View Issue Details

Jump to NotesJump to History
IDProjectCategoryView StatusDate SubmittedLast Update
000780830020: MDISDocumentation Erratapublic2022-02-28 11:492022-06-02 13:27
ReporterKenny Bohle Assigned ToPaul Hunkar  
PrioritynormalSeveritytextReproducibilityN/A
Status closedResolutionfixed 
Summary0007808: Handling of "State" variable when there is no feedback from subsea (DiscreteOut/DigitalOut)
Description

In https://mantis.opcfoundation.org/view.php?id=7549 the following new wording was proposed regarding the handling of feedback for Instrument/Discrete/Digital Out objects:

"The value of the State value will only update once the subsea system has provided a new value."

This works very well for writable setpoints.

But what shall be done when e.g. a DigitalOut or DiscreteOut object is used to realize one-way commands from the DCS to the subsea system?
For example, objects like "ResetTotalFlow" or "RebootController". The DCS could initiate the reset/reboot via the "SetState(true)" method but there won't be any feedback value in the subsea system (like ResetInProgress or RebootInProgress) which could be used to populate the "State" variable.

The MDIS companion spec should provide guidance for this use case. Possible implementation for the "State" variable could be:

  • The "State" variable is permanently set to "Bad" (StatusCode=TBD) because no feedback value exists
  • The "State" variable is permanently set to 0 with StatusCode Good (dummy variable)
  • ....
TagsNo tags attached.

Relationships

related to 0007549 closedPaul Hunkar WriteValue Method of InstrumentOut ObjectTypes (5.3.5, 5.4.5, 5.5.5): definition of the feedback value is unclear 

Activities

Paul Hunkar

2022-04-21 13:41

manager   ~0016604

was discussed in call - agreed to document the special use cases (i.e. where it is used as a command) - the value would be just set to the value written to the object (not feedback - since no feedback will occur)

Paul Hunkar

2022-06-02 12:53

manager   ~0016788

There are several options:
could extend the previous sentence with "For objects that are aggregated into or used not directly as an instrument, the value of the ProcessVariable can be updated directly by the method"
or "For objects that are aggregated into or used not directly as an instrument, the behaviour of the ProcessVariable is vendor specific"
or "For objects that are aggregated into or used not directly as an instrument, the value ProcessVariable shall be 0"
note: I don't like that last option - a hardcoded value (any value) is not recommended by me.

Paul Hunkar

2022-06-02 13:23

manager   ~0016789

Updated text as follows:

The value of the State value Variable will shall only be updated once the subsea system has provided a new value. For Objects that are used as a command, the value of the State Variable shall be updated directly to the value provided by the State parameter of the Method.

Paul Hunkar

2022-06-02 13:27

manager   ~0016790

Review text updates in call, agreed to change and closed issue

Issue History

Date Modified Username Field Change
2022-02-28 11:49 Kenny Bohle New Issue
2022-04-21 13:38 Paul Hunkar Assigned To => Paul Hunkar
2022-04-21 13:38 Paul Hunkar Status new => assigned
2022-04-21 13:41 Paul Hunkar Note Added: 0016604
2022-04-21 14:09 Paul Hunkar Relationship added related to 0007549
2022-06-02 12:53 Paul Hunkar Note Added: 0016788
2022-06-02 13:23 Paul Hunkar Status assigned => resolved
2022-06-02 13:23 Paul Hunkar Resolution open => fixed
2022-06-02 13:23 Paul Hunkar Note Added: 0016789
2022-06-02 13:27 Paul Hunkar Status resolved => closed
2022-06-02 13:27 Paul Hunkar Note Added: 0016790