Testing control circuits

Problem: How can you test 12 and 24-V control circuits in discrete relay and PLC control panels?

Solution: A 24-V LED panel lamp assembly with a concentric Fresnel lens and 6-in. long color-coded leads serves as an accurate, inexpensive test probe by tinning the ends of the leads. You can detect ac and dc from 5-33 V and one-shot voltage pulses as short as 1/10 sec, and identify the dc connection. Most of my plant’s power supplies have current limit protection and the short circuit condition of 4-5 V is readily apparent. At 33 V the tester only loads the circuit under test by 25 milliamperes. I have modified a second lamp by soldering booted alligator clips to the leads for hands-free operation.

Contributor: Allen Sellers, Machine Maintenance Electrician, Lancaster, OH

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