Emerson Exchange 365

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Modelock in Delatv

" What is the use of Modelock logic with respect to a standalone (nonPID loop hence kind of  open loop control) on/off valve.

What i understood is that it is use to put a valve in auto/man mode when it is supposed to remain in CAS mode as it is utilized in some SFC.

 Lets take example -  in step 4 of xyz SFC i gave an action to open XV5212

but operator accidentally changed its mode to Auto then what will happen. Does SFC remain stuck at this step as its not able to command valve so are we writing any special code in modelock logic code so that SFC don't stuck if it finds that valve in Auto mode instead of CAS mode?  "

Devpriy sahu

• 21 Dec 2017 4:34 PM
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6 Replies

• Ion Paidiu

  

  • 22 Dec 2017 8:30 AM

  In AUTO mode operator can command the valve, so it is necessary a message and alarm to operator to be provided in SFC step.
  I think it help
  Ion

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• Devpriy sahu

  

  • 22 Dec 2017 12:40 PM

  In reply to Ion Paidiu:

  Thanks

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• Rachelle McWright

  

  • 27 Dec 2017 5:23 PM

  Here's some additional info I received from Bob Read.
  
  " Modelock override is what we usually use, if the device is used in a sequence and equipment arbitration has been required. You take ownership through a sequence and set the device mode to CAS. If an operator should want to take back control, a tick-box appears on the faceplate to allow them to override the ownership, allowing them to put the device back in AUTO mode. "

  Best Regards,

  Rachelle McWright: Business Development Manager, Dynamic Simulation: U.S. Gulf Coast

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• Matt Stoner

  

  • 5 Jan 2018 8:38 PM

  First lets clarify that Modelock is "custom" logic and not a standard feature of DeltaV.
  
  The use case for modelock is typically to prevent operators from changing the mode and giving new SPs or OUTs while "higher" level logic is executing. This is to prevent operators from making mistakes, process has been validated and there should be no "manual" interventions while making product or sometimes for the safety of the equipment and/or personnel.
  
  Emerson PCSD modelock can also support times when a "Supervisor" needs to take over control (with the proper privilege) and "override" the active Modelock allowing the mode to be changed. It can also support NOT allowing this modelock "override" if required.
  
  As far as your question on the SFC logic getting stuck, that depends on how the SFC and the valve itself have been designed/configured. In the Emerson PCSD valve module for your example, the valve would get a failure if in AUTO mode with valve in a different state than commanded and if the Equipment Module (EM) was monitoring that valve it would execute some configured "HOLD" logic. If the EM wasn't monitoring the valve for failure in this situation it would continue doing what it was implemented to do. I don't know what modelock, valve or SFC logic you would be using so I can't comment on what your system would do or not do.
  
  There are many different operational philosophies on locking modes, driving the mode (once or multiple times), waiting on valve, not waiting and logic moving on, failing and executing "HOLD" logic, etc and they all have their merits. The Emerson PCSD can support these philosophies based on configured module options and how SFC logic is written.
  
  The real question is what do you want it to do? DeltaV is flexible enough to support really anything you want.

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• Devpriy sahu

  

  • 7 Jan 2018 4:40 AM

  In reply to Matt Stoner:

  Thanks alot, very useful. I will go through the specific application and get back.

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• Devpriy sahu

  

  • 7 Jan 2018 4:41 AM

  In reply to Rachelle McWright:

  Thanks Rachelle, but this doesn't clarify much.

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