Written by Nicholas Kamuda
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Optical pyrometers are perhaps the most universally accepted alternative to infrared non-contact thermometers. The technology for the first pyrometers was developed over 100 years ago, and has been used in steel work and foundries consistently over the last century. Since the initial development of the optical pyrometer, other types of pyrometers have been developed, including the absorption-emission pyrometer.

The main principles for operating an optical pyrometer rely on the user's ability to match the apparent brightness of the object being measured with the brightness of a filament inside of the pyrometer. A glowing filament of a known temperature is projected via a series of mirrors into the user's field of view. By matching the color of the filament to the color of the object being measured, the user can find the temperature of the object to within one half of one percent of the object's temperature.

Comparing Pyrometers to IR Thermometers

Because the object being measured must be hot enough to glow, pyrometers are most commonly used for molten metal and other high-temperature industrial uses. The lowest temperature that many pyrometers can accurately measure is approximately 600 ° Centigrade, a temperature that corresponds to the upper range of many handheld infrared non-contact thermometers. However, simple pyrometers can often measure temperatures as high as 3,000° Centigrade, which is much hotter than many IR thermometers can measure.

Pyrometers have other strengths, as well. They can be focused to accurately measure temperatures of small objects from much further than infrared thermometers can accurately measure. Some models are also much smaller than IR thermometers, and can be worn conveniently on strap around the neck.

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