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Loop Detectors & Driveway Loops

Articles and Illustrations:
Overview - Introduction to Loops
Cut-in Loop Installation Diagram
General Loop Info
Technical Loop Info

Troubleshooting Loops
You can find vehicle loops here

Most common problem on the loops is a short to ground. This happens when the wire is abraded or nicked and moisture creates an electrical path to ground. This can occur in splices if there are any. The incorrect type of wire will also leak to ground.

To check leakage
disconnect loop from detector. Use a multi meter to measure the resistance from one loop wire to ground (stick long nail in dirt if operator does not have ground). Be sure that other loop wire is floating (not connected). If there is less than 10 Meg Ohm leakage to ground, loop is faulted. Most loop leakage to ground occur in wet conditions. The loop may work fine during the dry season.

To check loop continuity connect two meter leads to two loop leads. You should only read a few ohms at most. If resistance is higher, the loop is faulted.. This usually indicates that loop is severed.

Check loop detectors:
If loop passes test, replace detectors. If you have two loop detectors you can swap them for testing purposes.
Driveway Loop Troubleshooting Diagram
Loop Test 2 Diagram