Emerson Exchange 365

Ditners,
As Jason Brumfield mentioned, there a several ways to do this. I thought of characterizer blocks in the path from the Level controller output to the slave flow loop setpoint as well as in the path from the slave flow controller output to the AO block to handle the conditions you mentioned. Note that you have to use the "reverse" characterization feature of the characterizer block in the bkcal_out of the downstream block. But, this is kind of mess!

Note that we have to keep the level controller in automatic during the time the requested flow setpoint is less than 5% so it will continue to control properly (integral will be turned off since slave loop is low limited) and eventually raise the requested slave flow loop SP>5%. Thus, I don't think that Tracking on the slave would allow this since the master LIC Output will be set equal to the actual SP of the flow loop. However, building on Jason's idea for managing the out limits on the slave flow loop, try this:

Simplified code:

If (FLOW/PID1/SP<5%) or (FLOW/PID1/OUT <5%) THEN FLOW/PID1/OUT_LO_LIM :=0 AND FLOW/PID1/OUT_HI_LIM :=0;
If (FLOW/PID1/SP>5%) THEN FLOW/PID1/OUT_LO_LIM :=0 AND FLOW/PID1/OUT_HI_LIM :=0;

I haven't had time to test this but if you are interested in this method, let me know if you have question and we can dig into the details. Note that any method that interrupts normal PID control will cause a limit cycle of the level and flow when the process is in this region.
Good luck!
Jaems