|Posted on January 7, 2016 at 9:00 PM|
IEC 61131-3: What’s the acceptance rate of this control programming standard? Ladder diagram remains the simplest and most popular approach for PLC programming, but may not be the most efficient way. Lack of interoperability may be a problem. To learn what languages PLC programmers prefer and to understand the level of awareness and use of the IEC 61131-3 standard for industrial control, Control Engineering surveyed readers as part of a custom research project on behalf of AutomationDirect.
Although the IEC 61131-3 Programming Languages standard has been around for nearly 25 years, limited awareness of its scope and features has kept it from becoming a requirement in North America. A recent survey of Control Engineering readers showed that ladder logic remains the most popular programming method for programmable logic controllers (PLCs). Findings of the custom research project, on behalf of AutomationDirect, suggest that programmers could save time and money by using other standard programming languages more often. It also suggests that difficulty in code transportability among PLC brands may be an issue.
Overview: limited adoption
More than 586 responses were received from participants who met eligibility requirements, including relevant purchasing influence and authority, and also responsibility for hardware specifying or PLC programming. The results of the survey show low awareness and limited adoption of this standard in North America, indicating that situations where its application is required are rare.
The most common job functions of the respondents were system or product design; control or instrument engineering; or system integration or consulting. These functions accounted for more than 60% of the respondents. About one-third of the functions included process, production, or manufacturing engineering; operation or maintenance; or other engineering. Almost 10% of the participants were in general or corporate management, and this group was more likely to specify but not program PLCs.
The majority of the respondents, more than 60%, were employed at companies with more than 100 employees, some with 1,000 or more. However, the largest group of participants, at almost 40%, was from companies with fewer than 100 employees.
By company type, end users of PLCs were the largest group of respondents at almost 40%, and almost half of the respondents were system integrators, original equipment manufacturers (OEMs), or machine builders. The respondents were widely spread geographically throughout the United States.
What the experts say
The IEC 61131-3 standard has been around for nearly 25 years and includes a family of programming languages. IEC characterizes it as an international standard for programming PLCs. PLCopen, a nonprofit industrial trade organization, is mostly dedicated to IEC 61131-3 and contains significant information about the standard.
The PLCopen Website describes IEC 61131-3 as, "The only global standard for industrial control programming. It harmonizes the way people design and operate industrial controls by standardizing the programming interface." The organization says it is a standard programming interface with a common structure.
The standard includes a definition of the sequential function chart (SFC) language, used to structure the internal organization of a program. It adds four inter-related programming languages including two graphical ones, ladder diagram (LD) and function block diagram (FBD); and two text-based languages, instruction list (IL) and structured text (ST). Using logical elements, defined data types, task structure and scheduling, and execution control, each program can theoretically be structured to increase re-usability, reduce errors, and increase programming and user efficiency.
PLCopen has been working with technical committees to add extensions to the standard. There have been a number of functions added as a result of these activities including motion control, safety, OPC Unified Architecture communication (OPC UA from OPC Foundation), XML schema, reusability level definitions, and conformity level.
So how familiar are PLC purchasers and programmers with IEC 61131-3? When Control Engineering polled its readers, a whopping 85% of the respondents said they are either not familiar with or only somewhat familiar with it (see Figure 1). While this standard may have great acceptance and use in Europe or other parts of the world, it has not had as much impact in North America. Implementing it does not appear to be a priority or a requirement for many respondents in the United States since, after more than 20 years, an overwhelming majority of programmers working in North America are, at best, only somewhat familiar with the standard.
More than 40% of the respondents reported no familiarity with the standard, and the highest concentration of these respondents was among those who say they are PLC programmers. Turning it around, among those who say they actually write programs, only 15% claim a high level of familiarity.
Why use PLCs supporting IEC 61131-3 programming?
Among the respondents who use or specify PLCs, and who say they are familiar with IEC 61131-3, the next question asked in the survey was why they use it. The answers (see Figure 2) suggest its use does not appear to be a requirement for most in North American industrial automation markets. The reason cited most often (39%) is simply because the PLC product came with the language. A quarter of the end users specified IEC 61131-3 programming language, and some of this can be attributed to U.S. companies shipping machines into Europe or Asia.
The fact that fewer than 10% of the applications demand the features of IEC 61131-3, while a larger percentage of respondents who don't program PLCs say it's because it's specified, hints that some of the totals are driven by hardware choice and selection.