Study Questions

Apply Your Knowledge

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.











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

Feedback Control












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.










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














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













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

Level Process











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

Control Objectives








wpe11.gif (4458 bytes)










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.