Calculating The Manipulated Variable - Siemens SIMATIC Manual

Continuous Temperature Controller FB 58 "TCONT_CP"
Parameter Settings of a P or PD Controller with Operating Point
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:
•
I_ITL_ON = TRUE
•
I_ITLVAL = operating point;
Feedforward Control (DISV)
A feedforward variable can be added at the DISV input.
2.1.3

Calculating the Manipulated Variable

The schematic below is the block diagram of the manipulated variable calculation:
CONZONE
LMN_Sum
ER
CONZ_ON,
CON_ZONE
Parameter assignment user interface
FB call interface
Parameter assignment user interface, FB call interface
Control Zone (CONZ_ON, CON_ZONE)
If CONZ_ON = TRUE, the controller operates with a control zone. This means that
the controller operates according to the following algorithm:
•
If PV exceeds SP_INT by more than CON_ZONE, the value LMN_LLM is
output as the manipulated variable (controlled closed-loop).
•
If PV falls below SP_INT by more than CON_ZONE, the value LMN_HLM is
output as the manipulated variable (controlled closed-loop).
•
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).
Note
The changeover from controlled closed-loop to automatic closed-loop control
takes into account a hysteresis of 20% of the control zone.
2-6
MAN_ON
MAN
LMNLIMIT
1
0
LMN_HLM
LMN_LLM
QLMN_HLM
QLMN_LLM
LMN_NORM
LmnN
LMN_FAC,
LMN_OFFS
PULSEGEN
LMN
CRP_OUT
LMN_PER
%
PID Temperature Control
A5E00125039-02