Troubleshooting differential pressure transmitters in field applications

Abstract: The differential pressure transmitter can measure the liquid level through the pressure difference at both ends of the transmitter. It has been widely used in the petrochemical field. In order to make the differential pressure transmitter play a greater role in various fields This article conducts in-depth discussion and research on the fault diagnosis of differential pressure transmitters. Through comparisons between transmitters, it is shown that only the correct use and maintenance of differential pressure transmitters can ensure their effectiveness. Play a substantial role in the work.

1. Failure analysis and treatment of differential pressure transmitter in field application

As a device for measuring the liquid level at both ends of the transmitter, the differential pressure transmitter can It can accurately measure and display the pressure of the equipment, and can also measure and control the differential pressure and flow rate of various fluids. However, due to the frequent use of the differential pressure transmitter, failures during operation cannot be avoided. After testing, The sorting and analysis of fault conditions of differential pressure transmitters in field applications are summarized into the following common faults.

1.1 Faults caused by errors in the meter opening program

There are many types of differential pressure transmitters, and the steam differential pressure transmitter is a more common type. When using a steam differential pressure transformer, When the transmitter is running normally, if it is found that the condensed water disappears, the instrument display is abnormal, the pressure is uneven, or a vibration sound is made during the operation of the equipment, then it proves that the steam differential pressure transmitter has failed. After analyzing the meter opening procedure of the steam differential pressure transmitter, the main cause of the failure was: no flushing and sewage discharge work was performed before opening the meter, and then the "5", "4" and "4" valves in the three-valve group were opened respectively. The "3" valve causes an error in the meter opening procedure, which can easily cause a failure of the steam differential pressure transmitter, which may lead to a decrease in the metering value or an incorrect display. By searching relevant information on the steam differential pressure transmitter, we learned that the correct operation is: (1) Before opening the meter, purge and flush the inside of the equipment. First, clean 3, 4, 5, 6, and 7. The valve is closed, then valves 8 and 9 are opened, and then valve 4 is opened, and the operation is completed.

1.2 Differential pressure transmitter indicates failure

Under normal circumstances, chemical companies need to install a phosphorus ammonia device. If the pressure difference transmitter in the phosphorus ammonia device If there is no change in the indication value of the instrument, it proves that the instrument has malfunctioned and requires technicians to diagnose and repair the instrument. After technicians inspected the site, it was found that when the instrument pipeline was in its open state, the medium in the pipe filled the pipe, which proved that there was no internal fault in the pipe. When the pressure difference transmitter was opened, it was found that the medium inside the valve would induce pressure from Outflow from the root of the pipeline indicates that the cause of the fault is that the pressure pipeline is not blocked. In order to accurately locate and eliminate faults, it is necessary to use a combination of replacement detection and partial detection to detect faults. First, send the differential pressure transmitter instrument to the relevant testing department for testing to determine the operation of the instrument. situation, and thenTo replace the differential pressure transmitter, it is required that the equipment has no faults and has the same range. The zero point and range of the transmitter must be debugged until the normal state is displayed. The test report produced by the testing center shows the indicated value of the transmitter. If there is no change, then the possibility of transmitter failure is ruled out. Therefore, it can be judged as a circuit board failure. Then the same operation is performed to replace the circuit board and perform verification. The result shows that the transmitter is between 4 and 20mA. The range indication value is correct, which proves that the fault of the differential pressure transmitter instrument indication value is caused by damage to the circuit board. As long as the circuit board is replaced, the fault is solved satisfactorily.

1.3 Vapor-liquid two-phase pressure difference failure

A chemical company has installed 5 single-flange differential pressure transmitters in the potassium dihydrogen phosphate concentration device, which are mainly used for For the measurement of potassium dihydrogen phosphate solution, during the operation of the equipment, the problem of coexistence of vapor and liquid phases on the negative pressure side caused large fluctuations in the measured values, which in turn hindered the accurate measurement of the actual liquid level.