- Optical Pyrometer Definition: An optical pyrometer is a device that measures the temperature of glowing objects by comparing their brightness to a reference light.
- Construction: It is a simple device with a lens, lamp, colored glass, eyepiece, battery, ammeter, and rheostat.
- Working Principle: It operates by matching the brightness of the lamp filament to the brightness of the hot object.
- Calibration: The temperature is determined by the ammeter reading when the filament and the hot object’s brightness match.
- Measurement Range: This pyrometer measures temperatures from 1400°C to 3500°C and is limited to glowing objects.
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 uses an illuminated reference. The brightness of the hot object is matched by adjusting the electric current to the reference.
When the reference light’s brightness matches the hot object as seen through the eyepiece, the electric current is measured to determine the temperature.
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 colored 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 by controlling the filament brightness of a lamp using a rheostat connected to a battery. Adjusting the current changes the filament’s brightness.
At a certain point, the lamp’s filament will blend with the hot object’s brightness as seen through the eyepiece. When this happens, the ammeter reading, which is calibrated in temperature, shows the hot object’s temperature.
Limitations of Optical Pyrometer
There are some limitations of this pyrometer. Such as:–
- This type of pyrometer can measure the temperature of only those objects which are emitting light that means glowing objects.
- The optical pyrometer has a range of measuring temperature of 1400oC to near about 3500oC.
