Installation And Set-Up; Overview; Network Connection; Bus Termination - Danfoss VLT AutomationDrive FC 300 Design Manual

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

10.1 Overview

RS-485 is a 2-wire bus interface compatible with multi-drop
network topology. 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 each repeater
function 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, e.g. with a
cable clamp or a conductive cable gland. If necessary,
apply potential-equalizing cables to maintain the same
earth potential throughout the network. Particularly 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)
120 Ω
Impedance
Cable length Max. 1,200 m (including drop lines)
Max. 500 m station-to-station
Table 10.1 Motor Cable

10.2 Network Connection

One or more frequency converters can be connected to a
control (or master) using the RS-485 standardised interface.
Terminal 68 is connected to the P signal (TX+, RX+), while
terminal 69 is connected to the N signal (TX-, RX-). See
illustrations in 7.7.2 Earthing
If more than one frequency converter is connected to a
master, use parallel connections.
®
VLT AutomationDrive FC 300 Design Guide 90-1200 kW
Illustration 10.1 Parallel Connections
To avoid potential equalising currents in the screen, earth
the cable screen via terminal 61, which is connected to the
frame via an RC-link.
61 68 69
Illustration 10.2 Control Card Terminals

10.3 Bus Termination

The RS-485 bus must be terminated by using a resistor
network at both ends. For this purpose, set switch S801 on
the control card to "ON".
For more information, see 7.5.4 Switches S201 (A53), S202
(A54), and S801.
Communication protocol must be set to 8-30 Protocol.
MG34S202 - Rev. 2013-08-19
RS 232
68 69 68
+
USB
-
RS 485
39 42 50 53 54 55
Remove jumper to enable Safe Stop
12 13 18 19 27 29 32
33
69 68 69
10 10
20 37
241