Comparing Controller Tuning Methods
Process 3
Zeigler Nichols Open Loop Response Method
The first tuning method to be used is the ZN Open Loop Response Method.
Below is the open loop response to a unit step change in the input.
From this determine
- The steady state process gain
- The time delay
- The first order time constant
Hence it is now possible to evaluate
- The controller gain
- The controller reset time
Open Loop Correlations
From the above open loop response it is also possible to determine
Using this value and the correlations given previously it is possible to
evaluate
- The Ciancone dimensionless gain and reset time
- The Lopez dimensionless gain and reset time
From these evaluate the controller parameters.
Closed Loop Methods
The next tuning methods to be used are the Zeigler Nichols Closed Loop
Method and a similar damped response method. Both of these require the
process to be controlled using proportional only control. Below is a
Java Applet which does preciously this. All you have to do is change
the value of the gain.
Since the scale on the graph is sometimes hard to read accurately it is
ppossible to click anywhere and obtain the coordinates of that
particular point. This will help you to evaluate the Ultimate Period
and the Amplitude of the oscillations.
Hence it is possible to determine
- The ultimate gain
- The ultimate period
- The damped gain
- The damped period
and evaluate another two values for the controller parameters.
Relay-Based Control
The final tuning method to be tried in this experiment is a Relay-Based
Control Method. Below is an applet in which it is possible to change
the relay output amplitude. From the resulting change in output it is
possible to evaluate the controller parameters.
Comparing the Controller Values
The aim of this final section is to go through all the controller
parameter values obtained above and actually try them out in the process
to evaluate which tuning method gives the optimal control.
Check your answers!
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