4 Cabling the AC 800F
4-86
4.3.3.3 Redundant connection via RS485 interface
Contrary to RS232 and RS422, the primary and the secondary unit can actively
transmit signals in accordance with the RS485 specification in this case. The primary
and the secondary unit can communicate with each other via this interface.
• Deactivate the internal termination of the serial fieldbus modules.
• Activate the external termination with external supply at the external terminal
block. Connect an external 5 V power supply as seen in Fig. 4-59.
• Deactivate the termination of the internal terminal block.
• Link two redundant modules FI 820F with the terminal block TB 870F using cable
TK 821F. Only hand-tighten the screws.
• Put on the TK 821F cable shields. Connect them to the two AC 800F contact
ledges using clips TV 83xF.
• Cable the respective interface on the terminal blocks TB 870F to each other, using
the terminals specified below, and establish a connection to the nodes. Use a
twisted pair cable, e.g. 2 x 2 x 0.25 mm
2
.
• Apply the shield to terminal P of the terminal block.
• Keep branch cables to the nodes as short as possible.
• Observe the max. cable length of 1200 m.
• When touching the terminating jumpers take the necessary ESD
protection measures. Follow the instructions given in Section 2.
• If the shield is not put on properly, neither RFI suppression nor
EMI/RFI shielding of the system can be guaranteed.
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