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3 Common Medium in Pressure Sensor Measurement

The function of the pressure sensor is to measure medium pressure such as gas, oil or steam, and then convert the pressure signal into a standard current signal output to supply to secondary instrument such as alarms, recorders, regulators, etc. for measurement, indication and process adjustment. During the use of the pressure sensor, there are often many process parameters are incorrect. For example, the installation of throttling device, condensation tank and pressure guiding tube are not standard, the pressure guiding tube is blocked, electromagnetic interference as well as maintenance, etc. Many of the flow, level and pressure measured by the pressure sensor are involved in the automatic control of the system. Some pressure and differential pressure are also involved in the shutdown control. If the measurement accuracy is not high, it not only affects the accuracy of the automatic control, but also affects the stability of production. These put higher demands on the measurement accuracy and pressure sensor stability.
The following are some of the main problems and causes encountered in the use of pressure sensors.

1. Pressure sensor interference problem in gas pressure measurement

In the exhaust pressure measurement of the air compressor, the fluctuation of the exhaust pressure signal is large. After calibration, the pressure sensor meet the accuracy requirements so the failure of the pressure sensor itself can be eliminated at this time. Check the pressure guiding tube and the connector, and found no damage or air leakage, and the signal cable connection is also in good contact. However, the cable direction is introduced into the control room through the cable tray next to the high pressure chamber. There is a large amount of electromagnetic interference around the pressure sensor.

2. Fault of pressure sensor equipment itself in oil pressure measurement

In the measurement of the lubricating oil pressure, the pressure signal of the lubricating oil participates in the stop interlock control. The signal measured by the pressure sensor is transmitted to the computer for numerical display on the one hand. On the other hand, this signal is also used to program comparison. When the pressure is lower than 0.06MPa, a oil shortage stop signal is issued to stop the operation. In actual applications, there has been a sudden drop in lubricating oil pressure resulting in an accident, which was huge losses. When such a fault occurs, it is necessary to remove the pressure sensor and check if the internal module of the sensor is damaged. Although the user periodically checks the pressure sensor every year during use, if the sensor pass the test, the production is continued. However, after several years of operation, the performance and specifications such as accuracy, sensitivity, stability, etc. of the pressure sensor will gradually decrease, and the internal diaphragm as well as the integrated block will be damaged, resulting in malfunction.

3. Pressure sensor installation problem in steam pressure measurement

In the steam flow measurement, there are mainly two kinds of steam, one is external supply steam, and the other is superheated steam of the boiler. The external supply steam is the steam after desuperheating and decompression, the temperature is not high, and it is mixed with a large amount of water. This steam is not always used in production, and the steam flow can be changed according to the requirements of the user. In the actual flow measurement process, sometimes the flow rate is too large, and sometimes the flow rate is too small, which is very unstable. Therefore, it is often necessary to clean the pressure sensor. The pressure sensor measurement become accurate after each sewage, but if the number of sewages of the steam pipe is increased, it is easy to cause leakage at each joint on the pressure guiding pipe. When the pressure sensor is used to measure superheated steam, the biggest problem may be that it sometimes stops. After restarting the instrument, the flow will be deviated, resulting in misalignment, and sometimes there is still a small amount of flow displayed after stopping. The pressure sensor is usually installed at a lower position than the measuring pipe. However, in the actual installation, the condensation tank of the external supply steam flow and the pressure sensor are higher than the measurement pipeline. The superheated steam flow in the boiler also has the problem that the height of the condensing tank and the measuring pipe are inconsistent. It results in an unbalanced condensate height, causing a static pressure difference.
  • Blockage in the pressure tube of the pressure sensor
In pressure measurement, sometimes the pressure value displayed by the pressure sensor does not change with the operating conditions. Open the drain valve, there is no water flowing out after only a small amount of sewage flows out. This is due to the presence of a small amount of floating dust in the water or compressed air, which enter the pressure guiding tube with the water flows and produce sediment. After a long period of time, the wall of the pressure guiding tube will be corroded and fouling, resulting in blockage.

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