chp13SQ

Apply Your Knowledge

13.8
The velocity form of the PID controller was used in the simulation that produced the dynamic response in the figure. Why was this form used?

IMPLEMENTATION

	Only the velocity form can be implemented in a digital computer
	The velocity form gives more accurate values for the integral and derivative modes.
	The velocity and full position forms give the same behavior.
	None of the above.

13.9
The frequency response for a disturbance affecting a feedback control loop is plotted in the figure. Which statement describes the behavior in region A?

Frequency Response

	Feedback control is very effective.
	The process time constants reduce effects of the disturbance (without control).
	Feedback does not significantly reduce the effects of the disturbance.
	None of the above.

13.10
The frequency response for a disturbance affecting a feedback control loop is plotted in the figure. Which statement describes the behavior in region B?

Frequency Response

	Feedback control is very effective.
	The process time constants reduce effects of the disturbance (without control).
	Feedback does not significantly reduce the effects of the disturbance.
	None of the above.

13.11
The frequency response for a disturbance affecting a feedback control loop is plotted in the figure. Which statement describes the behavior in region C?

Frequency Response

	Feedback control is very effective.
	The process time constants reduce effects of the disturbance (without control).
	Feedback does not significantly reduce the effects of the disturbance.
	None of the above.

13.12
Slow sensor dynamics degrade feedback control performance more than an equivalently slow final element.

TRUE FALSE

13.13
The great majority (but not all) of feedback controllers use the proportional (P) and integral (I) modes.

TRUE FALSE

13.14
We want to determine whether the pressure inside the vessel (P-1) will remain below its maximum limit for a 20% step increase in feed. Which method would you recommend?

13.15
The integral mode of the PID controller provides which of the following performance characteristics?

13.16
We want to place a small tank in this process to reduce the effects of feed composition disturbances. Which location is the better?

Frequency Response

Note: Level control for tanks are not shown to simplify the drawing

	Location A.
	Location B.
	Either gives equivalent performance.
	Neither is a good location.

	Dynamic simulation of the closed-loop system for a 20% step in feed
	Frequency response of the closed loop system for a sine change in feed
	Simulate a +20% feed change with the pressure controller off

	Zero steady-state offset
	Stability
	Rapid response to a disturbance