ABB AC 800F

4 Cabling the AC 800F
4-62
To ensure RFI suppression in
accordance with Class B to
DIN/VDE install the ferrite ring RFI
suppressor from Würth-Elektronik,
ordering code 742 701 110. The
requirements of RFI suppression
Class A are always met.
Fig. 4-39 Profibus connector with ferrite-type RFI
suppressor, example
RFI suppression (Class B to DIN/VDE) is only ensured if the Profibus
cable is provided with the ferrite-type RFI suppressor specified
above.
Branch cables
The Profibus provides a wide range of possible transmission rates. The permissible
lengths of possible branch cables depend upon the baud rate used. No branches are
permitted for 12 Mbauds. With transmission rates of max. 1.5 Mbauds the total length
of all branch cables should be less than 6.6 m. When using branches with low baud
rates (≤ 93.75 kbauds), the ratio between branch cable length and next bus
termination should be at least 1:20.
In the past, a commonly used solution were bus terminals with nodes connected via
branches. This configuration, however, is only useful under certain conditions with 1.5
Mbaud transmission and should be avoided with higher transmission rates.
Please note that there is always a cable of several centimeters between a Profibus
connector and the transceiver of a node. When connecting 32 nodes to the bus, an
important total branch cable length will result from this. If you should encounter
transmission problems in your installation although everything works reliably at a low
transmission rate, it is recommended to perform a dynamic bus analysis. This
analysis will reliably detect mismatches.
4.3.1.2 Connecting the Profibus via fiber-optic cables (FO cables)
An off-the-shelf interface converter is needed for the transition from RS485 bus
technology to a fiber-optic cable. An FO cable consist of two glass fiber leads, one for
transmit data and one for receive data.
Usually, the RTS signal on the Profibus connector controls if data is transmitted or
received.
Note that this signal and the VP and GND signals additionally have to be applied to
an interface converter. Observe the instructions in the user manual delivered with
your interface converter.