What is Radiation Pyrometer?
The main base of the working process is connected with an ideal radiator named the black body. This black body radiates more energy than any other object at the same temperature. The radiation pyrometer is usually marked to indicate the black body or at the proper temperature. The temperature scale of the pyrometer is established on the Stefan Boltzmann Law.
According to the formula, the degree of released energy from any black body is proportional to the fourth power of absolute temperature.
Mathematically, E=KT4 There,
E= Black body dispersed energy rates, K= Proportional constant, T= Absolute temperature of the black body
The apparent temperature measured from, nonblack body material will always less than a proper temperature. Whose main reason the difference is of emissivity of substance. The ratio of the emissive rate of the radiant energy of the nonblack body’s substance and the emissive rate of the black body’s radiant energy at the same temperature is called emissivity.
That is to say, E= KTa4 or Ta = etT4
Here, Ta= Apparent absolute temperature measured by the pyrometer.
et= Total emissivity nonblack body.
Therefore, after knowing the total emissivity of substances it is possible to determine easily the temperature that was available in the black body environment by the pyrometer by reforming the marked temperature of substances.
The above figure shows the cover of a mirror type radiation-pyrometer. In this, through the window (A) a radiated ray falls on the mirror (B) from the radiation source and creates an image of the source by reflecting on the internal diaphragm (J). Then this image has been dropping on some thermocouple named thermopile (E) by the mirror (D). Identify the size of the image source whether it is able to cover the aperture or not by seeing the aperture (C) through the lens (H) and whether the pyrometer is placed properly or not for measuring the temperature. The increasing temperature of the thermocouple is almost proportional the radiant ray falls upon them, therefore EMF and T4 are proportional to it.
The receipt radiation from a hot object by radiation pyrometer is not only depended on temperature, rather it depends on following three matter-
a. External radiation falling on the object.
b. The emissivity of a hot object or hot body,
The advantages of radiation pyrometer:
a. The radiation pyrometer does not have to touch the hot body in case of temperature measurement. It can measure a minimum of 538° C and any rate of temperature above it, there is no definite limitation of temperature. The bit does not spoil easily.
b. Through it, there is a possibility of reserving records.
c. It can measure the temperature of moving objects such as steel ballet.
The disadvantages of radiation pyrometer:
a. Enough black bodies may not found in the environment and to get actual temperature it may necessary to rectify emissivity.
b. Different parts of associated tools may absorb some radiation by weather, smoke, dust etc.
c. The power of reflection can be changed if there is dirt on the lens and mirror.
d. The power of reflection can be changed if the lens or mirror becomes extremely hot.