Shameless Plug

[Tim Wescott]

I will be presenting two topics at the 2005 Embedded Systems Conference
San Francisco next March -- see http://www.esconline.com/sf/ 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.

 

[Jim Thompson]

I will be presenting two topics at the 2005 Embedded Systems Conference
San Francisco next March -- see http://www.esconline.com/sf/ 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.

I would sure like to receive copies of each!

...Jim Thompson

 

[Tim Wescott]

I would sure like to receive copies of each!

...Jim Thompson

The source material for both is on my website --
http://www.wescottdesign.com/articles/pidwophd.html gets you one click
away, and
http://www.wescottdesign.com/articles/zTransform/z-transforms.html is
the z-domain stuff.

 

[Joerg]

Hi Tim,

Just let us know what day and time. Do you plan to publish these? The
PID session sounds very interesting.

BTW, Scott Adams (Dilbert) is going to speak as well.

Regards, Joerg

 

[Jim Thompson]

The source material for both is on my website --
http://www.wescottdesign.com/articles/pidwophd.html gets you one click
away, and
http://www.wescottdesign.com/articles/zTransform/z-transforms.html is
the z-domain stuff.

Thanks, Tim. I last took a non-linear control systems course in 1968,
but I actually enjoyed it, still have my notes ;-)

...Jim Thompson

 

[Guy Macon]

I will be presenting two topics at the 2005 Embedded Systems Conference
San Francisco next March -- see http://www.esconline.com/sf/ 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.

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.

 

[martin griffith]

Hi Tim,

Just let us know what day and time. Do you plan to publish these? The
PID session sounds very interesting.

BTW, Scott Adams (Dilbert) is going to speak as well.

Regards, Joerg

"Mr. Adams held a variety of -- in his words -- "humiliating and low
paying jobs" .........and pseudo-engineer."

Any nice/apt/funny definitions of " pseudo-engineer"?


martin

Serious error.
All shortcuts have disappeared.
Screen. Mind. Both are blank.

 

[Winfield Hill]

Guy Macon wrote...

"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?"

proportional integral derivative - 253,000 hits = correct
proportional integral differential - 315,000 hits = wrong

 

[Francis]

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.

 

[Nicholas O. Lindan]

Why do half the engineers call [PID] "Proportional-Integral-Derivative"

and others call it "Proportional-Integral-Differential?"

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.

 

[Winfield Hill]

Francis wrote...

Try a searching the whole phrase

Google for "proportional integral derivative" gets 18,600
Google for "proportional integral differential" gets 3,060

Phew, that's a relief.

 

[Guy Macon]

Guy Macon wrote...

Please don't snip out the part where I wrote "a common question is",
thus making it look as if I am the one asking asking the question.

proportional integral derivative - 253,000 hits = correct
proportional integral differential - 315,000 hits = wrong

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.

 

[Tim Wescott]

Guy Macon wrote:
-- snip --

"Why do some controller boards have an option to reverse the
phase of the D? What is that good for?"

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 --

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.

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

Another gotcha that sometimes trips up software engineers:
non-monotonic ADCs causing a "bad spot" that has positive
feedback.

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.

 

[Tim Wescott]

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.

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.

 

[Roger Hamlett]

Guy Macon wrote...

proportional integral derivative - 253,000 hits = correct
proportional integral differential - 315,000 hits = wrong

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

Best Wishes

 

[Jim Thompson]

On Tue, 30 Nov 2004 12:54:01 -0500, Spehro Pefhany

[snip]

"proportional intergral derivative" 29 hits
"proportional intergral differential" 18 hits



Best regards,
Spehro Pefhany

"intergral" ?

...Jim Thompson

 

[Spehro Pefhany]

Please don't snip out the part where I wrote "a common question is",
thus making it look as if I am the one asking asking the question.


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

"proportional intergral derivative" 29 hits
"proportional intergral differential" 18 hits



Best regards,
Spehro Pefhany

 

[Jerry Avins]

Winfield Hill wrote:




Please don't snip out the part where I wrote "a common question is",
thus making it look as if I am the one asking asking the question.




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.

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

 

[Bruce Durdle]

Not acording to Sturgeon's Law:

90% of everything is C%&p

But that was before the internet - Internet Corollary to Sturgeon's Lwa:

99% of everything is C%&p

Bruce

Why do half the engineers call [PID] "Proportional-Integral-Derivative"
and others call it "Proportional-Integral-Differential?"

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.

 

[Bruce Durdle]

Yestedy i culdnt spel "Enginie - Now i are wun.

On Tue, 30 Nov 2004 12:54:01 -0500, Spehro Pefhany

[snip]

"proportional intergral derivative" 29 hits
"proportional intergral differential" 18 hits



Best regards,
Spehro Pefhany

"intergral" ?

...Jim Thompson