Study Questions

Apply Your Knowledge
18.7
What initial tuning approach would you recommend for the level controller given below to give tight control.

Level Process

Why do we call this an initial tuning?

 

Process reaction curve for the model and Ciancone PI tuning

Use correlations in equations (18.9) and (18.12) for "tight level control"

 

 Phone your lab partner, who seems to know everything.
 

 

 

 

 

 

 

 

 

 

 

18.8
When using proportional - only level control, be sure that KpKc < 1.0 to ensure that the closed-loop system is underdamped.

Feedback Control

TRUE        FALSE


 

 

 

 

 

 

 

 

 

 

18.9
In the derivation of the PI level tuning approach, the damping coefficient x =1 was selected because

Control Objectives

The damping coefficient is displayed below as either Greek letter xi  or  x, depending on the browser that you are using.

 

When x < 1, the system will be unstable

When x > 1, there are large oscillations
 

 When x = 1, non-oscillatory behavior is obtained

Not true, we did not specify x.

 

 

 

 

 

 

 

 

 

18.10
When tuning levels in series, we ensure that each level loop is overdamped because

Control Objectives

Many processes in series will behave like tanks in series.

 

otherwise, the system might become unstable

In a series of  underdamped levels, oscillations tend to amplify

 

 the manipulated flows will not overshoot their final values
 

 

 

 

 

 

 

 

 

 

 

 

 

 

18.11
Why does the non-linear PI feedback controller have a high-gain region?

Feedback Control

 

Two values for the controller gain confuses students.

The high gain is needed to take aggressive action when the level approaches it's maximum or minimum.

 

 To keep the system overdamped

 

 

 

 

 

 

 

 

 

 

 

 

18.12
Steam in a heat exchanger is condensed. The level of water in the exchanger is non-self-regulating.

Level Process

TRUE        FALSE


 

 

 

 

 

 

 

 

 

18.13
Select the inventories where the "tight control" objective is appropriate for the level controller.

Control Objectives

 

 

 

 

 

 

 

wpe11.gif (4458 bytes)

 

 

 

 

 

 

 

 

 

18.14
Which of the following can be used to measure liquid level.

Level Process

We need to measure the level, so that we can control it.

 

 

Throw in your teaching assistant, and see if he/she sinks.

Measure the position of a float on the surface.

 

 Measure the pressure difference between points above and below the interface.

Measure the weight of a mass partially immersed in the liquid.