Feed-Forward vs Feed-Back

  • Thread starter mXSCNT
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I'm reading about feedback and I came across the following paragraph from http://en.wikipedia.org/wiki/Feedback: [Broken]
The natural sense of feedforward is defined chemically by some irreversible reaction, or electronically by an active circuit element that has access to an auxiliary power supply, so as to be able to provide power gain to amplify the signal as it propagates from input to output. For example, an amplifier can use power from its controlled power reservoir, such as its battery, to provide power gain to amplify the signal; but the reverse is not possible: the signal cannot provide power to re-charge the battery of the amplifier.

This seems to imply that a feed-forward process is irreversible. The reason the signal can't provide power to recharge the battery is the 2nd law of thermodynamics.

Is the converse true - are feed-back processes reversible in some sense?
 
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  • #2
jim hardy
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to my simple way of thinking,,

It sounds to me like a chemist has drawn a poor analogy.

Power conversion equipment can be bi-directional but not 100% efficient,
but your average analog amplifier indeed puts out mostly heat and that is irreversible.

I personally have never seen a computer make anything besides heat and frustration.
 
  • #3
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Yes, bad analogy.

Feedback is when you examine the output of a system and compare it to a desired output. You then use that information to alter the input to the system to bring the output to the state you want. When you do this a new dynamic system is created that is different in behavior from the original system.

Feed forward control is when you make a "look-up table" of expected outputs for given inputs. To control the system, you simply command it to the desired output. The original system dynamics are retained but there can be error in the output which goes uncorrectd.
 

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