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Morning. What I’ve done for level when I was working more with food processing and some liquid process was to make a FBD routine and use the scaling functions. You then can scale your analog input and have the scale output (tag) be your process variable. You would still need a setpoint probably but that may come in handy someday. That works real well even what I’m doing now with the VFD’s on the air handler projects I’ve been working on.
Also you could use a compare and go open 100% til the level is at say 80% of what you need and then start the PID and throttle the valve closed on proportional gain only. That’s what we did with tank levels in big tanks at a water utility I worked for.
Lastly, you could create logic to say limit the level without a setpoint, say take the HH tank level in a subtract instruction and use the new tag as a target in another compare to close the valve, maybe without a PID. An example would be 26.5′ minus 3.0′ and the destination would be the new tag, which when used in a GEQ (23.5′) would close the valve. Hope this helps. I can’t possibly think that anything I would say you haven’t already though of. Have a great weekend!!