Common Faults of Pressure Transmitters and Troubleshooting Measures

In industries such as petrochemical, power, and water treatment, pressure transmitters are core instruments for process control, responsible for real-time pressure monitoring and feedback. They convert medium pressure into standard 4-20mA or digital signals, interfacing with PLC or DCS systems for closed-loop control. However, complex environments like high temperature, corrosion, vibration, and electromagnetic interference increase the fault rate. Minor issues can lead to measurement deviation or control inaccuracy, while severe problems may cause safety incidents or production stoppage. Nexisense, a provider specializing in industrial sensors, summarizes common fault types, causes, and targeted solutions based on years of field service experience, helping engineers troubleshoot efficiently and reduce downtime.

Basic Structure and Vulnerable Components of Pressure Transmitters

A typical pressure transmitter consists of a pressure-sensing element (sensor diaphragm), amplification circuit, process connection, and housing. Core sensitive components include piezoresistive, diffused silicon, capacitive, or ceramic diaphragms, which are most susceptible to external factors. Common faults often arise from mechanical damage, electrical issues, medium contamination, or improper installation. Understanding the structure helps locate problems quickly: diaphragm deformation causes zero drift, circuit aging leads to signal anomalies, and impulse tube blockage results in reading deviation.

Fault 1: Zero Output or No Output

This is one of the most frequent field faults, manifesting as a reading of 0 or no signal.

Main causes:

• Power supply issues: power not connected, voltage insufficient (<10VDC), or reversed polarity.

• Line faults: loose wiring, broken wires, short circuits, or poor connections.

• No pressure on the process side: valves closed, impulse tube blocked, or no medium flow.

• Sensor damage: diaphragm rupture, internal filling fluid leakage, or PCB failure.

• Lightning or surge: instantaneous overvoltage damages circuits.

Solutions:

1. Confirm whether there is actual pressure in the field using a pressure gauge or manual pump.

2. Check power supply: measure terminal voltage, ensure stable 24VDC and correct polarity (do not reverse positive and negative in two-wire systems).

3. Open junction box and check cables segment by segment using a multimeter for continuity and insulation resistance (>100MΩ).

4. If power is normal but still no output, disconnect the process connection and inspect diaphragm for deformation or corrosion.

5. In extreme cases, replace the sensor core or the entire transmitter. Preventively, install surge protectors and ensure reliable grounding.

Fault 2: No Response or Abnormal Output When Pressurized

The output does not change under pressure, or jumps suddenly and does not return to zero after depressurizing.

Main causes:

• Pressure valve not open or blocked.

• Impulse tube has liquid accumulation, blockage, or leakage.

• Zero/range drift: long-term overload, temperature drift, or aging.

• Sensor protection jumper not removed or internal limit set.

• Irreversible diaphragm deformation due to overpressure shock.

Solutions:

1. Check valve status and ensure fully open; discharge valves should be closed.

2. Flush impulse tube to remove blockage; ensure proper slope for liquid medium (upward 1/12) to eliminate air bubbles.

3. Calibrate zero and range with a standard pressure source; if drift is severe, perform on-site fine-tuning or return to manufacturer for calibration.

4. Inspect diaphragm; if deformed, replace sensor head.

5. When selecting transmitters, reserve 1.5–2 times margin to prevent overload damage.

Fault 3: Unstable or Fluctuating Readings

Output signal fluctuates, display value jumps up and down, affecting control accuracy.

Main causes:

• Electromagnetic interference: power lines laid parallel to signal lines, no shielding near inverters.

• Impulse tube issues: leaks, liquid accumulation, or debris inside.

• Medium pulsation: pump outlet directly installed without buffer.

• Corroded/deformed isolation diaphragm or poor internal sensor contact.

• Large temperature fluctuations: no compensation or out-of-range environment.

Solutions:

1. Optimize wiring: separate signal and power lines with distance >30cm; use shielded twisted pair with reliable grounding.

2. Check impulse tube sealing and remove leaks; gas medium lines should slope downward for drainage.

3. Add buffer tank or pulsation dampener to smooth pressure fluctuations.

4. Clean or replace isolation diaphragm; ensure temperature within −30℃~+85℃ or select wide temperature compensation model.

5. Field test with oscilloscope to locate interference source.

Fault 4: Line and Interference Issues

Communication interruption, signal attenuation, or erroneous readings.

Main causes:

• Cable cross-section too small or transmission distance too long causing attenuation.

• Multiple signal lines in the same conduit causing crosstalk.

• Poor grounding or lightning damage to circuits.

Solutions:

1. Select appropriate wire gauge according to distance (use ≥1.5mm² for >100m).

2. Separate power and signal lines or use metal troughs for isolation.

3. Ensure single-point grounding; shield grounded at one end only.

4. Install signal isolators or optocouplers to suppress common-mode interference.

Fault 5: Impulse Tube Related Issues

Blockage, air leakage, or liquid accumulation are the three most typical problems.

Main causes:

• Medium is dirty or viscous and not discharged in time.

• Too many joints with poor sealing.

• Improper installation: high points in liquid lines, low points in gas lines.

Solutions:

1. Regularly flush or clean impulse tubes.

2. Use reliable sealing materials to reduce joints.

3. Optimize installation: liquid lines slope upward, gas lines slope downward; avoid intermediate high/low points.

4. For viscous media, use remote diaphragm or chemical seal transmitters.

Preventive Maintenance and Selection Recommendations

• Match selection to environment: add heat dissipation for high temperature, use ceramic/tantalum for corrosion, choose anti-vibration type for vibration.

• Regular inspection: quarterly calibration, seal checks, diaphragm cleaning.

• Record historical data: monitor drift trends, replace proactively.

• Nexisense products have built-in diagnostic features, supporting HART protocol remote monitoring to reduce field risks.

FAQ: Common Questions on Pressure Transmitter Faults

1. What to check first for zero output? Power voltage and polarity.

2. Could no response to pressure be a valve issue? Yes, confirm valve fully open.

3. How to quickly locate unstable readings? Isolate interference source, check shielding and grounding.

4. How to handle blocked impulse tube? Flush or replace; use filters preventively.

5. Can a deformed diaphragm be repaired? Usually replace the sensor head.

6. Can a transmitter survive lightning strike? Check PCB; if damaged, replace entire unit.

7. How to solve drift caused by temperature changes? Select compensated model or calibrate on-site.

8. What to do for long transmission distances causing signal loss? Increase cable size or add repeater/amplifier.

9. Frequent zero drift cause? Possible overload or vibration damage.

10. How to prevent common faults? Proper selection, correct installation, regular maintenance.

Conclusion

Although pressure transmitter faults are common, systematic troubleshooting and targeted measures can restore function quickly. Output anomalies often stem from power/lines, no response relates to process side, and unstable readings require attention to interference and installation. Prevention—proper selection, correct wiring, regular calibration—is key. Nexisense provides high-reliability products and technical support. For complex field faults, consult our engineering team to analyze root causes and develop long-term solutions. Early intervention ensures production continuity and significantly reduces maintenance costs.