Cable And Wiring 721.96 Kb

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Fieldbus FoundationTM Facts and Figures about Cable and Wiring Raymond Ng Belden Singapore Pte Ltd 1 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 2 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% 3 CcS Drain wire CcS Jacket Shield Insulation Conductor Ccc 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 4 Lay Length Instrumentation –vs- FF Cable FF Cable • Polyolefin Insulation Instrumentation Cable • PVC or XLPE Insulation – Electronic grade insulation • 100 Ohm Impedance • 66% Velocity of Propagation • Designed with tolerances necessary to meet FF specifications 5 • 35-65 Ohm Impedance • 55 to 60% Velocity of Propagation • Designed to meet general minimum instrumentation cable requirements 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 6 Cable Selection • First consult with local authority having Jurisdiction to ensure regulatory compliance • Selection Guide – – – – 7 Conductor Size Shielding Armor Jackets Cable Selection – Conductor Size • Most common design is one pair 18 AWG • Larger AWG (16, 14) provide: – Improved pull strength – Electrical benefits, such as: Less Voltage Drop Longer Distance 8 Reduced Resistance Greater Current Capacity More Field Instruments 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 9 Cable Selection – Armoring • Interlock – Steel – Aluminum • SWA (Steel Wire Armor) • Protective Metal Tapes: – Smooth or Corrugated (Steel, Copper, Aluminum) 10 Cable Selection – Armoring • Why use Armor? – – – – – 11 Rodent protection Physical integrity Direct burial Reduces cost of conduit Hazardous Locations Cable Selection – Jacketing • • • • • 12 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) Cable Installation • Follow manufacturer’s recommendations – – – – 13 Bending radii: generally 10 to 12x cable diameter Maximum pulling tension Installation temperature Pulling lubricant selection 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 (+) or (-) wires or grounding at the device end 14 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 operation 15 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 16 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 17 www.fieldbus.org 18