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HART Multiplexer System KFD*-HM*-16
Operation
7
Operation
7.1
Device functions
Note
7.1.1
Channel number
7.1.2
Multiplexer table (module table)
7.1.3
Interface
7.1.4
HART communication
The software functions described in this section are normally integrated into the
operating software for the servicing station, i. e. the functions are not generally
(de-)activated via the described HART commands. In contrast the operating
software uses functions (menu commands) to control these procedures. However
the basic HART commands are described as well, because the functions may be
named different in the various operating softwares and the basic function may not
be obvious. Information on the supported commands can be found in section 9.1.
The HART Multiplexer Master KFD2-HMM-16 provides 16 channels for the
connection of SMART transmitters or control devices, which support digital
communication in accordance with the HART specification. A maximum of 15
additional KFD0-HMS-16 Slaves can be connected, each of which in turn support 16
channels. Thus in a full assembly, a loop of 256 channels can be achieved with just
one Master. When using the Multiplexer Master with the RPI product family, no Slave
units are necessary. On RPI, communication takes place via the Power Rail.
The Multiplexer Master and the connected Multiplexer Slaves must be designated as
available in a Multiplexer table (command 157). Only those modules defined as
available in this table are used in the communication process. The Multiplexer table
consists of 16 Bit, one for each possible Multiplexer address (default: module 0
(Master) and 1 activated).
In this way, the Multiplexer Master acts as a transparent gateway between the
service station (typically a PC with suitable software, see section 3.3.2) and the field
devices. The service station is able to communicate with up to 31 Multiplexer via up
to 38400 Baud RS 485 connection. Because each Multiplexer is able to
communicate with 256 field devices, up to 7936 field devices are controllable over a
single RS 485 interface.
As a digital communication system for servicing and configuration purposes, the
HART protocol is supported by many field devices with conventional analog
4 mA ... 20 mA current loops. The HART signal is thus modulated on the analog
current as an FSK signal (see section 3.2). The modulator/de-modulator circuitry
(Modem) required for this is integrated in the Multiplexer. Only one HART transmitter
can be connected at each Multiplexer HART connection (no multidrop functionality).
Special procedures in respect to HART communication:
•
On the host side (RS 485) always the long frame address is used (except for
command 0).
•
On the field devices side, either the short address or the long frame address is
used, depending on necessity.
•
The operating modes Primary Master and Secondary Master and the
corresponding time responses are supported on the field device side.
•
On the host side, only the commands 0 ... 3 and 11 ... 13 are accepted from the
secondary host. Other commands are not accepted/are ignored.
•
Commands to connected field devices are only accepted by the primary host.
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