Earlier this year I wrote an article about Vehicle Detector Loops Used in Lieu Of Roundabout At School. In the blog post I explained how these loops are able to detect traffic and then cause an output to open or close gates, control traffic lights or even signal a homeowner that someone is entering their premises.
Here’s a further explanation of how vehicle loop detectors work. The image is courtesy of Nice/HySecurity, a leading supplier to ECI.
An in-ground, coiled wire, closed-loop system is installed in the pavement (before or after laying) and attached to the vehicle detector. The powered detector sends a small amount of AC current through this loop. The current creates an inductance field in the loop.
The Vehicle Loop Detector Senses a Vehicle and Activates a Relay Output
An element within the vehicle detector measures the frequency of the inductance field. When a vehicle passes though a properly installed and active field, there is a disruptive drop in the measured inductance. The detector senses the drop and triggers an output like a relay to the vehicle access control system to control barrier gates, for instance.
Facility surveys should also be conducted to determine the type of traffic (i.e. cars, motorcycles, large trucks, etc.) so the proper detector is selected and settings adjusted accordingly. As pictured above, the top image indicates a high bed truck where the dimensions of the loop were too small and thus the detector was unable to sense the truck moving above it. The lower image shows a correctly set loop able to properly sense the passenger vehicle.
Care should also be taken by owners and managers with regard to placement of other electricity conducting metallic equipment. If placed too near the closed loop it can change the frequency and affect a reading.
As always, proper design applications, installation techniques and correct device locations are all required for a vehicle loop detector system to operate properly. For more information regarding vehicle loop detectors and other vehicular access control devices, call the experts, ECI today at 847.949.0134, or click below for contact information or an easy form to contact us.