Wuxi Slosson principle analysis of infrared thermometer emissivity
Emissivity, which is the ratio of the radiant energy of an actual object to that of a blackbody of the same temperature under identical conditions. By identical conditions we mean identical geometrical conditions (area of emitted radiation, size and direction of the steradian angle at which the radiant power is measured) and spectral conditions (spectral range at which the radiant flux is measured). Since emissivity is related to the measurement conditions, there are several emissivity definitions.
Hemispherical emissivity hemispherical emissivity is the radiant energy flux emitted per unit area of the radiant body to the hemispherical space (radiant output) and the same temperature of the blackbody radiant output of the ratio, which is divided into the full and spectral amount of two kinds.
Normal Emissivity
Normal emissivity is measured in the direction of the radiation surface normal to the small stereo angle of the emissivity, it is the normal direction of the radiant brightness and the same temperature of the blackbody radiant brightness ratio. Normal emissivity is important because infrared systems all detect radiant energy within a small stereo angle in the direction normal to the target surface.
For a blackbody, all emissivities are equal to 1, while for a real object, all emissivities have values less than 1. What we currently refer to as emissivities are average emissivities.
About emissivity correction:
The emissivity of different objects on the surface is different, in order to ensure the accuracy of temperature measurement, generally require emissivity correction. Since the pyrometer is calibrated to a blackbody, and the emissivity of any object surface is smaller than the blackbody emissivity.
The emissivity correction of the infrared thermometer is: according to the emissivity of different objects to adjust the amplifier amplification, so that with a certain temperature of the actual object's radiation in the system produces the same signal with the same temperature of the blackbody produced by the signal. For example, the emissivity of an object is 0.8, then you need to increase the amplifier amplification for the original 1/0.8 = 1.25 times can be. In the industrial field due to the measurement of the target material, shape and surface state is different, it is generally difficult to determine the target emissivity parameters. There are other factors caused by the measurement error will cause the measured value and the real value of the difference. The introduction of emissivity parameter adjustment can solve this problem without affecting the measurement linearity. Adjustments can be made on the basis of empirical or process temperatures in the following steps:
For example, the range of the pyrometer is 500-1400℃.
The real temperature is 1200 ℃, the measurement temperature is 1150 ℃.
At this time the emissivity parameter can be adjusted to:
(1150-500)÷(1200-500)=0.928≈0.93
After such an adjustment to make the measured value closer to the real value, you can also refer to the "material emissivity coefficient table" adjustment. However, the parameters in this table are not necessarily applicable to process needs. It must be made clear that the essence of the emissivity adjustment is introduced to correct for measurement errors.
