Minor Loop Control questions



I used Mathcad generate the data pdf995 to generate the .pdf file. Mathcad can generate html files but Mathcad is so screwed up that all the links to the pictures use Microsoft back slashes instead of UNIX forward slashes so the html files don't work well with non Microsoft browsers. I have a love-hate relationship with Mathcad. It does some things extremely well ( symbolic math ) and other things are totally brain dead. Still it is a good deal if you can get a student version. I don't think I could have learned what I have without Mathcad or some other symbolic math package. Matlab and Scilab are good for getting answers. Mathcad is good for figuring out how that answer are derived symbolically.
Peter Nachtwey
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Could you exlpain what is minor loop and how you converted your controller? Could you show block diagram or give a link to some pdf's or something. Try to use AACircuit v1.28.6 beta 04/19/05 www.tech-chat.de proposed by Tim Wescott. Try to configure Forte Agent to look diagrams nice an proper if they don't.
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My definition of plant is diffrent. Plant is something you can't split. Unless you have 3 or four plants in your Gp and among others there is one with Gxp=1/(1+s/100) transfer function. Yo cannot connect anything to any inner term of your plant. It's an abstraction. It could be radial acceleration of some wheel or third derivative of ions concentration or even something stranger and impossible to describe. This is just abstractive model. You can reach only input and output of it. That is what the transfer function represents, input-output relation.
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Mikolaj

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On Apr 23, 3:49 am, Mikolaj

That is limiting, but lets work with that. What about a hydraulic cylinder and servo valve with LVDT feedback. The servo valve LVDT is the inner loop feed back and actuator position feedback is the outer loop. Therefore by your definition the valve is one 'plant' and the actuator is another 'plant' . OK. As long as it works out the same mathematically. Motion controllers often have an inner velocity loop and an outer position loop. All of this is on one card or module. What about this? Adding an accelerometer can also provide feedback to an inner loop.

It is obvious that you can, but you are right. In some cases it is just an abstraction. Some motion controllers use the encoder feedback as the position feedback and the velocity feedback. It is just a couple lines of code. I think you are just hung up on the idea that the valve and the actuator can be consider just one 'plant'.

I agree that one shouldn't states that can't be measured as feedback in an inner loop. It wouldn't make sense to do so. But what if you can measure the acceleration with an accelerometer as I said above?
Peter Nachtwey
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Mikolaj wrote:

In practice when you see a "plant" on a block diagram it means little more than what the guy drawing the diagram wanted to call a "plant". If I'm building servo-controlled valves, then my "plant" is your "actuator". If you're buying my valves to build diesel engines, then your "plant" may be a crane-building company's "actuator".
So, in general, you can't say that a block labeled "plant" is irreducible, and you can't say that a reducible block that's labeled "plant" is done so incorrectly.
I have absolutely no argument to the idea that you can't reach inside of an irreducible block and pluck out an inner state, however.
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Tim Wescott
Wescott Design Services
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I agree, but there are plants that cannot be describe analyticaly. (I worked with thermal process that is known only experimentally and I can't connect anything inside it's transfer function) I agree that simple mechanism can be described exactly (more or less we know there is a mass and a viscosity friction and a spring).
That is not the point. When talking about homeworks we use "blocks" but we must remember of reality. We should specify what we can and can not do with our blocks.

I saw models of hydraulic valves but who in practice analyses it's gap shape influence on some transfer function (well, maybe valve inventors )? Can you get inside the valve? We know it's block model. That's why we need observers. To observe something that maybe has interpretation but not necessarily.
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Mikolaj

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