ABB AC 800M User Manual page 53

Section 2 Transmission Technology
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.
The ambient conditions described in the topic line technology and the following
conditions must be fulfilled to ensure that the network configuration functions
correctly:
•
•
•
The master tries to address this device cyclically and waits for a reply only until the
configured slot time has been exceeded ("GAP request"). Most optical link modules
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:
•
If this requirement is not fulfilled, the optical line will not be closed into a
redundant optical ring after segmentation.
The slot time must be set to approximately twice the value required in a non-
redundant network.
3BDS009029R5001 B
The operating mode "Redundant optical ring" must be set at both optical ports
of all the optical link modules (Hirschmann).
All modules in a ring must be connected to one another by fiber lines. The ring
may not include an RS485 bus line.
If a redundancy case occurs (for example a line break), there is a switching
time during that 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 shall 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 value of the parameter HSA (Highest Station Address) must be set at least
one value greater than the highest address of a subscriber connected to the bus
segment
Basics of fibre optics topology technologies
53