Key Performance Index of Blackbody in Infrared Thermal Imager

Key Performance Index of Blackbody in Infrared Thermal Imager

   JJG 856-2015 "Radiation Thermometer for Work" stipulates that the black body radiation source with the required brightness temperature calibration result is called the reference black body radiation source. With the development of infrared temperature measurement technology, the use of infrared thermal imaging cameras has become more and more widely used. It is the most commonly used and effective method to verify and calibrate it with a reference blackbody radiation source. According to JJF 1552-2015 "Calibration Specification for a 10-200℃ Blackbody Radiation Source for Radiation Temperature Measurement" and JJG (Military Industry) 162-2019 "Verification Regulation of Reference Blackbody Radiation Source for 50-1000% Radiation Temperature Measurement", multi-wavelength is effective When calibrating the reference blackbody radiation source with the overall traceability of the brightness temperature, the comparison method is generally used.

   The reference blackbody radiation source is calibrated by the method of multi-wavelength effective brightness temperature overall traceability. The calibration method is to set the standard blackbody radiation source and the calibrated reference blackbody radiation source at the calibration temperature points, and use the transmission radiation thermometer to measure the standard blackbody radiation separately The brightness temperature of the source and the calibrated reference black body radiation source can be calculated to obtain the brightness temperature of the calibrated reference black body radiation source.

Figure 1. Blackbody radiation source.

   The existing black body radiation source standard devices are mainly alcohol bath type standard black body radiation source (referred to as alcohol bath black body), sink bath type standard black body radiation source (referred to as sink black body), water heat pipe standard black body radiation source (referred to as water heat pipe black body), Naphthalene heat pipe standard black body radiation source (referred to as naphthalene heat pipe black body), potassium sodium alloy heat pipe standard black body radiation source (referred to as potassium sodium heat pipe black body), sodium heat pipe standard black body radiation source (referred to as sodium heat pipe black body) and supporting equipment such as radiation thermometer for transmission. The structural design of the heat pipe or constant temperature bath can achieve good uniformity of the temperature field, combined with the appropriate aspect ratio, sprayed with high emissivity material coating, obtain high and stable effective emissivity, and meet the requirements of the radiation temperature measurement system. Using it as a standard device, combined with a radiation thermometer for high-stability transmission of multiple wavelengths, using a comparison method, can achieve the traceability of the effective brightness temperature of multiple wavelengths.

   The key indicator that affects the performance of the standard blackbody radiation source is the effective emissivity. According to the shape of the blackbody radiation source cavity, the axial temperature distribution, the measured value of the spectral emissivity of the blackbody cavity surface material, and the effective emissivity according to the Monte-carlo method Calculation. A standard thermocouple temperature sensor is used to test the axial temperature field of the black body cavity. The steps are: put a standard S-type thermocouple in the standard hole of the standard black body radiation source and the black body cavity respectively. After the temperature stabilizes, record the temperature of the two standard couples. For temperature, move the standard thermocouple outward according to the distance. After the temperature stabilizes, record the temperature of the two standard couples, and calculate the temperature difference in the axial temperature field.