Installation And Setup; Network Connection - Danfoss VLT 2800 Series Operating Instructions Manual

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Installation and Setup

Modbus RTU is a transmission protocol developed for
process control systems. The Modbus standard does
not specify the physical interface for the protocol i.e.
a number of different interfaces can be chosen.
The Modbus RTU protocol is based on the build-in
RS-485 (EIA-485) interface.
RS-485 is a two-wire bus-interface that allows
multi-drop network topology i.e. nodes can
be connected as a bus, or via drop cables
from a common trunk line.
A total number of 32 nodes can be connected to
one Modbus RTU network segment, and a total of
247 nodes in a network are supported.
Network segments are divided with repeaters.
Please note that each repeater counts for a node
in each segment it's installed.
Every node connected to the same network must have
an unique nodes address, across all segments.
Every segment must be terminated in both ends, either
with the termination switches (switch 2 & 3) of the VLT
6000 or with a biased termination resistor network.
For bus-cabling always use cable of screened
twisted pair type (STP), and make sure to follow
good common installation practice.
Make sure the screen of the Modbus RTU cable must
always be connected to ground at all nodes.
å Network Connection
Connect the adjustable frequency drive to the
Modbus RTU in accordance with the following
procedure (see Figure 1).
1. Connect signal wires to terminal 68 (P+) and
terminal 69 (N-) on main control board of drive.
2. The shield of the cable must be connected
to the cable clamps.
NOTE
It is recommended to use shielded, twisted-pair
cables to reduce noise between conductors.
MG.10.S1.22 - VLT is a registered Danfoss trademark
VLT® Serie 2800 and VLT® Serie 6000 Modbus RTU
It is very important to have a low impedance ground
connection of the screen, also at high frequencies.
This can be obtained by connecting a large surface
of the screen to ground, for example by means of
a cable clamp or a conductive cable gland.
Particularly in installation where there is long
cable lengths, it can be necessary to apply
potential equalizing cables to ensure same ground
potential throughout the network.
To prevent impedance mismatch, always use cable
of same type across the entire network.
When connecting a motor to the frequency converter,
make sure always to use screened motor cable.
Adress range:
1 - 247
Baud Rate:
300 - 9600 bps
Cable:
Screened twisted pair (STP)
Impedance: 120 Ohm
Cable length:
Max. 1200 m (including drop lines)
Max. 500 m station-to-station
Figure 1 Network Terminal Connection
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