Sensors help to find leaves on the line

Electrical measurement specialist LEM has developed a system that could help to alleviate the disruption caused to Britain`s railways every year by "leaves on the line".

One of the problems caused by autumn leaves landing on the UK`s railways tracks is that they can cause trains to become "lost". Individual trains usually relay their position to a control room by short-circuiting the left and right rails via their axles. This tells the controllers which section of track the train is on.

However, during the autumn, the train wheels compress the falling leaves into a mulch which increases the electrical resistance between the two rails eventually insulating the axle. When this happens, the train disappears from the controller`s network map. The "invisible" train becomes an extreme safety hazard.

LEM`s system monitors the conductivity between the two rails and transmits the information to central computers. This allows the build-up of mulch to be monitored and "leaf-busting" trains to be directed to the sections most at risk.

Neil Hayden, LEM`s UK business development manager, is reluctant to divulge too many details of the sensing technology being used, but says it is a hybrid technology based on "a development of the DC current transformer".

At present, the technology can resolve current changes as small as 1mA in a 50A range. Eventually, LEM hopes to boost this operating range to 100A or even 1,000A while maintaining a 1mA resolution. Hayden points out that this could be useful in other applications such as monitoring car electrics where peak starter currents can exceed 600A but the electronic engine management systems may draw currents measured in milliamps.

The leaf monitoring system is being tested at present in the Woking area of Surrey and is expected to go commercial early in 2001.