Foundation fieldbus
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Transcript of Foundation fieldbus
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