Lancie1 - I rather believe you did, or how can you use LIMs with different data...
Lancie1 said:
I use the LIM comparison instruction, which combines two into one, so you might only need two LIM's.
Anyway I replied to critiscism with :-
daba said:
An example only - Minimum Quantities required for successful production.
I suppose I should have asked in the rhetoric - "Can we make pancakes today?"
But I think it served it's purpose.
and people still kept coming back at me - let it go !
'nuff said .....
As for a practical examples Lancie1, yes I'm sure I could find several if I needed to, I do know I have needed this logic construction in the past, but here's one from memory :-
Pastuerisation Temperature >= Minimum Temperature
Pastueriser Flowrate >= Minimum Flowrate
Regen Section Return Flow >= Minimum Flowrate
Steam Pressure >= Minimum Pressure
Coolant Flow >= Minumum Flowrate
Coolant Pressure >= Minimum Pressure
Inlet Buffer Tank Level >= Minimum Forward Flow Level
Sterile Buffer Tank Level <= Maximum Holding level
= Allowed to go Forward Flow
If I had coded this as a series of GEQs LEQs etc. on the same rung (and I'm not admitting whether I did or not, to avert any response), then there would be nothing wrong with it, It would work.
Like I said in my first post, there is absolutely
nothing wrong with constructing logic with all the conditionals in series on one rung, I didn't say it made the code easier or harder to follow, or that it made the program execute faster or slower, I simply stated that it is logically OK to do it. In fact in ControlLogix, it
can make the program execute faster if you place the instruction most likely to be false at the beginning of the rung, the controller stops evaluating further conditional instructions because nothing can make it true again.
Lancie1 said:
EDIT: I looked through my accumulation of PLC programs. The cloeset thing I found was 3 EQU (equal) comparisons. In another case I used 2 GEQ's and 1 NEQ on the same rung in series. By induction, it seems that the case of 4 comparisons in series would rarely NEED to occur.
so ! : just because you've never done it - don't assume no-one else has either.