Special Loops; Loop Slot Details; Loop Turns And Feeder Lengths - Siemens BH17 7ER Installation Manual

stopline is required, chevron loops away from the direction of traffic should be
used.

2.3.10 Special Loops

Figure 13 illustrates queue loops and special purpose loops whereby fixed
and limits of variable dimensions are shown. These loop configurations can
be connected to Siemens/Plessey, Microsense and Sarasota detectors
observing the calculations for loop turns as listed in section 2.5 of this
handbook.
2.4

Loop Slot Details

Loop and loop tail slots will be cut in the surface of the roadway with a motor
driven saw.
Prior to cutting the slots refer to section 2.1 to determine minimum slot widths,
and minimum slot depths. Refer to Figure 14 for typical examples.
When adjacent loops are connected to different detectors, their loop tails must
be laid in different slots spaced 150 mm apart and connected to separate
feeder cables to each detector unit.
When cutting loops, the saw blade should be lowered to form a dip in the floor
of the slots at the point where the slots cross. This will allow the extra bulk of
crossing cables to lie in the dip while still maintaining the 50 mm covering for
the top cable (See Figure 15). The same rule applies to all loops at the point
where the feeder cables join the loop.
The corners of slots should not be cut away at diamond loop crossovers but
must be cut away to ease the bend on loop cables turning through an angle of
less than 90 (See Figure 16). An alternative is to protect the cable from a
sharp corner by inserting a short length of 1 mm thick vinyl or plastic strip
formed by bending to fit the corner (Figure 17 refers).
Slots must be cleared of stones, loose material and free water before cable
laying. Drying out can be assisted by using a compressor and air line. It is not
acceptable to lay cables in a wet slot as backfilling materials do not bond to
wet surfaces although the slightly damp surface obtained after using the air
line is acceptable. (Definition of a wet slot is a slot that contains free-standing
water.)
NOTE: If the saw breaks through into the hardcore bed, work should be
stopped and the customer informed that loops cannot be installed
to this Siemens specification.
2.5

Loop Turns and Feeder Lengths

All loops shared on one detector channel are to be connected in series.
The maximum feeder length quoted below includes the total length of any
separate pairs fed back for series connection in the controller and the lengths
of loop tails.
667/HE/20663/000 Issue 13
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OOP ETECTOR ANDBOOK
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