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InfraredInfraredThermometersThermometers

Supervisor: Prof. H. Taghirad

Produced by: Mahya Shahbazi

K. N. Toosi University of Tech

Introduction Theory ConstructionClassificationApplicationConditioning CircuitsError in MeasurementSmart Pyrometers

What is Infrared?

• Wavelength range : 0.7-1000 micron• Wavelength range used in IR Thermometers :0.7-14

Infrared and vision in Animals!

• The ability of bats and dolphins to "see" with sonar

• specialized organs near vipers’ eyes to sense the infrared radiation

Why Infrared Thermometers?!

Measuring the temperature of hot & moving targets. Not to require contact with the target, then no interface with or damage the objectNot to remove heat or disturb the processthe only solution when the product is small, fragile or in a vacuum or controlled atmosphere

Stefan Boltzmann

4Tw σ=

• Wien Planck :When the detector is used in specific range

λελλ λ dCJd TC /51

2−−=

We can do the classification in two ways.

First Classification:

Narrow band thermometers Broadband thermometers Band-pass thermometers

Second Classification:

Ratio thermometersOptical pyrometersAcoustic Pyrometers (For gas temperatures) Imaging pyrometers

Narrow-Band Thermometers

Narrow band wavelengths (For example: Thermometers with silicon detector, wavelengths: 0.9 - 1.1 micro)Accuracy: 0.25 - 2%Using “Filter” to be narrow bandHigh Accuracy when choosing narrow-bands (For example the bandwidth of 8 – 14 suitable for avoiding the humidity interference or the bandwidth of about 3.6m to avoid the CO2 interference ) Coverage of narrow range of temperatures

Broad Band Thermometers

Wide Range of wavelengths: 0.3 – 20 micronTotal Radiation thermometer

Sensitive to smoke, vapor and other emissivity absorbing gases

Needing to have a clean optical system

Economical because of low price and wide range of measurement

Band Pass Thermometers

Broad band Thermometers with some changes in optical systems

Suitable for a special range of wavelengths (For example one with range of .02 – 5 m useful for glass industry )

Doing so weak when using in another range

Optical Pyrometers

Ration Thermometers

Acoustic Pyrometers

Imaging Pyrometers

Optical Pyrometers

Narrow band measurementvisible Wavelengths (Red & Yellow)Single color thermometer (Red and Yellow)

Optical Pyrometers

Narrow band measurementvisible Wavelengths (Red & Yellow)Single color thermometer (Red and Yellow)Disappearing Filament Thermometer

Optical Pyrometers

Narrow band measurementvisible Wavelengths (Red & Yellow)Single color thermometer (Red and Yellow)Disappearing Filament ThermometerAccuracy of 1 – 2%Rheostat-typeWedge-type

Ratio ThermometersTwo color Pyrometer

Ratio ThermometersTwo color PyrometerNot sensitive to changes in target's parameters, effect of vapor and other absorbing gases and somehow differential!Multi-wavelengths ThermometerHigh accuracy(0.5 – 2%) and repeatability

Acoustic PyrometersGas temperature measurementGas temperature and the sonic speedFlight time

MrRT

tdc ==

Imaging Pyrometers

A combination of “video & signal processing” and “Pyrometry”

Imaging Pyrometers

A combination of “video & signal processing” and “Pyrometry”2Dimentional picture with false color

humans’ eyes and similarities

Lens, retina, brain• Optical Systems• Detector• Recorder or Indicator

MirrorsIndependency between Reflectivity and wavelength in Industrial rangeCopper, silver and goldShould be protected against tarnish by a protective filmGenerally used in fixed focus optical instruments

LensesEasier to be used in varying focus optical instruments rather than mirrors

WindowSo effective on the band of wavelengths (For example Glass does not transmit well beyond 2.5 microns)

Thermal Detectors

Quantum (Photon) Detectors

Pyroelectric Detectors

Thermal Detectors

Changes in resistance and voltage by receiving radiation Thermopile: consists of multiple thermocouples in series Bolometer: resistance thermometers arranged for response to radiationbroadband detectorsrelatively slow and having time constants of a second or more.less sensitive than other types

Quantum Detectors

Are directly excited by photon in the infrared rangePhotoconductive: Exhibit increased conductivity with received radiation. Photovoltaic: Convert received radiation into electric current. Have a sensitivity 1000 to 100,000 times that of the thermal detectorResponse time about microsecond

Pyroelectric Detectors

Changing in surface charge in response to received radiation.

No need to reach thermal equilibrium when the target temperature changes despite two other types.

The detector change can be likened to a change in charge of a capacitor

AMPLIFING

AVERAGING

LINEARIZATION

SAMPLE AND HOLD

allowing bidirectional, serial communications between sensors on the manufacturing floor and computers in the control roomThe smaller sensor so easier installation in tight or awkward areas. No need to shut down the process when some setting is needed No need to buy a new unit and calibrate it or remove the sensor to upgrade the itEasily changing the sensor parameters from a remote P.C.Being able to active an alarm when it fails

•Errors due to background radiation

•Errors due to transmission losses

Field of view

Field of viewSensor positioning

Pathteff εεε ×= Targe

Fever measurement in human (ear thermometers )Electrical systems

Fever measurement in human (ear thermometers )Electrical systemsGlass mold temperature

Fever measurement in human (ear thermometers )Electrical systemsGlass mold temperatureFood Industry

Fever measurement in human (ear thermometers )Electrical systemsGlass mold temperatureFood IndustryBuilding science

Teif Pardazane Sepehr the only company producing IR thermometers

Typical datasheet