Common Causes and Troubleshooting Methods for Pressure Sensor Zero Drift and Signal Fluctuation

Pressure sensors are important measuring components in industrial automation systems and are widely used in hydraulic equipment, water supply systems, chemical pipelines, intelligent equipment, air compressors, and process control applications. In actual use, zero drift and signal fluctuation are relatively common faults: the former is characterized by the output value gradually deviating from the initial zero point under no-pressure conditions, while the latter is characterized by pressure readings suddenly rising, falling, or fluctuating frequently.

These two issues can affect the accuracy of PLC data acquisition, variable-frequency control, interlock alarms, and production data statistics. Especially in analog control loops such as 4mA-20mA and 0V-10V, minor errors may be amplified into significant pressure deviations after program conversion, potentially causing false equipment alarms, frequent start-stop cycles, or protective shutdowns.

Troubleshooting should not focus solely on the sensor itself. A comprehensive assessment should also consider the power supply, signal cables, installation location, medium condition, control system, and on-site electromagnetic environment. The following explanation covers fault characteristics, common causes, on-site procedures, and preventive measures.

I. First Distinguish Between Zero Drift and Signal Fluctuation

Zero Drift Is Usually a Gradual Change

Zero drift refers to the gradual deviation of the sensor output signal from its original calibrated value while the actual pressure remains unchanged, especially under pressure-release or no-load conditions. For example, for a pressure transmitter with a range of 0MPa-1.0MPa and an output of 4mA-20mA, the theoretical output under no pressure should be close to 4.00mA, but it may gradually become 4.08mA, 4.15mA, or even higher in the field.

This type of fault is generally progressive and may occur after the equipment has operated for several hours or days, or after temperature changes. If the drift value remains stable and persists after repowering and pressure release, priority should be given to checking the sensor pressure diaphragm, internal circuitry, long-term overload history, and zero calibration status.

It should be noted that certain high-precision measurement applications have stringent error requirements. For example, Class 0.25 products have a relatively small permissible error under full-scale conditions. When the selected measuring range is excessively large, even an output change of only 0.1%FS may cause the actual measured value in the low-pressure range to lose reference significance.

Signal Fluctuation Is Commonly Characterized by Sudden Variations

Signal fluctuation refers to discontinuous changes in sensor output over a short period. For example, a displayed pressure may instantaneously jump from 0.60MPa to 0.95MPa and then fall back, or the PLC analog value may fluctuate repeatedly around its normal value. The magnitude of fluctuation may be only a few bits or may reach more than 10% of the measuring range.

If the fluctuation is highly consistent with events such as motor startup, variable-frequency drive speed regulation, solenoid valve operation, or welding machine operation, electromagnetic interference, improper grounding, or power supply fluctuations should be considered first. If the fluctuation occurs only during pump startup, valve switching, or pipeline pulsation, it is necessary to further confirm whether actual pressure shocks are present.

For digital pressure sensors, communication status must also be observed. RS485 communication interruption, address conflicts, missing termination resistors, or inconsistent baud rate settings may all cause abnormal display on the host computer. In this case, distinguish between “acquired signal fluctuation” and “actual output fluctuation” to avoid directly determining that the product has failed.

II. Main Causes of Pressure Sensor Zero Drift

Overpressure Shock and Diaphragm Damage

Although pressure sensors have a certain overload capacity, long-term operation near the upper limit or exposure to instantaneous high-pressure shocks may still cause irreversible micro-deformation of the sensing element. For example, for a product with a rated range of 1.6MPa, if the on-site pressure frequently approaches 1.5MPa and the system experiences water hammer or hydraulic shock, the risk of zero offset increases significantly.

Hydraulic pump startup and shutdown, rapid valve closing, and high-speed directional valve switching may all generate instantaneous peaks far higher than the steady-state pressure. Ordinary pressure gauges may not display such peaks due to their slower response, but the sensor diaphragm may already have been subjected to impact. For systems with pronounced pulsation, it is recommended to reserve a safety margin of 1.5 to 2 times the measuring range.

During troubleshooting, first completely depressurize the system, then slowly apply pressure using a standard pressure source and record the output data at 0%, 25%, 50%, 75%, and 100% of the measuring range. If there is obvious hysteresis between the rising and falling processes, or if the zero point cannot be restored, professional calibration or sensor replacement is generally required.

Temperature Changes, Medium Effects, and Long-Term Aging

Changes in ambient temperature and medium temperature can cause thermal expansion and contraction of the sensing core, circuit components, and housing materials. Although industrial pressure transmitters generally have temperature compensation functions, temporary or cumulative zero drift may still occur under alternating high and low temperatures, large day-to-night temperature differences, or medium temperatures exceeding the rated range.

Corrosive media, viscous media, crystallizing media, and particle-containing fluids may also affect the pressure port and isolation diaphragm. Partial blockage of the pressure port can slow the sensor response; when medium residue or crystallization covers the diaphragm, the zero point may shift in either the positive or negative direction. Before cleaning, confirm whether the material and sealing structure allow contact with cleaning agents.

Changes in the parameters of electronic components after long-term service should not be overlooked. Sensors that have been in use for more than 24 months and perform critical control functions should be included in a periodic verification plan. For applications with strict metrological requirements, comparative calibration may be conducted every 6 or 12 months, with records retained for zero point and full scale.

Quick Zero Drift Inspection Items

First confirm that the pressure connection has been completely depressurized and that gauge pressure products are properly vented to the atmosphere; absolute pressure products cannot have their zero point assessed in the same manner as gauge pressure products. Then use a multimeter to measure the supply voltage. For a 24VDC system, it is recommended to confirm that the actual voltage is within the allowable range of the equipment and check whether the power supply ripple is abnormal.

Next, isolate the sensor from the on-site control loop and directly measure the output terminal. For 4mA-20mA products, an ammeter can be connected in series; for 0V-10V products, measure the output voltage. If the deviation remains after disconnecting from the PLC, the fault is more likely to originate from the sensor itself or the pressure connection rather than the acquisition module.

Finally, compare readings using a standard gauge or pressure calibrator. If the entire range output shifts in the same direction, zero adjustment may be considered. If the error is inconsistent at different pressure points, or if linearity deteriorates significantly, zero adjustment alone is not advisable; recalibration should be performed by qualified personnel.

III. Common On-Site Factors Causing Pressure Signal Fluctuation

Power Supply, Wiring, and Electromagnetic Interference

Unstable power supply is an important cause of abnormal analog signals. When multiple solenoid valves, relays, or contactors share the same 24VDC power supply, the voltage may drop momentarily when loads are energized, causing temporary distortion of the sensor output. Priority should be given to checking power supply capacity, common terminal connections, and the filtering condition of the DC power supply.

Signal cables routed too close and parallel to power cables can also easily pick up interference. Especially near variable-frequency drive output cables, high-power motor cables, and welding machine power cables, analog signal lines may experience spike noise. It is recommended to use shielded twisted-pair cables for sensor signals and route them separately from power cables; the shield layer should generally be grounded at one end to avoid ground loops.

Loose, oxidized, water-damaged, or poorly crimped wiring terminals can also cause intermittent fluctuations. During on-site inspection, gently pull the wires, check whether terminals are blackened or overheated, and focus on M12 circular connectors, cable joints, and common terminals inside the control cabinet. Poor contact should not be ruled out based solely on a normal appearance.

Actual Pressure Pulsation and Improper Installation

Some fluctuations are not electrical faults but are caused by unstable pressure itself. For example, plunger pumps, diaphragm pumps, air compressors, and high-speed hydraulic systems generate periodic pulsations. If the sensor is installed directly at the pump outlet or near a valve, it often detects transient pressure, and significant fluctuations in the displayed value are a normal physical phenomenon.

For such operating conditions, subject to confirmation that the process permits it, dampers, buffer tubes, throttling orifices, or pulsation absorption devices may be added, and the filtering time should be properly set in the controller. Filtering should not be increased blindly. For example, setting the sampling response excessively slow may stabilize readings but could delay overpressure alarms and equipment protection actions.

The installation location should also avoid areas with strong vibration. Long-term mechanical vibration can cause joint loosening, solder joint fatigue, or internal connection abnormalities. For equipment with significant vibration, flexible impulse tubing, vibration-damping brackets, or remote installation methods may be used. At the same time, ensure that the sensor is properly oriented to prevent installation torque from being directly transmitted to the housing.

IV. On-Site Troubleshooting Sequence and Preventive Recommendations

Troubleshoot in the Sequence of “Operating Conditions, Electrical System, Sensor, and System”

It is recommended to first confirm whether the process-side pressure is genuinely fluctuating by comparing it with a mechanical pressure gauge, standard digital pressure gauge, or calibrator. If both values change synchronously, first address issues related to the pump, valves, pipeline pulsation, or medium. If the standard gauge is stable while the sensor output is abnormal, proceed to inspect the electrical system and the product itself.

The second step is to inspect the power supply and wiring, with emphasis on measuring the actual supply voltage at the sensor terminals rather than only checking the power indicator in the control cabinet. For two-wire 4mA-20mA transmitters, also calculate whether the loop load is within the allowable range. When the supply voltage is too low or the load resistance is too high, the full-scale output may be limited and become abnormal.

The third step is to conduct an independent sensor test. Connect the product to a stable power supply and standard pressure source, and observe the zero point, full scale, linearity, and repeatability. If the offline test is stable but abnormalities occur online, continue checking the PLC analog module, signal isolator, terminal block, and program filtering parameters. If abnormalities persist offline, calibration, repair, or replacement should be arranged.

Reduce the Probability of Faults Through Selection and Maintenance

During product selection, clearly define the medium type, normal operating pressure, maximum pressure, temperature range, installation connection, output signal, and protection requirements. A larger measuring range is not always better: an excessively large range reduces resolution in the low-pressure section, while an excessively small range is more likely to experience overload. A reasonable margin can generally be reserved based on normal operating pressure and possible peak values.

For high-temperature, highly corrosive, high-viscosity, or easily crystallizing media, select matching diaphragm materials, sealing materials, and isolation structures. For sites with strong interference, give priority to industrial-grade pressure transmitters with strong anti-interference capability, together with standardized shielding, grounding, surge protection, and independent power supply measures.

Establishing equipment records is equally important. Record the sensor model, measuring range, installation date, calibration results, abnormal occurrence time, and corrective actions. When the zero offset exceeds the process allowable value, the output fluctuates frequently, or the product has been subjected to a noticeable overpressure shock, promptly contact qualified technical personnel for inspection. Xi'an Shenghongchuang Instruments & Meters Co., Ltd. can provide pressure sensor selection, fault analysis, calibration and maintenance, and non-standard customization support based on the on-site medium, pressure range, output method, and installation conditions.