Proline Prowirl 72 FOUNDATION Fieldbus 4 Wiring
Endress + Hauser 21
4.1.2 Maximum overall cable length
The maximum network expansion depends on the type of protection and the cable specifications.
The overall cable length combines the length of the main cable and the length of all spurs
(>1 m/3.28 ft ). Note the following points:
• The maximum permissible overall cable length depends on the cable type used (Page 20).
• If repeaters are used, the maximum permissible cable length is doubled.
A maximum of three repeaters are permitted between user and master.
4.1.3 Maximum spur length
The line between the distribution box and field device is described as a spur.
In the case of non-Ex applications, the max. length of a spur depends on the number of spurs
(>1 m/3.28 ft):
4.1.4 Number of field devices
In accordance with IEC 61158-2 (MBP), a maximum of 32 field devices can be connected per
fieldbus segment. However, this number is restricted under certain conditions (explosion
protection, bus feed, field device current consumption).
A maximum of four field devices can be connected to a spur.
4.1.5 Shielding and grounding
Optimum electromagnetic compatibility of the fieldbus system can only be guaranteed if the system
components and, in particular, the lines are shielded and the shield forms as complete a cover as
possible. A shield coverage of 90% is ideal.
To ensure an optimum shield effect, connect the shield as often as possible to the reference ground.
Where applicable, national installation regulations and guidelines must be observed!
If there are large potential differences between the individual grounding points, only one point of
the shielding is directly connected to the reference ground. In plants without potential matching,
therefore, cable shielding of fieldbus systems should only be grounded on one side, for example for
the fieldbus supply unit or safety barriers.
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Caution!
If the shielding of the cable is grounded at more than one point in systems without potential
matching, mains frequency equalizing currents can occur that damage the bus cable or shielding or
have a serious effect on signal transmission.
Bus termination
The start and end of each fieldbus segment must always be terminated with a bus terminator. With
various junction boxes (non-Ex), the bus termination can be activated via a switch. If this is not the
case, a separate bus terminator must be installed. Note the following points:
• In the case of a branched bus segment, the device furthest from the segment coupler represents
the end of the bus.
• If the fieldbus is extended with a repeater, then the extension must also be terminated at both
ends.
Further information
General information and further pointers on wiring can be found on www.fieldbus.org, the website
of the Fieldbus Foundation.
Number of spurs 1 to 12 13 to 14 15 to 18 19 to 24 25 to 32
Max. length per spur 120 m (393 ft) 90 m (295 ft) 60 m (196 ft 30 m (98 ft) 1 m (3.28 ft)
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