Coding Guidelines For Qualitative and Standardized PLC Programming
Can we bring more discipline to PLC programming in industrial control?
Discussion swirls at every gathering of automation professionals about the new generation of engineers entering (we hope) the industry. One thing for sure, the new generation begins with a much deeper computer science background than any before. Will they want to continue to code programmable logic controllers (PLCs) in the same relay graphical representation as their predecessors? Even the Structured Text language popular in Europe and other places can string together like an old BASIC program.
I am guessing they will bring more discipline to the craft of coding industrial control than ever before. Evidently PLCopen, the organization devoted to developing standards for PLC programming, does also. It has just announced a new set of coding guidelines.
The organization notes in its press release, “Software is becoming increasingly responsible, complex, and demanding. This does not come without its challenges. Due to the greater complexity, programs are more difficult to maintain, more time consuming, and potentially therefore more expensive. This is why quality is taking such an important role these days.”
Continuing, they note, “Unlike in other industries, such as that of embedded software and computer science, there has not previously been a dedicated standard for Programmable Logic Controller (PLC) programs. This has meant that programs were not measured against anything and were often of a poor quality. But that’s where the independent association PLCopen has come in and set the standard with the release of their coding guidelines. These guidelines are a set of good practice programming rules for PLCs, which will help to control and enhance programming methods within industrial automation.”
PLCopen, whose mission is to provide industrial control programming solutions, collaborated with members from a number of companies in different industries to create these coding guidelines. These companies include PLC vendors such as Phoenix Systems, Siemens, and Omron, to software vendors such as Itris Automation and CoDeSys, and educational institutions such as RWTH Aachen. These guidelines were inspired by some pre-existing standards from other domains such as IEC 61131-3, JSF++ coding standard and MISRA-C, and they are the product of three years of work by the working group. PLCopen’s reference standard can be used for testing the quality of all PLC codes, independent of brand and industry.
PLCopen’s coding guidelines are made up of 64 rules, which cover the naming, comments and structure of the code. By following these guidelines, the quality of the code will be improved and there will be greater consistency amongst developers. This will result in greater efficiency, as better readability means a faster debug time, and a program that is easier to maintain. This then results in lower costs as less time is required in order to maintain the program, and the maintenance should be easy enough for both an internal or external programmer as the code will be more straightforward. If the original developer fails to follow certain guidelines when creating a program, this could obstruct other developers and maintenance teams when working with the code during the product lifecycle, thus creating delays and additional costs.
In safety-critical industries, there is the standard IEC 61508 which in 2011 was also extended to PLCS. However, as quality is becoming an ever more important factor across the board, as programs become bigger and more complex, it is generally good practice to follow a set of rules or a standard in all industries. PLCopen’s coding guidelines suggest a standard that can be used across all industries to greatly improve the quality of the code and, as a result, to help companies save time and money. The introduction of such a standard will allow PLC programs to be verified not only from the simple functionality perspective but also from a coding perspective by confirming that good practice programming rules have been followed in their creation. Consistency across PLC programs can only be achieved through the respect of a global corporate or industrial standard, with PLCopen now being the de facto standard in the automation industry.
With quality playing a greater role in industry and with companies always looking for cost saving methods, the answer is to use some sort of standard or set of rules in order to meet these goals. PLCopen have created this standard to improve quality and consistency across PLC programs and so that individual industries and companies don’t have to go to the effort of creating a set of rules themselves. In addition to the internal benefits, this standard will also allow companies to enforce their quality requirements on suppliers, software contractors and system integrators. The only issue for now is that the process for verifying these rules is done manually by most users as they are unaware that some tools are available to do this automatically. But overall, following a standard such as the one proposed by PLCopen, will greatly improve the quality of the program and will save time and money throughout the whole duration of the product lifecycle.
The PLCopen coding guidelines v1.0 are available to download for free from the PLCopen website.
