FAQs

Benfits of OTDR technology

In both the sensing and telecommunications industries two types of technologies are used for distributed sensing and for checking the quality/health of the fibre optic. These two technologies are known as OTDR (Optical Time Domain Reflectometry) and OFDR (Optical Frequency Domain Reflectometry).

Within the telecommunications industry OTDR is the main technology utilised. The same trend is following within the distributed sensing industry and the majority of DTS (Distributed Temperature Sensors) including Sensornet are OTDR based.

The reason OTDR has come to prominence both for telecoms equipment and within distributed temperature sensing is that OTDR offers a number of technical benefits.

  • Robustness of Measurement

For distributed temperature measurements the OTDR is a robust measurement and is less affected by potential anomalies within the fibre and accessories (e.g. bends, connectors, reflections).

  • Range

The Sensornet Distributed Temperature Sensing technology based on OTDR currently measures along sensing cables of distances greater than 30km.

  • Temperature Resolution

OTDR based Distributed Temperature Sensors are able to resolve temperature changes down to 0.01°C.

  • Measurement Parameters

OTDR is a more versatile technology for distributed sensing and it is possible to measure both distributed temperature and distributed strain.

  • Laser Safety

The majority of the OTDR distributed temperature sensing systems are classified as 1M units. (The laser safety classification of all DTS units must be clearly marked on the outside). The implication is that this is safe under all reasonable working conditions and the majority of OTDR DTS systems are safe for use in hazardous zone ratings and comply with EU regulations EUR16011EN (1994).

OTDR Principle of Measurement

OTDR was developed more than 20 years ago and has become the industry standard for telecom loss measurements which detects the - compared to Raman signal very dominant - Rayleigh backscattering signals. The principle for OTDR is quite simple and is very similar to the time of flight measurement used for radar. Essentially a narrow laser pulse generated either by semiconductor or solid state lasers is sent into the fibre and the backscattered light is analysed. From the time it takes the backscattered light to return to the detection unit it is possible to locate the location of the temperature event.

Sensornet therefore highly recommends OTDR technology due its all-round technical superiority.


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