Controlled Products Systems Group SLIDESMART DC 10F - Manual (Page 105)

Installing Vehicle Detectors and Loops
Revision D Reference 6-7
9. This guide is written from a design perspective, but installation workmanship practices are equally
important to insure proper operation and long loop life. The best way to insure a quality installation is to
employ a professional installer experienced with detector loops. A few important practices are:
• The slot in the surface of the road should be cut ¼-inch wide x 1½-inch deep (6.3mm x 38.1mm).
• The corners of the cut must be at an angle or core drilled to relieve stress on the wires.
• After the wire is installed, the slot must be completely backfilled with a non-hardening sealer. If the
loop wires are able to move in the slot after the sealer has set, the detector may give false calls.
Figure 6-6.
Detector Logic
HySecurity recommends that vehicle detectors be used for free open and obstruction sensing logic only.
Because of their slower speeds, closing logic is a poor choice for security gate systems. Since there are several
ways that the gate may be left standing open and because there is a loss of safety, our circuit has not been
designed to accommodate “detect to close” logic.
Loop Diagnostics
The following tests cannot guarantee a functioning loop, but failure of either test means that the loop is
definitely suspect, even though it may still be functioning at the time.
1. Test the resistance of the loop and lead-in wire. It should not exceed 4 Ohms.
2. Test the resistance between the loop and earth ground with a 500V Megohm meter. It should be 100
Megohms or more. Loops may function at 100 Megohms or less but will not be reliable (e.g. when the
ground is wet from rainfall). Low resistance indicates broken or moisture saturated insulation. This is
common if inappropriate wire insulation has been used.
A schematic for a slide gate loop layout is shown in Figure 6-7.