Electrical Troubleshooting Quiz - March 7, 2017

An important production line has vibration monitoring sensors at various points. When vibration exceeds the preset limit, the monitoring system sends a text message to the area’s maintenance supervisor. Yet when he sends a technician out to investigate with a handheld vibration tester, nobody has ever found anything wrong.

The mechanical supervisor suggested performing alignment checks on all of the equipment and also using some angle iron to reinforce the motor pedestals. All this work was done, but the problem persists. His department went through the couplings, gearboxes, and other mechanical points of failure and now he insists the problem must be electrical. He recently gave you an article on harmonics, suggesting you look there.

It’s probably not harmonics. Visually inspect that wiring to ensure there’s no inductive coupling from, say, motor wiring. Look at the motor supply voltage history for anomalous dips or spikes.

But the intermittent nature of this problem points toward another type of cause entirely. Install time-stamped cameras at each point where product enters or exits the equipment or where a conveyor curves to change direction. Note the time of the next vibration alert, and view the camera footage for that time. Most likely, movement of the product itself is causing the vibration. A mechanical alteration or a time-delay in the monitor should end the “ghost” alarms.