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The Concept of PID Control
The function blocks (FBs) of the PID Control package consist of controller
blocks for continuous control (CONT_C), for step control (CONT_S), and
the FB for pulse duration modulation (PULSEGEN).
The controller blocks implement a purely software controller with the block
providing the entire functionality of the controller. The data required for
cyclic calculation is stored in data blocks assigned to the FB. This allows the
FBs to be called as often as necessary.
FB PULSEGEN is used in conjunction with FB CONT_C to implement a
controller with a pulse output for proportional actuators.
Basic Functions
A controller created with the FBs consists of a series of subfunctions that you
can activate or deactivate. In addition to the actual controller with its PID
algorithm, integrated functions are also available for processing the setpoint
and process variable and for adapting the calculated manipulated variable.
Applications
A controller implemented with the two controller blocks is not restricted to
any particular application. The performance of the controller and its
processing speed is only dependent on the performance of the CPU being
used.
With any given CPU, a compromise must be made between the number of
controllers and the frequency at which the individual controllers are
processed. The speed at which the control loops must be processed, in other
words, the more often the manipulated variables must be calculated per unit
of time, determines the number of controllers that can be installed (faster
loops mean less controllers).
There are no restrictions in terms of the type of process that can be
controlled. Both slow processes (temperatures, tank levels etc.) and very fast
processes (flow rate, motor speed etc.) can be controlled.

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