Pid Basic Functions; Cont_C; Description Cont_C - Siemens SIMATIC S7-1200 Function Manual

9.4

PID basic functions

9.4.1

CONT_C

9.4.1.1

Description CONT_C

The CONT_C instruction is used on SIMATIC S7 automation systems to control technical
processes with continuous input and output variables. You can assign parameters to enable
or disable sub-functions of the PID controller and adapt it to the process. In addition to the
functions in the setpoint and process value branches, the instruction implements a complete
PID controller with continuous output value output and the option of manually influencing the
value of the output value.
Application
You can use the controller as a PID fixed setpoint controller, or in multi-loop control systems,
also as a cascade, blending or ratio controller. The functions of the controller are based on
the PID control algorithm of the sampling controller with an analog signal, if necessary
extended by including a pulse shaper stage to generate pulse-width modulated output
signals for two or three step controllers with proportional actuators.
Call
The CONT_C instruction has an initialization routine that is run through when input
parameter COM_RST = TRUE is set. During initialization, the integral action is set to the
initialization value I_ITVAL. All the signal outputs are set to zero. COM_RST = FALSE has to
be set after the initialization routine has been completed.
The calculation of the values in the control blocks is only correct if the block is called at
regular intervals. You should therefore call the control blocks in a cyclic interrupt OB (OB 30
to OB 38). Enter the sampling time in the CYCLE parameter.
If you call the instruction CONT_C as a multiple instance DB, no technology object is
created. No parameter assignment interface or commissioning interface is available. You
must assign parameters for CONT_C directly in the multiple instance DB and commission it
via a watch table.
Error information
The error message word RET_VAL is not evaluated by the block.
PID control
Function Manual, 03/2017, A5E35300227-AC
Instructions
9.4 PID basic functions
449