Emc Precautions; Fc Protocol; Overview; Fc With Modbus Rtu - Danfoss VLT HVAC Basic Drive FC 101 Design Manual

RS485 Installation and Set-...

7.1.5 EMC Precautions

NOTICE
Observe relevant national and local regulations
regarding protective earth connection. Failure to ground
the cables properly can result in communication
degradation and equipment damage. To avoid coupling
of high-frequency noise between the cables, keep the
RS485 communication cable away from motor and brake
resistor cables. Normally, a distance of 200 mm (8 inches)
is sufficient. Maintain the greatest possible distance
between the cables, especially where cables run in
parallel over long distances. When crossing is
unavoidable, the RS485 cable must cross motor and
brake resistor cables at an angle of 90°.
7 7
1
2
90°
1 Fieldbus cable
2 Minimum 200 mm (8 in) distance
Illustration 7.3 Minimum Distance between Communication
and Power Cables

7.2 FC Protocol

7.2.1 Overview

The FC protocol, also referred to as FC bus or standard bus,
is the Danfoss standard fieldbus. It defines an access
technique according to the master-slave principle for
communications via a serial bus.
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VLT HVAC Basic Drive FC 101
One master and a maximum of 126 slaves can be
connected to the bus. The master selects the individual
slaves via an address character in the telegram. A slave
itself can never transmit without first being requested to
do so, and direct message transfer between the individual
slaves is not possible. Communications occur in the half-
duplex mode.
The master function cannot be transferred to another node
(single-master system).
The physical layer is RS485, thus utilizing the RS485 port
built into the frequency converter. The FC protocol
supports different telegram formats:
•
•
•

7.2.2 FC with Modbus RTU

The FC protocol provides access to the control word and
bus reference of the frequency converter.
The control word allows the Modbus master to control
several important functions of the frequency converter:
•
•
•
•
•
•
•
The bus reference is commonly used for speed control. It is
also possible to access the parameters, read their values,
and where possible, write values to them. Accessing the
parameters offers a range of control options, including
controlling the setpoint of the frequency converter when
its internal PI controller is used.
Danfoss A/S © 04/2016 All rights reserved.
A short format of 8 bytes for process data.
A long format of 16 bytes that also includes a
parameter channel.
A format used for texts.
Start.
Stop of the frequency converter in various ways:
- Coast stop.
- Quick stop.
-
DC brake stop.
- Normal (ramp) stop.
Reset after a fault trip.
Run at various preset speeds.
Run in reverse.
Change of the active set-up.
Control of the 2 relays built into the frequency
converter.
MG18C702