8205
E-41-
pH CONTROLLER 8205
On the basis of Kcrit and Tcrit, the controller parameters can then be calculated in accordance with
the following table:
Parameter settings according to Ziegler und Nichols :
Controller type
Parameter settings
P controller
Kp = 0,5 Kcrit
P controller
Kp = 0,45 Kcrit
Tn = 0,85 Tcrit
P controller
Kp = 0,6 Kcrit
Tn = 0,5 Tcrit
Tv = 0,12 Tcrit
The Ziegler and Nichols adjustment rules were determined for P systems with a time delay of the first
order and a dead time. However, they apply only to controllers with a disturbance response, but not
to controllers with a command response.
Adjustment rules according to Chien, Hrones and Reswick (manipulated variable methode):
When using this method, the controller parameters are adjusted on the basis of the control system's
transition response. A 100% change in the manipulated variable is output. The time Tu and Tg are
derived from the progression of the actual value of the control variable (following figure). Ks is the
proportional action coeffficient of the control system.
APPENDIX
t
X
Tu
Tg
KS.
Y
X
t
t
Figure : Progression of the controlled variable after a manipulated variable change
∆
Y
Method :
- Set the controller to MANUAL mode.
- Output a manipulated variable change and record the controlled variable with a recorder.
- Switch off in good time if you encounter critical progressions (e. g. a risk of overheating) (Pay
attention to the fact that, in thermally inert systems, the actual value of the controlled variable may
increase further switching off).
Actual value
