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Mass flowmeter inaccurate flow rates and totalizer

Hi, 

We have quite a few flowmeters a few of them have some issues but one of them is very critical. 

The model is MVD 2700 Coriolis mass flow meter and it was giving inaccurate flow rates and very high totalizer quantities. This is known as there are pumps which are running at a certain RPM and giving approximate known fixed flow rates. Also, the quantity being pumped is known. So the totalizer should not go more than that and when there was no flow it still shows some flow readings. So, to resolve all these issues I tried to zero the flow and it didnt help much. Then i restored the factory calibration and it helped a bit, however, the erratic and heavily fluctuating flowrates exist and the totalizer also doesnt give the correct quantity. 

Please can anyone provide more insight into this on what to do

Thanks

  • First question would be are you sure it’s false. Next I would if possible block it in and verify zero cal or do a zero cal with the sensor full. Third, if the Process has any potential for two phase flow micromotions don’t like that ALOT. Lastly if it is a new installation make sure to verify the sensor information is entered in the transmitter correctly, if they are not paired/matches with all the variables it will false indicate.
  • In reply to Jason.Brumfield:

    could foreign material, like plastic or other material pressing on one of the tubes can cause erratic readings, false counting when not flowing. have you attempted to back flush the meter?
    are the sensor flanges used to support plumbing? Flange strain can cause errors.
  • In reply to Jason.Brumfield:

    Yes pretty much confident that the readings were false as there was no flow all upstream and downstream valves were closed.
    I tried it that way, filled the sensor with fluid, closed the downstream valve and then the upstream valve and zeroed it.

    Yes its a new installation and i have checked the sensor details are correct. It is a curved tube and the direction is also forward.
  • In reply to armandos3:

    Its a possible cause that foreign material might exist. I had purged a lot of water through the sensor in forward direction after installation. However, never tried flushing or purging in the reverse direction. Will try that one out pretty soon.
    No the piping supports are different and have adequate support and do not put extra stress on the flanges.

    Thats why i am very much surprised why its behaving erratic.

  • In reply to Ghufran Ahmed:

    Are you seeing flow on the local indicator or in AMS? Reason I ask is to make sure the 4-20mA output channel is set to the proper variable for either volumetric or mass flow and the units are what you expect.
  • In reply to Jason.Brumfield:

    I am checking it at both. Initially i checked in AMS and then went to the field as well to the check the local display. At both locations its the same. They protocol is Foundation Fieldbus (FF) and the units and variables are same and configured properly.
  • In reply to armandos3:

    it does sound like you have something blocking the flow. if possible remove the meter at flanges and check the sensor for fore. once sensor is removed look down the flanged face into the sensor check for any foreign material,
    operate the removed meter you should observe density is zero and no flow, if you have values for either then push something, a towel for instance , through each tube. recheck meter values. should both be
  • Hello Ghufran, there are quite a few reasons why the reading from a Coriolis flow meter may not match a reference - to troubleshoot, we typically we start from easy and work toward hard. It sounds like you've already confirmed that the sensor calibration factors are correct in the electronics, and the sensor has been zeroed under "no flow" conditions. That's a good start. Are there any alarms present? Any issues with the wiring or moisture in the junction box? If the meter is still reporting flow when there is none, you should check that a reasonable "low flow cutoff" value is set (as high as possible without negating any real flow rate is recommended). Zero noise can also be an indication that some bubbles are entrained in your liquid, or something less desirable has occurred inside your sensor - such as erosion, corrosion, coating or scaling, or mechanical interference (sometimes caused by close proximity to other vibrating equipment). If you have Smart Meter Verification (SMV), you should run it. If something was actually plugging one of your tubes, it wouldn't present as a simple offset to the measured flow rate - there would be a host of other symptoms. If you suspect bubbles, try adding some backpressure by pinching down a downstream control valve. If these don't work, there are other variables that can be used to diagnose issues - such as drive gain, pickoff voltages, and tube frequencies. I highly recommend contacting Emerson's free Flow Technical Support at 1-800-522-6277, or by emailing flow.support @emerson.com.