Overview
of HART Revisions
An introduction to the latest HART capabilities
from Emerson Process Management
The industry is moving to HART Revision 7.
With Emerson solutions, you can transition your
operations with confidence.
Overview of HART Revisions
Introduction
What is HART?
• Simply put, the HART (Highway Addressable Remote Transducer) Protocol is the
global standard for sending and receiving digital information across analog wires
between smart devices and a control or monitoring system.
• More specifically, HART is a bi-directional communication protocol that provides
data access between intelligent field instruments and host systems. A host can be
any software application from a technician's hand-held device or laptop to a plant's
process control, asset management, safety or other system using any control
platform.
www.hartcomm.org
What is a HART Revision?
• A HART “revision” defines a standard set of features and functionality for the HART
protocol. Revision 5 was developed to improve configuration and maintenance of
analog devices. It was developed by Emerson and opened up to the process
automation industry in the late 1980s so that users could order instrumentation and
systems from different manufacturers and ensure interoperability.
• Revision 6 added features to improve digital system integration of wired HART
devices. It was released in 2001, but very few manufacturers have developed
products based on this revision.
• Revision 7 added features to optimize wireless communications. It also provides a
single standard for wired and wireless HART communications . The standard was
released in 2007. While WirelessHART devices have been available since 2008,
wired HART revision 7 products are just now becoming available.
What is changing with HART products?
• As of March 31st, 2011, all new products developed using the HART protocol must
use Revision 6 or 7 and be registered with the HART Communications Foundation.
Previously, device and system registration was not required.
What does this mean to me?
• This means that new HART products will include the latest HART features. It also
ensures that all systems and devices will be interoperable and backwards
compatible moving forward.
Overview of HART Revisions
Revision Overview
Revision 5
Makes up 99% of the
installed base
Revision 6
Improves digital
system integration
Revision 7
Optimizes wireless
communications and
creates a single
standard for wired and
wireless
communications
Overview of HART Revisions
Key Features – Revisions 6 & 7
Long Tag: Increases software tag length from 8 to 32 characters. This is by far the
most requested feature from users. As projects become larger and larger, so do the
descriptions necessary to track each unique device. The long tag allows a user to
automate commissioning processes by matching the software tag of the device in the
system exactly to the device ID on engineering drawings – saving start up time and
resources.
Locate Device: Flashes a unique message on the display of a device “0-0-0-0”. This
feature allows the personnel in the field and control room to verify they’re looking at
the same device.
Digital Loop Check: Sets the analog and digital outputs. HART Revision 5 included
analog loop check, which allows a user to set the analog output to a specific value
and confirm the loop is working as expected. This feature adds to analog loop check
by allowing the user to also confirm the HART output values are outputting correctly,
and that the device is configured.
HART Software Lock: Prevents configuration changes. This is another form of
security to prevent device configuration changes by unauthorized personnel.
Multi-Variable Statuses: Provides output quality information for all variables. This
allows users to confirm the quality of their measurements beyond the primary
variable.
Overview of HART Revisions
Key Features – Revision 7
Wireless: WirelessHART is the first global standard for wireless communications.
HART Revision 7 provides a standard for wireless communications, which allows
users to expand insight into their processes with minimal effort.
Expanded Manufacturer ID: Allows new manufacturers to register devices. HART
manufacturers have increased beyond initial estimations, and this solves that
problem. The expanded manufacturer ID has caused some trouble with device
identification in legacy systems.
Enhanced Multi-Variable Communication (8): Increases device output capability
from 4 to 8 variables. Allows users to access more information about their
measurement devices.
Time Stamp: Devices must have an internal clock. This allows a user to configure
the time between measurements for wireless devices.
Trends: A device can store up to 12 measurement points. Tracking trends in the
device is beneficial for wireless devices used in monitoring applications. For wired
devices, this feature requires a user to manually record each data point.
Synchronized Sampling: A wireless feature that enables multiple devices to
measure at a specific, synchronized time. This is not available with wired HART.
Overview of HART Revisions
Key Features – Revision 7 Cont’d.
A Note on Broadcast Messaging (Burst Mode)
All HART Revisions (5, 6 and 7) include Broadcast Messaging capabilities, more
commonly referred to as burst mode. When set to burst mode, a device proactively
sends out messages about once per second instead of waiting for the host to request
it. Note that both the host and device must be configured to communicate in burst
mode to work. Almost all HART host systems today are designed to communicate in
poll / response mode, not burst mode. Some non-traditional hosts such as the
Rosemount 333 Tri-Loop use burst mode to convert multi-variable information to 420mA analog signals. A wired HART Revision 5 or 6 device can be configured to
burst all process variables.
Changes to Broadcast Messaging with HART Revision 7
Enhanced Broadcast Messaging: A wired HART Revision 7 device improves on
the burst capability by adding variable status to the burst message – showing the
quality of that measurement.
Report by Exception: Along with message 1 that includes process variables and
status, new messages 2 and 3 can be configured to communicate at a scheduled
rate or when a trigger condition is met – i.e. Report by Exception. An example would
be if the primary variable (PV) exceeded a defined value (trigger), the device would
burst message 2 or 3 instead of message 1 to communicate that an exception had
occurred.
Event Notification: Allows the user to select which device status information will be
reported. Like the Report by Exception mode, a device can interrupt Message 1 with
a notification that a specific event (as defined by the user) has occurred. Examples of
selectable events are device diagnostics, process alerts, over-pressure limit, and
more. Note that message 1 already includes the variable status based on all of these
potential events.
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