1660604273400 Cd1002 Safety

Programmable Safety Controllers Are Slow to Gain Acceptance

Jan. 25, 2010
Safety and Control Converge: Despite the Evolution of Programmable Safety Controllers, Users Are Slow to Adopt Them

By Jim Montague, Executive Editor

Some revolutions take a while to get moving. It's been more than a few years since the National Fire Protection Assn. (NFPA) amended its NFPA-79 regulations to allow safety and control communications on the same network, but it took longer for suppliers to release updated programmable safety controllers, and it's taking even longer for users to adopt them.

"Because it's about safety, people are even more hesitant to change what they did in the past," says Jeff Gellendin, Rockwell Automation's (www.rockwellautomation.com) product manager for safety PLCs. "However, when they see the potential savings in setup, maintenance and troubleshooting, then attitudes begin to change. For example, a machine that can show which gate is open can be up and running again much quicker. This usually takes a lot more time and work because problems are harder to find, and so users just shut everything down. Now, once the light bulb goes on, they might add a safety controller in a pilot project and then convert more lines."

This acceptance and growing emergence of programmable safety controllers enable suppliers to bring safety and control components together in more closely unified devices, explains Christian Vitale, Turck's (www.turck.com) senior product manager for network I/O. Turck has been drawn further into safety technologies by its recent partnership with Bihl+Wiedemann, which designed its own AS-i safety monitor. The AS-i protocol's Safety at Work specification uses its physical layer to transmit and receive safety signals on the same wire as standard communications.

"Users want their machines to be safe, but they also want more data on everything from uptime to e-stops, and old safety systems don't have the data to do it," says Vitale. "Plus they need redundant wiring. So, where we used to need multiple devices to collect data, process it safely and transmit it to higher levels, we now can do it all in one device."

Mike Carlson, Banner Engineering's (www.bannerengineering.com) safety product marketing manager, adds, "About five or six years ago, a middle area opened up for safety controllers that were easier to configure, that had more straightforward software and that could do safety PLC functions without a lot of complexity. Now, the most recent push by these devices is into the safety bus worlds, using DeviceNet Safety or Profisafe, which means we'll soon see a safety version of Ethernet, too."

Gellendin argues that, whether they're using a dedicated safety PLC that just runs or they use a PAC that can run a safety task, most people love the idea of co-joining control and safety. "Once they get their heads around having third-party safety certification by an organization like TÜV, users learn they can take it at face value and run with it and put their machines together much more easily," he says. "So, instead of having a separate safety controller with separate software, and instead of having to do a second set of safety tags to corresponding tags in the controller database, customers implement one controller, one software package and one tag database, and they can cut their development time in half."

Gellendin says programmable safety controllers aren't adding many new core capabilities these days, but they are easier to implement with predefined instructions for e-stops and light curtains and with pre-configured HMI faceplates that make it easier to see what's going on in the safety system. In the future, he says Rockwell Automation will push GuardLogix's integrated safety functions ever lower into the overall control platform.

Mark Nehrkorn, Omron STI's (www.sti.com) division manager for safety integration, adds that programmable safety controllers are taking off along with the rise in Ethernet-based control in automation. "Automation end users and OEMs finally see a reason to use integrated safety platforms with general automation and welcome in this technology to help them solve problems," says Nehkorn. "For instance, safety screens that used to run off to the side of the regular process screens are now integrated and run safety I/O, general purpose I/O, configuration and reporting all seamlessly together. We develop a lot of end-user systems and retrofit a lot of process lines and machinery to meet safety standards, and now we can augment the control system and its process by seamlessly interweaving the safety layer with it."

When machine builders create new equipment, they can add safety at the beginning, which is a lot better than doing it later, he says. "In fact, we envision that someday all PLCs and basic controller platforms will have safety built-in as a standard capability," says Nehkorn.

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