HARTBy:- Amol Dudhate

2011BIN044

HART Communication

Introduced in 1989.

HART (Highway Addressable Remote Transmitter) is an open

process control network that supports hybrid communication.

Provides additional bidirectional digital communication channel

over the same 4-20mA signal wiring.

HART protocol extends existing 4-20 mA current loop with

intelligent measurement and control.

It uses FSK(Frequency Shift Keying) technique to superimpose

digital signal on 4-20mA current signal.

Network Data Communication

Analog transmission

Hybrid transmission

Digital transmission

FSK

TRANSMITTERRECEIVER

HART network communication

Used in point to point communication.

Multiplexer is used to connect one of the multiple

current loops to host for increasing number of

accessible devices.

Multidrop connection is also possible through HART

protocol which allows 15 devices to connect in

parallel to a single wire pair.

Telephone lines using convertors can be used for

communication over long distances.

Slaves

MasterPC/DCS

/PLC

SENSORS

TRANSMITTERS

ACTUATORS

MASTER-SLAVE COMMUNICATION

WITH HART PROTOCOL

Communication Modes

MASTER-SLAVE COMMUNICATION

simultaneous digital communication with 4-20mA analog signal.

Provides 2 updates/sec.

BURST COMMUNICATION –

It allows a single slave device to continuously broadcast HART reply messages

with 75ms short breaks.

It is all digital communication.

Provides 4 updates/sec.

Should be used with single slave

HART Protocol Layers

HART COMMANDS

-

-

-

-

HART TELEGRAM

BELL 202,FSK

APPLICATION LAYER

PRESENTATION LAYER

SESSION LAYER

TRANSPORT LAYER

NETWORK LAYER

DATA LINK LAYER

PHYSICAL LAYER

OSI VS HART PROTOCOL LAYERS

Physical layer

It defines physical and mechanical properties of connectors and cables.

Also it defines signal characteristics.

FSK Digital signal communication through wire is based on Bell 202

communication standard.

It defines

SIMPLEX CHANNEL FOR 4-20mA ANALOG SIGNAL

HALF DUPLEX FOR FSK DIGITAL SIGNAL

It uses asynchronous transmission.

Masters & slaves are connected in parallel.

Twisted pair cable with single shielded cable length of 3000 m.

Data link Layer

Responsible for reliable transfer of message over

network.

Organizes data and control byte into frames, adds

error detection codes to data stream.

Assures symmetric access to communication channel

by both master and slave.

Each HART transaction consists of master command

& slave response.

PREAMBLE SD AD CD BC STATUS DATA PARITY

Structure of HART telegram

HART telegram• Short frame format uses 1byte

• Long frame format uses 5bytes in

address field of telegram

• Telegram contains min. of 10 control

bytes & max. of 25 bytes.

Application layer

Defines commands ,responses, data type, and

status reporting.

HART commands enable a master device to

send instruction to field devices to return data

Field devices respond by sending

acknowledgement telegram which contains data

or requested status.

CO

MM

AN

DS

Universal commands

Common practice commands

Device specific