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What is an Optical Pyrometer?

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  • Written By: Mal Baxter
  • Edited By: Daniel Lindley
  • Last Modified Date: 02 November 2016
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An optical pyrometer is simply a thermometer wand, shaped like a gun or handheld scope, that remotely measures very high temperatures. This equipment reads high temperatures from 100 to 1,999°F (37.8 to 1,092.8°C). These devices are often used to protect technicians from taking readings close to dangerous equipment or processes. Pyrometers permit noncontact temperature measurements using various techniques, such as the heated expansion of a metal rod, or intensity of a thermo-electric current. The optical type can detect thermal radiation, which is heat emitted in the form of electromagnetic (EM) waves.

Thermal energy emits outside the range of visible light, in the infrared (IR) spectral band. The optical pyrometer is calibrated to filter wavelengths of the EM band to detect incandescence from heated objects. It contains an optical system that captures the light wavelengths and a detector that measures the intensity of the radiation and matches it to a temperature.

Based on a scientific principle that all black bodies emit similar color incandescence at a corresponding temperature, the optical pyrometer measures intensity via calibration that corresponds material emissivity to temperature and time intervals. Modern devices also calculate statistical error through measurement repetitions. These tools can read not only extremely hot elements such as production processes and furnaces, but also moving and difficult to reach equipment.

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Some handheld devices are not simple scopes, but have become increasingly capable of intelligent computations. An internal computer can allow the optical pyrometer to eliminate data error that can occur around industrial conditions. It may contribute data from multiple bands to increase its accuracy. The device can take into account factors like dust and smoke, islands of slag on molten metal, and other obstructions.

The computer may conduct statistical processing of the data. It may alert operators to problem signals or material obstructions, and it can even signal them when temperatures run outside a specified range. This permits greater sensitivity to potential problems before they occur, a vital safety measure when dealing with dangerously hot technology.

One disadvantage of some optical pyrometer designs is that they rely upon user judgments to compare color bands. Another is the need to have a direct line of sight to the target being measured. Found in numerous industries and technical services, innovative devices permit consistent readings of unstable or moving objects and molten fluids. They can detect differing surface and core temperatures. In plants with adverse conditions, these units operate through pollution, heat, and vibrations.

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