Thermistors can be divided into two types based on the relationship between their resistance values and temperature changes: positive temperature coefficient and negative temperature coefficient. The so-called positive temperature coefficient refers to the decrease in the resistance value of a thermistor as the ambient temperature increases.

The nominal resistance value of a thermistor refers to the resistance value of the environment at 25 degree . Therefore, when measuring the resistance value of a thermistor, it is necessary to pay attention to the influence of environmental temperature on its resistance value. When the ambient temperature is 25 degree , the resistance value of the thermistor measured by the multimeter is its nominal resistance value. If the ambient temperature is not 25 degree , it is a normal phenomenon that the measured resistance value does not match the nominal resistance value of the thermistor.

Depending on the capacity of the electrolytic capacitor, the R value of the multimeter is usually selected × 10. R × 100, R × 1 K gear for testing and judgment. The red and black probes are connected to the positive and negative poles of the capacitor respectively (before each test, the capacitor needs to be discharged), and the quality of the capacitor is judged by the deviation of the meter needle. If the watch needle quickly swings to the right and then slowly returns to its original position to the left, a capacitor is generally good. If the watch needle does not rotate after swinging, it indicates that the capacitor has broken down. If the watch needle gradually returns to a certain position after swinging, it indicates that the capacitor has leaked electricity. If the watch needle cannot swing, it indicates that the electrolyte of the capacitor has dried up and lost its capacity.

It is difficult to accurately determine the quality of capacitors with leakage using the above methods. When the withstand voltage value of the capacitor is greater than the battery voltage value in the multimeter, according to the characteristics of the electrolytic capacitor, which has a small leakage current during forward charging and a large leakage current during reverse charging, R can be used × At 10K gear, charge the capacitor in reverse and observe whether the meter needle remains stable (i.e. whether the reverse leakage current is constant), in order to determine the quality of the capacitor with high accuracy. The black lead is connected to the negative pole of the capacitor, and the red lead is connected to the positive pole of the capacitor. The watch needle quickly swings up and then gradually retreats to a certain position without moving, indicating that the capacitor is good. If the watch needle is unstable at a certain position or gradually moves to the right after stopping, the capacitor has leaked electricity and cannot be used anymore. The watch needle generally stays and stabilizes within the scale range of 50-200 K.