B&R MAPPC700A-ENG, User Manual

Page: 212 / 524

212
Technical data • Individual components
Panel PC 700 with 945GME N270 CPU board User's Manual V 1.16
The voltage drop caused by long line lengths can lead to greater potential differences between
the bus stations, which can hinder communication. This can be improved by running ground wire
with the others.
The line ends of the RS485 interface should (at least for longer line lengths or larger transfer
rates) be closed. Normally a passive terminator can be used on the bus ends by connecting each
of the signal lines with 120
Ω
resistance.
RS485 - Bus length and cable type
The maximum transfer rate of 115 kbit/s depends on the cable type being used.
The material used for the cable should preferably have all or most of the following properties in
order to reach an optimal transfer rate.
Distance [m] Transfer rate [kbit/s]
1200 Typ. 115
Table 90: RS485 - Bus length and transfer rate
RS485 cable Property
Signal lines
Cable cross section
Wire insulation
Conductor resistance
Stranding
Shielding 4 x 0.25 mm² (24AWG/19), tinned Cu wire
PE
≤
82
Ω
/ km
Wires stranded in pairs
Paired shield with aluminum foil
Grounding line
Cable cross section
Wire insulation
Conductor resistance 1 x 0.34 mm² (22AWG/19), tinned Cu wire
PE
≤
59
Ω
/ km
Outer sheathing
Material
Characteristics
Total shielding PUR mixture
Halogen free
From tinned cu wires
Table 91: RS485 - Cable requirements