Safety Controllers: Yea or Nay?

Feb. 5, 2013
New Standards Makes Machine Builders Question Whether to Integrate Safety or Not
About the Author
After working as a semiconductor process engineer, Hank Hogan hung up his cleanroom suit and now writes about process control and other technologies from Austin.New standards have stirred interest and raised concern about programmable safety controllers. The question is whether to integrate safety or not.

Count some in the yes camp. The advent of new standards ISO 13849-1 and IEC 62061 caused a spike in the demand for programmable safety technology, says Tony Rigoni, regional sales manager and safety specialist at Beckhoff Automation.

During reevaluation and redesign of systems, companies can bring the control and safety functions together with FailSafe over EtherCAT (FSoE), Rigoni says. "This is the technology driver that allows all machine and safety controls to be on the same network, coexisting side-by-side from design to installation. Machine builders will enjoy reduced hardware costs, less required programming and, most importantly, speedier development times."

SEE ALSO: Programmable Safety Controllers Are Slow to Gain Acceptance

Beckhoff has a PLe-approved, $200 safety terminal that can function as a low-cost safety controller. The company will release a software-based safety controller this year that can run on one core of a multicore industrial or embedded PC, Rigoni says, adding that Beckhoff helped pioneer core-splitting technology for safety applications.

The question of whether or not and what type of programmable safety controller to use comes down to application size, says Tim Roback, safety systems marketing manager for the control and visualization group at Rockwell Automation. For the simplest situations, a standard controller and a safety relay might suffice. Midrange applications might employ a compact safety controller. Moving beyond that in complexity changes the calculation.

"For applications requiring a standard controller and a safety controller, it is more cost-effective to combine the two into one integrated safety system," Roback says.

Doing so minimizes equipment redundancies, improves productivity and cuts costs. Machine manufacturers can reduce outlays thanks to common components. Additional savings appear during application programming. There also can be reductions in training and support costs.

Examples of such integrated systems can be found in Rockwell Automation's GuardLogix controllers. With regard to safety, they can perform drive, motion, high-speed sequential and safety functions up to and including SIL 3, PLe Category 4 classification, Roback says.

Not everyone is convinced, however, that a single system combining control and safety is the way to go. Control engineers do a great job making machines move, but stopping systems in a safe manner can be complicated and time-consuming, says Mike Carlson, safety product marketing manager at Banner Engineering. Thus, preventing faults and dealing with faults that can't be prevented are natural tasks to offload to third-party, certified, safety-logic devices instead of trying to accomplish them on a standard PLC.

Consequently, programmable safety controllers have been catching on for years. The future might hold application-specific devices, such as might be needed when controlling a press. An advantage of this approach is that setup becomes easier. "You don't need to go in and configure as much; 80 or 90% of it is already done for you," Carlson says.

For example, one of Banner Engineering's safety controllers can be programmed to handle a machine's safety functions in minutes, Carlson says. He adds that the alternative can mean hours of coding that still might yield an incorrect outcome.

Because Pepperl+Fuchs focuses on software programmable safety controllers, Helge Hornis, manager of the intelligent systems group, can't say what the effect of new safety standards has been on conventional safety relays. He does note, though, that sales of the company's safety control technology have been growing year over year for the past decade.

Since Pepperl+Fuchs' products are based on the AS-Interface, cost reduction is built in and the cost of safety has been steadily falling, Hornis says. He puts the price today of a solution involving 26 safety devices, networking cable and a safety controller at less than $5,000. Configuration and connection of the hardware takes at most a few hours — considerably less than needed in the past.