Hart Communication - Allen-Bradley 1719 Ex I/O User Manual

Chapter 5 1719 Ex I/O HART Analog I/O Modules

HART Communication

The Highway Addressable Remote Transducer (HART)
protocol supports two-way digital communication,
complements traditional 4...20 mA analog signals,
and includes the following features:
• Predefined commands
- Common practice
- General purpose
- Device specific
• Large installed base
• Worldwide support
44
The HART field communication protocol is widely accepted in industry as a
standard for digitally enhanced 4...20 mA communication with smart
(microprocessor-based) field devices. A digital signal is superimposed on the
4...20 mA current loop to provide two means of communication from the device.
The 4...20 mA analog channel lets the primary process variable be communicated
at the fastest possible rate while the digital channel communicates multiple
process variables, data quality, and device status. The HART protocol lets these
simultaneous communication channels be used in a complementary fashion.
The 1719 Ex I/O HART analog I/O modules support the HART protocol and
perform these operations:
• Conversion of 4...20 mA analog signals to digital numeric values in
engineering units that are used in the Logix controller.
• Conversion of digital numeric values in engineering units to 4...20 mA
analog signals to control process devices.
• Automatic collection of dynamic process data from the connected HART
field device (for example, temperature, pressure, flow, or valve position).
• Facilitation of configuration and troubleshooting of the HART field
device from your control room with FactoryTalk® AssetCentre service.
(1)
This figure shows information about the HART protocol.
+0.5 mA +0.5 mA
0
20 mA
-0.5 mA
Analog
signal
R
C
4 mA
0
With the 1719 Ex I/O HART analog I/O modules, both the controller and
software for device maintenance and management can access field device data.
The 1719 Ex I/O HART analog I/O modules support command-response
communication protocol and point-to-point wiring architecture. Multipdrop
wiring architecture is not supported.
(1) The figure is from the HART Communication Protocol Specifications, April 2001, Revision 6.0, HART Communication Foundation, All
Rights Reserved.
Rockwell Automation Publication 1719-UM001C-EN-E - August 2018
HART Signal
1200 2200
Hz Hz
"1" "0"
C
R
C
1
Time (sec)
R
C
R
C = Command
R = Response
2