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Vehicle Loop Detectors Installation(1)

Tips & guidelines for installation of vehicle detector loops in pavement.

Inductive loop vehicle detection is still the most reliable and cost-effective method of vehicle detection in today's traffic and parking applications.

The electronic circuitry in the Diablo Controls vehicle detectors is very reliable, and its production and testing are controlled very tightly. This assures the customer of getting the most reliable electronic package available. But this is only part of the story.

The proper installation of the loop system is something for which the installer must take responsibility, and indeed, is the key to reliable vehicle detection. It has been the experience of most agencies and installers that a properly installed loop system should last the life of the roadbed. The loop "system" includes the loop wire in the street and all of the feeder cable back to the detector unit located at the gate operator or traffic controller cabinet.

We would like to offer a few tips and guidelines to follow for the proper installation of vehicle detectors and street loops.

If there are old loops present, remove all of the existing street loop(s). An old  loop in the pavement can act as a shorted turn and can cause a low sensitivity situation.

The loop wireto be installed in saw-cuts, should be #18 AWG or larger, stranded and tinned copper wire. We recommend the use of at least #16 wire for mechanical strength. Good wire is typically inexpensive compared to the re-work expense if a failure occurs.Cross-link polyethylene (XLPE) insulation with a voltage rating of 600V is the wire to use if a cold sealant is used. If a hot tar sealant is used then a cross-link polyethylene with an additional polyester jacket should be used, also with the 600 volt rating.Cross-link polyethylene wire is recommended over PVC insulated wire or nylon jacketed wire such as THHN or TFFN.

The lead-in wire should also be two conductor twisted, #16 AWG or larger stranded wire . It is recommended that this wire also have a high density polyethylene insulation.

The sawcut is one one of the most important parts of the loop installation process. The pavement is typically cut to a depth of approximately 4 to 5 cm (1-1/2 to 2 inches) using a 6 mm (1/4 inch) wide blade. The slot is then cleaned with water and then blown out with compressed air. This will assure that all sharp particles are removed from the slot. The corners of all square or rectangular loops should have 45 degree cuts to prevent sharp corners from puncturing the loop wire. Start the 45 degree cuts about 8 to 12 inches from the corners of the loop. The turns of wire are then installed in the bottom of the slot and held into place with foam backer rod (See figure 2 ). This will assure that the wire is held in place when the sealant is added to the slot.

Loop wires should be twisted at least 6 turns per foot from the point where they leave the loop and start toward the side of the roadway - down the lead-in slot. The sealant used in the loop and lead-in slot should be pliable and should "give" with temperature changes in the pavement.

The roadway loop shown above is a typical configuration for a street or roadway installation. The loop shown is cut with a street saw with straight slots. The corners are cut with 45 degree cuts to prevent sharp corners. The two wires leave the rectangular loop and are placed in another slot to exit the roadway. The wires used in the main loop and the exit slot must be one continuous piece. No splices can be made in any part of the installation. The two wires are twisted around each other at least 6 times per foot and placed in the saw cut leaving the roadway.
Apply loop sealant to this saw cut as well as the main loop. The wires are then spliced to the lead-in cable at the concrete pull box. All splices must be soldered!

As shown in the part(2).....

Ordering Information:
*LD-100 single channel, boxed, 1 type 11 pin connects 100-240VAC (EU standard)
*LD-102 single channel, boxed, 1 type 11 pin connects 12-24VADC (EU standard)
*LD-105 single channel, boxed, 2 type 11 pin connects 100-240VAC (USA standard)
*LD-106 single channel, boxed, 2 type 11 pin connects 12-24VADC (USA standard)

*LD-200 single channel, boxed, 1 type 11pin connects 100-240VAC(EU standard)
*LD-202 single channel, boxed, 1 type 11pin connects 12-24VADC(EU standard)
*LD-205 single channel, boxed, 2 type 11pin connects 100-240VAC(USA standard)
*LD-206 single channel, boxed, 2 type 11pin connects 12-24VADC(USA standard)

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