Big Breakthrough for Intrinsic Safety
06 May 2008
For 40 years intrinsic safety (EX i) has meant limiting the amount of electric power to less than two watts in dangerous areas, for fear any spark could ignite an explosion. A whole industry has grown up of companies who supply isolators and barriers to build this type of protection
Phil Saward shows MTL’s display of its ‘Fast Switch’ technology
At Interkama this year, two of these companies, MTL and Pepperl + Fuchs, were showing a new approach that could potentially alter the future course of IS practice. They were displaying technology that allows comparatively large amounts of power—50 watts and maybe even way beyond that number—into areas that were previously considered too dangerous for live electricity.
The new method uses fast electronics to monitor fieldbus circuits and detect surges in current and voltage that are characteristic of a suddenly broken line or from a module being unplugged from a backplane. Sparks always lead to a sudden peak of the current and voltage within the respective circuit, peaks that show very specific characteristics which the electronics can detect within five microseconds and shut down the power supply. The idea is to shut off power before any critical situation can arise, before the current is able to reach a level to build up sufficient heat for ignition.
For its efforts, Pepperl+Fuchs was one of five Hermes Award finalists at Hannover Messe (the Hermes Award is the world’s largest technology prize; the winner receives €100,000). The system is called DART for Dynamic Arc Recognition and Termination.
Dipl-Ing Thomas Kleinbongartz, Director, Global Marketing, says his company will offer DART in two versions, one for high power devices up to 50 watts inside the Ex area such as industrial PCs, LED lighting systems, analysis instruments and solenoid valves. A second system will offer, via a fieldbus infrastructure, up to 8 watts of electric power per segment inside explosion hazardous areas.
Since factors such as cable length and device characteristics can greatly influence the response time for spark detection. DART deals with these differences by connecting the device via a decoupling module to the energy supply. The module ensures a clearly defined electrical response pattern, always providing the DART system with a signal that allows the dependable detection of critical situations requiring immediate shutdown of the circuit.
MTL Instruments Group’s managing director Graeme Philp was on hand to introduce his company’s version of the concept, which he calls ‘Fast Switch.’ MTL will implement the technology in conjunction with its PoEx™ Intrinsic Safety Ethernet range, which was a major product launch at Interkama.
‘The ability to run fieldbus networks over a longer distance while maintaining the ability to live work is solved by the use of certified switching components that permit the safe interruption of non-intrinsically safe circuits,’ Mr. Philp said. ‘This, together with the launch at Interkama of Redundant power for FISCO (Fieldbus Intrinsically Safe Concept) networks, allows users to enjoy the highest availability on the market, while retaining the ability to live work in applications requiring long cable lengths.’
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