13 - Non-Contact Temp Measurement 2011

8/6/2019 13 - Non-Contact Temp Measurement 2011

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NonNon--Contact TemperatureContact TemperatureMeasurementMeasurement

Pyrometer systemsPyrometer systems Optical pyrometerOptical pyrometer

Radiation pyrometerRadiation pyrometer

Infrared ThermocoupleInfrared Thermocouple


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The PyrometerThe Pyrometer

One of the methods or heat transmission isOne of the methods or heat transmission iselectromagnetic radiationelectromagnetic radiation

A Pyrometer measures the electromagneticA Pyrometer measures the electromagnetic

radiation emitted by a body.radiation emitted by a body. A body will radiate heat if its temperature is higherA body will radiate heat if its temperature is higher

than the ambient temperature.than the ambient temperature.

The amount of radiation emitted is based on notThe amount of radiation emitted is based on not

just heat but on two things:just heat but on two things:1.1. The temperature of the bodyThe temperature of the body2.2. The body's ability to send radiation, or its emittanceThe body's ability to send radiation, or its emittance

A body will emit both visible and infrared radiationA body will emit both visible and infrared radiation


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The Optical PyrometerThe Optical Pyrometer

Also referred to as Narrowband pyrometers.Also referred to as Narrowband pyrometers.

Used in the visible light spectrum onlyUsed in the visible light spectrum only

Matches the colour of a lamp filament to the colourMatches the colour of a lamp filament to the colour

of the object to be measuredof the object to be measured By matching the colours, the temperature of theBy matching the colours, the temperature of the

body can be determined.body can be determined.

Requires human to view and set the filament colourRequires human to view and set the filament colour


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Optical Pyrometer OperationOptical Pyrometer Operation

While viewing theWhile viewing thefilament, current isfilament, current isadjusted until theadjusted until thefilament matches thefilament matches thetarget colourtarget colour

Temperature is thenTemperature is thenread from theread from thecalibrated rheostat.calibrated rheostat.


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Radiation PyrometerRadiation Pyrometer

Also known as broadband pyrometerAlso known as broadband pyrometer

Responds to both the visible light andResponds to both the visible light and

the infrared radiation spectrumthe infrared radiation spectrum Based on a relationship betweenBased on a relationship between

radiation emission and temperatureradiation emission and temperature


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Lens Collector PyrometerLens Collector Pyrometer


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Mirror Collector PyrometerMirror Collector Pyrometer


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Handheld IR PyrometerHandheld IR Pyrometer

A couple of examples from OmegaA couple of examples from Omega


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Radiation Pyrometers useRadiation Pyrometers use

ThermopilesThermopiles A thermopile is a densely packed groupA thermopile is a densely packed group

of thermocouples that are connected inof thermocouples that are connected in

seriesseries The radiation from the heat source isThe radiation from the heat source is

concentrated by a lens or concaveconcentrated by a lens or concave

mirror onto the thermopile whichmirror onto the thermopile which

produces a voltage output based on theproduces a voltage output based on theradiation.radiation.


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Thermopile examplesThermopile examples

Thermopile

Receiving

Element

Output

Leads

Hot

Junctions

ColdJunctions


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EmissivityEmissivity

The radiant energy emitted by a body dependsThe radiant energy emitted by a body dependson other things besides heaton other things besides heat

Factors that effect a bodys emissivity include:Factors that effect a bodys emissivity include:

Surface roughness, MaterialSurface roughness, Material

Shape, colourShape, colour

Emissivity is defined as the ratio of the energyEmissivity is defined as the ratio of the energy

radiated by an object at a given temperature toradiated by an object at a given temperature to

the energy emitted by a perfect radiator, orthe energy emitted by a perfect radiator, orblackbody, at the same temperature.blackbody, at the same temperature.

The emissivity of a blackbody is 1.0. All valuesThe emissivity of a blackbody is 1.0. All valuesof emissivity fall between 0.0 and 1.0.of emissivity fall between 0.0 and 1.0.


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EmissivityEmissivity

When the emissivity of a body is known aWhen the emissivity of a body is known acompensation can be applied to thecompensation can be applied to the

pyrometer to receive a more accuratepyrometer to receive a more accurate

temperature readingtemperature reading

Emissivity is low for a good reflector, andEmissivity is low for a good reflector, andhigh for a poor reflector.high for a poor reflector.

Polished silver has an emissivity of .02Polished silver has an emissivity of .02

Dark asphalt has an emissivity of .95Dark asphalt has an emissivity of .95


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Blackbody CalibratorBlackbody Calibrator

Used to calibrateUsed to calibrateIR ThermocouplesIR Thermocouplesand handand hand--held IRheld IRpyrometers.pyrometers.

The target surfaceThe target surfacehas an emissivityhas an emissivityof near 1.0of near 1.0

Heated to aHeated to aspecific indicatedspecific indicated

temperature.temperature.

Use twoUse twotemperature pointstemperature pointsto calibrate and IRto calibrate and IR

pyrometer.pyrometer.


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Infrared Thermocouple or IRt/cInfrared Thermocouple or IRt/c The IRt/c sensorsThe IRt/c sensors areare

unpowered, low cost, andunpowered, low cost, andcancan measure surfacemeasure surfacetemperatures oftemperatures of materialsmaterialswithout touching.without touching.

They canThey can be directlybe directlyinstalledinstalled instead ofinstead ofcconventionalonventionalthermocouplethermocoupless..

All IRt/cs have aAll IRt/cs have aspecialized Optical &specialized Optical &Thermopile system whichThermopile system which

receives thereceives the heat energyheat energyradiated from objects theradiated from objects thesensor is aimed at, andsensor is aimed at, andconverts theconverts the heatheat ininto anto anelectrical millivolt signal.electrical millivolt signal.


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Infrared Thermocouple LinearityInfrared Thermocouple Linearity

IRt/c act like their standard thermocouple counterparts but have aIRt/c act like their standard thermocouple counterparts but have areasonable linearity over a very limited temperature range.reasonable linearity over a very limited temperature range.

They are therefore specified by their T/C type but in addition by theThey are therefore specified by their T/C type but in addition by the

desired temperature range..desired temperature range..


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Omega IR t/c Selection Example:Omega IR t/c Selection Example:

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13 - Non-Contact Temp Measurement 2011