Software Engineering for PLCs

Software engineering is a pivotal, yet often overlooked aspect of Programmable Logic Controller (PLC) programming. There is a core problem with automation engineering that stems from most PLC projects usually being viewed as hardware first. Many books, workshops, and so on are focused on PLC projects as hardware-first systems. Usually, programming is secondary to the overall hardware design of the system. In other words, the software is there to operate the hardware.

Many PLC programmers are not formally trained software developers and have backgrounds ranging from electricians to electrical and mechanical engineers. Though there is nothing wrong with a PLC developer not being a formally trained programmer, there are techniques that are usually taught in programming classes that are often lost when a non-formally trained programmer tries to program a PLC. This book aims to teach and apply software engineering practices to PLC programming. By learning these techniques, PLC developers can utilize the full gamut of the IEC 61131-3 standard and create advanced software faster and cleaner.

The hot topic in today’s fast-paced industrial world is Artificial Intelligence (AI) and automation. In short, machines are getting smart, and a major component of that is the software that controls the systems. The first PLC was introduced around the late 1960s and early 1970s; as such, PLCs (and by extension, automation) are nothing new. However, what has changed is the complexity of the systems that PLCs control. With the lower costs and rising computing power of PLCs, the applications that PLCs control are now becoming more complex seemingly by the day. The days of PLC programmers getting through the day with basic programming techniques and ladder logic are quickly becoming a thing of the past. To survive and be competitive in today’s market, a new way of thinking about PLC code is needed. Today’s world now needs PLC programmers that can function as software engineers.

In this chapter, we’re going to cover the following topics:

• Software engineering for PLCs
• The IEC 61131-3 standard
• Ways of programming a PLC
• CODESYS
• A ladder logic Hello, World! program to test the installation of CODESYS