ABB RER 133 Descrizione tecnica - Pagina 12
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Bus Connection
Module
12
RER 133
Technical Description
The EIA RS-485 Specification labels the data wires "A" and "B", but many
manufacturers label their wires "+" and "-". In our experience, the "+" wire should
be connected to the "A" line, and the "-" wire to the "B" line.
When wiring RS-485 , use a shielded twisted pair cable with an internal impedance
Ω
of 100-120
. Examples of recommended cables are CAT 5, Belden RS-485 (9841-
9844) and Alpha Wire (Alpha 6222-6230).
The shield of the cables must be directly connected to ground in one
of the nodes. In the other nodes the connection should be made via a
capacitor, i.e. if the shield of the cable is connected to pin 1 in node
1, all the other nodes must be grounded using pin 2.
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Fig. 6.-3 Example on a cable shield connection
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1MRS755163
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A050325