Magnetic Flow Sensor Factor

I

Thread Starter

Imran Ahmed

Pls. I need to know when we should change the sensor factor for ABB Mag flow meter. In fact I am facing almost 50% decrease in reading. I changed the Main PCB also but no change. So now I change sensor factor from 2.4 to 4.2 and reading is now Ok. I assume the sensor (1000 mm dia) which is 25 years old now has become unresponsive. So is it the correct method to adjust the flow sensor? Pls. guide.
 
W
NO! Do not change the meter factor. The meter factor is essential for proper calibration of the mag meter. Changing the meter factor will obscure what is really wrong with the meter.

First, do you know what the flow should be? How do you know? What changes have there been in the piping over the last 25 years? Is the meter full of fluid, with minimal or no entrained air or gas?

Have you taken the primary out of line and inspected it? What kind of lining does it have? Could the lining be leaking? Do you have removable electrodes? Have you removed them and inspected them?

Have you used a primary simulator to see if the converter (what most people call the transmitter) is working correctly? If you have not, get a primary simulator and hook it up instead of the primary and see what happens.

There is no way to know whether it is the primary or the converter, or a combination of the two, without examining the primary and testing the converter. Please, refer to your instruction manual for the procedures. IF YOU HAVE LOST YOUR INSTRUCTION MANUAL, CONTACT ABB FOR A NEW ONE. THEY WILL PROBABLY SEND YOU A PDF OF THE ORIGINAL MANUAL.

My guess is that the installation was built without a meter bypass. What I would do is to fabricate a spool section the same laying length as the meter primary. I would shut down flow, pull the primary, and put the spool section in line. It should take not more than three or four hours to do this. If flow is diurnal, do it when the flow rate is the least, so you don¹t have backup problems.

Once you pull the primary and test the converter, you will know what the problem is.

ABB can help you do this, if you call them for service.

Walt Boyes, Life Fellow, ISA; FInstMC, Chartered M&C Technologist
Spitzer and Boyes LLC
Editor and Publisher, <i>The Industrial Automation and Process Control INSIDER</i>
 
Several factors, electrode coating buildup is the usual issue.
Be sure to keep track of your adjustments, eventually you will have to pull the meter and clean the electrodes.

There are a number of shop tricks to clean the electrodes in place, but that is only in some services.

Good luck
 
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