and service to meet market requirements.”

Charles Larson points to the importance of newer industry standards in opening the door to networked safety, and thus making possible the “freedom of choice from suppliers” that Duran spoke of. “The advent of the [International Electrotechnical Commission] IEC 61508 standard provides a means to determine the risk of failure for microcontroller- and software-based systems, and thus makes it possible to determine the safety level of safety systems that will use a digital communications network, such as Foundation Fieldbus,” notes Larson, the director of technology for automation components vendor Moore Industries-International Inc., North Hills, Calif.

Standards

IEC 61508, primarily for suppliers, and its complementary IEC 61511, primarily for process industry end-users, along with [American National Standards Institute/International Society of Automation] ANSI/ISA 84.01, which follows the IEC 61511 standard, apply to safety-instrumented systems. They include performance and lifecycle criteria that allow users to quantify system reliability through failure rates based on fault detection, fault tolerance and probability of failure on demand (PFD).

Networked safety is software-dependent safety, and, as Larson notes, “As anyone who has worked on safety software can attest, certifying the reliability of software for safety purposes is an involved and time-consuming process.” Another caveat comes from Helge Hornis, manager, intelligent systems, Pepperl+Fuchs Inc., a Twinsburg, Ohio-based automation components vendor. Although keen on the value of networked solutions, he cautions that buyers should ascertain the degree of backward and forward compatibility. Another important issue is configuration software and tools, says Hornis.  Will the tool that’s available today still work in five years?  And if not, what is the cost of keeping up with software developments?

Still, the benefits of networked safety are considerable, and Larson insists they are felt not only in the realm of cost, but in the realm of safety as well. “The increased diagnostics that are available with digital networks make it possible to identify failing components before they trigger a system shutdown. These factors can contribute both to reducing the risk of a dangerous failure and to higher availability.

“If one has any doubts about the future direction of safety systems,” Larson adds, “one only has to consider that the aircraft with the best safety records—records which are good enough to meet SIL (Safety Integrity Level) level 4—operate completely on computer-controlled fly-by-wire systems. Despite the complexity of software based systems, with proper design, they can provide greater protection and availability than ever before.”

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