Hi,
Out of curiosity, I tried out the approach gamella has suggested in one module.... It works really fine with the use of BG blocks. A clean solution.....
Thanks for sharing this method on the forum.
I had left the BG block IN as "0" considering both PID's in same range, & PID output is connected to CAS_IN. Backcalculations were connected from BG to PID as well.
As Matt has correctly indicated, 'the question is what happens to the the non-selected Loop'. In this case, since the BG block is in LO mode, the respective PID goes to IMAN & hence tracks the CTLSL block back calculation.
The only issue is, if operator wants to keep both loops working & compare the outputs before switching. With a calc block (option 3), it is really easy to customise this by controlling the cascade handshake statuses. But can also be achieved by removing the backcalculations from BG to PID blocks.
(Last time when I implemented this, the requirement was that operator can only switch when this difference is less than 3%. Until then he can still monitor both loops, as they continue to generate outputs like in a automatic override control.) PID coming out of tracking (LO) to AUTO can also have bump on the output, if SP-PV tracking is disabled to mantain SP.
Best Regards,
Amod.