Fiber optic vibration sensing is often referred to as Distributed Acoustic Sensing (DAS).
It is a technology that uses the properties of light combined with the material properties of fibre optic cables to measure acoustic vibrations along the cable length. This allows for the continuous monitoring of long lengths of fiber optic cable listening for a variety of events. For railways applications, such events include rockfalls, landslides, track trespass and of course the vibrations a passing train generates.
DAS works by injecting a short pulse of light into the fiber optic cable. As the pulse of light travels down the fiber, it is scattered by tiny imperfections in the fiber. Many of these imperfections are caused by a strain of the fiber, i.e., movement of it. Even extremely small fibre movements such as those caused by acoustic vibrations cause the scattered light signals to change.
The scattered light is collected by a sensor at the same end of the fiber where light was injected. The sensor measures the time it takes for the scattered light to return, which is used to determine the distance from the sensor to the imperfection that caused the scattering.
By measuring the time taken for scattered light to return from the multiple imperfections along the length of the fiber, it is possible to create a fingerprint of the acoustic signature along the fiber, a digital twin / SonicTwin®. This acoustic fingerprint can be used to detect and monitor a variety of events, such as:
DAS has several advantages over traditional sensing methods that rely on point sensor.
Whilst DAS is a relatively new and innovative technology for the rail sector, it is well established in both securing and monitoring long linear assets such as borders, pipelines, and cable networks. It can revolutionise the way railways are operated and maintained by providing continuous monitoring of railway assets even in remote locations – something that is not traditionally achievable.
Distributed Acoustic Sensing has the potential to both improve railroad safety and reduce railway maintenance costs enabling a more efficient railway.
This article was originally published by Sensonic.
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