So I was watching the Tiger's playoff game at home tonight with my son Steven and I started telling him about a problem from work about a pump that couldn't hold its pressure set point when the system's flow demand increased. They rebuilt the pump but that didn't eliminate the pressure fluctuations. They were now speculating the problem was air entrainment through pipe fittings. I said I thought it was more likely just a bad PID loop than a mechanical issue. For those who aren't familiar, PID stands for Proportional-Integral-Differential and it describes the combination of calculus functions that use a feedback signal of a process variable to adjust an input to the system in order to hold that process variable near its set point when subjected to a varying load. Think of how cruise control in your car works on a hilly road.
So anyway, my knowledge of controls systems was always sketchy at best. It was a "dummy rule" class for me. In other words, He can't fail all of us dummies so I just have to be average to pass and never worry about this stuff again. The math never made much sense to me. I just memorized some things and wrote down formulas and followed the "integrate something" rule on the exams and prayed for partial credit, and it worked enough. phew.
Except I still do encounter this stuff occasionally at work so it would be helpful to understand the math a bit more before just using trial and error to see if a combination of PID constants stabilizes a process or makes it start oscillating out of control until it faults out and people start yelling at you.
So the conversation with the whiz kid electrical engineering major during a commercial between innings was very helpful. Steven scribbled down this diagram on a sheet of loose leaf and explained how the math works better in 30 seconds than I can remember from sitting through a lot of classes back in 1986. ha, Really, now it all makes sense. Being a dad is cool.