Analysis of Common Faults of Pressure Transmitters (Classified by Working Conditions with Examples)

What common faults will occur during the operation of pressure transmitter? This article sorts out practical operation problems combining typical phenomena, causes and actual cases based on various on-site working conditions. It covers mainstream industrial medium application scenarios including chemical industry, power plants, water treatment, oil & gas and metallurgy. The content helps instrument maintenance staff conduct rapid transmitter troubleshooting and complete efficient equipment failure analysis, and also serves as professional popular science for industry practitioners.

General Common Faults

1. Zero drift & severe output fluctuation

Phenomenon: The output is not 4mA under zero pressure, or the reading jumps randomly during normal operation, resulting in obvious measurement deviation. Causes: Large temperature variation leading to sensor thermal drift; unstable power supply and electromagnetic interference; gas/liquid blockage in pressure guiding pipes. Case: The transmitter installed outdoors in winter suffers zero drift due to large temperature difference between day and night.

2. Inaccurate readings (higher/lower than standard)

Phenomenon: Large data gap compared with on-site pressure gauges and DCS display, typical measurement deviation. Causes: Leakage or blockage of pressure guiding pipes; deformation and damage of diaphragm. Case: Slight leakage of pressure guiding pipe on steam pipeline causes the measured value to stay 10%~20% lower for a long time.

3. No output & lost signal

Phenomenon: DCS displays fault signal or disconnection, and the output keeps below 3.9mA or 22mA. It is a typical case for equipment failure analysis. Causes: Power failure, loose wiring; damaged sensor or burnt circuit board; breakdown caused by lightning and surge. Case: Multiple transmitters lost output simultaneously as the instrument cabinet in the plant was not equipped with lightning protection on thunderstorm days.

Typical Faults Under Different On-site Working Conditions

1. Steam & high-temperature medium (Power plant, Heating, Chemical industry)

Faults: Condensate failure & diaphragm damage caused by high temperature Phenomenon: Unstable readings, measurement deviation, even permanent damage of the transmitter. Causes: Unfilled condensate tank and gas blockage; no condensate bend installed against high temperature; diaphragm impacted by water mixed in steam. Case: The main steam pressure transmitter of boiler was not fitted with condensate bend, the sensor was burnt by high temperature and the reading jumped sharply.

2. Viscous & particle-containing medium (Slurry, Sewage, Crude oil)

Faults: Pipe blockage & material adhesion & stuck measurement Phenomenon: Unchanged pressure value and slow response. Causes: Blocked pressure guiding holes by crystallized or viscous medium; solid particles deposited in front of diaphragm. Case: The transmitter on sludge pump outlet of sewage treatment plant gets blocked within one week without flushing, and the pressure reading remains unchanged.

3. Strong corrosive medium (Acid, Alkali, Brine, Chemical reactor)

Faults: Diaphragm corrosion, leakage & reading drift Phenomenon: Continuous zero drift, rusted shell and medium leakage. Causes: Mismatched diaphragm material; aging and corrosion of sealing parts. Case: The ordinary stainless steel transmitter used on dilute sulfuric acid tank was scrapped in one month as the diaphragm was perforated by corrosion.

4. Negative pressure & vacuum environment (Distillation, Drying, Refrigeration)

Faults: Air ingress & inaccurate measurement & data fluctuation Phenomenon: Failed to reach required negative pressure and violent reading jump. Causes: Slight air leakage of pressure guiding pipes and connectors; poor sealing performance of transmitter. Case: Aged seal of connectors on vacuum dryer transmitter leads to failure to reach the required vacuum degree.

5. High vibration environment (Pump outlet, Compressor, Fan)

Faults: Severe data jitter & loose connectors Phenomenon: Jagged curve on DCS and loose transmitter connectors. Causes: Mechanical resonance; no buffer bend or damper equipped. Case: The pressure curve of reciprocating pump outlet transmitter jitters severely without damper, which cannot be applied to automatic control.

6. Easy-crystallization & easy-solidification medium (Urea, Molten salt, Syrup)

Faults: Blocked pressure guiding pipes by crystallized medium Phenomenon: Slow measurement response and complete failure once heat tracing stops. Causes: Medium crystallizes at normal temperature without heat preservation and heat tracing device. Case: The pressure guiding pipes of transmitters in urea workshop were fully blocked by crystallized medium overnight due to heat tracing failure in winter.

7. High static pressure & high pressure environment (High-pressure reactor, Long-distance pipeline)

Faults: Overpressure damage & zero drift Phenomenon: Permanent zero offset and sunken diaphragm after overpressure. Causes: Pressure impact, water hammer and failed safety valve. Case: Sudden opening and closing of valves on high-pressure pipeline generates water hammer, leading to permanent deformation of transmitter diaphragm which needs factory repair.

8. Humid, outdoor & dusty harsh environment (Mining, Metallurgy, Outdoor pipeline network)

Faults: Water ingress, damp junction box & corroded circuit board Phenomenon: Intermittent signal loss, more frequent faults on rainy days. Causes: Aged sealing and unsealed cable inlet. Case: Rainwater entered the junction box of outdoor pipeline transmitter and caused intermittent signal loss.

9. Explosion-proof & flammable gas environment (Oil & gas, Chemical explosion-proof area)

Faults: Failed explosion-proof seal & potential safety hazards Phenomenon: Water ingress in explosion-proof cavity and damaged gaskets, failing to meet Ex explosion-proof standards. Case: Poor sealing of transmitter used in hydrogen environment brought safety risks, and it was required to be replaced compulsorily by safety supervision department.