Chitt,
As Adrian and many others have pointed out, you will have issues with this scheme when you have multiple operator stations as well as reliability/maintainability concerns.
Which Operator Station login info do you use if Usernames are different between multiple stations?
How do Area Assignments affect this logic?
What happens if the mode has to change based on process?
The reason I ask is I'm not understanding your requirement to essentially modelock exclusively to the operator based on a computer login and possibly disregard control schemes and/or logic that may be determining what should be occuring based on process conditions.
In my opinion this seems to be backwards and you should want to prevent the operator from making changes/mistakes based on process conditions instead of giving him/her exclusive use.
What I have typically seen is modelock regardless of who is logged in and then allow certain priviledge users bypass this if needed.
So your choices are:
- Write a bunch of custom VB logic somewhere what will be hard to maintain, troubleshoot, etc
- NOT allow Operators to change the mode as some have suggested (which doesn't seem like a very good idea to me)
- Don't allow him to change the mode during "certain" situations (i.e. Supervisor has bypassed, Process is running they cannot change the mode but when in Hold/Shutdown state they can).
The last option could just be a visibility option of the graphic buttons so they can't do it from the graphic (Control Studio would allow) or it could be an enforcment type that would put the mode back if somehow it was changed from Control Studio Online.
Good luck