Further Examples in Closed Loop Tuning

Pre-Experimental Questions

Below are some questions to think about while you are running the various processes. The answers will be given once the simulation has been run.

Run the process with proportional only control (set reset time to 0). Now determine:
- The Ultimate Gain?
- The Ultimate Period?
What are the corresponding values of the controller gain and reset time for a PI controller using the ZN tuning method?
Try running the process with the ZN parameters. Comment on how you can obtain a better response.
Now take time to investigate the response with control using very large and very small values of controller gain and reset time.

Run Simulation

It is now possible to choose the required process in the form below and run the simulation. Initially the relevent process will be run with no control. When the button is clicked the open loop response will appear given a unit increase in the input. Once this has been analysed different gains and/or integral times can be tried until an understanding of these two parameters is gained.

To choose the type of process simply click on the button beside the short description.
To choose a gain click in the relevent box and change the value.
To choose an integral reset time click in the relevent box and change the value.
Note that the setpoint value is always 0.

Once you are happy with the inserted values, click on the Enter Values button and wait for the computer to generate the results and produce a graph. It is possible to run the experiment as many times as necessary until you think you understand the process and can answer the above questions.

Choose A Process

The first problem deals with a case with which it is impossible to use the Zeiglar Nichols Open Loop Tuning Method:

Delay Only

Next there are a couple more examples of "real processes" which do not follow the ideal ZN first order response:

Lags in Series - 1
Lags in Series - 2

Finally there are some processes which introduce the problems with inverse responses:

Lag and Delay in Parallel
Lags in Parallel - 1
Lags in Parallel - 2

You can also specify the type of control desired. Proportional Integral is the default. If you specify a reset time of 0 however, the integral action will be removed and the controller will function as a proportional only controller.

Gain Reset

Look at answers?

Once you have finished answering the questions, look at the .

Return to Virtual Control Laboratory to try a different experiment