1. Feedback Loops Andrew McCarthy

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

3. 4 Elements of Feedback  Sensor  Reference Input  Comparator  Control Mechanism

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

5. Reference Input This specifies the value the controlled variable should have.

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

7. Control Mechanism Takes the output of the comparator and corrects the sensed value in the direction of the reference input.

8. Practical Examples  Cruise Control  Pitch Control of Airplane

9. Practical Examples  Inverted Pendulum

10. 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.

11. Environmental Context

12. 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.