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7 RS-485 Installation and Set-up
7.1 RS-485 Installation and Set-up
7.1.1 Overview
RS-485 is a two-wire bus interface compatible with multi-
drop network topology, i.e. nodes can be connected as a
bus, or via drop cables from a common trunk line. A total
of 32 nodes can be connected to one network segment.
Repeaters divide network segments. Note that each
repeater functions as a node within the segment in which
it is installed. Each node connected within a given network
must have a unique node address, across all segments.
Terminate each segment at both ends, using either the
termination switch (S801) of the frequency converters or a
biased termination resistor network. Always use screened
twisted pair (STP) cable for bus cabling, and always follow
good common installation practice.
Low-impedance earth connection of the screen at every
node is important, including at high frequencies. Thus,
connect a large surface of the screen to earth, for example
with a cable clamp or a conductive cable gland. It may be
necessary to apply potential-equalizing cables to maintain
the same earth potential throughout the network - partic-
ularly in installations with long cables.
To prevent impedance mismatch, always use the same
type of cable throughout the entire network. When
connecting a motor to the frequency converter, always use
screened motor cable.
Cable
Screened twisted pair (STP)
Impedance
120
Ω
Cable length
Max. 1200 m (including drop lines)
Max. 500 m station-to-station
Table 7.1
7.1.2 Network Connection
One or more frequency converters can be connected to a
control (or master) using the RS-485 standardized interface.
Terminal 68 is connected to the P signal (TX+, RX+), while
terminal 69 is connected to the N signal (TX-,RX-). See
drawings in
5.7.3 Earthing of Screened/Armoured Control
If more than one frequency converter is connected to a
master, use parallel connections.
Illustration 7.1
In order to avoid potential equalizing currents in the
screen, earth the cable screen via terminal 61, which is
connected to the frame via an RC-link.
Illustration 7.2 Control Card Terminals
RS-485 Installation and Set...
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