Manual Fine Tuning In Control Mode - Siemens SIMATIC Manual

Controller Tuning in FB 58 "TCONT_CP"
3.12

Manual Fine Tuning in Control Mode

To achieve a setpoint response free of overshoot, you can take the measures
described below:
Adapting the Control Zone
During the tuning, a control zone CON_ZONE is calculated by FB58 "TCONT_CP"
that is activated (CONZ_ON = TRUE) if the process type is suitable (process type I
and II) and a PID controller is being used. During control, you can modify the
control zone or turn it off completely (with CONZ_ON = FALSE).
Note
Activating the control zone with higher order processes (process type III) does not
normally bring any benefit since the control zone is then larger than the control
range that can be achieved with a 100% manipulated variable. There is also no
advantage in activating the control zone for PI controllers.
Before you activate the control zone manually, make sure that the control zone
width is not too small. If the control zone band is too small, oscillations will occur
in the manipulated variable and process variable.
Continuously Weakening the Control Response with PFAC_SP
You can weaken the control response with the PFAC_SP parameter. This
parameter specifies the amount of P-action that is effective in setpoint step
changes.
Regardless of the process type, PFAC_SP is set to the default 0.8 by the tuning
function, you can then modify the value if required. To limit overshoot during
setpoint step changes (with otherwise correct controller parameters) to
approximately 2%, the following values are adequate for PFAC_SP:
Process Type I
Typical temperature
process
PI 0.8
PID 0.6
Adapt the default factor (0.8) particularly in the following situations:
•
Process type I with PID (0.8 -> 0.6): Setpoint step changes within the control
zone lead to approximately 18% overshoot with PFAC_SP = 0.8.
•
Process type III with PID (0.8 -> 0.96): Setpoint step changes with
PFAC_SP = 0.8 are damped too strongly. This leads to a significantly slower
response.
3-16
Process Type II Process Type III
Intermediate range Higher order temperature process
(high lag)
0.82 0.8
0.75 0.96
PID Temperature Control
A5E00125039-02