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11
ELECTRICAL CONNECTIONS
Transmission rate
Total of stub cables *
> 1.5 Mbit/s
none
1.5 Mbit/s
6.7 m
500 kbit/s
20 m
187.5 kbit/s
33 m
93.75 kbit/s
100 m
19.2 kbit/s
500 m
* Total of all stub cables within a segment for PROFIBUS cable
of 30 pF/m
Stub cables are never allowed if the transmission rates
exceed 1.5 Mbit/s. Stub cables may be used for trans-
mission rates of less than or equal to 1.5 Mbit/s, if the
limit values stated in the table are not exceeded.
Stub cables
Stub cables (
2
) (with Y or T distributing piece) are branches from the main bus line (
1
)
to the node.
Transmission rate
Maximum cable length
> 1.5 Mbit/s
100 m
1.5 Mbit/s
200 m
500 kbit/s
400 m
187.5 kbit/s
1000 m
93.75 kbit/s
1200 m
45.45 kbit/s
1200 m
19.2 kbit/s
1200 m
9.6 kbit/s
1200 m
The maximum cable length depends on the transmission
rate. For transmission rates greater than 1.5 Mbit/s, a
minimum cable length of 1m between two nodes is re-
commended.
Bus cable
Cables with the following specifications must exclusively be used for new installations:
■
Characteristic impedance 135…165 ohm (resistance for high-frequency signals)
■
Capacitance <30 pF/m
■
Loop resistance 110 ohm/km
■
Wire diameter 0.64 mm
■
Wire cross section> 0.34 mm²
1
2
