What is Instrumentation cable?
Instrumentation cables are used to transmit and receive control system, analogue and digital signals to and from sensors and equipment.
Most of these cables operate at 24 to 110 v voltage levels and/or 4-20 mA current ratings. Instrumentation cables should be isolated from external electrical interferences.
Instrumentation cable should not install in the same tray where the power line is installed, or a minimum of 30cm distance should maintain.
Conductor in Instrumentation cable:
Stranded copper or aluminium. Copper is more dense and heavier than aluminium, but more conductive. Aluminium conductors that are electrically equivalent have a cross-sectional area about 1.6 times larger than copper but are half the weight.
Annealing - Annealing is the process by which the conductor material is gradually heated and cooled to make it more malleable and less brittle.
Coating - Copper conductor surface coating (e.g. tin, nickel, silver, lead alloy) is common to prevent isolation from attacking or adhering to the copper conductor and to prevent copper deterioration at high temperatures. In the past, tin coatings have been used to protect against corrosion from rubber insulation containing traces of the sulfur used in the vulcanization process.
Insulation:
Commonly thermoplastic(eg. PVC) or thermosetting(eg. EPR, XLPE) type materials are used. Insulated conductors are bundled in groups.
Individual Screen:
Occasionally an individual screen is applied over each bundle of insulated conductors for noise / radiation shielding and interference from other bundles of conductors. Metallic (copper, aluminum) or semi - metallic (PETP / Al) tape or braid screens are usually used.
Drain Wire:
Each screen has an associated drain wire, which assists in the termination of the screen.
Overall Screen:
An overall screen is applied across all bundles of insulated conductors for noise / radiation shielding, interference from other cables and protection against surge / lightning. Metallic (copper, aluminum) or semi - metallic (PETP / Al) tape or braid screens are usually used.
Armour:
To protect the conductor bundle mechanically. Usually steel wire armor or braid is used. Galvanizing or galvanizing is used to prevent rust. Also used is the bronze phosphorus or tinned copper braid when steel armor is not allowed.
Outer Sheath:
Outer sheath comes over the armour for overall mechanical. Typically a thermoplastic (eg. PVC) or thermosetting(eg. CSP) compound, and often the same material as the bedding.
Outer sheath is normally colour coded to differentiate between LV, HV and instrumentation cables. Manufacturer’s markings and length markings are also printed on the outer sheath