Rs-485 Installation And Set-Up - Danfoss VLT HVAC Basic Drive FC 100 Series Design Manual

RS-485 Installation and Set...

7 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. 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
7 7
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. 1200m (including drop lines)
Max. 500m station-to-station
7.1.2 Network Connection
Connect the frequency converter to the RS-485 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.
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VLT HVAC Basic Drive Design Guide
61 68 69
MG.18.C2.02 - VLT
7.1.3 Frequency Converter Hardware Set-
up
Use the terminator dip switch on the main control board
of the frequency converter to terminate the RS-485 bus.
Illustration 7.1 Terminator Switch Factory Setting
The factory setting for the dip switch is OFF.
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