Emerson 5081-T instruction manual Overview of Hart Communication, Hart Interface Devices

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

Model 5081-T-HT

Two-wire

Transmitter			Control System
	Hand Held
	Communicator	Bridge
	(“Configurator”)
				Computer

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.

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