Overview
ISO 8056-1:1985 defines the design requirements and test methods for conductors used in aircraft thermocouple extension cables made from nickel‑chromium (Ni‑Cr) and nickel‑aluminium (Ni‑Al) alloys. It applies to conductors installed in aircraft temperature indicator and control systems and includes annexed methods for determining the thermo‑e.m.f. of conductor wires against platinum.
Key topics and requirements
- Conductor materials: Conductors must be bright, annealed nickel‑chromium (non‑magnetic, positive conductor) and bright, annealed nickel‑aluminium (magnetic, negative conductor).
- Construction: Positive and negative conductors are stranded wires; joints in single wires may be welded, brazed or silver‑soldered, but the completed conductor must not be joined. Conductors must be free from kinks, broken wires or other irregularities.
- Dimensional and mechanical allowance: A maximum increase in length of 4% due to stranding is assumed for design calculations.
- Thermo‑electric performance: Thermo‑e.m.f. characteristics of wires and finished conductors against platinum are specified over the relevant temperature range; tables in the standard give required characteristic limits and assumed DC resistances.
- Testing methods:
- Thermo‑electric tests on individual wires and finished conductors (annex methods).
- Magnetic significance checks (Ni‑Cr non‑magnetic; Ni‑Al magnetic).
- DC resistance tests on finished cable lengths at 20 °C ±1 °C using a suitable bridge (IEC Publication 564) of accuracy class ≤0.5.
- Annex test procedures: Two precise e.m.f. measurement methods are described:
- Direct comparison against platinum (A.1) - sampling, junction formation, reference at 0 ±0.1 °C, measurement uncertainty ~±0.02 mV.
- Differential method using a traceable substandard (A.2) - measurement uncertainty ~±0.03 mV.
- Test precautions: Requirements for isothermal media, immersion depth (≥80 mm), thermometer traceability (IPTS‑68), prevention of electrical contact, and thermal gradients.
Applications and users
ISO 8056-1:1985 is intended for:
- Aircraft cable and wire manufacturers designing and qualifying thermocouple extension cables.
- Avionics/aircraft systems engineers specifying wiring for temperature indicator and control systems.
- Quality, test laboratories and maintenance engineers performing acceptance or traceability testing on thermocouple conductors.
- Regulatory and certification organizations ensuring wiring meets established thermo‑electric and resistance performance for aviation use.
Keywords: ISO 8056-1:1985, aircraft thermocouple extension cables, nickel‑chromium conductors, nickel‑aluminium conductors, thermo‑e.m.f. testing, conductor resistance tests, aviation wiring standards.
Related standards
- IEC Publication 564 - D.C. bridges for measuring resistance (referenced for resistance testing).
- IPTS 68 - International Practical Temperature Scale of 1968 (temperature traceability).
- ISO/TC 20 - technical committee responsible for aircraft and space vehicle standards.
Open preview (PDF)Aircraft — Nickel-chromium and nickel-aluminium thermocouple extension cables — Part 1: Conductors — General requirements and tests
