ISO 6859-1:1982

Overview

ISO 6859-1:1982, published by the International Organization for Standardization (ISO), specifies the general requirements for proximity switches in aircraft applications. These proximity switches are designed for use in nominal 28 V d.c. systems or 115/200 V, 400 Hz a.c. systems, consistent with the electrical characteristics set out in ISO 1540. The standard defines two classes of switches:

• Class 1: For use in unprotected positions on aircraft, exposed to harsher environmental conditions.
• Class 2: Intended for less arduous environments, offering flexibility for more protected installations.

This standard addresses both the construction and performance requirements needed to ensure reliable operation of proximity switches in demanding aerospace settings.

Key Topics

Classification and Use

• Class 1 switches are suitable for exposed, harsh conditions on aircraft, such as landing gear or control surfaces, where durability is critical.
• Class 2 switches are used in less severe environments, possibly inside compartments or protected zones.

General Requirements

• Compliance with electrical system voltages and frequencies as specified in ISO 1540.
• Performance under varied environmental factors such as temperature, pressure, humidity, vibration, and exposure to contaminants.
• Clear marking and identification for ease of installation, maintenance, and replacement.
• Mechanical strength and robust earth bonding of both sensors and targets to withstand operational loads.

Design and Testing

• Design must account for mounting orientation, target speeds, and ease of alignment.
• Suppliers must declare limitations, especially regarding magnetic influence or cable lengths.
• Proximity switch systems are subject to thorough testing and quality assurance protocols, including production, type, and serviceability tests.

Electrical and Mechanical Ratings

• Declare and test for overtravel, differential travel, and precise operating positions.
• Compliance with tests for insulation resistance, voltage drop, overloads, short circuit protection, and resilience to environmental stressors like icing and fluid contamination.

Applications

Proximity switches in accordance with ISO 6859-1 are essential components in:

• Aircraft landing gear and door position detection
• Flight control surface actuation monitoring
• Cargo bay and hatch security systems
• General aircraft equipment sensing applications

Their robust construction and adherence to strict operational and environmental requirements make them suitable for critical safety and control applications in both civil and military aircraft. The differentiation between Class 1 and Class 2 ensures that the correct switch type can be selected based on the exposure and reliability needed.

Related Standards

Implementing ISO 6859-1 often requires consideration of other international aerospace standards, including:

• ISO 1540: Aerospace - Characteristics of aircraft electrical systems
  (Specifies foundational system properties for electrical equipment compatibility.)
• ISO 2653: Environmental tests for aircraft equipment - Ice formation
• ISO 2669, ISO 2678, ISO 2683: Environmental tests covering acceleration, insulation resistance, and explosion proofness
• ISO 2859: Sampling procedures and tables for inspection by attributes
• ISO 7137: Aircraft - Environmental conditions and test procedures for airborne equipment
• ISO 1467: Performance requirements for circuit breakers in aircraft systems

These standards ensure a harmonized approach to equipment compatibility, durability, and safety throughout the aviation industry.

ISO 6859-1:1982 provides a critical framework for the durability, safety, and performance of proximity switches in aviation, supporting the reliability and efficiency of aircraft systems worldwide. For organizations in the aerospace sector, adherence to this standard enhances operational safety and mitigates the risks associated with equipment failure in demanding flight environments.