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Groups > comp.arch.embedded > #29692
| From | Hans-Bernhard Bröker <HBBroeker@t-online.de> |
|---|---|
| Newsgroups | comp.arch.embedded |
| Subject | Re: PID controller: dummy questions |
| Date | 2020-06-25 21:14 +0200 |
| Message-ID | <hlkbd5Fkd9kU1@mid.dfncis.de> (permalink) |
| References | <rd2odq$oiv$1@dont-email.me> |
Am 25.06.2020 um 19:55 schrieb pozz: > Goal = 80°C. Kp = 0.1V/°C. > > FIRST STEP > T = 20°C. Error = 60°C. P = 6V. > Should I set the power supply output voltage to 6V? I think so. > > SECOND STEP > T = 30°C. Error = 50°C. P = 5V. > Should I set Vout=5V or increase Vout by 5V so setting it to 11V? 5 V > The mathematics say the output of PID controller *is* Kp*err, but I'm > not sure. With the increase of temperature, the errore decreases to a > minimum, so the Vout. At the steady state the error should be zero, but > the voltage from the power supply can't be zero. It can be, if your heater overshoots --- for a while. Then your water will begin to loose heat, and the P controller will reactivate your heater. Lather, rinse, repeat. Voila, oscillation: your P controller devolved into the even simpler 2-point controller: Apply heat when too cold, otherwise don't. That's it But more likely, it'll just reach a state a couple degrees below your target, where Kp times that difference yields a heating power that just about compensates the heat loss. In the absence of actual disturbances, that's the state this system will remain at indefinitely. In other words: congratulations, you've just understood what they mean when they say a pure P controller will never actually reach a steady zero-error state. And if the control is sign-constrained (you only have a heater, but you cannot cool), that may apply even more strongly. One somewhat hand-wavy possibility to avoid the latter trap is to artificially bias your control. E.g. define that "control output zero" means "50% of the actual swing of the output", so negative control outputs can have an effect, too. That 50% point may later profit from some more strategic positioning, a.k.a. tweaking.
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PID controller: dummy questions pozz <pozzugno@gmail.com> - 2020-06-25 19:55 +0200
Re: PID controller: dummy questions Hans-Bernhard Bröker <HBBroeker@t-online.de> - 2020-06-25 21:14 +0200
Re: PID controller: dummy questions DJ Delorie <dj@delorie.com> - 2020-06-25 15:29 -0400
Re: PID controller: dummy questions David Brown <david.brown@hesbynett.no> - 2020-06-26 08:43 +0200
Re: PID controller: dummy questions Richard Damon <Richard@Damon-Family.org> - 2020-06-25 22:21 -0400
Re: PID controller: dummy questions pozz <pozzugno@gmail.com> - 2020-06-26 10:59 +0200
Re: PID controller: dummy questions David Brown <david.brown@hesbynett.no> - 2020-06-26 11:07 +0200
Re: PID controller: dummy questions Rick C <gnuarm.deletethisbit@gmail.com> - 2020-06-26 09:10 -0700
Re: PID controller: dummy questions Richard Damon <Richard@Damon-Family.org> - 2020-06-26 12:29 -0400
Re: PID controller: dummy questions Rick C <gnuarm.deletethisbit@gmail.com> - 2020-06-26 12:00 -0700
Re: PID controller: dummy questions Richard Damon <Richard@Damon-Family.org> - 2020-06-26 22:24 -0400
Re: PID controller: dummy questions Paul Rubin <no.email@nospam.invalid> - 2020-06-26 21:41 -0700
Re: PID controller: dummy questions DJ Delorie <dj@delorie.com> - 2020-06-27 01:15 -0400
Re: PID controller: dummy questions Paul Rubin <no.email@nospam.invalid> - 2020-06-26 23:12 -0700
Re: PID controller: dummy questions Rick C <gnuarm.deletethisbit@gmail.com> - 2020-06-27 00:07 -0700
Re: PID controller: dummy questions pozz <pozzugno@gmail.com> - 2020-06-27 16:53 +0200
Re: PID controller: dummy questions David Brown <david.brown@hesbynett.no> - 2020-06-27 17:31 +0200
Re: PID controller: dummy questions Rick C <gnuarm.deletethisbit@gmail.com> - 2020-06-27 10:09 -0700
Re: PID controller: dummy questions Rick C <gnuarm.deletethisbit@gmail.com> - 2020-06-27 15:44 -0700
Re: PID controller: dummy questions Richard Damon <Richard@Damon-Family.org> - 2020-06-27 12:34 -0400
Re: PID controller: dummy questions DJ Delorie <dj@delorie.com> - 2020-06-27 11:51 -0400
Re: PID controller: dummy questions Rick C <gnuarm.deletethisbit@gmail.com> - 2020-06-26 23:06 -0700
Re: PID controller: dummy questions Paul Rubin <no.email@nospam.invalid> - 2020-06-26 23:18 -0700
Re: PID controller: dummy questions Rick C <gnuarm.deletethisbit@gmail.com> - 2020-06-27 00:23 -0700
Re: PID controller: dummy questions Tauno Voipio <tauno.voipio@notused.fi.invalid> - 2020-06-27 10:28 +0300
Re: PID controller: dummy questions Richard Damon <Richard@Damon-Family.org> - 2020-06-27 18:13 -0400
Re: PID controller: dummy questions Hans-Bernhard Bröker <HBBroeker@t-online.de> - 2020-06-26 22:30 +0200
Re: PID controller: dummy questions Phil Martel <pomartel@comcast.net> - 2020-06-28 13:10 -0400
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