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Table of Contents



Loops and Loop Detectors
Information Manual
LOOP INFO REV G, 3/02
Copyright 2001 DoorKing, Inc. All rights reserved.
DoorKing, Inc.
120 Glasgow Avenue
Inglewood, California 90301
U.S.A.
Phone: 310-645-0023
Fax: 310-641-1586
www.doorking.com
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Table of Contents


INTRODUCTION
The
Underground
Loop ........................................................................................................................ 5

The Lead-In Cable ............................................................................................................................... 5
The
Loop
Detector ............................................................................................................................... 5
Design
Facts........................................................................................................................................ 6

HOW THE LOOP SYSTEM WORKS
Field
of
Sensitivity ................................................................................................................................ 9
Height
of
Detection .............................................................................................................................. 9
Loop
Phasing ....................................................................................................................................... 10

Field Cancellation Effect ...................................................................................................................... 10
Field
Enhancement
Effect .................................................................................................................... 11
Phasing
Loops ..................................................................................................................................... 11

LOOP INSTALLATION GUIDELINES
Saw
Cut
Guidelines.............................................................................................................................. 13
Preformed
Loop
Guidelines.................................................................................................................. 14

TYPICAL LOOP LAYOUTS
Slide
Gates .......................................................................................................................................... 15
Swing
Gates......................................................................................................................................... 16

TROUBLE SHOOTING LOOP SYSTEMS
Loop
Diagnostics ................................................................................................................................. 17
Poor
Connections ................................................................................................................................ 17
Shorted
Loop
Wire ............................................................................................................................... 17
Detector
Adjustments........................................................................................................................... 17

DOORKING LOOP DETECTORS AND ACCESSORIES..................................................................................... 18
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A loop detection system is a method of sensing vehicles and is typically used in automated gate
applications to prevent a gate from automatically closing on a vehicle or to automatically open the
gate when a vehicle is exiting a property. Vehicle loops can also be used to activate card readers,
ticket spitters, etc. When properly installed, loops are an extremely reliable form of vehicle detection.
The loop detection system operates by creating a field of sensitivity that tunes to the surrounding
environment. When a metallic object enters this field, the loop detector senses a change in the field
and generates an output, usually in the form of a relay closure, which can then be used to control a
gate operator or other devices. There are three basic components in a loop detection system: the
underground loop, the lead-in cable, and the loop detector.

The Underground Loop
The loop is made from a continuous piece of wire (NO SPLICES) that is coiled around for a number
of turns in a square or rectangular pattern. The wire is embedded into pavement either as a
preformed loop placed prior to paving, or into a saw cut that is cut into existing pavement. Both ends
of this wire are then extended to the edge of the pavement.

The Lead-In Cable
The lead-in cable extends the two ends of the loop wire back to the loop detector. On short runs (ten
feet or less), the two wires exiting the loop can be twisted together and connected directly to the loop
detector. This wire must be twisted a minimum of five turns per foot. For runs longer than ten feet,
you may want to splice on a separate lead-in cable to simplify installation. The lead-in cable must be
a twisted pair, shielded cable with a direct burial rated jacket or be placed in conduit. All splices must
be soldered and placed in a watertight J-box.

The Loop Detector
The loop detector is the electronic component that controls the loop system. DoorKing offers loop
detectors (Models 9405, 9406) that plug directly into the gate operator control board, eliminating the
wire harness and wiring connections other than the loop lead-in wires. These detector boards have a
terminal strip where the loop lead-in wire connects. There are also various other types of standalone
detectors available on the market that can be hard wired into the gate operator control board.
INTRODUCTION
Underground
Loop
Lead-in Cable
Loop
Detector
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Design Facts Read Carefully!
Proper installation of the loops is essential for reliable functioning of the detector system. Most
detector problems are caused by improper loop installation! The geometry (size and shape) of the
loop defines the detection zone characteristics.
Loop size may vary and will depend on lane width, traffic patterns, and types of vehicles to be
detected.
Small loops (6 feet x 8 feet) are used to detect motorcycles and automobiles. Minimum
size for loops to detect typical vehicular traffic is 4 feet x 6 feet. It is always
recommended to use a larger loop whenever possible.
Large rectangular loops (8 feet x 20 feet) are used to detect large, high bed vehicles such as
trucks.
The short leg of any loop used for vehicle detection should never be less than 4-feet.
The height of detection is directly related to the length of the short leg of the loop. A general
rule of thumb to follow is that the height of detection is 2/3 the length of the short leg of the
loop.
Loops can be saw cut into concrete or asphalt, and can be placed under a preformed road
surface, such as concrete and brick pavers.

Physically adjacent loops operating on separate detector modules may interfere (cross talk) with each
other. Changing the operating frequency on one of the loop detectors can eliminate this interference.

The detector must operate from stable AC power. If the detector is subjected to excessive line voltage
variations, the detector may cause either false outputs or may drop an output when a vehicle is over
the loop. For example, if a gate operator is located some distance from the power distribution panel
and the feeder wires are undersized, the inrush current when the motor starts will cause a momentary
drop in the line voltage. If this voltage drop is more than 25% of the nominal line voltage, the loop
detector will see this as a power failure and will reset when the voltage returns to the nominal level. If
a vehicle is over a loop when the detector resets itself, the detector will no longer sense the vehicle
presence.

When connecting more than one loop to a detector, always connect the loops in series. If the loops
are close together, the direction of the windings should be considered. Loops physically near each
other and wound in the same direction electrically (i.e. both CW or CCW) will cause field cancellation
effects (a dead zone) between the loops. This may be desirable when two loops (reverse loops) are
placed on each side of a sliding gate. Wiring the loops in this manner will allow the gate to slide
between the two loops without causing the loops to detect the gate. If the loops are wound in
electrically opposite directions (i.e. one CW and one CCW), field enhancement will occur between the
loops, effectively extending the field of sensitivity for the loop system.

Use the table below to determine the number of turns required for a single loop installation. Loop area
(Sq. Ft.) is determined by multiplying loop width by loop length.


Loop Area (S