Technology: Fibre optics lie in wait to catch overburdened axles

日期:2019-02-28 06:10:12 作者:戴獯 阅读:

By MICK HAMER RESEARCHERS at the British government’s Transport and Road Research Laboratory in Berkshire hope to set up a burglar alarm on roads to catch overweight lorries. The researchers at the TRRL have already carried out trials with the burglar alarm – a fibre optic cable – buried in the M4 motorway at Theale in Berkshire. In six months some 6 million axles have unknowingly passed over this cable. As vehicles pass along the road surface, they cause the fibre optic cable to bend beneath its rubber cover. This reduces the amount of light reaching the far end of the cable. The loss of light is proportional to the weight of the axle. The trials are designed initially to distinguish cars from lorries, as part of the national traffic census. At present, vehicles passing over a conventional cable induce a current and a counter adds up the blips that the vehicles create. This method has two problems. The first is that the cable registers only the number of axles. A complex computer program then has to sort out the difference between a four-axle juggernaut and two cars close together. Secondly, the counting stops if the traffic slows to a crawl, because the technique depends on a quick change in pressure to register on the counter. The fibre optic cable has the advantage that it not only counts the axles, but also checks their weight, thus removing any possibility of confusing cars and lorries. And the axles register on the fibre optic cable at all speeds, from standstill upwards. The TRRL has just awarded the University of Liverpool a contract worth Pounds sterling 12 000 to develop the system. So far ithas asked the university to look at twotypes of fibre optic cables. One is the burglar alarm, which is made by Pilkington. The other system, made by Herga Electric based in East Anglia, is a pressure-sensitive fibre optic cable which is normally employed to open automatic doors. The researchers in Liverpool will concentrate on designing a detector that incorporates the fibre optic cable. The detector at Theale is housed under its rubber pad in a slot 22 millimetres deep; however the TRRL believes that this is not the best design to optimise the response of the fibre optic cable. The researchers will also examine the sort of movement which will produce the best results. The TRRL had the idea for this application after going round an electronics show. It is also keen to hear of other makers of pressure-sensitive fibre optics. If this development work is successful,