How to deal with large flow fluctuations in electromagnetic flowmeters?
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Many of the electromagnetic flowmeters we have installed show large fluctuations in flow rate; it’s not clear whether their readings are accurate or not
Possible reasons for large flow fluctuations in electromagnetic flowmeters: 1. Underfilled pipe； 2. Magnetic field interference ； 3. Incorrect grounding ； 4. There are bubbles ； 5. Mismatch between the electrode and the dielectric. For more detailed technical information on fault analysis, please visit: http://bbs.hcbbs.com/thread-755890-1-1.html
As a supplementary note, an incorrect installation location – installing it behind the control valve – can also lead to large fluctuations.
If nothing else works, consider reducing the measurement frequency. See if it works
The reasons for the large fluctuations have been mentioned on both the first and second floors: it’s due to installation and setup issues. To determine whether these fluctuations are accurate or not, it’s necessary to compare the readings with those from other instruments and flow meters. If still unsure, one can take the device to a quality inspection laboratory for verification.
The issues have been outlined on the 2nd floor; I’ll add a few more points. The large fluctuations in flow rate of electromagnetic flowmeters may be caused by the following reasons: 1. The fluid itself may be pulsating or fluctuating, and in this case it’s not a problem with the flowmeter. 2. The pipeline may not be fully filled with liquid, or the liquid may contain bubbles. 3. External electromagnetic interference such as stray currents. 4. Properties of the liquid itself (such as uneven electrical conductivity or slurries containing variable-sized particles/fibers). 5. Incompatible electrode materials with the liquid. Solutions: (1) Determine whether it’s due to process operations – if the fluid is indeed pulsating, then the flowmeter is simply reflecting the actual flow conditions, and the issue will resolve itself once the pulsations stop. (2) Electromagnetic interference caused by external stray currents, etc. Check whether there are any large electrical appliances or welders in operation in the environment where the instrument is located; it is important to ensure that the instrument is properly grounded and that its operating environment is suitable. (3) When the pipeline is not filled with liquid or contains bubbles, both situations are caused by process-related reasons. At this point, it is possible to ask the process technician to verify whether the output value can return to normal once the tube is filled with liquid or the bubbles subside (to determine if there are any installation issues). (4) The transmitter circuit board has a plug-in design; due to the significant vibrations in the pipelines or liquids at the measurement site, this often leads to the loosening of the power supply board of the flow meter. If it becomes loose, the flow meter can be disassembled and the circuit board resecured.
If the fluctuations occur in a few cases, it may be related to the properties of the medium, such as incomplete filling of the pipe, two-phase flow, or vibration interference. However, if this issue occurs in many cases, it is likely that the installation was not carried out in accordance with standards; in particular, it is uncertain whether the grounding of the electromagnetic flowmeter was properly done.