Instrument Cable - Complete Guidelines

● Dimensions of the conductor cross-section. In order to decide the size of the conductor, the working voltage and current, cable length and reliability of the instrument are required as these would lead to the voltage drop through the cable. The instrument cable manufacturer sizes the cable and guarantees the system operates correctly at given stress at the end of the cable.

● The material of the conductor, which is widely used is copper. Coated copper can also be chosen to remove copper oxides that are more stable and resistant to corrosion.

● Conductor construction, whether sturdy, stretched, versatile. The stranded conductor is not one but consists of a variety of smaller conductors providing greater flexibility.

The instrument cable comprises, in general, the conductive, the padding, the screen/shield, armour, and the outer jacket. However the instrument cable specification for each project may vary and the following information shall be assessed on the basis of the event, therefore the specifics mentioned herein are not to be copied or used directly.

Different criteria are added to the isolation material choice: electrical transmitting properties, minimum and maximum temperature, burning behaviour, abrasion and corrosion resistance.

Determined by the necessity of voltage rating and cable strength are the collection of the thickness of insulation, along with the driver specification. Please notice that the thickness of insulation also makes the cable flexible.

The screen is made of aluminium foil/tape of polyester to protect against external interference. The aluminium tape is spirally wrapped with a 25% overlap to ensure 100% cable coverage in the bending region, too. The screen is also made of an electrically contacted copper-drain wire along the cable with the screen.

The selection of cable armour depends primarily on cable assembly and mechanical characteristics such as maximal tensile charges, pressure loads, rodent protection, limited bending radius, installation of the direct burial device. There are different types of cables such as galvanised steel wire tissue, galvanised steel wire tapes and galvanised round armour with benefits over each other.

For the following consideration, the material of the outer cable sheath/jacket is selected:

● State of the environment (humidity, temperature, solar radiation)

● The installation process (indoor, outdoor, buried directly, on trays, etc.

● Gas, chemical spills or abrasion possibilities

● Fire behaviour (low smoke, zero halogens to avoid toxicant)

● Fire suppressant or fireproof

Future extension and repair shall be considered for deciding the amount of wire in the multipair or Multicore cable.

In order to reduce the interfering effect, the twisted pair is defined in the 4-20mA analogue signal cable. Twisted wire shall have at least six crossovers per foot, as indicated by the API 552 Transmission Method. A regular feature is eight crossovers per foot. There are various instrument cable exporters who deal in all kinds of cables.