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Separate loop detector module
!
If your
SECTOR
vehicle traffic barrier has not been fitted with an onboard inductive
loop detector, it is possible to install an external detector using one or both of the bases
provided on the
SECTOR
termination board. Bases are provided for both Free-exit and
closing loop connections. Setup will be as per the individual detector. For more
information on the different configurations and Modes of Operation as well as
connecting closing and Free-exit loops, please refer to section 15, Electrical Setup
12V loop detectors MUST be used.
Tips for successful loop installation
!
The loop and feeder should be constructed from XLPE (cross-linked polyethylene)
insulated multi-stranded copper wire with a minimum cross-sectional area of 1.5mm².
The feeder should be twisted at a rate of at least 20 turns per metre to improve
reliability (Remember that twisting the feeder will shorten its length, so ensure a long
enough feeder wire is used). Feeders which may pick up electrical noise should use
screened cable, with the screen earthed at the detector
!
Joints in the wire are not recommended, but where required must be soldered and
made waterproof
!
Faulty joints will lead to unreliable operation
!
The loop should be either square or rectangular in shape with a minimum distance of
1m between opposite sides
!
Two to six turns of wire are typically used in the loop – See table below:
Loop perimeter (metres)
3-4
4-6
6-10
10-20
>20
Number of turns
6
5
4
3
2
!
When two loops are laid in close proximity to each other, it is recommended that
different numbers of turns are used in each loop to prevent cross-talk
!
Cross-talk describes the interference between two adjacent loops, and can cause
reliability issues
!
To minimise cross-talk, adjacent loops should be at least two metres apart, and
different frequency settings
!
The most reliable form of loop is preformed and enclosed in conduit. This prevents
water ingress, and minimises the effects of vibration
!
Where a pre-formed loop is not practical, slots should be cut into the road using a
masonry cutting tool. A 45° cut should be made across the corners to prevent damage
to the wire on the corners. The slot should be about 4mm wide and 30mm to 50mm
deep. Remember to extend the slot from one of the corners to the roadside to
accommodate the feeder. After the loop and feeder wires have been placed in the slot,
the slot must be filled with an epoxy compound or bitumen filler