Programming PLCs using Structured Text

An ever increasing part of the industrial and safety-critical processes is presently controlled by Programmable Logic Controllers (PLCs). As its name already suggests, a PLC can be and has to be programmed to perform its task. Since its birth, a wide range of different PLCs has been put on the market that makes use of an even wider range of programming languages. Recently, the IEC 1131-3 standard has been published in an effort to reduce chaos to order in the universe of PLC programming languages. This paper takes a closer look at one of the programming languages defined by the IEC 1131-3 standard, namely the Structured Text programming language. A comparison is made between Structured Text and the language upon which it was based, the Pascal programming language. The primary differences that result from this comparison are then discussed and some conclusions are drawn about the IEC 1131-3 standard. 1 The Programmable Logic Controller 1.1 Introduction As the Industrial Revolution stor..