02.05.16
Testing rail assets with video software
Source: RTM Apr/May 16
At Infrarail this year, Matthew Lock of Korec presented information on a new measurement tool that is delivering information to track engineers. Dr Paul Waterfall, product manager at Imetrum, manufacturer of this technology, explains how this is done.
The first use of video measurement in rail was at Tacoma Narrows Bridge in 1940, but the technique has only taken off in the last decade – due to a combination of increasing monitoring requirements and advances in digital technologies. The potential for understanding train/track interaction was recognised by Bowness et al. back in 2007, but has mostly been advanced by Imetrum since 2010.
A video gauge has the potential to be a useful tool for assessing a number of important parameters for the rail and trackbed engineer, including:
- Dynamic deflection for ride quality (and subsequent speed limits)
- Detailed investigation at switches and crossings
- Monitoring during construction.
- Track stiffness
All of these are possible by measuring deflection, rotation and strain from a point of safety, several metres from track. Imetrum’s Dynamic Monitoring Station (DMS) allows the measurement of multiple points simultaneously in two or three dimensions, using cameras running at over 100Hz, all from a position of safety. It provides the opportunity for quick, cheap and accurate dynamic displacement information.
Benchmarking
Whilst the concept is appealing, being able to demonstrate that capability reliably takes time and effort. Since 2010, Imetrum has been working with several stakeholders in the rail industry to demonstrate, benchmark and advance the technique.
This started with a proof-of-concept on a local preserved railway, but has also included work on many live track locations, including the West Coast Main Line, and at the Rail Alliance test facility at Long Marsden.
To date, the technique has been used on rail track in the UK, the Netherlands, the USA and Australia, both for outputting live data, and for recording images for off-line analysis.
Example project: High Speed Line
For this test, the camera was positioned on an embankment, just over 7m from the track, with a lens zoomed in on a couple of sleepers.
Site conditions on this occasion were wet, with rain falling throughout the test. The site was chosen as it was to undergo ground stabilisation works, and was therefore known to have relatively large amounts of train-induced movement.
Figure 1
As can be seen in Figure 1 (above), vertical and horizontal displacements were successfully achieved on track, sleeper, clips and ballast, during the passage of a high speed train at 90mph. It was even possible to track displacement of an individual stone forming part of the ballast between the rails – zero values were reported when a wheel was blocking the view, but it was tracked immediately afterwards.
Four load events were recorded – two on the far track and two on the near track. Average resolutions for this zoomed-in view were just over 0.01mm, with data output live – a useful feature enabling track engineers to make a quick assessment of safe running speeds when a problem is first reported, or after track renewal.
Whilst this data was particularly zoomed-in, other tests have shown resolutions of 0.1mm for a 10m length of track.
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