Facts and Figures about Cable and Wiring Raymond Ng Belden - - PowerPoint PPT Presentation

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Fieldbus FoundationTM Facts and Figures about Cable and Wiring

Raymond Ng Belden Singapore Pte Ltd

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Agenda

• Foundation Fieldbus Cable Standard

– IEC 61158-2 – FF-844

• Cable Selection

– Standard instrumentation cable –vs- FF cable – AWG size, Shielding, Jacketing, Armor types

• Cable Installation & Termination
• Q & A

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IEC 61158-2 Type “A” Cable Specification

• Impedance: 100 Ohms
• Attenuation: < 3 dB/km
• Capacitance Unbalance:

4nF/km max.

• Conductor DC

Resistance: 24 Ohms/km max.

• Maximum Propagation

Delay Change: 1.7 μs/km

• Wire Size: .8mm sq.

(18 AWG) nominally

• Shield Coverage > 90%

CcS Ccc Insulation Drain wire Shield CcS Conductor Jacket

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FF-844 – Cable Test Specification

• Builds on IEC Requirements to further qualify

cables

• Addition to IEC requirements

– Expands on shielding requirements – Specifies 10 to 22 pair twists/meter – Jacket Resistance – Required and optional cable ratings – Recommended connector characteristics

• Cable registration is in process

Lay Length

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Instrumentation –vs- FF Cable FF Cable

• Polyolefin Insulation

– Electronic grade insulation

• 100 Ohm Impedance
• 66% Velocity of

Propagation

• Designed with tolerances

necessary to meet FF specifications Instrumentation Cable

• PVC or XLPE Insulation
• 35-65 Ohm Impedance
• 55 to 60% Velocity of

Propagation

• Designed to meet general

minimum instrumentation cable requirements

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Instrumentation –vs- FF Cable

• FF cable has lower Capacitance
• FF cable is designed to a specific impedance to

reduce signal reflections and maximize network length

• FF cables are tested during production to meet

specific requirements:

– Capacitance Unbalance – Impedance – Conductor D.C. resistance

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Cable Selection

• First consult with local authority having

Jurisdiction to ensure regulatory compliance

• Selection Guide

– Conductor Size – Shielding – Armor – Jackets

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Cable Selection – Conductor Size

• Most common design is one pair 18 AWG
• Larger AWG (16, 14) provide:

– Improved pull strength – Electrical benefits, such as:

Greater Current Capacity More Field Instruments Less Voltage Drop Longer Distance Reduced Resistance

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Cable Selection – Shielding

• Most common design:

foil shield only

– ~ 35 dB of Shield effectiveness – Most effective at high frequencies (>10 MHz) – Drain wire for easy termination

• Combination shields

– Foil in addition to braid – Shield effectiveness of ~ 80 dB – Effective from 60 Hz to GHz

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Cable Selection – Armoring

• Interlock

– Steel – Aluminum

• SWA (Steel Wire Armor)
• Protective Metal Tapes:

– Smooth or Corrugated (Steel, Copper, Aluminum)

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Cable Selection – Armoring

• Why use Armor?

– Rodent protection – Physical integrity – Direct burial – Reduces cost of conduit – Hazardous Locations

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Cable Selection – Jacketing

• PVC – most common jacketing material
• CPE – good chemical and abrasion resistance
• LSZH – low smoke zero halogen applications
• HDPE – direct burial applications
• FEP – high or low temperature applications (-70

to 200C)

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Cable Installation

• Follow manufacturer’s recommendations

– Bending radii: generally 10 to 12x cable diameter – Maximum pulling tension – Installation temperature – Pulling lubricant selection

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Cable Termination

• Ground shield at one end only – The near or “host” end

– Use provided drain wire or “pigtail” the braid – Grounding both ends results in ground loops – Required to prevent noise ingress, which could distort the signal

• Shields should be trimmed back flush with jacket

– Isolate shield using heat shrink tubing or tape – This keeps the shield from being inadvertently shorted to the (+)

• r (-) wires or grounding at the device end

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Post Installation Verification

• Follow FF Engineering Guide AG-181

– Procedure for installing and commissioning fieldbus segments – Use DMM for Resistance & Capacitance measurements – Use Fieldbus Handheld tester to verify installation and

• peration

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Common Installation Issues

• Cable shield shorted to (+) or (-) wires
• Cable shield grounded at both ends, increasing

noise susceptibility

• Routing of cables in parallel with AC power lines

– Minimum of 6” separation per IEEE 518 – Minimize parallel runs – Cross power lines perpendicularly, when possible

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Summary

• FF-844 created to clarify cable requirements &

register products

• FF cable requirements are much more stringent

than Instrumentation cabling requirements

• Select cable that is compatible with application
• Consult manufacturer for installation &

termination recommendations

• Follow AG-181 guidelines for testing FF

segments

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