ABB AC 800M User Manual page 61

Section 3 Fieldbus Topologies
PROFIBUS provides a wide range of possible transmission rates. The permissible
lengths of possible spur cables depend upon the transmission rate used. No spurs are
permitted for transmission rates over 1,5 Mbit/s. With transmission rates less than
1,5 Mbit/s the total length of all spur cables should be less than 6,6 m. When using
spurs with low transmission rates (93,75 kbit/s), the ratio between spur cable length
and next bus termination should be at least 1:20.
There is always a cable of several centimeters between a PROFIBUS connector
and the transceiver of a node. When connecting 32 nodes to the bus, an important
total spur cable length will result from this. If there should encounter
transmission problems in the installation although everything works reliably at a
low transmission rate, it is recommended to perform a dynamic bus analysis. This
analysis will reliably detect mismatches.
3BDS009029R5001 B
Line Topology with spurs
61