How to Test a Relay?
1 Answers
Relay (English name: relay) is an electrical control device that causes a predetermined step change in the controlled quantity in the electrical output circuit when the change in the input quantity (excitation quantity) meets specified requirements. It establishes an interactive relationship between the control system (also known as the input circuit) and the controlled system (also known as the output circuit). Typically used in automated control circuits, it essentially functions as an "automatic switch" that uses a small current to control the operation of a larger current. Therefore, it plays roles in automatic regulation, safety protection, and circuit switching within a circuit. Test contact resistance. Use the resistance setting of a multimeter to measure the resistance between the normally closed contact and the moving contact, which should be 0, while the resistance between the normally open contact and the moving contact should be infinite. This helps distinguish between the normally closed and normally open contacts. Test coil resistance. Use the R×10Ω setting of the multimeter to measure the resistance of the relay coil to determine if there is an open circuit. Measure pull-in voltage and pull-in current. Use an adjustable regulated power supply and an ammeter to supply voltage to the relay while monitoring the current in series. Gradually increase the power supply voltage until the relay pulls in, then note the pull-in voltage and current. For accuracy, repeat the test several times and calculate the average. Measure release voltage and release current. Connect the test setup as described above. After the relay pulls in, gradually reduce the supply voltage until the relay releases again, then note the voltage and current. Repeat the test several times to obtain the average release voltage and current. Generally, the release voltage 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), the relay cannot be used normally, posing a threat to circuit stability and reliability.
