8
PLACING THE VEHICLE DETECTOR LOOPS
Proper
placement of vehicle detector wire loops is critical if the loops
are to provide satisfactory, extended service. The most important
considerations are: 1) Proper wire type and, 2) Good, tight connections
from the loop to the loop terminating connector. When a "Stand
Alone" vehicle detector is used, the detection loop is connected to the
wire harness on the detector itself. (See WIRING VEHICLE
DETECTORS, Page 10.)
The LP1000 provides for the use of two loop systems: 1) A "reversing"
loop that will prevent the gate from closing on a vehicle that has
stopped in the path of the gate and, 2) A "free exit" loop that will open
the gate by detecting a vehicle which is inside the gated area and wishes
to leave. If "free exit" detection is not desired, this loop will not be
needed. Note the "reversing” loop is normally made up of two loops
connected to one detector. See Figure 10 above.
Two different types of installations will usually be encountered: 1) If
the driveway material is already in place, saw cuts will be needed to
accommodate the loop wires.
2) For loops where the paving material will be installed after the loop is
positioned, it is necessary that the loop wires be placed in Schedule 40
PVC pipe to maintain uniform loop spacing with respect to the surface
of the pavement. The loop should be placed 1.5 inches below the
surface of the pavement and at least 2" above any reinforcing steel The
lead-in wires need not be in PVC, but must have at least six (6) twists
per running foot.
For a saw-cut installation, observe the method recommended in
Figure
z
10 for the corners. When installing a two-loop reversing system
it is best to bring the twisted lead wires from each loop to the operator
so that the loops may be properly phased. The saw cut must be to a
depth of 1.5 inches, clean and with no sharp corners. After placing the
wires, it is essential that the wires be held tightly in place by the foam
backing and that no voids exist that can collect water which might
freeze and push the loop wires out of the slot. The sealant used should
match the paving material and should not be hard setting. The lead-in
wires must have at least six (6) twists per foot.
NO SPLICES ARE ALLOWED IN THE LOOP OR THE LEAD-IN
WIRE TO THE FIRST JUNCTION BOX Above ground splices may
be used providing the wire is twisted, soldered and moisture sealed.
For best long term results, do not use wire nuts anywhere in the loop
system. For connections to the loop detector, gas tight crimp type
terminals should be used, and soldered if possible.
THE WIRE USED FOR THE LOOPS MUST BE HEAT AND
WATER RESISTANT. CROSS-LINK POLYETHYLENE
INSULATED, TYPE XLPE OR RHW IS BEST. U.S.E. IS ALSO
SATISFACTORY. DO NOT USE PVC INSULATED WIRE. WIRE
SIZE SHOULD BE #16
z
GA STRANDED OR LARGER
Figure 10: Loop Diagrams
104886
B
: PREPARING THE SITE
RISK OF ENTRAPMENT
VEHICLE DETECTOR LOOPS WILL NOT DETECT
SMALLER VEHICLES SUCH AS MOTORCYCLES
OR GOLF CARTS, OR BICYCLES OR
PEDESTRIANS. PHOTOELECTRIC DETECTORS,
EDGE DETECTORS AND SEPARATE
PEDESTRIAN ACCESS MUST BE INSTALLED.
W A R N I N G !
