Emerson Exchange 365

Electrode Saturation Error

Do you know other possible causes for "Electrode saturation error" message for a 8732E/8705 magmeter ?

I know the official explanation: 

"The Electrode Saturation error is a process related error. There are two situations that can lead to the electrode saturation: 

1)       The average voltage coming in through the electrodes is greater than 600 mV.  Typical max voltage for flow signal is less than 2 mV.  This would typically mean there is some stray DC current in the process fluid and/or piping system.

This can be induced by improper grounding. See Chapter 2.11 from page 21 of attached manual for proper grounding instructions. If the transmitter is remote, please make sure that they use the Rosemount cable and that it is properly connected.

2)       The difference in voltage coming in through each electrodes is greater than 600 mV.  This can be caused by a coating on one electrode or a partial short in one electrode causing an imbalance it the resistance of the electrode circuits.

 The standard front-end circuitry is DC coupled and when saturated  it can turn that front-end circuitry into a capacitive circuit.  This allows a charge to build up until the transmitter can no longer read the flow signal (front-end saturation).  When this happens the transmitter will drop to an output reading of 0 flow. 

It usually takes cycling power and/or disconnecting sensor wires to dissipate the charge and allow the transmitter to start reading flow again.

However, without resolving the issue the transmitter will become saturated again and drop to 0 flow.  This saturation can take anywhere from a few minutes to several months to happen depending on the severity of issue."

In fact this message appeared for 3 flowmeters of this type produced in 2016. None of the above described causes has been found (by Emerson's representative), another flowmeter from another company works smoothly. Is it possible to be a bug ?

leirbag

• 15 Nov 2017 12:50 PM
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7 Replies

• Mike Schaefer

  

  • 16 Nov 2017 6:48 PM

  Can you please provide more information about the application and the installation. Applications that are electrolytic (have a forced electrical charge on the process fluid) can cause issues with electrode saturation if the installation isn't handled carefully. The same can happen with piping systems that have cathodic protection. I would suggest you review this technical note which discusses magmeter grounding for typical and special applications:
  www.emerson.com/.../Technical-Note-Installation-and-Grounding-of-Magmeters-in-Typical-and-Special-Applications-en-77556.pdf
  
  While the grounding and wiring may be sufficient for a normal application, it may not be correct for this particular case.
  
  If needed, we can also supply a special transmitter construction with an AC coupled frontend to try and help prevent the saturation issue. I would guess that the other manufacturer's magmeter is using an AC coupled frontend and that is why those meters aren't seeing the same issue.
  
  Please let us know if you have any additional questions.
  
  Best Regards,
  Mike

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• leirbag

  

  • 18 Nov 2017 3:22 AM

  In reply to Mike Schaefer:

  Thanks Mike, I already knew the technical note, and I'm familiar with electrolysis plants for over 20 years. My application is very simple: NaOH 50% solution metering skid with magmeter (constant density, 50-60 Celsius degrees temperature).
  1. The discussed flowmeter (I'm just talking about mounting position) is powered from the same source - 230VAC, with other 2 old (produced in 2011) 8732/8705 flowmeters. Same installation for all , metal pipe, one of the old flowmeters working with the same fluid. No problems with the old flowmeters.
  2. The first claimed flowmeter worked for 4 months, the second one tried on this position 1 week.
  3. Conclusion of Emerson service: changing connector between tube and transmitter, problems with software with all of them, something with the baseline (I don't know what means).
  4. I borrowed from oher plant another old 8732/8705 flowmeter to continue working.
  5. With the new connector , I reinstalled first claimed flowmeter ( only for 2 weeks ) and after that the second one for 3 months. The first flowmeter was changed with a new one, but a I have no report about what was found in the claimed one.
  6. My first conclusion: I decided to change the flowmeter manufacturer and to not try another new 8732/8705 solution yet.
  
  Do you have another suggestion ?

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• Mike Schaefer

  

  • 20 Nov 2017 4:23 PM

  In reply to leirbag:

  We have had experience with 50% NaOH application acting like electrolytic applications even though they are not.
  
  I would suggest treating the application as electrolytic in terms of installation practices. See if provideing better isolation for the transmitter will help.
  
  The other choice would be to replace the transmitters with a special AC coupled front-end. We have had succes with this option in similar applications. If you are working with an Emerson salesperson, inquire about the F0100 special option for mag transmitters.
  
  The "baseline" the service team was referencing is probably part of the SMART Meter Verification diagnostic. The transmitter takes baseline values of key sensor parameters and can measure those same parameters at later dates to compare against the baseline. Too much deviation from the baseline values would indicate an issue.

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• leirbag

  

  • 21 Nov 2017 7:24 AM

  In reply to Mike Schaefer:

  Thank you for your reply. However I need more informations :
  1. When 50% NaOH application is like electrolytic one ? We have a storage tank and a recirculation pump for two charging lines of tankers (and manual flow rate valves of course ) . One is with the "bad flowmeter" and the other with the old (2011) 8732/8705 magmeter. Is it possible to act like a electrolytic application only on one line ? Why ?
  2. Can you indicate by a link supplementary data about "F0100 option for mag transmitters" ?

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• salehatiyyat

  

  • 27 Jan 2018 8:45 AM

  In reply to leirbag:

  Have you measured resistance between electrodes? Also could you please advise the material of electrodes? And how are you doing grounding?

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• leirbag

  

  • 29 Jan 2018 6:47 AM

  In reply to salehatiyyat:

  Hi Salehatiyyat, did you read the whole topic discussion ?
  1. The measurements and checks were made by Emerson's representative, according with :
  www.emerson.com/.../Technical-Note-Installation-and-Grounding-of-Magmeters-in-Typical-and-Special-Applications-en-77556.pdf
  and with :www2.emersonprocess.com/.../00809-0100-4662.pdf (table 6-6 sensor test). I have no results of these tests, I was gone that day. No reports submitted. The electrodes are Pt_Ir.
  2. Conclusion of Emerson representative: changing connector between tube and transmitter, problems with software with all of them, something with the baseline (I don't know what means).
  3. I borrowed from oher plant another old (2011 produced) 8732/8705 flowmeter to continue working (fine, same installation).
  4. With the new connector , I reinstalled first claimed flowmeter ( only for 2 weeks ) and after that the second one for 3 months. The first flowmeter was changed with a new one, but a I have no report about what was found in the claimed one.
  5. My first conclusion: I decided to change the flowmeter manufacturer and to not try another new 8732/8705 solution yet.
  6. If you know more technical details about what I should have checked in this case, please tell me.

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• salehatiyyat

  

  • 22 Feb 2018 9:10 PM

  In reply to leirbag:

  I am susspecting grounding I dont know If you have verified it

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