Pre-Experimental Questions

Part 1 - No Disturbance

For this option simply click on the button to obtain the open loop response. This shows the response of the concentration when the diluent flow is constant at 1.0 units/time and there is a step change in the manipulated variable (the concentrate flow) from 1.0 - 1.5 units/time.

Look at the response and ask yourself these questions before looking at the ANSWERS.

• What is the gain of the system?
• Will the controller gain be positive or negative?
• How quick is the response?
• Is there a time delay?
• What controller parameters does this give (ZN open-loop method)?

Part 2 - An Increase in the Diluent Flowrate

In this experiment the diluent flowrate increases from 1 - 1.5 units/time and the concentrate flowrate is used by the controller as the manipulated variable to counteract this change.

First try running the experiment with no control:

• How does the system respond to this change?
• How quick is the response?

Now try running with proportional only control (set reset time to zero):

• Is the gain +ve or -ve?
• What is the smallest gain which gives a constant amplitude oscillation (the ultimate gain)?
• What is the period of this oscillation?
• What controller settings does this give (ZN closed-loop method)?
• What is happening in the system at this point?

Finally run the simulation with proportional/integral control:

• Compare the two ZN tuning methods
• What controller settings give the best response?

To run the simulation click on the button below. This will give the response to an increase in the diluent flow with no control when the gain and reset are both 0. Then simply change the parameters and re-run the simulation until you are able to answer the above questions before looking at the ANSWERS.

Part 3 - A Decrease in the Diluent Flowrate

In this experiment the diluent flowrate decreases from 1 - 0.5 units/time and the concentrate flowrate is used by the controller as the manipulated variable to counteract this change.

Please answer the same questions as for the above section - An Increase in the Diluent Flowrate.

As before the response of the concentration to a decrease in the diluent flowrate but with no control can be obtained by clicking on the button below with a gain and reset of 0: ANSWERS.

Return to Virtual Control Laboratory to try a different experiment