instrumentation cables rev2
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Instrumentation - Cables
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Introduction to Instrumentation CablesUsed within industrial manufacturing plants for control, communication, data and voice transmission signals. These cables are used typically in industrial projects. They are used to connect electrical instrument circuits and provide communication services in and around process plants with detail signal transfer.
PurposeInstrumentation cables are multiple conductor cables that convey low energy electrical signals used for monitoring or controlling electrical power systems and their associated processes. Applicable Standards BS 5308 or EN 50288-7 Basic Design; IEC 60332-1 Flame Retardant; IEC 60332-3 Fire retardant (cat. C or A according to requirements); IEC 60754-1 Halogen free properties (only for LSZH cables) IEC 61034-2 Low smoke emission (only for LSZH cables)
Instrumentation Cables -Typical ConfigurationBS 5308Part list:1. Conductor 2. Insulation to conductor3. Individual Screening4. Overall Screening5. Bedding6. Armoring7. Sheath8. Drain wire9. Non hygroscopic Type 1Polyethylene insulated Un ArmoredPVC SheathedIndividually and collectively ScreenedPart 1Type 2Polyethylene insulatedArmored- Steel wireIndividually and collectively Screened
Type 1PVC insulatedUn ArmoredPVC SheathedIndividually and Collectively ScreenedType 2PVC insulatedArmored Steel wirePVC SheathedIndividually and collectively Screened
Part 2Screening:Collectively screened by a laminated, bonded aluminum/ polyester tape.Drain WiresThe metallic side of the screen are in contact with one or more tinned annealed copper drain wirePairTwo insulated conductors uniformly twisted together to form a pair with max. lay length of 100mm
Conductors For instrumentation cables conductors are generally plain annealed electrolytic copper wire for signal transmission or special alloy, for thermocouple /compensating cables. Conductors can generally be according to EN 60288: class 1 (U) Solid, class 2 (R ) stranded and class 5 (F) flexibleType of conductors are chosen according to electrical characteristics, required flexibility, type of connection systems or specific installation conditions, for example: Class1 solid conductor is preferable for permanent installation, crimping termination, In presence of vibration or movement or reduced bending radius is preferable class 5 flexible conductor, In presence of corrosive atmosphere, high temperature or to facilitate the soldering is preferable tinned conductor.
ConductorSize BS EN 60228
Bare or Tinned
Conductors Class 1, Class 2 and Class 5&6 Plain Or Metal coated annealed Wire Coatings:Applied on the conductors to prevent some insulations from attacking or adhering to copper. Also helps in soldering and prevents deterioration of copper at high temperaturesAnnealing:A process in which the conductor is heated to over 700 deg F and allowed to cool. This will allow conductors to bent without breaking, remove stiffness and improve flexibility.Bunch Strand (ASTM B-174)A conductor formed by simple twisting in one direction of many small wires. Used in flexible cords, flexible control cables and flexible lead wiresConcentric Strand ( ASTM B 8)A conductor is formed as a layer with 7,19,37,61 or 91 wires. Normally adjacent layers are reversed direction. Control cables favor 7 and 19 wires.Rope Lay Bunch Stranded members and Concentric stranded members (ASTM B-172&3)7 or 19 strands form a conductor. Used in portable power cables and welding cables
Insulation and JacketInsulation applied over conductors for electrical isolation between conductors or from groundJacket applied over conductor insulation or cable core for mechanical, chemical or electrical protection0102030405060708SizeElectricalPhysicalChemical ResistanceEnvironmental ConditionsService lifeReliabilityFlexibilityWall ThicknessCapacitance, Attenuation, velocity of propagation, Dielectric Strength, working voltage and Dielectric constantElongation, Tensile Strength, Temperature rating , Flexibility, Flammability, Resistance, Specific gravityChemicals can destroy cable materials.Extreme temperatures brittle at low and soft at high. Vaccum leaches oils out of cables. Radiation cause damage to cablesIdeal cable system should be engineered to last the life of the product in any environmentligula Ability of a cable to bend09Radiation resistance10Smoke Generation and Flame Resistance Ability of a cable to burn, construction dependent and industry standard applyIs based on the both durability and signal integrityRadiation index is the absorbed dose in Gray (Gy) of the material after exposure having 50% elongation of brake of its unaged value at least.
Insulation Working conditions need to be taken into consideration to choose the right insulation material.Material can be divided into thermoplastic and thermoset (cross linked). Thermoplastic material are more sensitive to high temperatures, as material melts at the increase of temperature, while thermoset, due to stable polymeric chain bonds are more resistant to temperature and deformation. Most popular insulations are PE and PVC for general installation conditions and LSZH thermoplastic materials (low smoke zero halogen). Other class includes, XLPE, silicone rubber, other rubbers such as EPR, HEPR, EVA. Special techno polymer can be used in case of specific installation condition, such as fluoro- polymer or techno-polymer materials.For fire resistant cables two types of insulation are used: silicone or mica tape plus XLPE (or other thermoset compounds).
InsulationType BS 6234/50363/7655
ScreeningElectrostatic noise can be reduced by screening around the cable, around each pair or bothMagnetic noise can be reduced by increasing distance between cable and offending power cable and screening the cable
Screening Cross-talk from adjacent pairs or triples; Interference induced by external source Aluminum /polyester tape with a tinned copper drain wire, the most popular construction. Aluminum /polyester or copper/polyester tapes normally have a total thickness from 25 to 100 m, according to standards and are wrapped with an overlap > 125% to assure a full coverage even in case of bending.Bare copper braid for electromagnetic interference or when the cable is subject to movements.Tinned copper braid for electromagnetic interference in presence of corrosive atmosphere or high temperature. Copper braid normally has a coverage from 80% to 95%. This type of screen presents a lower electrical resistance, a very good protection also to electromagnetic noises and a higher mechanical resistance compared to aluminum /polyester tape.
In continuous contact with metallic side there is a drain wire, normally tinned copper, 0.5 sq mm, stranded or solid. Screens can be applied to each pair/triples (individual screen) and/or on the bundle of the cable (overall screen).
Basic Design BS 5308 or EN 50288 - 7ArmoringMetallic armor are used when cables have to be installed direct buried, or if mechanical protection is required. Required tensile load Expected pressure on cable during service Protection against rodent Protection against accidental damage Minimum required bending radius.
SWA: Single layer of galvanized steel wires, with diameters according to relevant standards, coverage min. 90%. This armor assures a very good mechanical protection and tensile strength. An additional counter spiral tape increases solidity, if required.
GSWB: Galvanized steel wire braid, diameter of wire: 0.20 0.25 0.30 0.40 mm, with coverage of > 80%. It assures a good mechanical resistance, allowing a lower bending radius compared to other armor. It is preferable when there is movement or vibration. For special application is possible to use stainless steel, tinned copper or special alloy wires.
ArmoringDirectionBS EN 1027
GSTA: Galvanized steel tape armor, composed by two tapes with overlapped edge; thickness of each tape: 0.20 0.30 0.40 mm, according to cable diameter. It grants a coverage > 100%. Very good crush resistance, but fair tensile strength. Brass tape of minimum thickness 0.075 mm can be used for special applications.
GSFA: Galvanized steel flat armor. It is composed by flat wire of thickness 0.6 mm or 0.8 mm, it is similar to SWA, but with higher mechanical protection.
Sheath Many compounds can be used as internal/external protection of cables. Working condition need to be considered for the right choice. PVC, PE and LSZH are the most popular materials, but we have to consider that different grades are available to meet specific working conditions. Anyway the following conditions have to be evaluated:Type of installation (indoor/outdoor, direct buried)Possible presence of humidity, oil, chemicalsBehavior in case of a fire (fire propagation, fire resistance, emission of gases and smoke)Range of temperatureUV resistance in case of sun exposure
Basic Design BS 5308 or EN 50288 - 7ProtectionProtectionIn a