HART Multiplexer System KFD*-HM*-16
Product specification
DO
C
T-0
120D
06/
2014
13
3.3
System construction
3.3.1
System description
In process engineering plants, there are many field devices distributed over a large
area. The characteristic values of these field devices must be monitored, for
example, in the context of ISO 9000 and recorded and adapted to changes in
process parameters.
The HART Multiplex System from Fuchs enables on-line communication
between a PC and "smart" field devices that support the HART protocol.
SMART transmitters and intelligent valve positioners enable information such as
measurement range and tag number to be stored in the field device itself. Access to
these data is usually obtained using a handheld terminal. This means, that when
changes to information are required, connection to the field device must be carried
out "by hand".
When specific data has to be recorded in the context of quality assurance - in
accordance with ISO 9000 - this means that there is an increased demand on the
process control system or the DCS. For example, the data has to be cyclically
interrogated and then stored by the system in a database.
The HART Multiplex System from Fuchs provides the coupling between the
PC and the intelligent "HART capable" field devices. All access to the field device
takes place in parallel with the transfer of the 4 mA ... 20 mA measuring signal and
therefore has no affect on the processing of measured values by the process control
system.
The system thus provides a subordinate service interface. It is also possible to obtain
measured values through the HART Multiplex System. On field devices, which are
installed in hazardous areas, the coupling takes place on the safe area side of the
current repeaters.
Fuchs can supply the appropriate SMART transmitter power supplies
(e. g. KFD2-STC4-**) and SMART repeater (e. g. KFD2-STV4-**). Similarly, the
HART Multiplex System can also be connected to other SMART Ex-isolation stages.
This means that existing systems can be expanded very easily, thus taking full
advantage of the HART communication system.
The system comprises a max. of 31 HART Multiplexer Masters, which are connected
to the PC via a RS 485 interface. Each HART Multiplexer Master can control up to 15
HART Multiplexer Slaves. Each Multiplexer, irrespective of Master or Slave, can
connect up to 16 transmitters.
Thus one PC can be used to address up to 7936 field devices for the exchange of
data. Operation using a handheld terminal also remains possible, since the HART
protocol accepts two Masters in one system, i. e. PC and handheld terminal.
3.3.2
Service station
Besides the control system a PC is frequently used as the service station, with which
the parameter functions or data logging functions can be carried out. Operating
programs for the PC are available from various manufacturers (see section 3.3.3) to
provide the necessary back-up for this purpose.
However, in some cases the communication is provided by a process control system
via a RS 485 interface direct (via the HART Multiplexer) to the field devices without a
connected service station. But the low speed of the HART communication imposes
limitations on this method of operation.
