Bus Detection
Loop Detector Application Notes SLD4
667/HQ/45200/101
11
3.
Bus Detection
3.1.
Loop Type for Bus Applications
Note
This application note is to be read in conjunction with the SLD4 User Manual
(667/HB/45200/000).
When using the SLD4 advanced detector the following points
must
be considered as they have
big influence on the performance of the detector:
•
The Quality of loop and feeder installation. For example the loops must be cut and in-
stalled into stable Tarmac or Concrete.
•
When cutting the loops, chamber lids, expansion joints and rebar should be avoided
since they distort the loops field and can make the loop insensitive or inconsistent.
This detector can be used in locations where traditional Classification might otherwise be dif-
ficult such as areas where vehicles are slowing e.g. braking zones or in queuing traffic.
Note
The suggested default loop for bus detection is 10M by 3M with 2 turns.
Larger loops can be used if detection is to be limited to larger buses.
Note
When using large loops, smaller vehicles such as cars/vans do not occupy sufficient area of the
loop at any one time and the majority of the length of these types of vehicle has a much larger
ground clearance. Therefore they will not cause a large enough deviation in the inductance
and have a smaller frequency change. This allows the threshold of the loop to be set above the
detection range of these types of vehicles.
3.2.
Basic Setup of Detector
The inductance range needs to be set for the appropriate loop channel, 1 to 4, being used for
the Bus detectors. The recommended bus loops have a higher inductance than smaller loops,
so links PL3 to PL6 must be set to 2-3 and 4-5, this is the medium inductance range.
These ranges are for guidance only, and for short feeders it may be possible to use the range
below that recommended and achieve greater performance.
