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Talk to your favorite system supplier to find out what's up. You may be thinking fieldbus-based networks, while your vendor has something else that will work. Meanwhile, here's a rundown of recent developments, based on the rankings from VDC.
Profisafe--The most popular safety network worldwide, Profisafe is based on the Profibus fieldbus system (Figure 1). According to Wolfgang Stripf of Siemens AG (www.siemens.de), and head of the Profibus Application Profiles technical committee, it can be used for factory and process automation tasks. Stripf says Profisafe's big breakthrough came at the 2002 Hanover Fair, when dozens of products were demonstrated, ranging from safe mini PLCs to light arrays, laser scanners, and remote I/O. "In other words, there is a complete selection for performing safe automation tasks, from the simplest to the most complex," says Stripf.
Profisafe is also writing its own specs. "As most security standards do not take a bus mode into account, the boundary conditions for safe communication had to be defined in a separate specification," Stripf says. "To keep the expense of certification as low as possible, an almost fully automatic Profisafe layer test was developed."
Siemens Energy & Automation in the U.S. (www.siemens.com) recently launched Safety Integrated USA, a new organization for applying safety technology, including networks, across all its product lines. Siemens sees two distinct markets for safety automation ,“ process and discrete ,“ so its process safety will be lead from Spring House, Pa., while discrete industry safety initiatives will be managed out of Norcross, Ga.
Figure 1: Profisafe Rules
Profisafe, the most popular safety bus, is based on the Profibus fieldbus. It allows
control and safety devices to share the same network.
Source: Profibus Nutzerorganisation e.V.
AS-Interface Safety at Work--Ranked number 2, AS-i is a two-wire master-slave system that has gateways to CAN, DeviceNet, Interbus, and Profibus, among others. Master controllers can be industrial PCs, PLCs, and process controllers. It has been around since 1991, and has become a European standard (EN 50295 and IEC 62026-2). AS-i boasts many successful installations, particularly in the automotive industry.
Helge Hornis, Ph.D., intelligent systems manager for Pepperl+Fuchs (www.us.pepperl-fuchs.com), says AS-i is a much simpler system than some of the others, which tends to keep costs down. "No safety PLC is required with AS-i and normal and safe data can be transmitted over the same wire," he adds. According to tests at a German manufacturer, AS-i costs about 85% of what it would cost for a standard hardwired safety system.
DeviceNet Safety/CIP--Ranked third, this DNS achieved T…"V approval in July 2003 for its system specifications. Richard Galera, marketing manager, safety controls, for Rockwell Automation (www.ra.rockwell.com) says products will be submitted for T…"V approval in 2004, and products will arrive on the market in 2005. "DeviceNet Safety will meet the requirements of IEC 61508 up to SIL 3," says Galera.
DNS is based on the Control and Information Protocol (CIP) found in DeviceNet, ControlNet, and Ethernet/IP, says Galera. ODVA received concept approval from T…"V for the CIP safety protocol in 2002. "In the second phase of CIP Safety Development, companies will be able to link distributed DeviceNet Safety segments to standard CIP-based networks, such as Ethernet/IP," says Galera.
Which means current DeviceNet users can use existing wiring, and implement a safety system by adding DNS devices to an existing network (Figure 2).
Figure 2: DeviceNet Framework
Multiple DeviceNet Safety segments can be interconnected
using a high-speed EtherNet/IP Safety backbone, with all the
nodes communicating as if on the same segment.
Source: Rockwell Automation
Safety Ethernet--"Peer-to-peer networks are alive and well," argues Lawrence Beckman, president of SafePlex Systems, Houston, and member of the ISA S84 Safety Committee. Safety Ethernet, ranked fourth by VDC, is a modified version of Ethernet that is both safe and deterministic, and Beckman is using it in offshore platform applications (Figure 3). "We have employed them in many projects over the past five years, and most recently in several exploration and production safety applications in the Gulf of Mexico."
Figure 3: Offshore Safety Net
It's easier and less expensive to use
a safety network than to run wires
all over an offshore drilling platform.
Safety Ethernet was originally developed by HIMA (www.hima.com). It allows safety-related data to be integrated in a standard Ethernet network operating at speeds up to 100 Mbps, making it one of the fastest safety networks around. Safety Ethernet has been certified by T…"V and BG for use up to Category 4 and SIL 3. Triconex' P2P network is based on Ethernet.
Safety Bus P--Although the SafetyBus P Club Intl. is now the official driving force behind SafetyBus P, Pilz Automation Safety (www.pilz.com) still makes the controller hardware.
SafetyBus P is based on Controller Area Network (CAN) technology. "Conventional fieldbus networks are not suitable for safety related controls," says Piggin, "because additional error detection and avoidance mechanisms are required. An additional safety layer is necessary to detect connection or device failures and implement the required emergency shutdown action to avoid danger."
Pilz accomplishes this by adding an application layer, plus a triple-redundant safety controller. The safety controller is divided into two sections, failsafe and standard. The failsafe section processes all safety-related functions.
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