefield of ambient air monitoring. They areunique in the fact that they can detect bothtoxic and explosive gases, in concentrations aslow as several ppm or as high as 100% LEL andabove. Today, solid state sensors are available forthe detection of over 150 different gases, includ-

ing many which could otherwise only be detect-ed using expensive analytical instruments. Anadded advantage of solid state sensors is thatthey have a long life expectancy, typically 10years or more, and come with a three year war-ranty. They are also quite rugged—they can takeoccasional exposure to high gas concentrationswithout damage and are not poisoned by sub-stances which often harm other sensor types.Many IST solid state sensors installed in the1970’s are still in operation today.

Figure 1.Solid State Sensor

COLLECTOR

IH TO

A

D

B

(SENSOR SURFACE TEMP.)

+VS

VOUT

2


2.2 PRINCIPLE OF OPERATION

A solid state sensor consists of two electrodesembedded into a solid state metal oxide materi-al. The presence of gas changes the resistance ofthe material, with the magnitude of changedirectly related to the gas concentration. Theresistance change, and hence the gas concentra-tion, is measured through the sensor’s corre-sponding electronic circuitry. The sensor is keptat a specific operating temperature by applying a‘heater’ voltage to it. The choice of heater volt-age is critical in determining the response char-acteristics of the sensor. By varying this voltageand by using different materials and processingtechniques, sensors can be made which are moresensitive to one gas or group of gases and lesssensitive to others.

2.3 CHARACTERISTICS

Gases Detected: Refer to “Solid StateSensor Gas Data” table.

Calibration Interval: 30 days to 6 months, depending on the

application.

Expected Sensor Life: 10 years or more. Comes with a 3 yearwarranty.

Environmental:Temperature: -40° to +60°C

-40° to +140°F

Humidity: 10% - 95%,non-condensing.

3. CATALYTIC BEADSENSORS

3.1 GENERAL

Catalytic bead sensors find use in applicationsrequiring the detection of combustible gases wheretoxicity is of no concern. They only respond well tothe higher gas concentrations, from 1000 ppm up to% LEL levels. Catalytic bead sensors are non-specif-ic, and will respond to a wide variety of com-bustibles. The quality and performance of a catalyt-ic bead sensor can vary from one manufacturer toanother. Historically, catalytic bead sensors havebeen known to be susceptible to poisoning fromH2S, silicones, and other substances. However,recent developments have led to the introduction ofcatalytic bead sensors which are poison resistant.Among these is IST’s Catalytic Sensor. In additionto being poison resistant, these and other well-madecatalytic bead sensors will provide good stability anda long life expectancy.


A catalytic bead sensor consists of an active ele-ment and a reference element. At the heart ofeach of the elements is a heated platinum coilwhose resistance varies with temperature. Aslong as both elements are at the same tempera-ture, their resistances will be equal. In the pres-

ence of gas, however, the active element willburn the gas on its surface, raising the tempera-ture of the platinum coil, while the referenceelement will show no response to the gas.Hence, a differential is created in the resistancesof the two elements. When both elements areplaced in a Wheatstone bridge circuit, this dif-ferential acts to throw the bridge out of balance,producing a signal which is proportional to thegas concentration. Because catalytic sensorsoperate on the combustion principle, they mustbe used in environments containing oxygen.

3.3 CHARACTERISTICS

Gases Detected: Combustible gases in% LEL ranges.

Calibration Interval: Depends on application1 month is typical.

Expected Sensor Life: 2 years typical. Comeswith a 1 year warranty.

Environmental:

Temperature: -40° to +75°C-40° to +167°F

Humidity: 0 - 99%,non-condensing.

Figure 2.Catalytic Bead Sensor

OUTPUT

Active

Bea

d

Reference Bead

D.C

. P

OW

ER

RB

RB

R1

4. ELECTROCHEMICALSENSORS

4.1 GENERAL

The oldest electrochemical sensors, used for O2

monitoring, date back to the 1950’s. Today, elec-trochemical sensors are available for the detectionof about a dozen toxic gases in ppm ranges,including CO, H2S, and NH3. For some gases,electrochemical sensors can exhibit fairly goodsensitivity and selectivity and therefore are a pop-ular choice for certain applications. They havean added advantage in that they require lowpower to operate. However, dryout of the elec-trolyte used in these sensors can result in areduced life, and the sensor is also subject to poi-soning which can lead to the need for frequentcalibration, premature drift, and sensor failure.These sensors also should not beexposed to high gas concentrations forlong periods of time, as this will dra-matically reduce their useful life.


Electrochemical sensors operate byreacting with the gas of interest andproducing a signal proportional to thegas concentration. A typical electro-chemical sensor consists of a sensingelectrode, a counter electrode, and areference electrode separated by a thinlayer of electrolyte. Gas which comes incontact with the sensor first passes through a dif-fusion barrier, which is designed to limit theamount of gas entering the sensor. Gas diffusingthrough the barrier reacts at the surface of thesensing electrode by either oxidation or reduction.Reactions are catalyzed by electrode materials spe-cially developed for the gas of interest. As an exam-ple, for a Carbon Monoxide Sensor, the gas wouldreact at the sensing electrode according to the fol-lowing equation:

CO + H2O � CO2 + 2H+ + 2e-.

Similarly, electrochemical sensors for other gaseswould produce reactions based on the gas theyare designed to detect. Selectivity can be achievedthrough the choice of the electrode material, elec-trolyte, operating voltage, and through selectivefiltration.

4.3 CHARACTERISTICS

Gases Detected:Following is a partial list of typical gases and rangesavailable for detection using electrochemical sensors.Other gases/ranges are also available.

Calibration Interval: 1-2 times per month typical.

Expected Sensor Life: 1-2 years typical.

Environmental:

Temperature: -5° to +40°C+23° to +104°FContinuous.

-15° to +50°C+5° to +122°FIntermittent.

Humidity: 15 to 90%non-condensing Continuous.

0 to 99%non-condensingIntermittent.

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GAS FORMULA TYPICAL RANGES (in PPM except O2)

Ammonia NH3 50

Carbon Monoxide CO 20, 50, 100, 200, 300, 500, 1000, 2000, 3000, 4000,10000, 20000, 40000

Chlorine Cl2 5, 10, 20, 30, 50, 100, 200,

Hydrogen H2 50, 200, 300, 500, 1000, 2000, 20000, 30000,50000

Hydrogen Chloride HCl 5, 10, 20, 30, 50, 100, 200

Hydrogen Cyanide HCN 100

Hydrogen Sulfide H2S 5, 10, 20, 30, 50, 100, 200, 300

Nitric Oxide NO 10, 20, 30, 50, 100, 200, 300, 500, 1000, 2000

Nitrogen Dioxide NO2 5, 10, 20, 30, 50, 100, 200, 300

Oxygen O2 0 - 25%, 0- 30% Oxygen

Sulfur Dioxide SO2 5, 10, 20, 30, 50, 100, 200, 300, 500,1000, 2000

Figure 3.Electrochemical Sensor

CapillaryDiffusionBarrier

CounterElectrode

Electrolyte

ReferenceElectrode

SensingElectrode

Membrane

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5. SENSORSELECTION

Gas monitoring generally consists of two cate-gories: Toxic Gas monitoring and CombustibleGas monitoring. In actuality, many gases areboth toxic and combustible. Carbon monoxide,for example, has a TLV of 25 ppm and also has aLower Explosive Limit (LEL) of 12.5% by vol-ume, or 125,000 ppm. Thus, it is the concentra-tion range of the gas to be monitored whichdetermines whether the monitoring fits into thecategory of toxic or combustible. Toxic gases arenormally associated with low gas concentrationsin the ppm range, while combustible gases areassociated with high gas concentrations in the%LEL range.

For monitoring toxic gases, either a solid stateor, where available, an electrochemical sensorcan be used. For monitoring combustible gases,either a solid state or catalytic bead sensor can beused. This section will present a comparison ofthese sensor types to help you determine whichsensor may be best for your particular applica-tion.

As mentioned previously, when using any ofthese sensors, it is important to remember thatthey will not be 100% specific to the gas ofinterest. Depending on the gas to be monitoredand the sensor type chosen, you may encountervarying degrees of interference from other gaseswhich are present in your environment.Additionally, for toxic gases especially, the choiceof the appropriate concentration range to moni-tor is very important. For example, if you aremonitoring to protect workers from toxic gases,typically a full scale range of 3 to 10 times theTLV of the gas being monitored is chosen. It isimportant to remember that the TLV for a gas isdefined as a SAFE level which workers can beexposed to for the entire work day. Thus, it iswise to choose a full scale range which is higherthan the TLV to enable you to set alarm points atconcentration ranges above the TLV, where thegas levels are hazardous. For combustible moni-toring, a range of 100% LEL is typically chosen,and other ranges are available.

5.1 COMBUSTIBLE GAS MONITORING

For combustible gas monitoring, either a solidstate or catalytic bead sensor can be used. Solidstate sensors are rugged and have a long life

expectancy. It is not uncommon for a solid statesensor to operate for 10 years or more withoutneeding replacement. They are resistant to poi-soning and can take occasional exposure to highgas concentrations without damage.

Catalytic bead sensors are also quite rugged. Asmentioned earlier, several manufacturers nowoffer catalytic bead sensors which are poisonresistant. Additionally, the typical life expectan-cy has been improved to two years. One of themain differences between catalytic bead andsolid state sensors is that solid state sensors tendto be more sensitive. Catalytic bead sensors areonly sensitive to combustible gases in high con-centrations and will not see any concentrationlower than about 1000 ppm. If the user does notindicate a specific gas to calibrate to, they aretypically calibrated to methane, and because ofthis they are less sensitive to most other com-bustibles. As a result, they are less likely to pro-duce a reading than a solid state sensor exposedto the same gases. In some instances, this char-acteristic can make them more practical, as theyare less likely to produce spurious alarms due to“interference” gases. This is advantageous in sit-uations where the user wants to detect only oneparticular combustible gas, and doesn’t wantother lower level combustibles which may alsobe present to be detected.

The choice between the two sensors thereforeinvolves two major considerations: lifeexpectancy and interferences. If interferencegases are not a problem in your application,then a solid state sensor is usually the bestchoice. It will likely perform better than a cat-alytic bead sensor in applications where multi-ple combustible gases are present and the userwants to detect all of them. It will also provideyears of trouble free operation and save on sen-sor replacement costs. However, in applicationswhere interference gases present a problem, thecatalytic bead sensor may be the way to go. Itstill has a fairly good life expectancy and will bemore selective than the solid state sensor.

5.2 TOXIC GAS MONITORING

For toxic gas monitoring, the two sensors whichcan be used are solid state or electrochemical.Solid state sensors are available to detect over 150toxic gases, while electrochemical sensors exist forapproximately 15 to 20. As a result, for a largemajority of gases, the choice of sensors is limitedto solid state. Thus, in comparing the two sen-sors, the discussion only applies to those gasesdetected by electrochemical sensors.

H2S

NH3

CO5


One of the major differences between the sen-sors is the life expectancy. While solid state sen-sors have a long, predictable life expectancy, atypical electrochemical sensor lasts only one ortwo years, and sometimes much less.Additionally, it is important to note that not allelectrochemical sensors are the same and the lifeexpectancy of the sensors can vary greatlydepending on the gas being monitored. Forexample, while a CO sensor will typically lastover a year, a comparable ammonia sensor peri-odically exposed to even relatively smallamounts of gas will have a much shorter life.

The response characteristics of both solid stateand electrochemical sensors can vary dependingon which toxic gas is being monitored.Therefore, the comparison of the two sensorsmust be done on a gas by gas basis. Followingare some general points about the two sensorsfor various gases:

5.2.1 Carbon Monoxide

Both the solid state and electrochemicalsensors for CO utilize charcoal filters toblock interference gases and as a result bothare fairly selective. Because of the long lifeof the solid state sensor, it is made so thatthe charcoal filter can be replaced withoutreplacing the sensor itself. The charcoal fil-ter on an electrochemical sensor is notreplaceable.

The readings of solid state sensors for COcan be affected by humidity. Specifically, invery low humidity, they tend to read lowand as a result it becomes important to addmoisture to the sample whenever calibratingthe sensor using a compressed gas bottle.Without doing so, the sensor may beimproperly calibrated and give inaccuratereadings.

Humidity does not have this affect on theelectrochemical sensor and therefore it mayproduce more stable readings overall. In thelong term, though, these sensors willrequire more frequent replacement and willneed more frequent calibration than a solidstate sensor, and these factors should all beweighed when choosing between the sen-sors.

5.2.2 Hydrogen Sulfide

For H2S, the solid state sensor performs verywell with excellent response and selectivity.For H2S applications, it is generally recom-mended to use a solid state sensor becausethese applications tend to be in hostile envi-ronments, where a solid state sensor will faremuch better than an electrochemical sensor.

While electrochemical sensors will respondwell on a short term basis, they ultimatelydo not survive long and require replacementtoo frequently. As a result, they should notbe used in systems with large numbers ofsensors, as the replacement costs of the sen-sors will be extremely high. A better applica-tion for them is in portable instruments,where they are not constantly exposed to theharsh environment. Even under these condi-tions, though, the sensor will require period-ic replacement.

5.2.3 Chlorine/Hydrogen Chloride

These gases are very active and corrosive,and regardless of whether a solid state orelectrochemical sensor is used, the monitor-ing of these gases is very difficult.Monitoring ranges are typically low, andbecause the gases are so active, it becomesvirtually impossible to prepare an accuratecalibration mixture with confidence.

Solid state sensors used in these applicationstend to be sensitive and read upscale. As aresult, they sometimes have problems withfalse alarms. On the other hand, electro-chemical sensors tend to lose sensitivityquickly in this environment and thereforeneed to be checked frequently for properoperation. They can provide a false sense ofsecurity by showing low or zero readingswhen, in fact, the sensor is simply insensi-tive.

5.2.4 Ammonia

Electrochemical sensors for ammonia have avery short life span. The sensor’s life is dra-matically reduced from exposure to gas,even in low concentrations. Solid state sen-sors are therefore a much better choice forammonia applications. They perform wellover a long period of time and have beenused extensively in refrigeration applica-tions.

6


6. SENSORINSTALLATION NOTES

There are no set rules regarding where sensors mustbe located, however the judgment of trained per-sonnel and good common sense should always beused. Sensors which are properly installed can savehours of maintenance and provide trouble freeoperation. Following are some guidelines forinstalling sensors:

1. In order to select meaningful sensor locations,a specific objective should be defined. Study thebuilding or plant layout to determine the loca-tion of various equipment, machinery, controlvalves, doors, vents, etc. as well as the general airflow pattern. Observe locations where gas is like-ly to leak from or accumulate. Generally, sensorsshould be located where they will indicate anaverage reading of the area in which the sensor isto cover.

2. It is recommended that sensors be mountedapproximately 5 or 6 feet from the ground toenable easy access for maintenance and calibra-tion. Also, avoid installing sensors too close towalls or the floor. These surfaces can absorb andemit gases with changes in temperature, affectingthe reading of the sensor. At least 6” of clearancefrom any surface should be provided.

3. Gases have different densities, and some arelighter than air while others are heavier.However, this does not mean that sensors shouldbe installed on the floor or ceiling to monitorthese gases. Gases disperse easily and develop aconcentration gradient, which means, for exam-ple, that a gas which is heavier than air will stillbe detected several feet off the ground. Animportant point to remember is that sensorsmust be accessible for calibration and mainte-nance, so installing them on the floor or ceilingis normally not a good idea.

4. In areas of new construction, sensors should beinstalled after operations such as sandblasting,painting, welding, etc. are completed. Duringsuch operations, sensors present should be pro-tected by using a sensor plug, such as IST’s P/N F44-P which installs over the rainshield.Remember that the sensor will not be operativewith the plug installed, so remember to removethe plug when reactivating the instrument.

5. Don’t install the sensor near sources of steam.Steam will damage the sensor.

6. Don’t install sensors next to sources which areconstantly leaking gas.

7. The number of sensors required for an appli-cation depends on a number of factors, includ-ing the plant layout, air flow pattern, type ofgas to be monitored, and the degree of protec-tion required. Choosing the proper number ofsensors is a matter of common sense. Gas sen-sors are similar to smoke detectors, meaningthey will only detect gas which directly comesin contact with the sensor. Thus, the sensorrelies on the dispersion of the gas in order todetect it.

7. DEFINITIONS

1. Threshold Limit Values (TLV’s): TLV’s represent conditionsunder which nearly all workers may be repeatedly exposed day after daywithout adverse health effects. The accuracy of these TLV’s, issued by theAmerican Conference of Governmental Industrial Hygienists (ACGIH),are subject to variation and the latest TLV Documentation should be con-sulted. The categories of Threshold Limit Values (TLV’s) are defined asfollows:

A. Threshold Limit Value - Time-Weighted Average (TLV-TWA): These values represent the time-weighted average concentra-tions of substances to which nearly all workers may be repeatedlyexposed for a normal 8-hour workday and a 40-hour workweek, dayafter day, without adverse effect.

B. Threshold Limit Value—Short-Term Exposure Limit(TLV-STEL): STEL is defined as a 15-minute TWA exposure whichshould not be exceeded at any time during a workday even if the 8-hour TWA is within the TLV-TWA. Exposures above the TLV-TWA up tothe STEL should not be longer than 15 minutes and should not occurmore than four times per day.

2. Immediately Dangerous to Life or Health (IDLH): IDLHconcentrations represent the maximum concentrations from which onecould escape within 30 minutes without a respirator, in the event of res-pirator failure, without experiencing any escape-impairing (e.g., severeeye irritation) or irreversible health effects. These values are obtainedfrom NIOSH: Pocket Guide to Chemical Hazards, 1990 Edition.

3. Flammable (Explosive) Limits — Lower Explosive Level(LEL) and Upper Explosive Level (UEL): LEL and UEL are usu-ally expressed as percent by volume of the material in air (or otheroxidant). A substance below the Lower Explosive Level (LEL) is too“lean” to burn, while a substance above the Upper Explosive Level istoo “rich” to burn. These values are obtained from NFPA 325M -Fire Hazard Properties of Flammable Liquids, Gases, andVolatile Solids, 1991 Edition.

4. Parts Per Million (PPM) and Percent By Volume: PPM andPercent By Volume are volumetric units of measurement commonlyused in gas monitoring. For instance, one PPM of Hydrogen Sulfidein ambient air would mean that there is one part of hydrogen sul-fide for every million parts of air. One Percent By Volume equals10,000 PPM (1 % by Volume = 10,000 PPM).

GAS TLV-TWA STEL IDLH LEL UEL FULL-SCALE RANGES

Acetic Acid 10 ppm 15 ppm 1000 ppm 4% 19.9% 100, 200 ppmAcetone 750 ppm 1000 ppm 20,000 ppm 2.5% 12.8% 100, 200, 500, 1000, 5000 ppm, % LELAcetonitrile 40 ppm 60 ppm 4000 ppm 3% 16% 100 ppmAcetylene 2.5% 100% 50 ppm, % LEL, 3% by VolumeAcrolein (Acrylaldehyde) 0.1 ppm 0.3 ppm 5 ppm 2.8% 31% 50 ppmAcrylic Acid 2 ppm — 2.4% 8% 100 ppmAcrylonitrile 2 ppm — 500 ppm 3% 17% 50, 60, 80, 100, 200, 500 ppm, % LELAllyl Alcohol 2 ppm 4 ppm 150 ppm 2.5% 18% % LELAllyl Chloride 1 ppm 2 ppm 300 ppm 2.9% 11.1% 200 ppmAmmonia 25 ppm 35 ppm 500 ppm 15% 28% 50, 70, 75, 100, 150, 200, 300, 400, 500,

1000, 2000, 2500, 4000, 5000 ppm, 1%,2%, 10% by Vol., 10%, 25%, 100% LEL

Anisole 100 ppmArsenic Pentafluoride 5 ppmArsine 0.05 ppm — 6 ppm 1, 10 ppmBenzene 10 ppm — 3000 ppm 1.2% 7.8% 50, 75, 100, 1000 ppm, % LELBiphenyl 0.2 ppm — 0.6% 5.8% 50%, 100% LELBoron Trichloride 500 ppmBoron Trifluoride — 100 ppm 500 ppmBromine 0.1 ppm 0.2 ppm 10 ppm 20 ppmButadiene 2 ppm — 20,000 ppm 2% 12% 50, 100, 3000 ppm, % LELButane 800 ppm 1.9% 8.5% 400, 1000 ppm, 100%, 200% LELButanol — 8000 ppm 1.4% 11.2% 1000 ppm, 100% LELButene 1.6% 10% 100% LELButyl Acetate 200 ppm — 10,000 ppm 1.7% 7.6% 100 ppm, % LEL Carbon Disulfide 10 ppm — 500 ppm 1.3% 50% 50, 60, 100 ppm, 5% by VolumeCarbon Monoxide 25 ppm — 1500 ppm 12.5% 74% 50, 100, 150, 200, 250, 300, 500, 1000,

3000, 5000 ppm, 3%, 5% by Volume, % LELCarbon Tetrachloride 5 ppm 10 ppm 300 ppm 50, 100, 10000 ppmCellosolve Acetate 100 ppmChlorine 0.5 ppm 1 ppm 30 ppm 10, 20, 50, 100, 200 ppmChlorine Dioxide 0.1 ppm 0.3 ppm 10 ppm 10, 20 ppmChlorobutadiene 10 ppm — 4% 20% 100% LELChloroethanol — 4.9% 15.9% 200 ppmChloroform 10 ppm — 1000 ppm 50, 100, 200 ppmChlorotrifluoroethylene 8.4% 16% 100% LELCumene 50 ppm — 8000 ppm 0.9% 6.5% 100% LELCyanogen Chloride — 20 ppmCyclohexane 300 ppm — 10,000 ppm 1.3% 8% 100 ppm, 100% LELCyclopentane 600 ppm — 1.5% 50 ppmDeuterium 5% 75% 50%, 100% LELDiborane 0.1 ppm — 40 ppm 0.8% 88% 10, 50 ppmDibromoethane — 50 ppmDibutylamine 1.1% 100% LELDichlorobutene 0.005 ppm — 1% by VolumeDichloroethane (EDC) 10 ppm — 4000 ppm 5.4% 11.4% 50, 100 ppm, % LELDichlorofluoroethane 100, 1000 ppmDichloropentadiene 50 ppmDichlorosilane 4.1% 99% 50, 100 ppmDiesel Fuel 50 ppm, 100% LELDiethyl Benzene 0.7% 6% 100% LELDiethyl Sulfide 10 ppmDifluorochloroethane 6.2% 17.9% 100% LELDifluoroethane (152A) 100% LELDimethyl Ether 3.4% 27% 100% LELDimethylamine (DMA) 5 ppm 15 ppm 2000 ppm 2.8% 14.4% 30, 50 ppmEpichlorohydrin 2 ppm — 250 ppm 3.8% 21% 50, 100, 500, 1000 ppmEthane — — 3% 12.5% 1000 ppmEthanol 1000 ppm — 3.3% 19% 200, 1000, 2000 ppm, % LELEthyl Acetate 400 ppm — 10,000 ppm 2% 11.5% 200, 1000 ppm, % LELEthyl Benzene 100 ppm 125 ppm 2000 ppm 0.8% 6.7% 200 ppm, % LELEthyl Chloride 1000 ppm — 20,000 ppm 3.8% 15.4% 100 ppm, % LELEthyl Chlorocarbonate 1% by VolumeEthyl Ether 19,000 ppm 100, 800, 1000 ppm, % LELEthylene — — 2.7% 36% 100, 1000, 1200 ppm, % LELEthylene Oxide 1 ppm 800 ppm 3% 100% 5, 10, 20, 30, 50, 75, 100, 150, 200, 300,

1000, 1500, 2000, 3000 ppm, % LELFluorine 1 ppm 2 ppm 25 ppm 20, 100 ppmFormaldehyde — 30 ppm 7.3% 7% 15, 50, 100, 500, 1000 ppmFreon-11 — 1000 ppm 10,000 ppm 1000, 2000, 5000 ppmFreon-12 1000 ppm 50,000 ppm 1000, 2000, 3000 ppmFreon-22 100, 200, 500, 1000, 2000 ppmFreon-113 1000 ppm 1250 ppm 4500 ppm 100, 200, 500, 1000, 2000 ppm, 1% by Vol.Freon-114 1000 ppm — 50,000 ppm 1000, 2000, 20000 ppmFreon-123 1000 ppmFuel Oil or Kerosene 0.7% 5% 100% LELGasoline 300 ppm 500 ppm 1.3% 7.1% 100, 1000, 2000, 20000 ppm., % LELGermane 10, 50 ppmHeptane 400 ppm 500 ppm 5000 ppm 1.05% 6.7% 1000 ppm, % LEL

8. SOLID STATE SENSOR GAS DATAThe following gases are available for detection using IST’s Solid State Sensors. The full-scale ranges listed are standard ranges available. For toxic gas monitoring, ranges are typically chosen whichare higher than the TLV so that hazardous levels will be detected (TLV is defined as a SAFE level). For combustible gases, the typical range is 0-100 % LEL. Other ranges can also be provided—pleasecontact IST for information. The following information is valid as of 3/95.

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8

GAS TLV-TWA STEL IDLH LEL UEL FULL-SCALE RANGES

Hexane 50 ppm — 5000 ppm 1.1% 7.5% 50, 100, 200, 2000, 2500, 3000 ppm, % LELHexene % LELHydrazine 0.1 ppm — 80 ppm 2.9% 9.8% 5, 10, 20, 100, 1000 ppm, 1% by VolumeHydrogen — — 4% 75% 50, 100, 200, 500, 1000, 2000, 5000 ppm,

3%, 5% by Vol., 2% to 100% LELHydrogen Bromide — 3 ppm 50 ppm 50 ppmHydrogen Chloride — 5 ppm 100 ppm 50, 100, 200, 400, 500, 1000 ppmHydrogen Cyanide — 4.7 ppm 50 ppm 5.6% 40% 20, 30, 50, 100, 200, 1000, 10000 ppmHydrogen Fluoride — 30 ppm 20, 50, 100, 200 ppmHydrogen Sulfide 10 ppm 15 ppm 300 ppm 4% 44% 5, 10, 20, 30, 50, 100, 300, 1000 ppm,

% LELIsobutane 1.8% 8.4% 1000, 3000 ppm, % LELIsobutylene 1.8% 9.6% % LELIsopentane 1.4% 7.6% 1000 ppm Isoprene 1.5% 8.9% % LELIsopropanol 400 ppm 500 ppm 12,000 ppm 2% 12.7% 200, 400, 500, 1000 ppm, % LELJP4 1.3% 8% 1000 ppm, % LELJP5 1000, 5000 ppm, % LELMethane — — 5% 15% 100, 200, 1000, 1500, 2000, 5000 ppm,

1%, 2% by Volume, 100%, 200% LELMethanol 200 ppm 250 ppm 25,000 ppm 6% 36% 200, 300, 400, 500, 1000, 2000, 5000 ppm,

15%, 30%, 100% LELMethyl Acetate 200 ppm 250 ppm 10,000 ppm 3.1% 16% 30 ppmMethyl Acrylate 10 ppm — 1000 ppm 2.8% 25% 60 ppmMethyl Bromide 5 ppm — 2000 ppm 10% 16% 20, 50, 60, 100, 500, 1000, 10000,

40,000 ppmMethyl Butanol 1.2% 9% % LELMethyl Cellosolve 2000 ppm % LELMethyl Chloride 50 ppm 100 ppm 10,000 ppm 8.1% 17.4% 100, 200, 300, 2000, 10000 ppm, % LELMethyl Ethyl Ketone 200 ppm 300 ppm 1.4% 11.4% 100, 500, 1000, 4000 ppm, 100% LELMethyl Hydrazine — 50 ppm 2.5% 92% 5 ppmMethyl Isobutyl Ketone 50 ppm 75 ppm 200, 500, 2000 ppm, 50%, 100% LELMethyl Mercaptan 0.5 ppm 400 ppm 3.9% 21.8% 30 ppmMethyl Methacrylate 100 ppm 4000 ppm 1.7% 8.2% 100 ppm, % LELMethyl-Tert Butyl Ether 40 ppm — 100% LELMethylene Chloride 50 ppm — 5000 ppm 13% 23% 20, 100, 200, 300, 400, 500, 600, 1000,

2000, 3000, 5000 ppm, % LELMineral Spirits 0.8% 200, 3000 ppm, % LELMonochlorobenzene 10 ppm — 1.3% 9.6% 100% LELMonoethylamine 5 ppm 15 ppm 4000 ppm 30, 100, 1000 ppmMorpholine 20 ppm — 8000 ppm 1.4% 11.2% 500 ppmNaptha 10,000 ppm 1.1% 5.9% 1000 ppm, 100% LELNatural Gas 1000, 2000 ppm, 2%, 4% by Volume, % LELNitric Oxide 25 ppm — 100 ppm 20, 50 ppmNitrogen Dioxide 3 ppm 5 ppm 20, 50, 100 ppmNitrogen Trifluoride 10 ppm — 50, 500, 1000 ppmNonane 200 ppm — 0.8% 2.9% 2000 ppmOxygen 25% by VolumePentane 600 ppm 750 ppm 15,000 ppm 1.5% 7.8% 200, 1000 ppm, % LELPerchloroethylene 25 ppm 100 ppm 500 ppm None 200, 1000, 2000, 20000 ppmPhenol 5 ppm — 250 ppm 1.8% 8.6% 100 ppmPhosgene 0.1 ppm — 2 ppm 50 ppmPhosphine 0.3 ppm 1 ppm 200 ppm 3, 5, 10, 20, 30, 50 ppmPhosphorus Oxychloride 0.1 ppm — 200 ppmPicoline % LELPropane — — 20,000 ppm 2.1% 9.5% 100, 1000 ppm, 100% LELPropylene — — 2% 11.1% 100, 200, 1000, 5000 ppm, %LELPropylene Oxide 2000 ppm 2.3% 36% 100 ppm, % LELSilane 5 ppm — 10, 20, 50 ppmSilicon Tetrachloride 1000 ppmSilicon Tetrafluoride 1000 ppmStyrene 50 ppm 100 ppm 5000 ppm 0.9% 6.8% 200, 300 ppm, % LELSulfur Dioxide 2 ppm 5 ppm 100 ppm 50, 100 ppmTetrahydrofuran 200 ppm 250 ppm 20,000 ppm 2% 11.8% 200, 300, 1000 ppm, % LELTetraline 0.8% 5% 100 ppmToluene 50 ppm — 2000 ppm 1.1% 7.1% 50, 100, 200, 500, 2000, 5000 ppm, % LELToluene Diisocyanate 0.005 ppm 0.02 ppm 10 ppm 0.9% 9.5% 15 ppmTrichloroethane 10 ppm — 500 ppm 7.5% 12.5% 50, 100, 500, 1000 ppm, 1% by VolumeTrichloroethylene 50 ppm 100 ppm 1000 ppm 8% 10.5% 50, 100, 200,300, 500, 1000, 2000 ppm, %LELTriethylamine (TEA) 1 ppm 5 ppm 1000 ppm 1.2% 8% 100 ppmTrifluoroethanol 25, 100 ppmTrimethylamine (TMA) 5 ppm 15 ppm 2% 11.6% 50 ppmTungsten Hexafluoride 50 ppmTurpentine 100 ppm — 1500 ppm 0.8% % LELVinyl Acetate 10 ppm 15 ppm 2.6% 13.4% 1000 ppm, % LELVinyl Chloride 5 ppm 3.6% 33 % 20, 50, 100, 200, 400, 500, 1000, 4000,

10000 ppm, 10%, 100% LELVinylidene Chloride 5 ppm 20 ppm 6.5% 15.5% 50 ppmXylene 100 ppm 150 ppm 1000 ppm 0.9% 6.7% 100, 200, 300, 1000 ppm, 1% by Volume

SOLID STATE SENSOR GAS DATAThe following gases are available for detection using IST’s Solid State Sensors. The full-scale ranges listed are standard ranges available. For toxic gas monitoring, ranges are typically chosen whichare higher than the TLV so that hazardous levels will be detected (TLV is defined as a SAFE level). For combustible gases, the typical range is 0-100 % LEL. Other ranges can also be provided—pleasecontact IST for information. The following information is valid as of 3/95.

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9. PRODUCT GUIDE

In addition to the three sensor types available forgas detection, there are also a wide variety ofinstruments to choose from. International SensorTechnology (IST) o�ers a complete line of instru-mentation to meet your needs. �e instrumentsavailable fall into two basic categories, stationaryand portable.

9.1 STATIONARY INSTRUMENTS

9.1.1 Transmitters

SM95

�e SM95 is a standard sensor transmitterhoused in an explosion proof casing. It oper-ates on 14-24 VDC and provides a 4-20 maoutput relating to gas concentration.Calibration is performed via adjustmentslocated inside the housing.

4-20 IQ

�e 4-20 IQ is an intelligent sensor trans-mitter housed in an explosion proof casing.It operates on 14-24 VDC and provides alinear 4-20 ma output as well as a digital dis-play of gas concentration. �is microproces-sor based unit also features automated cali-bration and a magnetically operated frontpanel so that calibration can be performedwithout removing the front cover, allowingthe unit to be calibrated without declassify-ing hazardous areas.

9.1.2 Conventional Systems

MP SERIES

IST’s MP Series consists of both rack mount-ed and weatherproof wall mounted micro-processor based controllers. Because of itsslim design, up to 24 channels can beinstalled in a standard 19” rack space. Or,from 1 to 4 channels can be housed in aweatherproof enclosure. �e MP Series con-troller can accept any sensor module whichprovides a 4-20 mA or 1-5 VDC output,including IST’s intelligent 4-20IQ sensor

module (see above). A digital display of gasconcentration is provided for each channeland relays are provided for activation of alarmdevices. Alarm and fault LED’s are also pro-vided for each channel. �e MP Series alsoprovides non-intrusive, automated calibra-tion, even for non-intelligent transmitters.

9.2 PORTABLE INSTRUMENTS

9.2.1 Single Gas

IQ250/IQ350

�e IQ250 and IQ350 are single gas porta-bles available to detect any one of the over150 toxic and combustible gases listed in thisguide. Both units provide a digital display ofgas concentration and an audible alarm, aswell as 3 alarm LED’s. �e IQ250 samplesby di�usion, while the IQ350 includes abuilt-in sampling pump.

4-20 IQ

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9.2.2 Multi-Gas

IQ1000

The IQ1000 gives you the ability to detectover 100 toxic and combustible gases using asingle instrument. It accepts solid state, cat-alytic bead, and electrochemical sensors andcan accommodate up to four sensors at atime. Thus, it is an instrument which can beconfigured to meet a wide range of applica-tions. The IQ1000 can also be equipped withIST’s Mega-Gas Sensor, a solid state sensorcapable of detecting over 100 gases. Thisability makes the unit ideal for determining

whether an area contains any hazardous gasesat all. The unit samples either by diffusion or via the built-in sample pump.Datalogging is available as an option.

IQ200

The IQ200 is a confined space entryportable which detects % LEL combustibles,CO, H2S, and oxygen deficiency. LED’s areprovided to indicate whether gas levels aresafe or not, and an audible buzzer is provid-ed for alarms. Unlike other confined spaceunits, four gases are detected using just twosensors instead of the usual four, making theunit very affordable. A long life electro-chemical sensor is used for oxygen, and asolid state sensor is used for the other gases.Typical confined space units utilize electro-chemical sensors which require replacementevery year or so. In the long run, this resultsin high operating costs and a low level of

user confidence concerning the reliability ofthe instrument and its readings. With theIQ200, however, both sensors are long lifesensors. The electrochemical sensor has afive year life expectancy and the solid statesensor has an indefinite life. This results ina unit with low maintenance requirements,low sensor replacement costs, and a highdegree of reliability.

NEW INFRAREDSENSORS!

DETECT CO2 AND METHANE

Many of IST’s instruments can now beequipped with state-of-the-art INFRAREDsensors to detect either CO2 or Methane. Formore information, please contact IST.

IQ1000

IQ200

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Notes

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INTERNATIONALSENSOR TECHNOLOGY

The Leader In Gas Detection Since 1972

3 Whatney, Irvine, California 92618-2836 • Telephone 949-452-9000 • FAX: 949-452-9009 • TLX: 4722070

Documents

SENSOR SELECTION GUIDE1 Sensor Selection Guide 1. INTRODUCTION T he detection of hazardous gases has always been a complex subject, making the choice of an appropriate gas monitor-ing