How does a pyrometer work?

Many times you have to measure a temperature  that is very difficult to reach (either because of very high temperatures, because the site is dangerous or because the object to be measured is moving). For these situations the correct thing is to use a pyrometer .

What is a pyrometer?

A pyrometer is a device to measure temperatures with great precision, without having to be in contact with it (it does so through a laser). They are very useful in applications where conventional sensors cannot be used.

These instruments, in addition to being very precise, have a very wide measurement range. They can measure temperatures from -50 ºC to 4000 ºC, therefore the applications are of all kinds.

Types of pyrometer

There are 3 types of pyrometers according to the way they capture temperature radiation.

  • Radiation Pyrometer: Through the radiation captured by the pyrometer, the calorific power is determined and then through a thermal sensor the temperature is determined. They are used to measure  temperatures from 550 ºC to 1600 ºC
  • Optical Pyrometer  : It captures the radiation through the human eye, and detects the variation of its bandwidth to calculate the temperature. They  are used to measure temperatures greater than 700 ºC .
  • Infrared Pyrometer : The operation is the same as the radiation pyrometer, only that it detects radiation with a wavelength between 0.4 and 0.7 microns, allowing the degree aspectr to be measured to be much greater (from -50 to 4000 ºC).

How does a pyrometer work?

Radiation pyrometers base their operation on Stefan Boltzmann’s law [1] , which states that the intensity of radiant energy emitted by the surface of a body increases proportionally to the fourth power of the absolute temperature of the body, that is, W =KT4 .

Therefore, the pyrometer collects the energy radiated by the body, stores it in a detector that will generate a signal proportional to the temperature. The following video is a complete sample of the operation of a pyrometer.

Characteristics  of a pyrometer

  • non-contact measurement
  • High accuracy
  • Wide spectrum of ºC to be measured
  • fast response speed
  • Low cost of use and maintenance.
  • Enormous versatility and possibility of uses due to remote work.

Applications of a pyrometer

  • To measure the temperature of glowing metals   in foundries.
  • Where atmospheric contamination does not allow a thermocouple to be used .
  • To measure the temperature of surfaces and not of the interior of the object.
  • To determine the temperature of objects that are in motion.
  • For temperatures that exceed the range of conventional thermometers.
  • To measure rapidly varying temperatures and a high speed of response is required.
  • Where to put a thermocouple is not recommended since due to the atmosphere its useful life is shortened.
  • Where the area to measure the temperature is difficult to access .

Differences between pyrometer and thermometer

  • While both measure temperature, the pyrometer measures non-contact .
  • The pyrometer has a greater measurement range than the thermometer.
  • The thermometer directly measures the temperature. The pyrometer measures temperature through radiation.
  • The pyrometer has a higher response speed (it is practically instantaneous).

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