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On Tue, 30 Nov 2004 16:39:45 +0000, the renowned Guy Macon <http://www.guymacon.com wrote:>


"proportional intergral derivative" 29 hits "proportional intergral differential" 18 hits
Best regards, Spehro Pefhany
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On Tue, 30 Nov 2004 12:54:01 -0500, Spehro Pefhany
[snip]

"intergral" ?:-)
...Jim Thompson
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Yestedy i culdnt spel "Enginie - Now i are wun.
Jim Thompson wrote:

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On Wed, 01 Dec 2004 07:14:01 +1300, the renowned Bruce Durdle
I like the French word for engineer better:
"ingιnieur"
Sounds like it has more to do with ingenuity than pistons and connecting rods. Of course, the Latin root "ingenium" (ability?) is the same for both words.
Best regards, Spehro Pefhany
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Guy Macon wrote:

It's simple: the level of literacy, even among "college boys", is appallingly low. Consider how many write "there" when they mean "their" or "they're".
"Differential" as an adjective refers to the the difference or the distinction between two quantities or states, as in "differential amplifier" and "differential diagnosis". A PID controller is governed by three terms: one is proportional to error, another is the integral (in the mathematical sense) of something, and the third is the derivative (in the mathematical sense) of (probably) something else.
The proportion of people who write "proportional integral differential" is not large considering the proportion of people who say "nucular" and swear it's correct because it derives from "nuculus". I find the reason for that totally uncular. :-D (uncular:nucular::unclear:nuclear)
Jerry
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With few exceptions, hyphens are equally effective--perhaps more so, because e.g., it finds things with 'online' when you enter 'on-line'.
When posting a link, hyphenated search strings are superior. (A double-quote mark tacks a '%A' onto the front of a search term making it difficult to search the Google archive for that term.)
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message

Both are right... Guess what, a 'differential equation', is one including a 'rate of change' (derivative) term...
Best Wishes
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Guy Macon wrote: -- snip --

OK, I'll bite -- what _is_ it good for? I've never done closed-loop control with prepackaged controllers and I've never seen that done elsewhere. I can certainly see reversing the phase of the whole thing, or reversing the phase of the D term if it's coming from some other feedback source (which would imply a second input) but I _can't_ see the point in intentionally establishing an unstable zero in your control system.

-- snip some more --

Many, many software engineers, particularly embedded software engineers are gearheads, and almost all of them drive to work.

Yes, this could be _very_ counter-intuitive to my target audience. There isn't room for it in the talk, but I'll have to think about writing a "pitfalls" paper -- unfortunately I've internalized those pitfalls pretty deeply, so it may be hard to remember all of them.
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Tim Wescott
Wescott Design Services
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Tim Wescott wrote:

My experience is more hands-on than theory, but here is the answer I gave my classes:
In N years of setting up servos, I have never once found a use for it, nor have I found any literature that explains when it might be of some use. I think that somewhere back in the early days someone was told to put in a jumper that reverses the phase of the entire servo (quite handy when someone miswired a section that is really hard to get to), got it wrong, and some other manufacturers have been copying the "feature" ever since.
If one of the theory boys has a better answer, I am all ears.
--
Guy Macon <http://www.guymacon.com


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Guy Macon wrote:

Being able to reverse the sign of the whole thing is good -- one of the old curmudgeonly engineers from whom I learned practical control liked to say that when designing one of these things you should count up all the sign changes in the loop -- then throw in one extra for the one you missed. His circuits always had at least one spot where you could rearrange the inputs to an op amp and reverse the sense of a signal. I follow that now: there's always at least one place in my software where one can insert a '-' and change the sign of the whole thing.
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Tim Wescott
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On Tue, 30 Nov 2004 10:59:17 -0800, Tim Wescott

All controllers I've seen, be they in software or hardware, have a flag or switch to reverse the controller action. Some even let you reverse the output action. Eases up a lot in initial implementation.
I've seen the ones that let you reverse the terms individually but haven't found a need for trying them out. One accidentally had the integral term reversed and I went bonkers trying to tune it before finding the error.
The derivative term is useful when you have a slow process with inertia. Once the controlled variable starts to respond it puts a lid on further controller action which might cause unacceptable overshoot. On the few occasions I do apply it it's usually in homeopathic doses.
- YD.
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OTOH ...
One of the early power system simulation packages developed (I think) by IBM (dates from the days of punched cards so that gives an indication) had a reasonably well documented (for those days) program, luckily...
In the main body of the program prior to calling a subroutine to simulate the voltage regulator was a line of code that reversed the sign of a variable, with a brief note to state that the standard equation assumed the quantity was positive when it was actually negative (or something). Immediately after the start of the subroutine was a line of code that reversed the sign of the same variable, with a brief note to state that the standard equation assumed the quantity was positive when it was actually negative.
We found this after several days of wondering why the simulation of a power system transient indicated an unstable voltage regulator.
But I guess if you get the action of controller wrong it's nice to be able to reverse it very quickly - hopefully before the operators notice!
Bruce
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On Tue, 30 Nov 2004 18:49:28 +0000, the renowned Guy Macon <http://www.guymacon.com wrote:>

According to Liptαk, it's primarily used to introduce a lag into the control loop when the process is very fast or noisy.
Best regards, Spehro Pefhany
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Spehro Pefhany wrote:

I'll search for that. Have you ever used it? It seems like introducing a low-pass would be a much better way to kill noise and add lag at the same time.
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Tim Wescott
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On Tue, 30 Nov 2004 11:08:27 -0800, the renowned Tim Wescott

I've not used it. I may have run into a case, once, where it would have come in handy. The controller really had to be detuned to make it stable.
Best regards, Spehro Pefhany
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Guy Macon wrote:

Shortly after VJ day, Japanese military electronic software began turning up in the surplus stores on Cortland Street (razed to make way for the World Trade Center). I bought a small panel meter, probably out of an airplane cockpit, that had Japanese markings molded into the inside of the case. The design itself had been blindly copied. Prominent in the inside center of the back cover were the letters, "Simpson".
Jerry
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Jerry Avins wrote:

Aaah! Hardware! Hardware!

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Jerry Avins wrote...

Right. Bart Simpson.
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Thanks,
- Win
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Winfield Hill wrote:

http://www.simpsonelectric.com/anaind.htm
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Guy Macon <http://www.guymacon.com wrote in

Could it just be because tachs have no polarization standard? If your system runs away, flick the switch!
Scott
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