Siemens SIMATIC NET OBT Operating Instructions Manual page 29

Table of Contents

A = CH2, optical receiver

B = CH2, optical transmitter

C = CH3, optical receiver

D = CH3, optical transmitter

Connect the individual PROFIBUS OBTs using a duplex fiber-optic cable fitted with two pairs of

simplex connectors.

Make sure that an optical input is connected to an optical output (crossover connection).

Provide adequate strain relief for the fiber-optic cable and remember the minimum bend radii of

the FO cable.

Close unused FO cable sockets with the supplied plastic plugs. Incident light from the

surroundings can cause disturbances on the PROFIBUS network particularly, if the surroundings

are very bright.

Remember the minimum and maximum length of the FO cable and the permitted fiber types

listed in Table 1 and in the technical specifications.

Make sure that no dust gets into the optical components. Dust in the optical components can

make them unusable.

The fiber of the FO cable must be flush with the surface of the connector.

Note

If the fiber juts out beyond the surface of the connector, the connector must not be inserted in

the socket. Otherwise there is a risk of destroying the optical components.

Connecting the electrical RS-485 cable

Channel CH1 is used to connect a single PROFIBUS DP end device or an RS-485 segment. CH1 is

designed as an electrical RS-485 interface with a 9-pin D-sub female connector.

1. As the RS-485 bus cable, use only shielded and twisted SIMATIC NET two-wire cables for

PROFIBUS.

2. Do not connect any RS-485 bus cables that are laid entirely or partly outdoors. Otherwise,

lightning strikes in the surroundings could destroy the PROFIBUS OBTs. If you have bus

connections that leave the building, use fiber-optic cables whenever possible.

3. Disconnect the RS-485 bus cable from the OBT if you have not connected a node to the other

end of the cable. Coupling in interference can cause disturbances on PROFIBUS.

PROFIBUS Optical Bus Terminal (OBT)

Operating Instructions, 06/2022, C79000-G8976-C122-08

Commissioning

6.2 Installation

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