Emerson 5081-T - Manual (Page 11)

5
MODEL 5081-T SECTION 1.0
DESCRIPTION AND SPECIFICATIONS
1.6 HART COMMUNICATIONS
1.6.1 OVERVIEW OF HART COMMUNICATION
HART (highway addressable remote transducer) is a digital communication system in which two frequencies are superim-
posed 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 compo-
nent to the analog signal. HART permits digital communication while retaining 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 internet
address is http://www.hartcomm.org.
1.6.2 HART INTERFACE DEVICES
HART communicators allow the user 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 Figure 1-3.
If your communicator does not recognize the Model 5081-T transmitter, the device description library may need updating.
Call the manufacturer of your HART communication device for updates.
4-20 mA + Digital
250
ohm
Control System
Computer
Model 5081-T-HT
Two-wire
Transmitter
Bridge
Hand Held
Communicator
(“Configurator”)
FIGURE 1-3. HART Communicators.
Both the Rosemount Model 375 (or 275) and a computer can be used to communicate
with a HART transmitter. The 250 ohm load (minimum) must be present between the
transmitter and the power supply.