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General description: The following items are more general methods for measuring the radiation coefficient of the test chamber wall. They are applicable to test AT and test B. It is worth noting that for some materials and process measures, the radiation coefficient will vary greatly with temperature Therefore, the emissivity must be measured within a suitable temperature range.
Measurement of the emissivity value: measurement of the surface temperature of a test sample that performs radiative heat exchange with the surrounding box wall in a vacuum and whose heat dissipation is known, if a standard test with a known surface emissivity coefficient and size close to the sample to be tested Samples, this method can basically best reproduce the actual environmental conditions when simulating the environment in the test box. Therefore, the effective radiation coefficient of the wall of the box can be calculated according to the measurement data. For comparative measurement of surface radiation with known emissivity at the same temperature, in order to calibrate, a portion of the surface immediately adjacent to the emissivity measured surface shall be locally coated with a paint film with known emissivity, and the heat between the two selected areas The resistance should be as low as possible so that the two surfaces have the same temperature. First, measure the radiation temperature of the area with known emissivity by adjusting the emissivity scale to a known value, and then align the detection instrument with the one to be tested Surface, and adjust the emissivity scale until the reading of the same radiation temperature is obtained, at this time, the E value read by the emissivity scale It is an average value, which is higher than the true value. The instrument detects two types of radiation, reflection and emission. The former radiation varies with the distance between the surface and the detection instrument.
If more accurate measurements are required, a reference standard with known emissivity can be used and compared with the test strip taken from the wall of the test chamber. This method requires specialized equipment and must be performed by professionals.
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