1、Designation: E 2561 07aStandard Practice for theInstallation of Inductive Loop Detectors1This standard is issued under the fixed designation E 2561; the number immediately following the designation indicates the year oforiginal adoption or, in the case of revision, the year of last revision. A numbe
2、r in parentheses indicates the year of last reapproval. Asuperscript epsilon (e) indicates an editorial change since the last revision or reapproval.1. Scope1.1 This practice describes the recommended procedure forinstalling inductive loop detectors in sawed slots in roadwaypavement for use as a tra
3、ffic monitoring device or to actuatetraffic control devices such as a traffic signal. Although thepractice is not intended for installing preformed loops, thepractice does contain information of value for this type of loopsuch as recommendations for the number of turns of loop wire,number and direct
4、ion of twists in the lead-in wire and cable,splice location (if needed), and grounding options.1.2 The values stated in inch-pound units are to be regardedas standard. The values given in parentheses are mathematicalconversions to SI units that are provided for information onlyand are not considered
5、 standard.1.3 This standard does not purport to address all of thesafety concerns, if any, associated with its use. It is theresponsibility of the user of this standard to establish appro-priate safety and health practices and to determine theapplicability of regulatory limitations prior to use.2. T
6、erminology2.1 Definitions of Terms Specific to This Standard:2.1.1 electronics unit, na card or free-standing modulethat transmits energy into the wire loops typically at frequen-cies between 20 kHz and 100 kHz; special applications such asvehicle classification may use electronics units that transm
7、it atfrequencies above 100 kHz; electronics units allow control ofsensitivity, frequency, pulse or presence operation, and timingfeatures (that is, delay and extension) in some models andindicate system failures.2.1.2 inductance, nproperty of an electric circuit or oftwo neighboring circuits that ge
8、nerates an electromotive forcein one circuit when the current changes in that circuit or in theneighboring circuit; expressed in units of Henrys (H).2.1.3 inductive loop detector, nthose parts of an inductiveloop detector system that consist of the wire loops, lead-inwires, and lead-in cable and whi
9、ch responds to the passage orpresence of a vehicle with a decrease in inductance of the wireloop.2.1.4 inductive loop detector system, na sensor to detectvehicles and their traffic flow properties, whose major compo-nents are: (1) one or more turns of insulated loop wire woundin a slot sawed in the
10、pavement, (2) lead-in wires extendingfrom the loop wire to a curbside or shoulder pull box (3)lead-in cable spliced to the lead-in wires that extends from thepull box to the controller cabinet, and (4) electronics unithoused in the controller cabinet.2.1.5 insulation resistance, nthe resistance meas
11、ured witha megohmmeter between a conductor and the outer insulatingjacket of a wire or cable.2.1.6 lead-in cable, nshielded wire that is spliced to thelead-in wires in the pull box and which extends from the pullbox to the controller cabinet, where it is connected to theelectronics unit; also known
12、as home-run cable, transmissionline, or feeder cable.2.1.7 lead-in wires, na continuation of the loop wire thatruns from the physical edge of the loop to the pull box; usuallytwisted together to form a wire pair.2.1.8 loop system sensitivity, nsmallest change of induc-tance at the electronics unit t
13、erminals that will result in a signalthat indicates the passage or presence of a vehicle.2.1.9 loop wire, none-conductor insulated wire used forboth the wire loop and the lead-in wire; may be jacketed orencased in tube.2.1.10 pull box, na container that encloses the splicesbetween the lead-in wires
14、and the lead-in cable; when installedunderground, the removable cover is aligned flush with theground surface; also known as a handhole, splice box, orjunction box.2.1.11 quadrupole loop, ntypically a rectangular wireloop configuration with a longitudinal slot extending along thecenter of the loop s
15、o that the wire can be installed in afigure-eight pattern; the quadrupole loop produces four elec-tromagnetic poles instead of the normal two, thus improvingthe sensitivity to small vehicles and minimizing splashover;quadrupole loops are also used in a diagonal configuration todetect bicycles (1)2.2
16、.1.12 saw cut, nopening made in the roadway pavementusing a pavement saw into which the wire loop or lead-in wiresare inserted; also referred to as a slot.1This practice is under the jurisdiction of ASTM Committee E17 on Vehicle -Pavement Systems and is the direct responsibility of Subcommittee E17.
17、52 onTraffic Monitoring.Current edition approved on, July 1, 2007. Published August 2007.2The boldface numbers in parentheses refer to the list of references at the end ofthis practice.1Copyright ASTM International, 100 Barr Harbor Drive, PO Box C700, West Conshohocken, PA 19428-2959, United States.
18、2.1.13 splashover, nunwanted actuation caused by a ve-hicle in a lane adjacent to the lane in which a sensor is located.2.1.14 traffc monitoring device, nequipment that maycount and classify vehicles and measure vehicle flow charac-teristics such as vehicle speed, lane occupancy, turning move-ments,
19、 and other parameters typically used to portray trafficmovement.2.1.15 wire loop, none or more turns of loop wire woundin a slot sawed in the pavement.3. Summary of Practice3.1 The major steps in installing an inductive loop detectorsystem are:3.1.1 Preparing plans and specifications,3.1.2 Securing
20、the work zone,3.1.3 Installing underground conduit and pull box,3.1.4 Cutting a slot for the loop wire and lead-in wires,3.1.5 Installing the wires,3.1.6 Twisting the lead-in wires,3.1.7 Testing for proper operation of the wire loop andlead-in wires,3.1.8 Sealing the saw cuts,3.1.9 Splicing the lead
21、-in wires to the lead-in cable in a pullbox,3.1.10 Connecting the lead-in cable to the terminal strip inthe cabinet,3.1.11 Testing for proper operation of the wire loop, lead-inwires, and lead-in cable assembly, and3.1.12 Connecting the terminal strip to the electronics unit.3.2 Procedures needed to
22、 ensure work zone safety, trafficcontrol, and installation of conduit, pull box, controller cabinet,and any equipment usually placed in the cabinet, such as theelectronics unit, are not covered by this practice.4. Significance and Use4.1 This practice provides a method for the in-road instal-lation
23、of an inductive loop detector that consists of wire loops,lead-in wires, and lead-in cable. The practice is intended forinstalling wires in saw cuts made in the roadway surface andnot for installing preformed loops that may be encased in aprotective enclosure such as plastic conduit. Typical compo-n
24、ents of an inductive loop detector system are illustrated in Fig.1. Modern inductive loop detector electronic units are capableof detecting vehicles even if the wire loop is laid on reinforcingsteel before concrete is placed.5. Procedure5.1 Scale drawings of the installation site showing thegeometry
25、 of the roadway and the exact location of thecomponents of the inductive loop detector in relation to thepavement or lane markings are required. The drawings shallindicate the location and specifications for the wire loop(typically centered in the middle of the lane) and lead-in wires,lead-in cable,
26、 pull boxes, conduit, power sources, pavementmaterials and sealants, cabinets, and electronic units requiredfor the installation. The accuracy of the drawings has a primaryeffect on the quality of the installation as it provides funda-mental guidance for the installation crew and becomes part ofthe
27、procurement package used to acquire the needed compo-nents.5.2 The dimensions of the loops and number of turns areselected according to the types of vehicles to be detected,vehicle under-carriage height, lane width, length of lead-incable, and, for some applications, the data desired. Inductiveloops
28、 should not be wider than 6 ft (183 cm) in a 12 ft (366 cm)lane. Loops should not be less than 5 ft (152 cm) wide becausethe detection distance between the road surface and the vehicleundercarriage becomes limited as the detection distance isapproximately equal to one-half to two-thirds of the loop
29、width(such as, the minimum loop dimension). Since the inductanceof the loop must be greater than the inductance of the lead-incable that is, 21 H per 100 ft (69 H per 100 m) of #14 AWGlead-in cable for the loop system to have sufficient sensitivity,Klein et al (2) recommend that the inductance of si
30、ngle loopsand series, parallel, or series-parallel combinations of loops begreater than 50 mH to ensure stable operation of the inductiveloop detector system. Guidance for the number of turns neededto produce the required inductance value is found in Klein et al(2) as follows: “If the loop perimeter
31、 is less than 30 ft (9 m),use three turns of wire; if the loop perimeter is greater than 30ft (9 m), use two turns of wire.” Appendix X1 contains tablesshowing the inductance values for various size loops andshapes (such as, rectangular, quadrupole, and circular).5.3 Manpower and the type and amount
32、 of installationmaterial and equipment must be determined before the instal-lation is begun. The required materials should be available inFIG. 1 Inductive Loop Detector System (Notional) (2)E 2561 07a2sufficient quantities to avoid any interruptions in the installa-tion process. Table 1 contains a t
33、ypical materials list forconstructing an inductive loop detector. Table 2 containstypical equipment needed to install inductive loops. Theequipment required for traffic control and installation ofconduit, pull box, controller cabinet, and any equipmentusually placed in the cabinet are not included.5
34、.4 To protect the integrity of the pavement and loopinstallation, cracks and joints in the roadway pavement shouldnot be located closer than 18 in. (45 cm) upstream ordownstream of the inductive loop detector being installed.Some agencies relax this constraint to 1 ft (0.3m) (5). Saw cutsfor other w
35、ire loops or other in-roadway sensors must not belocated closer than 2 ft (0.6 m) upstream or downstream of theinductive loop detector being installed (6). The distancebetween lead-in saw cuts shall be 6 in. (15 cm) minimum untilthey are within 1 ft (0.3 m) of the edge of the pavement or curb,at whi
36、ch point they may be placed closer together (7). Lead-insaw cuts shall not be closer than 12 in. (30 cm) from adjacentloop edges (6).5.5 After securing the work zone with appropriate barri-cades, cones, and so forth to divert traffic from the work area,mark the pavement to show the size and shape of
37、 the loop andlead-in wires to be installed and the required saw cuts. Lumbercrayon, chalk, or spray paint is typically used for this purpose.If available, a template of the proper size and shape for the wireloop is recommended. However, a straight edge or a tightenedstring can be used as a marking g
38、uide. It is critical that themarkings reflect the location shown on the construction plans.5.6 Cut slots into the roadway pavement for the loop wireand lead-in wires using a pavement saw. Do not allow the sawcut in the pavement to deviate by more than 1 in. (25 mm) fromthe markings for the cut (7).
39、The depth of the saw cut shall besufficient to allow at least a 1-in. (25-mm) cover of sealant tobe placed above the top loop wire or backer rod if such is used(7, 9). Some agencies use 3 and 4 in. (76 and 102 mm) slotdepths for multiple wire-turn loops to prevent future grindingand overlay procedur
40、es from destroying the loop (9). Saw cutdepth should be verified at several points during the cuttingprocess to ensure a constant value. The width of the saw cutshall be sufficient to allow encapsulation of the wires by thesealant. Several methods are available to prevent damage to thewire at the co
41、rners of a square or rectangular loop by removingthe 90-deg angle. In the first method, diagonal cuts are sawedat the four corners, allowing a minimum margin of 1 ft (30 cm)from the apparent corner as shown on the left of Fig. 2. Whenapplying this method, ensure that the bottom of the saw bladecompl
42、etely passes through all intersections creating saw cutsthat are clean and well defined. All jagged edges and protru-sions must be removed with a small chisel and hammer. In thesecond method depicted on the right of Fig. 2,114-or112-in.(32- or 38-mm) holes are drilled at the corners of the loopbefor
43、e the slots are sawcut. Drilling the corners is faster (15 secper drilled hole) than cutting diagonal slots and the integrity ofthe pavement is better preserved (5, 8, 9).A3-in. (76-mm) holecentered on the circumference of a circular loop may be drilledto reduce stress on the lead-in wires run to th
44、e pull box (8). Inthe third method (not illustrated), straight sawcuts are over-lapped at the corners (i.e., no diagonal sawcuts are made) andthen the inside corner is removed using a small hand chisel andhammer or small air-powered impact chisel, thus creating asmooth curve for the wire to follow.5
45、.7 Clean out debris from saw cuts. Cleaning should takeplace immediately after the sawing is complete. Cutting dust,grit, oil, and contaminants must be removed from the slots byTABLE 1 Typical Materials List for 6-ft 3 6-ft (1.8-m 3 1.8-m)3-Turn Inductive LoopDescription Quantity/LoopLoop and lead-i
46、n wires, such as., IMSA513 or 51-5 (3)200 ft (60 m)ALead-in cable, e.g., IMSA 50-2 (3) 200 ft (60 m) or moreATape34 in. (20 mm) rubber splicingB1 roll per 6 loopsLoop sealant (per loop) 6 tubes or appropriate number of galloncontainersSealant per 4 ft (1 m) of lead-in cable 1 tubeCaulking gun 1Backe
47、r rod As requiredCement, sand, or talc 1 bagDuct seal for conduit 1 blockPull box (sized as required) 1 per splicing locationConcrete As required per pull boxSplice kits 1 per loopSolder As requiredSurge voltage protector As requiredConduit As requiredAQuantity varies according to site requirement i
48、ncluding loop location.BSome states specify a first layer of PVC tape followed by a layer of rubber tapeor heat shrinkage polyolefin tubing as insulation on the lead-in wire-to-lead-incable splice (4).TABLE 2 Typical Installation Equipment List for Inductive LoopDetectorsItem Description and UsePave
49、ment saw Creates saw cut for inserting wires. Typicallya self-propelled 18- to 65-hp saw equippedwith14-to38-in. (6- to 10-mm) thick blade(abrasive or diamond), water valve, depthgauge, and horizontal guideWater supply Cools diamond blade and cleans out sawedslotsJackhammer Bores holes through concrete curbAir compressor Used with jackhammer and to clean and drysawed slotsChisel and hammer Removes sharp edges at corners of sawcutsBlunt tool316-in. to14-in. (5-mm to 6-mm) thick woodpaddle for seating wire in sawed slotWire twisting tool Provides symmetrical t
