Investigation Of Thermal Radiation And Temperature Measurement By Optical Pyrometer

Investigation of thermal radiation and temperature measurement by optical pyrometer.

Objevtives: By using optical Pyrometer deduce temperature of heated object and deduce Stefan-Boltzmann constant.

Equipment: Pyrometer, heating lamp, voltmeter, ampermeter, power source.

Method and basic formulas: When bodies are heated to particular temperature they start to glow electromagnetic waves. Such emission of waves is called thermal. Thermal glowing can be described by its energy flow. The energy flow can be expressed by its emittance:

Experimental emittance correlation with frequency of different temnperatures T1 and T2 can be shown as:

All bodies more or less absorbs electromagnetic waves. The maximum absorption can reach 1 (total black body). Stefan and Boltzmann deduced the law which shows the relation of total black body integral emittance with temperature:

Heated body with temp. T in environment of tem. T0 then its emittance is:

If the body is heated with current I and at voltage U, than its emittance is:

Thus, it is possible to express Stefan-Boltzmann constant:

Now we need to measure electric circuit parameters I, U and temperatures of the body and environment.

1.Preparation of the Pyrometer device. The lamp wire is heated to 500 degrees and through red filter with ocular help we focus sharp view of glowing wire.

2.Turn on the lamp which temperature will be measured.

3.With ocular focus the image of the investigating lamp wire so that it would overlap with glowing red wire.

4.Carry on 4-5 measurements by changing I and U.

5.Data table, comparison and calculations.

6.Conclusions.

Counting Stefan-Boltzmann const.:

As it is possible to see the received constant is quite a lot smaller than theoretical one. It is possible to conclude that the deviation of the value could be affected due to wrong indications of temperature. It was difficult to compare the intesity of the wires seen through the ocular as the overlapping wire parts were unclean and the image was not with sharp edges.