After the thermal resistance is used for a long time, it needs to be calibrated to see whether the relationship between its resistance value and temperature change is accurate. The instruments, meters and their wiring methods required for technical inspection are shown in Figure 9-28.
The technical test method and steps are as follows
(1) Put the thermal resistance in the thermostat to make it reach the temperature to be calibrated, then adjust the voltage divider so that the indication of the milliampere meter is about 4mA (not more than 6mA, otherwise the heat of the thermal resistance will affect the accuracy), and turn the switch To the horse end of the standard resistor, read the indication value V 0 of the potentiometer , and then immediately turn the switch to the charging end of the thermal resistance to be verified, and read the indication value V t of the potentiometer ,
(2) Obtain the follow-up value of the thermoelectric superchasing 
. The same point shall be measured several times and the average value shall be taken.
(3) Compare the average value of the thermal resistance calculated at each calibration point with the resistance value found in the graduation table based on the readings of the standard thermometer to see if it is out of tolerance. The civil value is qualified.
(4) Take a few more tests, if they are all qualified, then the calibration of the thermal resistance is completed.
