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.


Cover image: Once ladder diagram programming is removed, four options are in the second tier of programming methods, with function block diagram as a strong choice for a second programming language. Cover design by Control Engineering using a PLC image frLow 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. 

Awareness levels

Figure 1: How familiar are you with the IEC 61131-3 programming standard? About 85% of the respondents don’t know much about it. Courtesy: AutomationDirectSo 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.

Figure 2: About 40% of respondents use IEC 61131 just because it comes with the hardware. Courtesy: AutomationDirect

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.

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DENNIS , AZ, United States, 12/30/15 10:24 AM:

As a former Plc programmer the position of most Plc manufactures is that that want you to use their software and keep buying their products so they make software that slightly different so you want move to another manufacturer and have to relearn another version of software. I am also sure their are some small companies that have interoperative software that cover several versions of Plc programming but they have long term reliable function issues.
KHAMMONH , Non-US/Not Applicable, Thailand, 01/06/16 02:16 AM:

Ladder diagram is a champion is due to the inertia of professional industrial control and its simplicity and similarity to relay circuit as a discret DIO. Motion control, HMI and other are added later to enhance its functionality. My personal preference is also Ladder diagram when working with PLC other language I use in PC Base/Windows base programming
WILLIAM , CA, United States, 01/12/16 11:04 AM:

I expect most engineers know and use several IEC61131-3 languages. Indeed, most transitioning to PLC's would find ST much simpler than LD. The split w/ Europe might be partially due to most PLC programming in the U.S. being done by electricians who learned in trade schools or on-the-job where LD is dominant.
WILLIAM , MI, United States, 01/12/16 12:45 PM:

PLC programming also needs to be understood by those needing to service a machine without any support from the original programmers, often without any support from anyone. SO it is VITAL to use a language they understand. ALL qualified electricians understand ladder language, so that makes it a logical choice. Usability beats efficiency almost every time. Downtime spent waiting for some "Prima-Donna" programmer is very expensive, and when there is a good alternative all prudent folks choose it. Just like the survey shows, it is smartest to use what works, and usually cheaper in the long run as well.
Stephen , WA, Australia, 01/13/16 05:06 AM:

Having used ladder language for many years in Modicon, AB and Mitsubishi equipment, I am now a complete convert to FBD programming methods in IEC 61131 compatible software whenever possible and highly recommend anyone still using ladder to give it a go, as it's much simpler to follow the logic. STL may still a bit trickier for the average maintenance sparky to work, so I believe FBD is best from maintenance service POV.
Dimitri , TX, Germany, 01/18/16 10:06 AM:

Depending on the vertical market, IEC 61131-3 may be more or less used. In Factory Automation, IEC 61131-3 or at least Ladder are heavily used. Other markets like mobile automation (ECU), Power Distribution (RTU), Process Automation (DCS) start using more and more IEC 61131-3. The norm does evolve with lots of key features like Object Oriented Programming, Motion Control, Safety, etc... PLCOpen and its members have been doing a great job at making this norm remain up-to-date, like the cooperation with the OPC Foundation regarding OPC UA.

I recommend anyone wanting to learn IEC 61131-3 in an easy and user friendly way to check for a full IEC 61131-3 e-learning curriculum of 45 hours, based on CODESYS.
ED , British Columbia, Canada, 01/18/16 03:05 PM:

For OEM's or small simple PLC applications ladder diagram makes sense. When PLC become PAC's in large industrial plants and are essentially a small DCS then using function block, SFC and ST make way more sense than ladder logic. Using FB for building control templates for motors, VFD' and valves is far more efficient, powerful and modular than ladder diagram. Most of the big PLC companies provide the ability to build custom function blocks that embed a blend of IEC 61131-3 with in the function block. This flexibility is extremely powerful and elegant. Hopefully IEC 61131-3 is being taught in universities, colleges and trade schools as it is truly the future of PLC programming.
Anonymous , 02/17/16 09:31 AM:

Having spent 35 yrs in industrial controls going all the way back to 8 bit processors, (showing my age here), ladder logic and the "occasional" function block is the way to go for any application. In modern software we have function blocks for everything from custom software drivers to motion function blocks and they can ALL be put in a simple ladder logic rung for discrete control. The above posts are correct, that on occasion, it is necessary to use either flow chart or structured text for complex math functions. Each language has it's strengths and weaknesses and I have found over my decades of experience, that it totally depends on what you are programming as to what language works best. Lucky for us all, most processors don't care what language you use, as I mix them up quite frequently to achieve the easiest method of programming for myself and the end customer, be it an electrician or another controls engineer. Again we are all lucky that most modern software does come with all of the languages listed in IEC61131. To say that any one language is the end all be all, in my humble opinion, would be a huge mistake...
KENT , OH, United States, 02/17/16 02:30 PM:

I have been using IEC61131-3 programming for about 10 years now. My personal preference is to use Continuous Function Charting (CFC). This is by far the easiest language for a non-programmer to follow, especially when you put comments in describing the desired functionality of different parts of the code.

I have programmed in Sequential Function Chart(SFC), Structured Text (ST), and Continuous Function Chart (CFC) and I have had significantly fewer calls from end users of my products with the latter language.

In my opinion this is the most desirable effect for programmers, not to be entrenched in troubleshooting a problem and not get paid for it!

Give it a try, you will like it more each time you use it.
Anonymous , 03/08/16 10:43 AM:

I think a lot of people are using IEC-61131 and don't know it. If they're programming Wago, ABB, Bechhoff, Bosch Rexroth, Eaton and about 300 other automaton vendor's products they're using CoDeSys which is an IEC-61131-3 programming software.
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