Reference Manual
00809-0200-4975, Rev A
HART Interconnection
June 2017
5
HART Interconnection
Section 3 HART Interconnection
Overview . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . page 5
Point-to-point mode . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . page 5
Multidrop mode . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . page 5
3.1 Overview
The host connects to the Rosemount 975 Flame Detector through the two-wire 4-to-20mA current loop.
Refer to the User Manual for your Rosemount 975 Flame Detector for connection details.
This is the only output from the Rosemount 975 Flame Detector, representing the "Fire Detection"
channel. This output corresponds to the Primary Variable (PV). HART Communication is supported on
this loop.
3.2 Point-to-point mode
The HART Communicator can connect to Rosemount 975 Flame Detector at any wiring termination
point in the analog output signal loop. Connect the HART communicator in parallel with 500 Ohm load
resistor. The HART connections are non-polarized.
Turn on the HART Communicator. If a device is found, the HART Communicator displays the Main Menu.
If no device is found, check the connections and verify the presence of a 500 ohms load resistance in
series in the loop.
3.3 Multidrop mode
Optical flame detectors are life safety devices and require the 4-20 mA loop for transmitting important
detector status data. They should not be used in conjunction with multidrop mode, If multidrop mode
required, the alarm and fault relay contacts must be connected directly to the safety system or fire panel
for signaling purposes.
Figure 3-1. HART Connection Block Diagram
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