3 Network Topologies
3.3 Redundant optical ring
14
Version 2.4 04/07
This network topology represents a special form of line
topology. A high degree of network operating safety
is achieved by ”closing“ the optical line. A redundant
optical ring can only be realized with modules with two
optical ports of the same type.
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Monitoring mechanisms:
Send echo:
yes
Monitor echo:
yes
Suppress echo:
yes
Segmentation:
yes
An interruption of one or both optical fibers between two
modules is detected by the OZD Profi 12M … and the
ring is transformed into an optical line.
If one module fails only those terminals connected to this
module or the RS 485 segment are uncoupled from the
ring. The remainder of the network itself continues to
function as a line. The error is indicated by the LEDs on
the two OZD Profi 12M … connected to the malfunction-
ing optical fiber and their signaling contacts.
The segmentation is lifted automatically as soon as both
modules recognize that the segmented field bus network
is functioning correctly with the help of test frames. The
line forms itself into a ring.
Please note:
The following ambient conditions must be fulfilled to
ensure that the network configuration functions correctly:
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The operating mode ”Redundant optical ring“
must be set at both optical ports of all the
OZD Profi 12M ….
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All modules in a ring must be connected to one
another by fiber lines. The ring may not include an
RS 485 bus line.
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The parameter MIN T
SDR
described in the PROFI-
BUS standard EN 50170 must be set to a value
>
_ 11 on all terminals. This is usually the case, but
the setting should be checked if communication
malfunctions continuously arise.
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When configuring your network, select low bus
subscriber addresses wherever possible. This
ensures that master timeout times which may
arise are kept as short as possible in the event
of a malfunction.
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If a redundancy case occurs (e.g. a line break),
there is a switching time during which data cannot
be correctly transmitted. In order to ensure a
smooth transition, it is recommended that the
frame repeat setting (Retry) on the PROFIBUS
master be set to at least 3.
After the error has been corrected, no frames
should be present in the network when the optical
line is transformed back into an optical ring to
ensure that the process is completed smoothly.
This condition can arise when a master selects a
device whose address has been configured, but
which does not physically exist.
The master tries to address this device cyclically
and waits for a reply only until the configured slot
time has been exceeded (”GAP request“). The
OZD Profi 12M … recognizes this condition and
closes the optical line to an optical ring in the
middle of this request sequence.
This results in two configuration requirements for
the redundant optical ring:
– The value of the parameter
HSA
(Highest Station
Address) must be set at all terminals so that bet-
ween the bus address 0 and the value HSA at
least one address in the network has
not
been
assigned to a bus subscriber, i.e. so that there is
at least one address gap. This address gap can
also be created by simply setting the value of the
parameter HSA so that it is at least one greater
than the highest number of subscriber bus
addresses present in the network.
Attention:
If this requirement is not or no longer
fulfilled, the optical line will no longer be closed
into a redundant optical ring after segmentation.
The error report (LED and signaling contact) of
the two affected OZD Profi 12M … is not can-
celled even after the error has been corrected.
– The
slot time
must be set to approximately twice
the value required in a non-redundant network.
Further information can be found in Chapter 6
”Configuration“, p. 31.
Refer to the manufacturer’s documentation provided
with the terminal or configuration software for details
about how to adjust the settings.
