PLCs have the ability to communicate with each other on a global basis
and to send operational data to and be
controlled from a central computer terminal. Figure 13.13 shows a typical controller
setup, monitoring a single variable. The output from the sensor is conditioned
and transmitted to the input module of the controller; if the signal is
an analog signal it is converted to a digital signal and compared to a reference
signal stored in the computer. A decision can then be made and the appropriate
control signal sent via the output module to the actuator.