Optical Pyrometer working principle & Pyrometric cone – Engineers Advice

Optical Pyrometer

What is optical Pyrometer?

The optical pyrometer measures the temperature by comparing the brightness of radiant emissive ray from the heat source with an ideal source.
The general working principle of optical pyrometer and radiation pyrometer is almost the same. The only difference is, in the visible spectrum part of an optical pyrometer, a single wavelength or a group of very exquisite wavelength is used. In this case, a red filter is used to make the identification easily of color difference, which controls the visible radiation and makes only red radiation’s wavelength visualized. In the optical pyrometer, disappearing filament type pyrometer is used more in industry. This pyrometer consists of two major parts. One is a telescope and other is control box.
In the figure, a telescope is shown in which a red glass filter, and a lamp with a marked filament in front of the eyepiece on, which object lens focuses an image of the object which is going to be measured. There is a switch for separating electronic circuit and absorbing screen.
In the control box, the parts of temperature measurement are inserted. In the figure, a dry cell to light a lamp, a rheostat to fix filament current, an ideal cell and galvanometer to measure the filament current temperature with a potentiometer slideware is attached. Until the brightness of the object’s image becomes equal to the brightness of filament, the knob (R1) turned around and the filament is seen disappeared then figure. By turning the knob (P1), the degree of the galvanometer is made zero, and then the proper balance is found. With the scale attached to the potentiometer, the proper temperature can get. With the normal optical pyrometer, from 650° C to 1315° C temperature can be measured. In high temperature, the filament may damage and the light may intolerable for eyes, that’s why the high limit is determined. However, the temperature measurement of the pyrometer can be increased up to 5.535° C by using different types of absorbing screen.

What is Pyrometric cone?

Pyrometric cone

Segan cone (Pyrometric cone) is usually used as fusion pyrometer. Silica, lime, sodium oxide, potassium oxide, alumina etc are usually used to make small triangle shaped pyramid by mixing with different proportion. These elements are mixed in such a proportion. so that, every cone has become soft at a certain temperature. The range of being soft does not only depend on the elements, it also depends on the size of the particle of oxide and the time of holding cone for a specific temperature. The temperature at which the cone becomes bend, or weeps, that is to say, at which temperature the apex of the cone touches the ground is called softening temperature. Usually the Segar cone uses in ceramic industry. At the stage of 20°C temperature, Segar cone is made and with these, the temperature from 600°C to 2000° C can be measured.



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