Hart Interface - Honeywell XNX-AM Series Technical Manual

XNX Universal Transmitter

HART Interface

NOTE
!
Note: The procedures in this section must be performed only by qualified
service personnel.
All XNX transitters can communicate using the HART protocol
(defined at www.fieldcommgroup.org
Foundation). 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.
Multiplexer
Barrier
Note: Instrument power is provided by an interface
or external power source that is not shown.
Handheld Terminal
Field Device
Figure 231. HART point-to-point mode
HART Protocol
The XNX Universal Transmitter is registered
with the HART Communication Foundation.
by the HART Communication
Control System
or Other Host Application
HART devices are usually connected as point-to-point networks.
The analog output of the transmitter can also be disabled to
facilitate construction of multidrop, all-digital HART networks.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 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 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.
The XNX device descriptor (DD) file provides HART users with data
on the capabilities and features of the transmitter. Select HART
enabled devices are able to interface with XNX transmitters when
179
Handheld Terminal
Field Devices
Figure 232. HART multi-point mode