When temperature to be measured is high and physical contact with the heat body is impossible, radiation pyrometer are used. Radiation pyrometers are used under conditions where corrosive vapours or liquid would destroy thermocouples, resistance thermometer and Thermistor. These pyrometers also find applications where the temperatures are above the range of thermocouple. Basically, thermal radiations are electromagnetic radiation lies in the wavelength region from about 0.1 to 100 micrometer.
A typical Radiation pyrometer:
The energy radiated by the hot body whose temperature is measured is focused by the lens to the detector. The detector is a thermocouple or bolometer (bolometer is a thermal device that changes electrical resistance with temperature change). The detector output is given to a PMMC instrument, digital display or recorder.
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