DART update: Developer dialogue reveals tangible solutions
05 June 2009
At last year’s (2008) Hannover Messe, Pepperl+Fuchs introduced a new technology for intrinsic safety applications called DART (Dynamic Arc Recognition and Termination). Since that time, P+F in combination with the Physikalisch-technische Bundesanstalt (PTB) have been investigating the potential of the technology with other companies in Germany.
Dipl-Ing Thomas Kleinbongartz
Intrinsic safety (EX i) has traditionally meant limiting the amount of electric power to less than two watts in dangerous areas, for fear any spark could ignite an explosion. DART technology 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. It removes the power limitations of intrinsic safety because of its dynamic detection methods.
Dipl-Ing Thomas Kleinbongartz, Director, Global Marketing, shows DART technology at its launch at Hannover Messe 2008.
The 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.
Since last year’s launch, P+F in combination with the Physikalisch-technische Bundesanstalt (PTB) have been investigating the technology, which they say is ‘on the path to international standardisation.’ The two have conducted meetings with engineers from field instrument companies to determine the future of the product. PTB has been working on developing and fine-tuning certification tests and procedures.
PTB recently conducted a workshop in Braunschweig directed at development engineers for co-ordination of technical needs with regards to DART technology.
Participants at the workshop, who consisted of experts from interested manufacturers, PTB and Pepperl+Fuchs, discussed DART technology, its implementation in new products, and solutions for the process industry.
They quickly agreed that point-to-point supply with more available power would be beneficial to many applications with our methods of explosion protection today.
For example, the precision of a flow meter based on Coriolis measurement principles can be improved with increased power. The influence of cavitation on the measurement is smaller, or even irrelevant. The additional circuitry that is required is more than compensated by reduced material and installation costs, and sophisticated methods of explosion protection, such as flame-proof and increased safety, are no longer needed.
It became clear that a supply with 24 V and max. 12 W would satisfy the needs of all developers and would be easy to implement. The cable length is relevant to the amount of power available to the instrument. Cable lengths between 10 and 1000 m were discussed. Of interest, though possibly for a second step of development, is the transmission of digital data, which could be transmitted simultaneously with DC power through modulation.
PTB is promoting internationalisation. As a first step, the evaluation for system safety and the testing procedures are re-certified in close co-operation with other competent institutes. This collaboration helps to generate a universal acceptance for the envisioned testing procedures that will be introduced into a technical specification (TS) of the IEC and eventually find its way into the IEC-standard 60079. All parameters are to be defined relevant for safety and required for conception of such systems (supply, cable, load) including functional and safety-related constraints.
The common objective is extremely clear: to create interoperability for EPCs and end users such that plug-and-play becomes reality. Many participants have pledged their support for an industry-financed project. A paper covering the details regarding requirements for DART-system components will be published during Automation 2009, a conference hosted by German VDI.
Pepperl+Fuchs has registered a patent and trademark for DART (WO 2006/003445). Rights are licensed to all interested parties in two variations: the ‘small’ license for DART-consumers, and the ‘large’ license for the complete DART-technology: supply and load. As soon as an internationally applicable specification or standard becomes available that defines interoperability for power supply and loads, all license costs will be dropped. Today’s developments have progressed; first solutions will be available soon.
FOR MORE READING
For the first of a series of articles describing the operation of DART, CLICK HERE
For the original announcement of DART at Hannover Fair 2008, CLICK HERE
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