Integration in and of itself adds no value; solving real business problems does.
The need to get automation components and systems from different suppliers
to connect together became apparent as soon as the digital computer became the
basis for automation system design.
Although the programmable logic controller (PLC) was originally a solution for the
control of discrete manufacturing operations, manufacturers also found PLCs useful
for the control of operations in process plants. Process computers and PLCs soon
saw use in plants, each controlling separate, but related sections of the operation.
When manufacturers found they needed coordination of control between the plant
sections, it drove the need for communication between different process computers
and between process computers and PLCs, as well as for communication with other
intelligent devices.
In the case of PLC to process computer communication, if all that was required
was the connection of a few discrete field inputs and outputs, the first course of
action was often to connect the outputs from the PLC input/output (I/O) module to
inputs on the process computer I/O module and vice versa (Figure 17-1). This type of
connectivity offered an approach plant engineers or electricians familiar with wiring
control systems and real-time data transfer could easily implement. The downside
to this approach was a connection had to be set up for each field value being
communicated between the systems. That approach could become quite costly as the
number of values increases, and the only information communicated between systems
is I/O data from field devices.
