What follows is an excerpt from the recently released White Paper entitled 6 Reasons to Give PROFIBUS PA Another Look.
The high-power trunk with FISCO spurs is a de-facto standard for PROFIBUS in explosion hazardous areas. Based on this concept, PROFIBUS PA can be installed without difficulty or the need for major cost analyses in the chemical, pharmaceutical, food processing, bio-gas, offshore oil production, or mining industries.
The FISCO Model
The FISCO Model (Fieldbus Intrinsically Safe Concept; IEC 60079-11) serves as the basis for validation of explosion protection without application-specific engineering calculations. It was developed by PTB (the German Federal Standards Laboratory) and confirms that a communication network is intrinsically safe if the components deployed (i.e. field devices, cables, segment couplers, and bus terminators) comply with predefined voltage, current, power, inductivity, and capacitance specifications. Components in accordance with FISCO fulfill these requirements. With only FISCO certified components on a segment, the validation of intrinsic safety is provided by the bill of materials. It doesn’t get easier than that. FISCO, however, has limitations with respect to cable length (up to 1,000 meters) and the number of field devices that can be connected. This is where the high-power trunk comes in.
The High-Power Trunk
Ex-i “Intrinsic safety” with or without FISCO allows modifications of electrical systems without requiring a hot work permit. It is really only needed in process automation when intervention is required on a device during ongoing operation for maintenance purposes or when it is necessary to swap a device. At the trunk cable this is rarely necessary, thus higher power enabled with Ex-e “increased safety” ignition protection is normally sufficient. The High-Power Trunk concept combines elements from the Ex-e and Ex-i protection types. The trunk with Ex-e ignition protection carries high power permitting cable at lengths up to 1,900 meters and a higher number of devices. The devices are attached to fieldbus barriers and the installation is thereby FISCO compliant. With the high-power trunk, PROFIBUS PA is suitable for simple, device installation in explosion hazardous areas wherever the need arises.