I will be presenting two topics at the 2005 Embedded Systems Conference San Francisco next March -- see
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for show details.
"Basic Control Theory for the Software Engineer" is as much information on the z-transform as I can fit into 90 minutes. It gives a high-altitude overview of designing software control loops in a systematic manner.
"PID Without a PhD" is a primer on developing PID controllers in software, tuning them without using higher math, and avoiding some of the common pitfalls for this popular controller form.
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Tim Wescott
Wescott Design Services
http://www.wescottdesign.com
--
| 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 | |
| E-mail Address at Website Fax:(480)460-2142 | Brass Rat |
| http://www.analog-innovations.com | 1962 |
I love to cook with wine. Sometimes I even put it in the food.
Thanks, Tim. I last took a non-linear control systems course in 1968, but I actually enjoyed it, still have my notes ;-)
...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 | |
| E-mail Address at Website Fax:(480)460-2142 | Brass Rat |
| http://www.analog-innovations.com | 1962 |
I love to cook with wine. Sometimes I even put it in the food.
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
http://www.wescottdesign.com
I fear that my mind was poisoned long ago by a German instructor who pointed out that modern linguistic theory doesn't much recognize a "right way" and a "wrong way" -- it just records prevalent usage, and tries to keep out of the way of the steamroller.
When I write something that has two competing terms in use I'll often mention both of them (perhaps in a footnote), and I'll explain why I use the one I do.
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Tim Wescott
Wescott Design Services
http://www.wescottdesign.com
Cool! From many years teaching "practical PID" to technicians and engineers, here are some questions that came up a lot:
"Why do so many of the setups around here have only P and I or have D set to zero? How do I decide when to use D?"
"Why do some controller boards have an option to reverse the phase of the D? What is that good for?"
"How do I describe a thermostat with hysteresis using the same language that I use to describe a PID controller? It seems like P is infinity."
"Why do half the engineers call it Proportional-Integral-Derivative" and others call it "Proportional-Integral-Differential?" When I did a Google search on "proportional integral differential" I got 18,600 hits while "proportional integral differential" only had 3,060 hits, but most of the "proportional integral differential" hits seem to be by scientists and equipment manufacturers. Which is correct?"
BTW. for what it's worth, I found that relating position servos and velocity servos to a person controlling a car (speed and position within the lane) was helpful. I also found it helpful to show how to use a stopwatch and odometer to derive speed with no speedometer, a stopwatch and speedometer to derive distance without an odometer, and a speedometer and odometer to derive elapsed time with no stopwatch. Your audience is different, of course - this worked really well with mechanical engineers, but software engineers are quite different.
Another gotcha that sometimes trips up software engineers: non-monotonic ADCs causing a "bad spot" that has positive feedback.
-- | 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 | | | E-mail Address at Website Fax:(480)460-2142 | Brass Rat | |
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| 1962 | I love to cook with wine. Sometimes I even put it in the food.
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
Wescott Design Services
http://www.wescottdesign.com
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
Wescott Design Services
http://www.wescottdesign.com
Engineers, as a class, are notoriously bad spellers/grammarians.
...Jim Thompson
-- | 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 | | | E-mail Address at Website Fax:(480)460-2142 | Brass Rat | |
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| 1962 | I love to cook with wine. Sometimes I even put it in the food.
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"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
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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Engineering is the art of making what you want from things you can get.
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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
--
"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
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