The ultimate goal is to use this valve to control the water temperatures of boilers in a boiler testing lab. By varying the flow through the boiler, I can vary the temperature rise across the boiler. Some of the testing that we do in our lab requires that very tight water temperate tolerances (+/- 0.5 deg F) are maintained for hours while measurements are taken.
Currently, we do this with just regular ball valves. It works, however it can take hours to get the temperatures dialed in. More importantly, because we're in a lab with numerous boilers connected to the same primary flow loop turning off and on, the temperature in the loop can fluctuate up and down by a few degrees throughout the day. Thus, on the occasions when we are running tests which mandate tight tolerances, this can cause us to have to restart the test over several times before we get our results, which is very inconvenient. Hence the desire for automation.
I've played with PIDs before and have found that with careful tuning, they can work to control the valve so that the temperature tolerances are met. However, as soon as I connect a different boiler to the system, the tuning will be all out of whack and have to be re-tuned from scratch. That is why I'm looking into PID-alternative control strategies.
Thanks for the tip with the subroutines/submarines.