PD130 Enhanced - User Instructions
Page 10 of 12
The length of the loop will be determined by the width of the roadway to be monitored. The loop should reach to
within 300mm of each edge of the roadway.
In general, loops having a circumference measurement in excess of 10 metres should be installed using two turns of
wire, while loops of less than 10 metres in circumference, should have three turns or more. Loops having a
circumference measurement less than 6 metre should have four turns. It is good practice at time of installation to
construct adjacent loops with alternate three and four turn windings.
10.
Loop Installation
All permanent loop installations should be installed in the roadway by cutting slots with a masonry cutting disc or
similar devise. A 45° crosscut should be made across the loop corners to reduce the chance of damage that can be
caused to the loop at right angle corners.
NOMINAL SLOT WIDTH: 45mm
NOMINAL SLOT DEPTH : 30mm TO 50mm
A slot must also be cut from the loop circumference at one corner of the loop to the roadway edge to accommodate the
feeder.
A continuous loop and feeder is obtained by leaving a tail long enough o reach the detector before inserting the cable
into the loop slot. Once the required number of turns of wire is wound into the slot around the loop circumference, the
wire is routed again via the feeder slot to the roadway edge. A similar length is allowed to reach the detector and these
two free ends
are twisted together to ensure they remain in close proximity to one another (minimum 20 turns per
metre).
Maximum recommended feeder length is 100 metres.
It should be noted that the loop sensitivity decreases as the feeder length increases, so ideally the feeder cable should be
kept as short as possible.
The loops are sealed using “quick-set” black epoxy compound or hot bitumen mastic to blend with the roadway surface.
Figure 10.1
Slot details