If the manipulated variable is limited, the I-action is stopped. If the error moves the I-
action back in the direction of the manipulated variable range, the I-action is enabled
again.
The I-action is also modified by the following measures:
n The I-action of the controller is deactivated by TI = 0.0
n Weakening the P-action when setpoint changes occur
n Control zone
n The limits of the manipulated variable can be changed online
To prevent overshoot, you can weaken the P-action using the "proportional factor for set-
point changes" parameter (PFAC_SP). Using PFAC_SP, you can select continuously
between 0.0 and 1.0 to decide the effect of the P-action when the setpoint changes:
n PFAC_SP = 1.0: P-action has full effect if the setpoint changes
n PFAC_SP = 0.0: P-action has no effect if the setpoint changes
The weakening of the P-action is achieved by compensating the I-action.
n The D-action of the controller is deactivated with TD = 0.0.
n If the D-action is active, the following relationship should apply: TD = 0.5 * CYCLE *
D_F
In the user interface, deactivate the I-action (TI = 0.0) and possible also the D-action (TD
= 0.0). Then make the following parameter settings:
n I_ITL_ON = TRUE
n I_ITLVAL = operating point;
A feedforward variable can be added at the DISV input.
The schematic below is the block diagram of the manipulated variable calculation:
If CONZ_ON = TRUE, the controller operates with a control zone. This means that the
controller operates according to the following algorithm:
n If PV exceeds SP_INT by more than CON_ZONE, the value LMN_LLM is output as
the manipulated variable (controlled closed-loop).
n If PV falls below SP_INT by more than CON_ZONE, the value LMN_HLM is output as
the manipulated variable (controlled closed-loop).
n If PV is within the control zone (CON_ZONE), the manipulated variable takes its value
from the PID algorithm LMN_Sum (automatic closed-loop control).
Weakening the P-Action
when Setpoint Changes
Occur (PFAC_SP)
Derivative Action Element
(TD, D_F)
Parameter Settings of a P
or PD Controller with
Operating Point
Feedforward Control
(DISV)
Calculating the Manipu-
lated Variable
Control Zone (CONZ_ON,
CON_ZONE)
VIPA SPEED7
Standard
PID Control > FB 58 - TCONT_CP - Continuous Temperature Control
HB00 | OPL_SP7 | Operation list | en | 18-30 868
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