When testing, use the ohm gear of the multimeter (depending on the nominal resistance value to determine the gear, generally R1 gear), which can be operated in two steps: first, test at normal temperature (indoor temperature is close to 25 degree ), use alligator clips instead of test pens to clip them separately. Measure the actual resistance value of the two pins of the PTC thermistor, and compare it with the nominal resistance value. If the difference between the two is within ±2Ω, it is normal. If the actual resistance value is too different from the nominal resistance value, it means that its performance is poor or damaged. Secondly, heating test, on the basis of normal temperature test, the second step test - heating test can be carried out, a heat source (such as an electric soldering iron) is heated close to the thermistor, and the multi-function indicator is observed. It is seen that the multi-function indicator changes with the increase of temperature, which indicates that the resistance value is gradually changing (the NTC resistance value of the negative temperature coefficient thermistor will become smaller, and the PTC resistance value of the positive temperature coefficient thermistor will become larger) , When the resistance value changes to a certain value, the displayed data will gradually stabilize, indicating that the thermistor is normal. If the resistance value does not change, it indicates that its performance has deteriorated and cannot be used continuously.
The following points should be noted during the test: (1) Rt is measured by the manufacturer when the ambient temperature is 25 degree , so when measuring Rt with a multimeter, it should also be performed when the ambient temperature is close to 25 degree to ensure the testability. reliability. (2) The measurement power shall not exceed the specified value to avoid measurement errors caused by the thermal effect of the current. (3) Pay attention to correct operation. When testing, do not pinch the thermistor body with your hands to prevent human body temperature from affecting the test. (4) Be careful not to make the heat source and the PTC thermistor too close or directly contact the thermistor to prevent it from being scalded.
