Redundant FISCO "Removes a Level of Risk"

MTL's introduction of its Redundant FISCO (Fieldbus Intrinsically Safe Concept) technology at the 2008 Interkama was more than a little overshadowed by the simultaneous introduction of the MTL/Byres Security Tofino cyber security solution and, for INSIDER at least, by the unveiling of MTL's "Fast Switch" technology, not to mention the subsequent discussion of the differences and similarities between the latter and Pepperl+Fuchs' DART technology.

Hardly surprising then that, with the announcement that BP is adopting the MTL solution for its PSVM (Plutao, Saturno, Venus and Marte) development in Angola's offshore Block 31 oilfield, Fieldbus Products product manager Phil Saward was keen to grab the opportunity of another bite at the publicity cherry.

FISCO is defined by IEC standard 60079-27 and extends the benefits of Foundation fieldbus technology to hazardous areas. Since 2001, MTL has been offering FISCO power supplies which render the complete fieldbus segment Intrinsically Safe (IS), thereby eliminating any risk of an incendive spark being generated in the hazardous area. Not only do they allow ‘live working' in the hazardous area but support as many as a dozen devices per segment, depending on the gas group classification.

What they haven't been able to provide up until now, however, is redundancy and, since the highest availability is a key requirement offshore, as well as in such industries as refining, petrochemicals and pharmaceuticals, uptake has not been as rapid it might otherwise have been. Users for whom redundancy is mandatory have had either to take a non-FISCO approach or adopt solutions involving a mixture of IS and non-IS technologies and which rely essentially on maintenance staff adhering to tightly specified procedures in order to ensure safe operation.

Developing a fully redundant FISCO solution was, says Saward, "a significant technical challenge." Conventionally redundancy is best achieved simply by duplicating power supplies but such an approach cannot be used without breaching IS restrictions. Instead MTL's solution adopts an active and hot standby configuration with failover between the two being achieved in less than 500microsec, the minimum power outage which the Fieldbus Foundation requires devices to be able to survive without loss of data.

End-to-End Solution

MTL's 910x series power supply systems support redundant FISCO Power Conditioners and associated Supply Arbitration Modules for four fieldbus segments on a single backplane. When combined with its Megablock field wiring hubs, the result is a complete end-to-end solution from the power supplies mounted in the safe area through to the devices in the field. "No other system currently on the market gives full redundancy of the power system," claims Saward. Although another manufacturer is understood to be developing a rival offering, his understanding is that it is not as comprehensive as MTL's solution while he asserts that current alternatives only achieve a limited degree of redundancy.

For the Angola project, MTL is supplying BP with Redundant FISCO power supplies and field Junction Boxes containing FISCO Megablocks with surge protection for the network trunk. Spur short-circuit protection is already accommodated within the Megablock wiring hub.

BP's decision to adopt the solution for the current project actually predated MTL's gaining the necessary approvals and derives from its determination, perhaps reinforced since the Texas City accident, to maintain the highest levels of availability at the same time as achieving what Saward terms "self safety". "Other solutions are mixture of IS and non-IS and rely on the ability of the maintenance technicians for their safety," he claims. "With our solution, all circuits are IS so, even if the maintenance guy unplugs things, there is no risk of blowing up the plant. It removes a level of risk out of the field."

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