General Functions - Siemens SIMATIC NET OLM12M Description And Operating Manual

6ZB5530–3AB00–0BA0/01
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General Functions

3.1 Functions Not Dependent on Mode
Transmission Rate
The SIMATIC NET OLM12M optical link modules support the transmission rates12 Mbps (standard
setting), 1.5 Mbps, 500 Kbps and 187.5 Kbps.
Signal Regeneration
The SIMATIC NET OLM12M optical link modules regenerate the signal shape and amplitude of the
received data. With this function, it is possible to cascade any number of modules in a bus topology,
and up to 55 modules in a ring topology on fiber-optic cable connections. The sections below and
the appendix contain more detailed information.
3.2 Functions Dependent on Mode
Line Monitoring
With the "Monitoring", "Send Test Pulses" and "Monitor Echo" functions, the SIMATIC NET
OLM12M optical link module can monitor the connected optical paths for breaks on the FO cable.
Monitoring
The SIMATIC NET OLM12M optical link module monitors the bus activity on the optical receive
channels. If there is no bus activity, for example due to a cable break, the system LED is switched
to red and the signaling contact activated after approximately 200 ms on the single-fiber ring and
after approximately 600 ms on the optical bus.
Insecure fiber-optic cable connectors or extraneous light entering the open FO cable
are not detected as faults.
Echo Monitoring
If an optical link module sends a frame on an optical channel in the ring (active) mode, the OLM12M
expects an echo. If no echo is received for a specified number of frames, the system LED is
changed to red and the signaling contact is activated.
Segmentation
If a monitoring or echo monitoring error occurs on an optical channel, the optical link module
assumes a cable break and disables the transmitter on this channel for user data. This segments
(separates) the connected field bus subnet.
Following this, test pulses are sent on the segmented channels. These regular light pulses indicate
whether or not the optical path is functioning correctly or not (if there is a break on a single fiber of a
duplex FO cable).
These test pulses are suppressed internally and not passed on to the other channels.
The segmentation is canceled automatically as soon as the receiver detects a light pulse.
Copyright Siemens AG 1997
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SIMATIC NET OLM12M