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Electromagnetic flowmeter analysis of common problems

In the past, the calibration of the electromagnetic flowmeter had to be sent to a special calibration and calibration device for inspection. However, with the development of electromagnetic flowmeter manufacturing technology and the expansion of the application industry, the use of electromagnetic flowmeters is increasing, the caliber is getting larger and larger, and it is more and more difficult to check back on the verification equipment. Especially in the water supply industry, due to the large diameter of the application and the advantages of the industry, it is difficult to operate by taking off the flow and taking out the checkout. It is time-consuming and laborious, and even impossible to remove. However, according to the requirements of the ISO9001 quality management system, each enterprise needs to perform regular inspection as an electromagnetic flowmeter for measuring instruments. To this end, the application and manufacturer of electromagnetic flowmeters have been struggling to find an online electromagnetic flowmeter inspection method to replace the traditional offline calibration method. On-line inspection method of electromagnetic flowmeter commonly used at home and abroad: On-line verification method of large-caliber electromagnetic flowmeter In the 1990s, Shanghai Waterway System began to explore online inspection and verification. They used a dedicated analog signal detector to detect the converter, and the sensor inspection The test electrode is connected to the liquid resistance, and the in-vibration coil includes the insulation resistance and the copper resistance of the excitation connection cable, and the indirect method of checking the excitation current of the converter output and checking the magnetic field strength. In the pipeline with the stop flow condition, enter the hole from the vicinity of the sensor, check the electrode and lining for contamination, deposition and clean. In cooperation with the electromagnetic flowmeter manufacturer, Shanghai Water Supply Company and Raw Water Company explored and accumulated more than 300 large-caliber electromagnetic flowmeter inspection experience, and drafted the “On-line Calibration Method for Large-caliber Electromagnetic Flowmeter” from 1997 to 1998. The enterprises affiliated to the Shanghai Public Utilities Administration were piloted. On the basis of this document, the Shanghai Water Affairs Bureau is now formulating the local industry standard for the "On-line Calibration Specifications for Electromagnetic Flow Meters". The same concept is also mentioned in some literature, such as the Tokyo Metropolitan Water Authority and Japan.
Some common faults in the use of electromagnetic flowmeters are faults caused by damage to the components of the instrument itself, and some are faults caused by improper selection, improper installation, environmental conditions, fluid characteristics, etc., such as display fluctuations, reduced accuracy, and even instrument damage. It can generally be divided into two types: failures during installation and commissioning (debug during commissioning) and failures during normal operation (running faults). (1) Failure during commissioning The debugging expectation fault generally occurs in the stage of installation and commissioning of the instrument. Once it is excluded, it will not appear again under the same conditions in the future. Common commissioning failures are often caused by improper installation, environmental disturbances, and fluid characteristics. 1) The installation aspect is usually the fault caused by the incorrect installation position of the electromagnetic flow sensor. Commonly, the sensor is installed at the highest point of the pipe that is easy to accumulate gas; or it is installed on the vertical pipe from top to bottom, and may be drained; Or no back pressure after the sensor, the fluid is directly discharged into the atmosphere to form a non-full tube inside the measuring tube. 2) Environmental aspects It is usually mainly caused by stray current interference in the pipeline, strong electromagnetic wave interference in space, and magnetic field interference of large motors. Pipe stray current disturbances usually achieve good results with good separate grounding protection, but if you encounter strong stray currents (such as electrolysis shop piping, do you have?
Online electromagnetic calibrator GS9 electromagnetic flowmeter is the most used in Europe, and its online inspection technology is also the most mature. Some major electromagnetic flowmeter manufacturers have developed a special electromagnetic flowmeter online detection instrument according to the above method, such as KROHNE. GS9 online electromagnetic flowmeter calibrator. The instrument is used as a calibrator for comprehensive detection of electromagnetic flowmeter sensors and converters. The detection includes electrode signal, analog flow output measurement, field excitation current measurement, current and frequency output measurement, coil and electrode. Resistors, etc., and record the data, which can also be transmitted to a PC. The inspection process GS9 is very simple to use, as long as the cable is connected according to the identification of the flow meter (plug and play), and then the automatic verification is started, the data is stored in the internal memory (70 instruments), and then the data can be Transfer to a computer for processing. The tester automatically loads the meter's GK, range, aperture, field current, current and frequency output settings, and begins to measure the field current, detect coil and electrode resistance (short circuit or open circuit), verify the two measuring electrode signals and convert the pair Current and frequency output test. Give "Pass" or "fail" diagnostics to the different parts of the converter and store the entire calibration process. The entire process check is automatically controlled to upload the verification data to the computer through the RS232 communication port. The traceability GS9 can be traced directly to KROHNE's highest-end calibrator (GS100) and (Netherlands Metrology and Testing Institute NMI). The uncertainty of sensor calibration is 0.03%, and the measurement uncertainty of GS9 is 0.09%. In the field or instrument room, the GS9 and the PC are connected by RS232, and the above-mentioned online inspection or special diagnostic instrument is completed. Although the flow rate is not stopped after the pipeline flow is stopped, the flowmeter is inspected.
Above the fluid conductivity, the electrode circuit will be short-circuited and the meter will not work properly. Therefore, the fouling layer in the measuring tube of the electromagnetic flowmeter should be removed in time. 2) Lightning strikes Lightning strikes easily induce high voltages and surge currents in the instrumentation lines, causing damage to the instrument. It is mainly introduced through the power line or the excitation coil or the flow signal line between the sensor and the converter, especially from the control room power line. 3) Changes in environmental conditions During the commissioning period, the environmental conditions are still good (for example, there is no interference source), the flowmeter works normally, and it is often easy to neglect the installation conditions (for example, the grounding is not so good). In this case, once the environmental conditions change, a new source of interference occurs during operation (such as welding on the pipeline near the flowmeter, installing a large transformer nearby, etc.), which will interfere with the normal operation of the meter, and the output of the flowmeter. The signal will fluctuate.

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