9
Method 3:
A last method that can be used is the open loop test by doing a step change in output signal manually (output 9-10).
The goal is to suppose the response system temperature when a step change is done in output as indicated on the following picture:
1. Put the regulator in manual mode by setting parameter POE from PI to a value from 0 to 10V. Write this value (POE
1
).
2. Let the temperature stabilizes.
3. Increase the ouput voltage to do a step change. Write the value choosen (POE
2
).
4. Map the temperature as indicated on picture.
5. The gain of process is given from following expression
To set parameters manually, each parameter must be set. One can apply the method of test and error.
Method 1:
Proportional band setting
:
1. Set the parameter Ti to
no
I
in order to put the regulator in proportional regulator only.
2. Set a large proportional band.
3. Change the setpoint a little and observe how the system is reacting. The response will be sluggish.
4. Tighten by decreasing the value in half. Change the setpoint a little and observe how the system is reacting. If the system is
still sluggish and does not oscillate, tighten by decrease the value in half again.
5. Repeat the point 4 until the system begins to oscillate constantly.
6. Multiply last proportional band set by 2.
integral time added
1. Set a large integral time.
2. Change the setpoint a little and observe how the system is reacting. The response will be sluggish.
3. Tighten integral time by decreasing the value in half and repeat the point 2 until an oscillating response is obtained with a
small setpoint change.
4. Multiply last integral time obtained on point 3 by 2.
Method 2:
Another method is the Ziegler-Nichols method. Repeat point 1 to 4 of proportional band setting in order to find out the proportional
band that creates stable oscillations. By measuring the period of oscillations and the proportional band limit Bp
Lim
set, parameters
Bp and Ti are calculated for regulation.
Decrease of proportional band:
test 1: dotted line
test 2: line with points
test 3: continuous line
Decrease of Ti:
test 1: dotted line
test 2: line with points
test 3: continuous line
Bp= 2 Bp
Lim
Ti = 0.83 period
