How to test a thermistor with a multimeter?
Thermistor in the current electrical appliances used more frequently, it is through the change in ambient temperature and resistance changes, thereby changing the working state of the circuit, is widely used in temperature sensors and control systems.
Thermistor according to its resistance value and the relationship between temperature change, can be divided into positive temperature coefficient and negative temperature coefficient of two kinds. Positive temperature coefficient means that the resistance value of thermistor decreases with the rise of ambient temperature.
The nominal resistance value of thermistor refers to the resistance value of the environment at 25℃, therefore, when measuring the resistance value of thermistor, it is necessary to pay attention to the influence of the ambient 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 phenomenon that the measured resistance value does not match the nominal resistance value of thermistor.
If you need to test whether the thermistor has a positive or negative temperature coefficient, you can add heat around the thermistor when testing the thermistor, such as using a soldering iron to get close to the thermistor, and then if the measured resistance value increases, it is a positive temperature coefficient thermistor. If the resistance value increases, the thermistor is a positive temperature coefficient thermistor, and if the resistance value increases, the thermistor is a negative temperature coefficient thermistor.
How to test the bridge stack with a multimeter?
The bridge stack is essentially a bridge rectifier circuit encapsulated in a plastic housing, which not only reduces the area of the printed circuit board occupied by the diode, but also simplifies the circuit. The shape of the bridge stack and the internal circuit shown in Figure 3-12. Generally in the bridge stack corresponding pins of the external surface are marked with AC voltage input and DC voltage output symbols.
For the bridge stack quality testing, from the bridge rectifier circuit structure can be seen, the use of four pins of the bridge stack can be four diodes in the bridge stack to detect the detection of the same method as the detection of ordinary diodes.
In addition, in the repair process if the bridge is found to be damaged, the multimeter can be used to detect whether it is an open-circuit or short-circuit failure, if it is an open-circuit failure, the internal damage to the diode on the corresponding pins of the external connection of a rectifier current and reverse voltage and the same rectifier diode of the bridge, so that the bridge can be made to work normally.
