Pyrometer

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A pyrometer is a temperature measuring device, which may consist of several different arrangements. It was invented by Pieter van Musschenbroek (1692-1761).

A simple type of pyrometer uses a thermocouple placed either in the furnace or on the item to be measured. The voltage output of the thermocouple is read from a digital or analog meter calibrated in degrees Celsius (C) or Fahrenheit (F). There are many different types of thermocouple available, and these can be used to measure temperatures from −200 °C to above 1500 °C.

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. These are typically used to measure temperatures of glowing hot metals in a steel mill or foundry. 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. Both measurements are made over the same wavelength interval.

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 were very dependent upon operator judgement in deciding when the filament had disappeared and often two people would not be able to agree on the temperature.

DFPs are now old technology which have been replaced by modern Portable Infrared instruments which typically use a silicon sensor to measure the incoming radiation and have optical viewfinders with the temperature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. Certain instruments are manufactured to work at specific wavelengths for measuring difficult targets such as plastics and other materials.