How to judge the quality of various relays?

1 When the solenoid coil is applied to the rated voltage of bai, it can normally pull in du, and it can be restored normally after power failure. When the coil is not energized, the dao normally closed contact should be well connected, and the normally open contact should remain disconnected. After the coil is energized, the normally open contact should be connected well, and the normally closed contact should be ensured to be disconnected. Such a relay is good.

2 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. It can be distinguished which is a normally closed contact and which is a normally open contact. Use the R×1 block of a multimeter to measure the resistance value of the normally closed contact, which is normally 0; press the armature, and the resistance of the normally closed contact should be infinite at this time. If, when the armature is not pressed, a certain resistance value or infinity is measured for a certain group of normally closed contacts, it means that the group of contacts has been burned out or oxidized.

3 The resistance value of the electromagnetic relay coil is generally 25Ω～2kΩ. The electromagnetic relay coil with a low rated voltage has a lower resistance value, and the electromagnetic relay coil with a higher rated voltage has a higher resistance value. The resistance value of the relay coil can be measured with a multimeter R×10Ω block to determine whether the coil has an open circuit. If the measured resistance value is infinite, the coil has been broken and damaged; if the measured resistance value is much lower than the normal value, there is a short circuit fault inside the coil. If the coil has a partial short circuit, it is not easy to find with this method.