Discussion on On-line Temperature Calibration of Infrared Thermometer
Temperature measuring instruments are industrial automation instruments that measure the degree of heat and cold of objects. According to the measurement methods, temperature measuring instruments can be divided into two categories: contact type and non-contact type. When measuring, the detection part is directly in contact with the measured medium. The contact temperature measuring instrument does not need to be in direct contact with the measured medium when the contact temperature measuring instrument is measuring, so it can measure the temperature of the moving object. When we conducted on-site calibration of online temperature measuring instruments in tobacco companies, we found that in the tobacco shred production line, the temperatures of the moistening leaves, feeding drums, and outlet materials of the shred dryers are all measured and controlled by online infrared thermometers, that is, non-contact temperature measurement. At present, non-contact infrared thermometers have developed rapidly in technology, and infrared temperature measurement technology has played an important role in product quality control and monitoring in the production process. The infrared thermometer uses the relationship between the size of the infrared radiation energy of the object and the distribution of the wavelength and its surface temperature, and measures the temperature by measuring the infrared radiation of the object itself to accurately determine its surface temperature.
Infrared thermometer is composed of optical system, photodetector, signal amplifier, signal processing, display output and other parts. The optical system gathers the target infrared radiation energy in its field of view. To be sure, infrared energy is focused on a photodetector and converted into a corresponding electrical signal. The signal passes through the amplifier and signal processing circuit, and is converted into the temperature value of the measured target after being corrected according to the algorithm in the instrument and the target emissivity, so as to realize further signal processing and control. Most tobacco factories use miniaturized infrared thermometers on the silk production line. It uses miniature probes and 24VDC DC power supply. It has multiple output modes, temperature display and parameter adjustment. It has strong on-site applicability and fast response time. Non-contact, easy installation and use, long life and so on. Therefore, infrared thermometers have been widely used in tobacco shred production lines.
Si la température mesurée par le en ligne infrarouge thermomètre est précise ou pas affectera directement la qualité interne du tabac déchiqueté tabac. In order to ensure the process quality of the shred tobacco, the online infrared thermometer must be calibrated. Since this kind of infrared thermometer beens be to online temperature measurement, it is inconvenient to disassemble and send it to the laboratory for routine calibration. At present, there is no verification and calibration method for online infrarouge thermometer in China. Fournaise, also called dry well furnace, is actually a high-accuracy temperature source, or heat source, radiation source. This portable heat source and radiation source can be easy apportght to the site, or in the laboratory, to provide a standard temperature to complete various temperature tests, experiments, calibrations, etc.
Here we use the black body target in the dry well furnace as the radiation source to calibrate the infrared thermometer online. In infrared temperature measurement, the emissivity of an object has an impact on the accuracy of radiation temperature measurement. The main factors affecting emissivity are material type, surface roughness, physical and chemical structure, and material thickness. The amount of radiation of all actual objects is not only dependent on the radiation wavelength and the temperature of the object, but also related to the type of material constituting the object, thermal process, surface state and environmental conditions. Emissivity indicates how close the thermal radiation of the actual object is to the black body radiation, and its value is between {{0}} and a value less than 1. When performing calibration, find out the emissivity value of the measured infrared thermometer and perform emissivity correction so that the standard is consistent with the emissivity of the calibrated infrared thermometer, otherwise the emissivity correction calculation must be performed during the calculation process, so that Get reliable calibration results and increase calibration reliability. The temperature range of the dry well furnace used is 0 degree , plus 250 degree , the stability of the blackbody target is 0.3 degree , and the emissivity is 0.95. Put the blackbody target into the drywell furnace, turn on the switch, and set it according to the process requirements For a good temperature point, place the blackbody target of the dry well furnace vertically under the micro-probe according to the target distance. After the temperature is stable, read the temperature of the dry well furnace and the infrared thermometer respectively, and calculate the error, so that the staff can use it in actual work Correction is carried out to ensure accurate measurement of online temperature.
