Siemens SIMATIC NET PROFIBUS - Manual (Page 70)

Configuring Networks
3-4
PROFIBUS Networks SIMATIC NET
6GK1970-5CA20-0AA1 Release 2 05/2000
Length of the Tap Lines
If you do not attach the LAN cable directly to the bus connector (for example,when
using a PROFIBUS bus terminal), you must take into account the maximum
possible tap line length!
The following table shows the maximum permitted lengths of tap lines per bus
segment:
Table 3-2 Lengths of the Tap Lines per Segment
Transmission
rate
Max. length of the tap
lines per segment Number of nodes with tap line
length of ...
1.5 m or 1.6 m 3 m
9.6 – 93.75 Kbps 96 m 32 32
187.5 Kbps 75 m 32 25
500 Kbps 30 m 20 10
3.1.2 Segments for a Transmission Rate of 1.5 Mbps
Transmission Rate 1.5 Mbps
The following maximum segment length can be implemented with the SIMATIC
NET PROFIBUS LAN cable:
Table 3-3 Possible Segment Lengths
Segment Length for Cable Type
Transmission Rate
in Kbps
– FC Standard Cable
– FC Robust Cable
– FC FRNC Cable
– FC Food Cable
– FC Underground Cable
– SIENOPYR–FR Marine Cable – FC Trailing Cable
– PROFIBUS Flexible Cable
– PROFIBUS Festoon Cable
1.500 200 m 200 m
Node Attachments at 1.5 Mbps
Each attachment of a node to the LAN cable represents a capacitive mismatch that
has no effect at lower transmission rates. At a transmission rate of 1.5 Mbps,
however, problems can arise due to these mismatches if the following guidelines in
terms of type, number and distribution of node attachments are not adhered to.