Find Hidden Loop Problems with Ground Leak Detection
If you find a loop where the transmitter is calibrated correctly but all the readings elsewhere in the loop have a fixed offset this is due to a Zero Shift. This zero shift is typically caused by some current in the loop bypassing the transmitter. This might be caused by ground faults, moisture or corrosion.
Turn on Ground Leak Detection and use the PIE 901 to power up the loop. Any current that isn’t controlled by the transmitter or other current control element will be indicated as leakage on the calibrator’s display.
Typical problem found with Loop Diagnostics
Here is a loop where a technician has just recalibrated the transmitter but the control room still sees a problem. The problem started just after a rainstorm.
Using a PIE 901 to power the loop the technician detects a leakage of 0.51 mA – the same offset seen in the control room. He walks the loop and opens a junction box releasing a stream of water. The loop is again in control. Clink on the link Video of Loop Diagnostics to see a video demonstration of Loop Diagnostics in action.