Shameless Plug

I have the new issue and plan to read it on the plane tomorrow. Congratulations.

BTW, why is ESP so thin now? Embedded Systems Pamphlet ?????

I remember when it used to be 3 or 4 times longer, consistently.

John

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.)

Try a searching the whole phrase

Google for "proportional integral derivative" gets 18,600

Google for "proportional integral differential" gets 3,060

Search for both and you get 47

It was originally Derivative, and still is to me.

"W>>

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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Congratulations.

I tried to sell them an article a couple of months after the dot-com bubble burst. The word then was that advertising revenue was down, so they had to thin it out. The reduced page-count plus all the suddenly unemployed engineers writing stuff nixed my article for a while (but I have published there recently).

--

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

In 'Control Speak':

Differential: the amount of hysteresis in an on/off controller, such as a home thermostat.

Derivative: The term D * dPV/dT in a PID controller where: D == derivative gain; PV = process variable; T == time. Some controllers use D * dE/dT where E == error.

Lesson: Half of everything is bunk.

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Nicholas O. Lindan, Cleveland, Ohio
Consulting Engineer:  Electronics; Informatics; Photonics.
Remove spaces etc. to reply: n o lindan at net com dot com
psst.. want to buy an f-stop timer? nolindan.com/da/fstop/

system.

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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Engineering is the art of making what you want from things you can get.
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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

--
Engineering is the art of making what you want from things you can get.
¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯

Probably. Though I'm a good speller myself... I just have right-hand-index-finger-gets-out-of-sync-with-left-hand-index-finger typing problems, so I religiously use a spell-checker ;-)

...Jim Thompson

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|  James E.Thompson, P.E.                           |    mens     |
|  Analog Innovations, Inc.                         |     et      |
|  Analog/Mixed-Signal ASIC's and Discrete Systems  |    manus    |
|  Phoenix, Arizona            Voice:(480)460-2350  |             |
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I love to cook with wine.      Sometimes I even put it in the food.

proportional integral derivative - 253,000 hits "proportional integral derivative" - 18,600 hits proportional integral differential - 315,000 hits "proportional integral differential" - 3,060 hits

The quotation marks are important in this case. You want to count the times the phrase is used, not the times that all three words are found on different parts of the page.

I was taught that "Proportional-Integral-Derivative" is the proper term, but the Google search turns up some disturbing uses. It's in an article published in the Geotechnical Testing Journal on astm.org. It is used by Paul Brinks, who appears to be teaching a class on PID at a state univerity. It's used in a paper titled "A Closed Loop Controller for Electron-Beam Evaporators" published in _Review of Scientific Instruments_.

I still think "Proportional-Integral-Differential" is wrong, even a bunch of college boys and one out of six webpages says that it is correct. I just wonder why so many get it wrong.

--
Guy Macon

Both are right... Guess what, a 'differential equation', is one including a 'rate of change' (derivative) term...

Best Wishes

Wah! Hardware! Hardware!

--
Engineering is the art of making what you want from things you can get.
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I tend to agree, but the "wrong way" hinders communication if it is

*too* different from the "right way." If one decides to use a few non-standard fleemishes and the reader can still gloork the meaning from the context, but there ix a limit; If too many ot the vleeps are changed, it becomes harder and qixer to fllf what the wethcz is blorping, and evenually izs is bkb longer possible to ghilred frok at wifx. Dnighth? Ngfipht yk ur! Uvq the hhvd or hnnngh. Blorgk? Blorgk! Blorgkity-blorgk!!!!

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

Right. Bart Simpson.

--
 Thanks,
    - Win

True negative derivative is called (negative) velocity feedback and is used to decrease response time at the expense of overshoot. The frequency response of the system goes up. The system becomes stiff but 'nervous'. Can be used to stabilize systems as the same stiffness can be had with a lower proportional gain.

This is just what one would expect as plain-ole' derivative feedback is used to lessen overshoot at the expense of slower response time.

Think of D as oil: it can be used to slow something down by being thick and greasy or it can speed something up by lubricating it.

Speculation: if the controller is configurable to use derivative on error _or_ derivative on process then the sign of the derivative at the summing junction must change, most modern controllers do this automatically in software but I suppose there are those that don't. The same is true if feed-forward on SP is available.

Not so simple ... it doesn't necessarily make the system unstable: think Nyquist diagram.

I'm not sure what this has to do with software, except to know to shout 'Hardware Error!' and go for a cup of coffee.

FWIW: dual slope and V/F are preferred conversion techniques for process control as there are no 'bad spots'. Also work a charm if synched to the line frequency.

Er, maybe a new audience is needed?

The only requirements for control are monotonicity and repeatability, everything else is icing on the cake (though some sort of linearity is _really_ nice to have).

--
Nicholas O. Lindan, Cleveland, Ohio
Consulting Engineer:  Electronics; Informatics; Photonics.
Remove spaces etc. to reply: n o lindan at net com dot com
psst.. want to buy an f-stop timer? nolindan.com/da/fstop/

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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Hey, these guys are easy to find.

First Name, Last Name, P.E.

The Funny thing is that they think it makes them engineers!

Hardwired!