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Force Setpoint with EDC in Cascade Mode

I am using the EDC and DCC blocks for the first time but I am having an issue. I am using the Force Setpoint capability but I'm struggling to get it to work when the EDC block in in Cascade mode. I have the Force Setpoint in CAS option selected in DEVICE_OPTS but the Force Setpoint does not override the setpoint  externally wired to the CAS_IN_D. According to BOL, the Force Setpoint should be used but this is not the behavior that I am witnessing on my simulate system ( I have not tried it on a controller yet). The Force Setpoint works as intended in Auto mode. Any ideas?

From BOL:

If:
the Force Setpoint in CAS device option is selected, and
the actual mode is Cascade, and
FORCE_SP_D transitions from False to True, and
there is no shutdown or interlock active, and
the permissive conditions are satisfied (SHUTDOWN_D is False, INTERLOCK _D is True, and PERMISSIVE_D is True),
then CAS_IN_D is a copy of FORCE_SP_VAL, even if CAS_IN_D is wired externally (CAS_IN_D behaves like SP_D when SP_D is wired externally).

JoshC
  • Matt Stoner
    Josh,

    Change what you have wired to EDC/CAS_IN_D to be an internal reference to that parameter (remove the wire) and it should work properly. I thought that it was documented to not have a wire but your excerpt says otherwise. This is why the CAS_IN_D isn't show as an input parameter like the DC block was prior.
  • JoshC

    In reply to Matt Stoner:

    Good to know. Thanks Matt
  • JoshC

    In reply to Matt Stoner:

    I tried what you suggested and I guess it works as designed but still not that great. On the FORCE_SP_D pulsing true, the EDC does change to the FORCE_SP_VAL, but then on the next scan the EDC block reverts back to the CAS_IN_D internally referenced parameter. Is there a practical way to utilize the Force Setpoints when the EDC block is in Cascasde mode?
  • Matt Stoner

    In reply to JoshC:

    Do you have logic updating the parameter that use to be wired somewhere that is overwriting the Force SP on the next scan?

    Force Setpoints are one-shots which means the condition has to become false and then true again for them to occur again.
  • JoshC

    In reply to Matt Stoner:

    That's exactly what's happening but isn't that typical for Cascades? Is the intent behind Force Setpoints to override the operator when in Auto without having to change the mode of the block (as I've done in older versions of DeltaV) and therefore not really applicable to Cascade Mode?
  • Matt Stoner

    In reply to JoshC:

    The intent is to have condition "attempt" to change a SP once (You pick the mode(s) you want them to work in and it will respond if possible i.e. interlocks active it will attempt but not complete as example) and not continually keep changing overwriting every scan.

    In cascade we try to do the same thing with logic sending a SP once when needed and not continually writing the CAS_IN every scan.
  • JoshC

    In reply to Matt Stoner:

    How do you only write to the CAS_IN once? Use a PDE, NDE, and two ACTs (assuming two-state EDC)?
  • Matt Stoner

    In reply to JoshC:

    You can use pulse actions in Steps (Phases, EMs, SFC, etc) to write the SP. What are you controlling? Example Agitator or Sump pump you can just use Force SPs and don't require and logic. Set the modes they work and write the conditions and if block is in that mode it will change the SP.

    There is a Module Template (VLV_DCC_EDC) in v13 of a valve pre-configured with DCC and EDC, does your configuration look similar to that?
  • JoshC

    In reply to Matt Stoner:

    My configuration is similar to the VLV_DCC_EDC template. That makes sense with the pulse actions. With my particular application I was driving the CAS_IN with logic within my FB control mode. I can see how the Force setpoints would make sense when used in conjunction with PLM or SFC.

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