Talking about the Correct Use and Maintenance of Target Flowmeter

Publisher:悠闲之旅Latest update time:2015-12-30 Source: eefocus Reading articles on mobile phones Scan QR code
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  With the progress and development of detection technology and manufacturing process, pressure-sensitive strain gauge target flowmeters are increasingly widely used in the detection of various fluid media in industrial production. It has the characteristics of solid structure, small resistance drop, fewer leakage points than other flowmeters, high measurement accuracy and sensitivity, and easy maintenance. The process medium of the Torch Chemical Plant is special, and the reliability and leakage prevention of the flowmeter are required to be high. In the expansion project in 2001, the plant used about 70 WFV series pipeline and insertion target flowmeters from Welkin Company of the United States, which are mainly used for the measurement of process media, water, steam and other media.
  1 Causes of Error
  During the commissioning of the new device in 2002, the author summarized some experience in the use of target flowmeters. After the target flowmeters were installed according to the technical conditions (the target flowmeters were calibrated according to the design requirements when leaving the factory), they were put into operation according to the operating procedures. It was found that a few meters showed large errors, and some alarms showed full scale. After dismantling them on site and calibrating them using the weight removal method, it was found that the flowmeters were good. After analysis, the main reasons are as follows.
  1) Some larger debris in the fluid is entangled on the target rod, and it is easy to indicate full scale when there is flow. This phenomenon mainly exists in the working condition of measuring circulating water, which is due to the direct extraction of river water without filtration.
  2) Due to installation errors, it is not possible to ensure that the target plate of all insertion target flowmeters is located in the center of the pipeline, nor is it possible to ensure that the target plate is completely perpendicular to the pipeline. Therefore, there is a difference between the working conditions and the factory calibration conditions, which causes measurement errors of the target flowmeter.
  2 Solutions
  In view of the above reasons, and considering that none of the plant's flow measurement points had bypasses installed (to reduce leakage points and lower investment), the plant developed the following solutions.
  1) In order to prevent larger debris in the fluid from entangled with the target plate (rod), a filter is added at the pump outlet to filter out these larger debris.
  2) Use the comparison method to correct the error of the target flowmeter at the production site. Instruments used: 1 4.5-digit digital multimeter; 1 portable ultrasonic flowmeter; necessary wiring clamps and tools.
  The specific steps are as follows.
  First, install the portable ultrasonic flowmeter as required (pay special attention to the installed electrodes), and calibrate and adjust the ultrasonic flowmeter. Then use a digital multimeter to check and adjust the zero range, damping, etc. of the installed target flowmeter according to the calibration book provided by the factory, and finally turn the working switch to the measuring position. The installation diagram is shown in Figure 1:
  1) Set the valve openings at , 25%, 5000, 750o, and 1000o respectively, and record the displayed values ​​of the two flow meters at the same time.
  2) Set the valve opening to 10000, 7500, 5000, 25%, and 0 respectively, and record the displayed values ​​of the two flow meters at the same time.
  3) Analyze the errors of the two flow meters. If the indications of the two flow meters differ too much, find the reasons separately, check whether there are any problems with the installation of the ultrasonic flow meter (especially the two electrodes), remove the target flow meter for inspection (whether there are foreign objects on the target rod, bridge resistance, whether the bridge wiring is connected properly, whether the settings are correct, etc.), and recalibrate and install.
  4) If the difference between the two flow meters is small or a constant value, the zero position and full scale of the target flow meter can be adjusted appropriately, and the adjustment can be repeated until the measurement requirements are met.
  5) Repeat 1) and 2) to compare the indications of the two meters, and refer to other flow rates in the production system to calculate the material balance, and adjust repeatedly until the production requirements are met. After this method of adjustment and more than one year of production operation, especially during the start-up of the device in 2004, it was proved that the target flowmeter is stable and reliable in the production process, with sensitive response, few failures, less maintenance workload, and simple maintenance and adjustment. Economic operation was achieved in production, and the expected purpose was fully achieved.
Reference address:Talking about the Correct Use and Maintenance of Target Flowmeter

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