Feedback Loops

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Feedback Loops

• Andrew McCarthy

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Purpose of Feedback

• The primary reason for feedback control is to
  measure and compensate for the effect of
  disturbances.

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4 Elements of Feedback

• Sensor
• Reference Input
• Comparator
• Control Mechanism

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Sensor

• The sensor measures the variable that we seek to
  control, also known as the control variable.

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Reference Input

• This specifies the value the controlled variable
  should have.

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Comparator

• Compares the sensed value with the reference
  value. It also specifies the direction in which
  the correction needs to be made.

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Control Mechanism

• Takes the output of the comparator and corrects
  the sensed value in the direction of the
  reference input.

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Practical Examples

• Cruise Control
• Pitch Control of Airplane

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Practical Examples

• Inverted Pendulum

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Environmental Context

• It is possible, in the context of economic
  growth, to have two loops, one which works to
  reinforce growth, and the other which mitigates
  against further growth.

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Environmental Context
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How is pollution sensed?

• Monitoring agencies use EPA approved equipment.
  PM and lead are measured over a 24 hour period,
  whereas gaseous pollutants are measured hourly.
  Collected data is then compared to the Clean Air
  Act standards (NAAQS) for each pollutant.