Finding momentary drops

By Staff -- Plant Engineering, 9/1/1998

Problem: Momentary drops (or extremely short power outages) in control circuits are often intermittent in nature and a beast to locate with a volt-ohm meter or other visual techniques. These drops can cause strange or hazardous equipment operation, or just be an annoyance. Is there another way to locate the momentary drop?

Solution: Use a small, simple device with two pigtails and alligator clips on the ends. The other end of the pigtails terminate to a small "ice cube" style relay (120 Vac or whatever control circuit voltage is needed), which is mounted inside a plastic enclosure. The enclosure has a normally open pushbutton and a pilot light for a visual indicator.

After connecting to a point in the control circuit (usually behind/after the component to be tested), a depression on the pushbutton energizes the relay. A holding contact maintains the relay in the energized state after release of the button. Minor or short power interruptions caused by a defective limit switch, vibrating gate switch, or defective stopbutton usually show up as the relay drops out. It is typically sensitive and fast enough to pick up even extremely short power drops.

Continue moving within the circuit prior to or after whatever series elements are to be tested to locate the suspect component. The more frequent the anomaly, the quicker the problem is pinpointed.

Contributor: Larry J. Duzeski, Senior Electrical Engineer, Mirro Co., Manitowoc, WI