The loop placed under the road surface, usually in a rectangular shape, at a depth of around 50mm. This keeps it out of view and reduces the likelihood of anything going wrong. It is then connected to a loop extension cable, often using an M12 connector, which joins up with the actual loop detectors.
A magnetic field runs from the loop to the detector and if no traffic is present this remains at the same frequency. The detector monitors the frequency and if a vehicle passes over it will change the frequency. This causes the relay to close and triggers the reaction — for example, it opens a gate or changes the traffic lights. Once the vehicle has gone past, the relay will open again, closing the gate or changing the lights back again.
The loops can be purchased pre-assembled, allowing them to be easily fitted into the required position. They come in a number of different sizes, making them suitable for a range of applications.
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