I worked on but didn't design the control algorithm for a zone controller where each of the five zones interacted with each other because they were part of a si

I worked on but didn't design the control algorithm for a zone controller where each of the five zones interacted with each other because they were part of a six foot tall quartz tube. There was compensation for the heating elements being nonlinear. And because the thermal mass was basically nothing radiation losses dominated it's behavior. Some of the control variables were squared then scaled. And zero overshoot was allowed for the hottest zone. And because it was a batch process it had to heat up quick. I had to re-tune one after they replaced the quartz chamber. Blah.