How to measure the quality of the thermistor
October 10, 2021
Thermistors are divided into negative temperature coefficient (NTC) thermistors and positive temperature coefficient (PTC) thermistors.
Thermistor is a type of sensitive element, which is divided into positive temperature coefficient thermistor (PTC) and negative temperature coefficient thermistor (NTC) according to the temperature coefficient. The typical characteristic of thermistor is that it is sensitive to temperature and exhibits different resistance values at different temperatures. The positive temperature coefficient thermistor (PTC) has a higher resistance value when the temperature is higher, and the negative temperature coefficient thermistor (NTC) has a lower resistance value when the temperature is higher. They are both semiconductor devices.
But it should be noted that the thermistor does not belong to the semiconductor device under the tax heading 85.41 in the import and export link.
First test the resistance value in the indoor environment, and then hold the product to test to see if the resistance value becomes smaller. If the change indicates normal, otherwise it is abnormal.
Note: It is necessary to use special instruments for accurate measurement during testing.
The heating method can be used to detect the quality of the thermistor, as shown in Figure 1. Connect the two lead wires of the thermistor with the resistance gear of a multimeter, and then use a hot electric soldering iron (20W is fine) to heat the thermistor (close to the thermistor). For the PTC type thermistor, as the temperature increases, the resistance value should increase; for the NTC type thermistor, as the temperature increases, the resistance value should decrease. If the thermistor is heated, its resistance does not change, indicating that the thermistor has been damaged.
Figure 1 Use the heating method to detect the quality of the thermistor
Using a multimeter to measure resistance is a very basic job for engineers, and it is also something new engineers need to master. In today's knowledge sharing of multimeter resistance measurement, 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 the thermistor components. Let's take a look at it together.
Positive temperature coefficient thermistor (PTC) detection
When testing, use multimeter R×1 gear, the specific operation can be divided into two steps:
1. Normal temperature detection (the indoor temperature is close to 25℃); the actual resistance value of the two pins of the PTC thermistor is measured by touching the two test leads to the two pins of the PTC thermistor, and compared with the nominal resistance value. The difference between the two is within ±2Ω, which is normal . If the actual resistance value differs too much from the nominal resistance value, it means that its performance is poor or damaged.
2. Heating detection; on the basis of normal temperature test, the second step of testing—heating detection can be carried out. Place a heat source (such as an electric soldering iron) close to the PTC thermistor to heat it, and monitor its resistance value with a multimeter Whether it increases with the increase of temperature, if it is, it means that the thermistor is normal. If there is no change in the resistance value, it means that its performance has deteriorated and it cannot be used continuously. Be careful not to put the heat source too close to the PTC thermistor or directly touch the thermistor to prevent it from being burned.
Negative temperature coefficient thermistor (NTC) detection
1. Measuring the nominal resistance value Rt: The method of measuring NTC thermistor with a multimeter is the same as that of measuring ordinary fixed resistance, that is, according to the nominal resistance of the NTC thermistor, selecting the appropriate electrical barrier can directly measure the actual value of Rt value. But because NTC thermistor is very sensitive to temperature, the following points should be paid attention to when testing: ARt is measured by the manufacturer when the ambient temperature is 25℃, so when measuring Rt with a multimeter, the ambient temperature should also be close to 25 It is carried out at ℃ to ensure the credibility of the test. B. The measured power shall not exceed the specified value, so as to avoid the measurement error caused by the heating effect of the current. C pay attention to correct operation. During the test, do not pinch the thermistor body with your hands to prevent the body temperature from affecting the test.
2. Estimate the temperature coefficient αt: first measure the resistance value Rt1 at room temperature t1, then use an electric soldering iron as a heat source, approach the thermistor Rt, measure the resistance value RT2, and use a thermometer to measure the surface of the thermistor RT at this time The average temperature t2 is then calculated.