ISA Certified Automation Professional (CAP) program

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Certified Automation Professionals (CAPs) are responsible for the direction, design, and deployment of systems and equipment for manufacturing and control systems.

CAP question

What is the significance of the fieldbus intrinsic safety concept (FISCO)?

A. It decreases the number of field devices per trunk compared with traditional area classification practices.
B. It simplifies the rules governing energy storage in field cables and makes more power available to the fieldbus trunk.
C. It increases safety requirements for live-working on a trunk and spurs.
D. It standardizes safety documentation for fieldbus circuits in Division 2 hazardous areas, in which the explosion hazard is expected only in abnormal circumstances.

CAP Answer

The correct answer is B, It simplifies the rules governing energy storage in field cables and makes more power available to the fieldbus trunk. FISCO considers the segment circuit as a whole, including power sources, cabling, devices, and connectors.

Even though a FISCO approach allows more power on a segment trunk cable than the entity approach (field barrier approach), FISCO requires each part of the system, including devices, cables, and power conditioners, to be FISCO certified. In addition, FISCO design and installation rules must be strictly followed. The FISCO installation is still bound by the requirement that no more than 115 mA can be delivered through a segment installed in a hazardous area, so approximately the same number of devices (four or five) can be installed on a single segment.

Reference: Trevathan, Vernon L., A Guide to the Automation Body of Knowledge, Second Edition, ISA, 2006.

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