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PROFIBUS Optical Bus Terminal (OBT)
Operating Instructions, 04/2016, C79000-G8976-C122-07
9
Functional description
3
The OBT is a repeater with 3 channels.
3.1
Interfaces
The OBT has the following interfaces for connection of PROFIBUS DP segments:
●
Channel 1 (CH1) is an electrical RS-485 interface. It is designed as a 9-pin D-sub female
connector. A PROFIBUS DP node or a PC, PG, OP or an RS-485 segment can be
connected to the OBT via this channel. The copper segment should be kept as short as
possible since this can couple in disturbances into the optical PROFIBUS DP.
●
Channel 2 (CH2) and channel 3 (CH3) are optical interfaces. These are designed as
duplex female connectors. The end a two-fiber plastic or PCF fiber-optic cable fitted with
two simplex male connectors is connected to each of these duplex female connectors.
The OBT also has a 3-pin terminal for connection of the 24 V power supply and, if
necessary, a ground cable.
3.2
Opto-electrical signal conversion and signal regeneration
The OBT converts the RS-485 level received at channel 1 into an optical signal level that is
output via channels 2 and channel 3.
Signals received at channel 2 or 3 are converted to electrical signals and
●
output on channel 1 as an electrical signal
●
they are then converted into an optical signal again and output on the other optical
channel.
There is no echo on the receive channel; in other words, received signals are not sent back
on the same channel.
The OBT regenerates the signals in amplitude and time. This makes it possible to cascade
up to 126 modules in an optical bus. The cascading depth is simply limited by the monitoring
times of the connected devices.
The latency per OBT is 6 bit times.