How to use a multimeter to detect the quality of the thermistor
For the measurement of thermistor, the purpose is to measure its resistance and accuracy.
When performing the test, use the ohm setting of the multimeter. The operation is divided into two steps: first test at normal temperature, use alligator clips instead of test leads to clamp the two pins of the PTC thermistor respectively to measure the actual resistance value, and compare it with the nominal resistance value. , the difference between the two is within ±2Ω, which is considered normal. If the actual resistance value is too different from the nominal resistance value, it indicates poor performance or damage.
Secondly, heating detection, on the basis that the normal temperature test is normal, the second step of the test can be carried out: heating detection, put a heat source close to the thermistor to heat it, and observe the multi-function display. At this time, if the multi-function display Changes with the increase of temperature indicate that the resistance value is gradually changing. 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 continue. use.
1. Detection of positive temperature coefficient thermistor
Like most methods of measuring resistance with a multimeter, when using a pointer multimeter to detect the quality of the positive temperature coefficient thermistor, you need to adjust the multimeter to the R×1 gear. The operation steps are divided into two steps. When performing normal temperature detection, first touch the two test leads to the two pins of the PTC thermistor to measure the actual resistance value, and compare it with the nominal resistance value. If the difference between the two is within ±2Ω, it is considered normal. If the actual resistance value is too different from the nominal resistance value, it indicates poor performance or damage.
The heating test of the thermistor is carried out on the basis that the normal temperature test is normal. When the thermistor is detected to be normal using the method of measuring resistance with a multimeter introduced above, the second step of the test can be carried out: heating test , put a heat source close to the PTC thermistor to heat it, and use a multimeter to monitor whether its resistance value increases with the increase of temperature. If so, it means that the thermistor is normal. If the resistance value does not change, it means that its performance is not good. , can no longer be used. At this time, be careful not to bring the heat source too close to the PTC thermistor or directly contact the thermistor to prevent it from being burned.
2. Detection of negative temperature coefficient thermistor
When using multimeter resistance measurement technology to test the quality of the negative temperature coefficient thermistor, the method is the same as that of measuring ordinary fixed resistance, that is, selecting an appropriate electrical barrier based on the nominal resistance of the negative temperature coefficient thermistor. You can directly measure the actual value of Rt. However, because the NTC thermistor is very sensitive to temperature, special attention should be paid to several issues during testing:
(1) ARt is measured by the manufacturer when the ambient temperature is 25°C. Therefore, when measuring Rt with a multimeter, it should also be performed when the ambient temperature is close to 25°C to ensure the credibility of the test.
(2) The measurement power must not exceed the specified value to avoid measurement errors caused by current heating effects.
(3) Be careful not to pinch the thermistor body with your hands during the test to prevent human body temperature from affecting the test.
When using multimeter resistance measurement technology to estimate the temperature coefficient αt of a negative temperature coefficient thermistor, first measure the resistance value Rt1 at room temperature t1, and then use a soldering iron as a heat source close to the thermistor Rt to measure the resistance value. RT2, and use a thermometer to measure the average temperature t2 on the surface of the thermistor RT at this time and then calculate it, so that the test result is accurate.
