pyrometer

A type of thermometer for measuring high temperatures. In the optical pyrometer, the heat colour of the hot object is compared to that of a heated filament through which a controlled current is passed. When the colours match, the sample temperature is known via the previous calibration of the filament.

A pyrometer is a temperature measuring device, which may consist of several different arrangements.

The term can also be applied to the so-called optical pyrometer or radiation pyrometer, a class of non-contact instruments measuring temperatures above 600 °C. See also the infrared thermometer

One of the most common non-contact pyrometers is the absorption-emission pyrometer which is a thermometer for determining gas temperature from measurement of the radiation emitted by a calibrated reference source before and after this radiation has passed through and been partially absorbed by the gas.

To measure the temperature of incandescent metals, you look through the pyrometer at the glowing metal, and turn a knob or ring which adjusts the temperature of a glowing filament projected into your field of view. When the color of the filament matches the color of the metal, you can read the temperature from a scale on the filament color adjusting knob/ring.

The more common name for this type of instrument ia a Disappearing Filament Pyrometer (DFP).

DFPs are now old technology which have been replaced by modern Portable Infrared instruments which typically use a silicon sensor to measure the incoming radiation and have optical viewfinders with the temperature displayed in them.These instruments are state of the art with such features as emissivity correction, digital readout, data logging, etc.