IEC 61131-3: What’s the acceptance rate of this control programming standard?
Cover story, automation upgrades: Although the IEC 61131-3 standard for control programming languages has been around for nearly 25 years, limited awareness of its scope and features has kept it from becoming a requirement in North America.
Low awareness and limited adoption of the IEC 61131-3 Programming Languages standard in North America indicate that situations where it is required are rare. Control Engineering, as part of a custom research project on behalf of AutomationDirect, recently polled its readership to understand the level of awareness and use of the IEC 61131-3 standard for industrial control, and to find out what languages are preferred by programmers of programmable logic controllers (PLCs). [Note: This is a revised online version of the Control Engineering, January 2016, print and digital edition cover story: "More intelligent and efficient PLC programming." This online version clarifies previously approved edits.]
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 survey shows low awareness and limited adoption of this programming standard in North America, indicating that situations where its application are required are rare.
The most common job functions of survey 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.
In terms of 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 U.S.
What PLCopen says about PLC programming
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 non-profit industrial trade organization, is mostly dedicated to IEC 61131-3 and has 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 IEC 61131-3 provides a standard programming interface with a common structure.
The standard defines the sequential function chart (SFC) language, which is 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 theoretically can 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 UA communication, 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 survey respondents said they are either not familiar with or only somewhat familiar with it (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 U.S., 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 survey respondents who use or specify PLCs, and who say they are familiar with IEC 61131-3, the next question asked why they use it. The answers (Figure 2) suggest its use does not appear to be an over-arching requirement 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 can be attributed to U.S. companies shipping machines into Europe or Asia.
The fact that fewer than 10% of PLC 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.
See next page for more on user programming preferences, a table of important features, preference for a second programming language, and links to additional resources.