HART Communication

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.

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This figure is from the HART Communication Protocol Specifications, April 2001, Revision 6.0, HART Communication Foundation. All Rights Reserved.

PointMax analog HART 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 (such as kg, m, or percent) that are used in the Logix 5000 controller.
Conversion of digital numeric values in engineering units to 4…20 mA analog signals to control process devices.Producer/Consumer network communication model directly to each HART device.
Automatic collection of dynamic process data from the connected HART device. For example, temperature, pressure, flow, or valve position.
Automatic collection of device-specific variables from the connected HART device.
Execution of commands through Studio 5000 Logix Designer application using input and output tags.
Facilitation of configuration and troubleshooting of the HART field device from your control room using DTM supported software.

With the analog HART modules, both the controller and software for device maintenance and management can access field device data. The analog HART modules support command-response communication protocol in a point-to-point wiring architecture.

The analog HART module is the primary master device and continuously obtains information from the connected HART devices. The secondary master can be used for device maintenance, for example a handheld communicator.

Most 4…20 mA transmitters are available with a HART protocol interface. The type of data available depends on the type of instrument.

An example application is a HART-enabled mass flowmeter. The standard mA signal from the flowmeter provides one primary measurement - Flow. The mA signal with HART provides more process information. The mA signal that represents flow is still available. The HART configuration of the flowmeter can be set to communicate primary variable (PV), secondary variable (SV), tertiary variable (TV), and quaternary variable (QV). These values can represent mass flow, static pressure, temperature, total flow, and other conditions.

Dynamic variables, device-specific variables, device status, and command execution are all available through input and output controller tags in the Studio 5000 Logix Designer application.

Device status information is also provided through HART.

HART connectivity provides all this information with no changes to the existing 4…20 mA wiring.

DTM technology through HART connectivity is supported and also provides remote configuration and troubleshooting of HART devices through software.