HART

HARThighway addressable remote transducer

Ravikumar Koturwar 13MAC0038Rahul S Kore 13MAC0041Parth M Mehta 13MAC0048

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Why its Popular nowThe HART protocol directly contributes to these business goals by providing cost savings in:

Commissioning and installation

Plant operations and improved quality

Maintenance

Analog 4–20 mA and digital signals provide flexibility not available with any other communication technology.

Hand Held Communicators are often used to perform device set-up, calibration, commissioning and periodic maintenance

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Improved plant operations

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Operational Flexibility

Multi-master Operation?

Primary master ---- control system

Secondary master ---- A hand-held communicator or a maintenance computer.

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Instrumentation investment protection

Wiring, analog controllers, barriers, analog or smart instrumentation

exists widely

The HART communication protocol enables you to retain your previous investments in existing hardware and personnel. VIT Control and Automation’13-14

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Digital communication

The HART protocol enhances the capabilities of digital instruments by providing communication access and networking

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HART Vs. Fieldbus

HART is compatible with existing wiring in older plants.

Hart is understood, accepted and appreciated by virtually everyone involved.

Fieldbus costs a lot more to implement, especially for existing equipment.

Lot of instruments not radially available with Fieldbus.

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HART specifications?

Physical form of transmission

Transaction Procedures

Message structures

Data formats

Set of commands to perform required operation.

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Communication Modes of HART?

Master Slave Mode (Poll---Response Mode)

Maximum communication speed --- 2 messages/sec.

Configuration ---- Point-to-point or Multi-point

Master sends command (request) , slave responds (replies)

Request

Reply

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Burst Mode ( Broadcast Mode)

Slave transmits messages continuously (e.g. values of a measurand).

The communication speed --- 3 message/sec.

A slave device repeatedly sends a data message.

Used for fast updation of the value of a measured variable

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HART Signal Levels?

HART protocol specifies that master device transmit a voltage signal whereas slave device transmits a current signal.

The current signal is converted in to corresponding voltage by a loop load resistor(250 ohms), so all devices use voltage sensitive receiver circuits.

The wave shape is sinusoidal, but trapezoidal waveform is acceptable. A square wave is not acceptable.

Master Slave Operation?

The each message transaction is originated by the master station, the slave device only replies only when it receives a command message.

The reply from the slave device acknowledges that the command has been received and may contain data requested by the master.

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Different HART networks?

Point-to-point Mode

Both analog and digital communications are supported.

4–20 mA signal is used to communicate one process variable.

Additional process variables, configuration parameters, and other device data are

transferred digitally using the HART protocol

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Multidrop Mode

Only digital communication is supported

Requires only a single pair of wires

In case safety barriers and an auxiliary power supply for up to 15 field devices

All field device polling addresses are >0, and the current through each device is fixed to a minimum value (typically 4 mA).

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Different Groups of HART commands?

Universal : Provides functions which are implemented in all field devices. Examples : Read model Read serial number Read range

Common Practice : Provides functions common to many field devices but not all. If a device uses these functions, these commands should be used to perform them.

Examples : Read (up to 4) variables

Perform calibration check

Perform self-test

Device specific : Provides functions which are more or less unique to a particular filed device .

Examples : Select 0C/0F (temperature sensor)

Tune a control parameter (control device)

Write alarm set point (relay)

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Command Summary

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Types of Frame Formats in HART protocol?

Short frame format ---- Older HART instruments(Version4) used short frame format. In this the address of the slave device is ‘o’.

Long frame format ---- HART version 5 introduced ‘Long frame format”. In this the address of the slave device is world wide unique identifier.

It is a 38 bit number derived from the manufacturer code.

It contains the device code and device id no

Long frame format gives extra security against the possible reception and acceptance of command meant for another device, either due to external interference or due to excessive cross talk

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Some More Points

pass-through feature?

DD?

Interoperability?

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Wireless HART

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Introduction

Wireless HART is a wireless mesh network communication protocol.

It is designed to meet the needs for process automation applications

It is a KEY part of the HART field communication protocol Version 7

Less than 10% of the installed HART instruments have a direct communications link back to a host system.

The addition of low-cost wireless connectivity provides a pathway for remote host systems to read process and maintenance information from field instruments, both old and new.

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Wireless HART Network Structure

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Wireless Mesh

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Time Synchronization

Report by Exception – Time- and Condition-based Alerts

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Time Stamp

synchronized clock enabling it to transmit data at the correct time.

Used to stamp time and date

Wireless Co-existence

Uses channel assessment and short message sizes to coexist with neighboring networks

Wireless Diagnostics

Ensures the health of the network

Include indicators of battery life remaining, devices present, network join attempts and other network management indicators.

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Wireless Security

Join Key

Unique Message Integrity Code (MIC)

Message Encryption

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Loop Testing

No 4 to 20 mA signal

It checks that the process data is displayed correctly at the host and also tests other control functions.

Wireless HART Adapter

New HART device can be added to wired device to provides wireless Feature

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WIRELESS NETWORK

28

PART 2

FSK

HART signal

HART protocol

MUX

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CHARACTERISTICS

Simultaneously supports two communications channels. » 4-20mA "analog" communications and

» Modulated two-way "digital" communications.

Additional process data in Multi-Variable devices used to improve plant operation

Field devices can continuously publish their process data. » Operators alerted to impending problems before negative impact to the process = Real time device diagnostics.

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FSK

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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HART SIGNAL in Physical layer

HART allows additional information to be carried on the same pair of wires with

the 4-20 mA Analog Signal

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TWO COMMUNICATION CHANNEL

4-20mA "Analog" Channel

HART"Digital"Channel

4-20mA Analog support large part of Protocol Specifications One-way communication of one process value Simple Low Pass Filter isolates 4- 20mA signal

Compliments 4-20mABased on Analog Telephone Modems

» Long Cable Runs» High Noise Immunity» You can "hear" HART

Two-way Communications

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Example

Fig : Two Communication Channels

• Connecting a PC to a HART device or network

• PC application development tools > PC configuration software

• Universal handheld communicator >275 Universal

• Reading HART data into non-HART systems

• Commissioning HART networks > HART multidrop networks

• Control system interfaces > Control in field devices

• Multiplexers

• Device status and diagnostics

• Intrinsic safety(IS)

The following sections contain information that can help you to get the most from your HART system:

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CABLE LENGTH

TABLE: Allowable cable lengths for(#18 AWG) shield twisted pair

Theoretical Length max. :

Affected by: electrical characteristics ( mostly Capacitance)

& Combination of connected devices

It is also a good idea to buy a cable designed for HART. Belden 3105A is an example of such a cable.

3,000 meter (10,000 ft)

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HART PROTOCOL LAYERS

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• Controlled by HCF • Open and Available to Anyone• Easy-to-Read Language• Consistent and well-defined terms

Organization of HART SpecificationsVIT Control and Automation’13-14

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Protocol Structure

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LONG FRAME FORMAT

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Packet Structure

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RESPONSE

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General device status is always returned with COMMAND3

2 bytes of status info.

HART COMMAND 3

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STATUS MESSAGES ARE:

Status Messages

Field device malfunction (Bit 7)

Configuration changed (Bit 6)

Cold start (Bit 5)

More status available (Bit 4)

Analog output current fixed (Bit 3)

Analog output saturated (Bit 2)

Non-primary variable out of limits (Bit 1)

Primary variable out of limits (Bit 0)

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COMMAND 48

Device specific information is always returned with COMMAND48

25 bytes of additional status information

*Not necessary to use all the bytes Ex. Honeywell STT250 uses only first 3 bytes.

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MultiplexersTo interface numerous HART devices

Support point-to-point and all-digital (multidrop)

Communication between a multiplexer and host depends on the multiplexer capabilities

RS232C, RS485, Modbus, TCP/IP Ethernet

can be used as primary I/O front end for aHART-based control or monitoring system

When installing HART multiplexer systems, the following capabilities should be considered:

o Number of HART channels supported o Number of HART channels that share a HART modem o Burst mode supporto Multidrop supporto Method of communication with the host computer or control system

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1. PARALLEL MONITORING WITH A MULTIPLEXER

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PC acts as the host, providing the human-machine interface & perform high-level functions.

Mux passes HART commands from the host computer to the field devices.

continuously monitors the field devices, reports the current readings and instrument status to the host,

Figure: HART Multiplexer as the Primary I/O System

2. MULTIPLEXER AS THE PRIMARY I/O SYSTEM

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Multiplexer refresh time > function of no. of devices connected per channel

Refresh time = 0.8sec / device / modem

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3. CONTROL FIELD DEVICES

Figure: Transmitter with PID (HART Slave)

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Wireless HART vs. Bluetooth

vs. Zigbee

Range

Data security = Reliable message delivery

Industrial grade robustness = Industry acceptance

Reliability.

*No HART device use Bluetooth connectivity with data load.

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No frequency diversity > Entire network shares same static channel

Static Channel also susceptible to interference with wireless LAN

Makes it susceptible to both intended and unintended jamming

Can stop entire network communication

Designed from start for robust and secure Communication

Network works 24*7 > no option to turn it completely off

Mesh networking with graph routing > provide redundancy and self healing

ZigBee

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Comparison at layer level

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Versions

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Industry App’sPART 3

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Reading HART Data into Non-HART Systems

Many HART products are able to perform more than one measurement oroutput function (e.g., make multiple process measurements, calculateprocess information, and provide positioner feedback information). All ofthis information can be easily accessed digitally. However, existingcontrollers or interface equipment may not have the ability to read digitalHART data. Products are available that can read HART digital signals andconvert them to analog or contact information, which enables anytraditional analog/digital I/O to take full advantage of the benefits ofHART-communicating devices.

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The Tri-Loop module monitors a HART loop for a bursting message andconverts three of the four possible variables in HART communicator.

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The site programmable alarm( SPA )module continuously communicates with any HART-capabledevice and provides contact closure outputs (alarm trips) based on theinformation received (Figure 14). For example, the SPA can be configured to monitor the device-status information inherent in the HART communication protocol and trigger events such as local on/off applications or alarms. The SPA can also initiate emergency shutdown action if problems are detected with a field device in critical loop applications

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Industrial Application

Many companies in a wide variety of industries have already realized the advantages of using the HART communication protocol. This section describes some applications in detail and outlines the tangible benefits that result.

The applications have been grouped into the following sections:

Inventory-management applications

Cost-saving applications

Remote-operation applications

Open-architecture applications

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Inventory-Management Applications

Accurate measurements for inventory management are essential in all industries. The HART communication protocol enables companies to make sure inventory management is as efficient, accurate, and low cost as possible.

Tank level and inventory management is an ideal application for a HART multidrop network . The HART network digital update rate of two PVs per second is sufficient for many tank-level applications. A multidrop network provides significant installation savings by reducing the amount of wiring from the field to the control room as well as the number of I/O channels required.

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UNDERGROUND PETROLEUM

STORAGE WITH HART COMMUNICATION FOR

ACCURACY

Underground salt caverns are frequently used for crude oil storage. One customer pumps oil from barges into the storage caverns. An ultrasonic flow-meter records the total flow. To get the oil out of the caverns, a brine solution is pumped into the cavern through a magnetic flow-meter. Brine and crude oil flowing in both directions are measured and reported to the DCS using the HART communication protocol for accuracy.

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Cost-saving applications

A Texas wastewater treatment plant replaced stand-alone flow meters and chart recorder outstations that required daily visits for totalization with a HART system. HART-based magnetic flow meters were multidropped into HART RTUs to create a cost-effective SCADA network. The use of HART technology reduced system and cable costs, enhanced measurement accuracy, and eliminated time-consuming analog calibration proceduresVIT Control and Automation’13-14

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A consumer appliance manufacturer used the networking capability of the HART protocol to ensure level, flow, and pressure HART multidrop provided substantial wiring and installation savings as well as digital accuracy with the elimination of the analog to digital (A/D) and digital to analog (D/A) conversions of the instrument and PLC I/O. Figure shows pressure transmitters connected to a PLC via smart transmitter interface multiplexers.

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Remote-Operation Applications

Choosing the HART communication protocol for all-digital communicationin a wide-area network enabled one company to have real-time monitoringand control, access to diagnostics, and maintenance capabilities—all from aremote location.

Each platform’s RTU provided a link to approximately 50 temperature,pressure, and flow transmitters. The RTU used the multi-mastercapability of the HART protocol to enable the second RTU to act as a hotstandby, which monitored activity and was able to take over if a failureoccurred. The RTUs provided links with the emergency and safety systemsand a local interface for maintenance personnel. The Modbus protocol wasused for communication to the central SCADA system

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In a Venezuela gas-lift project, HART multidrop technology was used for remote operation of offshore gas-lift production wells at considerable savings:

30% decrease in installation costs

16:1 reduction of input modules

Reduced cost of I/O cards in the RTU

Remote re-ranging

Remote access to the transmitter status for improved process uptime

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Open-Architecture Applications

The best way to judge the openness of a communication protocol is by thenumber of products supported. By this standard, the HART protocol isperhaps the most open of any field-communication protocol availabletoday.

In a major refinery expansion, an oil company weighed the advantages ofusing either a proprietary system or a HART-based system. The resultsindicated that the company could use HART digital instruments in 92% oftheir applications, compared to only 33% with the proprietary system.Choosing HART products resulted in an incremental $23,000 in savingsdue to commissioning efficiencies and ongoing maintenance and diagnosticcapabilities.

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Intrinsic Safety

Intrinsic safety (IS) is a method of providing safe operation of electronicprocess-control instrumentation in hazardous areas. IS systems keep theavailable electrical energy in the system low enough that ignition of thehazardous atmosphere cannot occur. No single field device or wiring isintrinsically safe by itself (except for battery-operated, self-containeddevices), but is intrinsically safe only when employed in a properlydesigned IS system.

HART-communicating devices work well in applications that require ISoperation. IS devices (e.g., barriers) are often used with traditionaltwo-wire 4–20 mA instruments to ensure an IS system in hazardous areas.With traditional analog instrumentation, energy to the field can be limitedwith or without a ground connection by installing one of the following ISdevices

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Shunt-diode (Zener) barriers that use a high-quality safety groundconnection to bypass excess energy

Isolators, which do not require a ground connection, that repeat theanalog measurement signal across an isolated interface in the safe-sideload circuit Both Zener barriers and isolators

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When designing an IS loop using shunt-diode barriers, two additionalrequirements must be considered:

1. The power supply must be reduced by an additional 0.7 V to allow

headroom for the HART communication signal and yet not approachthe Zener barrier conduction voltage.

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HART is a backward compatible enhancement to 4-20mA instrumentation that allows two way communication with smart, microprocessor-based field devices.

Continuously Validate Integrity of Control Information –Ensure accuracy of system data/ Automatically detect any deviation between device and system

Continuous Real Time Diagnostics– Device Problems/ Loop Current Faults– Device Needs Maintenance

Unlock additional information in Multi-Variable devices

CONCLUDE

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Wireless HART is designed based on a set of funda- mental requirements: it must be simple (e.g., easy to use and deploy)

Self-organizing and self-healing.

flexible (e.g., support different applications)

Scalable (i.e., fit both small and large plants)

Reliable, secure, and support existing HART technology (e.g., HART commands, configuration tools, etc.)

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Questions??

Ravikumar Koturwar 13MAC0038Rahul S Kore 13MAC0041Parth M Mehta 13MAC0048

HART