Pressure Transmitter Signal Fluctuating Randomly
I’m dealing with an intermittent issue on a pressure transmitter. The process pressure is stable, but the transmitter output randomly fluctuates for a few seconds before returning to normal. Sometimes the problem disappears for several hours. Calibration checks are okay, and diagnostics don’t show any device faults. The wiring and junction box look fine at first glance. Has anyone faced a similar problem? What hidden issues should I investigate before considering transmitter replacement?
Pressure Transmitter Signal Fluctuating Randomly
Generally, random pressure transmitter fluctuations under steady process circumstances suggest an intermittent instrument fault rather than a failed transmitter. Having established that calibration and diagnostics and basic wiring are OK, concentrate on latent problems that only manifest under certain operational conditions. Start by measuring the 4-20 mA loop with a calibrated milliamp meter and trending the DCS value at the same time. If they both change together, the problem is in the field; if not, check the input card, signal conditioning, or communication path.
Hidden Causes to Investigate
- Loose or damaged conductor at terminals, cable glands or junction boxes.
- Transient leakage due to moisture infiltration on change of humidity/temperature.
- Electrical noise from poor grounding or shield termination.
- Variable Frequency Drives (VFDs) or high voltage connections resulting in electromagnetic interference.
- Loop powered transmitter, affected by an intermittent power source fluctuation.
- Blocked impulse lines, air trapped or vibrations producing short duration pressure disturbances.
- Corroded terminals with high contact resistance under vibration.
- Intermittent signal quality issues caused by marginal analog input cards or isolators.
Practical Field Checks
During the fluctuation, compare the transmitter output with DCS trend using a portable pressure calibrator and loop monitor. Check cable insulation with a megohmmeter . Check grounding resistance . Tighten each termination . Check for vibration , leaks , or partial blockage in impulse tubing . Check previous trends for any fluctuations that correlate with adjacent machine startup, weather changes, or maintenance.
The transmitter should be the last thing to replace. In many facilities, intermittent signal instability is ultimately found to wiring, grounding, dampness, vibration, or electromagnetic interference, not a faulty pressure transmitter. Systematic troubleshooting prevents unnecessary replacements, lowers downtime and increases long-term measurement reliability.
