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John Shaw
science forum beginner

Joined: 25 Mar 2005
Posts: 29

Posted: Tue Jan 03, 2006 5:10 pm    Post subject: Re: PID control

Tim Wescott wrote:
 Quote: I do high-performance motion control stuff, generally with full custom hardware. There are enough other contributors to phase delay that "dead time" per se is just not an issue.

That is one of the big differences between process control and other
types of control, and why it helps to know which world a question is
coming from.

John Shaw
www.jashaw.com/pid
A. Paul Montgomery
science forum beginner

Joined: 11 Nov 2005
Posts: 19

Posted: Wed Jan 04, 2006 7:00 pm    Post subject: Re: PID control

In article <2YqdnUktFon2VyTeRVn-pg@web-ster.com>, tim@seemywebsite.com
says...
 Quote: Define delay. The last time I look at first order response it was something like 1-exp(-a*t). Even at time t=0+ there is some response. I suppose that even an ideal RC circuit has some dead time if you consider the dead time due to the speed of electric current. Peter Nachtwey Classic phase delay. I'm surprised at your example, because it's not restricted to 1st-order systems: any continuous-time, linear system with a finite number of states has some response at time t = 0+; in a strict sense "dead time" only has meaning in sampled-time systems and systems with an infinite number of states (thermal, fluid flow and long strings of coax all come to mind). I've kept quiet on conversations that involve mathematical calculation

of control response. I must admit that I have been somewhat lost. Some
of this has to do with the way I came up in the field and some has to do
with the changes that have occurred while I have been absent so I am
trying to catch up to the point where I at least follow what is being
discussed. Most of the discussions to me have little practical usage in
my business anyway. So excuse me if my intrusions seem lost, they are.

Tim, you seem to think in electronic and/or digital terms. Part of my
problems may be definitions here. Can a definition of "dead time" be
given here thinking in physics terms and differentiate that from
hysteresis.
--
Paul Montgomery
Progressive Gauging Inc.
Tim Wescott
science forum Guru Wannabe

Joined: 03 May 2005
Posts: 292

Posted: Wed Jan 04, 2006 8:22 pm    Post subject: Re: PID control

A. Paul Montgomery wrote:

 Quote: In article <2YqdnUktFon2VyTeRVn-pg@web-ster.com>, tim@seemywebsite.com says... Define delay. The last time I look at first order response it was something like 1-exp(-a*t). Even at time t=0+ there is some response. I suppose that even an ideal RC circuit has some dead time if you consider the dead time due to the speed of electric current. Peter Nachtwey Classic phase delay. I'm surprised at your example, because it's not restricted to 1st-order systems: any continuous-time, linear system with a finite number of states has some response at time t = 0+; in a strict sense "dead time" only has meaning in sampled-time systems and systems with an infinite number of states (thermal, fluid flow and long strings of coax all come to mind). I've kept quiet on conversations that involve mathematical calculation of control response. I must admit that I have been somewhat lost. Some of this has to do with the way I came up in the field and some has to do with the changes that have occurred while I have been absent so I am trying to catch up to the point where I at least follow what is being discussed. Most of the discussions to me have little practical usage in my business anyway. So excuse me if my intrusions seem lost, they are. Tim, you seem to think in electronic and/or digital terms. Part of my problems may be definitions here. Can a definition of "dead time" be given here thinking in physics terms and differentiate that from hysteresis.

If _I'm_ not lost folks are using "dead time" to mean pure delay. Take
as an example an art installation that has a machine that's dropping
synthetic human excrement onto a conveyor*. A measurement of the weight
of the 'product' one foot away from where it is dumped (as it were) will
be wholly** independent of the weight of the product 1/2 foot away, so
there will be a pure delay in the measurement.

Contrast this with a one-state low-pass filter where (in theory) the
output starts to rise _immediately_ as the input is increased.

time, but it's a variable dead time that depends on the system state.
In process control (I believe) one is usually concerned with a constant
'real' dead time that arises from real honest-to-gosh mass transfer
issues like conveyors or flow in pipes***, or one is concerned with
effectively real dead times like heat transfer in a material****, or one
is trying to model something like hysteresis where the dead time varies
and generally messes everything up.

* No sh--! Um, I mean: No kidding! I saw a documentary on this on PBS.
They went to some lengths to achieve veracity with just the right
mixing and fermentation so they could put ham sandwiches in one end and
get 'art' out the other. I was profoundly thankful that it was a
European endeavor for two reasons: there would be no way that _I_ would
be expected to go to the opening and eat Brie and crackers next to the
thing while making witty comments, and I wouldn't have to fess up to my
tax dollars funding it.

** Belt stiffness, nothing's perfect, yadda yadda -- you know what I mean.

*** Which, come to think of it, would cause a varying dead time if the
flow is varied.

**** Depending on who's theory you use there will be some pure delay, or
there will be a minuscule 'immediate' response that only a theoretician

--

Tim Wescott
Wescott Design Services
http://www.wescottdesign.com
John Shaw
science forum beginner

Joined: 25 Mar 2005
Posts: 29

Posted: Wed Jan 04, 2006 9:22 pm    Post subject: Re: PID control

Tim,

I love your example. I will have to remember it. I am just glad that
the "stuff" is synthetic.

Paul,

In the process industries (refining, power, pulp and paper, etc.)
dynamics can usually be broken into two types.

Dead Time is just like Tim described it. Our stuff is usually carried
in pipes. The stuff is heated, reacted, mixed, etc. at one point and a
measurement is made at another point, hopefully, but not always, very
close. It takes time for the stuff to move through the pipe from where
something happened to where it is measured. For example, in a paper
mill, stock (fiber and water) may be diluted by injecting a stream of
water into the suction of a pump. At some convenient point on the pipe
leaving the pump (perhaps many feet away) a device will measure the
consistency (ratio of fiber to total flow) in order to control the flow
of water back at the pump suction. The delay of movement from the
mixing point to the measurement is dead time. It is hard to control. If
the only dynamics (or the major dynamics) is dead time, the control
loop will oscillate if the controller gain is too high.

The other kind of dynamics is a single order lag. This is similar to a
capacitor and resitor type of delay if you studied electrical
engineering, or the temperature of a rock thrown into a pot of boiling
water. Processes involving mixing, heating, reacting, etc. in a tank of
liquid respond with the lag. It is easy to control.

Both lags and dead time are often referred to as "delay", resulting in
frequent confusion when that term is used.

Tim:
I know of a waste treatment plant where the "sludge" (dried "stuff")
was carried to an incinerator on a conveyor belt using a load cell a
few feed away to control the amount of sludge dropped on the belt. I
never knew it was art.

John

Tim Wescott wrote:
Jerry Avins
science forum Guru

Joined: 03 May 2005
Posts: 534

Posted: Wed Jan 04, 2006 10:02 pm    Post subject: Re: PID control

John Shaw wrote:

...

 Quote: I know of a waste treatment plant where the "sludge" (dried "stuff") was carried to an incinerator on a conveyor belt using a load cell a few feed away to control the amount of sludge dropped on the belt. I never knew it was art.

Sludge in a sewage plant is a mass of bacteria, alive when first
extracted. Some of it is pumped back to the head of the process to serve
as a starter culture. At "my" plant, there are two such loops; one to
remove mostly carbon from the process stream, the other, mostly
nitrogen. Sludge has a mild but distinctive odor when still alive. I've
learned to distinguish the two cultures by nose. Like most animals (in
this case, animalcules), it stinks when dead.

http://sbrsa.org/

Jerry
--
Engineering is the art of making what you want from things you can get.
ŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻ
Tim Wescott
science forum Guru Wannabe

Joined: 03 May 2005
Posts: 292

Posted: Wed Jan 04, 2006 10:17 pm    Post subject: Re: PID control

John Shaw wrote:
 Quote: Tim, I love your example. I will have to remember it. I am just glad that the "stuff" is synthetic. The oddest part of the experience for me was that I came in on the

middle of it, the sound was turned down and I wasn't really paying
attention. First it took me a while to realize that a team of people
were working on making a machine that produces crap. Then I was
thinking "well this is gross, but I suppose there's good science in
understanding just what our guts do from one end to the other".

Imagine my surprise when they showed the room filling with the arty
crowd, and people were waxing enthusiastic over this new art form. Then
I was thinking "what a waste* of time".

* This whole subject is just filled with opportunities for double entendres.

--

Tim Wescott
Wescott Design Services
http://www.wescottdesign.com
John Shaw
science forum beginner

Joined: 25 Mar 2005
Posts: 29

Posted: Wed Jan 04, 2006 11:42 pm    Post subject: Re: PID control

Jerry,

I have had a little experience with waste treatment, but not much. I
did learn about what sludge is (dried "stuff" is rather simplistic, but
we know where it comes from). When the concept of return activated
sludge was explained, it was compared to taking a spoonful of yogurt to
start the next batch.

On the wall of the maintenance shop of the plant was a sign directed to
us from the outside: "It may be s*** to you, but it's bread and butter
to us".

John Shaw
www.jashaw.com/pid

Jerry Avins wrote:
 Quote: John Shaw wrote: ... I know of a waste treatment plant where the "sludge" (dried "stuff") was carried to an incinerator on a conveyor belt using a load cell a few feed away to control the amount of sludge dropped on the belt. I never knew it was art. Sludge in a sewage plant is a mass of bacteria, alive when first extracted. Some of it is pumped back to the head of the process to serve as a starter culture. At "my" plant, there are two such loops; one to remove mostly carbon from the process stream, the other, mostly nitrogen. Sludge has a mild but distinctive odor when still alive. I've learned to distinguish the two cultures by nose. Like most animals (in this case, animalcules), it stinks when dead. http://sbrsa.org/ Jerry -- Engineering is the art of making what you want from things you can get. ŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻ
John Shaw
science forum beginner

Joined: 25 Mar 2005
Posts: 29

Posted: Wed Jan 04, 2006 11:59 pm    Post subject: Re: PID control

When I was first involved in the control systems industry many years
ago I attended a large water/waste treatment trade show (commonly known
as the "S**** Show"). This was before computers and CRTs were common in
vendor's booths. Many equipment and process design firms had working
models of their processes and equipment, complete with plastic vessels
and pipes with water, some of which contained solid material that was
removed in the demo. I talked to a model maker who worked on the
exhibits and who told me that what I saw was "synthetic crap". At least
it was white, I guess to avoid grossing anyone out.

One thing I learned was that people in that industry had a sense of
humer in their work. We had an early eight color CRT on our system.
Many customers asked if brown was one of the colors! It wasn't.
Jerry Avins
science forum Guru

Joined: 03 May 2005
Posts: 534

Posted: Thu Jan 05, 2006 1:31 am    Post subject: Re: PID control

John Shaw wrote:

...

 Quote: One thing I learned was that people in that industry had a sense of humer in their work. ...

Not just people in the industry, but people associated with it. My kids
occasionally introduced me as the S*** Commissioner.

Jerry
--
Engineering is the art of making what you want from things you can get.
ŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻ
Setanta11
science forum beginner

Joined: 17 Nov 2005
Posts: 45

Posted: Mon Feb 13, 2006 7:04 am    Post subject: Re: PID control

"A. Paul Montgomery" <no@not.com> wrote in message
news:MPG.1e23ab8238758dd6989680@free.teranews.com...
 Quote: In article <2YqdnUktFon2VyTeRVn-pg@web-ster.com>, tim@seemywebsite.com says... Define delay. The last time I look at first order response it was something like 1-exp(-a*t). Even at time t=0+ there is some response. I suppose that even an ideal RC circuit has some dead time if you consider the dead time due to the speed of electric current. Peter Nachtwey Classic phase delay. I'm surprised at your example, because it's not restricted to 1st-order systems: any continuous-time, linear system with a finite number of states has some response at time t = 0+; in a strict sense "dead time" only has meaning in sampled-time systems and systems with an infinite number of states (thermal, fluid flow and long strings of coax all come to mind). I've kept quiet on conversations that involve mathematical calculation of control response. I must admit that I have been somewhat lost. Some of this has to do with the way I came up in the field and some has to do with the changes that have occurred while I have been absent so I am trying to catch up to the point where I at least follow what is being discussed. Most of the discussions to me have little practical usage in my business anyway. So excuse me if my intrusions seem lost, they are. Tim, you seem to think in electronic and/or digital terms. Part of my problems may be definitions here. Can a definition of "dead time" be given here thinking in physics terms and differentiate that from hysteresis. -- Paul Montgomery Progressive Gauging Inc.

Dear Paul Montgomery

Dead time is perhaps best described generally and for any process.

Consider a system that has one input and one output - and the input and
output are measured.
A system has a delay if there is no measurable output even though there is
an input that will eventually excite an output

Perhaps A good example would be to consider a system where the input is
energy and the output is the temperature of water/steam in say a steam
turbine is the output.
Using sufficient Energy as an input to the system - the output temperature
will rise to 100[deg. C] and then will cease to rise until the vapour
becomes superheated (pressure measurement required)

You can then argue that a delay in temperature rise is due to some physical
attribue of the system causing a DELAY to the MEASURED variable.

A delay can conceivably happen anywhere in a system.

Hysteresis would be present in the system IF you reversed the above process
and the deadtime didnt occur in exactly the same place. i.e.he reverse is
not truly true

All the above relates to the PHYSICAL PROBLEM

The DIGITAL DOMAIN of this problem is related to the ACTUAL MEASUREMENT and
control of the system - this is of course assuming DCS.
As a measurement of anything depends upon what frequency in the measured
signal needs to be represented.- the sampling frequency of the conversion
from analog to digital is linked to the process itself. The choice of
sampling frequency can become complicated for large systems especially when
there is an actual physical time delay in the system.

Hope this helps

Kieran
PLC Trainer
science forum beginner

Joined: 21 Feb 2006
Posts: 3

 Posted: Tue Feb 21, 2006 5:01 pm    Post subject: Re: PID control Hi : I thought readers of this informative discussion might be interested in more PID training. There is a two day seminar in Saint Louis coming up. http://www.bin95.com/PID_Process_Control_Saint-Louis.htm The Practical Process Control Training course (more than just a PID tutorial), will give you a firm foundation in Process Control and PID control tuning. They use a special software for training that helps clarify the topic. This training software evolved from their 13 years of experience and their existing PID tuning software. Check it out.
Johnson Luqaz
science forum beginner

Joined: 27 Mar 2006
Posts: 4

Posted: Wed Apr 19, 2006 7:44 am    Post subject: Re: How to stop Piracy?

Exterminate all chinese!!

On Tue, 18 Apr 2006 14:35:04 +0800, <synkore@gmail.com> wrote:

 Quote: Several days ago, I got one call from my under-classmate in Notre Dame. Now he worked as the sales director in one famous design software company. He asked me about the electronic design industry in China. He told me that everyone knows that China is a huge market but most company hesitates to enter China market due to piracy. Everyone knows that piracy has a significant impact on the high-tech industry, resulting in lost jobs, decreased innovation and higher costs. As a Chinese who has been working in USA for more than 10 yrs, I understand his worry and I also believe Chinese government has realized this. But it seems a mission impossible to stop piracy in a country like China. But could anyone tell me what's the best way to solve the piracy problem? Any advice will be greatly appreciated! Thank you in advance! Seeking for a customer centered PCB fabricator with high-quality and most cost-effective service? SynKore is your perfect option! Send email to sales@synkore.com or visit www.idealpcb.com, www.advpcb.com,

--
Kuala Lumpur
MALAYSIA : UTC +08:00
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Using Opera's revolutionary e-mail client: http://www.opera.com/mail/
Setanta11
science forum beginner

Joined: 17 Nov 2005
Posts: 45

Posted: Fri May 12, 2006 12:25 am    Post subject: Re: How to stop Piracy?

take away blackbeards pieces of ate

<synkore@gmail.com> wrote in message
 Quote: Several days ago, I got one call from my under-classmate in Notre Dame. Now he worked as the sales director in one famous design software company. He asked me about the electronic design industry in China. He told me that everyone knows that China is a huge market but most company hesitates to enter China market due to piracy. Everyone knows that piracy has a significant impact on the high-tech industry, resulting in lost jobs, decreased innovation and higher costs. As a Chinese who has been working in USA for more than 10 yrs, I understand his worry and I also believe Chinese government has realized this. But it seems a mission impossible to stop piracy in a country like China. But could anyone tell me what's the best way to solve the piracy problem? Any advice will be greatly appreciated! Thank you in advance! Seeking for a customer centered PCB fabricator with high-quality and most cost-effective service? SynKore is your perfect option! Send email to sales@synkore.com or visit www.idealpcb.com, www.advpcb.com,
fulliautomatix
science forum beginner

Joined: 01 May 2005
Posts: 34

Posted: Thu May 25, 2006 1:26 pm    Post subject: Re: Any Chemical Engineers Can Advise on Soda Ash?

BIGEYE wrote:
 Quote: We have a soda ash mixing plant that we want to use to make up batches of soda ash solution, and use this for pH control. The mixing plant consists of 2 x 900 litre tanks fitted with electric mixers. We will fill each tanks with 900 litres water, then add about 200 kg of dense soda ash powder to each tank. This gives a solution pH of about 11.8 when mixed. Can anyone advise how long this solution should be mixed to ensure that the powder is completely dissolved. Also, once the solution is mixed, if it is not used for some time and just sits in the tanks, can the soda ash re-crystallise and settle out in the bottom of the tank? Appreciate any advice. mmm - no but I can tell you about vinnipas in styrene for vinyl ester

pultrusion resins

seriously though...mix a scaled solution of 200 g/L with a mixer ~the
same speed as the one on your tank and see how long it takes; it is
probably best to feed it in slowly so as not to bog the mixer...if you
had 200 kg of stuff sitting on the bottom of a tank and turned the mixer
on it would not be happy

the bigger tanks usually have a slowish low powered mixer to keep the
solution stirred rather than do the initial dispersion...if the initial
dispersion is difficult, a couple of smallish (~100 L) high concentrate
batches in a shear mixer is the go, then dilute in the bigger tank

leave it for a while and see if it settles out...though the idea is to
leave the stirrer going or pulse it 10 min on, 1/2 hr off etc to keep
the solution from settling
Jerry Avins
science forum Guru

Joined: 03 May 2005
Posts: 534

Posted: Tue Jul 18, 2006 8:20 pm    Post subject: Re: GeneXproTools 4.0 - GEP modeling tools for Math and Boolean problems

Candida Ferreira wrote:
 Quote: I'm proud to announce that Gepsoft is releasing today GeneXproTools 4.0, a new version of the easy and powerful predictive analytics tool APS 3.0.

...

How refreshing! I've become accustomed (here and in other groups) to ads
that start, "I just happened to run across this here website, see, and I
though somebody else might be interested."

I hope your product does well.

Jerry
--
Engineering is the art of making what you want from things you can get.
ŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻ

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