Turn the clock back twenty years and a Programmable Logic Controller (PLC) was primarily utilized in discrete manufacturing processes, a Distributed Control System used for continuous process control and there was not Something Else (SE). A PLC used Ladder Diagram (LD) type programming and a DCS used Function Block Diagram (FBD) type programming and there was not SE. A PLC handled mainly discrete I/O (DIO), a DCS handled mainly Analog I/O (AIO) and SE didn’t handle anything.

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