Endress+Hauser Proline Promass 83, Operating Instructions Manual

Page: 26 / 118

4 Wiring Proline Promass 83 FOUNDATION Fieldbus
26 Hauser
Maximum overall cable length
The maximum network expansion depends on the type of ignition protection and the cable specifi-
cations. The overall cable length is made up of the length of the main cable and the length of all
spurs (>1 m). Note the following points:
• The maximum permissible overall cable length depends on the cable type used (see Page 25).
• If repeaters are used the maximum permissible cable length is doubled.
A maximum of three repeaters are permitted between user and master.
Maximum spur length
The line between distribution box and field unit is described as a spur.
In the case of non ex-rated applications the max. length of a spur depends on the number of spurs
(>1 m):
Number of field devices
According to IEC 61158-2 (MBP) a maximum of 32 field devices may be connected per fieldbus
segment. However, this number may be restricted in certain circumstances (type of ignition protec-
tion, bus power option, current consumption of field device).
A maximum of four field devices can be connected to a spur.
Shielding and grounding
The optimum electromagnetic compatibility of the fieldbus system is guaranteed only when system
components and in particular lines are shielded and the shielding provides the most complete cover-
age possible. Shield coverage of 90% is ideal.
Shielding should be connected as often as possible with the reference ground. The national regula-
tions and guidelines governing the installation of electrical equipment also apply where relevant!
Where there are large differences in potential between the individual grounding points, only one
point of the shielding is connected directly with the reference ground. In systems without potential
equalisation, cable shielding of fieldbus systems should therefore only be grounded on one side, for
example at the fieldbus supply unit or at safety barriers.
"
Caution!
If the cable shielding is grounded at more than one point in systems without potential equalisation,
network frequency equalisation currents can occur that damage the bus cable or the bus shielding
and substantially affect signal transmission.
Bus termination
The start and end of each fieldbus segment are always to be terminated with a bus terminator. With
various junction boxes (not ex-rated) 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 addition:
• In the case of a branched bus segment the device furthest from the segment connector 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 notes on connections can be found on the website (www.field-
bus.org) of the Fieldbus Foundation.
Number of spurs 1 ... 12 13... 14 15... 18 19... 24 25... 32
Max. length per spur 120 m 90 m 60 m 30 m 1 m