5 Using HART
®
communications
5.1 Overview
The Field Communicator is a handheld communications interface device. It
provides a common communications link to all microprocessor-based instruments
that are HART
®
compatible.
To interface with the Rosemount OCX8800, the Field Communicator requires a
termination point along the O
2
4-20 mA current loop and a minimum load
resistance of 250 ohms between the communicator and the power supply. The
Field Communicator accomplishes its task using a frequency shift keying (FSK)
technique. With the use of FSK, high-frequency digital communication signals are
superimposed on the 4-20 mA oxygen output signal. The communicator does not
disturb the 4-20 mA signal, since no net energy is added to the loop. HART
information is not available on the COe output signal.
If you install special software, you may interface the Field Communicator with a
personal computer (PC). You must have an interface adapter to connect the Field
Communicator to a PC. Refer to the proper Field Communicator documentation in
regard to the PC interface option.
5.2 Field Communicator signal connections
The Field Communicator can connect to the Rosemount OCX8800 oxygen analog
output signal line at any wiring termination in the O
2
4-20 mA current loop.
There are two methods of connecting the Field Communicator to the signal line.
For applications in which the signal line has a load resistance of 250 ohms or
more, refer to Method 1: For load resistance ≥ 250 ohms. For applications in which
the signal line load is less than 250 ohms, refer to Method 2: For load resistance <
250 ohms.
Manual Using HART
®
communications
00809-0500-4880 December 2022
Rosemount OCX8800A 81
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