"Jim Thompson" <To-Email-Use-The-Envelope-Icon@My-Web-Site.com> wrote in message news:c5h3025qdr8s1i0lc88vcm6jdkeje33i06@4ax.com...> On Sat, 25 Feb 2006 20:34:04 -0800, Tim Wescott <tim@seemywebsite.com> > wrote: > > [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) ...
Closing Control Loops
Started by ●February 24, 2006
Reply by ●February 26, 20062006-02-26
Reply by ●February 26, 20062006-02-26
On Sun, 26 Feb 2006 13:38:49 -0800, "Fred Marshall" <fmarshallx@remove_the_x.acm.org> wrote:> >"Jim Thompson" <To-Email-Use-The-Envelope-Icon@My-Web-Site.com> wrote in >message news:c5h3025qdr8s1i0lc88vcm6jdkeje33i06@4ax.com... >> On Sat, 25 Feb 2006 20:34:04 -0800, Tim Wescott <tim@seemywebsite.com> >> wrote: >> >> [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. ...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 | | http://www.analog-innovations.com | 1962 | It's what you learn, after you know it all, that counts.
Reply by ●February 26, 20062006-02-26
"Genome" <ilike_spam@yahoo.co.uk> wrote in message news:vLnMf.10240$57.9366@newsfe3-win.ntli.net...> Yes, I am use LabView so I am have no problims. Evin > cumputer get burn up coz ov over monkey mistak. :) :).... > > Also hav 'honest' backup what no-wun am figur owt. Bonus, > am also iso9005.02.03 > > Nise Coffeeee plus Doner Kebab...... Easy. > > DNAYep, monkeys with screwdrivers were a big problem in my plant (as was a raccoon who decided to have a barbecue in the business area of one of the 230 KV switching substations ;-) Seriously though, there is a subtlety buried here that should be brought out. We didn't really become focused on the problems I described until we started using various Data Historians in a big way (actually about the same time that people were getting interesting in things like ISO-9000 and Statistical Process Control.) After a lot of thinking, a lot more talking, and several demonstrations where our historical data showed us that what was happening was not what we thought was happening, we began to get a handle on some of the problems. I can't emphasize enough how important is the collection and long-term storage of process data to the health of a plant that has a lot of closed-loop control, but don't rely on the controller measurements to tell you anything about what's happening in the process. This principle should be pasted on every control engineer's forehead: "If a process variable is important enough that it needs to be automatically controlled it is important enough that it needs to be independently audited."
Reply by ●February 26, 20062006-02-26
On Sun, 26 Feb 2006 13:38:49 -0800, the renowned "Fred Marshall" <fmarshallx@remove_the_x.acm.org> wrote:> >"Jim Thompson" <To-Email-Use-The-Envelope-Icon@My-Web-Site.com> wrote in >message news:c5h3025qdr8s1i0lc88vcm6jdkeje33i06@4ax.com... >> On Sat, 25 Feb 2006 20:34:04 -0800, Tim Wescott <tim@seemywebsite.com> >> wrote: >> >> [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) ... >The train wicket guy in the UK who sold me the ticket to 'Lie-stir' looked at me funny, but sold the ticket to Leicester nonetheless. 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
Reply by ●February 26, 20062006-02-26
John E. Hadstate wrote:> "Jerry Avins" <jya@ieee.org> wrote in message > news:fvudnYRrKteSY5zZnZ2dnUVZ_tydnZ2d@rcn.net... > >>John E. Hadstate wrote: >> >> >>>Also, of course, we had the clever E&I technicians. >>>Operators would complain that the controller measurements >>>weren't the same as the auditor measurements, so some >>>dork with a 12-inch screwdriver would "re-calibrate" the >>>RTD-to-current-loop converters to make the auditors "read >>>right." >> >>If sensors are in the same place, they ought to read the >>same value. Audit probes did me the most good when they >>were located somewhat apart from the control probe. >> > > > No!! Between the sensors and the computer is usually a > device ("converter" or "amplifier") to produce a 4-20 mA (or > 10-50 mA) signal from whatever the sensor produces > (resistance, millivolts, etc.) Back in the computer room, > there is often another converter to change the 4-20 mA > signal to something like 0-10 Volts or 1-5 Volts. These > devices almost always have "Span" and "Zero" adjustments > accessible to "the dork with the 12-inch screwdriver". > Consequently, without a serious threat to "break fingers", > these converters are often used to make the computer say > whatever the operators want it to say.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. Jerry -- Engineering is the art of making what you want from things you can get. �����������������������������������������������������������������������
Reply by ●February 26, 20062006-02-26
Jim Thompson wrote:> <fmarshallx@remove_the_x.acm.org> wrote: >> "Jim Thompson" <To-Email-Use-The-Envelope-Icon@My-Web-Site.com> wrote >>> Tim Wescott <tim@seemywebsite.com> wrote: >>> >>> [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/>
Reply by ●February 26, 20062006-02-26
On Sunday, in article <v5adnZmFqdMffJzZRVn-qA@web-ster.com>
tim@seemywebsite.com "Tim Wescott" wrote:
>Paul Carpenter wrote:
>> On Saturday, in article
>> <lZ6dnS0pVYzZA53ZnZ2dnUVZ_v-dnZ2d@web-ster.com>
>> tim@seemywebsite.com "Tim Wescott" wrote:
>--snip--
>
>>>>Hopefully your book will not be like that.
>>>>
>>>
>>>I tried to keep it grounded in reality, to live up to the "Applied" in
>>>the title. Most of the examples are simplified, so that I can talk to
>>>the point that I'm trying to make, but I try to keep the other issues
>>>visible.
>>
>> 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.
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.
.....
>> Quite often I have seen customers who do not understand the limitations
>> and assumptions in their systems let alone any model they think they have
>> created.
>>
>> Some of the major control loop problems I have seen is applying open loop
>> blocks to an overall system that is closed loop. Mainly because they
>> did not understand the limits of the blocks they were using, most
>> notably delays, determinicity and sampling restraints.
>>
>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.
--
Paul Carpenter | paul@pcserviceselectronics.co.uk
<http://www.pcserviceselectronics.co.uk/> PC Services
<http://www.gnuh8.org.uk/> GNU H8 & mailing list info
<http://www.badweb.org.uk/> For those web sites you hate
Reply by ●February 26, 20062006-02-26
Jerry Avins wrote:>... 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/>
Reply by ●February 26, 20062006-02-26
CBFalconer wrote:> Jim Thompson wrote: > >><fmarshallx@remove_the_x.acm.org> wrote: >> >>>"Jim Thompson" <To-Email-Use-The-Envelope-Icon@My-Web-Site.com> wrote >>> >>>>Tim Wescott <tim@seemywebsite.com> wrote: >>>> >>>>[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 -- Engineering is the art of making what you want from things you can get. �����������������������������������������������������������������������
Reply by ●February 26, 20062006-02-26
"Paul Carpenter" <paul$@pcserviceselectronics.co.uk> wrote in message> "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
