Foundation Fieldbus Protocol

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Family of industrial computer network protocols

Multiple instruments- Single cable Used for real-time distributed control

What is fieldbus?

IEC 61158Standard

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Traditional 4-20mA field wiring

Rat’s nest of wires, cables and terminators

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Trunk Power conditioner Terminators Device couplers

Fieldbus configuration

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Carries both digital signal and DC power Connects up to 32 field devices to DCS Interface at DCS is called H1 card for FF Wiring and power requirement

◦Minimum device operating voltage : 9V◦Maximum bus voltage : 32V◦Maximum cable length (trunk + spur) : 1900m

Maximum distance◦9500m with 4 repeaters

Trunk

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Components of Fieldbus power supply.◦Isolation◦Power conditioning◦Current limiting

Fieldbus power supply

24VDC350 mA

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Two terminators are required on each segment

One at the control room end of cable

Other is in the junctionbox in the field

An extra terminator cause 300 mV drop in signal level

Terminator

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One or more fieldbus devices can connect tothe segment at one location

Short-circuit protection

Device couplers

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All communications andpower depend on singletwisted pair wire

If the trunk cable fails it can “take down” all the segments at one time

MooreHawke’s Fault- Tolerant fieldbus system

Redundant fieldbuses

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Fieldbus topologies

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System architecture

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Each layer addsa portion of themessage that istransmitted onthe fieldbus.

System architecture

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Converts received messages into physicalsignals and vice-versa.

Add, removepreamble, and

delimiters Signals are

encoded usingManchester code

Physical layer

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31.25 kbps fieldbus signaling◦Device delivers ±10 mA at 31.25 kbps ◦1.0 volt peak-to-peak voltage modulated on top of

the DC supply voltage

Physical layer

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DLL◦Controls transmission of messages◦Manages access to the fieldbus through LAS◦LAS is a deterministic

centralized bus scheduler

◦Basic device andLink master

Data link layer

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Scheduled communication◦LAS schedules publisher/subscriber communication◦Scheduled data transfers are done

deterministically.

Data link layer

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LASAlgorithm

Data link layer

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Fieldbus access sublayer Communication Relationships

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FMS services allows user applications to send messages to each other across the fieldbus

FMS describes◦Communication

services◦Message formats◦Protocol behavior

Fieldbus Message Spec.

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Types of blocks used in user application◦Resource block◦Transducer block◦Function block

User layer

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Resource block◦It describes characteristics of device.◦Used to configure devices

Function block◦Control system behavior◦FF has sets of standard function blocks.

Transducer blocks◦Calibration date, sensor type

User layer

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Functionblock

User layer

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Connecthigherlevel devices

Foundation HSE

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Wiring ◦98 % reduction in homerun

Control room◦84% reduction in terminations freed up

two third of cabinet space Cost saving

◦Lowers CAPEX and OPEX Commissioning

◦Easy to diagnose equipment problems◦Cut maintenance cost

Justifying fieldbus

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Questions?

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Nested messages in HSE