The VLX range of high intensity line lights has proven to be a successful illumination source for automated rail inspection applications.

With light intensity orders of magnitude higher than conventional LED line light technology, the VLX lights provide an extremely powerful focussed line of light at the subject. For rail inspection, the VLX lights can be installed within 400-600mm away from the track and still provide sufficient light for high speed imaging of the rail track assembly.

The VLX lights are typically mounted on the underside of the rolling stock along with a high speed line scan camera. The following image illustrates the installation.

For this application the lights were VLX1-400-LWD-RED. 400mm long line lights, RED (627nm) with long working distance optics. The working distance is around 500mm. The line scan camera was running at 68k.

The image to the left is a sample of the image acquisition. This was acquired at a speed of 120 kph. The customers system is designed to operate at a maximum train speed of 240 kph.

For this application one key area the customer is interested in is missing fixings and ties that hold the rail in place. Below we can see one area where the tie is missing at the point where the two tracks butt together.

In this application, the light was not fully optimised, which is the next step the customer will be undertaking. Using the profile control feature of the VLX lights, the light can be ‘tuned’ along its length so that the top of the rail profile has less light on it than the area where the sleepers and aggregate are located, which is also at a longer working distance.

With the VLX1 lights each segment of 33mm has its own individual intensity control. For an application such as this rail inspection, it is possible to reduce the light intensity at the middle sections allowing the track head to be imaged as well.

The lighting profile control is illustrated by the plot of light intensity versus light length. Here the light output at the middle of the light is reduced significantly to compensate for the rail track, which will allow for imaging the track in far more detail.