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Vehicle Loop Detectors Installation(2)

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

Followed by the first part:
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!
Do Not Use wire nuts or crimp type connectors! Tinned copper crimped connections can be used to hold the wires together as long as they are then soldered!

Most parking and access control applications use unshielded, twisted lead-in cable. Many times the lead-in cable used, is the same loop wire twisted with a drill to maintain at least the 6 turns per foot twist in the wire. Using lead-in wire that is twisted is even more important if lead in-wire from different loops are routed back to the detectors in the same conduit.

The detail above shows a cross section of the wire slot with 4 turns of wire installed. Notice the backer rod holding the loop wires in the slot. The sealant should completely fill the slot up to the surface of the roadway. The top of the backer rod should be at least 1 inch below the level of the pavement. The number of turns of wire used in the loop is determined largely by the size of the loop. Please refer to the table below for the suggest number of turns. Increase the number of turns by 1 if the lead-in length exceeds 150 m (500 ft).

Loop Size
Loop Size
Number of Turn
0.6 x 1.2 m or smaller
2' x 4' or smaller
1 x 1 m to 1.2 x 2 m
3' x 3' to 4' x 6'
2 x 2 m to 2 x 10 m
6' x 6' to 6' x 30'
2 x 15 m or large
6' x 50' or larger

Some years ago when detectors had limited sensitivity, people began experimenting with different loop configurations. Today we have a variety of loop shapes in use: rectangular, square, round, triangular and combinations of these. In addition, agencies have tried connecting multiple loops electrically in various series and parallel configurations. Several things must be considered when designing street loops for vehicle detection.
The length of the lead-in cable will affect the overall sensitivity of the detection area. This is a consideration only for extremely long lead-in cables from 150 to 300 m (500 to 1000 ft) or more. If the lead-in cable of a loop is less than 100 m (300 ft), as is the case of most installations, then the sensitivity will not be adversely affected. Many Diablo Conntrols detectors have a range of sensitivity settings which will compensate for even the longest lead-in lengths.
The biggest inductance change that a detector will "see" is when the loop area is entirely covered by a vehicle. For traffic applications where the detection zone must cover a large area, the vehicle detector sensitivity adjustment may have to be increased slightly for loops which cover an area larger than the area of the vehicle. For example, in traffic applications, a loop which is 2 m (6 ft) feet wide but 15 m (50 ft) long will be somewhat less sensitive to the presence of a small motorcycle than a smaller 1 x 1 m (4 ft by 4 ft) loop. The detector sensitivity may have to be raised one or two levels for the motorcycle to be adequately detected by this large loop.
Multiple loops are often connected to the same detector to provide a larger detection area. This practice can lead to sensitivity problems if the loop area is quite large. The same large area of detection can be obtained by connecting the loops to separate detectors or connecting a fewer number of loops to each detector. If multiple detectors, and multiple loops, are to be used for one detection area, it will be necessary to parallel the relay (or solid state) outputs together.
Many of the Diablo Controls Inc. vehicle detectors are covered with U.S. Patent number US 7,132,959 B2 - "Non-Interfering Vehicle Detection". This feature minimizes the effect of crosstalk between street loops. Cross talk is the result of two or more loops or feeder cables affecting each other. Detectors experiencing cross talk will usually intermittently pick up a false "detect" or worse, drop a "detect" when cars are indeed present. To minimize crosstalk possibility, the street loops should be placed as far apart as possible. A good rule is to place loops at least 1.2 m (4 ft) apart.
Loops installed in the vicinity of swinging or sliding gates, need special consideration. The gate should not come closer than 1.2 m (4 ft) from the loop at any time while it is closing or opening. 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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