Automatic Sliding Gates: How Loop Detectors Work

Automatic sliding gates are extremely convenient when they are installed in front of your house. They are usually positioned right in front of the drive way and may be connected to an intercom machine so that an approaching car may have to be buzzed in. The simple automatic sliding gates, however, open up as they sense a car approaching. These sliding gates are also seen in shops and malls when an approaching body causes the gates to automatically open up.

What Is the Technology Used?

There is nothing magical about the way an electric gate slides when it detects an approaching body or an object. There are different kinds of technologies that can detect the presence of a body. However, the simplest and most common technique is a loop detector. This loop detector is a small gadget that has an inductive loop, or a coil of wire, which is embedded in the surface of the flooring.

What Is a Loop Detector?

These inductive loops that form the loop detectors work by detecting whenever there is a change in the inductance. The process is simple. The wires that are planted are coiled into an electrical circuit. This coiled wire is known as an inductor. The electrical circuit is a simple one and is usually operated by an AC/DC outlet. This inductor in fact works as an electromagnet. This means that when current is passed through the coil, it takes on magnetic properties.

When the current is passed through the coil, the coil tries to build up a magnetic field; however, the coil also simultaneously resists the flow of current through it, not allowing the magnetic filed to build normally. The current can only pass through the coil normally when a magnetic field is built. The number of coils in the inductor and the core, or the material, around which the coil is wrapped, determines the capacity of the inductor. If the coil has an iron core, then the inductor has a larger inductance that can overcome the resistance of the current by the wire, thus completing the circuit.

How Do Loop Detectors Work?

Normally for an automatic gate, a coil of wire, which is about 4 to 5 feet in diameter and which has about 6 to 8 loops, is placed under the floor or the road. On the floor or the road, grooves are cut and the wire is placed into these groves. When a body or a car passes over this wire, the body or the car becomes the core of the loops magnetic field and the inductance of the coil is suddenly changed due to the presence of this new body. The sensors in the sliding gate are built to track the changes in the inductance of the coil. As the inductance increases, the sensors cause the circuit to complete and the automatic gate rolls open to welcome you inside.