9
Digital communications
9.1
HART communications
9.1.1
Overview of HART communication
HART (highway addressable remote transducer) is a digital communication system in
which two frequencies are superimposed on the 4 to 20 mA output signal from the
transmitter. A 1200 Hz sine wave represents the digit 1, and a 2400 Hz sine wave
represents the digit 0. Because the average value of a sine wave is zero, the digital signal
adds no dc component to the analog signal. HART permits digital communication while
restarting the analog signal for process control.
The HART protocol, originally developed by Fisher-Rosemount, is now overseen by the
independent HART Communication Foundation. The foundation ensures that all HART
devices can communicate with one another. For more information about HART
communications, call the HART Communication Foundation at (512) 794-0369. The web
address is
.
9.1.2
HART interface devices
HART communicators allow you to view measurement data (pH, ORP, and temperature),
program the transmitter, and download information from the transmitter for transfer to a
computer for analysis. Downloaded information can also be sent to another HART
transmitter. Either a hand-held communicator, such as the Rosemount Model 375, or a
computer can be used. HART interface devices operate from any wiring termination point
in the 4 - 20 mA loop. A minimum load of 250 ohms must be present between the
transmitter and the power supply. See
.
If your communicator does not recognize the 5081 transmitter, the device description
library may need updating. Call the manufacturer of your HART communication device for
updates.
Digital communications
Instruction Manual
121
Summary of Contents for Rosemount5081
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