With the nation adopting modern technology in every sphere the instrumentation cables are in increasing demand and are supplied as tailor made items. The interfacing and connection of most data transmission equipment can be effected using either coaxial cable, screened or unscreened twisted pair cables. For microcomputers, which use low speed data tramsmission over short distances, unscreened multicore or multipair cables can be used. For the interconnection of data processor, instruments and microcomputers where signal interface is a consideration, cables are generally screened. Minicomputers require medium speed data transmission and for these, interfaces with screen twisted pair cables are suitable. When signal speed are fairly low a braid screen is sufficient but for higher speeds a foiled screen or composite foil and braid screen is more suitable. A further refinement is to use individually screened pairs to minimize the effect of cross talk, thus making possible the transmission of data over long distances.
Instrumentation Cables have following components : -

Conductor material is Copper. It may be bare or tin coated to minimize oxidation and facilitate soldering. Conductors may be stranded or solid type. For higher cross section generally stranded type construction is preffered.

Insulation material depends upon the electrical and mechanical properties desired and the environments. The most common material are Polyethylene and PVC.

Shields is provided to prevent harmful electrostatic interface. These are three basic reasons for providing an electrostatic shield in a cable. The first, and the most common, reason concerns the need to keep external electrical disturbances from affecting the signal in the cable. The second reason is to prevent the signal in the cable from being detectable at location other than at the cable ends. The third reason is the combination of the first two. It is the elimination of unwanted transfer of signals between circuits in the same cable, commonly called cross talk.
Two types of shields as given below are commonly used :

Braided shields are reasonably flexible, quite durable and offer a good balance of shielding properties. The drawbacks in a braided shields are difficulty in terminating higher cable dimensions and cost. The practical limits of coverage is approach 96%.

It consists of a laminate of rolled aluminium foil, which is bonded with a high strength adhesive to the mylar film. The tape is applied spirally of longitudinally and provides total (100%) electrostatic shielding. An uninsulated conductor, drain wire is provided in intimate contact with aluminium side of the tape for the ease of shielded termination. The drain wire may be of solid tinned copper or stranded tinned copper and serves triple purpose.

(i) Provides easy and suitable grounding of the mylaraluminium shield.

(ii) Acts as conductors in relay, control of annunciator circuits.

(iii) Drains the accumulated static charges from the mylaraluminium shield to ground.

PVC compound is generally used for sheathing purpose. It may have additional fire retardant(FR) or fire retardant low smoke (FRLS) properties. Polyethylene sheath is recommended for low temparature application and aromatic hydrocarbon surrounding. However, polyethylene sheath does not have flame retarding properties.

Armouring is provided for mechanical protection and may be either of galvanized round steel wire or galvanized flat steel strips.

BS - 5308 ( Part - 1 & 2 ), VDE 0815, IS - 1554 ( Part - 1 ), in general and customers specifications.