Controller Hardware Structures

To understand the microprocessor-based controller needs a little understanding of the traditional analog controllers from which it evolved. Different vendors took different approaches to their respective designs based upon how they viewed the role their analog counterparts. Programmable logic controllers (PLCs) used in factory automation began as replacements for banks of relays, with no operator interface other than “start/stop” buttons to initiate action and lamps to follow the progress of an operation and notify the operator of its completion. The origins of process control were quite different. What starts to be quite unique about a microprocessor-based controller compared to the traditional controller is the opportunity for significant interconnection of the analog and discrete. They both had to be converted to the digital domain. More process vendors are beginning to employ one or more of the IEC languages in their control configuration.