How to test the relay?

①Measure contact resistance: use the electrical barrier of a multimeter to measure the resistance of the normally closed contact and the moving point. The resistance value should be 0; and the resistance value 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.
②Measure the coil resistance: use a multimeter to measure the resistance of the relay coil in the R×10 gear to determine whether the coil is open.
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 the power supply loop for monitoring. Slowly increase the power supply voltage, and record the pull-in voltage and pull-in current when you hear the sound of the relay pull-in. For accuracy, you can try to average multiple times.
④Measure the release voltage and release current: also connect and test like the above. When the relay pulls in, gradually reduce the power supply voltage. When you hear the relay release sound again, write down the voltage and current at this time. You can also try Get the average release voltage and release current several times. Under normal circumstances, the release voltage of the relay is 10%~50% of the pull-in voltage. If the release voltage is smaller than 1/10 of the pull-in voltage, it cannot be used normally, which will threaten the stability of the circuit and make it work. Unreliable.