Stahl 9411/21 Betriebsanleitung Seite 45

10.3 Cable lengths for trunk and spurs in accordance with IEC 61158-2, Annex B
for cable type "A"
For planning we recommend the usage of our free planning tool "Fieldbus
Wizard". It can be downloaded on the Internet from www.fieldbus-
solutions.info.
The maximum length for all cables (all trunks, all spurs) per segment must not
exceed 1900 m.
Max. cable length for spurs, 1
field device per spur
Max. cable length for spurs, 2
field devices per spur (e.g. for
redundant hosts)
The actual trunk and spur lengths can be shorter due to voltage drop.
The maximum length of an Ex i spur according to IEC 60079-27 (FISCO) is
60 m. From the viewpoint of the FISCO model, the Ex i spurs of a field device
coupler are to be considered as a new segment (whereby the maximum
segment length = trunk + spurs = 1000 m). The table above can be used for
this purpose.
The following generally applies: Spurs should be kept as short as possible.
Maximum spur length = 120 m
10.4 Examples of cable lengths
Cable lengths for trunk with 12 field devices with a current consumption of 15 mA:
Assumption:
Fieldbus power supply with U
X
Current consuption of host is 20 mA.
X
Type A fieldbus cables (loop resistance: 44 ohms/1000 m) are used.
X
Two field device couplers lie at the end of the trunk.
X
Maximum trunk length: approx. 600 m.
Cable length for trunk with 16 field devices with a current consumption of 15 mA
per device:
Assumption:
Fieldbus power supply with U
X
Current consumtion of host is 20 mA.
X
Type A fieldbus cables (loop resistance: 44 ohms/1000 m) are used.
X
Two field device couplers lie at the end of the trunk.
X
Maximum trunk length: approx. 450 m
166617 / 941160310040
S-BA-9411/21_8 Spur-02-en-27/03/2009
Number of all field devices on the segment, including
host(s)
1 ... 12 13 ... 14
120 m 90 m
90 m 60 m
> 25 V / I > 350 mA.
out out
> 25 V / I > 350 mA.
out out
Ex i Field Device Coupler (8 Spurs)
9411/21
15 ... 18 19 ... 24
60 m 30 m
30 m 1 m
Installation
25 ... 30
1 m
1 m
17