PID Controller

On Sep 24, 4:22 am, pnacht...@gmail.com wrote:
> On Sep 23, 8:28 am, Vladimir Vassilevsky <antispam_bo...@hotmail.com>
> wrote:
>
>
>
> > Peter Nachtwey wrote:
> > >  >> I sometimes add feed forwards, a 2nd derivative and/or an output
> > >  >> filter.  I would love to see your solution for the Bode plot below.
> > >  >>ftp://ftp.deltacompsys.com/public/NG/Bode%20Plot.rtf
>
> > Peter,
>
> > Your Bode plot does not make any sense because it is a response of the
> > *ideal* LTI system of the 2nd order. A properly designed PID can
> > compensate the 2nd order system to any accuracy. Which means that you
> > can choose whatever control loop parameters you like.
>
> > For example:
>
> > P = 0.5  Ti = 5ms, Td = 50ms
>
> > This provides for the control bandwidth of mere 32Hz with the overdumped
> > response.
>
> > If you ask me for good, I will design the PID function which compensates
> > your plant up to any given frequency :)
>
> > Sure, this is nonsense. In practice, there are other limitations such as
> > the accuracy of the model, the tolerances, etc. etc. Also, the control
> > systems theory says nothing about the engine oil getting tough in winter.
>
> > >  > Isn't a compensation of a single peak by zero in PID loop a scholar
> > >  > problem?
> > > Who needs a zero? This is not a scholar problem.
>
> > Ok, not a scholar problem, but rather tedious exersize in math. Solving
> > of the algebraic equations of the 3rd order.
>
> > > I must control these
> > > kinds of systems every day.  No problem for me but I haven't seen
> > > anybody else find a solution.  It isn't really that hard.
>
> > Reinventing the wheel?
>
> > >  > Unfortunately, the Bode plot makes sense only for LTI systems with the
> > >  > monotonic response.
>
> > > Well, what is it, are Bode plots useful or not?
>
> > Bode plots give some idea. However you should not overestimate their
> > validity.
>
> > >  >> Fine, where is your example filter?  I provided one.
>
> > See the explanations above.
>
> > >  >> How do you get the Bode plot?  Don't worry,  I have one.
> > >  >> What do you do with the Bode plot?
> > >  >> How do you use it to determine the filter and the coefficients?
> > >  >> What is your best solution?
>
> > I don't like the shamanism and prefer the analytic approach.
>
> > >  > I would try to notch out the peak and then apply a PID, may be with a
> > >  > higher order loop.
>
> > > Notch?  Who needs a notch filter for something so trivial?  It just
> > > takes some calculations for a small PID augmentation.   A higher order
> > > loop?  Hmmm.  Can't you see from the Bode plot that this is a type 0
> > > under damp system?
>
> > No idea what is type 0.  H(s) = 1/(S^2 + QS + 1) perhaps?
>
> > >  A PID should be able to handle this easily.
>
> > Not just easily, but *ideally*. There is no point of using the heavy
> > methods intended for more complex cases.
>
> > >  I can
> > > make it harder though.
>
> > What statement are you trying to prove or disprove?
>
> > > Listening to you one would think that industry would come to a halt
> > > because PIDs are NOT good enough.
>
> > Eh?
>
> > > I think it is people that aren't good
> > > enough.
>
> > The mass ignorance is a blessing for the shamans AKA consultants :-)
>
> > > I am waiting for the Vladi-filter. :)  At least show us a transfer
> > > function.
>
> > Here we go, Chekhov :)
>
> > Vladimir Vassilevsky
> > DSP and Mixed Signal Design Consultanthttp://www.abvolt.com
>
> OK, why did you provide such a miserable example of a PID in your
> first reply and suggest that is all one needs to know.  You know
> better.   Notch filters, lead compensators, double integrators,
> bashing PIDs, dead time,  none of this is necessary and is just a
> distraction that cluttered up the answer to an example of PID code.
> If the noise or quantizing is too great then add a low pass filter to
> the PID.  The PID is still valid.  Higher order system will require
> extra derivative gains but that is just an augmentation to the PID.
>
> Tuning a PID is hard enough for most people.  Throwing distractions
> like those mentioned above makes things even more confusing.  If you
> designed your Vladi-filter into a product then how do you expect the
> customers to tune it?  How many customers can tune a lead lag filter
> with an extra integrator?   One may be able to tune a PI controller
> with a low pass filter.   It works out to the same thing as the (s+a)/
> (s*(s+b)) you posted below so how can you bash a PI with a low pass
> filter?   I will stick to the PID for my products because it is what
> the customers are familiar with.  That doesn't mean I don't have all
> the augmentations I mentioned above.  The customers don't need to use
> them if they don't need them or are comfortable with them.
>
> Peter Nachtwey

Customers don't tune such a controller - you are missing the point.
These are fixed controller designs done at the factors for
applications that require high bandwidth and superior performance -
disk drives and the like.

On Sep 23, 11:34 am, gay.highlan...@yahoo.co.uk wrote:
> On Sep 24, 4:22 am, pnacht...@gmail.com wrote:
> Customers don't tune such a controller - you are missing the point.

No, it is you and others that have missed the point.  The OP wanted
code for a PID so I provided a simple example from a DSP book.  So far
I am the only one to provide such code after all these posts.
Vladimir's example wasn't incredible, it was pathetic because he
didn't scale the PID gains by the sample time. I hope he knows
better.  There have been many non-relevant and vague posts about PIDs
not being suitable, notch filters, phase leads, double integrators and
dead time. All that are just distractions given without examples.
Even if you did provide a Vladi-filter that worked do you think it be
understandable by the OP?  The OP is obviously a rooky asking a simple
question yet there are some that want to make a big deal out of a
small topic with big talk and not backing it up.  I am not
impressed.

Randy, do you still wonder why these newsgroups are dying?  It is hard
to get a simple answer to a simple question.

Peter Nachtwey

<pnachtwey@gmail.com> wrote in message
news:1190582613.618833.180060@g4g2000hsf.googlegroups.com...

> Randy, do you still wonder why these newsgroups are dying?  It is hard
> to get a simple answer to a simple question.

Peter,

Don't you meet enough of idiots in the real life so explaining the trivial
problems to them on your leisure time is fun for you? How far do you want to
go with it? All the way down to 2 x 2 = 4 ? Or feeding from a tea spoon and
changing diapers?
Only a retard can ask for the PID software code, and your explanations are
not going to help. The one who asks the questions like that will never be
any good.  It is fun to discuss the non-trivial things with the intelligent
people; not a homework problems or "give me this" requests.

VLV