If you study control theory you will encounter so-called block diagrams, which are schematic representations of control systems and help one to understand how they work. Below is the block diagram for a cruise control system.
Vin is
the
desired
speed,
set
by
the
driver.
Vout is
the
actual
speed
on
the
speedometer.
The
pale
blue
device
calculates
the
error: e
= Vin - Vout
The processor represents
the
engine
and
braking
system.
Action of the controller:
- if e > 0, then accelerate
- if e < 0, then decelerate