About electromagnetic flowmeter PROMAG 50W mady by E+H

[fjh502]

Dear all,

In our plant we have two same waste water line,we use electromagnetic flowmeter PROMAG 50W mady by E+H to measure, the real flow is about 660t/h but one flowmete reading is only 320t/h, the other one is ok, the parameter i have checked is same, i have check and clean the lining and sensor, exchage amplifier and I/O boards between this two flowmeter, but nothing changed, the abnormal one still show 320t/h, the good one still show 660t/h. So the transmitter should be no problem i think.
Any body could give me some advice,i will appreciate very mcuh.

 

[controlnovice]

Did they use to read the same?

How do you know the 660 is the correct reading, and the 320 is bad? Could the 320 be the good reading?

I'd try to clean both of them, if possible, again. The sensors on the Mag flowmeters can get coated in this type of service. We had something similar happen to us. I had them clean it a second time with a pipe brush cleaner, flushed it with water, and it finally worked.

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This is normally the space where people post something insightful.

 

[fjh502]

controlnovice:

Thank you first, for your question:

after putting both in service, their reading almost same about 660t/h.

when one reading came down to 320t/h, I have check the reading with portable ultrasonic flowmeter which show both flow are almost same about 600t/h, so i think the reading which is 230t/h is bad, the other one is good.

we put bad one out of service and cleaned lining which is hard rubber material and sensor, after that we had measure the resistence of lining between any point, some show insulation but most show less 1 mega ohm.
I think it's not normal.

thanks you again.

 

[roydm]

I have seen a mag reading half when one electrode was shorted to ground. Try measuring each electrode to ground with power off and the wires removed. Both should read about the same. If you can do it with the meter empty should be in the Megohm range. If one is low check for moisture at the point where electrodes pass through the wall of pipe. Might also be a loose connection between electrode and amplifier. Ether way it sounds like you are only getting half of the signal.
A side question - Are you using the both meters on the same pipe, one each end?
Good luck
Roy

 

[Cat3347]

1. Open electrode
2. Shorted Electrode
3. Shorted Coil

The fact that it is reading approx. 50% of flow...those three come to mind. Check your manual for specific directions on how to test.
If it was a smaller difference..I would say check grownding or maybe somebody changed the meter factor.

 

[fjh502]

Dear all,

After vendor check, It's said the cause is that the lining resistence became low for chemical penetration. Is it possible? lining material is PFA, Which kind of chemical can make linning conductible? Thanks!

 

[roydm]

fjh502 (Petroleum)
There is very little that will attack PFA (teflon). I suspect it was more likely leakage around the electrode, wrong electrode material (corrosion) or wrong material for the electrode seals.
You should have a compatibility chart for the chemicals you use.
How long was the meter in service before the fault showed up?
Why doesn't the other meter also fail?
Is the vendor telling you that the PFA is now conductive?
I suspect you may just have a bad one.

Roy

 

[fjh502]

Roy

Vendor and I have measured the resistence between two point in lining, the reading is less than 1 Mega ohm some ponits even less 10 kilo ohm, So we think the lining was damaged. After the meter put in service about 8 months the reading began inacurate, the other meter now also happen same problem. I am working in maintenance deparment, About the instrument type selection is project responsibility, I did not participate.
We use PTFE lining in same process in old unit, In new continuational unit there are two meter is using with PFA lining.
Is it clear for you?

 

[roydm]

fjh502,
There must be some nasty chemical in your process to attack PFA, do you have any idea what?
We do a lot of glass lined systems and have in-house experts on materials, I could make some enquiries.
Do you think it has penetrated the lining or is it just a coating on surface?
Have you measured each electrode to ground, are they both the same?
What's in the waste stream?
Temperature?
What is your industry?
What is your electrode material?

Regards
Roy