Best Book on PID ??

Are you saying that the people who design switcher chips don't know much about control strategies? Shocking, Shocking!

John

I'd agree if we were talking about PI controllers, but PID are somewhat different--the D term is there to compensate for slow transducers such as motors and heaters.

The slow transducers put a few wrinkles in practical control systems that are different from ordinary amplifers: windup in motors and asymmetrical slewing in heaters. The D term will turn the 2-pole response of a motor into 1-pole so that it can be stabilized, but the settling behaviour won't be anything pretty unless some sort of (nonlinear) windup control is in there somewhere.

Cheers,

Phil Hobbs

I am saying (albeit indirectly) that setpoint weighting/removal is not so easy/obvious in the analogue world. Actually its pretty counter-intuitive if you dont do the maths.

Cheers Terry

It has been writ:

I am the man who designed ABB's Commander line of process controllers, recorders and recording controllers.

If you are doing control of a real process - a heater, tank, pump, catalytic cracking tower, your mother's baking oven - do not follow the above advice.

If you are controlling a hamster exerciser, the above is fine, and will save an awful lot of explanation ...

The whole of ABB instrumentation (when it was Combustion Engineering) had one (count'em one) engineer with the above qualification (and it wasn't me). When I worked at (another process control firm that shall remain nameless) there were none. Figure if you are the above 'You', you are among 10, 50, 100? engineers in the world.

Yep. That sounds a lot like you are talking about Jim Thompson.

But follower amplifiers that drive big, slow, nonlinear devices have all those same problems. Slow is just not as slow. When I first got into process control, it seemed very strange, because I was unfamiliar with the jargon. Then I realized that I have been using oscilloscopes to study amplifiers doing all the things process control was doing, except that now, I could have a cup of coffee while the dynamics settled instead of it all happening in microseconds. but the principles are just the same. Gain bandwidth product, phase shift, slew rate limits, output nonlinearity, recovery from output overdrive, etc. all there.

When I saw the Star Trek episode about the people who moved so fast that they were invisible, I realized that they was how I felt while tuning a control loop.

By Golly, I think he's got it! That's why we can't see the Faeries! ;-)

Cheers! R.

Control System Design Guide.

The first edition is better than the second one. The book became a bit bloated in revision.

John Nagle

Pelvic Inflammatory Disease.

what did you think?

Doug

I don't disagree that there are lots of similarities, or that there's a lot of jargon in control system design that seems intended to preserve job security rather than make concepts clear. (There's a lot of that in some optics disciplines too--it isn't just an EE problem. Not to mention all of anthropology.) If I'm designing e.g. a laser temperature controller, I use Bode plots: one for each of several representative choices of ambient temperature and thermal forcing. PLL design with nonlinear tuning is similar. Not everything is that simple, however.

Lots of control systems have to work in situations where an ugly settling transient will cause destruction--from burned cookies and broken drive belts to loss of life and property. There are very few purely electronic situations (i.e. other than driving mechanical devices or large magnets) where a poor transient response is that serious.

Ordinarily, with an amplifier driving a speaker, say, you can have a few pops and bangs, but no great harm is done, and they can be tuned out during debugging. The nonlinearity is of a simple and intuitive sort, and there is no complex coupling. There is also usually no external forcing, unlike e.g. a motor controller which may have very different loads at different times. It isn't possible to test every situation, and it's the ones we haven't thought about that will turn round and bite us in the backside. Systems that are uncoupled during normal operation, but become coupled due to faults and transients, are a common source of this.

Cheers,

Phil Hobbs

It's interesting that a lot of real-world control loops leave theory way behind, except for the fairly boring region of near-steady-state operation around null. The hairy parts, the transient and exception conditions, revert to art, instinct, and maybe simulation.

I like systems like that.

John

I think you need to quit having sex with people who have open running sores.

Just like life! Imagine that!

Me, Too!

;^j R.

Too much. Its a good thing I read this group for the entertainment more than the technical.

Doug

see this?

-Lasse

So, did you laugh? ;^j R.

I've implemented similar anti-windup schemes (without the metaphysical reasoning); it works quite well for me.