Control Engineering: Block Diagram

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Discussion Overview

The discussion revolves around a block diagram in control engineering, specifically focusing on the validity of a particular arrow in the diagram and its implications for creating a Transfer Function and obtaining the Control Canonical Form. The scope includes theoretical considerations rather than practical homework problems.

Discussion Character

  • Exploratory
  • Technical explanation
  • Debate/contested

Main Points Raised

  • One participant questions whether the arrow in the blue box of the diagram can be ignored, expressing uncertainty about how to proceed with the Transfer Function and Control Canonical Form.
  • Another participant notes that without additional context, it is unclear if the arrow represents an unknown gain term.
  • A different participant suggests that the blue box might not represent a loose end but rather the input to a second integrator stage, indicating that such drawings were acceptable in their experience.
  • One participant seeks clarification on whether the block can be treated as having only input (U) and output (Y) points if nothing is connected to the blue box.
  • Another participant reflects on the diagram's complexity and suggests that it could have been drawn more clearly, proposing that it represents two cascaded lags with feedback.
  • There is a question about whether the system will oscillate, indicating further inquiry into the system's behavior.

Areas of Agreement / Disagreement

Participants express differing views on the interpretation of the blue box and its implications for the block diagram. There is no consensus on whether the arrow can be ignored or how to best approach the Transfer Function.

Contextual Notes

The discussion lacks a clear problem statement and does not provide specific definitions for terms used, which may affect the interpretation of the block diagram and the assumptions made by participants.

wantan7671
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Hi guys, this is quite an inbetween question , not really homework but still theory.

http://img850.imageshack.us/img850/1290/81696653.jpg

Came across this diagram and was wondering if the arrow (in blue box) can be ignored ? Quite irritated by it now since I can't be sure how I should create the Transfer Function or obtain the Control Canonical Form.

Any help would be fantastic !
 
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There is no way of knowing without more context. There might be some unknown gain term there... but without the problem statement for which that block diagram describes who knows.
 
the question is just to find the transfer function for that block diagram. I drew the blue box myself. Just wondering if it's actually valid to have a drawing like this with "loose ends"
 
"Just wondering if it's actually valid to have a drawing like this with "loose ends" "

Is it really a loose end? Looks to me like input to 2nd integrator stage.
in my day it would have been fine.

Were one building an analog computer that'd be a place one could hook a recorder.

I recognize that as a bear to analyze
would be lots quicker to build with opamps.

old jim
 
Thanks for the insight Jim. So for now, if nothing is connected there, can I assume the entire block only has U (input) and Y (output) points ? And obtain the Transfer Function directly? (or is there another technique for these sort of things?)
 
I think so. It was mid 1960's when i took controls course, so i am really rusty and shudder at the thought of all that algebra now.

But looking at that sketch it seems to me --

they could have drawn it as one horizontal chain
then the X2 line wouldn't have to cross X1 where X2 feeds back to sum with u, so it would look less formidable.

isn't it just two cascaded lags with output of 2nd fed back to input of first one?

i hope you'll post the transfer function.

Think it'll oscillate?

old jim
 

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