35
Setting up a Network
Section 2-4
Cable Type The PROFIBUS standard EN 50170 specifies Type A shielded, twisted- pair
cable as the recommended cable type for use in an RS-485 based PROFI-
BUS network. This cable type has the following characteristics:
Note The PROFIBUS standard EN 50170 also specifies a Type B cable with slightly
different cable characteristics. This Type B cable is no longer recommended
for use.
Maximum PROFIBUS
Cable Length
The transmission speed defines the maximum advised cable distance or
cable segment in metres before the use of a repeater is recommended. The
cable lengths specified in the following table are based on PROFIBUS type A
cable.
Note If the network must be extended beyond the range of the advised cable
length, the use of a fibre optic segment to cross the larger distance should be
considered.
Stub Lines Passive Stub lines (branches from the main line) should be avoided for data
transmission speeds of more than 500 kbit/s. Except at end stations with ter-
mination, it is recommended to always use plug connectors that permit two
data cables to be connected directly to the plug. This method allows the bus
connector to be plugged and unplugged at all times without interrupting data
communication between other stations.
Characteristic Value
Impedance 135 - 165 ohms
Capacitance per unit length < 30 pF/m
Loop resistance 110 ohms/km
Core diameter 0.64 mm
Core cross section
0.34 mm
2
Baud rate
(kbit/s)
Distance/segment
(m)
Baud rate
(kbit/s)
Distance/segment
(m)
9.6 1200 500 400
19.2 1200 1500 200
45.45 1200 3000 100
93.75 1200 6000 100
187.5 1000 12000 100
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