A pyrometer is a device used to measure high temperatures.
Various principles can be used.
the first apparatuses used the dilation of a metal stem; these apparatuses are cumbersome and difficult to implement.
the Thermocouple S consist of two metal wire of different nature, welded in two points; one of the weldings is maintained at a known temperature, the other is placed, according to the case, in contact with the object which one wants to measure the temperature, or in the enclosure carried at high temperature; according to the metal couple chosen, one can measure temperatures of -200 with 1500°C.
the sensors temperature (in English, RTD, Resistance Temperature Detectors ) consist of a wire of pure Métal whose resistance is a linear function of the Température; the materials usually used are the Platine and the Nickel because, in a pure state, they guarantee a linear function resistance-temperature; for example, a type of probe extremely used is Pt100, containing platinum, whose resistance is of 100 Ohms with 0°C.
to measure higher temperatures with 600°C (metallurgy, foundries, glassmakings…), one uses optical pyrometers , which measure the energy emitted in the infra-red.
The choice of a temperature gauge must be done according to the type of application, by taking account of the environmental conditions, the beaches of temperature and the desired measuring accuracy.
The thermometers with resistance can be of the type with two, three or four wire of connection. In connection with two wire, the measurement and the power supply of the probe are obtained using two drivers. The current circulating in these drivers causes small potential differences which distort measurement.
To avoid that, a connection with 4 wire is used: two drivers are used to make circulate a current in the probe whereas the two others, connected more close possible of the probe, are used for measurement of the potential difference; as they are traversed by no current, they do not introduce an error.
One finds also sometimes connections with 3 wire.
- a video explanatory on the optical pyrometer.
|Random links:||Policy of Ain | Pavel Rostovtsev | Saint Nicolas's Day (Flanders Eastern) | Denis Boileau | The Alps de Kitzbühel | John_Glashan|