Wednesday, July 4, 2012
Foundation Fieldbus Concepts-3
EPC School 2012 Series
I for Instrumentation
The design requirements for FNICO power supplies, field devices, cable and terminators are essentially the same as those for FISCO, except in the following respects.
1. The field wiring is classified as EEx nL in accordance with IEC 60079-15
2. The maximum permissible value of power supply output current is 570 mA.
3. Field devices may have a maximum of 20 microH internal capacitance, thereby permitting IS Entity certified field devices to be used in FNICO installations.
Typical FNICO power conditioners can supply 12.3 V and 215 mA.
FISCO/ FNICO Advantages
• More number of instruments in comparison to entity concept
• Elimination of intrinsic safety loop calculations
• Live maintenance of field wiring and devices possible
FISCO/ FNICO Disadvantages
• Overall cable length and spur length are theoretically limited to 1900m and 60 m respectively. But
current and voltage levels of available power supplies are very low, which result in significantly shorter
cable runs than the theoretical maximums.
• FISCO and FNICO power conditioners do no offer redundancy
• If the number of instruments is high, more number of power conditioners would be required in the control room to feed the higher number of segments.
High Power Trunk Concept
This concept does not limit the energy on the Fieldbus trunk cable to intrinsically safe or nonincendive levels, rather the energy on the spurs is limited. This allows more number of devices on a segment while also being able to achieve maximum lengths. Energy limitation is done in the field using special hardware called Field Barriers and Segment Protectors Class 1, Zone 1 and Class 1, Zone 2 applications respectively.
A fieldbarrier is used in Class 1, Zone 1 applications. It provides intrinsically safe, short circuit protected spur connections for either entity or FISCO based instruments. The trunk connections in the fieldbarrier are galvanically isolated from the IS spur connections.
Fieldbus segment protectors can be used only in Class 1, Div 2 applications. They provide short circuit protected, energy limited (non incendive) outputs. They can connect to either to nonincendive or IS rated field devices. Maximum cable length is 1900 m and spur length is 120m. Typical power supplies provide 30 V and 500 mA.
High Power Trunk Concept Advantages
• Redundant fieldbus power is achievable in control room with special hardware (power hub)
• More devices on a segment as compared to FISCO/ FNICO (Upto 12 devices per segment)
• Power conditioners with advanced online physical layer diagnostics capability available (segment
noise levels, voltage and current levels, ground faults etc can be diagnosed)
• This technology can be used with Entity, FISCO or FNICO certified instruments.High Power Trunk
Concept Disadvantages
• No live maintenance on a Fieldbus trunk cable is possible due to the high energies involved.
• Initial expenditure may be high due to specialised hardware requirements
• This technology is available only from a single vendor
• Very recent technology.
FISCO Entity FNICO High Power Trunk
Max. overall cable length in the hazardous area 1000 m 1900 m 1000 m 1900 m
Max. spur length in the hazardous area 30 m 120 m 30 m 120 m
Consideration of cable inductances and No Yes No No
capacitances
Conclusion
1. FNICO is applicable only in Zone 2. Hence not suitable for Zone 0 & Zone 1.
2. In view of the advantages and disadvantages of the various Foundation Fieldbus technologies as discussed above, it is suggested that eventhough High Powered Trunk concept is better with respect to number of devices per segment, redundant fieldbus power supply and physical layer diagnostic capability, it has major disadvantage of single vendor technology, higher initial
expenditure and inability to perform live maintenance on the trunk. FISCO concept is recommended to be adopted which has been in use for longer period of time with positive feedback from users.
Few Useful terms
The Fieldbus Foundation specifies two physical layer standards: H1 & HSE (formely H2)
H1 - 31.25 kbits/s, designed for fieldbus connection
HSE - 100 MBPS, serves as backbone, links H1 segments togather.
I for Instrumentation
FNICO (Fieldbus NonIncendive COncept)
FNICO is derivative of FISCO and is specifically intended for fieldbus installations in Class 1, Zone 2 hazardous areas.
It takes advantage of the relaxed design requirements for non incendive (energy limited) circuits compared to those of intrinsic safety. FNICO enjoys the same benefits as FISCO in terms of simple safety documentation and the elimination of cable parameter calculations, and retains the ability to connect and disconnect the field wiring in the hazardous area while under power and without gas clearance certificates. As for the FISCO model, the same basic rules and conditions apply
It takes advantage of the relaxed design requirements for non incendive (energy limited) circuits compared to those of intrinsic safety. FNICO enjoys the same benefits as FISCO in terms of simple safety documentation and the elimination of cable parameter calculations, and retains the ability to connect and disconnect the field wiring in the hazardous area while under power and without gas clearance certificates. As for the FISCO model, the same basic rules and conditions apply
for FNICO. The difference is that FISCO uses a higher safety factor for its electrical values versus FNICO. Due to the lower safety factor for FNICO, it is possible to supply more current into a Class 1, Div 2 hazardous location.
The design requirements for FNICO power supplies, field devices, cable and terminators are essentially the same as those for FISCO, except in the following respects.
1. The field wiring is classified as EEx nL in accordance with IEC 60079-15
2. The maximum permissible value of power supply output current is 570 mA.
3. Field devices may have a maximum of 20 microH internal capacitance, thereby permitting IS Entity certified field devices to be used in FNICO installations.
Typical FNICO power conditioners can supply 12.3 V and 215 mA.
FISCO/ FNICO Advantages
• More number of instruments in comparison to entity concept
• Elimination of intrinsic safety loop calculations
• Live maintenance of field wiring and devices possible
FISCO/ FNICO Disadvantages
• Overall cable length and spur length are theoretically limited to 1900m and 60 m respectively. But
current and voltage levels of available power supplies are very low, which result in significantly shorter
cable runs than the theoretical maximums.
• FISCO and FNICO power conditioners do no offer redundancy
• If the number of instruments is high, more number of power conditioners would be required in the control room to feed the higher number of segments.
High Power Trunk Concept
This concept does not limit the energy on the Fieldbus trunk cable to intrinsically safe or nonincendive levels, rather the energy on the spurs is limited. This allows more number of devices on a segment while also being able to achieve maximum lengths. Energy limitation is done in the field using special hardware called Field Barriers and Segment Protectors Class 1, Zone 1 and Class 1, Zone 2 applications respectively.
A fieldbarrier is used in Class 1, Zone 1 applications. It provides intrinsically safe, short circuit protected spur connections for either entity or FISCO based instruments. The trunk connections in the fieldbarrier are galvanically isolated from the IS spur connections.
Fieldbus segment protectors can be used only in Class 1, Div 2 applications. They provide short circuit protected, energy limited (non incendive) outputs. They can connect to either to nonincendive or IS rated field devices. Maximum cable length is 1900 m and spur length is 120m. Typical power supplies provide 30 V and 500 mA.
High Power Trunk Concept Advantages
• Redundant fieldbus power is achievable in control room with special hardware (power hub)
• More devices on a segment as compared to FISCO/ FNICO (Upto 12 devices per segment)
• Power conditioners with advanced online physical layer diagnostics capability available (segment
noise levels, voltage and current levels, ground faults etc can be diagnosed)
• This technology can be used with Entity, FISCO or FNICO certified instruments.High Power Trunk
Concept Disadvantages
• No live maintenance on a Fieldbus trunk cable is possible due to the high energies involved.
• Initial expenditure may be high due to specialised hardware requirements
• This technology is available only from a single vendor
• Very recent technology.
FISCO Entity FNICO High Power Trunk
Max. overall cable length in the hazardous area 1000 m 1900 m 1000 m 1900 m
Max. spur length in the hazardous area 30 m 120 m 30 m 120 m
Consideration of cable inductances and No Yes No No
capacitances
Conclusion
1. FNICO is applicable only in Zone 2. Hence not suitable for Zone 0 & Zone 1.
2. In view of the advantages and disadvantages of the various Foundation Fieldbus technologies as discussed above, it is suggested that eventhough High Powered Trunk concept is better with respect to number of devices per segment, redundant fieldbus power supply and physical layer diagnostic capability, it has major disadvantage of single vendor technology, higher initial
expenditure and inability to perform live maintenance on the trunk. FISCO concept is recommended to be adopted which has been in use for longer period of time with positive feedback from users.
Few Useful terms
The Fieldbus Foundation specifies two physical layer standards: H1 & HSE (formely H2)
H1 - 31.25 kbits/s, designed for fieldbus connection
HSE - 100 MBPS, serves as backbone, links H1 segments togather.
Labels: Fieldbus NonIncendive COncept, FNICO, foundation fieldbus, H1 cable, High power trunk, HSE cable, Rahul Kapoor, spur, wiring
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