Capacitive pressure transmitter failure cause analysis:
1, the installation problem
In steam flow measurement, steam mainly involves two types, one is external steam, and the other is superheated steam of the boiler. The external steam supply is steam after desuperheating and depressurization. The temperature is not high, and it is mixed with a large amount of water, and it is not needed when it is used. The steam flow rate is changed according to the requirements of the user. In the actual flow measurement process, sometimes the flow is too large, sometimes the flow is too small, very unstable, and often needs to be drained. The measurement of the transmitter is accurate after each discharge, but the number of discharges of the steam pipe is increased, and it is easy to cause Each joint on the pressure guiding tube leaks steam. In the measurement of superheated steam, the biggest problem was that it sometimes stopped. After the restart, the flow will be deviated, resulting in misalignment, and sometimes there is still a little flow after the stop. Generally, the transmitter is installed at a lower position than the measuring pipe. However, in the actual installation, the condensing tank and the transmitter for the external steam flow are higher than the measuring pipeline, and the pressure guiding pipeline which is discharged from the throttle device and laid down at least 1 meter is too short. The superheated steam flow rate of the boiler also has a problem of inconsistency in the height of the condensing tank and the measuring pipe, resulting in a height imbalance of the condensed water, causing a static pressure difference.
2, the pressure tube is blocked
In pressure measurement, sometimes the indicated pressure does not change with operating conditions. After opening the drain valve, there is only a small amount of sewage and no water flows out. This is because a small amount of floating dust is present in the water or compressed air, and it enters the pressure guiding tube to precipitate with the water flow. Over time, the pipe wall of the pressure guiding pipe will corrode and form a blockage.
3, the transmitter device itself failure problem
In the measurement of the lubricating oil pressure, the lubricating oil pressure signal participates in the stop interlock control. The signal obtained by the lubricant pressure transmitter is transmitted to the computer for display on the one hand. On the other hand, the signal is also compared by the program. When the pressure is lower than 0.06 MPa, the oil shortage stop signal is issued to stop. The 1# machine had a sudden drop in lubricating oil pressure and caused a trip accident, which caused a huge loss. From the trend diagram of the lubricant pressure signal, it is seen that the pressure is instantaneously falling and causing the machine to trip. After checking the transmitter, the internal module of the transmitter is found to be damaged. Although we routinely calibrate the transmitter every year, it is used for production after passing the test. After the transmitter has been running for several years, its performance indicators such as accuracy, sensitivity and stability will gradually decrease, and the internal diaphragm and integrated block will also be damaged.
4, there is interference problem
In the measurement of the air compressor exhaust pressure, the fluctuation of the exhaust pressure signal is large. After verifying the transmitter, it meets the accuracy requirements and eliminates the fault of the transmitter itself; check that the pressure guiding tube and the joint are not damaged or leaking, and the connection of the signal cable is in good contact. However, the direction of the cable is introduced into the control room through the cable tray next to the high compartment. There is a lot of electromagnetic interference around.
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