Instructions
9.4 PID basic functions
PID control
Function Manual, 03/2017, A5E35300227-AC
455
The CONT_S instruction is used on SIMATIC S7 automation systems to control technical
processes with binary output value output signals for actuators with integrating behavior.
During parameter assignment, you can activate or deactivate sub-functions of the PI step
controller to adapt the controller to the controlled system. In addition to the functions in the
process value branch, the instruction implements a complete proportional-plus-integral-
action controller with binary output value output and the option of manually influencing the
value of the output value. The step controller operates without a position feedback signal.
You can use the controller as a PI fixed setpoint controller or in secondary control loops in
cascade, blending or ratio controllers, however you cannot use it as the primary controller.
The functions of the controller are based on the PI control algorithm of the sampling
controller supplemented by the functions for generating the binary output signal from the
analog actuating signal.
The CONT_S instruction has an initialization routine that is run through when input
parameter COM_RST = TRUE is set. 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_S 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_S directly in the multiple instance DB and commission it
via a watch table.
The error message word RET_VAL is not evaluated by the block.
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