ABB AC 800M User Manual page 51

Section 2 Transmission Technology
Please take the following recommendations into account:
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3BDS009029R5001 B
Ensure that the electrical star segment is wired carefully. Keep it as small as
possible to avoid interference injection into the electrical star segment, and
from here into the entire network. This can be achieved by laying out the
optical link module in the electrical star segment directly next to each other on
a hat rail.
Switch on the terminating resistors in the bus port connectors at both ends of
the electrical star segment.
Do not connect a bus subscriber to the electrical star segment wherever
possible.
Modules with one or two optical ports can be used to create an active
PROFIBUS star coupler. Modules with one optical port are sufficient for
connecting a terminal or an RS 485 bus segment to the active star coupler.
If the link monitoring on the optical ports is activated, the fiber optic links are
monitored by the respectively connected optical link module.
Optical ports which are not assigned (for instance, because they are reserved
for a future system extension) indicate a fiber break if the link monitoring is
activated. To prevent this error from being issued by activating the operating
mode "Line without fiber link monitoring " at the non-assigned ports.
Please note that optical ports which are not connected must always be fitted
with protective caps to guard against extraneous light and dirt.
Basics of fibre optics topology technologies
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