The flow rate of the electromagnetic flowmeter suddenly dropped to zero
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This post was last edited by FightingNow on 2015-8-8 at 19:42. It is a main pipe for flow control; there are also branch pipes downstream with flow meters as well! The flow rate in the branch pipe remained at 50, while the flow rate measured by the electromagnetic flow meter in the main pipe suddenly dropped to zero at one point; during that time, the flow rate in the branch pipe did not change, and no valves were operated in the process ……I asked the process team to open the branch valves; there is flow indicated on the main pipe flow meter, but this flow rate is likely too low! ……This also shows that there is no issue with power supply; when the valve is opened fully, a flow rate display is available! But this traffic is definitely on the low side! ……The medium is industrial water! …… ……Simply put, it can be said that the reading on this gauge suddenly became smaller! Why is this? The exterior of the unit seems fine; how can I check whether there are any problems with the electrodes and excitation coils? Or what? What should the entire inspection process look like, without having to remove anything? …… This watch is split-style! 220V！ Two wires are led from the sensors on the pipeline to the secondary meter head! The wiring terminals 1 and 2 of the secondary meter are connected to a 220V power supply ； 3 and 4 are the excitation coil power supplies ； 5 and 6 are signal lines for transmitting to the control system ； 7, 8, and 9 should be the signal wires from the sensor to the secondary meter! I’m not sure if this wiring is correct; please help me check it as well! No photos were taken! Then how should I proceed to check for faults in the excitation coil and electrodes, or other faults? I read online that it involves measuring resistance, but I don’t understand it; so I hope you can explain it to me in detail based on the terminal connections I mentioned! Thank you!
The resistance of the excitation coil can be measured. For split-type units, first check whether there is a problem with the excitation coil, and then verify whether the output from the transmitter is normal. Could you tell me which brand the instrument is?
Could it be a problem with the flow range of the flow meter? The diameter of the flow meter in question is small, resulting in a low lower limit, which allows it to measure flow rates. However, if the diameter of the main flow meter is large and its lower limit is high, it becomes impossible to make measurements.
I hope it’s from Yokogawa. I also want to know why, so I’ll wait for the results
A simple comparison using external clamping ultrasonic devices is indeed inaccurate; it’s necessary to take it back to the factory for calibration or replacement
Measure the resistance between the lower electrodes, as well as the resistance of the electrodes relative to ground; the resistance should be very high (it should remain high even when there is water flowing, in the case of vacuum tubes)! But I can’t remember the exact figure; however, if they are all below megohms, it means the insulation lining is damaged!
1. First, check the excitation coil; the resistance of coils with a diameter between 50 and 500 should be around 80-150, with slight variations depending on the brand； 2. Check the insulation of the electrodes; the resistance between the electrodes and the casing should be greater than 20 M ohms. In the presence of a dielectric, the electrodes should conduct electricity with a resistance in the K ohm range. 3. If the sensor is functioning properly, then check the cable – make sure the signal cable isn’t broken and that the wires aren’t damaged. 4. Use an emulator to test the converter (professional tools are required). If that doesn’t work, contact the manufacturer or service provider directly
Based on experience, it’s likely that the electrode insulation has failed
It seems its lifespan is nearly over. Do you have spare parts? Just replace it; trying to find the cause is just asking for trouble
In most cases, the problem lies with the electrodes. To confirm this further, other possible causes should be checked, such as whether the connection terminals are secure, by measuring the current directly without using the output cable, or by replacing the transmitter’s circuit board. If none of these steps resolve the issue, then it can be confirmed that the problem is related to the electrodes.
For such issues, just ask the manufacturer directly