Emerson Exchange 365

• Not Answered

Deviation between two LTs in a vessel

Hello

Can you please guide me to the steps (from the simple/basic ones to the complex ones) to take to troubleshoot a deviation between two level transmitters  installed in a vessel.

Thank you very much

yacine

• 9 Jul 2018 9:52 AM
• Cancel

4 Replies

• Ingemar Serneby

  

  • 9 Jul 2018 11:06 AM

  Hello Yassin!
  In order to give you the best assistance, it would be necessary to know what level transmitter this is about. If it for instance is a standard pressure transmitter, it can be a relatively simple matter of span/offset adjustments. If it on the other hand is for instance a radar transmitter, the solution can be a bit more complex. Are the two level transmitters located at two individual nozzles for instance? It can in such case be a case where the two nozzles are not identically tall and that you in such case need to correct this with offset settings. Does the transmitters show different level readings when the vessel is full or when it is empty? Or all the way between empty and full? Is the deviation constant or increase/decrease with the distance? How are the transmitters installed?
  Best regards,
  Ingemar

  • Cancel
• yacine

  

  • 9 Jul 2018 1:21 PM

  In reply to Ingemar Serneby:

  Dear ingemar
  
  Thank you for your reply. for my case, they are two DP level transmitters installed in a horizontal vessel, located at two individual nozzles. the difference between the readings is constant (around 20%) between empty and full vessel. the vessel drawing shows a different length from high to low tappings when comparing the two transmitters. The element range in the data sheet is different for the two transmitters.
  
  please advise further if possible.
  Thank you
  
  Best regards
  yassin

  • Cancel
• Nathan Stokes

  

  • 9 Jul 2018 9:00 PM

  In reply to yacine:

  Yassin,
  
  Based on what you have shared, the two DP transmitters may need to have a change in the zero or 4mA point being that the offset is consistently different. Can you share the models of the devices you are using? Are you able to empty the vessel? If so, you should be able to empty the vessel and reset the 4mA or lower range point for the device that is 20% off.
  
  Nathan

  • Cancel
• Dale Perry

  

  • 10 Jul 2018 2:10 PM

  Yassin

  The linear 20% offset between the two transmitters indicates the two transmitters have the same span but different reference or 4mA values.

  The element range can be different as long as its range limits fall within the range limits of the application.

  The upper and lower range points can be different depending on how the 4mA value was set/zeroed.  

  What can’t be different is the span. Your offset is linear across the range of the tank so I know the span on both transmitters are the same.

   

  What you are seeing indicates that these transmitter were zeroed or not zeroed or the 4 mA value was set differently when the devices were installed. You need to empty your tank or flange off and vent the transmitters and get the two transmitters to both have the same reference, typically 4 mA values. It all depends on the installation, direct connect, capillary system, or filled legs, how you would go about getting them at the same reference.  Your choices would be to Zero Trim or set the 4 mA value with the Applied Pressure option, or use the Zero pushbutton.

  Dale Perry | Global Training Manager

  Emerson Automation Solutions | 6021 Innovation Blvd | Shakopee | MN | 55379|USA

  T +1 (952) 204-6476 | M +1 (952) 270-4062

  Dale.perry@emerson.com

   

  • Cancel