Warren, I understand your message as an afterwards try to put some sense in your original question, but if you write
> D = (Input - Last_Input) then this clearly denotes the differential part of a PID controller (with the multiplication with the coefficient for the differential part coming later) If you add now > In a complete controller the input to this > gain block would typically come from a > pre-filter, and the prefilter's input > from the error difference between > the setpoint and the feedback, etc. saying that "input is something complete different then I fear that this discusion is drifting into complete nonsense because if "Input" denotes an entity which contains an error signal in any form then > D = (Input - Last_Input) is something that is ill defined and has nothing to do with the differential part of a PID controller. > I wanted to keep the math as simple as possible... Good idea but if simplification creates something wrong then the simplification has gone one step to far. Best regards Ulrich > -----Ursprungliche Nachricht----- > Von: time-nuts-boun...@febo.com > [mailto:time-nuts-boun...@febo.com] Im Auftrag von WarrenS > Gesendet: Donnerstag, 17. April 2014 11:54 > An: Discussion of precise time and frequency measurement > Betreff: Re: [time-nuts] PI Math question > > > Ulrich > > That is correct, none of these simple code blocks form a > controller. This is just a block of code that could be used > for the PI gain function of > a controller. > In a complete controller the input to this gain block would > typically come > from a pre-filter, > and the prefilter's input from the error difference between > the setpoint and > the feedback, etc. > I wanted to keep the math as simple as possible by only > including this > section of code. > > My question was does the math in these four blocks of code > all provide the > same exact input to output function. > What the code is being used for is not really relevant to the answer. > > simple example: > Does the code X = 3Y have the same input to output function > as X = 4 + 2 + > (1+2) *Y - 6? > Just because they look different does not mean they are > different. The question was meant to be a simple math > exercise like does 3y = (1+2)y? The answer does not need any > high level math or depend on the value of y or > what the code is being used for. > > ws > > ******************* > ----- Original Message ----- > From: "Ulrich Bangert" <df...@ulrich-bangert.de> > To: "'Discussion of precise time and frequency measurement'" > <time-nuts@febo.com> > Sent: Thursday, April 17, 2014 1:14 AM > Subject: Re: [time-nuts] PI Math question > > > > Warren, > > > > the job of a controller, regardless of P, PI od PID, is to minimize > > the error between a process value and its setpoint. Since I see no > > setpoint value in any of your versions my 50 ct is that > none of them > > really incorporates a controller at all and that for this > reason the > > question whether they produce the same output is close to being > > irrelevant. > > > > Best regards > > > > Ulrich > > > >> -----Ursprungliche Nachricht----- > >> Von: time-nuts-boun...@febo.com > [mailto:time-nuts-boun...@febo.com] > >> Im Auftrag von WarrenS > >> Gesendet: Mittwoch, 16. April 2014 18:50 > >> An: Discussion of precise time and frequency measurement > >> Betreff: [time-nuts] PI Math question > >> > >> A question to the math time-nuts > >> > >> With the values of K1, K2 & K3 constant, > >> and the initial state of I#1, I#2 and Last_Input all zero assuming > >> there is no rounding, clipping or overflow in the math and that if > >> I've made any obvious dumb typo errors, that they are corrected, > >> > >> Given this PID type of controller; > >> D = (Input - Last_Input)) > >> Last_Input = Input > >> I#1 = I#1 + (K1 * Input) > >> I#2 = I#2 + (K2 * D) > >> Output = I#1 + I#2 + (K3 * Input) > >> > >> Is the above Input to Output's transfer function any > different than > >> any of the following more simplified versions of PI controllers? > >> Or asked another way, if each of the four codes are given the > >> exact same > >> input string and same K Gains, will the difference between > >> any of their outputs ever be non zero? > >> > >> > >> a) > >> D = Input - Last_Input > >> Last_Input = Input > >> I#1 = I#1 + (K1 * Input) + (K2 * D) > >> Output = (K3 * Input) + I#1 > >> > >> b) > >> D = (Input - Last_Input) > >> Last_Input = Input > >> Output = Output + (K1 * Input) + (K2 + K3) * D > >> > >> a) > >> I#1 = I#1 + (K1 * Input) > >> Output = I#1 + ((K2 + K3) * Input) > >> > >> ws > >> > > _______________________________________________ > time-nuts mailing list -- time-nuts@febo.com > To unsubscribe, go to > https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts > and follow the instructions there. _______________________________________________ time-nuts mailing list -- time-nuts@febo.com To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there.
