When you're driving in your car, and a gate automatically opens for you, you probably have a loop detector traffic to thank. This humble underground magnetic coil senses the metal in your car, triggering an electromagnetic impulse in the gate opener. You're coming through the gates as the VIP you deserve.
How to get in the loop?
If a loop detector traffic is part of the overall plan for a new home or business, the construction team digs a trench one to six inches deep and installs a preformed loop before placing concrete or asphalt. The loop is secured to the rebar before the concrete is poured.
How does it work?
The loop detector traffic plugs into the gate operator's main circuit board. The loop, a non-stop size of wire, resonates at a normal frequency. But the frequency increases when something large and metallic is rotating on the loop. Once this change is detected, a relay that is normally open will close and remain closed until the car is stopped. This same concept is used for other purposes, including traffic lights and intercom systems.
Generally, a loop can sense a vehicle that is about two-thirds as high above the shortest leg of the loop. For example, a five-foot loop can detect a large piece of metal about three and a third feet up. So if you have a lot of monster trucks or other high-bed vehicles coming to visit, you'll need a bigger loop.
Where do you put the loop?
Loop detector traffic systems must be properly maintained. Usually, they are designed to locate the front axle of a vehicle. If you have a speaker attached to a post, have an intercom system at the entrance gate of your mansion, or operate a fast food drive-thru, place your loop no more than two feet from the speaker post. The long axis of the loop should run perpendicular to the traffic lane.
SUVs can botch this equation. Firstly, because they are much taller, and secondly, because the wide bend radius means the SUV can move too far from the speaker post for accurate loop detection.
What are the other types of loops?
Loop detector traffic isn't just for entrances. Exit loops, usually placed about twenty yards from the gate, trigger the gate to open when someone leaves your property. Safety loops set off a gate to reopen when they feel an obstruction.
Shadow loops monitor the swing path of the gate, making sure any vehicles are off the road before allowing the gate to close. This is important because a 12-foot swing gate has a 20-foot area that your basic loop detector cannot detect. Inductive loops used for traffic signal operation are of three types and are described below.
Pre-Time Signals: Such signals have fixed cycle lengths regardless of the traffic flow along the arms.
Active signal: Based on the actual traffic length, the loop detectors will determine the cycle length for the signal.
Semi-active signal: This type of signal is a combination of actuated and pre-timed signals where mainstream traffic will have a fixed cycle length and actuated signals for oncoming traffic at cross streets.
Hope the blog will give you enough knowledge about inductive loop detectors and their associated features.
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