Emerson Exchange 365

8800CF020SA1N1D1I1M5Q4Q70 Vortex Flow meter showing erratic

8800CF020SA1N1D1I1M5Q4Q70 model Vortex flow meter has started showing erratic reading suddenly. It was working fine but all of sudden started showing eratic.

Sensor resistance between sensor tip and ground was checked and found ok.

Upstream Downstream valve closed, actual flow is zero(cross checked with other process parameters) but still Flow meter showing 7-8 Te/Hr.

Electronics replaced on doubt basis and all parameters entered in new electronics. Still same problem faced of false reading and huting.

Meter was dropped from flange to inspect shadder bar(Being Pure acetic acid service), it was observed neat and clean. No physical damage/pitting observed.

When meter was dropped and kept on floor, it showed 0 Te/Hr, but when installed in line with no process flow , started showing 7-8 Te/Hr.

Please suggest what could be the cause of such behaviour.

Filtering parameters, LFC cutoff, Low pass filter freq. and all checked and canged as per shadding freq. at normal process flow.

 

chetan.v.patel

• 17 Oct 2014 1:18 PM
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2 Replies

• Mike Schaefer

  

  • 17 Oct 2014 3:43 PM

  From your description of the issue and the results of your troubleshooting steps, I would suspect that the vortex sensor has experienced physical damage that has made it loose on the sensor post. In this situation, the resistance reading can still pass as the piezoelectric crystals are still good - it is the body of the sensor that it damaged.
  
  However, I will also ask if the resistance check was done at process temperature or ambient temperature (if process temperature is higher than ambient). The best practice for testing is at process temperature. The resistance of the sensor will change over temperature and will usually be at its lowest resistance value at the highest temperature.
  
  Since replacing the electronics didn't change results and the configuration was confirmed to be correct, I wouldn't suspect an issue with the electronics. You could further confirm by performing an internal flow simulation.
  
  The false flow rate indication you are experiencing is likely due to pipe vibration signals that have become more prominent (stronger signals) due to the sensor being loose on the sensor post. These could likely be eliminated by increasing the Low Flow Cutoff filter value, but that would decrease the measurable flow range as well and would only serve to cover up the issue.
  
  My suggestion would be to replace the sensor. The part number for a replacement sensor is 08800-0250-0002. Instructions for replacing the sensor can be found in the manual in section 5 - http://www2.emersonprocess.com/siteadmincenter/PM%20Rosemount%20Documents/00809-0100-4004.pdf

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• Tom-flow

  

  • 17 Oct 2014 4:45 PM

  Thanks Mike!

   

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