Infrared Temperature MeasurementAnswers and Solutions Handbook

IRCON has been solving indus-try’s toughest temperature measure-ment problems since 1962 Morethan 300,000 IRCON temperaturemeasurement instruments, includinga wide range of infrared thermome-ters, pyrometers, industrial thermalimaging systems and accessories,have been successfully installed inmanufacturing facilities around theworld. Designed for reliability andruggedness, our instruments provethemselves time and time again inthe most hostile environments.

To meet specific customer needsand applications, the IRCON productline offers a wide selection of on-line, non-contact infrared ther-mometers, including highly reliabletwo-color thermometers, portablethermometers, line scanners, cali-bration systems and accessories.

Each series of instruments offersa wide range of temperature spans

and spectral regions. In addition,IRCON infrared thermometers fea-ture through-the-lens focusableoptics that allow for viewing andmeasuring temperatures of smalltargets.

IRCON provides more than acomplete line of dependable equip-ment; it also offers total measure-ment solutions and a variety of sup-port services. IRCON sales represen-tatives and application engineersprovide years of experience in solv-ing application problems, analysis ofproduct or material in a laboratory toassist in selecting the correct instru-ment, and on-site demonstrations ofIRCON instruments.

In an effort to provide the bestpossible customer support, IRCONconducts easy-to-understand tech-nical training seminars coveringbasic infrared theory in practicalapplications, laboratory and indus-

trial measurement, and control prob-lem solutions.

The IRCON Technical ServicesCenter provides various field ser-vices, preventive maintenance con-tracts, calibration of instruments,and training for plant maintenancepersonnel.

With more than four decades ofexperience and a wide range of tem-perature measurement instruments,IRCON is constantly learning andinnovating to meet the needs of cus-tomers. Smart, rugged and powerfulIRCON sensing devices such asModline 5 infrared thermometers,Maxline 2 thermal imaging systems,and ScanIR II line scanners combined with dedicated and innov-ative software -- IRCON is one of theleading-edge global providers ofnon-contact temperature measure-ment solutions.

COMPANY HISTORY/CAPABILITIES

CHAPTER 1 PAGES 1-5INTRODUCTION TO IR

CHAPTER 2 PAGES 6 - 8TEMPERATURE EFFECTS CAUSED BY PRODUCT EMISSIVITY

CHAPTER 3 PAGES 9 -12TEMPERATURE EFFECTS DUE TO TRANSMISSION LOSSES

CHAPTER 4 PAGES 13 -16TEMPERATURE EFFECTS DUE TO BACKGROUND RADIATION

CHAPTER 5 PAGES 17-19TEMPERATURE EFFECTS DUE TO INSTRUMENT CHARACTERISTICS

CHAPTER 6 PAGES 20 -22WHEN TO USE TWO-COLOR IR THERMOMETERS

APPLICATION WAVELENGTH SELECTION GUIDE PAGE 23

TABLE OF CONTENTS

Infrared thermometers havethe ability to measure temperaturewithout coming into physical con-tact with a particular product. Thisability is based on the fact thatevery object emits radiant energy,and the intensity of this radiationis a function of that object’stemperature. The infraredthermometer simply mea-sures the intensity of radia-tion, thereby measuring anobject’s temperature.

The following sectionsare designed to present thefundamentals of radiationphysics upon whichinfrared thermometry isbased. Included in the dis-cussion will be several ofthe many ways of applyingthese fundamentals to thepractical methods of tem-perature measurement.

RADIANT EMISSIONWITH TEMPERATURE

When someone observesan object that has a suffi-cient amount of heat ema-nating from it, that objectwill emit light or visibleradiation. This phenome-non is called incandescence.A light bulb filament, asmoldering ember and a bil-let of “red hot” steel are allobvious examples of thisphenomenon. As the tem-perature of an objectincreases, its color and brightnesswill also intensify and increase. Infact, it is possible to estimate thetemperature of an object in thisway. Experienced workers in thesteel industry, for example, visual-ize estimated temperatures on aregular basis.

Incandescent objects also emita tremendous amount of “invisi-ble” infrared radiation. For exam-ple, the radiance of a steel billet at1,500°F is 100,000 times greaterin the infrared than in the visible.This radiance is a function of thebillet’s temperature.

The general relationship betweenthe radiance as a function of wave-length and temperature for a per-fect emitter is shown in Figure 1.Notice that the radiance in the visi-ble is quite low. Below 1,000°F thevisible radiance is so low that we

cannot see it. However, there isstill copious emission of infraredradiation. Note that the radiance atevery wavelength increases astemperature increases, and that thedetermination of the radiance atany wavelength can serve to estab-lish the emitter’s temperature.

NATURE OF RADIATIONThe difference between

infrared radiation and visible radi-ation is their wavelength. Redlight has a longer wavelength thanblue light, and infrared radiationhas longer wavelengths than bothof these colors. In all other aspects,

these radiations behave similarly; allcan be considered to be composed ofelementary packets of energy calledphotons. Ideally, all photons travelin a straight line at the “speed oflight” and can be reflected by appro-priate mirrors, and their paths can

be bent and focused byproper refractive elements orlenses.

All photons will dissi-pate their energy as heatupon being soaked up byan appropriate absorber.The only fundamental dif-ference between a bluephoton, a red photon or atwo-micron infrared photonis its wavelength and theamount of energy it carries.The energy of a photon isinversely proportional to itswavelength.

ELEMENTS OF ANINFRARED

THERMOMETERA simple analysis of the

eye, one form of radiationthermometer, clearlyreveals the basic compo-nents used in any practicalinfrared thermometer. Theeye contains a lens whichfocuses the photon flux(flow) from the emitteronto the retina or radiationdetector of the human sys-tem. The retina is stimu-lated by the incident radia-

tion and produces a signal that istransmitted to the brain. The brainserves as the indicator or recorderwhich measures the radiance of theemitter and, if properly calibratedby experience, relates this radianceto temperature.

The same basic elements makeup an industrial infrared ther-mometer. These elements includethe collecting optics, the radiationdetector and some form of indica-tor. It is the remarkable capabili-ties of available detectors thatresult in the capabilities of presentday infrared thermometers.

INTRODUCTION TO IRCHAPTER 1

0 1 2 3 4 5 6 7 8 9 10

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600° F

1000° F

1200° F

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T •

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AD

IAN

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MIC

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IBLE

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FIGURE 1Blackbody Radiation Characteristics

RADIATION DETECTORSRadiation detectors take many

forms, but all serve the same pur-pose of converting incident photonflux into an electrical signal (Fig. 2).The two main types are the ther-mal detector and the quantum

detector.A thermal detector absorbs

incident flux, and the power dissi-pated increases the detector’s tem-perature to change some measur-able physical property (for exam-ple, its resistance). This type of

detector generally has a completelyblack receiving surface so that it issensitive to all wavelengths. Sincethe detector depends on the risingtemperature within itself, it has aninherently slower response thanquantum detectors.

SILICON

LEAD SULFIDE

INDIUM ANTIMONIDE

THERMAL DETECTORS

0 2 4 6 8 10

WAVELENGTH, MICRONS

RE

LAT

IVE

RE

SP

ON

SE

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FIGURE 2Spectral Response Characteristics of Several Infrared Detectors

CALCIUM FLUORIDE

ZINC SULFIDE

CROWN GLASS

0 2 4 6 8 10

WAVELENGTH, MICRONS

100

50

0

TR

AN

SM

ISS

ION

, PE

RC

EN

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FIGURE 3Transmission Characteristics of Several Infrared Optical Materials

A quantum detector sensesradiation in a different way. Oneform of quantum detector, which isthe type that is generally used,consists of a semiconductor crystal.The incident photon interacts witha bound electron within the crystallattice. The photon’s energy, if suf-ficient in size, transfers to the elec-tron to free it from its immobilestate, permitting the electron tomove through the crystal. Duringthe time the electron is free, theelectron can produce a signal volt-

age in the detector. After a shortinterval, the electron will return toits bound state. This interval isgenerally far shorter than the ther-mal time constant of a thermaldetector.

The quantum detector is a pho-ton counter that is equally sensi-tive to all photons that have theminimum energy necessary to free abound electron. Each detector ofthis type will exhibit a fairly uniformresponse to all photons up to a par-ticular wavelength. Photons beyondthis wavelength will not have ade-quate energy to free enough elec-trons to produce a signal.

The great practical advantage ofradiation detectors is their ability toproduce electrical signals that faith-

fully measure the incident photonflux, without requiring humanattendance. This, of course, per-mits continuous temperature mea-surement and control without con-tact. While the eye is limited totemperature measurements above1,000°F, present day infrared ther-mometers extend the measurementrange down to and below -50°F.

OPTICAL ELEMENTSThe collecting optics of the

infrared thermometer are selected to

be compatible with the spectralresponse of the detector employedin a particular thermometer. Mirrorsare suitable for use over wide spec-tral regions. Lenses, on the otherhand, are restricted to those regionswhere the materials employedmaintain good transmission proper-ties. Certain design characteristicsstrongly favor the use of lenses formost practical systems. Figure 3shows the spectral transmissionproperties of several infrared lensmaterials. These same materialsare also employed as windows inthose applications where the targetis situated in a sealed chamber.

OUTPUTThe infrared thermometer pro-

vides an electrical voltage output

which can be used for simple tem-perature indication or any of themany forms of closed-loop tempera-ture control. The detector in someinfrared thermometers can providevoltages high enough to drivemeters and recorders directly. Otherinfrared thermometers, particularlythose covering the lower tempera-ture ranges, require built-in ampli-fiers to provide proper output levels.CHOICE OF SPECTRAL REGION

At first glance, it would appearthat an infrared thermometer

should utilize the entire spectrum,or at least a broad enough portionof the spectrum to capture most ofthe radiant emission of the targetin its particular temperature range.There are several reasons why thisis not always advantageous.

RADIANCE VS WAVELENGTHOne reason for using a limited

spectral region relates to the rate atwhich the radiance increases withtemperature. An analysis of Figure1 indicates that the radiance at twomicrons increases far more rapidlywith temperature than it does at,say, six microns. The rate of radi-ance change in temperature isalways greater at shorter wave-lengths. The greater this rate ofchange, the more precise the tem-

1.0

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02.5 3 4 5 6 7 8 9 10 11 12 14 16

3.43 MICRONS 4.8 to 5.3 MICRONS 7.9 MICRONS

WAVELENGTH (λ) IN MICRONS(µm)

0.009 In. Thick

0.027 In. Thick

0.061 In. Thick

0.124 In. Thick

0.231 In. ThickSP

EC

TR

AL

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AN

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AN

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,τ λ

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FIGURE 4Effect of Thickness on Spectral Transmittance Curves for Soda-Lime Glass

perature measurement and thetighter the temperature control.However, at a given short wave-length there is a lower limit to thetemperature that can be measured.For example, the eye becomes use-less for measuring temperaturesbelow approximately 1,000°F.Similarly, the spectral range of anappropriate infrared thermometershifts to longer wavelengths andbecomes less accurate as theprocess temperature decreases.

EMISSIVITY, REFLECTANCE AND TRANSMITTANCE

Another important reason for the use of different spectral regionsrelates to the emission characteris-tics of particular target materials.The curves in Figure 1 show theemission characteristics of the idealemitter, or “blackbody.” No mater-ial can emit more strongly than ablackbody at a given temperature.Many materials, however, can anddo emit less than a blackbody atthe same temperature in various

portions of the spectrum. The ratioof the radiance at wavelength (λ) ofa material to that of a blackbody atthe same temperature is called thespectral emissivity (ελ). The valueof ελ for the substance can rangebetween zero and one, and thisvalue may vary with wavelength.

The emissivity of a substancedepends on its detailed interactionwith radiation. A stream of radia-tion incident on the surface of asubstance can suffer one of threefates. A portion may be reflected

while another portion may betransmitted through the substance.The remainder will be absorbedand degraded to heat. The sum ofthe fraction reflected (r), the frac-tion transmitted (t) and the fractionabsorbed (a) will be equal to thetotal amount of radiation incidenton the substance. Furthermore, theemissivity (ε) of a substance isidentical to the fraction absorbed(a) and can be written as:

ε =– a = 1 – t – r

For the blackbody, the trans-mitted and reflected fractions arezero and the emissivity is unity.For any opaque substance the frac-tion transmitted is zero and:

ε = 1 – rAn example of this case is oxi-

dized steel in the visible and nearinfrared where the fraction trans-mitted is zero, the fraction reflectedis 0.20, and the emissivity is 0.80.

A good example of a materialwhose emissivity characteristicschange radically with wavelength is

glass. Figure 4 shows the overalltransmission of several specimensof soda-lime glass. The fractionreflected at the glass surface is about0.03 or less through most of the spec-tral region shown. At wavelengthsbelow about 2.6 microns, the glass ishighly transparent and the emissivityis essentially zero. Beyond 2.6microns, the glass becomes increas-ingly more opaque. Therefore, it isdetermined that beyond 4 microns,glass is completely opaque and it'semissivity is above 0.97.

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WAVELENGTH IN MICRONS

PATH LENGTH:

TEMPERATURE:

REL. HUMIDITY:

6 FEET

80° F

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10% REL. HUMIDITY

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50%

100%AT

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FIGURE 5Transmission for Atmosphere at 80°F, and Several Relative Humidities

This example of glass clearlyillustrates how the detailed charac-teristics of the material can dictatethe choice of the spectral region ofmeasurement. For example, con-sider the problem of measuringand controlling the temperature ofa glass sheet during manufactureat a point where its temperature is1,600°F. The rule that suggests ashort wavelength infrared thermo-meter, because of the product’s hightemperature, would obviously fail.

To use the region around onemicron would be useless becausethe emissivity is close to zero.Furthermore, since the glass ishighly transparent, the infraredthermometer will “see through”the glass and can give false indica-tions because of the hot wallbehind the glass. For this reason,glass can be used as an effective“window” for a short wavelengthinfrared thermometer.

By employing the spectral regionbetween three and four microns, theinternal temperature of the glass canbe effectively measured and con-trolled. By operating at five or moremicrons, the surface temperature ofthe glass is measured.

ATMOSPHERIC TRANSMISSIONThe third key consideration

affecting the choice of spectralregion is transmission through theatmosphere between target sub-stance and infrared thermometer.The normal atmosphere alwayscontains a small but definiteamount of carbon dioxide and avariable amount of water vapor.Carbon dioxide strongly absorbsradiation between 4.2 and 4.4microns and the water vaporabsorbs strongly between 5.6 and7.0 microns and somewhat be-tween 2.6 and 2.9 microns (Fig. 5).Analyzing this information indi-cates that these spectral regionsshould be avoided, particularly inthe region of the water bands. Ifnot avoided, the temperature cali-bration will vary with path lengthand humidity. If the air tempera-ture is comparable to, or higherthan, the target temperature, animproperly designed infrared ther-mometer could provide temperaturemeasurements that are stronglyinfluenced by air temperature.

PRACTICAL APPLICATIONSInfrared thermometers are cur-

rently used in a wide range of lab-oratory and industrial temperaturecontrol applications. A few lowtemperature examples includeextrusion, lamination and dryingof plastics, paper and rubber in thecuring process of resins, adhesivesand paints. Another low tempera-ture example of an infrared ther-mometer can be found in the steelindustry where these instrumentsare used in the cold rolling andforming of metals.

Some high temperature exam-ples include forming, temperingand annealing of glass; smelting,casting, rolling, forging and heattreating of metals; and calciningand firing of ceramics and cement.Other types of applications can befound on page 24.

In short, an infrared ther-mometer can be used in almostany application in the range from -50 to 6,500°F where the instru-ments’ unique capabilities can turna seemingly impossible measure-ment and control problem into apractical working process. Manyprocesses now controlled manuallycan be converted into continuous,automated systems.

5

The intent of the following chapters is to clarify some of the misconceptions aboutusing infrared thermometers and to show what some of the possible effects are thatcould contribute to an erroneous temperature indication. IRCON’S philosophy is thatif you understand the major contributors to misapplication of infrared thermometers,you will be better prepared to understand your temperature measurement results, andprepared to choose the correct instrument for your application.

The focus of the following fourchapters will be the examination ofareas that affect the decision-makingprocess in determining how andwhen to use brightness infraredthermometry. Chapter 2 will exam-ine emissivity as the cause of tem-perature error when using aninfrared brightness thermometer.Subsequent parts of this chapterwill examine optical path, trans-mission, hot backgrounds andthe infrared thermometer itselfas additional sources of temper-ature error in determining howand when to use an infraredthermometer.

COMPONENTS OFTEMPERATURE ERRORLearning that the indicated

target temperature may not be atrue target measurement is onlypart of the problem in determin-ing emissivity . The followingformula represents the total tem-perature error of a system(∆ΤSYSTEM) and the componentsthat contribute to this error.

∆Τ SYSTEM = ∆Τ EMISSIVITY +∆Τ TRANSMISSION + ∆Τ BACKGROUND +

∆Τ INSTRUMENT

This formula indicates that totaltemperature error is caused by acombination of the following compo-nents: an emissivity error, a trans-mission error, a background errorand an error in the instrumentitself. Each component error maybe positive, negative or zero.

The red areas of this formularepresent what are referred to asapplication errors. These are errorsthat may be controlled by theinstrument user. Improperapplications are the pri-mary contributors to thetotal error. The instrumenterror is often the smallestpart of the total error. Tounderstand temperatureerrors more completely,each variable componentof the formula will be ana-lyzed individually. With

care, all of these errors can bereduced to acceptable levels.

EMISSIVITY ANDTEMPERATURE MEASUREMENT

Infrared radiation thermometerusers have wrestled with emissivitysince temperature measurement

technology was first applied toleading industrial processes. Usersof infrared brightness thermome-ters have learned that a true targettemperature measurement can beachieved only when the correct tar-get emissivity is set on the instru-ment dial. When the instrumentemissivity dial is set incorrectly, atemperature error results.

How does target emissivityinfluence the temperature measure-ment of an infrared thermometer?An instrument is designed to collect

the radiation emanating from a tar-get and measure that radiancequantitatively. The circuitry of theinstrument produces a signal volt-age from which a temperature isthen indicated. This indicated tem-perature is proportional to the target

radiance. Figure 1 illustratessignal voltage versus targettemperature curves for three tar-gets with different emissivities.

The curve labeled ε = 1.00represents the signal voltageoutput when an instrumentviews a blackbody. The curveslabeled ε = 0.50 and ε = 0.25represent the signal voltageoutput when the same instru-ment views targets with loweremissivities. While the shapeof the latter curves are thesame, the signal magnitudesare reduced by the emissivities0.50 and 0.25.

In order for an instrumentto indicate true temperature,the emissivity dial setting mustcorrespond to the target emis-sivity. This dial is a calibratedgain adjustment which allowsthe user to trim the instrument

to the emissivity of a target. Whenit is set correctly, the instrumentindicates the target temperaturewithout error. Figure 2 illustratesthe position of the emissivity gainadjustment between the sensinghead and the linearizer.

COMPUTE THE TEMPERATURE ERROR

The magnitude of temperatureerror created by uncertainty in agiven emissivity depends on thespectral range of the infrared ther-

mometer and the targettemperature. The ErrorTables (1F and 1C) repre-sent indicated temperatureerrors caused by one-per-cent emissivity errors.These tables may also beused to compute tempera-ture errors caused byemissivity errors greaterthan one percent.

300 400 500

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SIG

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Τ TARGET °F

ε =1.

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FIGURE 1Signal Voltage/Temperature Curves

TEMPERATURE EFFECTS CAUSED BY PRODUCT EMISSIVITYCHAPTER 2

TARGETRADIANCE SENSING

HEAD

EMISSIVITY CONTROL(GAIN ADJUSTMENT)

TEMPERATUREINDICATOR

LINEARIZER

SENSINGHEAD

SIGNALINDICATOR PANEL

FIGURE 2Infrared Temperature Measuring System IllustratingEmissivity Control

Reasonable accuracy can beexpected with emissivity errors upto 40 percent. To compute a tem-perature error caused by an incor-rect emissivity setting, simply usethe following formula:

∆Τ = –100 x εDIAL – εTRUE x ∆Τ TABLE_______

εTRUE

EXAMPLE IEmissivity Dial is Set Incorrectly:

Calculate the temperature errorcaused by an emissivity error inmeasuring steel on the hot stripmill using the IRCON® Series oper-ating at 0.9 µm. The true tempera-

ture is 1,800°F and the εTRUE is0.82. An operator mistakenly setsthe εDIAL to 0.70. It will be neces-sary to refer to table 1F for thistemperature error.

∆Τ = –100 x εDIAL – εTRUE x ∆Τ TABLE_______

εTRUE

= –100 x 0.70 – 0.82 x 1.8°F_______0.82

∆Τ = +26°F

For this example, the temperatureerror is 26°F.

EXAMPLE IIVariations in Emissivity During aProcess Run:

The various paints used on acoil coating line exhibit varying emis-sivities to the series operating at 3.4µm. The values range from 0.91for the vinyls to 0.95 for the poly-esters.

The operator sets εDIAL to 0.93:the geometric mean for all painttypes. All paints are heated to400°F. Use the same formula todetermine ±2°F temperature errorfor this production run.See box on page 8 for summary of symbols.

7

EFFECTIVE WAVELENGTH 0.65µm 0.9µm 1.6µm 2.3µm 3.4µm 3.9µm 5.0µm 8.0µm 10.6µmTARGET

TEMPERATURE (°F)0 0.05 0.07 0.13 0.18 0.27 0.31 0.41 0.64 0.86

200 .10 .14 .27 .38 .57 .64 .85 1.3 1.7400 .18 .25 .46 .66 .97 1.1 1.4 2.2 2.8600 .28 .38 .70 1.0 1.5 1 .7 2.2 3.3 4.1800 .40 .55 1.0 1.4 2.1 2 .3 3.1 4.5 5.6

1000 .53 .73 1.3 1.9 2.8 3 .1 4.1 5.8 7.11200 .69 .95 1.7 2.5 3.6 4 .0 5.2 7.2 8.71400 .87 1.2 2.2 3.1 4.5 5 .0 6.4 8.8 101600 1.1 1.5 2.7 3.8 5.5 6 .1 7.6 10 121800 1.3 1.8 3.2 4.5 6.5 7 .2 9.0 12 142000 1.5 2.1 3.8 5.4 7.6 8 .4 10 14 162200 1.8 2.5 4.5 6.2 8.8 9 .7 12 15 172400 2.1 2.8 5.2 7.2 10 11 13 17 192600 2.4 3.3 5.9 8.2 11 12 15 19 212800 2.7 3.7 6.7 9.2 13 14 17 21 233000 3.0 4.2 7.5 10 14 15 18 22 253500 4.0 5.4 9.8 12 18 19 22 27 304000 5.1 6.9 12 16 21 23 27 32 344500 6.3 8.5 15 20 25 27 31 36 395000 7.6 10 18 23 30 31 36 41 44

For temperature errors caused by shifts in Emissivity greater than 1%, use the formula illustrated in the example below.

TABLE 1F – BRIGHTNESS THERMOMETER TEMPERATURE EFFECTS CAUSED BY A ONE PERCENT SHIFT IN EMISSIVITY (In Degrees Fahrenheit)

Example: INSTRUMENT SERIES(1.6µm)ΤIND 1000°FεDIAL 0.70εTRUE 0.82

∆Τ = –100 x εDIAL – εTRUE x ∆Τ TABLE_______

εTRUE

= –100 x 0.70 – 0.82 x 1.3°F_______0.82

∆Τ = +19°F

To determine ΤTRUE for this example, use the followingformula:ΤTRUE = ΤIND – ∆Τ

=1000°F – 19°FΤTRUE =981°F

8

EFFECTIVE WAVELENGTH 0.65µm 0.9µm 1.6µm 2.3µm 3.4µm 3.9µm 5.0µm 8.0µm 10.6µmTARGET

TEMPERATURE (°C)0 0.03 0.04 0.08 0.12 0.17 0.20 0.26 0.41 0.54

100 .06 .08 .15 .22 .33 .37 .49 .76 1.0200 .10 .14 .25 .36 .53 .60 .79 1.2 1.6300 .15 .20 .37 .53 .78 .87 1.2 1.7 2.2400 .20 .28 .51 .73 1.1 1.2 1.6 2.3 2.9500 .27 .37 .68 .96 1.4 1.6 2.1 3.0 3.6600 .35 .47 .87 1.2 1.8 2.0 2.6 3.7 4.4700 .43 .59 1.1 1.5 2.2 2.5 3.2 4.4 5.2800 .52 .72 1.3 1.8 2.7 3.0 3.8 5.2 6.1900 .63 .86 1.6 2.2 3.2 3.5 4.4 6.0 7.0

1000 .74 1.0 1.8 2.6 3.7 4.1 5.1 6.8 7.81100 .86 1.2 2.2 3.0 4.3 4.7 5.8 7.6 8.71200 .99 1.4 2.5 3.4 4.9 5.4 6.6 8.5 9.61300 1.1 1.6 2.8 3.9 5.5 6.0 7.3 9.3 111400 1.3 1.8 3.2 4.4 6.1 6.7 8.1 10 111500 1.4 2.0 3.6 4.9 6.8 7.4 8.9 11 121600 1.6 2.2 4.0 5.5 7.5 8.1 9.6 12 131800 2.0 2.7 4.8 6.5 8.9 9.6 11 14 152000 2.4 3.2 5.8 7.7 10 11 13 16 172200 2.8 3.8 6.8 9.0 12 13 15 18 192400 3.3 4.5 7.8 10 13 14 16 19 212600 3.8 5.1 9.0 12 15 16 18 21 232800 4.3 5.9 10 13 17 18 20 23 253000 4.9 6.6 11 15 18 20 22 25 27

For temperature errors caused by shifts in Emissivity greater than 1%, use the formula illustrated in the example below.

Example: INSTRUMENT SERIES(1.6µm)ΤIND 500°CεDIAL 0.70εTRUE 0.82

∆Τ = –100 x εDIAL – εTRUE x ∆Τ TABLE_______

εTRUE

= –100 x 0.70 – 0.82 x 0.68°C_______0.82

∆Τ = +9.95°CTo determine ΤTRUE for this example, use the followingformula:ΤTRUE = ΤIND – ∆Τ

=500°C – 10°CΤTRUE =490°C

TABLE 1C – BRIGHTNESS THERMOMETER TEMPERATURE EFFECTS CAUSED BY A ONE PERCENT SHIFT IN EMISSIVITY (In Degrees Celsius)

SYMBOL DEFINITIONΤIND Target Temperature Indicated by Instrument

ΤTRUE True Target Temperature∆Τ Indicated Temperature Error:

ΤIND – ΤTRUE

∆ΤTABLE Error Value in from Tables 1F and 1CεDIAL Actual Emissivity Setting on Instrument DialεTRUE True Target Emissivity

IMPORTANCE OF THETRANSMISSION PATH

An infrared brightness ther-mometer determines an object’stemperature by quantitatively mea-suring its radiance. In order tomeasure radiance, the instrumentmust have a constant and pre-dictable view of its target. Underideal conditions, ensuring this per-spective can be accom-plished by simply filling thefield of view with the target;the amount of radiantenergy received at the detec-tor is determined by the tar-get’s temperature. In reality,however, some radiation islost in the “transmissionpath” between the emittingsurface and the detector. Ifthis loss is significant, thebrightness thermometerdetects less radiation than itshould and indicates a tem-perature that is too low.

Transmission losses arecaused by objects, particlesand even gas moleculeswhich lie within the opticaltransmission path, as illustrated inFig. 1. The intervening materialsabsorb, reflect or “scatter” some ofthe emitted radiation before itreaches the detector within thesensing head. The transmissionlosses increase with longer pathlengths, yet the instrument cannotbe placed too close to a hot target.Close proximity to a hot target canresult in overheating and perma-nent damage. It is possible, how-ever, to minimize some transmis-sion loss problems. For instance,instruments can be designed toavoid particular wavelength bandsthat are absorbed in the transmis-sion path. Water vapor and CO2,which are the primary atmosphericabsorbers in the near infrared, havelittle effect on IRCON infraredbrightness thermometers.

AVOIDING TRANSMISSIONERRORS

Serious and unnecessary trans-mission losses can often be pre-vented with proper care, installationand use of a brightness thermome-ter. The lens within the instrumentand any windows must be keptclean of dirt, oil and other evapo-rated buildup. The unit must also

be focused so that its transmissionpath is clear of all solid, opaqueobjects. It is equally important thatany windows or sight holes aremade large enough that no part ofthe “cone of vision” is cut off.

Procedures for cleaning opticalcomponents and for sighting instru-ments are included in the opera-tions manuals and can be supple-mented by consulting the IRCONTechnical Service Department. Insome applications, transmissionproblems can be avoided simply.For example, transmission lossresulting from smoke can be elimi-nated if the angle of view is movedfrom the top of the product wheresmoke is rising, to the bottom of theproduct where a clear field of viewcan be established.

COMPENSATING FOR LOSSIn cases where transmission

losses are known, it is possible tocompensate for them. Just as an

emissivity (ε) value of 1.0 repre-sents a perfect radiator, a transmis-sion (τ) value of 1.0 represents acompletely transparent material orpath. When some radiation is lost,the transmission has a lower (frac-tional) value. When the radiation iscompletely blocked off, of course,the transmission is zero.

True temperature readings arepossible only if the signalvoltages are at the cali-brated levels obtained whenviewing an ideal (black-body) radiator. Figure 2shows that when bothεTARGET and τPATH are lessthan perfect, both factorscontribute to losses in thedetected radiant energy.These losses may simply belooked upon as an effectiveemissivity value (εEFF),since the source of the lossmakes no difference to theinstrument. Therefore, theemissivity dial can be set tocompensate for total loss.The signal voltages pro-

duced by the detector are correctlyamplified to blackbody levels whenthe dial is set to the value: (1)εEFF = εTARGET, x τPATH,

TRUE TRUE

For example, if a window is theonly object in the transmission paththat causes a significant loss,τPATH =τWINDOW. If εTARGET = 0.80 andτWINDOW = 0.85, the emissivity dialshould be set to 0.80 x 0.85 = 0.68.

ERROR CALCULATIONIf there is an error in the trans-

mission value used to determine thedial setting, there is also an error inthe indicated temperature. NOTE:It is assumed in this section that thetarget’s true emissivity value isalways known and correctly takeninto account. The magnitude of thistemperature error varies with boththe target’s temperature and theinstrument’s spectral region. Tables1 and 2 show representative tem-perature error values that result

IRCON

IRCON

Flames

Particles,Gases

SolidObstruction

Window

Steam,Smoke

TRANSMISSION PATHSENSING HEAD

A. IDEAL CONDITIONS

B. REAL CONDITIONS

Radiation Emitted from Target

TARGET

9

FIGURE 1Materials in Transmission Path Reduce RadiationEntering Sensing Head

TEMPERATURE EFFECTS DUE TO TRANSMISSION LOSSESCHAPTER 3

from a one percent transmissionerror. The effect of larger errorsmay be calculated by multiplyingthe percentage of transmissionerror* times the effect of a one per-cent error as follows: (2)

∆Τ = 100 x εEFF – εDIAL x ∆ΤTABLE_______

εEFF

Where εEFF is given by equation (1). See Figure 3 for summary of sym-bols. This formula may be used

with reasonable accuracy for trans-mission errors up to 40 percent.

TRANSMISSION THROUGH WINDOWS

Whereas most transmissionloss varies with changing environ-mental conditions, the transmissionloss caused by a window remainsconstant (as long as it is kept clean,stationary, etc.). Therefore, windowsafford the simplest example for cal-culating the effects of transmissionerrors. Errors can result fromuncertainty in the transmissionvalue or from the very commonmistake of neglecting the effect ofthe window entirely. It is alsoimportant to realize that transmis-sion of a window material is not thesame for all wavelengths.

EXAMPLE ICORRECTING FOR THE EFFECT

OF A WINDOW:Some silicon wafers are enclosed

in the quartz bell jar of an epitaxialreactor. For successful processing,the wafers must be heated to a tem-perature of 1,800° F. A typical ther-mometer operating at 0.9µm is usedto monitor the temperature of the

wafers, which have an emissivity of0.66. In order to do this, however,the instrument must view throughthe bell jar, which has a transmissionof 0.94 at 0.9µm. How is the indi-cated temperature affected if theoperator forgets to compensate fortransmission losses and corrects fortarget emissivity only? The answercan be found by using equation (2),as follows:

∆Τ = 100 x εEFF – εDIAL x ∆ΤTABLE_______εEFF

In this case,εEFF = εTARGET x τWINDOW =

.66 x .94 = .62εDIAL = εTARGET = .66

∆ΤTABLE = 1.8°so∆Τ = 100 x .62 – .66 x 1.8°= –12°F–––––––

.62

The indicated temperature is 12° Flower than the true temperature.

Notice from Tables 1 and 2 thatthe ∆ΤTABLE values increase with ris-ing temperatures. Therefore, thetemperature error in the aboveexample would be worse if theprocess temperature was increased.

EXAMPLE IISTEAM INTERFERENCE:

A steel strip in a rolling mill hasa temperature of 1,680°F as it exitsthe final finishing stand. A typicalthermometer operating at 0.9µmwith an emissivity dial setting of0.82, the emissivity of the steel,indicates the correct temperaturewhen the process begins. Gradually,water from nearby cooling sprays

starts to evaporate off the hot steel,generating steam. A recorder con-nected to the thermometer beginscharting a series of jagged spikesshowing temperature variations ofat least 80° F as the process contin-ues. Can the emissivity dial be set tocompensate for serious steam inter-ference? What is the temperatureerror?Answer: There is, of course, no dial

setting that always produces a cor-rect temperature indication. Vary-ing amounts of steam continuallyflow through the optical path caus-ing the transmission of the path tovary unpredictably. This results inthe instrument’s chart recorder pro-ducing a jagged tracing. Equation(2) can be solved for τPATH to find,for instance, that the transmissionwas 0.67 when the indicated tem-perature had dropped to 80°F(assuming the true temperaturestayed the same). Although theexact amount of error continuallyvaries, the steam clearly has a sig-nificant effect on the indicated tem-perature.

MINIMIZING TRANSMISSION ERRORSTransmission errors generally

are minimized by using the shortestwavelength unit capable of measur-ing the specified temperature range.Tables 1 and 2 show that the∆ΤTABLE error values become largerfor longer wavelength units. There-fore, transmission losses compara-ble to those in the above example

A. RADIATION LOSSES B. ELECTRONIC SIGNAL COMPENSATION

εIDEAL = 1 εTARGET = .75 τPATH = .75

BLACKBODYRADIATION EMITTED

RADIATION TRANSMITTEDRADIATION

100% 75% 56%

DETECTORSIGNAL

VOLTAGE56%

εTARGET + τPATH

=.75 x .75 = .56

εDIAL=.56

emissivitydial

BLACKBODYSIGNAL

VOLTAGE

100%

10

FIGURE 2An Infrared Brightness Thermometer can Compensate for Radiation Losses (A),If the Emissivity Dial is Set to the Proper Value (B)

*The percentage of transmission error is the same as the percentageof dial setting error when the target’s true emissivity value is known.

11

EFFECTIVE WAVELENGTH 0.65µm 0.9µm 1.6µm 2.3µm 3.4µm 3.9µm 5.0µm 8.0µm 10.6µmTARGET

TEMPERATURE (°F)0 0.05 0.07 0.13 0.18 0.27 0.31 0.41 0.64 0.86

200 .10 .14 .27 .38 .57 .64 .85 1.3 1.7400 .18 .25 .46 .66 .97 1.1 1.4 2.2 2.8600 .28 .38 .70 1.0 1.5 1.7 2.2 3.3 4.1800 .40 .55 1.0 1.4 2.1 2.3 3.1 4.5 5.6

1000 .53 .73 1.3 1.9 2.8 3.1 4.1 5.8 7.11200 .69 .95 1.7 2.5 3.6 4.0 5.2 7.2 8.71400 .87 1.2 2.2 3.1 4.5 5.0 6.4 8.8 101600 1.1 1.5 2.7 3.8 5.5 6.1 7.6 10 121800 1.3 1.8 3.2 4.5 6.5 7.2 9.0 12 142000 1.5 2.1 3.8 5.4 7.6 8.4 10 14 162200 1.8 2.5 4.5 6.2 8.8 9.7 12 15 172400 2.1 2.8 5.2 7.2 10 11 13 17 192600 2.4 3.3 5.9 8.2 11 12 15 19 212800 2.7 3.7 6.7 9.2 13 14 17 21 233000 3.0 4.2 7.5 10 14 15 18 22 253500 4.0 5.4 9.8 13 18 19 22 27 304000 5.1 6.9 12 16 21 23 27 32 344500 6.3 8.5 15 20 25 27 31 36 395000 7.6 10 18 23 30 31 36 41 44

TABLE 1 – BRIGHTNESS THERMOMETER TEMPERATURE ERRORS CAUSED BY ONE PERCENT TRANSMISSION ERRORS (In Degrees Fahrenheit)

would result in even more severetemperature errors if a longer wave-length unit were used.

There are several accessories forIRCON brightness thermometerswhich may be used to further mini-mize transmission problems.

Interferences like steam and smoke are carried on turbulent air currentswhich occasionally allow a clearglimpse of the target. A “peak pick-ing” option allows a unit to latchonto the highest “clear” reading,greatly improving the accuracy of

the indicated temperature. The“sight tube” option is useful forshielding the optical path fromtransmission interferences. Finally,the “air purge” option helps to pre-vent particles from settling on aninstrument’s lens.

SYMBOL DEFINITIONΤIND Target Temperature Indicated by Instrument

ΤTRUE True Target Temperature∆Τ Indicated Temperature Error:

ΤIND – ΤTRUE∆ΤTABLE Error Value in from Tables 1F and 1CεDIAL Actual Emissivity Setting on Instrument DialεEFF Emissivity Setting Required for ΤIND = ΤTRUE

εTARGET, TRUE True Target EmissivityτPATH, TRUE True Path Transmission

FIGURE 3

12

EFFECTIVE WAVELENGTH 0.65µm 0.9µm 1.6µm 2.3µm 3.4µm 3.9µm 5.0µm 8.0µm 10.6µmTARGET

TEMPERATURE (°C)0 0.03 0.04 0.08 0.12 0.17 0 .20 0.26 0.41 0.54

100 .06 .08 .15 .22 .33 .37 .49 .76 1.0200 .10 .14 .25 .36 .53 .60 .79 1.2 1.6300 .15 .20 .37 .53 .78 .87 1.2 1.7 2.2400 .20 .28 .51 .73 1.1 1 .2 1.6 2.3 2.9500 .27 .37 .68 .96 1.4 1 .6 2.1 3.0 3.6600 .35 .47 .87 1.2 1.8 2 .0 2.6 3.7 4.4700 .43 .59 1.1 1.5 2.2 2 .5 3.2 4.4 5.2800 .52 .72 1.3 1.8 2.7 3 .0 3.8 5.2 6.1900 .63 .86 1.6 2.2 3.2 3 .5 4.4 6.0 7.0

1000 .74 1.0 1.8 2.6 3.7 4 .1 5.1 6.8 7.81100 .86 1.2 2.2 3.0 4.3 4 .7 5.8 7.6 8.71200 .99 1.4 2.5 3.4 4.9 5 .4 6.6 8.5 9.61300 1.1 1.6 2.8 3.9 5.5 6 .0 7.3 9.3 111400 1.3 1.8 3.2 4.4 6.1 6 .7 8.1 10 111500 1.4 2.0 3.6 4.9 6.8 7 .4 8.9 11 121600 1.6 2.2 4.0 5.5 7.5 8 .1 9.6 12 131800 2.0 2.7 4.8 6.5 8.9 9 .6 11 14 152000 2.4 3.2 5.8 7.7 10 11 13 16 172200 2.8 3.8 6.8 9.0 12 13 15 18 192400 3.3 4.5 7.8 10 13 14 16 19 212600 3.8 5.1 9.0 12 15 16 18 21 232800 4.3 5.9 10 13 17 18 20 23 253000 4.9 6.6 11 15 18 20 22 25 27

TABLE 2 – BRIGHTNESS THERMOMETER TEMPERATURE ERRORS CAUSED BY ONE PERCENT TRANSMISSION ERRORS (In Degrees Celsius)

PROBLEM OF BACKGROUND SOURCESThe basic relationship used in

infrared thermometry is that the in-tensity, or brightness, of infrared radi-ation emitted by an object increasespredictably with its temperature.

Unfortunately, aninfrared brightness ther-mometer cannot distinguishbetween the radiationwhich a target emits andthe radiation originatingfrom other sources.

If the detected radiationincludes radiation from thetarget and an additionalcomponent originatingfrom background sources,the indicated temperature ishigher than the target’s truetemperature.

All spatial area is filledwith radiation emitted bythe physical matter in theenvironment. Any radia-tion emitted by sourcesother than the selected tar-get object is referred to as“background radiation.”

This radiation can encompasswavelengths throughout the electro-magnetic spectrum, including visi-ble and infrared. The intensities atthe infrared wavelengths (as withall the other wavelengths) are deter-mined by the temperatures andemissivities of the objects in thesurroundings, as well as by thepresence of absorbing materials inthe transmission paths.

Background radiation does notpresent a problem to temperaturemeasurement unless it has a signif-icant intensity. The intensity is sig-nificant when the brightness of thebackground sources at the detectedwavelength is comparable to, orgreater than, that of the target. Atthat point, the extra radiation con-tributed by the background maymake enough of a difference toincrease the indicated temperature.

Analogously, it is easy to seethat a flashlight beam adds signifi-

cantly to the light from a match, butmakes no real difference when it isadded to the beam from a search-light. The brightness of the flash-light is not significant if the targetsource is much brighter.

Since the human eye cannot see

infrared radiation, it is impossible toknow if background radiation is sig-nificant enough to produce an effect.We can estimate the significance ofthe background’s radiance, relativeto the target’s, simply by comparingthe approximate temperatures of thetarget and background sources.

Although many other factorsaffect how much background radia-tion is actually detected, this basicrelationship still provides a goodway to identify potential back-ground interferences.

For example, when a target isheated well above room tempera-ture, the radiation emitted by roomtemperature objects is negligible incomparison to the detected radiationfrom the target. If the room is litwith tungsten filament bulbs, how-ever, the radiation produced by thehigh-temperature filaments couldadd significantly to the detected tar-get radiation.

Similarly, intense plant lightingor inspection lighting can causeproblems. Other hot surfaces andhot objects near the target are alsoimportant sources of backgroundinterference.

DETECTION OF BACKGROUND

RADIATIONUnder what circum-

stances does the detectedradiation include an addedcomponent from back-ground sources? Anobvious case is when thetarget does not completelyfill the instrument’s fieldof view. Then the unitalso “sees” beyond thetarget into the back-ground.

A correctly operatedbrightness thermometer,however, is aimed so thatthe target completely fillsits field of view. Underthese conditions, no back-ground radiation can bedetected unless the targethas transmissive or reflec-

tive properties.Therefore, background radiation

can be a problem only if the targetacts something like a mirror, a win-dow, or both, in the detected infraredspectral region. Note that an objectwhich is reflective or transparent tovisible radiation is not necessarilyreflective or transparent to infraredradiation, and vice versa.

The target’s reflectivity (R) andtransmittance (τ) factors at thedetected wavelength affect the sizeof the contribution made by back-ground radiation to the detectedenergy. As shown in Figure 1, thesefactors can take on values from zeroto one, representing the fraction ofincident background radiation thatis reflected or transmitted.

Thus, even when there is a rela-tively large amount of backgroundradiation, there still may be very lit-tle error in temperature measurement.The target may reflect or transmit only

SENSING HEAD

TARGET

1

2

Background radiationincident on target could be1. Reflected2. Transmitted into the sensing head (as shown)

Radiation Emitted by Target

0 R 1If R = 0: no reflectionIf R = 1: perfect mirror (100% reflection)

0 τ 1

If τ = 0: no transmission

If τ = 1: perfect window (100% transmissio

13

FIGURE 1Background Radiation Can Contribute to Detected Radiation ifτTARGET or RTARGET is Greater than zero (The target absorbsthe portion of incident background radiation which is neitherreflected nor transmitted).

TEMPERATURE EFFECTS DUE TO BACKGROUND RADIATIONCHAPTER 4

a small fraction of the backgroundradiation to the infrared thermometer.

The target’s emissivity value is theindicator of how susceptible it is to back-ground interferences. This is becausean object’s emissivity (ε) is related to itstransmissive (τ) and reflective (R) prop-

erties by the formula: (1)ε = 1 - R - τFor instance, a “blackbody” is aperfect radiator and has an emissiv-ity of one. When the emissivityvalue equals one, both the reflectiv-ity and transmittance must bezero.

Because such a target doesnot reflect or transmit any radi-ation, the measurements do notcontain errors due to back-ground radiation. This is trueno matter how much back-ground radiation there is.

However, nearly all real tar-gets have emissivity valueswhich are less than one.Because of this, the detectedradiant energy usually has atleast some contribution (due toreflection and/or transmission)from the background.

It is clearly beneficial todetect radiation in a spectralregion where the target has a

high emissivity. This is one of thereasons that IRCON products offersuch a wide range of instrumentswith different spectral responses.

Generally instruments areselected so that the target has notransmission and as little reflection as

possible in the detected spectralregion. This makes the problem ofavoiding significant background radi-ation a little easier.

To summarize the preceding dis-cussion, the lower the target emissiv-

ity, the greater the fraction of radia-tion the target reflects and/or trans-mits from the background.However, if there is not much radia-tion in the background to begin with,the extra contribution to the detectedenergy is very small.

If there is a significant amount ofbackground radiation, there may beenough energy detected to cause anerroneously high temperature indication.

GEOMETRY OF VIEWINGARRANGEMENT

The actual contribution ofbackground radiation to thedetected energy is determinedby the geometry of the view-ing arrangement. That is, theposition of the target and thesensing head with respect tosignificant backgroundsources determines how muchof the background radiation isactually reflected or transmit-ted into the instrument’s opti-cal system.

If the sensing head can bepositioned to avoid thereflected or transmitted radia-tion, temperature measure-ment errors can be avoided aswell.

Two examples of this are 14

HOT OVENTARGET

1

2

Radiation Emitted by Target

Radiation Emitted by Background

R = 0.50

τ = 0TARGET

1 2

LAMP

Radiation Emitted by Target

Radiation Emitted by Background

R = 0.20τ = 0

Proper Positioning of the Sensing Head can Avoid Significant Background Errors. (A) Unit 2 Avoids First-Order Reflections;Unit 1 Receives 50 Percent of the Significant Radiation from the Heated Oven. (B) Unit 2 is Shielded by the Target; Unit 1Receives 20 Percent of the Incident Radiation from the High-Intensity Lamp.

Diffuse reflections

Specular reflections

Incident Radiation

Ø2Ø1

Ø1 = angle of (specular) reflection

Ø1 = Ø2

Ø2 = angle of incidence

FIGURE 3Specular Reflections Leave the Reflecting Surface atthe Same Angle the Incident Radiation Makes whenStriking the Surface. Diffuse Reflections, which Resultfrom Roughness in the Surface, are Scattered in OtherDirections.

FIGURE 2(A) FIGURE 2(B)

1

shown in Figure 2. Both targetsillustrated have some reflectivity butno transmittance, as is often thecase in real applications.

For each example, the instru-ment in position 1 receives radia-tion with a component from thebackground and indicates a temper-ature that is too high. Each instru-ment in position 2 avoids reflectionsfrom the background source.

In Figure 2 (A), the unit in posi-tion 2 is simply aimed so that noneof the background reflections enterits optical system. In Figure 2 (B),the unit in position 2 is shieldedfrom the background radiation bythe target itself, since it has notransmittance.

If this target had some trans-mittance at the detected wave-length, the sensing head could“see through” it to some extent.Then there would be less error ifthe instrument were aimed so thatit looked through the target in thedirection of a cooler background.

The kind of reflectionsdepicted in Fig. 2 are specularreflections, for which the angle ofincidence equals the angle ofreflection. An uneven or roughsurface can also produce diffusedreflections (Fig. 3) which scattersome of the radiation in other direc-tions. If the target material in Figure2 (A) produces diffused reflectionsthe brightness thermometer in loca-tion 2 is not completely safe frombackground reflections.

Because specular reflections aregenerally the most significant, how-ever, they are the most important toavoid. Note that although the reflec-tivity may be different for the visibleand infrared regions, it still may bepossible to observe the direction ofthe reflected energy if the back-ground source is incandescent.

If the background source is nothot enough to radiate at visiblewavelengths, the angles of inci-dence and reflection must be visu-ally estimated.

In some applications it is impos-sible to position the instrument sothat it avoids background radiation.When this is the case, a final possi-ble solution is to use some form of

shielding to eliminate the problem. An opaque shielding material

that is appropriately placed betweenthe background source and the tar-get can be used to block the back-ground radiation before it can bereflected off, or transmitted through,the target.

Of course, geometrical consider-ations are still important here, sinceit is necessary to know the path ofpotential reflections (or transmis-sions) in order to shield properly.

In particularly difficult situa-

tions, a cooled sight tube accessorycan greatly improve the accuracy oftemperature measurements. Thistube is attached to the sensing headto provide an almost completelyshielded view path.

Reflections from the back-ground that would have entered theoptical system are blocked by thepresence of the tube, as shown inFigure 4. It is imperative, however,that the sight tube be kept coolerthan the target. Otherwise, the hottube itself would emit a significantamount of radiation, defeating itsshielding action.

There are also special infraredthermometer systems which can elimi-nate background interferences in someapplications. These systems will useeither a second infrared sensing heador thermocouple to measure the back-ground.

PUTTING THE PIECESTOGETHER

Background interferences canget quite complex due to multiplereflections, multiple sources and thelike. Other complications can arisewhen hot gases or sooty flames liebetween the sensing head and thetarget. Then the hot molecules inthe transmission path have theeffect of both reducing and addingto the detected energy.

These molecules absorb or scat-ter some of the radiation emitted by

the target, and emit a significantamount of radiation themselves.

Some applications, however,lend themselves to a relativelysimple analysis. Although directviewing into an oven is not rec-ommended, it is an applicationthat allows for a more rigorousexamination of how error is pro-duced.

To determine the effect of thebackground on the detectedradiance, known conditions willbe assumed. To arrive at actualnumerical temperature error val-ues requires a knowledge of pre-cisely how radiance (which we willcall N) depends on temperature.Since this relationship, given by

the Planck equation, involves math-ematics beyond the scope of thischapter, the results will be translatedinto values, calculated in terms ofradiance, that relate to temperature.

EXAMPLE:VIEWING INTO AN OVEN

A brightness thermometer isused to measure the temperature of atarget which is contained within aheated oven. In order to accomplishthis, the unit must be aimed directlyinto the oven.

The instrument responds towavelengths of 2.0 to 2.6 µm, andthe target has an emissivity of 0.75and no transmittance in this spec-tral region: (a) If the target temper-ature is 700°F and the backgroundtemperature is 1,000°F, how muchof the detected radiance is emittedby the background and how muchof it is emitted by the target; and (b)what is the detected radiance if thetarget is removed from the oven

HOT OVEN

TARGET

Sensing Head

Water Cool

Air PurgeSight Tube

15

FIGURE 4A Cooled Sight Tube Accessory can be used to Prevent Background Reflections from Enteringthe Optical System.

and viewed in a much cooler envi-ronment?Answer: (a)The total detected radi-ation is given by: (2)

N TOTAL =N FROM TARGET + N FROM BACKGROUND

Because the target has an emissiv-ity of 0.75, it radiates 75 percent ofthe energy that would be emitted bya blackbody at 700° F. SoN FROM TARGET = N EMITTED = 0.75 N 700

It will be assumed that the ovenis much larger than the target sothat it approximates black-body characteristics. Theoven’s radiance equals thatof a blackbody at 1,000°F, orN1,000.

Since the target is essen-tially surrounded by theoven walls, it is not possibleto position the sensing headto avoid error. Radiation isreflected and/or transmittedin every direction accordingto the target’s R and T char-acteristics. So the detectedradiance from the back-ground is given by: (3)

N FROM BACKGROUND =N REFLECTED + N TRANSMITTED =

RN 1000 + τ N 1000

Since the target has zero trans-mittance, we know from equation(1) that the reflectivity must equal0.25. Substituting these values intoequation (3) gives

N FROM BACKGROUND = 0.25 N 1000

Therefore equation (2) becomes:(4)

N TOTAL = 0.75 N 700 + 0.25 N 1000

(b) When the background’stemperature is much lower than thetarget’s, the contribution from thebackground becomes negligible.That is, the second term in equation

(4) would be < 0.75 N700, so we cansay that the total detected radiation is just 0.75 N700.

Table 1 shows that when thebackground is 1,000°F, there is anerror of 169°F. Notice in the tablethat the error in this examplediminishes quickly as the back-ground temperature falls below thetarget temperature.

MINIMIZING THE EFFECTS OF HOT BACKGROUND

Various methods of minimizingbackground errors have been men-

tioned throughout this sec-tion of the chapter. The fol-lowing summarizes themost important points:• Use a spectral region

where the target emis-sivity is high.

• Avoid significant reflec-tions (and transmis-sions) through positioning or shielding.Although the general

causes of background errorhave been considered, thisdiscussion is by no meansall inclusive. If you providethe IRCON sales engineers

with the details of your application,these engineers can help you main-tain the accuracy of your tempera-ture measurements.

16

TABLE 1 BACKGROUND ERRORS (∆Τ)

BRIGHTNESS THERMOMETER (2.0 to 2.6 µm)

εTARGET = 0.75, ΤTARGET = 700°F

ΤBACKGROUND (ΤINDICATED - ΤTARGET)

(°F) ∆Τ400 1°500 5°600 15°700 36°800 69°900 114°

1000 169°

No measurement device pro-duces perfect measurements be-cause no real system is absolutelyperfect. Manufacturers of infraredbrightness thermometers, how-ever, establish limits to the uncer-tainty involved in determiningany given measurement.The instrument’s measure-ment uncertainty specifiedby a manufacturer repre-sents the worst case combi-nation of various unavoid-able built-in error sources.

In this final chapter,some of the more significantsources of instrument errorwill be analyzed. In addi-tion, user guidelines will beprovided so that the speci-fied uncertainty range for aparticular instrument is notexceeded.INSTRUMENT ERROR SOURCES

CALIBRATIONThe calibration of an infrared

brightness thermometer involvesadjusting the thermometer read-ing to match the temperature of aknown blackbody standard source.There is an uncertainty associatedwith an operator’s ability to makethis adjustment. The limitation isimposed by the accuracy of thethermometer’s temperature indi-cations. For example, if the unitbeing calibrated had a meter scalelike the one shown in Fig. 1, itwould not be possible to ensurethat the thermometer matched theblackbody temperature any moreclosely than approximately ±1°.

There is also calibration uncer-

tainty associated with the black-body standard’s value. This has todo, in part, with how closely thestandard approximates blackbodycharacteristics. Although a black-body, by definition, radiates theideal, maximum amount of energy

possible at each temperature, noreal object truly radiates ideally. Itis possible, though, to make verygood blackbody simulators (withemissivities very close to 1) usingreal materials shaped in the formof a cavity. Yet a margin of uncer-tainty remains, and its magnitude isdetermined by the design and con-struction of the blackbody used.

Not only is there some uncer-tainty about how much radiationthe blackbody standard source isemitting at each temperature,there is also some question as towhat the blackbody’s temperatureactually is. To know the black-body temperature, we must havesome other means of monitoringit. No matter what method isused, there is some degree ofuncertainty associated with this

measurement as well.COMPONENT TEMPERATURE

Another uncertainty exists because the temperature of theinfrared thermometer’s compo-nents can affect these instruments’

operation. Componenttemperature can alter notonly the action of the sen-sor and the circuitry, buteven the properties of fil-ters and other optical com-ponents. These effects areespecially important whenthe instrument is subjectedto a wide range of tempera-tures. A unit that was cali-brated with its outer case atroom temperature will notproduce the exact samemeasurements when posi-tioned near a high-temper-

ature furnace. Therefore, specificinstrument precautions such ascooling, for example, must betaken to maintain instrument cali-bration.

ELECTRONICSThe electronics in infrared ther-

mometers are used to process volt-ages generated by radiant energystriking the detector. Becausebrightness thermometers measurethis voltage quantitatively to deter-mine a target’s temperature, thevoltage levels cannot be allowed todrift or fluctuate arbitrarily. Anysituation which allows this to occurproduces an error.

Electrical noise, for instance,can produce significant fluctua-tions, especially if the signal issmall. Either very fast response

800810 820 830 840 850 860 870

DEGREES CENTIGRADE

TEMPERATURE EFFECTS DUE TO INSTRUMENT CHARACTERISTICSCHAPTER 5

FIGURE 1Temperature Values on this Meter Scale CannotBe Read Better than Plus or Minus One Degree.

Specified Coneof Vision

Target

99%

95%

FIGURE 2The Optical System Collects a Small Percentage of the Detected Radiation from Outside of the Cone of Vision.The Instrument’s Sensitivity to Stray Radiation Decreases with Angle Outward from the Cone of Vision.

17

times or very low target tempera-tures can degrade the signal tonoise ratio. Also, as electricalcomponents age and are subjectedto different environmental condi-tions, their circuit voltages have atendency to drift. IRCON instru-ments are “burned in” usingan environmental chamberto minimize this problem.

OPTICAL SYSTEMThe optical system

focuses radiation from thetarget onto the detector.Because optical systems arehigh precision devices, errorsintroduced generally are quitesmall. Of these small opticalerrors, the most significant isusually related to the instru-ment’s ability to reject radia-tion from outside its field ofview – or its sensitivity tostray radiation.

We usually assume that theoptical system collects only theradiation coming from the area onthe target’s surface which intersectsthe instrument’s specified cone ofvision. However, it is physicallyimpossible to make an optical sys-tem which has an absolutely dis-tinct cut-off to the area it measures.As a result, there is a relativelysmall percentage of contributionfrom sources outside the specifiedcone of vision. The contributiondiminishes as the angle from thecone of vision increases (Fig. 2).

Optical system errors presentvery few problems when the targetis much larger than the measuringarea. When this is true, most ofthe detected radiation outside thespecified cone of vision is emittedby the target object, as in Fig. 2.In this case, any error due to theinstrument’s sensitivity to strayradiation is negligible; the targetitself is the source of most of the“stray” radiation.

On the other hand, if the spotsize is about the same size as thetarget, much of this outside con-tribution comes from the back-

ground. If we assume that fivepercent of the detected radiationcomes from outside the specifiedcone of vision, then as much asfive percent of the detected radia-tion may come from the back-ground. Yet if the target diameter

is twice the specified spot size,only about one percent of thedetected radiation comes frombackground sources. Reducingthe contribution from backgroundsources reduces any resultingmeasurement error.

LINEARIZATIONThe electronic signal in an

infrared brightness thermometer isproduced by radiant energy strik-ing the detector. Because the tar-get’s radiance increases exponen-tially with temperature, so doesthe signal produced by the detec-tor. In order to get temperaturereadings, the infrared thermome-ter must relate ever-increasingvoltage changes (∆V) with a unittemperature change (∆Τ) as thetarget gets hotter. This signal pro-cessing, called linearization, maybe thought of as the projection ofthe nonlinear detector signal onto alinear (straight line) temperaturescale, as shown in Fig. 3.

In order to associate the righttemperature change with a givenchange in detector signal, theinstrument must know how the

signal varies with temperature.The characteristics of a blackbodyradiator define this universal ref-erence function. Since linear cir-cuits are the easiest and most reli-able to work with, the usualmethod of electrically implement-

ing this function is by usinglinear segments.

Figure 4 shows theslope increasing from onesegment to another so thatthe blackbody radiancefunction is approximated.The effect of a fixed changein the signal voltage on theindicated temperaturedepends on the slope of itssegment: the greater theslope, the smaller the tem-perature change.Although the characteris-

tics of this kind of linearcircuit are very close tothose of the true blackbody

function, the linear function isonly an approximation. In fact, itmatches the true function exactlyat only two points per segment,where the two graphs overlap.For every other detector voltagethere is a small error in the indi-cated temperature due to lin-earization. It is important to real-ize, however, that the approxima-tion is improved when more seg-ments are used in the design.Then, not only is the approxima-tion exactly right at more points,but the error is reduced every-where else as well.

USER GUIDELINESIf an instrument is used prop-

erly, it will operate with an accu-racy within its specified uncer-tainty. Note, though, that someinstrument errors can worsenwith time. Periodic maintenancechecks are a vital means of verify-ing that an instrument is operatingaccording to its specifications.There are other considerationswhich can be important in keepingthe effects of some of the instru-ment error sources to a minimum.

18

Temperature∆T

∆V

DetectorSignal

FIGURE 3Linearization Relates Increasing Changes in the Detector Voltage (∆V) to Constant Changes in Temperature (∆T).

COMPONENT TEMPERATUREFor applications where exact

temperature measurements are crit-ical, it is helpful to keep the unit’souter case temperature as close aspossible to what it was during itslast instrument calibration.

Also, be careful about relyingon uncertainty specifications if theunit has not recently undergone aroutine maintenancecheck. There is a chancethat such a unit may beoperating out of specifica-tions if its case tempera-ture is far from the centerof the allowable case tem-perature range. Aninstrument operates leastreliably when subjected totemperature extremes.

OPTICAL SYSTEMIf you are going to cal-

ibrate your own instru-ment, it is particularlyimportant to be aware ofthe possible influence ofstray radiation. Supposethe blackbody target usedfor calibration is exactlythe same size as the reti-cle in the sighting tele-scope. Then any radiationdetected from outside thespecified field of viewcomes from the back-ground.

Since the blackbody sourcesused in calibration usually arehotter than room temperature, thecontribution from the backgroundrepresents a much lower tempera-ture than the blackbody tempera-ture. Thus the average amount ofdetected radiation is lower than itshould be, and an energy levelthat is too low will be associatedwith the blackbody temperature.This throws off the calibrationand introduces an error into allsubsequent measurements.

Clearly the error would bereduced if the blackbody targetwere larger than the reticle. It isconsidered good practice to cali-brate an instrument using a black-body target which is at least twotimes the reticle diameter. If this

guideline is also followed for sub-sequent targets, sensitivity to strayradiation will not present a problem.

ELECTRONICSPreventing electrical problems

which result from poor installa-tion techniques is possible. Sinceleads from the sensing head or toa controller can pick up noisefrom electromagnetic interfer-

ences, it is very important to fol-low the wiring guidelines pre-sented in the IRCON operationsmanual. For instance:• Always use shielded cables.• Shield all low level outputs.• Use a “clean” power line.

Avoid power lines drivingbrush motors; loads driven bySCRs and contactors; andother intermittent, high in-rushloads which distort the powerline waveform.

• Before connecting any deviceto an output, verify that theimpedance values of the outputand the input are compatible.

• Avoid ground loops betweenthe sensing head, the signal pro-cessing unit, and remote indica-tor units.

MINIMIZING INSTRUMENTERRORS

The magnitude of instrumenterrors is highly dependent on thespecifics of the application. How-ever, most instrument errors aresubject to the same trends as emis-sivity and transmission errors.

For instance, suppose ambienttemperature conditions cause a

five percent increase inan instrument’s signalvoltage. This problemwill cause more signifi-cant errors in units whichdetect longer wave-lengths than in thosewhich detect shorterwavelengths. Similarly,the temperature errorincreases as the targettemperature increases.Thus, it is beneficial tochoose the unit whichmeasures the shortestwavelength possible forthe desired temperature.

Instrument errorstypically represent theleast significant of allpossible kinds of errors.Uncertainty about a tar-get’s emissivity value,for example, usually faroutweighs any problemswhich occur due to lin-

earization. Nevertheless, it makessense to try to minimize allsources of error. As we haveseen, the most practical ways tominimize instrument errors are:• Install the instrument with

care and always follow recom-mendations given in the oper-ations manual.

• View target where it is at least twice the instrument spot size.

• Avoid extreme instrument case temperatures.

• Use a clean power line.• Shield all signal wiring.• Institute a routine mainte-

nance schedule to guarantee continued reliability.Remember, the best way to

minimize all temperature mea-surement errors is by choosingthe right instrument for yourapplication.

19

∆Τ

Temperature

SignalVoltage

BlackbodyFunction

∆V

∆V

∆Τ

ApproximationFunction

FIGURE 4The Signal Voltages Produced by a Blackbody Radiator can beApproximated Using Straight Line Segments. A SmallerTemperature Change (∆T) is Associated with the VoltageChange ∆V at Higher Temperatures Since the Slope ofthe Segments Increases.

For most infrared thermometersto function properly, the hot objectbeing measured must fill the targetarea and no obstruction can inter-fere with the cone of vision. Whenan infrared thermometer looks at aspecific target, it measures intensityof radiant energyover an entire targetarea. The energytravels from the tar-get back to the lensin the form of cone,hence the term coneof vision (Fig. 1).

Therefore, aninfrared thermome-ter acts like a cam-era; if the lens isobstructed, with afinger for example,the resulting imagewill be underex-posed on the film.Similarly, obstructions in the coneof vision will cause the thermome-ter to read incorrectly.

Problems which will cause aninfrared thermometer to readincorrectly include:1. Small objects (too small

to fill the target area).2. Dust, smoke or steam

which obscure the line

of sight.3. Windows in the process get

dirty and are difficult to keep clean.

4. Emissivity of the product changes (due to changes in alloy or surface condition).

A two-color or ratio ther-mometer can usually solve theseproblems. A brightness ther-mometer has to have a clear unob-structed view of a target (Fig. 2)whereas some obstructed targetscan only be measured by using atwo-color thermometer (Fig. 3).

A two-color thermometer con-sists of two brightness thermome-

ter in the same package. By usingtwo detectors, a two-color ther-mometer operates at two separatewavelengths while both see thesame hot target simultaneously.

In basic terms, a two-colorthermometer works properly as

long as whateveraffects one wave-length affects theother wavelengthby the sameamount. This indi-cates that the onlyreason the ratioeddetector outputchanges is becauseof variances in tem-perature.

Every two-color thermometerhas a limit as tohow much signalcan be lost. This is

referred to as the reduction ratio.The reduction ratio can vary fromas low as 5:1 to as high as 25:1.In other words, 96 percent of thesignal could be lost and still readan accurate temperature. Alsokeep in mind that the loss in sig-nal can come from three sources:1. Low emissivity of the target.

CONEOF

VISION

d = –DF

D

d

FOCAL POINT

d = Diameter of cone (Spot Size) at Focal PointD = Distance from flange to Focal PointF = Resolution Factor of Sensor

20

FIGURE 1An Infrared Thermometer’sLens System Collects InfraredEnergy from a Specific TargetArea. The Energy Travels fromthe Target Back to the Lens inthe Form of a Cone, Hence theTerm Cone of Vision.

WHEN TO USE TWO-COLOR IR THERMOMETERSCHAPTER 6

FIGURE 2To function Properly, a Brightness

Thermometer Must Have an UnobstructedView of a Target.

FIGURE 3The Only Way to Measure Some Obstructed

Targets is by Using a Two-ColorThermometer.

2. Object too small to fill cone of vision.

3. Obstruction caused by smoke, steam, dirt or dirty windows.If an object has an emissivity

of 0.25, then 75 percent of thesignal is lost, which means onlyabout 10 percent more signal canbe lost as a result of obstructions.When the reduction ratio limit isreached, the instrument can sensethis and will indicate an“invalid” reading.

An invalid readingsimply says the signal is solow that a repeatable resultis not possible. Ratherthan indicate erroneousreadings, the instrument isforced to a below zero scaleoutput and provides analarm of its inability tocompute the temperature.

In some applications,adjustments must bemade for non-gray emis-sivity variations. A goodexample is in the mea-surement of molten met-als. Usually the metalwill have a different emis-sivity for each wave-length. Therefore, whena two-color thermometerlooks at the molten metal,the ratio or slope will beincorrect and an error willoccur in the reading.

To compensate forthese types of incorrectreadings, all two-colorthermometers have an emissivitycorrection, or E-slope feature.When viewing the molten metal,the E-slope control is turned untilthe instrument reads the correcttemperature. The correct temper-ature is obtained by using a dis-posable thermocouple.

The E-slope control simplymultiplies the measured ratio byan adjustable constant which cor-rects the instrument calibration forthe unequal spectral emissivitiesof the target. Once the E-slope isset, the problems of smoke, steam,dust, among others, are handledby the instrument.

Similar errors will occur if an

improper window material isused. Pyrex windows, for exam-ple, are slightly colored and trans-mit differently in the two spectralregions. Once again, the E-slopecontrol can be used to correct thisproblem.

Two-color thermometers solvemany application problems, butthere are some factors which mustbe considered when using them to

measure temperature. These factorsinclude reflections, small targets,scale and physical characteristics ofa target.

REFLECTIONSTwo-color infrared thermome-

ters do not solve the problemscaused by reflected energy. Forexample, steel in a hot gas firedoven may be at 900° C and theoven walls could be at 1,100° C.This means the hot steel is com-pletely surrounded by a sourcehotter than the steel (Fig. 4).

A two-color thermometermeasures the composite radiantsignals streaming from the billet

surface for each spectral channel,computes the ratio of these twosignals, and displays the tempera-ture equivalent of this ratio.Unfortunately, but quite naturally,this indicated temperature is nei-ther that of the steel nor of thebackground. Adjusting the E-slope will not correct this condi-tion. The only way to correctreflection problems is to remove

the interfering hot back-ground.

SMALL TARGETSAs previously noted,

the hot object does nothave to fill the entire tar-get area of the ther-mometer. Applicationssuch as hot wires, hotrods and molten glassstreams are usually verynarrow and do not fillthe field of view as seenin the telescope reticle.The problem that has tobe considered is what fillsthe remainder of the reti-cle. If the remainder isfilled with another hotobject, averaging the twoobjects may possiblycause an incorrect read-ing. If the backgroundaround the wire or rod iscool, the backgroundcontribution to the twotarget signals and theresulting ratio will benegligible, indicating a

correct temperature.THICK OXIDE

Many two-color thermometersare used in steel mills. A popularmisconception in the industry isthat a two-color thermometer cansee through scale. Unfortunately,that is not true.

Cold scale which fills theentire reticle will simply cause theinstrument to read a low tempera-ture. Usually the scale is some-what cooler than the steel but notsignificantly cooler. The instru-ment will average the reading,providing a low read out.Measuring the steel where the

STEEL (900 C)

OVEN WALLS1100 C

IRC

ON

1065 C

21

FIGURE 4Two-Color Infrared Thermometers do not Solve ProblemsCaused by Reflected Energy. An Example of this ReflectanceOccurs when the Walls of a Gas Fired Oven are Warmerthan the Steel in the Oven.

scale has been removed is thebest way to compensate for this.PHYSICAL CHARACTERISTICS

A two-color thermometer is asophisticated sensing head. Thereare many special features requiredto ensure the instrument readsthe proper temperature. Anachromatic lens and thru-the-lensoptics are two special featuresassociated with a two-color thermometer.

It is important for two-colorthermometers to have an achro-matic lens. This means a lens thathas the ability to focus both wave-lengths on the focal plane. If twodifferent wavelengths of energytravel through a lens, they will eachbend differently. The longer wave-length does not bend as much as

the short wavelength. An achro-matic lens corrects this problem byensuring that the two wavelengthsfocus the image of the target on thedetector plane.

Another special feature asso-ciated with two-color thermome-ters is thru-the-lens optics. Thisfeature provides an operator withthe ability to look through an eye-piece at the back of the sensinghead and see the hot target. Thisallows the eye to actually see thearea the detector is measuring.

Two-color thermometersrequire either two detectors at twowavelengths or one detector thatworks with two filters to obtaintwo separate signals.

TWO- COLOR TECHNIQUEThe IRCON dual detector mea-

suring technique (A)overwhelm-ingly provides faster and moreaccurate temperature measure-ment in comparison to instru-ments that use the filter wheeltechnique (B). In the IRCON two-color scheme, ratio computation ofthe two spectral signals takesplace simultaneously. In the filterwheel scheme, ratio computationis displaced in time resulting inslower operation and potentialerror. Superior temperature mea-surement under dynamic targetconditions (target moving in andout of the field of view or temper-ature fluctuations) is made possi-ble because both detectors viewand measure the same spot on thetarget at the same instant.

22

Should you require any assistance or further explanation, please call our ApplicationEngineering Department, toll free in the U.S. and Canada at 1-800-323-7660.

RotatingFilter Wheel

λ1 Signal

λ2 Signal

Signals displaced in time resulting in potential error

λ1 and λ2 Signals

Signals sensed simultaneously — for

more accurate readings

Lens

Lens

Lens

Lens

Target

Target

B Filter wheel technique

using one detector is time-delayed, resulting in potential error and slow response time.

A The two-color technique

using two detectors measures simultaneously, allowing accurate readings and fast response time.

APPLICATION WAVELENGTH SELECTION GUIDE

23

TYPICAL WAVELENGTH (µm)APPLICATIONS 0.65 0.9 1.0 0.7-1.08 1.55 1.65 2.0 3.43 3.9 5.0 7.9 8-14

&1.08 &1.68 RATIO RATIO

ALUMINUM • • • •ASPHALT • •AUTOMOTIVE • • • • • • • • •APPLIANCES • • • •AMMUNITION • • •BATTERIES • •CEMENT • • • • • • • •CONSTRUCTION • • •

MATERIALSPHARMACEUTICAL •FIBERGLASS • • • • • • •FOOD PROCESSING • • •FOUNDRY • • • • •GLASS - MELTING • • • •GLASS - FLAT •GLASS BOTTLES/ • • •

CONTAINERSHEAT TREATING • • • • •INDUCTION HEATING • • • • •KILNS • • • • • • •METAL WORKING • • • • •MINING •NON-FERROUS • • • •

METALSOVENS • • • • • • • • • • •PAPER • • •PLASTICS • • •RUBBER • • •SEMICONDUCTORS • • • • • • •STEEL • • • • • •TEXTILES • • • •UTILITIES • •

To determine the IRCON instrument that is most appropriate for your application needs, please refer to the latest edition of our Product Selection Guide brochure, part number 010128.

World Headquarters:

IRCON Inc (Serving North and South America)

7300 North Natchez AvenueNiles, Illinois, USA 60714Phone: 847 967 5151Toll Free: 800 323 7660 (USA and Canada)Fax: 847 647 0948E-Mail: info@ircon.com

European Headquarters:

IRCON BV(Serving Europe, Middle East, Africa and Russia)

Databankweg 6c3821 AL, Amersfoort, The NetherlandsPhone: 31 33 450 4321Fax: 31 33 450 4320E-Mail: info@ircon.nl

International Offices:

IRCON China Spectris China Ltd.Unit 101, Xin An Plaza, Building 13No. 99 Tianzhou RoadShanghai 200233 P.R. ChinaPhone: 86 21 6113 3735Fax: 86 21 6113 3788

IRCON IndiaSpectris Technologies Pvt. Ltd.14, Kasturba Gandhi Marg,6th Floor, Ambadeep BldgNew Delhi-10001 India Phone: 91 11 5152 0625Fax: 91 11 2332 2859

IRCON JapanSpectris Co., Ltd.1F JP Kaji-cho Bldg.3-5-2 Kandakaji-ChoChiyoda-kuTokyo 101-0045 JapanPhone: 03 5298 8170Fax: 03 3255 8154

IRCON KoreaSpectris Korea Ltd.8F, Turbotech B/D 16-6 Soonaedong, Bungdang-Gu Seongnam-City, Gyunggido 463-825 KoreaPhone: 82 31 786 0834Fax: 82 31 786 0833

IRCON Singapore31, Kaki Bukit Road 3#06-04/05 Techlink417818 SingaporePhone: 65 6846 4991Fax: 65-6846 4981

www.ircon.com

Part No. 010599 Rev B Note: The contents of this guide are being provided as reference only, and may be ©2006 Ircon, Inc. All rights reserved subject to errors, ommission and/or changes without notice.

About Us

If you are looking for solutions to difficult temperaturemeasurement and monitoring challenges, IRCON is thecompany to call. IRCON offers a product range andexperience that are unmatched in the industry.

In business since 1962, IRCON products perform withaccuracy and repeatability in the harshest and mostvolatile conditions requiring precise temperaturemeasurement and control.

Our solutions are designed to suit a wide variety ofapplications, with a product line capable of measuringtemperatures from -50° to 6500°F (-50° to 3500°C).

Whether you are in the business of manufacturing orprocessing metals, glass, plastics, ceramics, paper,textiles, chemicals, packaging, food or pharmaceutical,chances are IRCON has a solution to address yoursituation.

Global Service and Support Solutions

Beyond leading-edge products and expertise, you cancount on IRCON for a variety of valuable services andsupport options, including:

- Product warranty programs

- Fixed repair cost programs

- On-site repair and preventative maintenance

- On-site technical consulting and troubleshooting

- Operator training

- Sensor re-calibration and certification service

Through our network of nearly 150 distributors aroundthe globe, and service centers in North America,Europe, and Asia -- no matter where you are, IRCONspecialists are near you to assist.

Count on IRCON to Help You Find Solutions

Feel free to contact us for help in addressing yourtemperature monitoring challenges.

For additional information, please visit our web site,contact an IRCON specialist in your area, or submit arequest at http://www.ircon.com/tech_request

IRCON Inc is a Spectris company -- a leading globalsupplier of precision instrumentation and controls. For additional information, please visit http://www.spectris.com

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