A failure of a system that uses multiple electromagnetic relays at the same time can be caused by a failure of just one of them. This situation can only be prevented by regularly checking them.
Instructions
Step 1
Regardless of the method of testing the relay, during its testing, be sure to connect a diode of type 1N4007 in reverse polarity in parallel to its winding. It is advisable to install the same diode in a circuit where it works constantly, unless, according to the algorithm of its operation, a voltage of different polarity is not supplied in turn to the winding. Remove the relay and install it in the device when the latter is de-energized.
Step 2
If it is necessary to test the relay in static mode, simply apply a voltage to its winding equal to the minimum operate voltage. When it is applied, all normally closed contacts must be guaranteed to open and all normally open contacts closed. When the voltage is removed from the winding, the situation should be reversed with respect to all contact groups. Use a conventional ohmmeter or even a battery and bulb probe to check the condition of the contacts.
Step 3
Test the relay in dynamic mode using a conventional multivibrator with two transistors. Connect it as a load of one of the transistors. Changing the ratings of the frequency-setting elements, make the relay response frequency close to the limit for it (it is indicated in the documentation). To check one or another contact group, apply voltage to it through a light bulb or a power resistor so that the current through it does not exceed the limit. Connect an oscilloscope in parallel to the group. Make sure from the image on its screen that there are no interruptions in the actuation of the contacts. Check in this way all the groups one by one. Do not keep the relay in this mode for too long, as it will wear out if it is quickly triggered.
Step 4
In case of failure of the relay, proceed with further actions depending on its type. If it allows for the adjustment of the contacts, do it, if not, replace the entire relay. In the event that only one contact group is malfunctioning, simply use another one instead, or move the relay to a node where it is not used.
