Shameless Plug

[Tim Wescott]

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

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).

 

[Louis Bybee]

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!!!!

Finally someone who speaks my language!

The first clear, concise, and lucid post in quite a while!

A little off track at first, but you wrapped it up nicely towards the end!
)

Louis--
*********************************************
Remove the two fish in address to respond

 

[Jim Thompson]

[snip]

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".
[snip]
Jerry

Engineers, as a class, are notoriously bad spellers/grammarians.

...Jim Thompson

Hardwired!

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

 

[YD]

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.

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.

 

[Jerry Avins]

Guy Macon wrote:




Shortly after VJ day, Japanese military electronic software began Aaah! Hardware! Hardware!
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

 

[Winfield Hill]

Jerry Avins wrote...
Right. Bart Simpson.

 

[Geoff]

"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?"

The "D" part of PID refers to the presence of a rate-of-change term,
often able to be interpreted as a derivative of a position (or similar)
quantity. Derivatives are a concept deriving (!!) from the differential
calculus. Either term refers to the notion of infinitesimal differences
whose ratios are considered as they approach (under suitable existence
conditions) some limiting value.

Thus either version of the acronym is fine.
Elsewhere in this thread is a timely reminder about the danger of
reliance upon statistics (eg: Google hits) to "prove" something.
I've come to the conclusion that if the majority agree upon something,
it's probably false (works great in the stock market, but you have to be
careful about your audience when defining the principle as "the fallacy
of democracy"......<grin>)

Geoff.

 

[Jerry Avins]

Jerry Avins wrote...



Right. Bart Simpson.

http://www.simpsonelectric.com/anaind.htm

 

[Rich Grise]

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.

Stumbled on this while looking for something entirely different -
something about heavy boots on the moon leading to physics humor, over on
rec.puzzles - anyway, when I hit this on the physics joke page, I thought
of this post.
http://www.xs4all.nl/~jcdverha/scijokes/2.html#12

Cheers!
Rich

 

[Bruce Durdle]

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

 

[Daniel Haude]

["Followup-To:" header set to sci.electronics.design.]
On Tue, 30 Nov 2004 08:59:24 -0800,

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.

This reminds me of one of my favorite entries in Strunk & White, Modern
English Usage on "flammable" vs. "inflammable". The correct term is
inflammable, but on trucks that hold dangerous goods you'll always see
"flammable". Quoting from memory: "Unless you drive such a truck, and are
hence concerned with the safety of children and illiterates, use
inflammable".

According to my pedantic mind, there's no such thing as a flammable
substance, but the general public seems to think otherwise.

--Daniel

 

[Guy Macon]

Guy Macon <http://www.guymacon.com> wrote:

Please don't follow "Guy Macon wrote" with something that I
clearly labeled (in the part you snipped) as being not my
question, but rather a question typical of a student in a
class I taught.

The "D" part of PID refers to the presence of a rate-of-change term,
often able to be interpreted as a derivative of a position (or similar)
quantity. Derivatives are a concept deriving (!!) from the differential
calculus. Either term refers to the notion of infinitesimal differences
whose ratios are considered as they approach (under suitable existence
conditions) some limiting value.

Thus either version of the acronym is fine.

So you derive from deriving the derivative from the differential that
one should not differentiate between differential and derivative?
That's different.

Elsewhere in this thread is a timely reminder about the danger of
reliance upon statistics (eg: Google hits) to "prove" something.

Google hits prove commonness of usage on the World Wide Web.
All else is derivative - an important difference.

 

[Jerry Avins]

Guy Macon wrote:

...

So you derive from deriving the derivative from the differential that
one should not differentiate between differential and derivative?
That's different.




Google hits prove commonness of usage on the World Wide Web.
All else is derivative - an important difference.

Bravo!

Jerry

 

[Jerry Avins]

["Followup-To:" header set to sci.electronics.design.]
On Tue, 30 Nov 2004 08:59:24 -0800,

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.

This reminds me of one of my favorite entries in Strunk & White, Modern
English Usage on "flammable" vs. "inflammable". The correct term is
inflammable, but on trucks that hold dangerous goods you'll always see
"flammable". Quoting from memory: "Unless you drive such a truck, and are
hence concerned with the safety of children and illiterates, use
inflammable".

According to my pedantic mind, there's no such thing as a flammable
substance, but the general public seems to think otherwise.

--Daniel

The meaning of flammable is clear, while inflammable might be
disastrously confused with unflammable (not a real word either)
meaning non-flammable. The need for clear disambiguation on gasoline
tankers trumps the joys of pedantry.

Jerry

 

[Jerry Avins]

["Followup-To:" header set to sci.electronics.design.]
On Tue, 30 Nov 2004 08:59:24 -0800,

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.

This reminds me of one of my favorite entries in Strunk & White, Modern
English Usage on "flammable" vs. "inflammable". The correct term is
inflammable, but on trucks that hold dangerous goods you'll always see
"flammable". Quoting from memory: "Unless you drive such a truck, and are
hence concerned with the safety of children and illiterates, use
inflammable".

According to my pedantic mind, there's no such thing as a flammable
substance, but the general public seems to think otherwise.

--Daniel

The meaning of flammable is clear, while inflammable might be
disastrously confused with unflammable (not a real word either)
meaning non-flammable. The need for clear disambiguation on gasoline
tankers trumps the joys of pedantry.

Jerry

 

[Lasse Langwadt Christensen]

snip
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.

Maybe it's just me, but shouldn't this be obvious
to anyone who's had even basic physics in school?


-Lasse

 

[Guy Macon]

Maybe it's just me, but shouldn't this be obvious
to anyone who's had even basic physics in school?

Only those who went to school back when they were still teaching
how to apply basic physics to real-world problems.

To be fair, some schools do a great job of this, but I have
personal experience of a person who got an EE degree from a
state college without ever tumbling on to the fact that when
you send current down a wire there has to be an equal current
through a return path.

That engineer was put to work maintaining COBOL programs.
This was in the '90s, not in the age of COBOL.

 

[Geoff]

Please don't follow "Guy Macon wrote" with something that I
clearly labeled (in the part you snipped) as being not my
question, but rather a question typical of a student in a
class I taught.

My apologies.

So you derive from deriving the derivative from the differential that
one should not differentiate between differential and derivative?
That's different.

Essentially yes. (Ignores irony). But then, I'm not only a
mathematician, I'm also a linguistics freak....

Google hits prove commonness of usage on the World Wide Web.
All else is derivative - an important difference.

<grin>
As I intimated, "common usage" is to be distrusted. After all, the
planet's population is now so large that virtually any human-behavioural
parameter, via the central limit theorem, gets modelled as obeying a
Gaussian distribution, whose *central* area dominates the sample results.
I call the universal welcome currently accorded to this situation "the
cult of mediocrity" and it is an example of positive feedback.
Examples abound. Think about it.

The linguistics scene has "descriptive grammarians" (currently in the
ascendant) versus "prescriptive grammarians" (started declining maybe 50
years ago). That's why I regularly find books, and even learned papers,
which confuse "throes" with "throws", "pour" with "pore", and many more,
since schools ceased to bother students with (horror!) rules,
substantive examinations etc.

To pull things together: my derivative/differential fusion is based
upon a return to fundamentals (mathematical and linguistic). I find
that this approach is superior to all others I've tried.
YMMV.

Geoff.

 

[Jerry Avins]

Geoff wrote:

...

The linguistics scene has "descriptive grammarians" (currently in the
ascendant) versus "prescriptive grammarians" (started declining maybe 50
years ago). That's why I regularly find books, and even learned papers,
which confuse "throes" with "throws", "pour" with "pore", and many more,
since schools ceased to bother students with (horror!) rules,
substantive examinations etc.

That really peaks (or is it peeks?) my ire.

...

Jerry

 

[BFoelsch]

Geoff wrote:

...


That really peaks (or is it peeks?) my ire.

Piques. I'm prescriptive.

Years ago there was a weekly puzzle in our newspaper which used exactly that
principal, they would give clues (no, not clews) that required a true
prescriptive knowledge to answer. For example, they would give a clue along
the lines of "to overwhelm with fauna" and the crossword would be filled in
except for one letter. In this case the crossword would contain INFE?T. It
would be up to you to choose between INFECT and INFEST.

There was a $500 dollar prize for the correct answer to the crossword, which
probably neede you to fill in only about 12 letters as explained above. I
won twice over a period of 12 years.

I don't think they run that puzzle anymore.