The T73 relay is an automatic control device whose output changes abruptly when the input (electrical, magnetic, acoustic, optical, or thermal) reaches a certain value. So how do we test a relay? Let's take a look.
1. Measure the contact resistance
Using the resistance setting on a multimeter, measure the resistance of the normally closed contact and the moving contact. The resistance should be 0 (a more precise method can measure the contact resistance to within 100 milliohms); while the resistance of the normally open contact and the moving contact will be infinite. This allows you to distinguish which is the normally closed contact and which is the normally open contact.
2. Measure the coil resistance
The resistance of the 3FF relay coil can be measured using a multimeter set to the R×10Ω range to determine whether the coil has an open circuit.
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3. Measure the pull-in voltage and pull-in current.
Find an adjustable regulated power supply and an ammeter. Input a voltage to the relay and connect the ammeter in series in the power supply circuit for monitoring. Slowly increase the power supply voltage. When you hear the 12V relay click, record the pull-in voltage and pull-in current. For accuracy, you can try several times and calculate the average value.
4. Measure the release voltage and release current.
The connection test is conducted in the same manner as described above. After the relay engages, the supply voltage is gradually reduced. When the relay releases again, the voltage and current at that moment are recorded. This process can be repeated several times to obtain the average release voltage and current.
Under normal circumstances, the release voltage of a relay is about 10 to 50% of the pull-in voltage. If the release voltage is too low (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 operation unreliable.
