Loop Info-Q-2-16
3
Loops that are physically adjacent to each other and operating on separate loop detectors may interfere (cross-talk) with each
other if they are operating on the same frequencies. Changing the operating frequency on one of the loop detectors can
eliminate this interference. (See page 7 for more information)
When connecting two loops to a single loop detector terminal, 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 Clockwise or Counter-Clockwise) 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 Clockwise and one Counter-Clockwise), field enhancement will occur between the loops, effectively
extending the field of sensitivity for the loop system. (See pages 5 and 6 for more information)
•
During the construction of new installations (i.e. concrete or asphalt), a pre-formed loop may be used as an alternate to
the saw cut type. Pre-formed loops are typically encased in PVC or other durable materials to provide high reliability and
long life. Sizes may vary depending on the source of the pre-formed loop. DoorKing offers a variety of pre-formed loops
that come with 25 feet of lead-in wire. (See page 10 for more information)
•
The loop will tune to its environment. Stationary or static metal objects, such as conduits, pipes, metal grates, etc., will
not affect the loop field.
High voltage electrical power lines, either underground or overhead, can affect the loop field.
In addition, fluctuating electrical fields, such as heating coils, can cause loop lock-ups and false detection.
•
A heavy grid of reinforcing bars (re-bar) may affect the loop field. To minimize this,
DO NOT place a loop directly on the
rebar.
Support the loop 1 - 2 inches above the rebar. If possible, make cuts or bends in the rebar grid directly below the
loop. Bars and electrical wires running at angles to the loop have less effect on the loop than those running parallel to the
loop wires. (See page 10 for more information)
•
If a single loop is used with a long lead-in cable (500 feet or greater), it is advisable to add an additional turn in the loop.
This increases the ratio of the loop inductance to the total inductance, thereby improving loop sensitivity and overall loop
system
stability.
•
The inductance of the loop (in micro henries) must fall within the tuning range of the loop detector for the loop system to
operate properly. This is typically not a problem since most loop detectors have a very wide tuning range (20 - 2500
micro henries) and can accommodate most size loops.
To calculate the inductance of a loop use this formula:
Determine the Number of Wire Turns Required for Each Loop
Loop area (Sq. Ft.) - Multiply loop width by loop length.
Note: The number of turns should be increased by 1 turn if lead-in wire or cable length is 500 ft or greater.
Loop Area in Square Feet
Number of Turns Required
6 - 12
12 - 60
60 - 240
6
4
3
2
(
Side 1 + Side 2 + Side 3 + Side 4
)
Number of Turns
2
= Inductance
2
(
6 + 8 + 6 + 8
)
4
2
= 224 Micro Henries
Example:
To calculate the inductance of a typical 6 x 8 foot loop with four turns of wire:
Содержание 9409 Dual Channel
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