![]() ![]() Other IEC 61131 languages show some preference within certain industries, but aren’t as universally used or understood. Ladder logic is widely used, which makes it easy to find someone who can read it. Nine areas in particular can influence programming language selection. There are features of different languages that affect a programmer’s ability to make a readable program. ![]() When new functionality is desired, how easy is it to extend the program? Can problems be found quickly to minimize machine downtime?Ĭ. Can a programmer or maintenance technician look at the code and understand what it does?ī. Ask these three critical questions about your programming languages.Ī. A program has to make the automation work, which virtually any language can do, but the real world puts other demands on it as well. These languages are powerful, but haven’t found a strong foothold in automation.īefore comparing ladder logic to other potential options, it’s important to understand what a program really needs to do. Current examples of PC languages in automation include C++, Java, and C#. Pascal has since fallen out of favor, but it’s a great example of how the automation industry has borrowed from the PC industry in the past. Structured text (defined in IEC 61131) is a very similar to Pascal, a common PC programming language at the time IEC 61131 was introduced. That may include interfacing with databases or programming automation peripherals like cameras and robots. The languages drawn into automation from the PC world tend to be used for specialty/peripheral applications. Automation also tends to lean towards mostly digital input/output (I/O) or analog I/O. Generally, a process will operate as discrete or continuous. There’s certainly room for debate on which language is best suited to which task (see Figure 2). This defined four programming languages that generally were interchangeable-ladder diagram, function block diagram, structured text, and instruction list-and also a program organization language called sequential function charts.Įach language has its own strengths and weaknesses, and they can be used together within one program to best support different program functions. The IEC’s committee addressed this need with standard IEC 61131, and languages specifically in part three (61131-3). These languages usually are seen as complementary to ladder logic, rather than directly opposed.Īs PLCs became popular, the industrial community found the need for standards to guide programming. Industrial programming is influenced by two communities: the standard IEC 61131-3, the industrial control programming standard from the International Electrotechnical Commission and PC programming. Ladder logic is no longer such a convenient language for electricians to read and maintain, nor is it a broadly existing skill in the incoming workforce. As the language has evolved and automation has become more complex, programming PLCs has become a more specialized occupation. PLCs commonly are used for analog control, tracking part data (barcodes, test results, calibration), controlling motion, and a plethora of other tasks-and ladder logic is still the dominant language. Ladder logic does a lot more today than it used to. In turn, the programming languages used in PLCs have grown to reflect the increased capabilities. ![]() Today, the processor chip inside a PLC can do more than relays at a much lower cost of space, money, and implementation time. Even the largest, most complex automation systems were limited by the realities of physical relays, so the language of ladder logic didn’t have to do very much. ![]() Before PLCs, relays took up physical space in a cabinet, cost money to buy, and required time to wire.They were also limited to on/off functionality-without capabilities for analog, math, or data collection in relay logic (aside from some sparse timing and counting functions in special relays). ![]()
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