How to measure the resistance of a thermistor with a multimeter
Using a multimeter to measure resistance is a very basic task for engineers, and it is also something new engineers need to have a solid grasp of. In today's multimeter test resistance knowledge sharing, we will share a basic knowledge of multimeter resistance measurement technology for new engineers, that is how to use a multimeter to test the quality of thermistor components. Let's take a look at it below.
Positive temperature coefficient thermistor detection
As with most methods for measuring the resistance of a multimeter, when using an analog multimeter to check the condition of a positive temperature coefficient thermistor, we need to adjust the multimeter to R×1. The specific operation steps can be divided into two steps. For room temperature detection (room temperature close to 25 °C), the two table pens are first contacted with the PTC thermistor to measure the actual resistance of the two pins, and compared with the nominal resistance, the difference between the two within the ± 2Ω is normal. If the actual resistance value differs significantly from the nominal resistance value, it indicates that the performance is poor or has been damaged.
Thermistor heating detection is performed on the basis of normal temperature testing. When the resistance of the thermistor is measured using the multimeter measuring resistance method described above, the second step test can be performed—heating detection. , Heat a heat source (such as electric iron) close to the PTC thermistor to heat it, and use a multimeter to monitor whether the resistance value increases with the increase of temperature. If yes, the thermistor is normal, if the resistance does not change, It shows that its performance is degraded and cannot be used continuously. In this case, care must be taken not to place the heat source close to the PTC thermistor or directly contact the thermistor to prevent it from being burnt.
Negative temperature coefficient thermistor detection
When using a multimeter to measure the resistance of the negative temperature coefficient thermistor to measure the degree of good or bad, the method is the same as measuring the ordinary fixed resistance, that is, according to the nominal resistance of the negative temperature coefficient thermistor to select the appropriate resistance, It can directly measure the actual value of Rt. However, because the NTC thermistor is very sensitive to temperature, there are several issues that need special attention when testing. First of all, ARt is measured by the manufacturer when the ambient temperature is 25°C. Therefore, when using a multimeter to measure Rt, the page should be performed when the ambient temperature approaches 25°C to ensure the reliability of the test. Second, the measured power must not exceed the specified value to avoid measurement errors due to current heating effects. Then, be careful not to hold the thermistor body by hand during the test to prevent the body temperature from affecting the test.
When measuring the temperature coefficient αt of a negative temperature coefficient thermistor using a multimeter resistance measurement technique, first measure the resistance value Rt1 at room temperature t1, and then use the electric iron as a heat source near the thermistor Rt to measure the resistance. The value RT2 is measured at the same time using a thermometer to measure the average temperature t2 of the thermistor RT surface. The result of this test is the most accurate.
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