Loop Design Essentials /Loop wire/ Loop detector installation

Loop Design Essentials /Loop wire/ Loop detector installation

Proper installation of the loops is essential for reliable vehicle detection. Most vehicle detector problems are caused by improper loop installation! „ The geometry (shape and size) of the loop defines the detection zone. See the figures to the follow for typical loop geometries used for access or traffic control. „ Loop sizes may differ and will depend on lane width, traffic patterns, and types of vehicles to be detected. The following guidelines are typically used today with most access control applications: ƒ Large rectangular loops (4’ x 8’, 6’ x 8’, 6’ x 12’ are used to detect larger vehicles and high bed vehicles (trucks). ƒ Small size loops (i.e. 2’ x 5’, 3’ x 6’, 6’ x 6’) are used to detect smaller vehicles, such as motorcycles and automobiles. Important Note: Typical detection height is about 2/3 of the shortest leg of the loop.

Adjacent loops operating on separate vehicle detectors may interfere (cross-talk) with each other. This interference can be eliminated by changing the operating frequency on one of the detector modules. Note: The Eberle Design LMA DEFLECTOMETER Series detectors offer a built-in frequency meter. Upon power up or reset, the detector flashes the frequency on the front panel 7-segment LED (in kilohertz) in order to accurately separate detectors from cross-talking. Typically you want two adjacent detector loops to be separated by at least 5 kilohertz. „ The vehicle detector must operate from a stable power source. If the detector is subjected to excessive line voltage variations, the detector may cause either a false output or may drop an output when a vehicle is over the loop. An example would be a gate operator located some distance from the power distribution panel. If the line power wires are undersized, the voltage at the operator can momentarily drop, due to the inrush current when the operator motor is activated. The detector senses a voltage drop of more than 25% of nominal line voltage as a power failure. When the voltage returns to the proper level, the detector automatically resets. If a vehicle is over the loop, it will be lost when the detector resets. THE GOOD NEWS! All EDI vehicle detectors have a built-in SAFE GUARD for short interruptions of power. If POWER is interrupted for 4 seconds or less the detector will not drop a CALL with a vehicle on the loop.

Adjacent loops operating on separate vehicle detectors may interfere (cross-talk) with each other. This interference can be eliminated by changing the operating frequency on one of the detector modules. Note: The Eberle Design LMA DEFLECTOMETER Series detectors offer a built-in frequency meter. Upon power up or reset, the detector flashes the frequency on the front panel 7-segment LED (in kilohertz) in order to accurately separate detectors from cross-talking. Typically you want two adjacent detector loops to be separated by at least 5 kilohertz.

The vehicle detector must operate from a stable power source. If the detector is subjected to excessive line voltage variations, the detector may cause either a false output or may drop an output when a vehicle is over the loop. An example would be a gate operator located some distance from the power distribution panel. If the line power wires are undersized, the voltage at the operator can momentarily drop, due to the inrush current when the operator motor is activated. The detector senses a voltage drop of more than 25% of nominal line voltage as a power failure. When the voltage returns to the proper level, the detector automatically resets. If a vehicle is over the loop, it will be lost when the detector resets. THE GOOD NEWS! All vehicle detectors have a built-in SAFE GUARD for short interruptions of power. If POWER is interrupted for 4 seconds or less the detector will not drop a CALL with a vehicle on the loop.

The correlation between the loop perimeter and the typical number of turns for loop wire in a single loop installation varies. Please review some examples in the diagram at right. „ To receive detailed information on optimizing your loop installation (i.e. inductance of the loop, total inductance of the loop network, height of detection, loop efficiency, and number of turns of wire), 

Loop Perimeter (LP) Side A+B+C+D = LP	Number of Turns
12 Feet (2 x 4 Loop)	5 turns
24 Feet (6 x 6 Loop)	3turns
32 Feet (6 x 10 Loop)	3turns
52 Feet (6 x 20 Loop)	2turns
112 Feet (6 x 50)	1turns