304UM0001 Rev 00
PD160 Enhanced Series User Manual
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Stranded loop wire is preferred over solid wire. Because of its mechanical
characteristics, a stranded wire is more likely to survive bending and stretching than a
solid.
A heavy gauge conductor is definitely desirous in order to maintain the loop Q-factor. The loop and
feeder should preferably constitute a single length of insulated multi-stranded copper conductor, with
no joints and with the copper having a minimum cross section 1.5 mm
2
. The feeder is twisted to
minimise the effect of electrical noise.
Joints in the loop or feeder are not recommended. Where this is not possible, joints are to be soldered
and terminated in a waterproof junction box. This is extremely important for reliable detector
performance. Other forms of joins such as those available in kits, where the joint is properly sealed
against moisture, are also permitted
5.4 Sensing Loop Geometry
NOTE: 1) The circumference of the loop must not exceed 30 m.
2) The area of the loop must not exceed 30 m
2
and must not be less than 1 m
2
.
3) The loop must be constructed as detailed below.
Sensing loops should, unless site conditions prohibit, be rectangular in shape and should normally be
installed with the longest sides at right angles to the direction of traffic movement. These sides should
ideally be 1 metre apart.
Loops operating from the same detector module can share a common slot along one of the longer
sides, if so required. This type of configuration could be applied in a direction logic application. The
maximum separation permitted for this application is 1 metre, ensuring that a vehicle can straddle both
loops simultaneously in the required direction of travel.
The only factor which governs maximum separation between loops in all other applications is the
feeder length, with 100 metres being the maximum recommended length.
The length of the loop will be determined by the width of the roadway to be monitored. The loop
should reach to within 300 mm 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.
Loops having a circumference measurement less than 6 metres should have four turns.
It is good practice at time of installation to construct adjacent loops with alternate three and four turn
windings.
For additional Information on loop geometry refer to the following documents:
•
“INDUCTIVE LOOP VEHICLE DETECTION” - Nortech Doc. No. MKT0001.
•
“TRAFFIC DETECTION” - Nortech Doc. No. MKT0002.
•
“PARKING APPLICATIONS MANUAL” - Nortech Doc. No. MKT0003.
•
“LOOPS and LOOP INSTALLATION” – Nortech Doc. No. MKT05
