A�1 Hart ® Interface - Honeywell XNX Technical Manual

XNX Universal Transmitter
A.1 HART Interface
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Note: Only qualified service personel should perform the procedures in this section.
Every XNX gas sensor can communicate using the HART protocol
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(defined by the HART Communication Foundation at http://www�
hartcomm�org)� HART is unique among fieldbuses in that the digital
signal is superimposed on a traditional 4-20 mA current loop� This
provides the reliability of analog signaling with the advanced
diagnostic capability of a digital device�
HART devices are usually connected as point-to-point networks� The
analog output of the XNX transmitter can also be disabled to facilitate
construction of multidrop, all-digital HART networks�
Multiplexer
Note: Instrument power is provided by an interface
Barrier
or external power source that is not shown.
Field Device
Figure 233. HART Point-to-point Mode
If HART is not needed, the unit can be used as a 4-20 mA transmitter�
Since the transmitter is a slave, the internal modem will remain silent
if no master signal is present� Additionally the HART signal is at too
Appendix A - HART Protocol
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The XNX Universal Transmitter is registered with the
HART Communication Foundation.
Control System
or Other Host Application
Handheld Terminal
high a frequency (1200 Hz) to interfere with analog control equipment�
Another novel feature of HART networks is that two masters can
be present� The primary master is usually a distributed control
system (DCS), programmable logic controller (PLC), or a personal
computer (PC)� The secondary master can be a handheld terminal�
The XNX transmitter has been tested with the handheld Emerson field
communicator�
Control System or
Other Host Application
Input/Output (I/O) System
Note: Instrument power is provided by an interface
or external power source that is not shown.
Figure 234. HART Multi-point Mode
The XNX device descriptor (DD) file provides HART users with data
on the capabilities and features of the XNX Universal Transmitter�
Select HART enabled devices are able to interface with XNX
transmitters when connected via HART communication� A copy of
the file is included on the Documentation CD� This DD file can be
installed on HART-enabled Emerson field communicators using the
Emerson Easy Upgrade Utility� The DD files located on the resource
CD are compatible with the software integral to the transmitter� Older
transmitters using earlier versions of software require previous versions
of the DD files� Contact your local Honeywell representative with any
questions regarding software compatibility�
During manufacturing, Honeywell configures the 8-digit HART tag to
the XNX serial number� This can be used to confirm correct wiring
from the transmitter to the control system� If desired, the HART tag
can be modified� The fixed XNX serial number can also be read over
HA RT�
For convenience, the transmitter presents the HART signal on two
interfaces� The 1200 Hz AC signal is capacitively coupled to the main
20 mA analog output� This may be monitored at the control system
168
Handheld Terminal
Field Devices