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The use of modern multibarriers such as the Turck MBD-...-T415/Ex allows the use of a bus segment for the explosion hazardous area with the same segment structures as in the non intrinsically-safe area – without the danger of potential transfers.
Both the Profibus-PA as well as the Foundation Fieldbus operate conform to the IEC 61158-2 and utilise the voltage mode with a transmission speed of 31.25 kbps. Here the data packages are modulated upon the supply voltage and transmitted via a shielded two-wire cable. These bus physics have a decisive advantage: fieldbus communication and the voltage supply of the bus node can be implemented using just a single cable.
In the bus physics both fieldbus protocols are differentiated by the integration of the host systems which can be found today on the market. All other components can be used in the same way in both bus systems. Each segment requires a power supply. Specified fieldbus cables connect the host to the field. All the well-known topologies from the network technology field can be implemented with differing junction components, whereby these fieldbusses can be adapted to match every system structure. A segment must be terminated at each end with terminating resistors in order to avoid possible reflection of the signals.
Segment structures
The Field Intrinsic Safe Concept (Fisco) model has been developed in the explosion protection field for the supply of power. This enables the user to install and use the fieldbus in zone 1 with justifiable cost and effort. The proof of intrinsic safety has been made easier with fieldbus systems by the Fisco model. Intrinsically-safe networks can be engineered and expanded without complex calculations, and operated without system certification. Turck supports varying installation concepts in the intrinsically-safe field with a range of Fisco products. A segment structure has established itself in this area.
By the use of multibarriers it is possible to implement a bus segment for the explosion hazardous area with the same segment structures as in the non intrinsically-safe area. The supply of energy to the physical layer is implemented in the non-explosion hazardous area – in the control room. The segment cable is subject to the regulations governing enhanced safety (Exe). Junction boxes (multibarriers) can now be connected to this bus cable, which subdivide the Exe cable into 4 Exi trunk lines. As a result, it is possible to supply energy for segments designed for longer distances...
The Author:
Dipl.-Ing. Tim-Peter Henrichs,
Productmanager Fieldbustechnology,
Hans Turck GmbH & Co. KG, Mülheim an der Ruhr
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