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IEC PAS 62825:2013 – Fibre Optic Distributed Temperature Sensing
Methods of measurement and performance requirements for fibre optic distributed temperature sensing (DTS) systems
1. Principles of Distributed Fibre Optic Sensing
IEC PAS 62825:2013 specifies performance parameters, test methods, and requirements for fibre optic distributed temperature sensing (DTS) systems. Unlike conventional point sensors, distributed fibre optic sensing uses the entire fibre length as a continuous sensing element, enabling real-time temperature profiling from meters to tens of kilometers.
DTS systems operate on optical time-domain reflectometry combined with Raman scattering. Laser pulses launched into the sensing fibre generate temperature-dependent Raman backscatter (anti-Stokes component) analyzed to determine temperature at each point.
The standard covers Raman-based DTS and Brillouin-based distributed sensing systems for industrial process monitoring, pipeline leak detection, power cable monitoring, and fire detection.
2. Performance Parameters and Measurement Methods
| Parameter | Definition | Typical | Test Method |
|---|---|---|---|
| Temperature Resolution | Min detectable temperature change | ±0.1 to ±1.0 °C | Repeated measurements on constant-temperature section |
| Spatial Resolution | Min distance for distinguishable change | 0.5 m to 5 m | Step response hot/cold transition |
| Measurement Range | Max fibre length for specified performance | 1 km to 30 km | SNR at fibre end |
| Temperature Accuracy | Deviation from reference | ±0.5 to ±2.0 °C | Comparison with calibrated thermometer |
| Repeatability | Stability over time | ±0.2 °C | 24-hour consecutive measurements |
Performance parameters are interdependent: improving spatial resolution requires shorter pulses, reducing SNR and degrading temperature resolution.
3. Engineering Design Insights
Optical Design: 1550 nm lasers for long-range (lower attenuation), 1064 nm for short-to-medium range (better Raman efficiency).
Use GI 50/125 µm multimode fibre for Raman DTS and single-mode fibre for Brillouin systems. A 0.1 dB splice loss reduces range by ~1 km.
Calibration: DTS requires at least two known temperature zones. Incorporate a calibrated reference coil in the instrument or sensing cable.
4. Frequently Asked Questions
Q1: Difference between Raman and Brillouin?
Raman uses spontaneous scattering for temperature only. Brillouin uses stimulated scattering for simultaneous temperature and strain measurement.
Raman uses spontaneous scattering for temperature only. Brillouin uses stimulated scattering for simultaneous temperature and strain measurement.
Q2: Maximum measurement distance?
Raman: 2-15 km (multimode), up to 30 km (single-mode). Brillouin: 50-100 km.
Raman: 2-15 km (multimode), up to 30 km (single-mode). Brillouin: 50-100 km.
Q3: Can DTS detect temperature and strain?
Raman: temperature only. Brillouin: both, but requires techniques to separate the two effects.
Raman: temperature only. Brillouin: both, but requires techniques to separate the two effects.
Q4: How is spatial resolution defined?
The distance over which a 10 °C step transitions from 10% to 90% of final value. Typically 0.5-5 m.
The distance over which a 10 °C step transitions from 10% to 90% of final value. Typically 0.5-5 m.
