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Differential pressure transmitter working principle and common fault analysis introduction

In the industrial automation production, the differential pressure transmitter is the most widely used for the measurement of pressure and differential pressure flow. The problems encountered in production are also more and more, the timely judgment and analysis of the fault, and the ongoing production. It is said to be crucial.
First, the working principle of differential pressure transmitter
The differential pressure from the double-sided pressure guiding tube is directly applied to the double-sided isolating diaphragm of the transmitter sensor, and is transmitted to the continent measuring component through the sealing liquid in the diaphragm, and the measuring component converts the measured differential pressure signal into The corresponding electrical signal is transmitted to the converter, and is converted into a standard electrical signal output by amplification or the like. The most common methods for measuring differential pressure transmitters:
1. In combination with a throttling element, the liquid flow rate is measured using a differential pressure value generated before and after the throttling element.
2. Using the pressure difference generated by the gravity of the liquid itself, the height of the liquid is measured.
3. Directly measure the pressure difference between different pipelines and liquids.
Second, differential pressure transmitter fault diagnosis method
In addition to reviewing the occurrence of fire, smoke, odor, power supply change, lightning strike, moisture, misoperation, mis-maintenance, etc. before the failure; and observing the external damage of the circuit, the leakage of the pressure guiding tube, the overheating of the circuit, the state of the power supply switch, etc. In addition to the phenomenon, the fault should also be diagnosed by detection.
1. Open circuit detection side: Separate the suspected fault part from other parts to see if the fault disappears. If it disappears, you can determine that the fault is here. Otherwise, the next step can be found. For example, the intelligent differential pressure transmitter cannot normally perform Ha-type remote communication, and the power can be disconnected from the meter body. Use the power supply on site to power the transmitter to communicate to see if there is an electromagnetic signal about Zk - HZ superimposed to interfere with the communication.
2. Short-circuit detection: In the case of ensuring safety, the relevant part of the circuit is directly shorted. For example, the output value of the differential pressure transmitter is too small, the pressure guiding tube can be disconnected, and the differential pressure is applied from the first pressure regulating valve. The signal is directly bowed to both sides of the differential pressure transmitter, and the transmitter output is observed to determine whether the pressure guiding pipeline is blocked, leaked or connected.
3. Replacement test: Replace the suspected faulty part and judge the fault location. For example, if the transmitter board is suspected to be faulty, you can temporarily replace it to determine the cause.
4. Division inspection side: divide the measurement circuit into several parts (such as: power supply, signal output, signal transmission, signal detection), check each part separately, from simple to complex, from the table and inside, zoom out Range to find the location of the fault.
Third, common troubleshooting
1. Possible causes and solutions for excessive output:
(1) Pressure guiding tube. Check if the pressure guiding tube is leaking or blocked; check whether the shut-off valve is fully open; check whether there is liquid in the gas pressure guiding tube, and whether there is gas in the liquid pressure guiding tube; check the pressure chamber of the transmitter for deposits.
(2) Electrical connection of the transmitter. Check the sensor assembly connection of the transmitter. Ensure that the connector contacts are clean; check that the 8-pin is securely connected to the case.
(3) Transmitter circuit failure. Replace the board with a spare board, determine the faulty board, and replace the faulty board.
(4) Check if the output of the power supply meets the required voltage value.
2. Possible reasons and solutions for output too small or no output:
(1) Pressure guiding tube. Check if the pressure guiding tube leaks or is blocked; check if there is gas in the liquid pressure guiding tube; check whether there is any sediment in the pressure chamber of the transmitter; check whether the shutoff valve is open and the balance valve is closed.
(2) Electrical connection of the transmitter. Check if the lead wire of the transmitter sensor component is shorted; check if the pin No. 8 is securely connected to the case; ensure that the contact of the connector is clean; check if each adjusting screw is within the control range.
(3) Wiring circuit. Check that the voltage applied to the transmitter is normal; check the circuit for shorts or multiple grounds.
(4) Transmitter circuit failure. A replacement board can also be used instead to judge a faulty board or replace a faulty board.
3. Unstable output causes and solutions:
1) Wiring circuit. Check the circuit for intermittent short circuit, open circuit or multi-point grounding; check if the voltage applied to the transmitter is suitable;
(2) The measured liquid fluctuates. Adjust the size of the damping effect of the circuit.
(3) Check if there is liquid in the gas pressure guiding tube, and whether there is gas in the liquid pressure guiding tube.
(4) Ensure that the connector contacts are clean and check the grounding of the sensor components.
(5) Replace the faulty transmitter board with a spare board to determine the fault and replace the faulty board.
Due to the compatibility between the differential pressure transmitter and the pressure transmitter measurement application, some methods in this paper are also applicable to the fault diagnosis of the dry pressure transmitter.

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