SMART TRANSMITTER AND HART PROTOCOL

PRESENTED BY :

OMKAR KALE (1010) SAGAR RANA (1018)

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 TRANSMITTERSCHARACTERISTICS

1 Better Accuracy2 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 test7 Data Flow tantalization8 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

instruments • Standardization of instruments and hence less inventory

: SMART TRANSMITTER :

BLOCK DIAGRAM

1) Software : Configuration Options• User can select from various options on Ranges, response, EU, Display info, Outputs, etc….

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 compensation

• Drastically reduces drifts

Store (and transmit when required) info such as :• tag - for identification of transmitter• date modified - date of last or next calibration

or installation• message - name of person or some special

precaution etc.• 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 measurement. ..),

• 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

Process Transmitter• Re-ranging can be performed without applying

reference (pressure / temperature); uses Characterization data.

• Re-ranging done with reference will actually be more accurate calibration.

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, configurations, etc.

• helps reduce trouble shooting efforts, improves servicing.

• Newer transmitters can sense impulse line plugging conditions.

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 communication.

• Functions like sensor output compensation for drifts due to changing operating conditions,

• output linearization • or other computations, etc.

enable high accuracy of transmitted data.

11) Reduced Inventoryfacility 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 extraction, etc.,

implies that only one type of smart transmitter need to be purchased or maintained as spare for a wide range.

Advanced Capabilities

•Embedded control (PID)•Multi-variate transmitters•FIELDBUS (Fully Digital, Multidrop Networking)

•Smart Transmitter Manufacturers:

•Foxboro, Honeywell, Moore Products

•Rosemount, Emerson Process Management

•SMAR, ABB, Siemens, Yokogawa, FUJI

•Rosemount : HART (Highway Addressable Remote Transducer)

•Honeywell : DE (Digitally Enhanced)

COMMON SMART TRANSMITTER

COMMUNICATION PROTOCOLS

HOW HART TRANSMITTER WORKS ?

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 4-20mA signal.

HART Communication Protocol

• Bell-202 standard Frequency-shift-keying (FSK)

• 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.

• Communication

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.

What is the need of a 250 ohm resistor ???

HART Communication Protocol has transformed advanced modernization in the field of Automation.

Same transmitter can be used for various range by changing LRV /URV.

Spare part management has become easier. Any maker with HART protocol can be used.

Can be calibrated from control station.

Can be used in Hazardous area

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 slave device.

• The slave interprets these instructions as defined in the HART protocol.

• The slave responds with status information and data for the master.

Multidrop communication

Network More than one smart transmitter using same two-wire loop.

Each transmitter configured a unique Address (Non-zero) “1 to 15”.

Each can be individually read, configured, re-ranged or calibrated.

Each transmitter draws, outputs 4 mA OnlyIn conventional analog mode, address set to “0”

HART Commands

• Universal commands• Common practice commands• Device-specific commands

• HART follows the Open Systems Interconnections (OSI) model of the International Organization for Standardization (ISO).

• 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 connection? 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-detection DataLink

What messages can I send?

Coding: bits, characters, parity DataLink

Data types: bits, integers, floating point, text Application

What does a message mean?Standard functions Applicati

on

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 handheld communicators to be used without interfering with communications to/from the primary master, i.e. control/monitoring system.

IS CALIBRATION OF SMART TRANSMITTER IMPORTANT?

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 instrument calibration. 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 calibrationcan be accomplished by re-ranging field instruments using only a HART communicator.

Still another misconception is that the control system can remotelycalibrate smart instrumentsAll 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 the transmitter

CALIBRATION

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.

HART TRANSMITTER CALIBRATION

ZERO ERROR ( Constant all over the Range)

Span is correct but Zero Error

Zero Shift will change the whole scale identical value (Uniform Shift)

SPAN ERROR

Span shift will have different value throughout the scale

Wireless HART Protocol in Smart Instrumentation Systems

WIRELESS HART IS USED IN CONTROL SYSTEMS !

MISCONCEPTIONS CLEARED !!!!COURTESY : EMERSON PROCESS MANAGEMENT

PROGRAMMABLE AUTOMATION CONTROLLER (PAC)

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 requirements.

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.

THANK YOU !

ANY QUESTIONS ?