# PID contollers

Discussion in 'Electronic Basics' started by karthik, Dec 22, 2005.

1. ### karthikGuest

What r PID controllers.pls brief me

2. ### John PopelishGuest

A PID controller is a device that compares a measurement to a setpoint
and produces a control output signal that drives something that alters
the condition being measured, such that the measurement is forced
toward the setpoint.

I have written a non mathematical tutorial that explains the function
of the P (proportional), I (integral) and D (derivative) terms
generated in the controller, and how to tune them. It will give you a
feel for what a PID controller does.

http://www.tcnj.edu/~rgraham/PID/popelish.html

3. ### Dan HollandsGuest

A controller that controls an output based on a feedback input using
Proportion, Integral or Derivative (PID)control response

--
Dan Hollands
1120 S Creek Dr
Webster NY 14580
585-872-2606

www.QuickScoreRace.com

4. ### Rich GriseGuest

Good on you!

We need more webpages like this, that we can refer people to.

Thanks!
Rich

5. ### GenomeGuest

I'm an opinionated drunkard but.....

When you see the term PID controller you would do well to steer clear of the
general area where it was mentioned.

PID is an excuse for people to wibble about with things until something
works.

As you can see from Mr Popelish's explanation.... the recommendation is that
you wibble about until it works.

terms of P, I and D.

Since they don't know what you are talking about and you don't either then
you become an expert.

Obviously, since it is working, you must have been right.

Next Tuesday it blows up.... so, since you are the expert, they ask you back

If you are an experienced wibbler then your initial wibbles might be close
and you might make a sensible wibble but you are still a wibbler.

DNA

6. ### John PopelishGuest

You caught me. I am an expert wibbler. They call me in after the
analytical types have tried and failed. The real world is very messy
and nonlinear, and wibbling is sometimes the only way to arrive at a
reasonable solution in a finite amount of time. The method I describe
is orderly and goal oriented wibbling based on years of practical
experience with enough real world systems to fill a large industrial
museum. I do not claim it is the last word on the subject, but an
intuitive place to start in the process of understanding loop tuning.

The tutorial is a summary of my experience refined through several
courses for operators and chemists I taught at a DuPont plant on the
basics of PID control, which was used in conjunction with an elaborate
process simulator I wrote for the Honeywell 3000 DCS system for them
to play with.

7. ### GenomeGuest

One day I'd like to put my bum where my gob is. Next time your analyticals
fail give me a shout and we'll see just how shit I really am.

DNA

8. ### John PopelishGuest

I am sure you would enjoy the educational experience.

I have been called in to "fix" the tuning on a process that would cost
a million dollars a day if I shut it down. It is operating
chaotically (not cycling sinusoidally, but as if it were a strange
attractor), interacting with a half dozen or so other control loops in
various ways, and giving everyone heartburn. They tell me that I can
alter the output value, manually only plus or minus 2% (less than it
is swinging in automatic or cascade mode), but they really don't trust
me to put the loop in manual mode, at all. Essentially all I can do
is watch it (and the other loops) work. And I can change the P, I and
D constants, as long as I am willing to take the blame for any
worsening performance, and especially any out of limits operation or
shut downs.

Plug that into your analysis. ;-)

The thing that is neat about the graphical method I describe in my
tutorial, is that it gives you some simple rules to determine (in a
"you're getting warmer" or "you're getting colder" fashion) which term
is most likely to be causing the trouble and which way it needs to
change to back away, gracefully from that trouble, without having to
pass through any mine fields. And it even works, most of the time,
too.