Hi!
When I'm trying to add an external reference parameter into the program script in a calc functional block, I can see a few parameter's fields available, among them there is a field called ".REF" (not ".$REF", but ".REF").
According to the logic implemented in the system, the use of this field is the same (or pretty much the same) as the field ".CV". My question is what is the real use of this field (I mean ".REF")? Does anybody know if there is a
description of this parameter's field in DeltaV help?
Best Regards,
Rachelle McWright: Business Development Manager, Dynamic Simulation: U.S. Gulf Coast
I looked in to this a little bit the other day, and here's my assessment.
Using Watchit to try and read Parameter.REF does not return anything (v 11.3.1) except when referring to a unit alias (which just returns the configured value).
I'd theorize that .REF may be a hook into the default field of an external reference source (the one that is returned when no field is specified, which is different for different types of parameters).
Certainly, $REF returns the path of the reference, but I've never seen .REF in control logic other than for alias referencing. What version of DeltaV is being used here?
First, ".REF" looks to just use the same as ".CV" but I can't confirm that this is always the case in my quick testing.
Second, External Reference parameters can't be changed by logic running in the controller by writting to ".$REF" as it is only set by the download of the configuration.
If you do want to change a reference (".$REF") while the logic is running in the controller, you need to have the parameter type be a dynamic reference parameter.
Note: When changing the dynamic reference parameter with ".$REF", you should confirm that the ".CST" = 0 after changing before the changed reference value is used with any logic. Otherwise you will get a Failure if the value isn't resolved correctly.