The PLC: A logical development

Abstract

Programmable Logic Controllers (PLCs) have been used to control industrial processes and equipment for over 40 years, having their first commercially recognised application in 1969. Since then there have been enormous changes in the design and application of PLCs, yet developments were evolutionary rather than radical. The flexibility of the PLC does not confine it to industrial use and it has been used for disparate non-industrial control application. This article reviews the history, development and industrial applications of the PLC. The 1960s was a decade of intense technological development influenced by the political circumstances of the time; it was the height of the Cold War and the space-race and in the United Kingdom, Prime Minister Harold Wilson emphasised the role of technology in his famous "White Heat" speech. Sir Leon Bagrit, a leading industrialist, became chairman of Elliot Automation, a newly established company. Bagrit's BBC Reith lectures of 1964 on automation, encapsulated the industrial and technical ambitions of the time. Automation was a hot topic and transistor electronics and computers were unfolding as significant technologies.