User's Manual

Automation and Drives - SCE
T I A Training Document Page 39 of 64 Module
4.2 (S) FB 41 “CONT_C“
(S)FB 41 "CONT_C“ (continuous controller) is used for controlling technical processes with
continuous input and output variables on the PLC SIMATIC S7. By means of parameter
assignments, you can switch on or switch off subfunctions of the PID controller, and thus adjust it to
the controlled system.
Use:
You can use the controller as PID fixed setpoint controller individually, or in multi-loop control
systems as cascade controller, blended controller, or ratio controller. The working method is based
on the PID algorithm of the sampling controller with analog output signal; if needed, supplemented
with a pulse shaper step to generate pulse-width-modulated output signals for two position or three
position controller with proportional final control elements.
Description:
In addition to the functions in the setpoint and actual value, the (S)FB implements a complete PID
controller with a continuous manipulated variable output and the capability to influence the
manipulated value manually.
Depending on the CPU type, it can be used as FB 41 or as SFB 41.
The following subfunctions exist:
- Setpoint branch
- Actual value branch
- System deviation generation
- PID algorithm
- Manual value processing
- Manipulated value processing
- Feedforward control
Operating modes complete restart/restart
The (S)FB 41 (CONT_C) has a complete restart routine that is run if the input parameter is set to
COM_RST = TRUE.
At startup, the integrator is set internally to the initialization value I_ITVAL. When called in a time
interrupt level, it continues processing starting with this value.
The other outputs are set to their default values.
Error Information
The error signal word RET_VAL is not used.
Preface Fundamentals Discontinuous Action Controllerr Controller Block (S)FB41 Setting the System Appendix
B3
Issued: 02/2008 Control Engineering with STEP 7