How to detect thermistor with multimeter?
Answer: Thermistor is frequently used in current electrical appliances. It changes the resistance through the change of environmental temperature, thus changing the working state of the circuit, and is widely used in temperature sensors and control systems.
Thermistors can be divided into positive temperature coefficient and negative temperature coefficient according to the relationship between their resistance value and temperature change. The so-called positive temperature coefficient means that the resistance value of thermistor decreases with the increase of ambient temperature.
The nominal resistance value of thermistor refers to the resistance value when the environment is 25℃. Therefore, when measuring the resistance value of thermistor, we need to pay attention to the influence of environmental temperature on its resistance value. When the ambient temperature is 25℃, the resistance value of thermistor measured by multimeter is its nominal resistance value. If the ambient temperature is not 25℃, it is normal that the measured resistance value does not match the nominal resistance value of thermistor.
If it is necessary to detect whether the thermistor is a positive temperature coefficient or a negative temperature coefficient, it can be heated around the thermistor when detecting the thermistor. For example, if an electric soldering iron is used near the thermistor, if the measured resistance value increases at this time, it is a positive temperature coefficient thermistor. On the other hand, it is negative temperature coefficient.
How to detect bridge pile with multimeter?
A: The bridge stack essentially encapsulates a bridge rectifier circuit in a plastic shell, which can not only reduce the area occupied by the diode on the printed circuit board, but also simplify the circuit. The shape and internal circuit of the bridge stack are shown in Figure 3-12. Generally, the symbols of AC voltage input and DC voltage output are marked on the outer surfaces of the corresponding pins of the bridge stack.
As for the quality inspection of the bridge stack, we can see from the circuit structure of the bridge rectifier circuit that four diodes in the bridge stack can be inspected by using the four pins of the bridge stack, and the inspection method is the same as that of ordinary diodes.
In addition, if the bridge stack is found damaged during the repair process, the multimeter can be used to detect whether it is an open circuit or a short circuit fault. If it is an open circuit fault, a rectifier diode with the same rectifier current and reverse withstand voltage as the bridge stack can be externally connected to the corresponding pin of the internally damaged diode, so that the bridge stack can work normally.
