Fieldbuses Pave Way to Safety Networking

One of the many interesting aspects of Control Design's May cover article on machine safety will show how the emergence of fieldbuses eventually began to enable safety networking, too. For example, Stolle Machinery (www.stollemachinery.com) in Centennial, Colo., recently simplified the former point-to-point wiring on its machines that form, inspect and decorate cans by replacing it with fieldbus-type networking such as EtherNet/IP and DeviceNet to reach its I/O points and other devices. This saved on materials and interconnection time, but it also provided the networking concept and highway for later adding safety-related communications.

"Over the past five years, we networked a lot of regular I/O via fieldbus, but all our safety functions were still hardwired to our machines. However, our customers, especially those in Europe, have been getting more comfortable with the idea of safety on fieldbus," says James Chapman, Stolle's electrical engineering manager. Though its business was half domestic U.S. and half elsewhere just three to five years ago, Stolle now sells about 80% of its equipment overseas, mostly to Europe. Chapman adds that many of the Europe Union's machine safety standards are recognized and required internationally, especially since EN 954 was officially replaced by ISO 13849 this past January after a two-year delay. "So, we adopted the better-defined ISO 13849-1 safety standard, and we're in the middle of transitioning to safety networking and safety PLCs over 24-V Ethernet cabling, though we still use hardwiring for high-speed functions."

To learn to apply ISO 13849 and the European Union's latest machinery directive, Chapman reports that Stolle's engineers researched and educated themselves about them, brought in outside experts, explored how the new standards superseded older ones, and evaluated how this would affect decision support during machine design and construction. "Previously, we followed four safety categories, but ISO 13849 has five performance levels, A though E, which are better defined and less ambiguous. We also still use SIL levels. All of these give us a more complete overview of our machines, and then we also apply more specific standards for particular equipment, such as EN 692 for presses, which has an equivalent ANSI B11 standard."