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Closing Control Loops

C

CBFalconer

Jan 1, 1970
0
Jim said:
Jim Thompson said:
[snip]

My Thesis advisor once told me that the first time he visited WPI
he spent about an hour on the interstate -- he was looking for
Wu'sta. He passed by Wor-ches-ter several times before it sunk in...

Pronounced just like the sauce ;-)

And sort of like Gloucester.

Then there's Wooster, OH ;-)

and Warrik (RI) ...

I used to take the New Haven... RR from Boston to DC, then switch to
the C&O on into Huntington. Trying to figure out those conductor
calls was quite a challenge.

Montreal streetcars (remember them) used to roll along St.
Catherine until they arrived at "GeeGuy". Sometimes
"Laroogeeguy". Those are hard 'g's.

--
"If you want to post a followup via groups.google.com, don't use
the broken "Reply" link at the bottom of the article. Click on
"show options" at the top of the article, then click on the
"Reply" at the bottom of the article headers." - Keith Thompson
More details at: <http://cfaj.freeshell.org/google/>
Also see <http://www.safalra.com/special/googlegroupsreply/>
 
C

CBFalconer

Jan 1, 1970
0
Jerry said:
.... snip ...

I disn't say they /would/ read the same, but that thay /ought/ to.
When two thermometers in the same stirred pot of soup indicate
different temperatures, at least one of them is wrong. Loop or no
loop.

Or you have an unusually busy population of Maxwells demons.

--
"If you want to post a followup via groups.google.com, don't use
the broken "Reply" link at the bottom of the article. Click on
"show options" at the top of the article, then click on the
"Reply" at the bottom of the article headers." - Keith Thompson
More details at: <http://cfaj.freeshell.org/google/>
Also see <http://www.safalra.com/special/googlegroupsreply/>
 
P

Paul Carpenter

Jan 1, 1970
0
On Saturday, in article
<[email protected]>
[email protected] "Tim Wescott" wrote: --snip--


I realise that there has to be simplification, but a lot of theory does
not USUALLY cover the applied like what to do when an external sensor
or feedback in the loop says there is a fault and how to make sure the
loop (and the system) return to the correct state (whatever that may be).

An example would be printing shop guillotines that usually require two
spaced out buttons to be pressed at the same time for the whole of the cut
process. On the basis that if both hands are on the buttons then the
operator's hands are not in the machinery! Now dpending on how the system
operates there are basically three safety stop states - stop, move back
a little or return to start position.

I have seen some control systems really screwed by an 'abort' function
that need complete restarts or worse after that, basically because the
control loop hardware/software could not effectively reset correctly.
If you were to write an article about this (beyond "think hard about
your problem and deal with sensor failures") I'd be delighted to read it.[/QUOTE]

I don't know if I could really class my thoughts and experiences as an
'article' (so many different meanings to article as in length and depth
of content). I could probably summarise a few of the major ones in a
'War stories' page sometime.

......
I don't think it's just that people don't understand the limits of their
models. I think that people are so used to academic problems that they
forget that their models might possibly not be sufficiently accurate.
There's at least a few places in the book where the phrases "if your
model is accurate enough" or "if your linear model applies" appear. I
also made a point in the chapter on dealing with nonlinearities of
showing what happens when you blithely use a linear model to a design a
controller for a nonlinear system (a big scary/embarrassing oscillation,
in the example).

Common 'solutions' I hear too often from people (either customers or those
'advising' them) are

"just put a big computer in there that will solve the problem"

or "there are GigaBytes of bandwidth available in the RF spectrum"

or "This will be solved by the promised new version of product X"

If you want I could outline describe in email the worst closed loop complete
system with lots of open loop technology in the way that people were asking
to change things to make it better. I would asked to think about what could
be done with modifications to a company's products to give an answer to the
problem, they did not like my response, and got all three of the above
responses.
 
J

Jerry Avins

Jan 1, 1970
0
CBFalconer said:
Jim said:
[snip]

My Thesis advisor once told me that the first time he visited WPI
he spent about an hour on the interstate -- he was looking for
Wu'sta. He passed by Wor-ches-ter several times before it sunk in...

Pronounced just like the sauce ;-)

And sort of like Gloucester.

Then there's Wooster, OH ;-)

and Warrik (RI) ...

I used to take the New Haven... RR from Boston to DC, then switch to
the C&O on into Huntington. Trying to figure out those conductor
calls was quite a challenge.


Montreal streetcars (remember them) used to roll along St.
Catherine until they arrived at "GeeGuy". Sometimes
"Laroogeeguy". Those are hard 'g's.

I cot confused in Bawston when the MTA dispatcher told me to take the
Pack kah (rhymes with kaka). It took a while to sort that out.

Jerry
 
F

Fred Marshall

Jan 1, 1970
0
Paul Carpenter said:
"just put a big computer in there that will solve the problem"

I must say that I've had this experience with folks who should have known
better. When asked: "How are you going to do that?" they would say: "well,
there will be a computer inside". They had NO idea what they were going to
do or how they would do it. If the SNR was infinitely low, "well, there
will be a computer inside".

Fred
 
S

Spehro Pefhany

Jan 1, 1970
0
I must say that I've had this experience with folks who should have known
better. When asked: "How are you going to do that?" they would say: "well,
there will be a computer inside". They had NO idea what they were going to
do or how they would do it. If the SNR was infinitely low, "well, there
will be a computer inside".

Fred

Sort of the general case of the "put a PID controller in there", which
somehow answers all the questions about sensor and actuator response
etc. ;-)



Best regards,
Spehro Pefhany
 
J

John E. Hadstate

Jan 1, 1970
0
in message
Sort of the general case of the "put a PID controller in
there", which
somehow answers all the questions about sensor and
actuator response
etc. ;-)

Even better: a "self-tuning" PID controller.
 
J

Jerry Avins

Jan 1, 1970
0
Spehro said:
Sort of the general case of the "put a PID controller in there", which
somehow answers all the questions about sensor and actuator response
etc. ;-)

"We'll refer it to a lawyer" comes up in other contexts.

Jerry
 
M

Mark Borgerson

Jan 1, 1970
0
Hi Tim


They call me Software Engineer (they call me other names too when they find
bugs in the software, but I doubt you are interested in knowing), but my
business card says Software
Development Manager.


Nuts and Volt, Servo, Motorcyclist, Computer, IEEE Potentials, Dr. Dobbs


Google news, Orkut, CNN



Not so often, I wish I had the money/time to attend to more conferences. The
last one was IC-AI (International Conference on Artificial Intelligence)
which I published and presented a paper.



Yes. Yes. PID control; control theory; fuzzy control



Yes. A couple of books actually.
Got some hints from Schaums for control theory, and two other books that I
borrowed from the university's library.
The problem with all of them is that they go deep on the math of control
theory but are not practical (no relationship between CT and embedded
devices)



Do I get a free book? ;)

Good luck with your publishing... A man has three missions on Earth: Have
kids, plant a tree and write a book. I accomplish the first two... someday
I'll write a book.

Hey, I'm 3 for 3. I heartily recommend doing the writing before the
kids come along, or after they leave home. In the intervening
20+ years, content yourself with smaller projects and keep up with
the tree planting!



Mark Borgerson
 
M

Mark Borgerson

Jan 1, 1970
0
Sort of the general case of the "put a PID controller in there", which
somehow answers all the questions about sensor and actuator response
etc. ;-)

I'm in the middle of "let's put a faster computer in there" to solve
all the sensor noise and control response problems. The magic words
seem to be "Extended Kalman Filter". ;-)


Mark Borgerson
 
T

Tim Wescott

Jan 1, 1970
0
Spehro said:
Sort of the general case of the "put a PID controller in there", which
somehow answers all the questions about sensor and actuator response
etc. ;-)



Best regards,
Spehro Pefhany

From Chapter 1, "The Basics":

"A final 'problem' in this list is that control systems are not magic.
Real systems have real limitations, and nothing – not even an automatic
control system – can overcome the laws of physics. Limitations in the
strength of your actuators, in the response speed of every part of the
system, in your plant's tendency to allow itself to be driven nicely,
and in your sensor's ability to deliver noise-free measurements will all
limit the ultimate performance of your system."

--

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

Posting from Google? See http://cfaj.freeshell.org/google/
 
T

Tim Wescott

Jan 1, 1970
0
Paul said:
On Sunday, in article <[email protected]>
--snip--



I don't know if I could really class my thoughts and experiences as an
'article' (so many different meanings to article as in length and depth
of content). I could probably summarise a few of the major ones in a
'War stories' page sometime.

.....

War stories would be nice -- particularly of battles won as well as lost.

--

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

Posting from Google? See http://cfaj.freeshell.org/google/
 
E

Everett M. Greene

Jan 1, 1970
0
Jerry Avins said:
CBFalconer said:
Jim said:
[snip]

My Thesis advisor once told me that the first time he visited WPI
he spent about an hour on the interstate -- he was looking for
Wu'sta. He passed by Wor-ches-ter several times before it sunk in...

Pronounced just like the sauce ;-)

And sort of like Gloucester.

Then there's Wooster, OH ;-)

and Warrik (RI) ...

I used to take the New Haven... RR from Boston to DC, then switch to
the C&O on into Huntington. Trying to figure out those conductor
calls was quite a challenge.

Montreal streetcars (remember them) used to roll along St.
Catherine until they arrived at "GeeGuy". Sometimes
"Laroogeeguy". Those are hard 'g's.

I cot confused in Bawston when the MTA dispatcher told me to take the
Pack kah (rhymes with kaka). It took a while to sort that out.

I had the reverse situation occur once. I was going to
fly with an instructor one night at an airport where the
runway lights were out of service for construction work.
The instructor said he'd put a pot at the end of the
runway so we could find it to land. I was puzzled as to
how a /part/ (allowing for the instructor's heavy New
England accent) was going to help us find the runway.
As we taxied out to depart, I saw the pot and realized
that when he'd said "pot", he meant "pot"!

And there's the time the Texan was telling me how much
he hated "all-filled" capacitors. [Show me a capacitor
that isn't filled with something.]
 
R

Rich Grise

Jan 1, 1970
0
A self procreating **** up?


Ole came home from work one day, just terribly sad. "Ole, what's wrong?"
asks Lena. "Oh, Lena," says Ole, "You remember de oder night, vhen you vas
on top o me, and ve vas havin such fun?" "Oh, yah, Ole, dat was great!"
"Vell, Lena, ve can't do dat no more." "Huh?" "Yah, I'm so sorry, but da
boss at vork today, he says, if I **** up vun more time, I'm fired!"

Cheers!
Rich
--
Elect Me President in 2008! I will:
A. Fire the IRS, and abolish the income tax
B. Legalize drugs
C. Stand down all military actions by the US that don't involve actual
military aggression against US territory
D. Declare World Peace I.
 
R

Rich Grise

Jan 1, 1970
0
They call me Software Engineer (they call me other names too when they
find bugs in the software, but I doubt you are interested in knowing),

Oh, please! Do Tell!

Please don't be a tease! ;-P

Thanks!
Rich
--
Elect Me President in 2008! I will:
A. Fire the IRS, and abolish the income tax
B. Legalize drugs
C. Stand down all military actions by the US that don't involve actual
military aggression against US territory
D. Declare World Peace I.
 
T

Terry Given

Jan 1, 1970
0
Tim said:
War stories would be nice -- particularly of battles won as well as lost.

how about a draw?

we recently had a blowup in one of our videoscreens. we use telecomms
48Vdc power supplies, and the one in the burn-in rack failed - the
feedback network went open-circuit, it was in the airflow path and not
conformally coated, and managed to corrode. Boom, up goes the voltage;
it was a 25kW supply. Fortunately they put in a supervisory loop, which
shut the power supply down. Unfortunately, it took 10ms to do so.

Fortunately I had designed in some kick-ass transient clamping and
fusing (nearby lightning strike protection), which protected the
circuitry. Unfortunately the over-voltage was such as to limit the
current to a value which didnt immediately blow the fuse, and 10ms =
eternity as far as junction thermal time constants go, so the TVSs all
suicided, thereby snotting the fuses. best not to think about the 16
screws that need to be removed to repair each one....

Fortunately the problem happened in our factory, so the costs associated
with removing/dismantling/remantling/replacing all of the modules was
minimal. I am now working on a monster clamp, so the same problem doesnt
take out a customers $2,000,000 screen :)

Cheers
Terry
 
T

Tim Williams

Jan 1, 1970
0
Terry Given said:
I am now working on a monster clamp, so the same problem doesnt
take out a customers $2,000,000 screen :)

I bet that'd get those shunt-regulating, class-A'ing audiophools drooling.

Tim
 
P

Paul Carpenter

Jan 1, 1970
0
On Sunday, in article
<[email protected]>
I must say that I've had this experience with folks who should have known
better. When asked: "How are you going to do that?" they would say: "well,
there will be a computer inside". They had NO idea what they were going to
do or how they would do it. If the SNR was infinitely low, "well, there
will be a computer inside".

Reminds me of a cartoon on a Tshirt web site that has a blackboard and a
professeur wanting more detail on step two, bearing in mind the three
steps of maths on the backboard are:-


1. Complicated maths

2. "By a bit of magic we get to"

3. Less complicated maths

I do not have the URL to hand at present.
 
T

Terry Given

Jan 1, 1970
0
Tim said:
I bet that'd get those shunt-regulating, class-A'ing audiophools drooling.

Tim

yep. best I wire it with monster cables....

Cheers
Terry
 
R

Rich Grise, PLainclothes Hippie

Jan 1, 1970
0
On Sunday, in article
<[email protected]>


Reminds me of a cartoon on a Tshirt web site that has a blackboard and a
professeur wanting more detail on step two, bearing in mind the three
steps of maths on the backboard are:-


1. Complicated maths

2. "By a bit of magic we get to"

3. Less complicated maths

I do not have the URL to hand at present.

Vaguely reminds me of The Underpants Gnomes, on South Park. They would
sneak into your room while you're sleeping, and steal your underpants.
Their motivation, it was revealed, was Profit. The kids caught the
Underpants Gnomes stealing Tweek's underpants, and followed them to
the Underpants Gnome cavern. They had a chart much like that:

1. Steal Underpants.

2.

3. Profit.

And when anybody asked what step 2 was, they just stood there and looked
confused. And after a beat or two, "But, step 3 is Profit!" "Hooray!"

Guess you had to be there. :-/

Thanks,
Rich
--
Elect Me President in 2008! I will:
A. Fire the IRS, and abolish the income tax
B. Legalize drugs
C. Stand down all military actions by the US that don't involve actual
military aggression against US territory
D. Declare World Peace I.
 
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