How to check the quality of the thermistor with a multimeter
For the measurement of thermistor, its purpose is to measure its resistance and accuracy.
When testing, use the ohm gear of the multimeter, and the specific operation is divided into two steps: first, check at room temperature, use the alligator clip instead of the test lead to clamp the two pins of the PTC thermistor to measure the actual resistance value, and compare it with the nominal resistance value , the difference between the two is normal within ±2Ω. If the actual resistance value differs too much 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 testing can be carried out: heating detection, put a heat source close to the thermistor to heat it, and observe the multi-purpose indication. If the temperature changes, it means 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 is degraded 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 whether a positive temperature coefficient thermistor is good or bad, it is necessary to adjust the multimeter to the R×1 gear, and the operation steps are divided into two steps. When testing at room temperature, first touch the two test leads to the two pins of the PTC thermistor to measure its actual resistance, and compare it with the nominal resistance. If the difference between the two is within ±2Ω, it is normal. If the actual resistance value differs too much from the nominal resistance value, it indicates that its performance is poor or damaged.
The heating detection of the thermistor is carried out on the basis of the normal temperature test. When the thermistor is detected to be normal by using the method of measuring the resistance of the multimeter introduced above, the second step of the test can be carried out: heating detection , 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 it is, it means that the thermistor is normal. If the resistance value does not change, it means its performance is not good. , can no longer be used. At this time, be careful not to make the heat source too close to the PTC thermistor or directly contact the thermistor to prevent it from being scalded.
2. Detection of negative temperature coefficient thermistor
When using the multimeter resistance measurement technology to detect the quality of the negative temperature coefficient thermistor, the method is the same as the method of measuring ordinary fixed resistance, that is, to select the appropriate electrical resistance according to the nominal resistance of the negative temperature coefficient thermistor, The actual value of Rt can be directly measured. However, because NTC thermistors are 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, so when measuring Rt with a multimeter, it should also be carried out when the ambient temperature is close to 25°C to ensure the reliability of the test.
(2) The measured 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 the human body temperature from affecting the test.
When using the multimeter resistance measurement technology to estimate the temperature coefficient αt of the negative temperature coefficient thermistor, first measure the resistance value Rt1 at room temperature t1, and then use the electric soldering iron as a heat source, close to the thermistor Rt, and measure the resistance value RT2, at the same time, use a thermometer to measure the average temperature t2 of the thermistor RT surface at this time and then calculate, so that the test results are accurate.
A few points for attention when testing thermistors:
1. Rt is measured by the manufacturer when the ambient temperature is 25°C. When measuring Rt with a multimeter, it must be performed at an ambient temperature close to 25°C to ensure the reliability of the test.
2. The measured power cannot exceed the specified value, so as to avoid the measurement error caused by the thermal effect of the current.
3. Pay attention to correct operation. During the test, do not pinch the thermistor body with your hands to prevent the human body temperature from affecting the test.
4. Be careful not to make the heat source too close to the PTC thermistor or to touch the thermistor to prevent scalding.
