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bus, in computing, is a set of physical connections (cables, printed circuits, etc.) which can be shared by multiple hardware components in order to communicate with one another. The purpose of buses is to reduce the number of "pathways" needed for communication between the components, by carrying out all communications over a single data channel. This is why the metaphor of a "data highway" is sometimes used.
ΣΕ ΑΥΤΗΝ ΤΗΝ ΚΑΡΤΑ ΒΛΕΠΟΜΕ ΔΙΑΦΟΡΑ ΣΥΣΤΗΜΑΤΑ PAC ΤΑ ΟΠΟΙΑ ΘΑ ΑΝΑΛΥΣΟΥΜΕ ΣΤΗ ΣΥΝΕΧΕΙΑ
Smart transmitters & HART Protocol
AND HART PROTOCOL
PRESENTED BY :
OMKAR KALE (1010) SAGAR RANA
WHAT IS A ‘SMART’ TRANSMITTER?
A microprocessor-based smart transmitter has a memory that can
perform calculations, produce diagnostics and out-perform older, more
conventional transmitters, when it comes to accuracy and stability.
A Smart Transmitter would also have a digital communication protocol
that can be used for reading the transmitter’s measurement values
and for configuring various settings in the transmitter.
What is the need of “SMART” transmitters?
For engineer’s who need to configure and calibrate the transmitter, the
digital communication protocol makes the biggest difference.
Engineers need no longer simply measure the output analogue signal
– they need to be able to communicate with the transmitter and read
the digital signal.
HART (Highway Addressable Remote Transmitter) is a communication protocol.
A HART transmitter contains both a conventional analogue mA signal and a digital signal superimposed
on top of the analogue signal. Since it also has the analogue signal, it is compatible with conventional
installations. HART standard helps instruments to digitally communicate with one another over the
same two wires used to convey a 4-20 mA analog instrument signal.
SMART (Single Modular Auto-ranging Remote Transducer)
SMART transmitters compared to analog transmitters have microprocessor as their integral part , which
helps for self diagnostic abilities , non-linear compensations , re-ranging without performing calibrations
,and ability to communicate digitally over the network.
FLASHBACK IN TIME…..
• Evolution is the natural phenomenon of the mother earth and process industry is no
exception to the same. The process instrumentation philosophy has undergone a
tremendous facelift and all are looking for state–of-the-art technologies.
• Around 50 years ago, most plant used 3-15 psi pneumatic signal to control their
process. Then there was change in signal standard. This was the open protocol
HART digital communications format.
• The HART protocol provides simultaneous digital communications with the 4-20 mA
output. Almost all the Smart instruments operate on this protocol. The next protocol
change was the fieldbus. Fieldbus is entirely digital-there is no analog Signal.
Fieldbus also allows migration of control functions to field devices. Now is the time
for wireless systems. The system operates at 2.4 GHz frequency which is a fully
unrestricted band. The system doesn’t require any wireless / radio licensing for
usage in most other parts of the world.
HISTORY OF PROCESS CONTROL SIGNALS
• Process control Timeline :
• The Evolution of Signal Standard Signal standards have evolved over the years,
starting with the 3-15 psi standard.
• Year 1940-1975: 3-15 psi standard
• Year 1955-1990: 4 to 20 mA signal
• Year 1990-2005: HART protocol for smart instruments
• Year 2000 – to date: Field bus
• Year 2007: Wireless HART
• There are also other communication methods, but they have not gained widespread
acceptance. With many standards there is typically a slow transition period as plant
engineers and managers test period does gain widespread acceptance. However,
once the benefits of the new standard become tested and proven, more plant will
install new state-of-the-art standard because of its benefits and economic cost
THE CURRENT SCENARIO !!
• The list of SMART field instruments that are widely accepted and used in process industry:
• Smart Magnetic flow meters
• Smart DP pressure transmitters used for measurement of different parameters such as diff. pressure,
level, flow, absolute and gauge and vacuum pressure.
• Smart Coriolis Mass flow meters
• Hart multiplexers
• Smart pH and conductivity transmitters
• Smart Level radars
• Smart Ultrasonic flow meters
• Smart Ultrasonic level transmitters
• Smart Positioners for control valves
• Smart Temperature transmitters
• Smart capacitance type ( RF) level transmitters
• Smart level control type level transmitters
FEATURES OF SMART TRANSMITTERS
1 Better Accuracy
2 Higher rangeability
3 Built in PID controller
4 Output transfer function( linear, square root)
5 Special functions with multipoint characterization tables
6 Constant signal generation for loop test
7 Data Flow tantalization
8 Programmable LCD indicator
9 Password protection
10 Programmable failsafe level output for the control
11 Monitoring in engineering Units, configuration file, diagnosis
12 LOCAL adjustments: Zero, span, and all PID controller functions
13 HART protocol communication simultaneously with 4-20 mA
14 Remote calibration
15 True non interactive zero and span
• It is very interesting to know how smart instruments communicate with
the DCS or configurators. The careful and intelligent use of
microcontrollers, non volatile memories and advancement in digital
communications has made it feasible to overcome all the existing problems
and limitations of analog transmitters. This has given birth to smart
instruments. All the features of the smart instruments are derived by
exploiting the latest technology of microcontrollers / microprocessors.
Apart from above mentioned features, it is possible to achieve
• Reduction in the size
• Minimize hardware
• Light weight of the instruments
• Low cost
• No need to change in control systems because of introduction of smart
• Standardization of instruments and hence less inventory
1) Software :
• User can select from
various options on
Ranges, response, EU,
Display info, Outputs,
2) Sensor Characterization Data
• Sensor linearization Coefficients or
interpolation points for different T, P
• stored in the memory (EPROM)
• Sensor behavior at various operating
conditions is tested, and used for
• Drastically reduces drifts
Store (and transmit when required) info such as :
• tag - for identification of transmitter
• date modified - date of last or next calibration
• message - name of person or some special
• information on flange type, flange material O-
ring, seal type, sensor range etc.
3) Memory (EPROM) permits Storage
4) Processor: Enables Computations
and Output Signal Options
• linear (for pressure, differential pressure, level
• square root (for flow measurement with
differential pressure meters),
• square root of third and fifth powers (for flow
measurement in open channels..) etc,
• use values stored in table in the memory to
calculate the value of process variable
5) Re-ranging, Turn-down
• Adjust or Change the zero / span
• Send Command from Handheld/remote computer to the
• Re-ranging can be performed without applying
reference (pressure / temperature); uses
• Re-ranging done with reference will actually be more
6) Limits / Alarm values :
• High limit,
• low limit,
• high rate of change,
• low rate of change , etc.
depending on Make/Model
• Set output signal to 3.5 mA or 21 mA
7) Self-diagnostics :
•diagnostic to determine conditions of sensor,
communication line, power supply,
•helps reduce trouble shooting efforts,
•Newer transmitters can sense impulse line
8) Improved Safety
Re-ranging, calibration, etc., can
be done remotely without going
to the actual transmitter site
which may be in an hazardous
or unsafe location.
9) Time Savings
•Remote communication implies facility to
re-range, reconfigure, etc. for one or
more smart transmitters using the hand-
held communicator or configurator;
means fewer trips to the field.
•Self - diagnostics,
implies lesser time spent for
troubleshooting, repairs etc.
10) High Accuracy :
• The process of analog-to-digital and digital-
to-analog conversion of the 4-20 signal are
eliminated by the use of digital
• Functions like sensor output
compensation for drifts due to changing
• output linearization
• or other computations, etc.
enable high accuracy of transmitted data.
11) Reduced Inventory
facility to re-range the transmitter without
loss of accuracy,
facility to configure the transmitter when
using a different process media,
computational abilities like square-root
implies that only one type of smart
transmitter need to be purchased or
maintained as spare for a wide range.
•Smart Transmitter Manufacturers:
•Foxboro, Honeywell, Moore
•SMAR, ABB, Siemens,
•Rosemount : HART (Highway
Addressable Remote Transducer)
•Honeywell : DE (Digitally Enhanced)
COMMON SMART TRANSMITTER
HOW HART TRANSMITTER
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. This enables two-
way field communication to take place and
makes it possible for additional information
beyond just the normal process variable to be
communicated to/from a smart field instrument.
The HART Protocol communicates at 1200 bps
without interrupting the 4-20mA signal and
allows a host application (master) to get two or
more digital updates per second from a smart
field device. As the digital FSK signal is phase
continuous, there is no interference with the 4-
HART Communication Protocol
• Bell-202 standard Frequency-shift-
• bit ‘1’ : 1200 Hz
• bit ‘0’ : 2200 Hz
• Transfer rate :
• 1200 bit/s
• Signal structure:
• 1 start bit
• 8 data bits
• 1 bit for odd parity
• 1 stop bit.
Digital communication over the same
two wires used for analog transmission.
The digital communication is two-way
between the transmitter and the
configurator - A hand-held
communicator, a microprocessor based
system or a computer.
HART Communication Protocol
has transformed advanced
modernization in the field of
Same transmitter can be used
for various range by changing
Spare part management has
become easier. Any maker
with HART protocol can be
Can be calibrated from control
Can be used in Hazardous
HART Communication between
master and slave
• The master sends messages with requests
for actual/specified values, and/or any
other data/parameters available from the
• The slave interprets these instructions as
defined in the HART protocol.
• The slave responds with status
information and data for the master.
Network More than one smart
transmitter using same two-wire
Each transmitter configured a
unique Address (Non-zero) “1 to
Each can be individually read,
configured, re-ranged or
Each transmitter draws,
outputs 4 mA Only
In conventional analog mode,
address set to “0”
•Common practice commands
• HART follows the Open Systems
Interconnections (OSI) model of the
International Organization for
• The HART protocol uses a reduced
OSI model, implementing only layers 1,
2 and 7
• Layer 1, physical layer
• Layer 2, link layer
• Layer 7, application layer
Question Topics OSI layer
How do we make the
Plugs, sockets, cable Physical
What signals can I send? Voltage, current, frequency Physical
How do I address a message? None (point-to-point), numerical address, tag DataLink
When can I send a message?
Access rules: master-slave, token-passing, collision-
What messages can I send?
Coding: bits, characters, parity DataLink
Data types: bits, integers, floating point, text
What does a message mean?
Function blocks, Device Descriptions "User"*
PRIMARY AND SECONDARY MASTERS
The HART Protocol
provides for up to two
masters (primary and
secondary). This allows
secondary masters such as
to be used without
the primary master, i.e.
IS CALIBRATION OF SMART TRANSMITTER
Although a ‘Smart’ Transmitter is advertised as being smart and
extremely accurate, there is still a need to calibrate the instruments.
Calibration must always be a priority due to the following reasons:
Even the best instruments and sensors drift over time, especially when used in
challenging process applications.
Regulatory and quality standards often state the minimum time period for
Economical reasons – measurement of process parameters often has a direct
economical effect .
Calibration is necessary to achieve high and consistent product quality
and to optimize processes.
HART CALIBRATION IS REQUIRED!
A common misconception is that the accuracy and stability of HART
instruments eliminate the need for calibration.
Another misconception is that calibration
can be accomplished by re-ranging field instruments using only a
Still another misconception is that the control system can remotely
calibrate smart instruments
All instruments electronic components drift. Re-ranging
with just a communicator is not calibration
WHAT IS CALIBRATION?
Sensor trim is the correction of the digital reading from
the sensor after the A/D conversion.
Re-ranging is configuration of the lower and
upper range values corresponding to the
input values at which the transmitter output
shall be 4 mA and 20 mA respectively.
Current trim is the correction of the analog output from
CALIBRATION OF A HART PRESSURE TRANSMITTER
Press the Adjust soft key apply no
pressure . Select Sensor Lower
Trim value Trim and execute Lower
Trim value trim.
Apply the URV pressure,
press Upper value Trim.
Span is correct but Zero Error
Zero Shift will change the whole scale identical value (Uniform Shift)
Span shift will have different value throughout the scale
Wireless HART Protocol in Smart Instrumentation
WIRELESS HART IS USED
IN CONTROL SYSTEMS !
MISCONCEPTIONS CLEARED !!!!
COURTESY : EMERSON PROCESS MANAGEMENT
JOIN THE JOURNEY FROM PLC TO PAC…
Multiple Hardware Platforms & Multiple Application
Domains Through One Complete PAC System
SOME DETAILS OF THE PAC :
• Programmable Automation Controller or PAC a relatively new name
coined for small, local control systems. The name is derived largely
from the popular PLC or Programmable Logic Controller. One major
difference between a PLC and a PAC is the programming interface.
Most PLCs are programmed in a graphical representation of coils and
contacts called Ladder Logic. Most PACs are programmed in a modern
programming language such as C or C++.
• Since they are no longer handcuffed by the largely digital nature of
Ladder Logic, PACs have become extremely popular is systems with a
high percentage of analog I/O, in systems with extensive network
interface requirements or in systems with direct user interaction
PAC VS PC BASED CONTROL SYSTEM
• The primary difference between a PAC and a simple PC-based control system is that
in a PAC, the "box" containing the I/O, also includes the processor and software. In
fact the CPU running the system is actually built into the I/O system itself. While a
typical, slaved data acquisition system is hosted by some type of general purpose PC
complete with mouse, monitor and other human interface devices (HID), a
Programmable Automation Controller's processor is usually dedicated to controlling
the I/O system and often does not provide any direct human interface.
• Physical differences between a PAC and a standard PC-based DAQ system are
easily observed. However, the differences in software are equally noticeable. While
most PCs operating systems for your desktop and laptop computer are large (in
terms of RAM and hard drive space needed), operating systems developed for
embedded systems are likely to be smaller and have been developed without all of
the built-in GUIs as well as much of office equipment peripheral support.