Common Fault Analysis of Industrial Pressure Sensors

In modern industrial automation control systems, industrial pressure sensors are used in process sections that require pressure monitoring. They collect signals or serve as feedback signals to monitor and regulate process flows, enabling safe and orderly management and control.

Due to variations in process media characteristics and application conditions, it’s important to analyze the causes of pressure sensor failures by combining an understanding of their measurement principles with actual field usage. 

Types of Industrial Pressure Sensors:

Piezoresistive Pressure Transmitter

This type uses semiconductor pressure-sensitive materials. When pressure is applied, the resistivity of the material changes due to the piezoresistive effect, causing a voltage signal proportional to the pressure to be generated in a Wheatstone bridge circuit. This voltage signal reflects the change in pressure.

Capacitive Pressure Transmitter

This type uses a measuring diaphragm and electrodes placed on both sides of insulating plates to form capacitors. The measured medium applies two different pressures through the high- and low-pressure chambers, acting on the isolation diaphragms on either side of the sensing element. The diaphragm deforms depending on the pressure difference, causing changes in capacitance. These changes are converted into signals readable by a controller through oscillation and demodulation circuits.

Inductive Pressure Transmitter

Typically composed of a pointer-type pressure gauge and an electronic remote transmission unit. When pressure causes the Bourdon tube in the gauge to deform, the iron core inside an inductive coil also shifts position, changing the inductance. This inductance change is then converted into a DC current or voltage signal.

Strain Gauge Pressure Transmitter

This type also measures pressure by converting it into a change in resistance. Two strain gauges are glued axially and radially to a strain cylinder using a special adhesive. When the cylinder is compressed, the strain gauges deform, altering their resistance. Unlike the piezoresistive type, the strain gauge method involves a physical change in the shape of the strain material.

Industrial Pressure Sensor Failures

• Abnormal Pressure Readings

Abnormal pressure readings are one of the most common faults in industrial pressure sensors. In addition to typical issues such as zero drift and range shift, other potential causes include component failure, sensor malfunction, wiring issues, electromagnetic interference, and problems with the pressure or capillary tubing. Each of these factors should be systematically inspected and ruled out during troubleshooting.

• Component Damage

It’s important to consider whether the fault was caused by lightning strikes, overvoltage, incorrect wiring, or cable damage resulting in short circuits or open circuits. If inspection confirms that any electronic components are burnt out or physically damaged, they must be replaced promptly. It’s also critical to check whether the instrument’s grounding system is functioning correctly and carry out any necessary repairs or maintenance.

Special attention should be paid to possible water ingress, which can cause corrosion of internal electronic components. This often results from poor sealing at the cable entry point or aging of the transmitter’s sealing ring. In such cases, damaged components should be replaced, and proper sealing and routine inspection of the transmitter should be ensured.

• Sensor failure

The diaphragm of the diaphragm pressure transmitter will condense on the diaphragm due to the crystallization of the medium, or the medium contains blocky solids that impact the diaphragm for a long time, causing the diaphragm to deform and damage, affecting the measurement.

• Line failure 

Line failure is generally internal wiring, which can be checked by measuring resistance and voltage with a multimeter. Perform wiring operations according to the pressure transmitter manual to ensure the correct connection of the line.

•  Electromagnetic interference

This type of failure is generally difficult to troubleshoot, but it occurs very frequently. Avoid running the signal cable of the instrument in parallel with the electrical high-voltage signal cable, otherwise it is easy to cause signal interference, resulting in communication errors, inaccurate measurement values, and other problems. The pressure transmitter should also be installed away from locations with strong magnetic/electric fields or strong vibration sources.

• Pressure pipe and capillary problems

Pressure pipe problems usually occur due to the characteristics of the medium, non-clean medium, or medium with high viscosity, which causes the pressure pipe to be blocked and cannot feedback the accurate pressure value. Or the pressure pipe leaks due to long-term use, resulting in inaccurate measurement. In this case, the pressure pipe should be replaced in time and regular cleaning and maintenance should be done. Capillary problems may occur due to inaccurate selection of pressure oil temperature resistance. In low temperature conditions, it is necessary to select appropriate pressure oil to avoid the phenomenon of pressure oil solidification due to low temperature. Similarly, it is necessary to pay attention to the high temperature and avoid the pressure oil vaporization.

Abnormal display screen of industrial pressure sensor

1.  The instrument cannot display. First, it is necessary to check whether the voltage at both ends of the instrument is normal. If the voltage is abnormal, it is necessary to check whether the signal circuit is virtual or disconnected;

2. The instrument display is abnormal. After correct wiring, adjust the pressure within the range of the industrial pressure sensor and observe the changes in the pressure display value to determine whether the display screen is faulty.

If the flow signal output is abnormal, it is necessary to use professional measuring instruments to perform the following inspections:

• Check whether the input and output lines of the transmitter are short-circuited, whether the cable is damaged, and whether the component wiring is wrong or reversed;

• Measure whether the power supply voltage of the transmitter meets 24 V, and simultaneously check the signal line problem, whether there is interference or voltage attenuation due to long distance. If there is attenuation, consider replacing the thick wire cable to solve it;

• It is necessary to confirm whether the range of the instrument and the actual measured value are consistent with the parameters of the acquisition device; whether the acquisition device is intact.

Through the above analysis, common fault problems of industrial pressure sensor can be effectively solved. Of course, the actual fault conditions are varied, and solving the problems also requires specific analysis based on the specific situation, identifying the problem, analyzing the cause and taking corresponding measures.