Intelligent Safety Networks

By Ed Nabrotzky, Woodhead Industries -- Control Engineering, 7/1/2006

Intelligent Safety Networks (ISNs) for manufacturing are intelligent in more ways than one. These adaptable and fully programmable systems do a better job of ensuring safe machine operations than traditional hardwired safety systems, and they are also an intelligent choice for plant management, since they reduce operating costs and boost plant productivity.

At its most basic level, an ISN automatically takes an industrial process to a safe state when certain conditions are violated. An ISN features high integrity communications, stringent timing requirements, and a safety integrity level (SIL) 3 implementation (meaning a one in 100 million probability of a dangerous failure per hour). ISNs are typically based on safety PLCs and networked components. Since ISNs reside on "softwired" systems such as DeviceNet or Ethernet that are used to simultaneously control plant operations, they can be far more flexible and cost effective than the hardwired "safety only" systems they replace.

While implementation of ISN is optional today, it will soon be mandatory for suppliers to some large manufacturers. General Motors has announced that its suppliers must have ISN technology implemented in equipment supplied to GM plants beginning in 2009—a mandate likely to spread to other large manufacturing companies, just as use of radio frequency identification (RFID) tags spread once Wal-Mart required its use.

GM's controls, conveyors, robotics and welding systems (CCRW) automation and controls engineering group, formed in 1997, has been leading the company's initiative to establish common engineering processes, manufacturing systems, and components throughout its global operations. The wide-ranging initiative, called Common Controls Architecture (CCA), includes machine safety technology.

According to a June 2005 report by ARC Advisory Group report ("General Motors Drives Common Architecture for Global Operations"), GM's CCRW group created monitored power systems technology as the first step toward an intelligent safety solution. The CCRW also created a task-based risk assessment (TaBRA) process to increase employee confidence in the new technology.

As a result, GM's CCRW group is eliminating costly and complex safety relays in common control panels and replacing them with smaller, rack-mounted safety PLCs supplied by Rockwell Automation. "Replacing safety relays with a dedicated safety PLC significantly reduces control panel real estate by eliminating cabling, freeing up space, and reducing the overall complexity of the panel," said the ARC report. "Moreover, since unique safety circuitry has been eliminated, this has resulted in a more common panel overall."

As with other elements in the GM CCRW technology migration plan, Intelligent Safety is being implemented in five-year "steps." The Rockwell Automation-based ControlLogix Safety PLC and Safety Network was implemented in 2004, and by 2009 GM's EtherNet/IP Safety Network should be in place.

While the CCRW has developed standards and protocol, GM is leaving ISN implementation up to its vendors. As a result, GM vendors should be budgeting for discovery and a planning budget by 2007, pilot programs in 2008, and production with ISNs in 2009 after a pre-validation process. For GM vendors, time is running short.

The timetable for emerging ISN networks is likely to span 2009-2020. As with RFID, reports of "immediate adoption" of ISN have been greatly exaggerated. With GM's mandate set to begin in 2009, ISN is likely to be fully in place and operating by 2011 in GM plants and be adopted by other manufacturers by the middle of that decade.

As a result, the time is now to ask vendors for implementation roadmaps and evidence that they will be compliant with developing ISN standards. Five major platforms for intelligent safety networks already exist or are being developed: AS-Interface "Safety at Work," PROFIsafe, SafetyBUS p, DeviceNet Safety, and EtherNet/IP Safety. Initially, these systems are unlikely to interface with each other, so vendors and users may need to work with integrators invested understanding the multiple ISN systems on the market and how to link them.

Intelligent Safety Networks provide measurable business benefits, including a safety strategy to protect people while supporting the enterprise.