Inductive loop detector

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The standard and simplest approach for counting cars on tarmac roads is an inductive loop. A loop consists of a rectangle of wire inserted into a groove cut in the tarmac and sealed over.

 The loop is activated only when a car is directly on top. The loop controller and data logger is usually installed in a metal equipment pillar or otherwise hidden nearby.
Preformed loops made of tough multicore wire can be used on gravel type roads.
Loops in gravel roads will still work with a few inches of tarmac added later. You can also put the loop under hot tarmac as it is being laid if you are lucky with timing your installation.
When laying the wire in the road, always allow some slack. This will prevent the wire from snapping due to changes in the road structure. Feeder cable for loops must be twisted pair cable – straight untwisted cables do not work. Cutting tarmac is a technical job using power tools and there are obvious health and safety implications.

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