To 'PID' or to 'HomeBrew'. Very slow PV

[jazzplayermark 2]

I have an application that needs control of a flow that is very slow to respond. From the time a change is made on the CV until it's seen by the PV is in the neighborhood of 15 minutes. I'm using an SLC 5/03 so the maximum update time is only 10.23 seconds. What is the best way to handle this? Would the PID loop even work for something this slow?

[Michael Lloyd 85]

I would build a stepper. Start a timer, when the timer is done do a compare, if SP > PV increment or decrement CV else if SP is < PV go the other way. Use deadband to constrain CV to a range of PV or in other words don't change CV if the SP and PV are within X of one another. Once the compare is done restart the timer Edited 6 Apr 2014 by Michael Lloyd

[Mickey 71]

Why ? Can you describe the process (hardware)? Edited 6 Apr 2014 by Mickey