“The original standard came out in 1996, and that was the first attempt within Europe to categorize the control systems used for safety into various types, so builders could better align the systems with their tasks,” says Derek Jones, business development manager, safety, at Rockwell Automation, Wiggin, United Kingdom. EN 954-1 was the main standard for the design of safety-related control systems in the machinery safety sector. According to Jones, its major shortcoming was that it did not include the aspect of reliability.
The old standard was written for very simple systems, typically mechanically-based ones, and was essentially limited to defining categories for safety applications. The new standards retain the concept of categories, but also add the element of reliability. By quantifying reliability, they empower the use of more advanced safety-control systems technologies.
“The new standards give you information about the type, principle, nature, and structure of the system,” says Jones. “You can also analyze exactly what integrity a system delivers, so it becomes not just a categorical standard, but a hierarchical standard, which is precisely what is needed in today’s markets.”
A Natural Accommodation
To Jones, standards development is a natural process. As machinery has become more complex to increase productivity and flexibility, the inexorable trend has been to move from mechanical-based to digital-based systems. “To keep pace and monitor what is going on with machines and machine design, safety systems have to change as well,” he says. “Systems may be performing the same or similar safety tasks, but instead of using electromechanical or electromagnetic relays, they now are based on dual monitored microprocessors.”
The old standard was not sufficient to deal with this newer generation of safety components; to make sure that these components meet safety requirements, the new standards were developed to take greater account of the reliability of the components.
Jones contends there is no single cause for the Commission extending the deadline for compliance, but points to lack of data as a major factor. “I think it was assumed that by the end of 2009, everyone would know everything they needed to comply with the new standards. But what has become abundantly clear is that for some technologies—for people working with hydraulic and pneumatic systems, for example—getting the data has been a struggle.”
So it was decided an extra two years would provide all parties adequate time to make the transition to EN ISO 13849-1 and EN/IEC 62061.
The Advantages of Adoption
Early adopters of the new standards will move ahead of their competition by improving safety, efficiency, and sustainability while driving down developmental and operational costs. “First of all, adoption of the standards allows you to use programmable, flexible, configurable components, which in themselves make it easier to design systems,” says Jones. He stresses that it’s not just the components themselves; it’s leveraging the power of the functionality of safety.
“The new standards will help make your machine safer and they will also provide greater productivity,” says Jones. “Increasingly, you won’t make a machine safer by simply switching it off. On some sort of continuous process, you’re more likely to make it safer by changing from one run mode to another. It may be perfectly adequate to switch it down to a very slow speed or divert the flow if you need intervention. That in itself tells you that contemporary safety functionality is going to be based on sensing a number of factors on the machine: speed, position, temperature, or pressure. It can be all sorts of things.”
Using the new standards, Rockwell Automation is facilitating early adoption by working with customers to decide the best type of components to fulfill the functionality required; then, if necessary, Rockwell is working with them on the calculations to validate that system according to the standard.
“We recommend the use of a software tool called SISTEMA to do the calculations,” says Jones. The SISTEMA tool, developed by Germany’s BGIA organization, automates calculation of the attained Performance Level (PL) of the safety-related parts of a machine’s control system in the context of EN ISO 13849-1. SISTEMA is available in English and German language versions and may be downloaded free of charge on the BGIA website.
Two resources have been created as aids in determining the PL specs for a wide array of Rockwell Automation safety products. Data is now available in an electronic library or pdf datasheet, both available over the web at http://discover.rockwellautomation.com/SA_EN_Machine_SISTEMA.aspx. Each can be used with SISTEMA.
“When safety systems get in the way of productivity on a machine, that is when safety is most likely compromised,” says Jones. “If every time your safety system is upgraded, it takes a half hour to get your machine up and running, you can be sure that someone, somewhere is going to try to override that safety.”
That, in itself, is a significant cause of accidents, which is why Jones says you should never think about safety without thinking about productivity. “That is our message,” he says. “That is the reason the use of programmable safety technology is so useful—not because in its own right it is any better than simple technology, but because it allows you to integrate productivity and increased safety, therefore helping reduce the temptation to shortcut or bypass safety.”
