ABB AC 800M, User Manual

Page: 46 / 118

Basics of fibre optics topology technologies Section 2 Transmission Technology
46 3BDS009029R5001 B
• Send echo
A frame which is received by a module via any port is transmitted to all other
ports. If the receiving port is an optical port, the module sends the frame back
to the corresponding optical sender.
• Monitor echo
If a module sends a frame - no echo! – to an optical port, the module expects to
receive an echo. If the echo is not received after a predefined time, an echo
monitoring error is indicated.
• Suppress echo
The relevant receiver is separated from the other ports from the moment a
frame is sent until the echo has been received correctly.
Segmentation
If an echo monitoring error or a frame falsification arises at an optical port, the
module assumes that the line is faulty and blocks this port for user data. The
connected field bus partial network is then segmented (cut off). This segmentation
causes the module at the other end of the optical fiber to be segmented as well.
Both modules connected to the segmented field bus partial network send test frames
to the segmented ports. These test frames – which are to be received regularly – can
be used by both modules to check the status of the field bus partial network. The
segmentation is automatically lifted as soon as the test frames indicate to both
modules that the segmented field bus partial network is no longer disturbed. If all
active bus subscribers are deactivated in a previously active network, the modules
are segmented cyclically in order to check the fiber links to the neighboring
modules.
Basics of fibre optics topology technologies
Fibre optics topology technologies is part of Fieldbus Topologies with fibre optics
on page 84. However, to understand the basics of the fibre optic transmission
technology, the next pages show main topologies supported by fibre optics.
The next paragraph in this document describes the monitoring function within a
certain fibre optic topology.