Test #7 Flashcards
Sketch a block diagram of a cascade control system correctly labeling components and signal lines.
State the main factor to consider when using Cascade control.
The secondary controller and its associated loop should have a 5 to 10 times smaller time constant than the primary controller and its associated loop.
What are some other factors?
- Cascade control with two proportional mode controllers provides more precise control than a single-loop PID Controller.
- The secondary or inner loop should be tuned first, then the outer loop.
- The secondary proportional gain should be higher than the outer loop.
If cascade control was to be retrofitted to a closed loop position control system what variable would you choose as the manipulated variable?
The speed of the actuator would be my choice for the manipulated variable.
Explain the theory behind Feed forward Compensation.
Feedforward compensation assesses the effect of the disturbance before it hits and compensates for the disturbance as it arrives.
What is one of the weaknesses of Feed forward Control?
One of the weaknesses of feedforward is its reliance on the compensation network to accurately model the affect of the disturbance
In each case describe how each system will respond to a step input.
a) Stable system, b) Marginally Unstable system, and c) Unstable system
- Stable - In response to a step change in the input the output will eventually settle out (may have overshoot) at a given value.
- Marginally Stable or Marginally Unstable - In response to a step change in the input the output oscillates but its oscillations do not grow in amplitude.
- Unstable - In response to a step change in the input the output oscillates with ever increasing amplitude.
Determine the Gain and Phase Margin from the graph at the right.
How can we ensure the highest effective gain without changing the op-amp forward gain?
We can ensure the highest effective gain by increasing the load resistor.
We discovered that the addition of feedback to an op-amp will increase the bandwidth but decrease the maximum system gain.
a) Is this an acceptable tradeoff?
b) Why or Why not?
This is an acceptable tradeoff as gain can be increased by simply placing more sections in series; Bandwidth cannot be increased this way.
State how the addition of feedback affects the following:
a) System Gain b) System Sensitivity c) System Input Impedance d) System Output Impedance e) System Bandwidth.
a) System Gain decreases
b) System Sensitivity decreases
c) System Input Impedance increases
d) System Output Impedance decreases
e) System Bandwidth increases
