PTC thermistor is a sensitive element, which is divided into positive temperature coefficient PTC thermistor and negative temperature coefficient thermistor (NTC) according to different temperature coefficients. The basic characteristic of the thermistor is that it is sensitive to temperature, showing different resistance values at different temperatures. Positive temperature coefficient (PTC), the higher the temperature, the greater the resistance value, and negative temperature coefficient (NTC), the higher the temperature, the lower the resistance value, both belong to semiconductor devices.
Detection of positive temperature coefficient PTC thermistor:
When testing, use a multimeter R & TImes; 1 block, which can be divided into two steps:
1. Normal temperature detection (the indoor temperature is close to 25 ° C); measure the actual resistance value by touching the two pins of the PTC thermistor with two test leads, and compare with the nominal resistance value, the difference between the two is within ± 2Ω is normal . If the actual resistance value is too different from the nominal resistance value, it indicates that its performance is poor or damaged.
2. Heating test; on the basis of normal room temperature test, you can perform the second step test-heating test, heat a heat source (such as an electric soldering iron) close to the PTC thermistor, and use a multimeter to monitor its resistance value Whether it increases with the increase of temperature. If so, clarify that the thermistor is normal. If there is no change in the resistance value, clarify that its performance has deteriorated and cannot continue to be used. Be careful not to put the heat source too close to the PTC thermistor or directly touch the thermistor to avoid scalding it.
Detection of negative temperature coefficient thermistor (NTC)
1. Measuring the nominal resistance value Rt: The method of measuring the NTC thermistor with a multimeter is the same as the method of measuring the general fixed resistance, that is, the practice of selecting the appropriate electrical barrier according to the nominal resistance of the NTC thermistor can directly measure Rt value. However, because NTC thermistors are sensitive to temperature, the following points should be noted during the test: ARt is measured by the manufacturer at an ambient temperature of 25 ° C, so when measuring Rt with a multimeter, the ambient temperature should also be close to 25 At ℃ to ensure the credibility of the test. B. The measurement power shall not exceed the specified value, so as to avoid the measurement error caused by the current thermal effect. C Pay attention to correct operation. During the test, do not pinch the PTC thermistor body with your hands to avoid the influence of body temperature on the test.
2. Estimated temperature coefficient αt: first measure the resistance value Rt1 at room temperature t1, then use an electric soldering iron as a heat source, close to the thermistor Rt, measure the resistance value RT2, and use a thermometer to measure the appearance of the thermistor RT at this time The average temperature t2 is calculated again.