A major process area in the plant has been experiencing phantom problems. Tanks that appear nearly empty on the control console suddenly show full. At random intervals, the “level” will go up and down for several seconds at a time. This lasts for several minutes, but then stops completely.
The instrument techs have calibrated the level control loop and every instrument on it multiple times. They have also verified there’s no ground loop. Now one of the senior operators insists that it’s “bad power” and the problem has been handed to the electrical group for resolution.
Where do you start?
The instrumentation operates on control loop power rather than three-phase, 480V; “bad power” is an unlikely cause. But use a power analyzer to look at the control loop power, if the instrument techs have not already done so.
The timing indicates correlation to an activity that occurs in short bursts, over a short period, then stops. This sounds like one side of a radio conversation. Radio interference would cause exactly this problem. The radio need not be a construction radio; it can be a cell phone. Phone detectors are commercially available; use one during the phantom activity to find the culprit.
