How to Test Microprocessor Relays

Microprocessors can control relays in certain circuit applications.

The term "microprocessor relay" doesn't define any particular type of electronic device. A microprocessor controls most of the functions of the central processing unit (CPU) of a computer to control unlimited commands. A relay accepts a specific command to operate electrical contacts to control another device. You can test a relay controlled by a microprocessor using a voltmeter. But you must know how to make the microprocessor signal the relay to operate and then test to see if the relay actually operates. You need advanced technical skills to do this while the equipment is turned on.

Things You'll Need

• Multimeter

Instructions

1. 

   Check microprocessor circuits with a multimeter.

   Look on your schematic diagram to find both the microprocessor and the relay. The relay must have at least four leads: two to the coil and two to contacts to open and close a connection. There should be one connection between the two components.

2. Shut off the equipment and remove the covers so that the connections on the relay are exposed. Turn the equipment back on. If you need specific instructions on tools and methods to remove covers, you should not be doing this.

3. Set your multimeter to read DC volts. Read the voltage at both sides of the relay contacts. If they're the same, the contacts are making a connection. If they're different, the contacts aren't making a connection. Note the readings for later comparison.

4. Read the voltage at the lead that goes from the microprocessor to the relay. Note the reading. Typical readings should be either 5 volts or ground (zero volts).

5. Operate the equipment so that the microprocessor signals the relay to operate. Read the voltage again. If it was zero, it should now be 5 volts, and vice versa. If it doesn't change, the microprocessor isn't signaling the relay to operate. If it does, proceed to the next step to check operation of the relay.

6. Check the voltage at the contacts again. The readings should be opposite of the contact readings previously obtained, indicating that the relay has operated and the contacts have changed from one position to the other. If not, the relay isn't operating when signaled.

Tips & Warnings

• Don't remove the covers if you're not a qualified technician with experience working on energized equipment.

• Be extremely careful touching your meter leads to tiny components on printed circuit boards. You could easily short a circuit and cause damage to the equipment.

References

• Belarus Network: Intel Microprocessor Hall of Fame Technical Specifications
• OpAmp Electronics: Electromechanical Relays