Transcript
Fieldbus FoundationTM Facts and Figures about Cable and Wiring Andreas Agostin MTL Instruments Singapore, Part of Cooper Crouse-Hinds On behalf of the
Fieldbus FoundationTM 1
Vietnam FF Seminar 18 Mar 2010
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
Vietnam FF Seminar 18 Mar 2010
IEC 61158-2 Cable Specification for Compliance Test
Cable specification to test compliance of device with IEC61158-2: • Shielded twisted pair (type A) • Impedance@ f r = 100 Ω ± 20% CCS1 • Attenuation @ 1.25· f r Jacket ≤ 3 dB/km • Capacitive unbalance to shield (CCS1 - CCS2) ≤ 4nF/km (cables 30m or longer) • Conductor DC Resistance = 24 Ω/km (18AWG) • Propagation Delay Change 0.25· f r to 1.25· f r Conductor ≤ 1.7 µs/km • Shield Coverage ≥ 90%
Drain wire
CCS2
Shield
Insulation CCC
Note: f r = 31.25kHz
3
Vietnam FF Seminar 18 Mar 2010
FF-844 – Cable Test Specification
• Builds on IEC Requirements – Impedance, Attenuation, Capacitance unbalance
• Expands IEC requirements – – – –
On shielding requirements (e.g. drain wire resistance) Specifies 10 to 22 pair twists/meter Specifies Jacket Resistance Specifies Connector design and requirements
• Registered cable see www.fieldbus.org Lay Length (1 twist)
4
Vietnam FF Seminar 18 Mar 2010
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
Vietnam FF Seminar 18 Mar 2010
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: – – – –
6
Capacitance Unbalance Impedance Conductor D.C. resistance … Vietnam FF Seminar 18 Mar 2010
Cable Selection
• First consult with local authority having Jurisdiction to ensure regulatory compliance • Selection Guide – – – –
7
Conductor Size Shielding Armor Jackets
Vietnam FF Seminar 18 Mar 2010
Cable Selection – Conductor Size • FF-844 specifies minimum AWG18 for Trunk and minimum AWG22 for Spurs • Note: “Type A” specifies “shielded twisted pair” and does not specify wire gauge • Note: “Type A” cable is also available as multi-pair Drain wire
Type A, multi-pair
Shield 8
Vietnam FF Seminar 18 Mar 2010
Cable Selection – Conductor Size • Common designs use AWG16 on trunk and AWG18 on Spurs • Several designs use multipair type A for Trunk wiring • Larger AWG (16, 14) provide: – Improved pull strength – Electrical benefits, such as: Less Voltage Drop
Longer Distance
9
Reduced Resistance
Greater Current Capacity
More Field Instruments Vietnam FF Seminar 18 Mar 2010
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
10
Vietnam FF Seminar 18 Mar 2010
Cable Selection – Armoring
• Interlock – Steel – Aluminum
• SWA (Steel Wire Armor) • Protective Metal Tapes: – Smooth or Corrugated (Steel, Copper, Aluminum)
11
Vietnam FF Seminar 18 Mar 2010
Cable Selection – Armoring
• Why use Armor? – – – – –
12
Rodent protection Physical integrity Direct burial Reduces cost of conduit Hazardous Locations
Vietnam FF Seminar 18 Mar 2010
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)
Note: PVC = Polyvinyl Chloride, CPE = Chlorinated Polyethylene, LSZH = Low Smoke Zero Halogen, HDPE = High Density Polyethylene, FEP = Fluorinated Ethylene Propylene
13
Vietnam FF Seminar 18 Mar 2010
Cable Installation
• Follow manufacturer’s recommendations – – – –
14
Bending radii: generally 10 to 12x cable diameter Maximum pulling tension Installation temperature Pulling lubricant selection
Vietnam FF Seminar 18 Mar 2010
Cable Installation Choose right size
Lessons learned: • Torque screwdriver • Wire end ferrules • Right (!) wire strippers
Harms wire strands
15
Vietnam FF Seminar 18 Mar 2010
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
16
Vietnam FF Seminar 18 Mar 2010
Post Installation Verification
• Follow FF Engineering Guide AG-181 – Procedure for installing and commissioning fieldbus segments – Use DMM for Resistance & Capacitance measurements (not mandatory) – Use Fieldbus Handheld tester to verify installation and operation
17
Vietnam FF Seminar 18 Mar 2010
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
18
Vietnam FF Seminar 18 Mar 2010
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 19
Vietnam FF Seminar 18 Mar 2010
www.fieldbus.org 20
Vietnam FF Seminar 18 Mar 2010
