chapter14

Chapter 14 Cascade Control

The questions will be categorized according to the key concepts in the Chapter.

CASCADE DESIGN CRITERIA	DEGREES OF FREEDOM
IMPLEMENTATION ISSUES

Solidify the Concepts

14.1
Which of the following statement(s) does NOT appear in the cascade control design criteria?

DESIGN CRITERIA

	The secondary variable must indicate the occurrence of an important disturbance.
	Only one valve can influence the secondary and primary variables.
	The secondary variable dynamics must be faster than the primary variable dynamics.
	There must be a causal relationship between the manipulated and secondary variables.

14.2
The primary controlled variable in a cascade design is typically the product quality

DESIGN CRITERIA

TRUE FALSE

14.3
The secondary variable in a cascade can respond to more than one disturbance.

DEGREES OF FREEDOM

TRUE FALSE

HINTS:

What disturbances would effect the reactor effluent composition?

Which of these disturbances would be measured by the secondary variable?

14.4
Cascade control is limited to two levels, because of the delay in passing the decisions down the levels of controllers.

IMPLEMENTATION

TRUE FALSE

14.5
For the cascade control design in the figure the temperature controller can be referred to as:

We need to use terminology that other engineers understand.

14.6
Cascade control involves two controlled variables, but only one valve.

DEGREES OF FREEDOM

How are degrees of freedom satisfied?

	The description is not correct; cascade involves two controlled variables and two valves.
	The description is not correct; cascade involves one controlled variable and one valve.
	Cascade control involves two controlled variables, but only the primary variable is controlled independently by the valve.
	The degrees of freedom principle does not apply to a system with two controllers.

14.7
The principle reason for cascade control is to provide improved responses to set point changes

IMPLEMENTATION

TRUE FALSE

14.8
Which of the following statements are true for a valve positioner?

IMPLEMENTATION

To answer the question, you need to be able to describe a valve positioner.

14.9
Cascade control requires more instrumentation than the equivalent single-loop control.

IMPLEMENTATION

	Instrumentation includes valves, sensors, and signal transmission.
	TRUE FALSE

	It is a secondary in a cascade control system.
	It uses no measured variable.
	It can improve the control performance for a slow feedback control loop.