Safety in a Non-Exploding Circuit

Rob Spiegel

March 10, 2015

3 Min Read
Safety in a Non-Exploding Circuit

Rockwell Automationhas developed safety modules specifically designed to operate in hazardous environments. The Allen-Bradley Bulletin 937 intrinsic safety modules were designed to provide a signal interface bridge between hazardous locations and the control system by connecting intrinsically safe-rated equipment -- such as transmitters, solenoids, and proximity sensors -- with controls.

The modules were developed to help avoid dangerous short circuits in hazardous environments. An example of a problem that can occur is a short circuit that can start a fire in the coal mine gasses. In one instance, a miner triggered a short circuit (and explosion) when he touched a shovel to a bucket that was connected to a circuit that alerted those at the top of the mine that a bucket was full and needed to be pulled out. Investigators determined the explosion was due to the excess energy in the circuit.

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Rockwell's goal for the modules is to put the safety where the problem originates. If the circuit is designed to operate below the ignition point, it solves the problem of explosion due to circuit ignition. "It's very common to see different safety techniques; one is explosion-proof containers. Yet equipment circuits are where safety really shines," Mason Khan, global product manager for signal interface at Rockwell Automation, told Design News. "The electrical energy is kept at the minimum ignition for each hazardous area. If you know the level that will ignite, and if you keep the circuits low enough, you know you're going to be safe."

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Integrated diagnostics in the safety modules help simplify maintenance. Users can switch out modules during ongoing operations, and the modules can be installed in systems rated up to SIL 3 for reliable planning and documentation. Users can configure the modules using DIP switches or Field Device Tool software, and mount them horizontally or vertically with no reduction in operation ratings.

The modules were designed so plant managers don't have to turn off the circuit to work on it. "That's an advantage. They don't have to shut down to work on the live circuit and make sure it's inherently safe," Kahn told us. "The time it takes to repair a circuit is important. In the past it took a while -- you had to shut down the circuits to open them."

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Also, if the problem is solved at the level of ignition, standard cable is sufficient. "You have the containment in the control circuit, so you don't have to use specialized cable. That's a cost benefit," he said.

The Allen-Bradley Bulletin 937 product family includes zener barriers, galvanic isolators, and galvanic converters. The intrinsic safety modules are available in a range of options that provide a wide range of functionality in hazardous location applications in industries such as oil and gas, chemical, and petrochemical.

Rob Spiegel has covered automation and control for 15 years, 12 of them for Design News. Other topics he has covered include supply chain technology, alternative energy, and cyber security. For 10 years he was owner and publisher of the food magazine, Chile Pepper.

About the Author(s)

Rob Spiegel

Rob Spiegel serves as a senior editor for Design News. He started with Design News in 2002 as a freelancer and hired on full-time in 2011. He covers automation, manufacturing, 3D printing, robotics, AI, and more.

Prior to Design News, he worked as a senior editor for Electronic News and Ecommerce Business. He has contributed to a wide range of industrial technology publications, including Automation World, Supply Chain Management Review, and Logistics Management. He is the author of six books.

Before covering technology, Rob spent 10 years as publisher and owner of Chile Pepper Magazine, a national consumer food publication.

As well as writing for Design News, Rob also participates in IME shows, webinars, and ebooks.

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