F.J. Molina∗ , J. Barbancho∗ , C. Leon∗ , A. Molina∗ , A. Gomez∗
of Seville/Department of Electronic Technology, Seville, Spain
Abstract— In this paper, we review aspects relevant to industrial standards related to PLC programming: IEC 61131, IEC 61499 and a work about safety developed by the PLCOpen organization basedon IEC 61508. We propose to use these standards in PLC learning to ﬁx a common knowhow that allows one to reduce the gap between industry and education, and between different professionals. We show the application scope of these standards by analyzing the IEC 61131 limits. The IEC 61499 can be introduced in distributed control systems and in complex centralized systems with multiple operatingmodes. In critical applications, like safety functions, where functional safety is required, the IEC 61508 is a reference model.
I. I NTRODUCTION In PLC programming, there is a gap between industry and education that has been increasing, especially in the last few years. We identify two main reasons. Traditionally, automation control systems have been developed by engineers or technicians. Theirknow-how, design methodology and working procedures are compiled into standards. But usually, these standards are quite complex to be introduced in education because they are written to transmit clear information to experts, not to teach to nonexperienced students. The second reason is the increasing use and the integration, of programmable electronic systems (PES) and computers in all the levelsof the automation hierarchy: sensor/actuator level, supervisory level and the company management tools (databases, information systems, decision tools, etc). Due to the introduction of communications technologies and new programming concepts with PES, professionals from computer science have started working with industrial PES. Their methodology and their knowledge about industrial processes arequite different from traditional engineers and conversely. There is a mutual misunderstanding. The IEC 61131 standard was a ﬁrst attempt to give a reference model for industrial PES. It was deﬁned in 1993 and released in 2003. It uniﬁes concepts and proposes a common standardized programming interface to allow people with different backgrounds to create different pieces of a program that can bejoined to work together correctly. The standard also deﬁnes a set of programming languages and includes an easy way to apply new technologies like communication protocols and fuzzy-logic . The PLCOpen association is working to update and promote the IEC-61131 standard. Their working groups have developed much material to better understand and teach the standard  . They have alsobeen developing recommendations and solutions to many industrial problems such as safety and motion control.
The study of these works offers a clear perspective of the programming methodology that the standard draws. Currently, the IEC 61131 has been successfully introduced in the industry. Many commercial tools are compliant or, at least, include their main concepts. Nevertheless, severalstudies show that the languages and the execution model, deﬁned in the standard, are incomplete. Because of this, frameworks usually deﬁne additional language elements or characteristic, and non-compliant program execution models  . In section II, we analyze the main concepts of IEC 61131-3 standard. In certain applications, special reliability and availability are required for long periods oftime (e.g. safety in process and machinery). Programming restrictions and different methodologies are necessary to achieve that   . IEC 61508 standard introduces the main concepts on functional safety, recommendations and methods for programmable electronic devices in safety applications. In the section III, we present a work done by PLCOpen organization to adapt IEC 61131-3 to IEC 61508...