Table of Contents

Total Radiation Pyrometer – Diagram , Working , Advantages

Thermal radiation is an electromagnetic radiation emitted by a body as a result of its temperature. Thermal radiation is in the wavelength region from about 0.1-100 µm.

The total radiation emitted by a blackbody is given by , Eb = σ x T ^4

where

σ is the Stefan Boltzmann constant (5.669 x 10^-8 W/m^2 y,
Eb is the emissive power, and
T is the absolute temperature in K.

Construction :

The total radiation of pyrometer has one housing tube in which an adjustable eye piece is fixed at one end of the housing tube and the other end is free to receive radiations from the radiating object whose temperature is to be measured. A rack and pinion attachment is used to adjust the position of a concave mirror (Figure ). A thermocouple is also provided to receive the radiation and the thermocouple is
connected to the milli voltmeter to measure the temperature.

Working

Thermal radiations from the radiating object come inside the housing tube. These radiations fall on the concave mirror and they are reflected to the hot junction of the thermocouple. So, an e.m.f. will be produced in the thermocouple and it is measured by using a milli voltmeter. This change in e.m.f. will give the measure of temperature.

Application

It is used to measure the high temperature of 3500°C.

Advantages

It has high accuracy
There is no physical contact with the radiating object
The distance between radiating object and pyrometer is negligible

Disadvantages

1. It is not suitable for very low temperature measurement due to poor sensitivity.
2. Dust, smoke, gases in between radiating object and instrument will cause error.