HOW TO TEST RELAY with digital multimeter
RELAY TESTING. There are may model of relay and some model has many terminals. The terminal of relay is divided into 2 section ; Section 1 is coil , for supplying voltage to control to operate as switch ON or OFF. The coil of relay has some resistance so good coil will show some resistance when testing with ohmmeter. Section 2 is output contacts which consists of NC type contacts ( Normally Close ) and NO type contacts ( Normally open ).
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| NC type contact ( Normally Close ) , Terminal 1 and 2 is connected |
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| NO type contact ( Normally open ) Terminal 1 and 2 is not connected |
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| Basic output contacts form consist of NC and NO contact. |
Step to check relay.
As you have learned from above there are to type of basic circuit of contacts , connected and open. So we will use continuity test function of digital multimer to test the contact ; connected contacts must be connected as it be and open contacts must be disconnected.
1. Switch off or unplug circuit that want to test. Make sure there is not any voltage supply to relay before testing.
2. Find circuit diagram that printed on relay then find where is the coil terminals.
3. Test coil terminals , find coil terminal of relay and connect test leads to it. On the sample terminal 13 and 14 is coil terminals of relay.
4. Turn rotary switch to resistance test function.
5. Good coil present some resistance value when measuring , but bad coil of relay display
" OL " ( open circuit )
6. Test NO and NC contacts of relay , check all set of contacts.
7. Set digital multimeter to continuity test function.
8. Connect test leads to the NC contact. The meter will beep if it is a good NC contact.
Bad NC contact , the meter does not beep.
9. Connect the test leads to the NO contact. The meter will not beep if it is a good NO contact. Bad NO contact , the meter will beep ( short).
10. Test every NO and NC contact set. If there is 1 contact is bad , the relay is not good.
then find the replacement.
Find circuit diagram of relay under test that printed on relay's body.
Test coil terminals no. 13 and 14.
Good coil must present some measured resistance value.
Good coil must present some measured resistance value.
Test NC contact this example is terminals No. 10 and No. 2.
Connect test leads to the NC contact. The meter will beep if it is a good NC contact.
Test NO contact this example is terminals No. 10 and No. 6.
Connect test leads to the NO contact. The meter will not beep if it is a good NO contact.
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