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Fluctuant and Unstable Current Output in Pressure Sensor Failure

The pressure sensor current output fluctuation or instability is a failure often encountered in use. This article summarizes the maintenance experience for handling this fault, helping users quickly master the skills in pressure sensor fault repairing.
The pressure sensor output current fluctuation can be clearly seen on the DCS display curve. Therefore, when checking for a fault, we can switch the control system to manual mode to observe the fluctuation. If the measurement curve is still fluctuating frequently, it should be the cause of the process. If the fluctuation is reduced, it possibly be the pressure sensor fault or the PID parameter is improperly set. Sometimes adjusting the damping time of the pressure sensor appropriately can reduce the parameter fluctuation.
If the fluctuation is obvious, check the connection of the measurement circuit, that is, check whether the screws of the terminal block are loose, oxidized or corroded, resulting in poor contact. If you suspect the pressure sensor is fault, you can close the three-valve or sampling valve in the flow or pressure to maintain the pressure sensor within a fixed differential pressure or pressure. Then observe whether the output current of the sensor is stable. If the current is still unstable, the pressure sensor has faulty or interference.
What to do for unstable output in pressure sensor
The failure rate of measuring pipelines and accessories is much higher than that of pressure sensors. When judging the fault, it is important to check the pressure guiding pipeline and check whether there is gas in the measuring chamber (when measuring liquid and steam) or liquid (when measuring gas). The heating temperature in the pressure guiding tube is too high or too low, causing vaporization or condensation to the measured medium, which is also one of the causes for fluctuations in the pressure sensor output current. It can be discharged through the drain valve or through the emptying plug in the pressure sensor’s measuring chamber. There are impurities in the pressure guiding tube, and the dirt appears to be blocked and not blocked seemingly. It also causes the pressure sensor output current to fluctuate, whose solution is also sewage.
The inspection and processing methods for pressure sensor and differential pressure sensor output current fluctuation or unstable fault are shown in the following table. For the pressure sensor output current fluctuates, in addition to the above reasons, the fluctuation caused by the malfunction of the meter used with the sensor cannot be ignored. For example, faults in the distributor, safety barrier and valve positioner, large vibrations in the installation environment, and electromagnetic interference will cause fluctuations in the pressure sensor output current.
  • Inspection and solution for pressure sensor output fluctuations or unstable faults
Inspection
Solution

Is there any gas in the liquid pressure guiding tube?Is there any liquid in the gas pressure guiding tube?
Sewage disposal or flush for pressure guiding tube.
Whether the process production is too volatile.
Adjust the damping time of the pressure sensor.
If the supply voltage of the pressure sensor is normal? If the power supply line is in poor contact?
Check the power supply and power supply lines and make corresponding treatment.
Check the measurement circuit for intermittent, short circuit, open circuit, ground.
Check the connection line of the pressure sensor and make corresponding treatment.
Check the wiring , the pin and whether the plug contact are good or not for the sensing component.
Reconnect or plug the parts tight.
Replace faulty circuit board with spare parts.
Replace the faulty circuit board.
Check if there are some faults in the pressure sensor.
If there is a fault, it needs to be removed and repaired.

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