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Magnetic Flow Meter Operational Issue

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#1 JKM


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Posted 18 September 2019 - 08:54 AM

Dear All,


We are commissioning a new Dilute Phosphoric Plant and facing a problem in Magnetic Type Flowmeter. The designed service fluid is Phosphate Rock Slurry(70% solid) however we are currently conducting Water Run Tests, so the fluid is water.


The flow signal is coming quite erratic, the normal flow is 110 m3/h but it is indicating flow as 10000 m3/h . My Instrument team informed that signal is quite erratic because pipe line is not full. If the pipeline is full then the signal will be correct. 


I personally do not agree that the erratic value is because of pipeline not full. As I understand that magnetic flowmeter detects the flow based on the magnetic field generated proportional to the flow rate. Magnetic field in turn depends upon the conductivity. Conductivity of the Water and Phosphate Slurry(70% Solid) is quite different. That conductivity difference is causing the erratic signals.  


Kindly let me know the is it a requirement for the magnetic flowmeters that the pipeline should be full? Also let me know your opinion what could be the probable cause of different flowrate.



#2 PhilippM


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Posted 18 September 2019 - 10:10 AM

Didn't the vendor specify anything about the installation?


e.g.: See page 9 of this installation guide:




"The sensor should be installed in a location that ensures it remains full during operation. Depending on where it is installed, orientation must also be considered."

#3 thorium90


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Posted 18 September 2019 - 10:22 AM

Having half filled pipes can indeed be a cause of erratic readings. Then again, the half filled pipes can be due to an incorrect installation of the flowmeter. For example, if the flowmeter is placed near to a pipe open end and the pipe open end is facing downwards such as when entering the top of the tank, air will be present in the pipe, which will cause erratic readings.


Conductivity difference between actual fluid and real fluid will not cause erratic readings. If there was an issue that way, it would be a constant error won't it.


Perhaps you can take a photo or video of the erratic reading that you see, including the flowmeter installation. It will be easier to point out where the problem is.

Edited by thorium90, 19 September 2019 - 05:10 AM.

#4 breizh


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Posted 18 September 2019 - 07:01 PM





Consider the link attached . You need to have your pipe full of liquid .


Is this the right technology for a slurry ? I'm thinking about mass flow meter (straight tube) .

If you have solid deposit inside the meter (magnetic) you will loose accuracy .


Good luck


Edited by breizh, 18 September 2019 - 09:52 PM.

#5 JKM


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Posted 20 September 2019 - 03:58 AM

Dear Thorium, Breizh, Phillip,


Thanks a lot for your suggestion.


The OWNER is also the LICENSOR. They specified Flowmeter type and the orientation on the sloped line. Also the pipe type is flexible hose so it can not be made completely vertical.


It may be possible that with the actual flow the same problem may not occur.


I am putting forward this isse to the OWNER and will update the conclusion here in the forum later on. 



#6 thorium90


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Posted 20 September 2019 - 04:08 AM

The flowmeter is installed on a flexible hose? Thats definitely wrong installation. You need a proper pipe with adequate straight run before and after the flowmeter to get correct readings.

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