Introduction to thermistors

　　Thermistors are divided into negative temperature coefficient (NTC) thermistors and positive temperature coefficient (PTC) thermistors.

　　Thermistors are a kind of sensitive elements, which can be divided into positive temperature coefficient thermistors (PTC) and negative temperature coefficient thermistors (NTC) according to different temperature coefficients. The typical characteristic of thermistors is that they are sensitive to temperature and show different resistance values at different temperatures. Positive temperature coefficient thermistors (PTC) have higher resistance values at higher temperatures, while negative temperature coefficient thermistors (NTC) have lower resistance values at higher temperatures. They both belong to semiconductor devices.

　　However, it should be noted that thermistors do not belong to semiconductor devices under tax item 85.41 in the import and export link.

　　First, test the resistance value in the indoor environment, and then test the product with your hand to see if the resistance value becomes smaller. If it changes, it indicates that it is normal, otherwise it is abnormal.

　　Note: Special instruments shall be used 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 leads of the thermistor with the two probes of the multimeter resistance gear, and then heat the thermistor (close to the thermistor) with a hot electric soldering iron (20W). For PTC thermistors, the resistance value should increase with the increase of temperature; For NTC thermistors, the resistance value should decrease with the increase of temperature. If the thermistor is heated and its resistance value does not change, the thermistor is damaged.

　　Testing the quality of thermistor with heating method

　　Measuring resistance with multimeter is a very basic work for engineers, and it is also something that new engineers need to master. In today's multi meter resistance measurement knowledge sharing, we will share a basic knowledge of multi meter resistance measurement technology for new engineers, that is, how to use a multimeter to test the quality of thermistor components. Now let's have a look.

　　Detection of positive temperature coefficient thermistor (PTC)

　　When testing, use multimeter R × First gear, which can be operated in two steps:

　　1. Normal temperature detection (indoor temperature is close to 25 ℃); Measure the actual resistance of two pins of PTC thermistor with two probes, and compare it with the nominal resistance. If the difference is within ± 2 Ω, it is normal. If the difference between the actual resistance value and the nominal resistance value is too large, it means that its performance is poor or damaged.

　　2. Heating detection; On the basis of normal normal temperature test, the second step of test - heating detection can be carried out. A heat source (such as electric soldering iron) is heated close to the PTC thermistor. At the same time, a multimeter is used to monitor whether its resistance value increases with the increase of temperature. If yes, it indicates that the thermistor is normal. If the resistance value does not change, it indicates that its performance has deteriorated and it cannot be used any more. Be careful not to make the heat source too close to the PTC thermistor or directly contact the thermistor to prevent it from being burned.

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