The working principle and construction of an Optical Pyrometer are quite simple. We have drawn an experimental model of this type of temperature sensors. It is a measuring instrument that measures temperature of a hot glowing object. The instrument has an illuminated reference, with which the brightness of that of the hot body is matched by controlling the input electric current of the reference. When the glow of the reference matches with the hot object through an eye piece, that electric current is measured to calibrate the temperature of the hot body.
Construction of Optical Pyrometer
It is quite simple. Consider it as a cylinder, which has a lens in one end and in the other end there is an eye piece. In between there is a lamp. In front of the eye piece there is a coloured glass (usually red), to make lights monochromatic. The lamp is connected to a battery source through an ammeter and a rheostat as shown in the figure.
The optical pyrometer works in a certain simple process. The process is, the brightness of the filament of the lamp, that we are using through a battery source can be controlled by the rheostat. Now by controlling the incoming current, the brightness of the filament is increased or decreased. Going through this process there will be a certain point, when the filament of the lamp will not be visible from the eye piece. That very moment the brightness of the filament matches with the brightness of the hot body as seen through the monochromatic glass. From the reading of the ammeter of that particular condition we can get the temperature of the hot body, as the ammeter is previously calibrated in temperature scale.
Limitations of Optical Pyrometer
There are some limitations of this pyrometer. Such as:--
(i) This type of pyrometer can measure the temperature of only those objects which are emitting light that means glowing objects.
(ii) The optical pyrometer has a range of measuring temperature of 1400°C to near about 3500°C