fieldbus 1 physical layer fieldbus physical layer
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FieldbusPhysical LayerFieldbus
Physical Layer
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FOUNDATION Specification 31.25 kbit/s Physical Layer Profile Document FF-816 Revision 2.0; Sept 2001
IEC61158-2: 2000 Fieldbus Standard for Use in Industrial Control Systems Part 2 : Physical Layer Specification and Service Definition
ISA-S50.02-1992 Fieldbus Standard for Use in Industrial Control Systems Part 2 : Physical Layer Specification and Service Definition
SpecificationsSpecifications
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Additional devices may be connected toa Fieldbus networkat any point
Fieldbus Digital OperationFieldbus Digital Operation
T T
Host system doesnot have to be at thenetwork terminator
100R1 µF
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us Tree, Spur, & Daisy-chain topologyTree, Spur, & Daisy-chain topology
T T
Tree
Spur
Daisy-chain
X
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us Fieldbus Digital OperationFieldbus Digital Operation
T T
Up to 32 devices per segment(more with repeaters)
Total network length achievable depends on cable quality
A maximum of four repeaters recommended
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T T
10m10m
50m60m
80m
60m
30m
80m
Adding up all trunk + spurs= 680 metres
300m
Fieldbus max cable lengthsFieldbus max cable lengths
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CableType
CableDescription
Size MaxLength
Type ‘A’ Single twisted pairwith shield
0.8 mm2
18 AWG1900 metres
Type ‘B’ Multi-twisted-pairwith individual shields
0.32 mm2
22 AWG1200 metres
Type ‘C’ Multi-twisted-pairwithout shield
0.13 mm2
26 AWG400 metres
Type ‘D’ Multi-core, without twisted pairsand having an overall shield
1.25 mm2
16 AWG200 metres
Cable specificationCable specification
Recommendedmaximum length
680 m
680 m
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Type ‘A’ cable typically offers the following at 25OC :
characteristic impedance at 31.25 kHz : 100 ± 20% max attenuation at 39kHz (1.25 x 31.25) : 3.0 dB/km max capacitive unbalance to shield : 4nF/km,
tested using a 30m or longer sample max d.c. resistance (per conductor) : 24 /km max propagation delay change 8kHz to 39kHz : 1.7 us/km conductor cross sectional area : 0.8 mm2
: (18 AWG) min shield coverage shall be 90%
Fieldbus CablesFieldbus Cables
Where the field link is intrinsically safe : The use of a screened cable
removes the necessity for segregation of IS from non-IScables for safety reasons
removes the need to assess fault interaction segregation is desirable to ensure interference is minimised IS cables should be clearly identified where colour is used to identify the cables it should be light
blue
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R L C R L C R L C
Characteristic ImpedanceCharacteristic Impedance
Type ‘A’ cable typically offers the following at 25OC :
characteristic impedance at 31.25 kHz : 100 ± 20% max attenuation at 39kHz (11/4 x 31.25) : 3.0 dB/km
decibels = 20 log (V in / V out)
max capacitive unbalance to shield : 4nF/km max d.c. resistance (per conductor) : 24 /km
characteristic impedance at 31.25 kHz
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us Fieldbus Cables :
to IEC61158-2 & IEC60332-3 Cat C flame test
Fieldbus Cables :to IEC61158-2 & IEC60332-3 Cat C flame test
Manufact. Cat.No.
Type Conductors Gauge Resistance
Belden 3076F ‘A’ single pair 18 AWG 22 /km
Belden 3077F ‘B’ single pair 22 AWG 56 /km
All Belden cables are : Low Smoke Non Halogen (LSNH): optional in steel wire armour (SWA): outer covering in orange PVC
Belden UK Ltd. 10 Watergate RowWatergate StreetChester, Cheshire, UKCH1 2LDTel +44 (0)1244 350 535
Lapp
Kerpen
BICC Cables
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metres
TotalDevices
1 Deviceper Spur
2 Devicesper Spur
3 Devicesper Spur
4 Devicesper Spur
1-12 120 90 60 30
13-14 90 60 30 0
15-18 60 30 0 0
19-24 30 0 0 0
25-32 0 0 0 0
Maximum spur lengths are the sameirrespective of cable type
Recommended spur lengthsRecommended spur lengthsFigures
not
absolute
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Max length Type ‘A’ : 1900 m
Max length Type ‘C’ : 400 m
1200 / 1900 + 200 / 400 = 1.13
result > unity : not recommended
Type ‘A’1200m(1900)
Mixing cable typesMixing cable types
Type ‘C’200m(400)
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The ability to power the field devices over the networkis considered in detail later
Communication limitations