How many turns of wire should be in the loop?

Loop inductance depends on the total length of wire used to make up the loop.  Two things determine the length of wire, loop perimeter and the number of turns in the loop.  Once the loop geometry has been established, the number of turns in the loop must be determined in order to obtain a loop with the proper inductance level needed to maintain a stable system. To ensure stable operation in most applications, loop inductance should be in the range of 50 to 150 ?H.

Use the following table as a preliminary guide to determining the number of turns in a loop.

Notes: Reliable detection height of a loop is 2/3 of the short side of the loop.

Increasing turns in the loop does not increase sensitivity of the loop or the detection height of the loop.

What is the most critical element when installing a loop?

Because the inductive loop in the road surface is critical to the performance and operation of the detector, it is important to use the best materials possible. It is recommended that any wire used for a loop has cross-linked polyethylene insulation (XLPE). The loop wire insulation resistance to earth ground can be tested using an insulation tester (Megohmmeter) rated for 500 VDC. Disconnect the loop from the detector. Attach one test lead of the insulation tester to the loop, and the other test lead to earth ground. A new loop should have at least 100 megohms to earth ground. If the reading is below 50 megohms, the loop may be suspect. If the loop is below 20 megohms, the loop should be replaced. The lower the loop resistance to earth ground the more prone the detector will be to intermittent operation. Multiple shorts to ground can short part of the loop inductance and appear as if a vehicle is over the loop. The detector will hold the "call" for as long as the short exists. Reno A&E offers special XLPE loop wires and prefabricated loops, which have been specifically manufactured to provide reliable detector operation. The quality of the loop wire and installation techniques are just as important as the quality of the loop amplifier, as this is an integrated detection system, not just isolated elements of vehicle detection.

What is the most common loop problem?

A very high percentage of loop problems result from poor connections. Solder all loop splices and crimp type connections. As soon as the insulation is removed from the wire the copper conductors begin to oxidize, i.e. corrode. Over a period of time the corrosion will increase resistance in the connection. Since a loop detector uses very low power to energize the inductive loop, the slightest series resistance in a connection can cause intermittent detector operation. Note: All Reno A&E loop wires and prefabricated loops have tinned copper conductors to minimize oxidation.  Environmentally seal all splices to prevent moisture from contacting the conductors. Moisture can provide an electrical path that may result in leakage current between the loop and ground. Moisture can also increase the connection resistance (corrosion). Both can cause intermittent detector operation.