JUTAI Inductive loop vehicle detection is still the most reliable and cost-effective method of vehicle detection in today’s traffic and parking applications
JUTAI 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 JUTAI vehicle detectors is very reliable and we control our production and testing 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.
First, 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 wire to 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.
One of the most important parts of the loop installation process is the saw cut. The pavement is typically cut to a depth of approximately 1 1/2 to 2 inches using a 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.
We would like to offer a few tips and guidelines to follow for the proper installation of vehicle detectors and street loops.
First, 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 wire to 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.
One of the most important parts of the loop installation process is the saw cut. The pavement is typically cut to a depth of approximately 1 1/2 to 2 inches using a 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 here, on the right, 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 sealant to this sawcut 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 produce at least the 6 turns per foot twist in the wire. All lead-in wires must be twisted to avoid cross-talk between two or more detectors! Twisting all detector lead-in wires for each loop will minimize other problems such as street loops that have intermittent shorts to ground and/or radio frequency interference from other devices not related to traffic control devices. 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 below, 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.
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.
JUTAI . vehicle detectors are covered with United States 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 crosstalk will usually intermittently pick up a false “detect” or worse, drop a “detect” when a car is 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 4 feet apart. The lead-in wires from each detector must also be a twisted pair.
JUTAI . vehicle detectors are covered with United States 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 crosstalk will usually intermittently pick up a false “detect” or worse, drop a “detect” when a car is 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 4 feet apart. The lead-in wires from each detector must also be a twisted pair.
Loops installed in the vicinity of swinging or sliding gates, need special consideration. The gate should not come closer that 4 feet from the loop at any time while it is closing or opening.
For any specific application information, problems, or additional details , contact JUTAI and we will be glad to help!
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