Functional Description; Interfaces; Opto-Electrical Signal Conversion And Signal Regeneration - Siemens SIMATIC NET OBT Operating Instructions Manual

Functional description

The OBT is a repeater with 3 channels.
4.1

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.
4.2

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.
PROFIBUS Optical Bus Terminal (OBT)
Operating Instructions, 06/2022, C79000-G8976-C122-08
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