Best Book on PID ??

There is a book called PID Primer for sale on the these groups every now and then. It seems to cover the basics very well.

And for Rich PID = Proportional Intregral Differential

as applied to tuning instrument control circuits. This applies equally to both electronic and pnuematic instrumentation.

If you mean the controller, here's a start:

It's much more for writing software more than for building circuits but there's some generally useful information in there -- and I think you'll be able to figure out how to do integrators & differentiators with op-amps.

--

Tim Wescott
Wescott Design Services
http://www.wescottdesign.com

Behold, Jim Thompson signalled from keyed 4-1000A filament:

PID?

Jim....you really oughtta see a doctor :-/

;-p

--
Gregg t3h g33k
"Ratings are for transistors....tubes have guidelines"
http://geek.scorpiorising.ca

Proportional-Integral-Derivative. It was invented more than 75 years ago. It refers to feedback control with terms proportional to the error, the integrated error and the derivative of the error wrt time. (error being Process Variable (PV) - Setpoint (SP)).

Determining the three proportional terms is "tuning" the controller. Over 90% of process control loops are PI or PID.

Try

for some GREAT stuff especially the PID controls.

OK, I'm biased, I actually built a lot of his equipment and was impressed with the precision of the mechanics and the true realtime software in Windows.

Jay

of which 1/3 provide a significant process improvement, 1/3 provide little or no process improvement and 1/3 make the process worse - due almost entirely to the inability of users to tune them correctly.

I wonder if autotuning has helped the situation any - probably not much, I imagine the installed base of non-auto-tuning units isnt going to be replaced in a hurry.

Cheers Terry

There is PID without tears on Embedded.com (I think), which a simplistic view.

Then there is the text (Astrom) I have which goes from the basics to adaptive controllers etc. PID controllers Theory ,design tuning. Lotsa good stuff.

s=books&n=507846

Cheers

Best book? It all comes down to some nasty math.

"Servo Mechanism Analysis", by Thaler and Brown, is probably as good a book as any... It's probably even on your bookshelf, as it is a good 50 years old.

There is no easy way out of these problems, either you characterize the open loop system, and design a proper PID equation to control it, or you fudge things and hope for the best. Computer based servo loops have made fudging things much easier than it used to be... but I am pretty sure, based on your relationship with computers, that you aren't planning to do a computer based PID.

-Chuck Harris

Jim Thomps> Recommendations for Best Book on PID ??

There are two aspects of this: the most obvious is the linear loop dynamics, the classic Laplace-transform closed-loop response. Then there's the far trickier nonlinear stuff: auto/manual control, bumpless transfer, overshoot, integrator windup, process slew limits (just ask a boiler to go from 0 to 100% steam flow in 30 seconds! Or

100 to zero, even worse!), autotuning, noise, feedforward, and protection from runaway under various conditions. It's the latter messy stuff that most of the textbooks tend to ignore.

John

Computers also make it easy to characterize the open loop and design a pretty good controller, so all is not lost.

You can often make things work well enough by fudging, though. It sometimes amazes me how quickly I can get within 20% of the optimal solution just by rule of thumb. Of course, if you need to be within 5% then you have a lot of work ahead of you...

--

Tim Wescott
Wescott Design Services
http://www.wescottdesign.com

"PID Without a PhD", and that's a "simplified" view, please. Inspired by the directions given to union millwrights by control engineers who aren't allowed to touch the equipment in many, if not most, mills. Written by some schmo named "Wescott". Available through

It certainly doesn't teach control theory, but it will let you twiddle the knobs to get a working system most of the time (predicting how well you'll like the result before you start requires control theory, however).

controllers etc.

I have Astrom's adaptive control book, and I love it. Part of my admiration is inspired by the fact that he devotes a whole chapter to alternatives to adaptive control -- anyone who's writes a book about a pretty new theory then tells you when you don't really need it has integrity, in my view.

--

Tim Wescott
Wescott Design Services
http://www.wescottdesign.com

For learning (i.e., some math but not dense page after page of it) look at "Control System Design Guide," George Ellis, ISBN 0-12-237461-4. I have (and enjoyed) the 2nd edition of the book; the ISBN is for the 3rd, published in 2004.

Web site, free companion software:

--
Rich Webb   Norfolk, VA

You say that like it's a bad thing! ;-)

Best regards, Spehro Pefhany

--
"it's the network..."                          "The Journey is the reward"
speff@interlog.com             Info for manufacturers: http://www.trexon.com
Embedded software/hardware/analog  Info for designers:  http://www.speff.com

Sorry Tim ;D

PID with out a PHD is a very good beginning spot. Its where I had started, and wound up later with Astrom.

I never made the connection.

Cheers

view.

adaptive controllers etc.

the

True. Spent early years on petrochemical plant control&instrumentation. Safe pneumatics, 3-15psi range (Foxboro, Honeywell, Taylor etc). Air driven analogues of all the elecronic stuff that's about now, such as square root extractors, multipliers, mass flow computers etc. All process control by pneumatic PID controllers/recorders. The control courses all offered numerous pat equations for optimising the plant dynamics. We learnt to our dismay the equations looked neat in a textbook but useless on real plant. Most of the control systems ended up proportionally slugged down to near stupidity, with only the occasional bit of integral to wind down sticky setups. 'Reset' never had chance to get a look in. I never did identify one of those mooted ideal systems that could be classically tuned. The real world stuff had many processes at work in // and they -all- interacted. Lowest common denominator was the tuning rule. regards john

Right. I've rarely seen derivative do much to a real-world process but make it go nuts, the main exception being fast motion control servos. I read that derivative feedback was discovered accidentally because of a manufacturing defect in a pneumatic p+i controller, circa 1930 or something. There's a story somewhere.

I did manage to fry a few hundred k$ worth of NMR probes a while back. The main system control software (a c++ horror) would occasionally ask my box to go to +3000 centigrade, so I dutifully turned the heater power to max and waited for null. We had to add a battery-backed serial-protocol blackbox recorder to our uP code to catch them in the act. Then added a max_temp variable that can *only* be manually set from the front panel of our controller. This controller includes a setpoint slew limiter that creeps even slower when we're within 5 degrees of the setpoint, to guarantee no overshoot; a few degrees over and we can poach an enzyme that a thousand rabbits died to make.

John

Oh yes. One of the best papers I have read lately is: "An Electronic Throttle Control Strategy Including Compensation of Friction and Limp-Home Effects" Deur, Pavkovic et al, IEEE industry apps may/june 2004 vol 40 no.3 pp821-834

These guys take the whole shebang into account. Interestingly enough they optimise the large-signal step response by omitting the setpoint from the P & D terms (something Astrom et al talk about).

Cheers Terry

Do you want to understand it or do you just need to tune it?

If the later, search on "Ziegler-Nichols". It's a technique that will get your loop tuned and running smooth in short order. If the former, there is no end to the options but before you spend money, search on "PID Controller" and you'll find plenty of info.

73 K3PID Ron H.

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Well done. What's a few hundred k$ here and there. :-) Would hope the C++ programmers were terminated with maximum predjuduce. Best I've done is poisoning (ISTR) 10 tons of Platinum oxide catalyst. Was told the stuff is biblically expensive but they never brought up its value. At the time there was an explosion and fire and I'd been called out to overide some auto ESD trips allowing isolation of a plant segment. regards john