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34 Chapter Two
Control
system
FlcauRE 2-11 Interactions between process and control system with interfaces.
connections between the process and the control system: analog
inputs and outputs, digital inputs and outputs, and/ or serial inputs
and outputs. At first glance it may be overwhelming but after the
dust has settled, one can look beneath the surface of the process where
the lines come from and leave to the control system. At each point
there is some sort of conversion of electrical to mechanical,
mechanical to thermal, kinetic to electrical, and so on. Some of
these conversions can be explicit as in a motor turning a screw but
all can be conceptually represented by the small black boxes as
shown in Fig. 2-11. It is the inside irregularly shaped object that can
be simulated. In Fig. 2-12 a rectangle (a purposely crude approxima-
tion to the irregularly shaped object representing the real process) is
the simulated process that can be used to test the control system. All
of the small black boxes must be simulated, too.
Control
system
FIGURE 2-12 Interaction between the simulated process and the control
system.
