Installation And Set-Up; Overview; Network Connection; Bus Termination - Danfoss VLT AutomationDrive Design Manual

RS-485 Installation and Set...
11 RS-485 Installation and Set-up

11.1 Overview

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. 1200m (including drop lines)
Max. 500m station-to-station

11.2 Network Connection

One or more frequency converters can be connected to a
control (or master) using the RS485 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 8.8.3 Earthing of Screened Control Cables
If more than one frequency converter is connected to a
master, use parallel connections.
FC 300 Design Guide
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 11.1 Control Card Terminals

11.3 Bus Termination

The RS485 bus must be terminated by a resistor network
at both ends. For this purpose, set switch S801 on the
control card for "ON".
For more information, see 8.6.4 Switches S201, S202, and
S801 .
Communication protocol must be set to 8-30 Protocol.
®
MG.33.BD.02 - VLT is a registered Danfoss trademark
RS 232
68
+
USB
-
RS 485
61 68 69 39 42 50 53 54 55
Remove jumper to enable Safe Stop
12 13 18 19 27 29
69 68 69 68 69
32 33 20 37
11
255
11