I used it in the past ( temperature and conveyor speed) it worked fine. I read that a thermistor could not be used as an PID input. You would have to convert in to temperature first. I passed it up on a battery charger rewrite, because I read the battery dynamics change during the charge. This would mean the constants would have to vary. This would make tuning impossible with a single set of constants. Does this sound right?
Neil
Hello Paul,
I read an excellent article (although I do not remember where) a few years ago about a guy that built a microprocessor control system for fuel injection on a two cylinder engine (lawnmower I think). I read many magazines, and stuff online, so I'm not certain if it was circuit cellar, or on the net. Googling around might find the article. The author had done a fantastic job, I just wish I could remember where the article went..
It may or maynot be useful to your efforts.
James
Actually, with the stepper motor, we don't necessarily need position feedback. Provided there are no missed steps, we can constantly track position.
Funny you should mention, I am working on linearizing - I've collected the data already and have a nice curve. Implementing a characterizer table which has throttle position versus load.
Paul
Yeah, I know, provided you zero it at power-on, of course (which could be as simple as ramming it up against the stop for long enough). Goes without saying perhaps that I don't like to make that presumption.
How nonlinear is it?
Best regards, Spehro Pefhany
That is exactly the presumption made by floppy disk head positioning systems. They usually do not have any sensor to indicate the home position.
-Robert Scott Ypsilanti, Michigan (Reply through this forum, not by direct e-mail to me, as automatic reply address is fake.)
So by having an intergrating stepper motor placed after a positional PID algorithm, what exactly does that yield? A PI controller with amplified I?
Paul
Overall I suppose you could call it a "PII" controller, but so many plants have integrating action that you may as well just call it a PID with an integrating plant and be done with it.
There's noth> So by having an intergrating stepper motor placed after a positional
Engines are notorious for being *very* non-linear - that's about the only way I can express it. If you think about a throttle plate (butterfly valve) and its geometry, you can see how the airflow would be drastically different at low loads versus high loads. So at low loads, small changes in throttle make a huge jump in speed, and this changes a lot at higher loads.
Paul
Wouldn't that have serious problems with noise? Or did you have an unusually clean signal? I guess a temperature loop might indeed qualify as really smooth and that is why you are using DD in the first place.
Walter.
But isn't that the problem with all integrating systems,: "Providing there are no missed steps." You need some way of re-syncing the position once in a while. Murphy's going to get you.
Walter.
First, the driver was inherently integrating (it was actually integrating in software because we had a strict limitation on the speed that we could ramp up the cooler, so it went PDD -> limit -> integrate). Second, the loop closure was at a Hertz or two, so the differentiators were leveled off at around 5-10Hz, which really kept the noise down. And finally, it sits in a proprietary product next to a bunch of other control loops and video acquisition, all of which need to be good to
14-16 bits, so the we _really_ knew our noise reducti> Wouldn't that have serious problems with noise? Or did you have anHave something to add? Share your thoughts — no account required.
Ask the community — no account required