HART
Field Communication Protocol
Control Pooyan Engineering Co.
By: Atefeh Saberi
Control Pooyan Eng. Co.
Contents
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What is HART?
Why HART?
HART Benefits
HART Data
HART Principles
Installation
HART Protocols
HART Commands
Control Pooyan Engineering Co.
What is HART?
HART:
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Stands for Highway Addressable Remote Transducer
Was developed by Fisher-Rosemount to retrofit 4-20mA
current loop transducers with digital data communication
A master-slave, bi-directional industrial field communication
protocol developed in the late 1980's used to communicate
between smart field instruments and host systems
Makes use of the Bell 202 Frequency Shift Keying (FSK)
standard to superimpose digital communication signals at a
low level on top of the 4-20mA
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Why HART?
There are several reasons to have a host communicate with a
field instrument. These include:
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Device Diagnostics
Device Troubleshooting
Reading the values of additional measurements provided by the device
Device Health and Status
And much more!
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HART Benefits:
Information in HART enabled devices when fully used provides benefits in
different phases including the Planning and Engineering phase, Installation and
Commissioning, Operations and Maintenance, and Asset Productivity
Improvement phase.
Key benefits of this unique open standard communication technology are:
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4-20mA compatibility with simultaneous digital information available
Easy to use and understand
Low risk - highly accurate and robust
Cost-effective implementation for both users and suppliers
Available in a wide variety of device types
Supported by most industry device and systems suppliers
Fully interoperable and reliable
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HART Data
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Digital data: 35-40 valuable data items standard in every HART device
Device identification: device tag, supplier, device type and revision, device
serial number
Calibration data: upper and lower range values, upper and lower sensor limits,
PV damping, last calibration date
Process variables: primary variable plus secondary measurements and
multivariable parameters
Status/diagnostic alerts: device malfunction, configuration change, power fail
restart, loop current fixed or saturated, primary or secondary variable out of
limits, communication error, plus more
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HART Principles
9 The HART protocol makes use of
the Bell 202 Frequency Shift Keying
(FSK) standard to superimpose digital
communication signals at a low level
on top of the 4-20mA
9 HART uses relatively low
frequencies (1200 and 2200 Hz) and
this restricts it to communicate at
1200 bps without interrupting the 420mA signal and allows a host
application (master) to get two or more
digital updates per second from a field
device
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Installation
Point-to-point mode:
Here the the digital signals are
overlayed on the 4-20mA loop current
Both the 4-20 mA current and the
digital signal are valid output values
from the instrument
Only one instrument can be put on
each instrument cable signal pair
HART provides for up to two masters (primary and secondary). This
allows secondary masters such as handheld communicators to be used
without interfering with communications to/from the primary master, i.e.
control/monitoring system.
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Installation
Multi-drop mode:
Only the digital signals are used and
the analog loop current is fixed at 4 mA
It is possible to have up to 15
instruments on one signal cable
The polling addresses of the instruments
will be in the range 1-15
Each meter needs to have a unique
address
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HART Protocol
Hart communicates point-to-point, with a slave e.g. hand-held device,
under the control of a master
Master
Slave
command
Request
Indication
time-out
response
Response
Confirmation
Hart frame format (character-oriented):
preamble
start
address
5-20 (Byte)
1-5
command Byte count status
data
1
1 (Master response 0)
(slave response 2)
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data
0-25
checksum
1
10
HART Frame Format
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HART Commands
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Universal commands (mandatory):
Must be implemented by all HART devices and provide interoperability across the large and growing base of
products from different suppliers of HART technology, like:
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Read primary variables and units
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Read manufacturer and device type
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Read current output and percent of range
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Read sensor serial number and limits
Common practice command (optional):
Common practice commands provide functions implemented by many, but not necessarily all, HART
communication devices, like:
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Read a selection of up to four dynamic variables
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Write damping time constant
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Write transmitter range
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Set fixed output current and perform self-test
Device Specific command (user-defined):
Represent functions that are unique to each field device. These commands access setup and calibration
information, as well as information about the construction of the device, like:
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Read or write sensor type
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Start, stop or clear totalizer
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Read or write alarm relay set point
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HART commands summary
Universal Commands
Read manufacturer and device
type
Read primary variable (PV) and
units
Read current output and
percent of range
Read up to four predefined
dynamic variables
Read or write eight-character
tag, 16-character descriptor,
date
Read or write 32-character
message
Read device range values, units,
and damping time constant
Read or write final assembly
number
Write polling address
Common Practice Commands
Device-Specific Commands
(example)
Read selection of up to four
dynamic variables
Write damping time constant
Write device range values
Calibrate (set zero, set span)
Set fixed output current
Perform self-test
Perform master reset
Trim PV zero
Write PV unit
Trim DAC zero and gain
Write transfer function (square
root/linear)
Write sensor serial number
Read or write dynamic variable
assignments
Read or write low-flow cut-off
Start, stop, or clear totalizer
Read or write density
calibration factor
Choose PV (mass, flow, or
density)
Read or write materials or
construction information
Trim sensor calibration
PID enable
Write PID set point
Valve characterization
Valve set point
Travel limits
User units
Local display information
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Examples of commands
Universal Commands:
Common Practice
Commands:
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Device access
device
volumetric flow rate
type
FlowPro
manufacturer
ABB
volumetric flow rate
field device
network
adapter
Hand-held
device
cross sectional area:
3 cm2
pipe inside diameter
2 cm
velocity
13.32 m2/s
diff. pressure
9.8
Pa
density
0.8
kg/l
SCADA
network
modem
adapter
network
adapter
4-20 mA loop for HART
13.32
9.8
0.8
transmission system (HART or field bus)
Control Pooyan Engineering Co.
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Device Description Language
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Device Description Language
DDL allows a field device
(slave) product developer to
create a description of his
instrument and all relevant
characteristics, such that it can
be represented in any host
(master) device. The objective
is common look-and-feel,
independent of the hand-held
or SCADA, similar to HTML
for a web server.
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Thanks for your attention
For more information refer to these websites please:
http://www.thehartbook.com/default.htm
http://www.hartcomm.org/
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