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Pyrometers are used for the measurement of very hot surface just by observing its radiation.

The equipment’s required in an optical pyrometer are: –

1. Filter
2. Absorption screen
3. Lens
4. Bulb
5. PMMC meter
6. Battery
7. Rheostat

These are basics elements required for the construction of pyrometer.

The filter, absorption screen and lens are enclosed in a structure which can sustain heavy temperature.

Operation: –

1. The heat source emits radiation of different wavelengths. This radiation is radiated through lens of pyrometer.
2. The incandescent bulb has filament in it which it is made to glow giving an electrical supply which is measured through a PMMC meter and a rheostat is provided for varying the electric current flowing through it.
3. The lens produces an image of the heat source radiation and the lamp is made ON. The light of Bulb and radiation of heat source are matched and compared with the color scale for various temperatures.
4. Every wavelength has a fixed color.
5. The radiation of energy is expressed as brightness or intensity.
6. When the filament brightness and the source radiation are equal, we are not able to see the outline of the filament.
7. If the filament glows brighter than the heated source, then the filament glow appears
   brighter than the background.
8. If the filament glows less bright than the heated source then the filament can be seen outlined.

The temperature of the bulb is restricted to a certain temperature, so the optical pyrometer measurement range has also limitations.

These optical pyrometers give accurate measurements of various temperatures if furnaces, molten metals etc.

Reference: –

• Image credits(instrumentstoday.com)
• Adapted from ELECTRONIC INSTRUMENTATION by H S KALSI