Shameless Plug

[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

 

[Guy Macon]

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.

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!!!!

 

[Guy Macon]

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.

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.

 

[Tim Wescott]

Tim Wescott wrote:




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!!!!

Well, that's why if I know there's two markedly different ways if saying
the same thing I'll footnote it.

 

[Tim Wescott]

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.

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.

 

[Spehro Pefhany]

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

I like the French word for engineer better:

"ingénieur"

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

 

[Tim Wescott]

According to Lipták, it's primarily used to introduce a lag into the
control loop when the process is very fast or noisy.


Best regards,
Spehro Pefhany

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.

 

[Spehro Pefhany]

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.

According to Lipták, it's primarily used to introduce a lag into the
control loop when the process is very fast or noisy.


Best regards,
Spehro Pefhany

 

[Spehro Pefhany]

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.

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

 

[Nicholas O. Lindan]

OK, I'll bite -- what _is_ it good for?

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.

but I _can't_ see the point in intentionally establishing an
unstable zero in your control system.

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.

Yes, this could be _very_ counter-intuitive to my target audience.

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).

 

[Rich Grise]

Well, that's why if I know there's two markedly different ways if saying
the same thing I'll footnote it.

I'd think that at least in the case of PID, the "right" way would be the
one that most accurately reflects what the thing is doing. Just from a
high-school algebra edjamacaited bench tech, it sounds like "derivative"
is more the effect you're going after - a "differential" is something else
entirely - it's not even on the same axis, as it were.

But anyway, now that I know which word "should" be used, do I have to go
to school for four years to grasp the transfer function, or is it
basically a critically-damped filter with a cutoff freq of .01 Hz? And, of
course, you've got the asymmetric hysterisis and all that stuff to contend
with - basically, the control circuit has to predict the future. ;-)

Thanks!
Rich

 

[Jerry Avins]

Tim Wescott wrote:

system.


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.

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

 

[Jerry Avins]

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.

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

 

[Clarence]

"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"?

Hey, these guys are easy to find.

First Name, Last Name, P.E.

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

 

[Clarence]

[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!

 

[Winfield Hill]

Guy Macon wrote...

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!!!!

ROFLOL, LOL-LMAOXD, ROXCGHRKFITR! YUREBDH!

 

[Scott Seidman]

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.

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



Scott

 

[Jerry Avins]

Guy Macon wrote:




Shortly after VJ day, Japanese military electronic software began Wah! 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

 

[John Sampson]

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 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

 

[JeffM]

...I did a Google search...

...The quotation marks are important...
Guy Macon

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.)