1. Measure contact resistance
Use the resistance gear of the multimeter to measure the resistance of the normally closed contact and the moving point, and the resistance value should be 0; The resistance between the normally open contact and the moving point is infinite. It can be distinguished from normally closed contact and normally open contact.
2. Measure coil resistance
Use the R of the multimeter × 10 Ω can measure the resistance value of the relay coil to judge whether there is an open circuit in the coil.
3. Measure the pull in voltage and current
Find an adjustable regulated power supply and ammeter, input a group of voltages to the relay, and string the ammeter in the power circuit for monitoring. Slowly increase the power supply voltage. When you hear the pull-in sound of the relay, record the pull-in voltage and current. For accuracy, you can try several times to get the average value.
4. Measure the discharge voltage and current.
This is also the connection test described above. When the relay is pulled in, the power supply voltage gradually decreases. When the relay is released again, record the voltage and current at this time, and try several times to get the average release voltage and current. Under normal conditions, the release voltage of the relay is about 10~50% of the pull-in voltage. If the release voltage is too small (less than 1/10 of the pull-in voltage), it cannot be used normally, which will threaten the stability of the circuit.