IEC 61757-1-4:2025

Overview

IEC 61757-1-4:2025 - "Fibre optic sensors - Part 1-4: Strain measurement - Distributed sensing based on Rayleigh scattering" defines terminology, structure and standardized measurement methods for distributed fibre optic sensors that perform absolute strain measurements using spectral correlation analysis of Rayleigh backscattering in single‑mode fibre. The standard covers distributed sensing over a measurement range from about 10 m to tens of km, applies to hybrid systems combining Brillouin and Rayleigh effects, and specifies key performance features and test procedures. It explicitly excludes point sensors and dynamic strain measurements.

Key Topics and Requirements

The document sets out standardized definitions, test setups and measurement procedures so manufacturers and testers can report consistent performance metrics for Rayleigh‑based distributed strain systems. Major technical topics include:

• Terminology and system structure for a Distributed Sensing System (DSS) and sensor topology.
• Performance parameters and test procedures, including:
  • Strain measurement error
  • Spatial resolution
  • Strain repeatability
  • Spatial strain uncertainty
  • Warm‑up time
  • System performance with altered attenuation (long‑distance and short‑distance/high‑loss scenarios)
  • Distance measurement range and measurement time
• General test setup requirements (single‑ended configurations, documentation) and procedures to calculate and report each parameter.
• Support for hybrid Brillouin–Rayleigh systems to optimise measurement quality.
• Informative annexes: Annex A lists relevant application areas; Annex B summarises the Rayleigh cross‑correlation measurement principle.

Keywords embedded: distributed strain measurement, Rayleigh scattering, single‑mode fibre, spectral correlation, spatial resolution, distance measurement range.

Practical Applications

While Annex A of the standard lists application areas, Rayleigh‑based distributed strain sensing is typically used where continuous spatial strain profiles are required over long distances, for example:

• structural health monitoring of bridges, tunnels and buildings
• pipeline and containment integrity monitoring
• geotechnical and landslide monitoring
• rail track and asset condition monitoring
• long‑range civil and industrial infrastructure surveillance

This standard helps ensure reliable comparison of product specifications and consistent field validation.

Who Should Use This Standard

• Sensor and interrogation unit manufacturers (product specification and verification)
• System integrators and commissioning teams (acceptance testing)
• Test and calibration laboratories (performance measurement)
• Asset owners and engineers (specification, procurement and compliance)

Related Standards

• IEC 61757 (generic fibre optic sensors)
• IEC 61757-1-2:2023 (Brillouin‑based distributed strain sensing)
• IEC 61757-2-2, IEC 61757-3-2 (related distributed measurement parts)
• ISO/IEC Guide 98-3 (GUM: uncertainty of measurement)

IEC 61757-1-4:2025 provides the standardized framework for specifying, testing and comparing Rayleigh‑based distributed fibre optic strain systems, enabling clearer procurement, certification and field deployment of long‑range distributed strain sensing solutions.