5 - Programmable logic control (PLC) systems

Abstract

This chapter deals with the programmable logic control (PLC) systems. PLC has been initially developed for the automotive industry, where the automation of the continuous production lines required a controller capable of carrying out the basic repetitive type control operations on the production lines. PLCs developed very rapidly for the automotive industry and quickly found use in other applications where similar operations were required. PLC control requires some means of inputs and outputs to allow the operator to action controls and get feedback of control status. PLCs are programmed by using a specially designed programming device, or in some cases a PC, communicating via a modem, or similar communicating device, running dedicated special software. Moreover, PLCs do have the advantage over many other control types, that their operating speeds can be extremely fast, but only a few units available today are “multi-tasking.” The chapter concludes that, if the future development of the plant or site encompasses more continuous control than cyclic control, or if additional facilities other than control are needed, it may be worthwhile considering an alternative to PLCs.