Instrumentation cable is a low-voltage cable specially used for transmitting weak measurement signals in industrial automation. Its main function is not to deliver high-power electric energy, but to ensure signal integrity and anti-interference. It connects field sensors, transmitters to DCS and PLC control systems.
Main Applications
It transmits 4-20mA analog current signals, millivolt-level temperature signals and digital discrete signals. It is widely used for pressure, flow, level and temperature transmitters, RTDs and thermocouple compensation circuits in chemical, power, oil & gas, pharmaceutical and other process industries. Rated voltage: typically 300/500V or 450/750V.
Typical Construction (from inner to outer)
- Conductor: high-purity copper. Solid copper for fixed installation, stranded flexible copper for moving applications; tinned copper for corrosive environments.
- Insulation: PE (low capacitance, preferred for long-distance signal transmission), PVC, LSZH, fluoropolymer, etc.
- Twisted pair: two conductors twisted together to counteract electromagnetic noise, the signature design of instrumentation cables.
- Shielding (critical part): aluminum foil, copper braid. Types include individual pair shield, overall shield, individual pair plus overall double shield. A drain wire is equipped for shield grounding.
- Sheath: PVC / LSZH / PE. Light blue sheath is normally used for intrinsically safe circuits in hazardous areas. Steel tape armouring is available for anti-crushing, anti-rodent or direct burial installation.
Difference from Ordinary Control Cable
- Instrumentation cable: prioritizes signal integrity, mostly twisted pair structure, focusing on shielding and low capacitance to avoid crosstalk, for low-level signals.
- Control cable: mainly for on-off control, common multi-core structure with optional shielding, applied to relay, contactor and other high-power switching circuits.
Common Types
- General twisted pair shielded instrumentation cable (KJYVP): widely used for 4-20mA loops.
- Intrinsically safe instrumentation cable (IA): for explosive hazardous areas, light blue sheath.
- Thermocouple extension / compensation cable & RTD cable: dedicated for temperature signal transmission.
- Armoured instrumentation cable: for cable tray or direct burial, resisting mechanical damage.
