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EDC Block Modes (RCAS?)

I work at a facility where I am the sole maintainer of a new DeltaV (14.3.1) system.

I'm working through creating some new logic for one of our systems and I'm trying to come up with some philosophical guidelines that I will use going forward for uniformity. One thing that I struggle with a bit is what the purpose of "RCAS" and "ROUT" is. Coming from other systems, I take RCAS/ROUT to indicate that a loop is being controlled by something "supervisory" rather than simply being commanded by another loop via the standard Cascade approach (parent loop and a child loop).

I have some discrete valves (open/closed) that I intend to operate in a sequence, and I want to take control of those valves and indicate to the operator that supervisory controls are in command. In my mind, I would simply place these discrete valves in RCAS and set the SP of the valve according to what I want it to do.

However, I've come to realize that EDC blocks do not appear to allow RCAS, and the documentation supports that finding by specifying explicitly that only AUTO and CAS are valid modes. Can someone help me understand why this is the case? Is there something that I am missing that will allow me to put these discrete devices into RCAS? What do you recommend as the intuitive approach to what I'm trying to do? Just use CAS instead?

Joshua Granger
  • vmvmhatre
    EDC block does not have 'RCAS' as permitted mode. EDC block have following permitted modes:
    1. AUTO: In this mode SP_D can be written through HMI (also can be written through logic).
    2. CAS: In this mode SP_D is calculated from CAS_IN_D. This CAS_IN_D value can be set in following ways:
    a. By Equipment Module owning this discrete device
    b. External logic (e.g. other control module logic)
    c. Phase or SFC logic (supervisory logic)
    d. EDC block itself by Force setpoint

    Normally EDC block is operated in CAS mode (writing setpoint to CAS_IN_D) when supervisory control (like phase or SFC) is active.

    Following way can be used to indicate operator that supervisory control is active:
    Owner name can be written in string parameter and can be displayed to operator through faceplate.
  • gamella

    In reply to vmvmhatre:

    Also note that SP_D may be internally written by EDC block itself, as explained in CAS mode EDC block copies CAS_IN_D into SP_D but also when interlocked and EDC settings are set to track PV. Writting into SP_D from an external module may generate unexpected behavior due to SP_D concurrent overwrite; specially if something is wired into EDC SP_D.
  • gamella
    DeltaV Native:
    When in CAS EDC Setpoint is set by supervisory control, and EDC generates OUT_D and OUTPUT values as defined into state mask for current OUT_D
    When in AUTO EDC Setpoint is set by OPERATOR, and EDC generates OUT_D and OUTPUT values as defined into state mask for current OUT_D
    When in MAN EDC OUT_D is by OPERATOR and EDC sets OUTPUT values as defined into state mask for current OUT_D

    RCAS and ROUT are specific to regulatory control in DeltaV.
    Remote modes, RCAS and ROUT, provide MODE SHEDDING additional functionality . This is, when SHED_TIME > 0 and RCAS_IN (or ROUT_IN if target mode is ROUT) value is not changed within SHED_TIME time ACTUAL mode of block changes as defined into SHED_OPT parameter.
    This feature may be used in when setpoints are set from an external software implementing advanced control (third party predictive/adaptative control software packages in example) to prevent issues if connection between that external software and DeltaV is broken.
    Note also that CAS/RCAS and ROUT have their own set of related parameters:
    - CAS: CAS_IN, BKCAL_OUT
    - RCAS: RCAS_IN, RCAS_OUT
    - ROUT: ROUT_IN, ROUT_OUT
    So, it is not really required to include logic to store/recover SETPOINT for each mode because each mode has it's own placeholder.
    It is even possible to include CONTROL MODULE into three different regulatory control loops and select which one is active by performing a mode change.
  • Joshua Granger

    In reply to gamella:

    This is very helpful - thanks for sharing. I did not know about the inclusion of mode-shedding capabilities. I will do my controls in CAS mode when in "supervisory" command.

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