①Measure the contact resistance: Use the electrical barrier of the multimeter to measure the resistance of the normally closed contact and the moving point, and the resistance should be 0; while the resistance of the normally open contact and the moving point is infinite. From this, it can be distinguished which is a normally closed contact and which is a normally open contact.
②Measuring the coil resistance: You can measure the resistance of the relay coil with a multimeter R×10, so as to judge whether the coil has an open circuit phenomenon.

③Measure the pull-in voltage and pull-in current: use an adjustable regulated power supply and an ammeter to input a set of voltages to the relay, and connect an ammeter in series to the power supply loop for monitoring. Slowly increase the power supply voltage, and when you hear the sound of the relay pulling in, record the pull-in voltage and pull-in current. For accuracy, try averaging multiple times.
④Measure the release voltage and release current: It is also connected and tested as above. After the relay is pulled in, the power supply voltage is gradually reduced. When the relay is heard to release the sound again, write down the voltage and current at this time, and you can also try The average release voltage and release current were obtained for several times. Under normal circumstances, the release voltage of the relay is 10%~50% of the pull-in voltage. If the release voltage is larger (less than 1/10 of the pull-in voltage), it cannot be used normally, which will threaten the stability of the circuit and make the work Unreliable.