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2.11
Loop Detector Settings
2.11.1 Sensitivity
For normal VA purposes the detectors should be set to give bicycle detection.
This requires a sensitivity setting of 0.01% or 0.02%. If the setting is too
sensitive the detector will be unduly sensitive to vehicles in adjacent lanes.
This is most likely where a single small loop is installed on a detector channel
i.e. without sharing. If this is a problem on a particular site the sensitivity may
be reduced but not to below 0.04%.
For SDE/SA the two loops must be set to the same sensitivity.
For SCOOT, the sensitivity setting depends on the feeder length and loop size
(all SCOOT loops are 2 metres in the direction of travel and vary in width).
The diagram below may be used as a guide to sensitivity settings. However
the target response for a SCOOT detector is that a 'detect' output should start
as the first metal part of a normal 4-wheeled vehicle crosses the front of the
loop and no response should be obtained from vehicles in adjacent lanes.
This should be confirmed or the sensitivity altered to achieve this before
leaving the site.
MOVA loops should be set to medium sensitivity (~0.1%) with the exception of
stop line loops that should be high sensitivity (~0.1% - 0.5%).
6
5
4
3
2
1
0
0m
2.11.2 Presence Time
This is defined as the time for which a 'detect' output is held when a vehicle
enters and stops within a loop. After the presence time has expired the
detector retunes to the new value of loop inductance. For Road Traffic use it
is normally set to 4 minutes.
667/HE/20663/000
0.08%
100m
Feeder Length
Issue 13
L
D
OOP
ETECTOR
0.02% - Not
recommended
0.04%
200m
H
ANDBOOK
300m
Page 19
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