# Pid Controllers



## mlappin (Jun 25, 2009)

Anybody have any experience with them, about how to choose one?

From another forum an ideal has been tossed around about using an O2 sensor to constantly adjust the secondary air on a gasifier OWB. Manually adjust the boiler until it's decided that this is the best setting, then program the pid to constantly adjust to keep the O2 sensor at that reading by allowing more or less air into the secondary chamber by having a servo motor make adjustments to the secondary air inlet baffle.

Unfortunately the guy that claimed to have it all figured out hasn't been seen nor heard from in months.

http://www.haytalk.com/forums/topic/21364-outdoor-wood-boilers/#entry119120


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## askinner (Nov 15, 2010)

My irrigation setup is on PID control, the PID controller is integrated in the VFD. I have it set to maintain a set pressure that I dial in either by the controller or serial commands over the web. Took me ages to get the PID setup to maintain the set pressure without hunting, but works excellent now.

I read heaps of articles on tuning, but stumbled across one that gave a starting point for pressure controlled applications, tried that, and pretty well nailed it other than a bit of fine tuning, although still a little overshoot at startup I need to be careful with. Some of the calcs used for working out PID tuning are professor level! I think most of the tuning is trial and error from my experience.


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## Mike120 (May 4, 2009)

Most newer process control systems do not require manual loop tuning because trial and error can take forever to find a stable set of loop values. It was a black art and a lost one. Most of the new systems I've been involved with either use loop optimization algorithms or, if the response time is longer, they'll have a self-tuning feature where very small changes are introduced which allow the controller to calculate the optimal tuning values. I've still got a set of old instrumentation and control text books but you're probably better off buying a package like Fireye's Fuel Air Ratio Controller. I've used it in the past for industrial applications and it was almost painless........but not quite.


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## mlappin (Jun 25, 2009)

Ouch, Fireyes system is a third the cost of what I could buy a Portage and Main boiler for. That's what the discussion was about, using a cheap, off the shelf generic controller.

Use a VFD on our drying setup with a built in pid controller, definitely was a PITA to get set up to work correctly most of the time.


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## slowzuki (Mar 8, 2011)

I had all the autocontrols classes at one point to do the differential equations to setup PID controllers but its long gone now. I do remember using derivative aspect of the controls is a lot easier than the integral aspect in terms of getting system stability.

Trying to remember some of the stuff, Laplace transforms, stability calculations, etc. Its not so bad once you do it a bit. Start with large values of damping so you don't break anything.


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## mlappin (Jun 25, 2009)

Very nice people here, very patient and helpful.

http://www.instrumart.com


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