| April 1, 2011
Safety Networks are Getting Wired with Control
While safety and control are not necessarily blended, they are certainly getting braided onto the same bus-based network.
Safety networks—whether blended or braided with control networks—are becoming popular across most industries. At Astec Inc., an original equipment manufacturer (OEM) in Chattanooga, Tenn., that markets continuous and batch-process hot-mix asphalt facilities and soil remediation equipment, safety networks have delivered significant benefits. “Before we started using safety networks, we had dozens of hard-wired e-stops (emergency stops) connected to multiple safety relays controlling multiple zones. Safety stops routinely took 20 to 30 minutes to troubleshoot,” says Mark Harned, vice president of controls at Astec. “Following the implementation of safety networks, e-stop wiring decreased by thousands of feet, wiring [installation] decreasedEthernet networks are becoming increasingly popular as the backbone of the safety network. “Not long ago, people were deadly afraid of using Ethernet for control,” says Kevin Colloton, product manager for integrated safety at supplier Rockwell Automation Inc., in Milwaukee. “Now, everybody’s saying they’re moving to Ethernet. They say, ‘We want to see more devices on Ethernet. We want light curtains on Ethernet.’ Costs have come down and we’re seeing Ethernet ports in products that never would have been considered before. Things are changing. This is accelerating.”
by hundreds of hours, and troubleshooting became fast and easy on the same panel as control.”The benefits also transferred to Astec customers. “Our customers quickly found out they didn’t have to use voltmeters to troubleshoot everything on their machines,” says Harned. “They could actually monitor from a computer and know which station was causing the problem. All they had to do was look at the operator interface.” Astec programmed the network so that customers could see all functions— specifically, down to which node was causing the problem, and down to the individual e-stop.Astec uses Profisafe as the backbone of its safety network. This avoids the need to bring all wires back to the motor control center. “It’s tied right in there to monitor each individual point,” says Harned. Safety networks have also made Astec more attractive to prospective customers. “Profisafe functionality has become a large part of our presentations on a new crushing machine,” says Harned. “Users like the simplicity of the network, and they like the ability to monitor every safety stop and every safety device on the machine.”Networked safety winsAfter years of resistance when safety networks were first introduced and plant operators were not comfortable with safety running on the same network as control, the networks have won the day. They are now widely accepted and overwhelmingly preferred for their low cost, efficiencies and diagnostics. Safety networks also provide a modular approach to safety, which allows a plant to troubleshoot a portion of the line without a complete shutdown. Newest among the changes in safety networks is the emergence of wireless safety networks that deliver even more savings and efficiencies.The safety network on Ethernet has become widely accepted at plants across all industries. Not only have plant managers conceded that safety is not breached when safety controls are networked, the view has taken hold that safety is actually improved when it’s networked.Using an Ethernet network for safety not only delivers efficiencies and savings, it also increases overall safety. “The big trend in safety networks is to integrate the transport of safety data into standard fieldbus communication protocols, thereby eliminating a dedicated safety network,” says Joey Stubbs, North American Representative at the EtherCat Technology Group (ETG), in Volente, Texas. “Using higher-performance Ethernet-based networks for safety means a single run of standard cabling can be used for the safety and control data, as well as increased functionality for more protective safety implementation.”Networked safety also lends itself to earlier consideration during the design of the plant. “Safety is being implemented earlier in the design cycle now. Before, hard-wired systems were glommed on after a plant was up,” says Chantel Polsonetti, vice president of advisory services at ARC Advisory Group Inc., in Dedham, Mass. “Once you get beyond hard-wiring, it really expands your possibilities in doing safety earlier in the design. Safety used to be an afterthought.”
With an Ethernet-based system, less wire is needed and more intelligence can flow across the network. “We certainly see reduced wiring vs. hardware. You can attach the safety device to a bus-based network easier than to a hard-wired system,” says Polsonetti. “The base value proposition for a safety network is smaller panels, fewer components and greater configuration capability. You can also add intelligence in diagnostics and get greater modularity.”
Integrate or not?
While safety networks have become accepted, there is still a sizeable number of plant engineers who keep a church-and-state separation when it comes to safety mixing with control or business data. “They’re apprehensive about using the same network for safety. Generally, they’re worried about the business enterprise data on the same line,” says Colloton. “They want a physical braid with a different EtherNet/IP port to handle their automation requirement. There is still a pretty high percentage of customers who like to split off their HMI (human-machine interface) traffic and control from safety.”
In an integrated safety network, diagnostics can be more sophisticated. “One of the advantages is diagnostics. Usually, when you have an integrated safety solution, you have full visibility. You can get more detailed information from an integrated system,” says Stephen Stricker, product manager for safety at vendor B&R Industrial Automation Corp., in Roswell, Ga. “It’s easier to detect if there is a problem with an input. In a standard system, if you have a safety relay and somebody changes it, you have no way to know if it’s the correct one.”
Part of the reason that safety networks have become popular is because they can accommodate greater complexity. And unlike electromechanical systems, complexity translates into greater reliability for networked electronics. Plus, plant operators gain the benefit of greater visibility and diagnostics capabilities.
Unlike mechanical hard-wired safety, additional complexity on a safety network can improve reliability. “If you add more layers of complexity with electromechanical, it just increases the chance of failure. If you move to electronics, adding complexity actually reduces your chance of failure and increases your diagnostics,” says Gary Thrall, senior products support engineer at automation supplier Bosch Rexroth Corp., in Hoffman Estates, Ill. “With electronics, we can control the failure modes. Electronics have overtaken electromechanical because it’s more reliable.”
Complexity, though, can make installation more of a challenge. “As with any system, the more technologies that are integrated together, the more complex they become,” says Brent Lekx-Toniolo, director, Automation Division, at Toniolo Research and Development Inc., a system integrator in Oxford Mills, Ontario, Canada. “In the case of integrating safety communication over an already established networking system, you have the advantage of decreasing the infrastructure costs.” Yet, complexity also comes with costs. “The disadvantage is that the integrated system can be more complex to design, implement and troubleshoot than other systems,” says Lekx-Toniolo.
The modularity that is possible with networked safety is also a significant benefit. With a modular network, plant operators can troubleshoot, diagnose and correct a problem within a specific machine or area of the operation without shutting down production completely. “One of the main drivers is that as machines are becoming more automated, they’re also becoming more modular,” says Craig Nelson, product manager for motion control at automation supplier Siemens Industry Inc., in Alpharetta, Ga. “If you have a modular safety network, you don’t have to deactivate the entire machine if you’re troubleshooting or changing a single area of the machine. That helps with production, and it also provides a safer environment for both man and the machine.”
The increased modularity can quickly translate into measurable savings. “The modularity translates into minimized downtime,” says ARC’s Polsonetti. “That’s important, because of the overallrevenue saved by the end-user. You can isolate failure and not bring down the line—you’re still producing product.”
Wireless is growing
On the cutting front edge of safety networks is the wireless safety network. “We see a lot of Ethernet-based safety now. We also see—though it’s further out on the horizon—more wireless safety devices,” says Polsonetti.
While wireless safety is new, many plants are not necessarily resistant to the concept. “The wireless safety network is the same thing as the wired safety network. It’s new to the market, but we’ve worked on some wireless systems, and our customers are comfortable with it,” says John D’Silva, business development manager for safety at Siemens Industry Inc. “They ask, ‘What happens if I lose my connection?’ Well, it doesn’t matter if you lose a connection for a wired or wireless network. It’s the same.”
Overall, the development of safety networks has a bottom line of improved safety. “It’s a complicated subject. Safety isn’t something you do to avoid a lawsuit. It’s to build a better machine,” says Thrall from Bosch Rexroth. “What you’re really looking to do is set up a system where safety doesn’t get in the way of the guys doing their jobs, and use it to improve the product—not put up barriers to the guy doing his job. To do this, you have to get into the machine function, not just the safety.”
While wireless safety networks are new, and only a relatively small percentage of plants are adopting wireless safety, the safety networks themselves have gained wide acceptance. In greenfield plants, there is not even a discussion about whether safety should be on a network. The decision is a forgone conclusion.
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