The word pyrometer is derived from the Greek words pyro, meaning fire and meter, which means to measure. Hence, by cumulative definition as by function, a pyrometer is a device to measure the surface temperature of an object. It is a gun shaped instrument that can detect temperature by non-contact methods. These could include irradiance, emissivity and infrared radiation. All pyrometers essentially follow the StefanBoltzmann law for temperature detection and calculation. They can typically measure temperatures in the range of 100 to 1999 F.
The first pyrometer was invented by a potter to measure the temperature of his kiln. Development of the Brightness Pyrometer and the Ratio Pyrometer then followed. Today the primary types of pyrometers in use are Optical Pyrometers, Resistance Pyrometers and Radiation Pyrometers.
An optical pyrometer is constructed with an optical system and a detector. Every heated object undergoes a change in colour and brightness and emits small amounts of radiation, about 0.4 to 0.7 microns. The optical pyrometer determines the temperature of the hot object by using colour matching. Another variation of the optical pyrometer is determining temperature of the filament by varying strength of current to match the colour of the detector filament with the one being measured. Optical pyrometers require
temperature calibration.
A resistance pyrometer (RTD) determines temperature by measuring the change in resistance of the heated materials electricity. This type of pyrometer is used when the object of temperature measurement cannot be used. These pyrometers require
RTD calibration every couple of years or whenever they may function improperly.
Radiation pyrometers use the concept of infrared radiation for temperature measurement. The pyrometer senses, records and compares the temperature of an object from the radiation it gives off. Heat-sensitive elements such as a thermocouple, a device that produces an electric current when part of it is heated, are used. The current generated in the thermocouple due to the heated object operates a dial that indicates temperature. Periodic
thermocouple calibration is required to maintain the accuracy of these pyrometers.
Different types of pyrometers are used for different temperatures and applications. The optical systems also vary accordingly. Pyrometers find applications in many industries but are primarily used for electrical testing. They help read the heat on power meters ensuring that the electrician or handler is safe from burns. This tool allows the person to avoid any contact whatsoever with the object being measured.
