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7 RS-485 Installation and Set-up

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

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

7.1.1 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.

61 68 69

COMM. GND

130BB795.10

7.1.2 Frequency Converter Hardware Set-

Use the terminator dip switch on the main control board

of the frequency converter to terminate the RS-485 bus.

130BB966.10

Illustration 7.1 Terminator Switch Factory Setting

The factory setting for the dip switch is OFF.

RS-485 Installation and Set... VLT HVAC Basic Drive Design Guide

64 MG.18.C2.02 - VLT

is a registered Danfoss trademark

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