Weidmuller Transclinic 8i+ Bedienungsanleitung Seite 58

• This equipment loads the RS–485 bus with 1 UL (Unit Load), equivalent to 12 kΩ
• It is recommended not to mix Transclinics and other RS–485 slaves in the same bus.
• When daisy chaining combiner boxes, the D+ and D– of each Transclinic should use
one twisted pair of the cable, leaving the remaining wire (in cables with 1.5 pairs)
or the remaining twisted pair (in cables with 2 pairs) for the C connection. Always
make sure that D+, D– and C use the right color-coded wire of the cable. It is a must
to connect the C pin of all the Transclinics and the RS–485 master together(see the
RS-485 wiring diagram). IMPORTANT: in each combiner box always wire the C pin
first and afterwards the D+ and D– pins.
• The shield of the cable can be handled in two alternative ways. It is very important
NOT to connect the shield to the C pin in any combiner box (see the RS-485 wiring
diagram).
a) Daisy-chained shield running non-stop from end to end of the RS–485 bus.
Leave the shield floating (i.e. unconnected) at the far end of the RS–485 bus
(i.e. the combiner box farthest from the RS–485 master in terms of cable length).
Tie the shield directly to protective earth at the RS–485 master end
b) Segmented shield (i.e. one segment between each combiner box). Leave the
shield floating (i.e. unconnected) at one end of each segment and tie the other
end directly to protective earth. The shield segment closest to the RS–485 master
must have the end closest to the master tied to protective earth.
• Tie the C pin to protective earth at the RS–485 master end (see RS-485 wiring
diagram). Before doing this please ensure that the C pin is not connected to
protective earth anywhere else in the whole RS–485 bus (keep in mind that some
RS–485 masters may already tie internally the C pin to protective earth or to their
power supply ground!). This connection makes sure that the RS–485 common-mode
voltage stays close to earth potential instead of rising to dangerous voltages due to
stray capacitances and conductances in the network.
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