Rs485 Installation And Set-Up - Danfoss VLT Micro Drive PK18 Design Manual

RS485 Installation and Set-...

8 RS485 Installation and Set-up

RS485 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. Please 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: 120Ω
Cable length: Max. 1200 m (including drop lines)
Max. 500 m station-to-station
8.1.1 Network Connection
Connect the frequency converter to the RS485 network as
follows (see also diagram):
1. Connect signal wires to terminal 68 (P+) and
terminal 69 (N-) on the main control board of the
frequency converter.
2. Connect the cable screen to the cable clamps.
NOTE
Screened, twisted-pair cables are recommended in order to
reduce noise between conductors.
61 68 69
VLT Micro Drive Design Guide
8.1.2 Frequency Converter Hardware Set-
Use the terminator dip switch on the main control board
of the frequency converter to terminate the RS485 bus.
Illustration 8.1 Terminator Switch Factory Setting
The factory setting for the dip switch is OFF.
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