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Infrared Sensors for Counting, Classifying, and

1. aae Ra 1 CHAPTER 2 PHOTOELECTRIC FUNDAMENTALS sees Contrasto Reworeflectors CHAPTER 3 VEHICLE CLASSIFICATION SCHEMES Federal Highway Administration sssssssssssesenessseassnseeeesensesrenseeceequeecessanasssescensecsoet Oklahoma Turnpike Authority T T e American Association of State Highway and Officials lease ess A tiet American Society for Testing and Materials CHAPTER 4 SENSOR ARRANGEMENTS Roadside P v nientL evel CHAPTER 5 APPLICATIONS recess Pea sea see 000004 co sa sees see ees ese cet eo QN QN tA tA tA oon DIENEN Vehicle A Weighing vi CHAPTER 6 FIELD EVALUATIONS Single Dual Tire Identification and Vehicle Classification csssssscsssssssecssssssnssosccesesesssesssesssensessessssuecnsensorcesesenseaasenscesee ss 21 REFERENCES ECK 949999900090004044022440440440009044044 6004000400090 90909 90 00000004500 DEE DE EGET EEE SEES SHOR ES PROPOSTE 24 vii CHAPTER 1 INTRODUCTION Transportation engineers require information about traffic and traffic loadings in order to design pavements and other structures that will endure and function ad equately throughout the
2. Provide some flexibility in the mounting setup EN CE Two Axes 2 Mounting Whenever possible position the sensor looking down or at slight downward angle to avoid dirt build up on the lens Since the retroflector is a low cost component H it should be mounted on the side of the detection RUN region most subject to damage during normal opera tion Allow some room to move the reflector from side Alignment to side as well as up and down for alignment purposes Indicator To prevent misalignment due to large amplitude vibra tions both the sensor and reflector should be mounted rigidly with respect to each other Provide some means to aim the sensor for alignment For most installations Opcon recomends the use of its 6180A Universal Mounting Bracket For special applications or if dif ficulties are encountered contact Opcon s Applications Engineering Staff 1 800 426 9184 Opcon also sup 4 ply on request a user s manual industrial Photoelectic Possible mounting options using Rotation Controis PN 102264 the 6180A mounting bracket Select the mounting site carefully Reflex sensors operate by establishing a beam of in Retroreflector frared light between the sensor and a distant Working ur retroreflector The infrared light beam defines a detec Source and Range _ T a tion region having two important characteristics De
3. Streeter Amet Counter using reflex infrared sensor Fig A 4 Cast aluminum housing for mounting miniature infrared sensor on lane line 1 2 Fig A 5 Opcon reflex infrared sensor mounted on metal post off edge of shoulder MEM Fig Three types of Banner sensors used in study Reflex Sensor Module Installation Instruction Introduction Opcon s 14808 Reflex Sensor Module is designed to plug directly into the 80 Series Blue Eyes Control Modules The power supply and output device are contained in the control module The sensor head contains the infrared source and detector elements and all related Circuitry All required power and output wiring between the sensor head and con trol module is accomplished through the plugin connec tion Reflex control systems operate by establishing a beam of infrared light between a control unit and a distant retroreflector Retroreflectors because of their special sur face geometry reverse the direction of incoming light rays returning them to their source Retroreflectors will tolerate a certain amount of misalignment with the light source at lit tle or no loss in reflective efficiency Since the reflector is a low cost component it may be placed wherever there is a high probability of damage during normal operation The more expensive control components can be placed in a sheltered location Specifications Input Power Suppiied onty by Opcon Series 80
4. DISTANCE PERT OST ANCE Opposed mode sensors have higher excess gain than other models and therefore should be used whenever posmble The small sus of these sensors makes them ideal for many conveyor applications and their small effective beam size particularly of the ESR RSR models enables them to reliably detect relatively small objects VALU BEAM opposed mode sensors nave a visible red tracer beam which greatly simplifies sensor alignment ESR RSR models have a wide beam angle for very forgiving alignment within the 10 foot range ER models have narrow beam spread and should be used when it is important to minimize opucal crosstalk between adjacent emiter receiver pairs at close range in 1000 i eS EA SMASTESF SMS RSR SMAS1ESR SM2AS RSR X b uamowm 2 2 a PPOSEG O STANCE EET e M SM2AS 2Ly 5 SM912LV SM2A912UY z Q mammum 8 3 8EFLEZ OR i 4 8 24 ue 7 H DISTANCE TO REFLECTOR FEET DISTANCE H 5 4 2 Li 5 visible red light beam reduces the potential for false signals from highly reflective objects proxing and simplifies alignment AG giare models polarize ihe emuted light and filter cut unwanted reflections making thar use possible in applications otherwise unsuited r
5. Fig 6 9 Projected diagonal dimension of tire contact areas versus weight for front axle of drive tandem 550 Front Axle of Drive Tandem Right Side P 22 6W 299 R 2 0 72 33 Length Diagonal sq in 1 2 3 4 5 6 7 8 9 Wheel Weight kips Fig 6 10 Product of tire contact length and projected diagonal dimension versus weight for front axle of drive tandem 20 Front Axle of Drive Tandem Right Side 19 WD 0 121W 16 2 R 2 0 045 Tire Contact Width in on gt Wheel Weight kips Fig 6 11 Tire contact width versus weight for front axle of drive tandem 340 Front Axie of Drive Tandem ight Side 2 b a 300 A 10 3W 210 S 5 R 2 0 60 lt 5 260 5 amp 240 220 200 Wheel Weight kips Fig 6 12 Tire contact area versus weight for front axle of drive tandem Front Axle of Drive Tandem 19 Right Side 0 505W 13 1 Tire Contact Length in 1 2 3 4 5 6 7 8 Wheel Weight kips Rear Axle of Drive Tandem 19 Right Side L 0 566W 12 8 R 2 2 0 71 Tire Contact Length in 1 2 3 4 5 6 7 8 Wheel Weight kips Fig 6 13 Tire contact length versus weight for both axles of drive tandem 95 P All Axles Right Side L 0 547W 66 6 2 0 72 75 149 Vehicies Sum of Tire Contact Lengths in 10 15 20 25 30 35 40 Sum of Whee Weights kips Fig 6
6. ew SUMMARY Five field tests of infrared sensors were performed The objective of the first two tests was to determine the possibility of weighing vehicles with infrared sensors The objective of the other three tests was to determine the feasibility of improving or replacing current vehicle classification systems with infrared sensor systems In the tire contact area study performed at San Marcos Texas it was determined that the tire contact length but not the width could be calculated with reasonable accuracy from infrared measurements of vehicles moving at high speeds In the test at Junction Texas it was determined that infrared sensors could estimate only roughly the dynamic weight of vehicles by measuring the tire contact area The lateral position of tires was also measured In these two tests it was demonstrated that 22 infrared sensors could accurately measure vehicle speed and axle spacing patterns In the HOV high occupancy vehicle lane test in Houston it was shown that infrared sensors can replace inductance loop detectors which are currently used to measure vehicle speed length and headway In the endurance test at Jarrell Texas it was shown that infrared sensors can function for several months with minimal or no maintenance It was also demonstrated that axle counts by infrared sensors are at least as accurate as axle counts by piezo cables or human observers In the turnpike test performed in Oklahoma C
7. 1383B 1383R 1480B 1480R 1481R or 1580B Mechanical Case Noryi Plastic Terminais No 6 slotted screws in barrier strip Weight 1739 6 002 Sensor Head included Vibration or 06 inch displacement whichever is less over a frequency range of 10Hz to 2000Hz Module can be mounted from the bottom with two 20boits or from the side with three 10 32 x 2 boits Wiring Port 2 inch NPS conduit port is molded into the case bottom Adjustment Access Provided a removable panel the module s side Adjustment access is possible without disturbing mounting or alignment Power On Oelay Specifications subject to change without notice Z888 34 Rear View Cover Side 774 19 7 d 42 Sensor Head not included with control Dimensions in inches millimeters Sensitivity Adjustment turn fully clockwise for maximum sensitivity input and Output Label Note The pin guide ust be removed m if a logic card 18 used Front View Minimum Clearance for Head Removal Mounting The control module s mounting site s largely determined by the job to be done Whenever possible however avoid mounting sites that will subject the control module to Severe vibration or impact shocks protect the lens trom abrasive materiais or exposure to chlorinated halogen ated or aromatic hydrocarbons Exercise special care if you must open the cont
8. Figure A 3 shows a StreeterAmet traffic counter normally connected to a road tube connected to an Opcon sensor A retroreflector is also shown Figure A 4 shows a cast aluminum housing which can be mounted on the lane edge a Banner sensor is shown both inside and next to the housing 25 Figure A 5 shows an Opcon sensor mounted off the shoulder edge on a metal stake Figure A 6 shows three different Banner sensors used in the field tests At the top left is a sensor with a built in counter with liquid crystal display The sensor at the top right was used in some preliminary tests The sensor at the bottom was used at Junction inside the cast aluminum housing Detailed descriptions of the infrared sensors shown in Figs A 1 through A 6 appear in the following pages Descriptions of the Opcon reflex sensor the DC NPN control modules and the three Banner sensors pictured in Fig A 6 are included The OR gate circuit diagram used on the HOV lane in Houston is shown in Fig A 7 Figure A 8 shows the system layout for the three sensor vehicle classification system used in the field tests at San Marcos Junction and Jarrell Figure A 9 shows the system layout of the two sensor vehicle classification system used in the Okla homa City field test 26 Fig 1 Metal box housing two Opcon infrared sensors HOV lane in Houston ig A 2 Infrared sensors loop detector Motorola Evaluation Board and IBM portable computer Fig
9. ee The dirtier the conditions the shorter the range shouid be for reliability Reflector 25 in 6 25 at 12 5 out 4 the detector 9x e Basic Reflex Alignment Reflex alignment consists basically of aiming the Retroreflector positioned in sensor at the reflector to establish the infrared light the center of the sensor s beam and adjusting the reflector s position so that field of view it is on the sensor s optical centertine Acjust the control moduie s sensitivity to max fully clockwise Detection 2 Aim the reflex sensor at the retroreflector The Region contro module s indicator light will glow red when the infrared light beam is established Move reflector from side to side as well as up and down mark the points where the reflec tor moves out of the sensor s of view the alignment indicator will go off at that point Position the reflector in the center of the sen sor s field of view as shown Secure both the sensor and reflector Be sure that the reflector and sensor are rigidly mounted with respect to each other Severe Limits of the sensor s field of vibration or impact shock could shift the view the alignment indicator will relative positions of the sensor and reflector A turn off if the reflector is moved false detection event could occur if the posi past these points tion shift was large enough to move the reflec tor out of the sensors fiel
10. m OBJECT AETBOREFLECTIVE TARGET i Ei i i RECEIVER i Models SMA9IE amp SM9IR Voltage 10 30V dc CE 10 250 Range 200 feer 60 m Response Sms on 4 off Beam infrared 880m visible red tracer beam Effective heam 0 5 dia SMA9IE amp SM2A9IR Voitage 24 to 250V ac 10 250 ac dc Range 200 feet 60 m Response 8ms on 4 off Beam infrared 880nm Effective beam 0 5 dia SMASIESR amp SM91RSR Voltage 10 to 30V de CESR 10 250 ac dc Range 10 feet 3 Response on 4 off Beam infrared 880nm Effective beam 12 SMASIESR amp SM2A91RSR gt Voltage 24 to 250V ac Range 10 feet G m Response 8ms 4 off Beam infrared 880nm Effective beam 12 dia SM912LV Voluge 10 to 30 dc Range 30 feet 9 m Response 4ms on off Beam visible red 650nm SM2A912LV Voltage 24 to 250V ac Range 30 feet 9 m Response 8ms on off Beam visible red 650nm SM912LVAG anti glare filter Voltage 10 to 30V de Range 15 feet 4 5 m Response 4ms on off Beam visible red 650nm with polarizing filter SM2A912LVAG anti glare filter Voltage 24 to 250V ac Range 15 feet 4 5 Response 8ms on off Beam visible red 650nm with polarizing filter Excess Gain Beam Pattern amp SM9 R amp 7 SM2A91R OFT
11. The correlation coeffi cients are 0 64 for tire contact length versus weight and 0 72 for projected diagonal dimension versus weight It might be possible to indicate whether trucks are empty or loaded but the accuracy is insufficient to warrant any fur ther study at this time Accurate estimation of weight is not feasible SUMMARY The tire contact area dimensions of the front axle are very poorly correlated with the weight The tire contact lengths and projected diagonal dimensions have similar values indicating that the tire contact patch for single tires is close to circular Many of the front tires had lengths longer than the projected diagonal dimension partially due to dynamic forces acting on the tire A rect angular tire contact patch is assumed for the tire contact width calculation This assumption is not valid especially for the front tires Values calculated for width are not correlated with weight On the plots for tire contact length and projected diagonal dimension versus weight for the tandem axles there are two definite clusters of data points representing the empty and loaded trucks However the accuracy is not adequate even for estimating weight to within 10 000 pounds Closer estimates of weight do not seem to be possible at this time More information is needed than can be sensed by infrared sensors i e tire pressures and shapes of the tire contact patches If remote tire pressure sensing technology were d
12. and axle spacings were tape measured For the in motion measurements infrared sensors were set at the edge of the shoulder and aimed at retroreflectors in the middle of the adjacent lane Two infrared beams perpendicular to 12 the lane edge measured vehicle speed and tire contact length while a diagonal beam measured a projection of the diagonal dimension of the tire contact area as shown in Fig 6 1 Assuming a rectangular shape for the tire contact area the length and projected diagonal dimension were calculated by multiplying vehicle speed by the time of beam interruption for each tire Width was computed by subtracting the length from the projected diagonal dimension then dividing this remainder by the tangent of the angle between the diagonal and perpendicular beams Static tire contact lengths and widths were measured directly with the special calipers The axle spacings measured by infrared sensors and tape corresponded closely which implied that speed cal culations were accurate The lengths and widths of the tire contact areas are shown graphically in Figs 6 2 and 6 3 and are summarized in Table 6 1 If there were per fect agreement between the two sets of measurements shown in the figures all data points would fall on the 45 degree line The length values agree more closely than the width values The widths measured manually are closely spaced around 21 inches while the widths mea sured in motion are more widely dispers
13. quick disconnect QD models available optionally one connector pin goes unused Three conductor cable for QD models mast be purchased separately ADJUSTMENTS LIGHT DARK OPERATE select switch and SENSITIVITY control potentiometer both located on rear sensor g ADJUSTMENTS LIGHT DARK OPERATE select switch and SENSITIVITY potentiometer both located on rear of sensor INDICATOR LED exclusive patented Alignment Device system AID US patent 4356393 lights wp nd LED ime dU ong agerent the light signal strength the stronger the signal the pulse rate Md SMASIE has a visio ned toe INDICATOR LED top mounted red LED indicator lights when output is conducting Model SMAQIE emitter has visible red tracer beam which indicates power on and enables easy line of sight alignment OPERATING TEMPERATURE RANGE 20 w 70 deg rees C 4 158 degrees F iE OPERATING TEMPERATURE RANGE 4 to 158 degrees F FUNCTIONAL SCHEMATIC SM912 SERIES DC VALU BEAM SENSORS 20 to 70 degrees FUNCTIONAL SCHEMATIC SM2A912 SERIES AC VALU BEAM SENSORS Tresaient Protection Voltage 46 VALU BEAM 912 Series Sensors Sensing Mode o OPPOSED MODE EMITTER 1 true RETROREFLECTIVE MODE
14. quired to operate the system Signal Received Threshold Signal High excess gain values for a given range indicate that a system has reserve signal strength to overcome the effects of dirt and contamination The accompanying graphs are performance estimates calculated for clean air clean lens and optimum alignment Conditions in the working environment will vary considerably The plotted values are based on the signa returned from Clear ptastic retroreflector Curves for 3in and 1 Yin diameter reflectors are given A curve lor a seven reflec tor array is also shown The graphs are useful tools for achieving the highest excess gain consistent with mounting requirements Specifications subject to change without notice Josues Reflector Arrays 1908 wah ym A antec Ll Li Larger diameter reflectors can increase performance at ex 2a M ded treme range Effectively this can be achieved by arranging KANN or several retroreflectors in a circular array Of course there is m 4 Y MB ven spen advantage in increasing the reflectors diameter beyond the pM ee E boundary of the sensor field of view Note also that since the effective beam diameter of a reflex unit is related to reflector diameter a larger object will be required to block a larger diameter beam The accompanying excess gain curve shows the typical
15. s University Sup port Program in Austin furnished at no cost numerous microprocessor devices and electronic components and also supported the research through Motorola s facilities in Phoenix Southwestern Materials provided retroreflec tors of various types for experimentation these con tributions and others not mentioned specifically are sin cerely appreciated ABSTRACT In this study five field tests were conducted to determine the feasibility of using commercially available infrared light beam sensors for counting classifying and perhaps weighing vehicles It was demonstrated that a single reflex type infrared sensor mounted just off the shoulder and working off a retroreflective raised pavement marker in the center of the outside traffic lane can be used to count the tires on one end of each axle of a moving vehicle with accuracy comparable to that of human observers or that of a flush mounted piezo strip sensor Sensor installation involved no pavement cuts and only minimal interference to traffic Tests were not conducted in snow or heavy rain Arrays of two or more infrared light beam sensors can be used to sense vehicle iii body presence to calculate vehicle speed axle spacing and tire contact patch dimensions to indicate single or dual tires to detect direction of vehicle movement and to sense over height vehicles Off shoulder reflex type infrared sensors with retroreflective raised pavement mark
16. Controi Modules do not connect the head to external power Response Time LT to DK Transition 5ms DK to LT Transition Note For total response time add the contro module s response time Environmentai Operating Temperature 40 C 40 F to 55 131 F Storage Temperature 40 C 40 F to 75 C 167 F Operating Humidity 95 Relative Humidity Storage Humidity 95 Relative Humidity Max NEMA 3 4 12 13 NOTE The 14808 meets NEMA 4 specification wash down proof when used with the following control modules 8880C 81C 84C 6501 8880C 81C 84C 6502 and 88828 6501 Sunlight Immunity 10 000 Foot Candies Note 10 000 Foot Candles is equivalent to direct suntight reflecting off a diffuse white surface Mechanical Case Plastic Lens Clear polycarbonate Note Avoid exposing the lens or case to chlorinated halogenated or aromatic hydrocarbons Vibration 5G or 06 inch displacement whichever is less over a frequency range of 10Hz to 2000Hz Alignment Aid Gunsight groove on the case top opcon 4 80 121 Reference Dimensions for Center of Lens Dimensions in inches millimeters Optical Optical performance is measured in units of excess gain Gx Excess gain is the ratio of received infrared signal strength to the minimum signal threshold re
17. Highway 24 and Transportation Officials Washington D C 1990 7 Standard Specification for Highway Weigh in Motion WIM Systems with User Requirements and Test Method E 1318 90 American Society for Testing and Materials Philadelphia 1990 8 Schulz Jeff University of Colorado personal corre spondence 9 Overheight Vehicle Warning Systems in Mississippi Hanchey Craig M and Slade F Exley TE Journal June 1990 pp 24 29 10 Test of a System to Classify Vehicles for Toll Collec tion Gattis J L and Clyde E Lee Report to Traffic Engineering Consultants Inc October 1990 APPENDIX Photographs and descriptions of the equipment and circuit diagrams of the systems used in the field evaluations are included in this appendix Figure A 1 shows the metal box housing two Opcon infrared sensors which was placed on top of a concrete median barrier on one side of the Houston HOV lane Figure A 2 shows from left to right a loop detector two Opcon reflex type sensors mounted on a tripod a Motorola evaluation board and IBM computer The M68HCIIEVBU universal evaluation board manufactured by Motorola can be used to process and store the output signals of infrared sensors The board is a single chip microcontroller unit which can operate programs down loaded from an RS 232C compatible host computer Space is provided on the board for custom interfacing The primary power requirement is 5 0 Vdc 950 mA
18. POSITION Measurements at Junction Texas Infrared Sensors vs Weigh in Motion Axle Spacing Dimensions ft 12 1823 IR34 1845 9 13 411 23 39 3 89 21 03 4 90 53 39 4 17 Mean 15 10 431 31 35 Std Dev 2 94 0 07 3 25 Speed mph 60 18 57 38 Lateral Position in Theoretically the diagonal dimension and projected diagonal dimension cannot be less than the tire contact length or width A circular tire contact area for which all these dimensions are equal represents the limiting case Some of the single tires on front axles were mea sured with lengths and projected diagonal dimensions close to the same value Inconsistencies in the in motion measurements are due in part to the dynamic behavior of the vehicle and the tires during the time of sensing The location and cross section of the rolling tire changes be tween the time the length is measured and the time when the projected diagonal dimension is measured The eleva tion of the tire may also change slightly i e the tire may ride into a depression or bounce off the pavement caus ing a different cross section to be measured If the height 4 02 IR12 and WIM 12 represent the spacing between the first and second axle etc WIMI2 WIM23 8 80 3 90 25 70 3 60 WIM34 WIM4S5 20 20 4 90 51 70 4 10 14 57 4 18 30 31 3 90 2 83 0 11 3 11 0 09 above the pavement of the two infrared beams is slightly different at the two measuring locations different tir
19. SMA99R PAm mm an TL GPEOSED DISTANCE FEET DISTANCE 1900 Opposed mode sensors have higher excess gain than other models and therefore should be used whenever possible Opposed mode is the most reliable sensing mode for counting opaque materials The small size of these sensors makes them ideal for many conveyor applications and their small effective beam size particu larly of ESR RSR models enables them to reliably coum relatively small Objects ESR and RSR models also have a wide beam angle for very forgiving alignment within the 10 foot range VALU BEAM opposed mode sensors have a visible red tracer beam which greatly simplifies sensor alignment eS KL SMAS ESR amp So EON s RS EET R P eomm 4 5 8 OPPOSED DISTANCE FEET DISTANCE iti 8RT 3 REFLECTOR 5 E Ei 24 FT P DIS ANCE TO FEET OISTANCE A visible red light beam reduces the potential for false signals from highly reflective objects proaing and simplifies alignment The AG anti glare model polarizes the emitted light and filters unwanted reflections making use possible in applications otherwise unsuited to retroreflective sensing and where reduced excess gain is acceptable Maximum range with all units is attained when using the model BRT 3 3 comer cube retrorefl
20. and are so marked on their labels P N 03403C7D 37 38 SM2A312LV s wide array of mounting optons is designed to simplify mounting and atignment in any indust ral environment Its 18 mm threaded barrei allows it to be physically interchanged with existing 18 mm barrel sensors and proximity switches t may also mounted using an adjustable stainless steel side mounting bottom mounting bracket models SMB312S and SMB3 2B re MOUN PTI SMB312S Side Mounting Bracket 4 Mounting Front of sensor C L tilts vertically from horizontal SMB312S Bracket stainless steel SMB312F Mounting Foot bottom view Mounting peg requires 270 clearance SM8312F mounting foot Lower barrel esay mourting screw hokis mounting toot lo sensor body spectively which allows two axes of sensor movement and thus greatly simplifies alignment Alternatively the SMZA 312LV can be cusiom mounted via its built in mounting peg and a special accessory mounting foot model 5 8312 with brass threaded screw insert SMB3128 Bottom Mounting Bracket SMB312F Mounting foot supplied with SMB3128 SMB312B Bracket stainless steel Sensor rotates horizontally on bracket 10 degrees frorn position shown Bracket tilts vertically 10 degrees from position shown pee m we ee DIMENSION DRAWINGS FRONT VIEW Lens SIDE VIEW Mounting holes 2 4 screw cl
21. axle acounts 9 Retroreflector Infrared Reflex Sensor Inductance Loop Detector TRAFFIC Guardfence Post 12in Gin pau o a gt 12 ft Lane Fig 6 18 Sensor arrangement at Oklahoma City system required both loop detectors shown in Fig 6 16 and it was not possible for the loops to be used by both systems simultaneously Figure 6 17 shows a comparison between axles counted by infrared sensors piezo sensors and by three human observers The three human observ ers never agreed exactly so an average count is shown in the figure Except for period one the infrared sensor axle counts were greater than the piezo sensor axle counts Using the manual axle counts as a basis the ex pected error for the piezo sensor was ten axles per 15 minutes and for the infrared sensor two axles per 15 minutes This calculation is based on only five periods Infrared sensors can be used for long term traffic sur veys if proper precautions are taken to protect the sensors and retroreflectors from the environmental effects Envi ronmental effects include rain road film temperature ex tremes and shock and vibration from vehicles SINGLE DUAL TIRE IDENTIFICATION AND VEHICLE CLASSIFICATION A system for classifying vehicles for auditing toll collection was tested on Interstate 44 Turner Turnpike in Oklahoma City in August 1990 At the test site about 500 yards downstream of a toll plaza vehicles were trav e
22. contact patch is not rectangular and constantly changes the in motion tire contact widths did not agree very well 23 Another study was performed at Junction Texas to determine the feasibility of using infrared sensors to weigh vehicles Infrared sensors measured tire contact dimensions and WIM transducers measured wheel weights simultaneously It is not feasible to estimate weight from tire contact dimensions measured in motion Infrared sensors can be used to determine the lateral posi tion of tires with respect to the WIM transducer thus im proving the performance of WIM systems A third field test was performed on an HOV lane in Houston to determine the feasibility of replacing an array of three inductance loop detectors used for calculating vehicle speed length direction and headway with an ar ray of two infrared reflex sensors With minor modifica tions of the sensor housings and the current computer software infrared sensors can replace the loop detectors Five infrared sensors were installed near Jarrell Texas to test long term performance For applications longer than about a week it is necessary to mount pavement level sensors off the shoulder to protect them from the shock of heavy vehicles and the accumulation of road film Small retroreflectors used on the pavement surface for measuring tire contact dimensions accumulate road film and must be cleaned every two or three days Larger retroreflectors or reflectorize
23. contain a built in 6 digit totalizing counter Sensor models are available for opposed retroreflective and convergent beam sensing modes In addition there are models for use with both glass and plastic fiberoptics A special infrared retroreflective version is available which is de signed for counting people passing through ways It has built in on off time delays to minimize the chance of multiple counts The 990 series VALU BEAM s 6 digit LCD counter is reset simply by touching the area of the housing shown with the permanent supplied with the sensor see dimension draw ing below Standard models automatically reset to zero upon power up Memory backup option SMA990 series sensors with internal 990 Series Counter BANNER the photoelecinc specialist memory backup for maintaining count memory while power is removed are available by special order These models will hold a count for over 100 hours and are indicated by the model number suffix MB i e SMA990L VMB is the memory backup version of sensor model SMA990LV Contact the factory for availablility and pricing of these models SMA990 series sensors wire directly to either 10 250V 50 60Hz or 12 to 115V de PECIFICATIONS SMA99 SUPPLY VOLTAGE 10 to 250V ac 50 60 2 or 12 to 115V dc at less than 20 milliamps SENSOR RESPONSE 15 milliseconds LIGHT 15 milliseconds DARK 100 milliseco
24. downstream The output signals of the two presence sen sors should be connected with a logical AND Infrared sensors mounted on the pavement surface at the lane edge have been used in a bridge research study to detect approaching vehicles and indicate the lane of operation in advance of the instrumented bridge Ref 8 Tape switches had been used earlier but required closing lanes and re taping after rain The lenses of the infrared sen sors and retroreflectors can be wiped clean without clos ing lanes COUNTING Only one infrared sensor is necessary for counting vehicles or tires though an array of sensors may be desir able Overhead or roadside mounted sensors may be used instead of inductance loop detectors to count vehicle bodies Infrared sensors mounted at the pavement level may be used instead of pneumatic road tubes or piezo cables to count tires or axles DIRECTION The direction of a vehicle can be determined when two infrared sensors are used Roadside or overhead mounting is recommended but pavement level mounting may also be used When a vehicle breaks the beams in the wrong order a warning of wrong way travel may be given to the driver This application may also be used for directional traffic counts on lightly traveled two way roads VEHICLE HEIGHT Infrared sensors mounted on the roadside may mea sure the height of vehicles or at least give the range of 10 height Two or more sensors should be mounted at di
25. films Spherical bead retroreflectors consist of glass beads embedded in a diffuse reflecting binder Ref 3 Both types have the property of returning incident light beams straight back to the source as long as the angle of light incidence is less than about 15 degrees The corner cube type is more efficient than the spherical bead type If a polarizing filter is used on the sensor the corner cube retroreflector will reflect polarized light The comer cube type is commonly used on streets and high ways in raised pavement markers and in guide signs Both types are also available as reflective sheeting For best efficiency provision must be made to protect retrore flectors from accumulations of dust and moisture This is usually accomplished with a clear plastic or glass cover The size and efficiency of retroreflectors determine the excess gain as described above and also the sensing range Larger retroreflectors or an array of retroreflec tors will reflect more light energy thus increasing the range excess gain and effective beam size SUMMARY Photoelectric sensors have been used for many years In the past decade it has become feasible to use infrared sensors for traffic engineering applications The three TABLE 2 1 EXCESS GAIN GUIDELINES Source Ref 2 Minimum Excess Gain Required Operating Environment 1 5X 5X Slightly dirty slight build up of dust dirt oil moisture etc on lenses or reflectors lenses are cl
26. have one current sourcing PNP and one current sinking NPN open collector output transistor with each output capable of sinking 250mA continuous SM 912 series DC sensors interface directly to PCs and other solid state circuitry including Banner series modules MICRO AMP logic modules and MULTI AMP CL series modules see hookup diagrams page 6 SM2A912 series 2 wire AC sensors connect in series with a load exactly like a limit switch and have solid state switching element which switches up to 500mA 60VA continuous 4A inrush SM2A912 series AC sensors interface direcdy to PCs and also may be connected in senes or in parallel with other sensors or relay contacts for applications Specifications SM912 series dc sensors SUPPLY VOLTAGE 10 to 30V dc at 20mA exclusive of load except for SMA91E and EQD emitters which operate from 10 to 250V ac or de 10 OUTPUT CONFIGURATION one current sourcing and one current sinking NPN open collector transistor PNP SM2A912 series 2 wire ac sensors continued next page Printed in USA BANNER the photoelectric specialist requiring complex logic functions see hookup diagrams page 7 All VALU BEAM s nsors have an easily visible top mounted ted LED indicator to assist in alignment and system moni toring SM912 series DC sensors have Banner s exclusive patented AID system Alignment Indicating Device US patent 4356393 which lights
27. in Motion ft Fig 6 5 Comparison of axle spacing supported by the WIM transducer Measurements resulting from all off transducer vehicles were excluded from this analysis A summary of field measurements is shown at the bottom of Table 6 2 Figures 6 6 through 6 15 present tire contact area di mensions of various tires or sets of tires versus weight All dimensions and weights are for the right side tires Tire contact lengths projected diagonal dimensions of tire contact area and weights are summarized in Table 6 3 FRONT AXLE Figure 6 6 presents tire contact length versus weight for front axles A least squares regression line of these data points is shown assuming that weight is the inde pendent variable Dynamic measurement of tire contact length is probably accurate to within about 1 inch slightly more than the standard deviation for the front axle 0 8 inches The regression line is valid only for ob served tire contact lengths from about 16 to 18 inches while weights ranged from about 2 500 to 5 500 pounds Therefore it is not feasible to estimate weight adequately from dynamic measurement of tire contact length The standard deviation of tire contact length for the front axle is smaller than that for the other axles but tire contact length is a poor estimator of weight Projected diagonal dimension versus weight for front axles is shown in Fig 6 7 A least squares regression line is shown assuming that weight is
28. is not attenuated Each sensor has an excess gain curve which shows ex cess gain versus range For reflex sensing excess gain also depends on the type and size of the retroreflector Excess gain is greatest at close range and falls to one at the maximum range Guidelines for choosing sensors on the basis of excess gain are given in Table 2 1 The oper ating environment includes a cleaning schedule for lenses An excess gain of 1 5X for a clean environment includes a safety factor An excess gain of 50 will pen etrate see through paper or thin cardboard In this study the environmental effects of concern were dust dirt oil moisture and shock and vibration from cars and heavy trucks CONTRAST Contrast is defined as the ratio between light re ceived by the detector in the light condition and in the dark condition The dark condition occurs when the light 3 beam is blocked When the beam is completely blocked light received is zero and contrast is infinite Contrast should be as high as possible for optimum reliability This is important when the light beam is partially blocked or when a specular reflection is returned to the detector Contrast can be controlled by adjusting the sen Sitivity or excess gain of the detector RETROREFLECTORS There are two basic types of retroreflectors used for the reflex sensing mode corner cube and spherical bead Corner cube retroreflectors consist of tiny plastic prisms embossed in thin
29. one tenth second on off delay helps prevent multiple counts Maximum retroreflective signal strength is attained when using the model BRT 3 comer cube retroreflector Other retroreflective may also be used see the Banner calalog for descriptive information 1000 cSMASSOCV K Q 8 5 5 so 0n DISTANCE C 90 WHITE TEST CARO NCHES DISTANCE VALU BEAM convergent sensors produce a precise 06 diameter visible red sensing spot at a focus point 1 5 in front of the sensor lens Due to very narrow depth of field this model excels at counting smal objects only a fraction of an inch away from backgrounds This convergent sensor may be used forreliable counting of some radiused products which flow past ata fixed distance from the sensor lens Z Q owm xm E O DISTANCE 90 WHITE TEST CARD ACHES DISTANCE ENVIRONMENTAL FACTORS FOR PLASTIC FIBEROPTICS OPERATING TEMPERATURE OF FIBEROPTIC ASSEMBLIES 30 to 70 20 10 158 CHEMICAL RESISTANCE OF FIBEROPTIC ASSEMBLIES the acrylic core of the monofilament optical fiber will be damaged by contact with acids strong bases alkalis and solvents The polyethylene jacket wil protect the optical fiber from most chemical environments however materials may migrate through the jacket with long term exposure Samples of plastic fiberoptic material are available fr
30. spacing pattern are the classification criteria The number of tires is not used There is an overlap in the axle spacings be tween the three axle single trailer truck and the passen ger car with trailer An ASTM task group is currently de veloping a standard vehicle classification scheme SUMMARY Both FHWA and OTA use the number of axles per vehicle and the number of tires per axle for their vehicle classification schemes In addition FHWA uses the num ber of trailer units AASHTO considers the number of units and axle spacings but not the number of axles per vehicle or number of tires per axle ASTM considers the number of axles per vehicle and axle spacing pattern but not the number of trailer units or number of tires per axle The next chapter considers the infrared sensor arrange ments which can be used to count or measure the differ ent classification criteria CHAPTER 4 SENSOR ARRANGEMENTS Different arrangements of infrared sensors count or measure different criteria used to classify vehicles Each type of arrangement has different properties and potential applications These arrangements include overhead roadside and pavement level as shown in Fig 4 1 1 2 3 4 and 5 represent sensor positions while R1 R2 and R3 represent retroreflectors or receivers In the first two arrangements vehicle bodies are detected in the third arrangement tires are detected In the pavement level arrangement the infrared lig
31. status Response Time Instantaneous ON and OFF Controls Switches and Indicators Alignment indicator Light An alignment indicator light is visible through a lens located on the back of the module The indicator giows red whenever the detector element sees infrared light from the source beam complete On Thru Beam systems only the detector module s indicator light functions as an alignment aid the source module s light serves as a power 07 indicator LT ORK Mode An active output on beam complete LT or beam blocked DRK can be obtained by selecting the ap propriate wiring configuration Sensitivity Adjustment A potentiometer varies the controi module s responsiveness to the level of incoming infrared light detected by the sensor head The sensitivity adjust ment range is 20 to 1 At minimum sensitivity a propor tionally greater amount of infrared light is required to turn the output ON Normally the control module is set at max imum sensitivity fully clockwise which insures reliable operation even through dust in the air and dirt build up on the sensor s lens Environmental Operating Temperature 40 C 40 F to 55 C 131 F 40 C 40 F to 75 C 167 F 95 Relative Humidity 95 Relative Humidity Max 3 4 12 13 NOTE NEMA 4 wash down proof specification is met when these control modules are used with the following sensor heads 1180R 1180B 1280B 1380B 1381B 1382B
32. term performance A piezo cable and two loop detectors were also installed as shown in Fig 6 16 The infrared sensor array consisted of a set of three sensors with the beams inside a loop and a set of two sensors placed upstream and downstream of another loop detector Prior to installing the sensors shown in the figure a set of five low profile sensors not shown in the figure was placed on the pavement surface at the edge of the lane Cast aluminum and epoxy housings were used to protect the miniature infrared sensors approximately 1 5 X 2 0 X 0 5 inches After about two weeks in summer temperatures the sensors became nonfunctional because the beams were no longer high enough to crest the high point beside the wheel path rut since they were depressed into the flexible pavement Small 1 2 inch diameter retroreflectors in a similar but smaller cast aluminum housing endured for about two months A larger circular segment sawn from a 1 5 inch diameter retroreflector and housed in a special aluminum casting was first used but water migrated past the epoxy seal of the saw cut and accumulated on the plastic reflecting surface preventing retroreflection of the light beam A second set of five infrared sensors approximately 2 0 X 2 0 X 4 0 inches was placed on steel stakes driven into the ground a few inches off the shoulder edge The locations of these sensors are shown in Fig 6 16 They performed well for over two months and could be ea
33. the independent vari able The regression line is valid only for projected di agonal dimensions between 17and 20 inches while weights ranged between 2 500 and 5 500 pounds The standard deviation 2 6 inches is greater than the ex pected accuracy about 1 inch therefore it is not appro priate to use the projected diagonal dimension of the tire contact area to estimate weight Evaluation of the data shown in these two figures indicates that wheel weights cannot be estimated from the tire contact lengths nor pro jected from diagonal dimensions with acceptable accu racy The front axle tires had longer contact lengths than the tandem axle dual tires As expected for single tires the projected diagonal dimensions of the front axle tires were considerably shorter than those of the tandem axle ures which were all dual Some of the front axle tires in fact had measured in motion lengths longer than their projected diagonal dimensions The technique described in the previous section for calculating tire contact width yielded negative values for tire contact widths in these cases The dual tires all had measured in motion lengths less than the corresponding projected diagonal dimen sions Analysis of the field data indicated that the calcu lated tire contact width for tires on tandem axles was not correlated strongly enough with weight to serve as as an adequate weight estimation basis 15 TABLE 6 2 AXLE SPACING SPEED AND LATERAL
34. the indicator LED whenever the sensor sees its modulated light source and also pulses the LED at a rate proportional to the received light signal strength This feature grea y simplifies alignment in most situations alignment becomes simply a matter of positioning the sensor for maximum LED pulse rate On the SM2A912 series 2 wire AC sensors the LED lights steadily whenever the load is energized VALU BEAM 912 series sensors offer a choice of light or dark operate in the same sensor switched via a convenient rear panel control VALU BEAM sensors may be mounted from either the front or the rear using their two through mounting holes or by the outside threads of their base mounting nut supplied making them ideal for conveyor and other production line applica tions versatile 2 axis steel accessory mounting bracket model SMB900 simplifies mounting and alignment The bases of standard VALU BEAMs have a 1 2 NPS integral internal conduit thread and are supplied with a 6 foot PVC covered cable Models with a NEMA 4 rated quick disconnect connector QD models are available optionally page 8 Specifications SM2A912 series 2 wire sensors SUPPLY VOLTAGE 24 w 250V ac 50 60Hz except for SMA91E and EQD emitters which operate from 10 to 250V ac or de 10mA max OUTPUT CONFIGURATION solid state switching element continued next page P N 03467A8A VALU BEAM 912 Series Sensors ac specificatio
35. unwarranted after observing disabling amounts of road film accumulating on sensor lenses and retroreflec tors after only two or three days of traffic This report will first describe how infrared sensors operate Next it will list a few of the vehicle classifica tion schemes currently in use It will then discuss differ ent ways in which sensors and retroreflectors can be ar ranged Finally it will discuss various applications and field experiments using infrared sensors CHAPTER 2 PHOTOELECTRIC FUNDAMENTALS A basic knowledge of photoelectric fundamentals is essential to understanding the arrangements applications and limitations of infrared sensors as they are used to count and classify vehicles in motion This chapter gives a brief history of photoelectric sensors and introduces concepts and terminology DEVELOPMENT ELECTRIC EYES Photoelectric sensors have been around since the 1950 s when incandescent lamps were used with cad mium sulfide photocells in systems commonly called electric eyes When sufficient light hits the surface of the photoceli it conducts current to an output device When the light is blocked the cell stops conducting current and the output device directs an electric circuit to open a door or perform some other action Several drawbacks of this system are that the incandescent bulb burns out rather quickly and is susceptible to vibration and temperature both the bulb and the photocell are covered by
36. 12LV requires that it be mounted securely and aligned properly Excessive movement or vibration can in intermittent or false operation caused by loss of alignment to the retro target For best results the SM2A312LV should be mounted using one of the four methods described on page 2 Alignment of the SM2A312LV is quite simple and is accomp lished as follows 1 With power applied to the SM2A312LV direct its visible red light beam at its retro target while observing the red LED indicator on the back of the sensor Temporarily reducing the ambient light level in the room will make the red sensing beam easier to see and align With the GAIN control set at the clockwise end ol rotation maximum gain center the sensing beam on the target 2 Place the object to be sensed in sensing position between sensor and target Best retrorefiective sensing results are usually obtained when the sensor is operating at the maximum excess gain possible without buming through the object or reacting to light reflected from the object proxing the red LED indicator remains on with the object in sensing position an indication of burn through or proxing reduce the GAIN control until the LED goes out then reduce the gain by two more full turns Remove the object fram the sensing position while observing the LED If the LED goes on with the object removed from the sensing position alignment is complete Proxing occurs wh
37. 14 Sum of tire contact lengths versus sum of weights for all axles 140 All Axles Right Side B 5 PDD 0 671W 107 110 R 2 z 0 64 149 Vehicles 35 Sum of Diagonal Dimensions in 10 15 20 25 30 Sum of Wheel Weights kips 40 Fig 6 15 Sum of projected diagonal dimensions of tire contact areas versus sum of weights for all axles TABLE 6 3 SUMMARY OF TIRE CONTACT AREA AND WEIGHT 149 Five Axle Semi Trailer Trucks Right Side Only Tire Length Axle Axle Axle Axle Axle Tan Tan In d 2 3 4 _5 demi Minimum 15 40 1347 13 15 12 84 11 96 26 62 25 06 Maximum 19 48 18 20 1839 1846 19 26 36 00 37 26 Mean 17 15 1607 15 96 15 82 15 99 32 03 31 81 4 Dev 0 76 1 05 1 10 1 30 1 29 2 10 2 51 Projected Diagonal Dimension in Minimum 903 24 26 23 97 20 73 20 73 48 24 4147 Maximum 22 03 2965 2933 29 13 28 90 57 51 56 99 Mean 18 73 2688 26 81 2623 26 23 53 68 52 46 Std Dev 2 63 1 18 1 12 1 63 1 61 2 23 3 18 Weight tb Minimum 2 528 2 008 2 128 1 288 1 296 4 136 2 680 10 984 Maximum 5 544 8504 8344 9 424 9 936 16464 17 560 35 848 Mean 4 145 5 903 5 639 5 229 5380 11 542 10 608 26 295 Std Dev 527 1 698 1 640 2 123 2 087 3 292 4 133 7 423 estimate weight from infrared sensor measurements with reasonable accuracy In an attempt to explore other possible weight esti mation techniques from infrared sensor measurements the plots shown in Figs 6 10 6 11 and 6 12 were gener
38. 2A312LVs are electrically interchangeable with many existing photoelectrics and inductive proximity switches They are fully protected Printed in USA SM2A312LV 2 WIRE AC RETROREFLECTIVE SENSOR Excess gain curve SM2A312LV 9 15 turn sensitivity adjustment Compact size only 2 6 long x 1 2 high x Rugged BA N Yo EVER the photoelecine specialist OS TANCE C4 5 wide and epoxy encapsulated meets NEMA standards 1 2 3 3S 4 4X 12 and 13 against false pulse on power up and inductive load transients The SM2A312LV operates on 24 to 250V ac 50 60 NOTE use on low voltages requires care ful analysia of the load to determine if the leakage current or on state voltage the sensor will interfere with proper operation of the load A convenient control on the back of the SM2A312LV allows a choice of either light or dark operate sensing mode A rugged 15 turn slotted brass screw clutched GAIN control enables very precise adjustment of system sensitivity The maximum sensing range of 15 feet will be attained when using the model BRT 3 3 corner cube retrorefiective target The SM2A312LV is fully encapsulated and gasketed against moisture and other contaminants and conforms to NEMA standards 1 2 3 3S 4 4X 12 and 13 is supplied with 6 feet of rugged PVC covered 2 conductor Early models are rated for use only up to 120V ac
39. TOR LED top mounted red LED indicator lights whenever the sensor sees its modulated light source OPERATING TEMPERATURE RANGE 0 to 50 degrees C 32 to 122 degrees F HOOKUP DIAGRAM Brown Blue 10 250V 50 602 i i i t Qt 12 10 15V dc H i Observe proper polarity for OC hookups AC have no polarity _ This warranty does not cover damage or Liability for the improper application of Banner products This warranty is in lieu of any other warranty P N 03366 41 Sensing Mode VALU BEAM 990 Series Sensors Models BECEPOR ITO rm i OBJECT RETROREFLECTIVE MODE at xc sg ra TINE TARGET em oA Ld OBJECT SMA9IE amp SMA99R Voltage 10 to 250V or 12 to 15 de E 10 250V ac dc Range 200 feet 60m Beam infrared 880nm visible red tracer beam Effective beam 0 5 dia SMA9IESR amp SMA99RSR Voltage 10 to 250V ac or 12 to 115V dc ESR 10 250V ac dc Range 10 feet 3m Beam infrared 880nm visible red tracer beam Effective beam 12 dia SMA990LV Voltage 10 to 250V ac or 12 to 115V dc Range 30 feet 9m Beam visible red 650nm SMA990LVAG CAG anti glare filter Voltage 10 to 250V or 12 to 115 dc Range 15 feet 4 5m Beam visible red 650nm with polarizing filter Excess Gain Beam Pattern 7 SMABIE amp
40. Technical Report Documentation Page 1 Report No 2 Government Accession No 3 Recipient s Catalog No FHWA TX 91 1162 1F 4 Title and Subtitle 5 Report Date December 1990 6 Performing Organization Code INFRARED SENSORS FOR COUNTING CLASSIFYING AND WEIGHING VEHICLES 8 Performing Organization Report No Research Report 1162 1 7 Author s Joseph E Garner Clyde E Lee and Liren Huang 9 Performing Organization Name and Address 10 Work Unit No TRAIS Center for Transportation Research The University of Texas at Austin Austin Texas 78712 1075 11 Contract or Grant No Research Study 3 10 88 0 1162 13 Type of Report and Period Covered 12 Sponsoring Agency Name and Address Texas State Department of Highways and Public Transportation Transportation Planning Division P O Box 5051 14 Sponsoring Agency Code Austin Texas 78763 5051 15 Supplementary Nates Study conducted in cooperation with the U S Department of Transportation Federal Highway Administration Research Study Title Infrared Detectors for Counting Classifying and Weighing Vehicles 16 Abstract Final In this study five field tests were conducted to determine the feasibility of using commercially available infrared light beam sensors for counting classifying and perhaps weighing vehicles It was demonstrated that a single reflex type infrared sensor mounted just off the shoulder and working off a retro reflective
41. atch constantly changes and is sometimes considerably different after the vehicle travels only a few inches Attempts were made to correlate the in motion dimensions of tire contact patches with wheel weights of 149 semi trailer trucks which were measured simultaneously with weigh in motion force transducers Only a rough correlation was found for the dual tires on tandem axles and virtually no correlation was found for the single tires of the front axles These correlations be tween infrared light beam sensor measurements and weight were not judged to be sufficient to make adequate weight estimates practicable WIM system measure ments can be aided by using infrared light beam sensors to make lateral position calculations which identify off transducer tires In a field test in a high occupancy vehicle HOV lane in Houston an array of two infrared sensors was the basis for calculating vehicle speed length and headway and for indicating direction The current array of three loop detectors can possibly be replaced with infrared light beam sensors after only minor modifications of the infrared sensor housing and the currently implemented computer software In an extended performance test it was determined that off shoulder infrared sensors and in lane retroreflec tors can be operated for three months or longer without cleaning or adjustment These tests were conducted in the summer and fall months in Texas In another field test an a
42. ated Figure 6 10 presents the product of tire contact length and projected diagonal dimension versus weight The correlation coefficient for the product is 0 72 only slightly higher than the values of 0 67 and 0 70 for the two factors taken individually Figure 6 11 presents the tire contact width versus weight The tire contact width was calculated by subtracting the tire contact length from the diagonal dimension and dividing by the tangent of the angle between the perpendicular and the diagonal infra red beams This calculation assumes a rectangular tire contact patch This assumption is perhaps more appropri ate for dual tires than for single tires since all the calculated widths were positive for dual tires With the poor correlation obtained calculated tire contact width cannot be used to estimate weight satisfactorily Figure 6 12 presents the calculated tire contact area i e the product of tire contact length and width versus weight The linear correlation is again poor None of the depen dent variables described here can be used to estimate weight with reasonable accuracy The tandem axles were found to be similar to each other when tire contact lengths and projected diagonal di mensions were compared as can be seen from the values in Table 6 3 The tire contact length for the drive tandem had standard deviation values of 1 05 and 1 10 inches while the trailer tandem had standard deviation values of 1 30 and 1 29 inches Th
43. ation and DC common While one output is conducting to DC com mon the other is not The accompanying wiring diagrams il lustrate a simple DC hookup for the light LT mode output turned on when the light beam is complete and the dark mode output turned on when the beam is blocked A reflex system is shown for illustration purposes Additional diagrams illustrate a parallel wired or hookup and how the complementary outputs of a single control module can be us ed to drive two independent loads LT Mode Beam Blocked I Un 36 DRK Mode Beam Blocked DRK Beam Complete Two i loads driven wo independent by single TTL CMOS Hookup if the control module will be used to drive a TTL or CMOS load then a pull up resistor is required Opcon suggests a 1K ohm resistor The illustration shows the general wiring re quirements for LT mode TTL CMOS operation ORK mode Operation is similar 106832 885 Printed in U S A 720 9 S W EVERETT WA 98203 6299 Free 800 426 9184 or 206 353 0900 or TLX 152 963 MINI BEAM FEATURES Retroreflective sensor to 15 used with 3 or with range retroreflect Physically and electrically inter changeable with Inductive proximi ty switches and 18 mm photoelec tric switches exceas Small effective beam 1 2 dla at 1 distance from lens Modulated visible red
44. beam for immunity to ambient light and ease of alignment 9 Switch selectabie tor operate Solid state output switches up to 300 ma light or dark Easy interfacing to programmable control lers iow leakage current low saturation voltage LED gized 24 250V 50 60 Hz operation indicator lights when load is ener No faise pulse on power up DESCRIPTION The Banner MINI BEAM series SM2A312LV is a self con tained visible light retroreflective sensor having a sensing range of 15 feet Ks small effective beam 1 2 inch dia at 1 foot from the lens makes it a good choice for sensing relatively small objects and its visible red light beam makes it extremely easy to align SM2A312LV retroreflective sensors consist of an LED light source a sensitive phototransistor an alignment indicator and a custom designed state of the art CMOS integrated modulator demodulator amplifier circuit Digital modulatior demodulation makes the SM2A312LV nearly immune to in terference from ambient light A red LED indicator on the rear of the sensor makes alignment and system monitoring easier by lighting whenever the load is energized The SM2 A312LV s solid state output is capable o switching up to 300 ma at 50 degrees C ambient 100 ma at 70 degrees C and its low output leakage and low saturation voltage make it ideal for interfacing to programmabie controllers and Other solid state circuitry SM
45. ce of the tire from the center line or edge can be de termined as a function of the time when a tire breaks the diagonal beam and the time when that tire breaks a per pendicular beam time tp or crosses some other thresh old a weigh in motion transducer The projected diagonal dimension of the tire contact area is Calculated similarly to the tire contact length ex cept the interruption time of the diagonal beam time td is used The diagonally measured dimensions of tires of the same vehicle can be compared to give an indication of single or dual tires The first tires of a vehicle are as sumed to be single following tires of the same vehicle Loop Detector Fig 4 2 Pavement level sensors having dimensions significantly longer are indicated as dual The vehicle with the signal shown in Fig 4 3 has single tires on the front axle and dual tires on the rear axle A factor of 1 2 has been found to be sufficient to distinguish between the diagonal dimensions of single and dual tires 1 diagonal dimensions of dual tires are at least 1 2 times longer than single tires on the same ve hicle This factor is a variable in the computer program which can be changed to account for different field con ditions or observations Output using the values of 1 1 1 5 and 1 8 was compared with visual observations of approximately twenty vehicles with dual tires The 1 1 factor was not acceptable the larger factors were accept able but n
46. cle number of tires per axle and number of trailer units are used to classify the non pas senger types Passenger cars are not distinguished from passenger cars with trailers Buses constitute a separate category OKLAHOMA TURNPIKE AUTHORITY The classification schedule used by the Oklahoma Turnpike Authority shown in Table 3 2 Ref 5 distin guishes between passenger cars with and without trailers but does not include trucks with more than six axles nor does it distinguish between single and multi trailer trucks Buses are classed with two axle and three axle trucks Four tire trucks are in the same class as passenger cars TABLE 3 1 FHWA VEHICLE TYPES Passenger Vehicles Motorcycles Passenger Cars Other Two Axle Four Tire Single Unit Vehicles Buses a WN Non Passenger Vehicles 5 Two Axle Six Tire Single Unit Trucks 6 Three Axle Single Unit Trucks 7 Four or More Axle Single Unit Trucks 8 Four or Less Axle Single Trailer Trucks 9 Five Axle Single Trailer Trucks 10 Six or More Axle Single Trailer Trucks 11 Five or Less Axle Multi Trailer Trucks 12 Six Axle Multi Trailer Trucks 13 Seven or More Axle Multi Trailer Trucks TABLE 3 2 OKLAHOMA TURNPIKE AUTHORITY VEHICLE CLASSIFICATION SCHEDULE Automobile Station Wagon Motorcycle Any Two Axle Four Tire Truck Class 1 Vehicle Towing One Axle Trailer Class 1 Vehicle Towing Two Axle Trailer Two Axle Bus Two Axle Six Tire Truck Three Axl
47. controls TTL or CMOS inputs with pull up resistor The 88828 will accept Thru Beam Proximity and Reflex Sensor Heads In addition Time Delay and One Shot Logic Modules are available A complete OC control package con sists of One 1 8882B DC NPN Controli Module Note A Thru Beam controi package requires two 2 contro modules 80 Series Sensor Heads 1180B 80F 1280B Thru Beam Source Detector pair 1380 81 82 83B 83R Proximity Sensors Reflex Sensor Dual Time Delay Non Retriggerable One Shot Retriggerable One Shot Universal Mounting Bracket a 3 Inch Reflector 6200A 1 5 1 5 Inch Reflector Note Reflectors are for reflex control pkgs only Specifications input Power Voltage Current 10 to 30VDC unregulated less than 90ma 30V 20V 25 F 78 30 35 40 4 5 55 60 86 95 104 113 122 131 140 Note Operation outside the recommended supply voltage envelope will resuit in erratic performance at high temperature opcorr 8882B 6501 Output Characteristics Output Active On Less than 500mv at 200ma Output Inactive orf Output will shut off up to 30VDC at less than 20ua leakage Transient Protection Outputs are protected from inductive load switching for energy signals of less than 0 18 Joule Watt Sec and power signals of less than 200mw Outputs are inactive for 100 to 300 ms after power up regardless of the beamvs
48. d of view Alignment is complete Rotation 6160A Mounting Bracket 106899 1185 Printed in U S A Guarantee Service Quarantees standard products Output Me promem ad MUN a contact Dereon Opcon has a Question concerning the repair Send the unit prepaid with a purae order to athorized Opcon repair center Corn tact Opcon for the repair center nearest you Morir olet Dy no s produ assumed This guarantee is in leu of any other warranty either expressed or usa nor for any ririn af patents or ther righ impted use No icense If service is required package the unit carefully since transit not covered by the guarantee Include letter desori otherwise under any patent or patent ODCORY SENANG neos 20 80th St S W EVERETT WA 96203 6290 Tol Free 800 426 9184 or 20d 363 0800 or TLX 152 063 DC NPN Control Module Installation Instructions Introduction 5 88828 Control Module is the OC power and output base for Opcon s 80 Series Blue Eyes Sensors The 88828 provides high and low logic levels through a pair of open Collector transistor outputs An open collector output func tions as an electronic switch between the load cicuit and DC common At any given time one output is conducting to DC common while the other is not The outputs may be applied to relay coils DC switching
49. d raised pavement markers may be used for measuring speed counting and classifying The fifth test was performed on the Turner Turnpike in Oklahoma City with the objective of identifying single and dual tires and classifying vehicles for auditing toll collection Ninety six percent of the vehicles were iden tified correctly with the array of two infrared sensors and a loop detector The accuracy can be improved with an additional infrared sensor The cost of a reflex type infrared sensor and retroreflector unit is about 100 and installation can be accomplished without pavement cuts usually without traffic barricades Thus infrared sensors are accurate and economical alternatives to sensing devices currently used to count and classify vehicles Infrared sensors can also be used with weigh in motion systems to sense off transducer vehicles REFERENCES Opcon Catalog of Photoelectric Controls OPCON 720 80th Street S W Everett WA 98203 p 13 8 1984 Banner Engineering Product Catalog Banner Engi neering Corporation 9714 10th Ave No Min neapolis MN 55441 1987 Photoelectric Sensors and Controls Selection and Application Juds Scott M Marcel Dekker Inc New York 1988 Traffic Monitoring Guide Federal Highway Admin istration Office of Highway Planning 1985 Classification Schedule Oklahoma Turnpike Au thority A Policy on Geometric Design of Highways and Streets American Association of State
50. diagonal light beam sensors to indicate single or dual tires and classify vehicles was tested All field tests were performed on interstate highways Except for the HOV lane in Houston all tests were in rural or semi rural ar eas EQUIPMENT AND SOFTWARE The two brands of sensors used in the research de scribed herein were manufactured by Banner and Opcon Refs 1 and 2 Some sensor housings were manufac tured by Rainhart Co 604 Williams Street Austin TX 78752 and others were fabricated at The University of Texas at Austin The retroreflectors were manufactured by Stimsonite and 3M In the field tests a portable or convertible IBM computer was used Motorola donated several evaluation boards and microprocessors that were used to collect the raw data make time lists and commu nicate with the computer A research engineer on the staff of the Center for Transportation Research The Uni versity of Texas at Austin wrote all the software and de veloped support hardware for the microprocessor TIRE CONTACT AREA A field study of tire contact areas was conducted on Interstate 35 near San Marcos Texas in September 1988 Infrared sensors measured speed axle spacings tire contact lengths and diagonal dimensions of tire contact areas while vehicles were in motion Vehicles were then stopped by Department of Public Safety personnel The length and width of the tire contact area was measured manually by calipers built on a meter stick
51. e 10 amps for 1 cycle non repetitive RESPONSE TIME 10 miliseconde ON and OFF plus re sponsae time of load STEADY STATE LOAD CAPABILITY 300 miliamps up to 50 degrees C ambient 122 degrees 100 milliamps up to 70 degrees C ambient 158 degrees F INDICATOR LED Red indicator on rear of unit is when load is energized Banner Engineering Corporation 9714 10th Ave No Minneapolis Mn 55441 TEMPERATURE RANGE 158 degrees F POWER UP INHIBIT less than 300 milliseconds switch is non conducting during this time 20 to 70 degrees C 4 to CONSTRUCTION reinforced Valox housing totally encapsulsted acrylic lenses o ring sealing stainiess steel screws Meets NEMA standards 1 2 3 4 4X 12 and 13 CABLE LENGTH AND MATERIAL conductor cable 6 long PVC jacketed 2 MOUNTING fron mounting via 18 mm nut supplied through 18 mm clearance hole Side mounting via two no 4 clearance holes on 95 centers use with or without optional model SMB312S stainless steel two axis mounting bracket Bottom mounting via sensors mounting peg and optional model SMB312F mounting foot or via SMB312B stainiess steel two axis mounting bracket supplied complete with mounting foot Tai 612 544 9164 FAX 612 544 3213 9 Sensors with Built in Tota VALU BEAM 990 series sensors boast the same high optical per tormance offered by the front line 9 12 serics and also
52. e cross sections are sensed TANDEM AXLES Plots of tire contact area dimension versus weight for the front axle of the drive tandem set are shown in Figs 6 8 through 6 12 along with least squares regression lines Figure 6 8 shows the tire contact length versus weight while Fig 6 9 shows the projected diagonal dimension versus weight For the tire contact length versus weight regression line the correlation coefficient is 0 67 while for the projected diagonal dimension versus weight regression line the correlation coefficient is 0 70 There is some linear correlation but it is not sufficient to Front Axle Right Side Tire Contact Length in L 0 527W 15 0 io pis 149 Vehicles 1 2 3 4 8 6 7 8 9 Wheel Weight kips Fig 6 6 Tire contact length versus weight for front axle Front Axle Right Side 21 2 19 5 2 17 3 8 id PDD 0 459W 16 5 13 F 2 0 009 amp n 9 9 Wheel Weight kips Fig 6 7 Projected diagonal dimension of tire contact areas versus weight for front axle Front Axle of Drive Tandem Right Side Tire Length in a 0 505 13 1 R 0 67 1 2 3 4 5 6 7 8 9 Wheel Weight kips Fig 6 8 Tire contact length versus weight for front axle of drive tandem 30 Front Axle of Drive Tandem e Right Side PDD 0 582W 23 4 R 2 0 70 e 5 e e M Projected Length Wheel Weight kips
53. e Bus Three Axle Truck Single or Combination Four Axle Combination Truck Five Axle Combination Truck Six Axle Combination Truck SOON ee Only eight classes are used since toll operators must clas sify vehicles quickly and accurately by sight AMERICAN ASSOCIATION OF STATE HIGHWAY AND TRANSPORTATION OFFICIALS AASHTO Design Vehicles Ref 6 as shown in Table 3 3 are defined by their dimensions which include over all length wheelbase and overhangs The numbers of axles are not considered but axle spacings are The chief purpose of AASHTO s design vehicles is that of design ing streets and highways Other purposes are planning enforcing regulations and collecting tolls or taxes TABLE 3 3 AASHTO DESIGN VEHICLES Vehicle Symbol Passenger Car Single Unit Truck SU Single Unit Bus BUS Articulated Bus A BUS Combination Trucks Intermediate Semitrailer WB 40 Large Semitrailer WB 50 Semitrailer Full Trailer WB 60 Interstate Semitrailer WB 62 Interstate Semitrailer WB 67 Triple Semitrailer WB 96 Turnpike Double Semitrailer WB 114 Recreational Vehicles Motor Home MH Car and Camper Trailer P T Car and Boat Trailer P B Motor Home and Boat Trailer MH B 6 AMERICAN SOCIETY FOR TESTING AND MATERIALS The ASTM Standard for Weigh in Motion Systems Ref 7 has an optional vehicle classification scheme that may be used instead of the FHWA Vehicle Types In the optional system the number of axles and the axle
54. e projected diagonal dimension for the drive tandem had standard deviation values of 1 18 and 1 12 inches while the trailer tandem had values of 1 63 and 1 61 The mean values of tire contact length for both tandem axles were very close between 15 82 and 16 07 inches The mean values of projected diagonal dimension for each tandem were very close 26 88 and 26 81 inches for the drive tandem and 26 23 inches for both axles of the trailer tandem Figure 6 13 compares the regression lines of tire contact length versus weight for the front and rear axles of the drive tandem The lines are very similar with slopes at 0 505 and 0 566 and the intercepts at 13 1 and 12 8 Since the axles have a common suspension point it is expected that the weights will be similar The data taken in this field test show that the tire contact area di mensions are also similar ALL AXLES In Figs 6 14 and 6 15 the dimensions of all the tires on each vehicle are summed The least squares regres sion lines and correlation coefficients are also shown Figure 6 14 presents the sum of all the tire contact lengths versus the sum of all the weights Figure 6 15 presents the sum of the projected diagonal dimensions 12 ft Main Lane m 6RXS ft 12 ft Main Lane Loop 10 ft Shoulder ci Reflex Sensors Piezo Cable 6 ft X 8ft Loop Fig 6 16 Sensor arrangement at Jarrell versus the sum of the weights
55. eaned on a regular schedule Clean air no dirt build up on lenses or reflectors 10X Moderately dirty obvious contamination of lenses or reflectors but not obscured lenses cleaned occasionally or when necessary 50X Very dirty heavy contamination of lenses heavy fog mist sensing modes commonly used are direct reflex and dif either corner cube or spherical bead types The next fuse Each mode has different operating characteristics chapter discusses vehicle classification schemes used by these include effective beam and excess Retrore several transportation organizations flectors integral components of the reflex sensing mode CHAPTER 3 VEHICLE CLASSIFICATION SCHEMES Different criteria for classifying vehicles are used by organizations concerned with various aspects of transpor tation The criteria commonly used include the number of axles per vehicle axle spacing number of tires per axle number and type of units in a vehicle combination and weight Before designing and testing infrared sensor classification systems it is important to know which clas sification criteria are to be used This chapter describes the vehicle classification schemes used by four different organizations FEDERAL HIGHWAY ADMINISTRATION The Federal Highway Administration s Traffic Moni toring Guide Ref 4 as shown in Table 3 1 divides ve hicles into passenger and non passenger vehicles The number of axles per vehi
56. earance use for side mounting M BASIC SINGLE SENSOR AC HOOKUP see SPECIFICATIONS REAR VIEW 2 GAIN Control 3 LED Indicator 4 LIGHT DARK OPERATE switen Cable 18 1 mm thread Mounting Nut 71 diameter supplied Optional SMB312F mounting fool Mounting peg circular 25 diameter 1 Molded acrylic lenses interchangeable in the field for replacement repair or for different sensing ranges 2 GAIN sensitivity control rotate clockwise to increase gain 3 LED indicator lights when output is energized 4 LIGHT DARK OPERATE SELECT control DARK OPERATE fully counterclockwise LIGHT OPERATEsfuily dockwise 5 6 PVC jacketed 2 wire cable supplied 6 Optional SMB312F mounting foot used for bottom mounting of sensor with or without SMB3128 Bottom Mounting Bracket Mounts at front of sensor body beneath barrel Supplied with SMB3128 bracket order or order separately PARALLEL HOOKUP NOTE in a parallel hookup the load leakage increases vAC with the number of sensors i e 2 sensors together have two times the leakage of one sensor alone etc SERIES HOOKUP NOTE in a seres hookup the total saturation voltage across the sensors increases with the number of sensors i 8 2 sensors to gether have 2 times the saturation voltage of one sensor atone ate see SPECIFICATIONS POR 40 INSTALLATION AND ALIGNMENT Proper operation of the SM2A3
57. ecause they emit more light intensity than visible light LEDs and because most photodetectors are more sensitive in the infrared range In some applications LEDs operating in the less efficient visible light wavelengths are preferred for ease of align ment SENSING MODES As shown in Fig 2 1 photoelectric sensors are used in three main types of sensing modes or configurations each having distinct properties and applications The first sensing mode is called direct opposed or through beam The source and detector are in separate opposing locations and the object to be sensed passes between them and breaks the light beam The second mode called retroreflective or reflex has the source and detector side by side usually in the same housing A retroreflector receives the beam from the source and reflects it back to the detector The object to be sensed passes between the source detector and the retroreflector The third mode called diffuse or proximity has the source and detector side by side with both aimed at a Opaque Object Direct Sensing om Opaque Object Reflex Sensing Receiver li Diffuse Sensing Object with Reflective Surface Fig 2 1 Sensing modes point in space An object is sensed when it is at this point and reflects light from the source back to the detector Direct sensing has the longest range since the light beam travels the distance between source and detector only once and en
58. ector See the Banner catalog for details about available retroreflective materials 1 3 SMASSQLVAG p i PIT IP x o DISTANCE VALU BEAM 990 Series Sensors Sensing Mode RETROREFLECTIVE MODE continued CONVERGENT MODE OBJECT FIBEROPTIC MODE plastic fiberoptics OPPOSED OBIECT Models SMA 990LT Voltage 10 to 250V ac ot 12 to 115V dc Range 30 feet 9m Beam infrared 880nm DOORWAY Ren reniector SMAS90LT SMA990CV Voltage 10 to 250V ac or 12 to 115V dc Focus at 1 5 38mm Beam visible red 650nm COLNTING GUIDED RADI SED PRODUCTS SMA990FP Voltage 10 to 250V ac or 12 to 115V de Range see E G curves Beam visible red 650nm The powerful modulated visible beam of this sensor makes it compatible with all Banner piastie fiberoptic assemblies Banner plastic fibers are an economical alemat ve to glass fibers when environmental condi tions allow see below Banner plastic fiberopties are available in two core diameters and with various sensing tip styles Standard length 6 feet More infor mation on plastic fiberop tics may be found Banner catalog Excess Gain Beam Pattern gt 5 DIS ANZE REFLECTOR DISTANCE VALU BEAM model SMA990LT is designed specifically for counting 15 strong 30 foot range infrared beam is invisible io the eye and built in
59. ed around 19 inches The tire contact area for moving vehicle tires changes and is not the same as the static tire contact area Neither the dynamic nor the static tire contact patch has a rectangular area as is assumed for the in motion width calculation For dual tires the width of the tire contact area includes the gap between tires and is greater than the tire contact length One reason for doing this test was to determine a correction factor for the gaps between dual tires which could not be measured by infrared sensors Gap size de pends on tire size construction materials and inflation pressure vehicle design and other factors Because of Width Beam Time 2 Projected Diagonal Dimension Fig 6 1 Tire contact area dimensions Manual Tire Length in 35 Vehicles Dual Tires 4 5 6 7 8 9 10 1 12 13 Infrared Tire Length in Fig 6 2 Comparison of tire contact lengths Manual Tire Width in 29 Vehicles Dual Tires 16 17 18 19 20 21 22 23 Infrared Tire Width in Fig 6 3 Comparison of tire contact widths the rather large amount of scatter in the data a suitable correction factor could not be determined from the avail able information WEIGHT In December 1989 a three sensor pavement level sensor array was field tested on Interstate 10 at Junction Texas The objective of this test was to determine the possibility of estimating weight from measurements of in motion t
60. en a retroreflective sensor reacts to light reflected from the object being sensed instead of only to light reflected from the retro target Proxing may often be problem when sensing shiny objects such as bottes metal cans or objects wrapped in cellophane shrink wrap Proxing can be reduced or eliminated by direct ing the sensor beam at an angle of 10 to 15 degrees off of the line perpendicular to the object s reflecting surface Both a horizontal and a vertical displacement may be necessary The sensing beam may be angled as far as 15 degrees away from straight on to the rellector without compromising efficiency is not usually necessary to do away with al retiections The goal is rather to reduce the strength of the unwanted signals while maintaining or increasing the strength of the signal trom the retro target For more information refer to Section 7 of the Banner Catalog Reference Manual portion for an in depth discussion of sensor alignment and adjustment ELECTRICAL AND MECHANICAL SPECIFICATIONS SM2A312LV SENSOR SUPPLY VOLTAGE 24 to 250V ac 50 60 Hz Use on low voltages requires careful analysis of the load with respect to the leakage current and on state voltage of the sensor See note page 1 OFF STATE mil amp kamps rms LEAKAGE CURRENT 1 7 ON STATE VOLTAGE lt SV at 300ma lt 10V at 15 load MINIMUM LOAD CURRENT 5 milllampe INRUSH CAPABILITY 3 amps for 1 second non repetitiv
61. ent thereof or any variety of plant which is or may be patentable under the patent laws of the United States of America or any foreign country PREFACE Throughout this research study a number of agen cies companies and individuals cooperated in providing information helpful suggestions materials personnel and other resources to support the work The study con tact individuals representing respectively the State De partment of Highways and Public Transportation and the Federal Highway Administration were Jeff Seiler and Ted Miller Their timely contributions of administrative and engineering support made the research possible Person nel in D 10 Transportation Planning Division cooper ated generously in all phases of the effort especially in scheduling and conducting the field studies at Seguin Junction San Marcos and Jarrell and by loaning hard ware Similarly D 9 Materials and Tests Division fur nished sample retroreflectors and epoxy Posts and retro reflectors were furnished by District 14 Austin Department of Public Safety officers cooperated in the field measurements of tire contact dimensions and weigh ing of trucks at San Marcos The sensor tests in the high occupancy vehicle HOV lane in Houston were made possible by the efforts of Dick McCasland and Gene Ritch with the Texas Transportation Institute and those of Lynn McLean and his associates with Houston Metro Chet Freda representing Motorola Inc
62. ergy is not lost by reflection Reflex sensing has a shorter range since the light beam crosses the distance between sensor and retroreflector twice and energy is lost by reflection An object with high reflectivity might not be detected in the reflex mode if it reflects sufficient light back to the detector To alleviate this effect polarizing filters may be used to filter out specular reflections but the resulting sensing range will be reduced The range of the diffuse sensing mode de pends on the amount of light reflected by the object to be detected EFFECTIVE BEAM The effective beam is the energy that an object must block for detection For direct and diffuse sensing the effective beam is determined by the overlap of the radia tion pattern from the source and the field of view of the detector For the reflex mode the effective beam is de fined by the edge rays traced from the sensor lenses to the edges of the retroreflector Ref 1 For reliable detec tion the object to be detected must shadow the entire ret roreflector at one time Larger retroreflectors may be used to increase the sensing range but the effective beam size is also increased and therefore so is the necessary size of the object to be detected EXCESS GAIN Excess gain is the ratio of the light energy received by the detector to the minimum energy required for de tection under ideal conditions Ideal conditions are clean air and clean lenses i e the beam
63. ers operated for up to three months without cleaning A two sensor array tested in the Houston high occupancy vehicle HOV lane indicated promise as a replacement for loop detector arrays Infrared sensors can supplement weigh in motion systems by indicating off transducer vehicle tires but correlations between infrared light beam sensor measurements and weight were not sufficient to make adequate weight estimates from such measurements practicable SUMMARY Infrared sensors can be used in three sensing modes direct reflex or diffuse The reflex mode which re quires a retroreflector can be used in all applications dis cussed in this report For a few applications such as ve hicle height detection the direct sensing mode which requires the transmitter and receiver to be in separate lo cations can also be used The diffuse sensing mode is not recommended for traffic applications Overhead roadside and pavement level are the three different arrangements of infrared sensors which can be used In the overhead and roadside arrangements vehicle bodies are sensed and vehicle speed length and headway can be calculated In the pavement level arrangement tires are sensed and speed axle spacing tire contact patch dimensions and lateral position of tires can be calculated Also with this sensor arrangement single and dual tires can be identified In the first two field studies it was determined that the in motion tire contact p
64. esence signal may be generated by a separate infrared beam array which senses the vehicle body or by another presence sensor such as an inductance loop detector When a loop detector is used the retroreflectors are normally placed on the pave ment inside the loop as shown in Fig 4 2 so that the presence signal begins before the first tire is sensed and ends after the last tire is sensed Speed is calculated by dividing the distance between the perpendicular infrared light beams D1 by the time taken for one tire to travel between beams time tv shown in Fig 4 3 If it is assumed that the vehicle and all tires are traveling at a constant speed then speed may be de termined in a similar manner with a second loop detector two piezoelectric cables or two WIM transducers Axle spacing is calculated by multiplying the speed by the time between successive breaks of one beam time ts Tire contact length can be calculated by multiplying the speed by the time that a perpendicular beam remains broken by one tire time tl Tire contact length is mea sured more accurately when the sensor is placed on the pavement at the edge of the lane so that the beam size is smaller and response is quicker The retroreflector should be small in size to further reduce the effective beam size Other quantities may be measured with an infrared light beam aimed diagonally across a vehicle path as shown in Fig 4 2 When the speed is known the lateral distan
65. etroreflective sensing when reduced excess gain is acceptable Maximum range with LV ums is a ained when using the model BRT 3 3 comer cube reflector details on retroreflective target materials see the Banner catalog SMSIZLVAG SM2AST2LVAG BRT 3 REFLECTOR z o OifTANCE 3 5 3 2 DISTANCE TO REFLECTOR FEET VALU BEAM Sensors Hookup Diagrams for dc SM912 Series Sensors OT wu has a max mum load capacity of 250 HOOKUP TO DC RELAY HOOKUP TO LOGIC OR SOLENOID using Sinking output The diagram below shows hookup of dc The diagram below shows hookup of 4 VALU BEAM to logic gate A logic zero VALU BEAM to a dc load using the sensor s voka is applied to the gare input sinking output which is rated st 250mA when the VALU BEAM output is energized maximum The BLACK wire is not used When de cnergized a logic one is applied The logic supply negative must be common 1o the VALU BEAM supply negative HOOKUP TO DC RELAY OR SOLENOID using sourcing output The diagram below shows hookup af VALU BEAM dc load using the sensor s sowcing ORR which is med 250 HOOKUP TO PROGRAMMABLE CONTROLLER sinking output This diagram shows hookup of dc VALU BEAM to programmabia controller requiring sink using the sensors sinking out p
66. eveloped infrared sensors could be used to calculate the weight of vehicles quite accurately For the present infrared sensors are not recommended for calculating individual vehicle weights HOV LANES A two beam infrared sensor array was field tested in a high occupancy vehicle HOV lane on Interstate 10 in Houston in May 1990 The two reflex type infrared sen sors were placed 2 feet apart in a special metal box on top of one concrete median barrier the retroreflectors were placed on the nearly vertical face of the other bar rier 22 feet away This system was tested as a possible substitute for an array of inductance loop detectors that are currently used to determine vehicle speed length di rection and headway in the reverse flow HOV lane The system performed well for the first two weeks until the lid on the metal box became ajar and road film accumu lated on the lenses It is felt that a sensor unit of this type will perform well over extended periods of time after a few minor modifications to the mounting hardware are made Occasional cleaning of the lenses and retroreflec tors may be necessary Only minor modification of the currently implemented computer software is required be fore a single pair of infrared sensors can be used to re place the existing array of three 6 foot by 6 foot loop de lectors 20 ENDURANCE Five infrared sensors were installed on Interstate 35 north of Jarrell Texas in June 1990 to test long
67. f ferent heights depending on the level of reliability de sired Infrared sensors can warn drivers of over height vehicles that they are approaching a low clearance bridge or tunnel This system has been used in Mississippi and other states Ref 9 The direct sensing mode should be used because it has greater reliability than reflex sensing An application that is being considered is detecting trucks on a ramp and warning the drivers if they are going too fast and might be at risk of overturning SPEED Two infrared sensors are necessary for measuring speed Speed is equal to the distance between sensors di vided by the time between successive beam interruption Sensors mounted overhead or on the roadside measure vehicle speed while pavement level sensors measure axle speeds which can be averaged for the vehicle speed CLASSIFICATION Classification can be done in a number of ways de pending on the desired classification scheme One pave ment level infrared sensor and a presence sensor can be used to count the number of axles per vehicle Two pave ment level sensors measure the axle spacing and indicate whether axles have single tandem or triple spacing If an indication of dual or single tires is desired the infrared beams can be aimed diagonally across the lane rather than perpendicularly Alternatively the first two beams may be perpendicular and a third beam diagonal If over all vehicle length is desired an additional senso
68. f the effective beam and thus enhanced the measurement accuracy of tire contact dimensions SPEED AXLE SPACING AND LATERAL POSITION Figures 6 4 and 6 5 compare the speed and axle spac ing for infrared sensors and WIM while Table 6 2 sum marizes this information In this test speeds measured by infrared sensors were slightly higher than speeds mea sured by WIM as shown by the data points above the 45 degree line in Fig 6 4 The speed measurements for the WIM system were made with two 6 foot by 6 foot loop detectors separated by an 8 foot space These two loops were not calibrated perfectly and their response times were inherently affected by the different heights of the 14 vehicles above the road surface The axle spacings from the two measuring techniques show close agreement but the effect of higher speed computed from the infrared sensors makes the corresponding axle spacings lie above the 45 degree line in Fig 6 5 The speeds calculated from the infrared sensor measurements are probably more reli able than those from the loop detectors The lateral position of tires from the lane edge were measured by the diagonal infrared beam This measurement determined whether vehicle tires were fully 75 70 65 60 55 Infrared mph 50 45 149 Vehicles 40 40 45 50 55 60 65 70 75 Weigh in Motion mph Fig 6 4 Comparison of speed Axle Spacing 596 Axle Pairs Infrared ft 0 10 20 30 40 50 60 Weigh
69. ht beams can be perpendicular or diagonal to the lane edge The reflex sensing mode may be used in all cases but the direct Sensing mode requires mounting the transmitter in the roadside position and the receiver on or beyond the opposite lane edge or shoulder The diffuse sensing mode is not suitable for sensing vehicles OVERHEAD Bridges or other overhead structures can be used to mount infrared sensors 51 in Fig 4 1 The direct sensing mode is not well suited for this arrangement since the unit on the pavement surface R1 must have either a power source or an external output connection is difficult to protect and must be very rugged A suitable retrore flector array has been designed for this purpose In the overhead arrangement vehicles may be counted by lane and their speed and overall length may be calculated This is the only arrangement which can accurately sense vehicles in lanes other than the outside lane or the me dian lane Only specially designed and placed retrore flectors are durable enough to be used directly on the pavement for long periods of time Fig 4 1 Sensor arrangements Some combination vehicles may interrupt a single light beam more than once and be counted as more than one vehicle A sensor that extends the interruption time so that small gaps are not detected can be used in this case The beam must be broken or unbroken for a longer time period before the sensor changes the output signal The le
70. infrared sensors for counting and classifying vehicles described herein began in 1988 Ina test near San Marcos Texas in motion infrared sensor measurements of tire contact area and axle spacing were compared with manual measurements taken after the vehicles were stopped by Department of Public Safety personnel In another test near Seguin Texas infrared and WIM measurements were taken concurrently and compared Overhead mounting was tried in a series of tests in Austin In 1989 a test was performed on a high occupancy vehicle HOV lane in Houston to determine the feasibility of a two sensor system to calculate speed headway length and direction and to possibly replace loop detectors at locations where pavement cuts were not feasible A test similar to the one at Seguin was performed at Junction Texas with improved infrared equipment In 1990 a test was made near Jarrell Texas to determine long term performance and durability Comparisons were also made of vehicle classification systems using loop detectors and a piezo cable sensor Another test was made on the Turner Turnpike in Oklahoma City to determine the possibility of using infrared sensors for auditing toll collection based upon eight vehicle classes Other tests were performed on several streets in Austin A self contained data collection and storage unit to be mounted on the pavement surface at the lane line was designed and constructed but field testing was consid ered
71. ir design life Pneumatic road tubes piezoelectric cables and inductance loop detectors are some of the sensing devices commonly used to count and classify traffic Weighing is done both statically and dynamically Static weighing uses special scales to mea sure the tire forces of a standing vehicle Static vehicle weights can also be closely approximated by measuring the dynamic tire forces of a moving vehicle with weigh in motion transducers and by processing the force signals with electronic instruments Most of the sensors cur rently in use for counting classifying and weighing moving vehicles require mounting in the pavement or on the pavement surface in the traveled lane The purpose of the research described herein was to determine the feasibility of using commercially available infrared light beam sensors for some or all of these pur poses A primary objective was to sense the presence of a vehicle or a tire traveling in a highway lane without cutting into the pavement surface or having hardware on the surface where it would be impacted by the tires of ev ery vehicle It was felt that commercially available infra red sensors have potential for use in counting classify ing and weighing vehicles The considerations in selecting candidate photoelectric sensors designing the needed hardware and software installing the systems at selected field sites and evaluating their performance are presented in this report The tests of
72. ire contact area dimensions The sensors were installed on the edge of the lane and the beams passed 13 TABLE 6 1 COMPARISON OF TIRE CONTACT LENGTH AND WIDTH MEASURED MANUALLY BY TAPE AND BY INFRARED All Dual Tires Dimensions in Width Width IR Manual IR Manual Number 29 Tires Ma us mw Mas o9 Tire contact width includes gap between dual tires Length Length just above a flush mounted Radian WIM transducer in the right side wheel path so that tire contact length and projected diagonal dimension could be measured as each right side tire was being weighed Both systems shared a loop detector to sense vehicle presence but computed vehicle speed and axle spacing independently The infrared light beam system also calculated the tire contact length projected diagonal dimension of the tire contact area and the lateral position of the tire with respect to the edge of the pavement All calculations were done on site with a portable microcomputer Both the infrared sensors and retroreflectors were smaller and closer together than those used in the test at San Marcos The retroreflectors were 3 4 inch diameter rather than 4 inch long raised pavement markers as were used before The infrared sensors were placed on the lane edge rather than off the shoulder The new sensors had a range of about 20 feet rather than 50 feet This arrangement reduced the size o
73. ity it was demonstrated that infrared sensors can identify almost all single and dual tires Vehicle classifications by the infrared sensor system were as accurate as classifications by off duty toll booth operators The cost of a reflex type infrared sensor and retrore flector unit is approximately 100 A traffic lane closure is usually not required for installation of the unit In comparison a piezoelectric cable costs approximately 300 and installation requires closing a traffic lane and sawing a groove The infrared sensors examined in this study were not tested to failure so their life expectancy and long term reliability are not known CHAPTER 7 CONCLUSIONS Infrared sensors may be used in a variety of traffic studies They can be installed to count and classify ve hicles accurately without requiring pavement cuts or bumps as do loop detectors or road tubes Classification criteria which can be calculated with information ob tained from infrared sensors include number of axles per vehicle axle spacing pattern and single or dual tires In frared sensor information can also be used to calculate overall length or height of the vehicle speed and head way These data can supplement weigh in motion sys tems by identifying tires of vehicles not fully in contact with the force transducers The reflex sensing mode is recommended for most traffic detection applications The direct sensing mode may be used for over height detec
74. lenses which must be carefully focused and the photocell can be activated by other light sources such as the sun Be ginning in the 1940 s unmodulated visible light beams were used for traffic sensing but with only limited suc cess LIGHT EMITTING DIODES Light emitting diodes LEDs were developed in the 1960 s and became available in the 1970 s They are now widely used in calculator displays watches and op tical sensors LEDs are semiconductors made from mate rials such as gallium arsenide which emit light in a single wavelength when current flows through them in the for ward direction They have life spans much longer than those of incandescent bulbs and are not sensitive to shock vibration or extreme temperatures LEDs are much smaller which makes it possible for the packaging to be more rugged and weather resistant Probably the biggest advantage of LEDs is their abil ity to be modulated or turned on and off thousands of times per second Photodetectors tuned to this same modulation frequency ignore all other light sources though the source may be thousands of times brighter This alleviates the problems of critical alignment partial blocking and extraneous light LEDs operate in several visible light wavelengths as well as infrared Infrared light has a wavelength greater than about 800 nanometers nm Gallium arsenide LEDs emit infrared light in a tight band around 940 nm Infra red LEDs are often preferred b
75. ling about 50 to 65 mph The system included a loop detector and two diagonal beam sensors and retroreflec tors placed 23 inches apart as shown in Fig 6 18 Single tires interrupted the beams sequentially while dual tires interrupted them simultaneously It was found by field observation that a distance of 23 inches between infrared light beams was optimum At a 22 inch dis tance some large diameter single tires were classified as dual while at 24 inches some small diameter dual tires were classified as single Generally only the relatively small diameter dual tires of pickup trucks were identified as single at the 23 inch distance An initial value of 24 inches was established after measuring truck tires in a parking lot In the field test approximately twenty large trucks were observed visually and compared with the computer output based on 24 inches several dual tires were misidentified At the 22 inch distance several single tires were misidentified At the 23 inch distance almost all vehicles were identified correctly for approxi mately one hundred observations This system using two diagonal beams a fixed distance apart was designed for use at toll gates where speed of vehicles would not be constant The tire contact length diagonal dimension three beam system described in Chapter 4 could not be used since constant velocity is assumed The system described here might be improved with a three diagonal beam array Tires in
76. nd delay on power up no counts are entered during this time Models with memory backup have no power up delay Note Some models with memory backup may increment 1 count upon reapplication of power COUNT ENTRY counts are entered on DARK to LIGHT transition COUNT RESET in standard models counter is reset to zero auto matically upon applying power to the sensor All models may be reset by touching the housing on top of the sensor see below with a permanent magnet supplied with sensor DIMENSIONS SMA990 SERIES VALU BEAMS Raett counter t0 tere by WIth magnet bere is smm tareene Threed 41 14 expressed or implied Printed in USA VALU LED Indicator WARRANTY Banner Engineering Corporation warrants its products to be free from defects for period of one year Banner Engineering Corporation will repair or replace free of charge any of manufacture found to be defective at the time it is retumed to the factory during the warranty period ENSOR CONSTRUCTION reinforced black Valox housing totally en capsulated circuitry molded o ring sealed lenses or fittings stainless steel hardware Meets NEMA standards 1 2 3 35 4 4X 12 and 13 CABLE 6 feet 2m of PVC jacketed 2 conductor cable is standard Three pin quick disconnect models are available optionally one conductot goes unused see page 4 INDICA
77. ngth of extension or delay depends on speed and length of gaps in the vehicle body The shorter delay should be used for vehicles at higher speeds and the longer delay at lower speeds This solution will not work well with highly variable speeds or with short vehicle headways ROADSIDE Either the direct or the reflex sensing mode may be used for the roadside mounting arrangement If the direct mode is used the transmitter and receiver must be placed on opposite sides of the lane or roadway If the reflex mode is used the sensor may be S2 or S3 and the retro reflector may be placed either on the pavement R1 or R2 or on the opposite side R3 With the units on oppo site sides there will be some mistakes if there is more than one lane of traffic and if vehicles interrupt the beam s simultaneously This arrangement is recom mended only if the traffic volume is low It is however the required arrangement for measuring vehicle height If two sensors are used in this arrangement direction can be determined by knowing which beam is broken first When the reflector is on the pavement the infrared beam is at an angle to the vertical If only one beam is used it will be difficult if not impossible to place the beam so that all passenger cars and all large trucks will break it One beam would not be able to detect both a low car near the shoulder edge and a truck with high clearance near the lane line Therefore two or more sen sors sh
78. ns continued specifications continued OUTPUT RATING 250mA continuous each output OUTPUT RATING 500 60VA continuous 4A inrush OUTPUT PROTECTION protected against false pulse on power up inductive load transients power supply polarity reversal and continuous overload or short circuit of outputs OUTPUT PROTECTION protected against false pulse on power up and inductive load transients RESPONSE TIME 4 milliseconds ON 4 milliseconds OFF ex cept reciever only units which are 8 milliseconds ON and 4 milliseconds OFF 100 millisecond delay power up outputs non conducting during this time CONSTRUCTION reinforced Valox housing totally en capsulated molded acrylic lenses stainless steel hardware Meets NEMA standards 1 2 3 3S 4 4X 12 and 13 RESPONSE TIME 8 milliseconds ON 8 milliseconds OFF except receiver only units which are 8 milliseconds ON and 4 milliseconds OFF 300 millisecond delay power up non conducting during this time CONSTRUCTION reinforced Valox housing totally en capsulated molded acrylic lenses stainless steel hardware Meets NEMA standards 1 2 3 3S 4 4X 12 and 13 CABLE 6 of PVC jacketed cable standard 2 conductor for emitters 4 conductor for all other models Quick disconnect QD models available optionally of PVC jacketed 2 conductor cable standard Three pin
79. om Banner for tesung and evaluation 44 VALU BEAM 912 Series SM2912 series dc sensors FEATURES SM912 series 10 30V dc 3 wire operation SM2A912 series 24 250V ac 2 wire operation All sensing modes available opposed retroreflective diffuse proximity convergent and fiberoptic Switch selectable light or dark operate Totally encapsulated circuitry in a rugged molded plas tic housing NEMA 1 2 3 3S 4 4X 12 and 13 Integral conduit fitting and 6 PVC covered cable supplied on standard models NEMA 4 Quick Discon nect QD cable connector combination optional Adjustable sensitivity Versatile mounting options Banner 912 series VALU BEAMs are a family of rugged self contained photoelectric sensors designed for especially demand ing industrial applications where economy performance and durability are important 912 series VALU BEAMs have solid state outputs and are available in either 10 30V dc powered or 24 250V ac powered models see specifications below Powerful modulated LED light sources give 912 series VALU BEAM sensors greater sensing range than competitive units and a high degree of immunity to ambient light All models are totally epoxy encapsulated and housed in molded Valox housings for the ultimate in shock vibration moisture and corrosion resist ance VALU BEAM sensors conform to NEMA standards 2 3 35 4 12 and 13 SM912 series DC sensors
80. ot optimal A different method with diagonal beams has been used to distinguish between single and dual tires Two beams at a 45 degree angle to the center line and 23 inches apart may be used to calculate speed and axle spacing in the manner previously described Single tires interrupt only one beam at a time while dual tires inter rupt both beams simultaneously In field tests performed on the Turner Turnpike outside Oklahoma City the 23 inch distance was found to be critical For closer spac ings some single tires broke both beams at once and for larger spacings some dual tires broke the beams one at a time At the 23 inch distance only a few small dual tires 9 i e pickup truck dual tires were identified incorrectly Approximately twenty large trucks and five pickup trucks with dual tires were visually observed and compared with the output for each distance tested If this method were to be combined with the diagonal dimension method then almost all vehicles should be classified correctly ex cept motorcycles SUMMARY Infrared sensors can be mounted in overhead road side or pavement level arrangements In the overhead and roadside arrangements vehicle bodies are detected and vehicle speed length and headway can be measured In the pavement level arrangement vehicle tires are de tected and vehicles can be classified according to the number of axles per vehicle the axle spacings and the sizes of the tire contac
81. ould be used at different levels with their output signals connected with a logical OR to give more cover age and accurately sense all vehicle types Some combination vehicles may interrupt the light beam more than once and be counted as more than one vehicle as in a manner similar to the overhead arrange ment previously described A solution to this problem might be to use a sensor with a time delay as stated above If the sensor is close enough to the edge of the pavement it is possible for specular reflections from highly polished cars to give a false signal This problem was discovered while data were being collected on a high occupancy vehicle HOV lane in Houston where some vehicles passed within about 4 feet of the reflex sensor receiver unit A possible solution might be to use a polarizing filter over the lens but this approximately halves the sensing range The manufacturer suggested offsetting the retroreflectors from the sensors i e using diagonal light beams to cut the vehicle paths Specular reflections are strongest along the angle of reflection which is equal to and opposite from the angle of incidence Therefore if the sensors are offset by 15 degrees or more they will not receive strong specular reflection from flat reflecting surfaces parallel with the lane lines PAVEMENT LEVEL When tires are being sensed both sensors and retro reflectors should be placed at the pavement level The beams are broken by the
82. performance of the 1480B sensor when used with an of seven 6200A 3 reflectors Performance in the work ing environment may vary tt L an 1 Seven reflector array TES HUM a 00 e n 2 em LL EXCESS GAIN Installation 1480B For parts identification and orientation during installation refer to the accompanying exploded view Before plugging the sensor head into the control module check that the bayonet pins are straight and that there is a sealing gasket on the con trol module Aiso check that there is a gasket on the hold down bolt insert a pin guide or logic card If used into the controi module Line up the bayonet pins as shown and seat the head on the gasket The bayonet pins are a snug friction fit but excessive fource should not be necessary Tightening the hold down boit will compress the gasket and complete the seal To remove the sensor head from the control module unscrew the hoid down bolt be sure that it is completely free Pull up whiie cartully rocking the sensor head from side to side The head may release suddenly when the pins clear the recep tacies 8 EXCESS GAIN Hold Bown Front Align the two End Bayonet Pins with these 5 Slots Top View of Control Module Pin Guide or Proximity Mount Logic Card
83. r should be mounted on the roadside or overhead to detect the presence of the vehicle body If vehicle height is desired an array of sensors should be mounted at different heights along the roadside Any of these arrangements can be used to distinguish between passenger cars and trucks WEIGHING Tire contact area multiplied by tire inflation pressure is an approximation of the downward force or weight of a tire if the pressure is uniformly distributed Many other factors such as pavement roughness speed and suspension systems affect the dynamic tire force Pavement level infrared sensors can measure tire contact lengths and calculate widths of tires on a moving vehicle Field evaluations showed that tire contact lengths measured by infrared sensors compared favorably with those measured statically but widths did not see Chapter 6 Tire contact areas and consequently weight can be estimated only roughly by infrared sensor measurements Lateral position of tires from the edge of the pave ment can be measured with infrared sensors This infor mation can be used to detect tires passing off the edge of WIM transducers Lateral position measurements can also be used to estimate the percentage of loads running on or near the pavement edge SUMMARY Infrared sensors can be used in several transportation engineering applications Single sensors may be used to count vehicle bodies or axles Other applications require an array of t
84. raised pavement marker in the center of the outside traffic lane can be used to count the tires on one end of each axle of a moving vehicle with accuracy compar able to human observers or to a flush mounted piezo strip sensor Sensor instal lation involved no pavement cuts and only minimal interference to traffic Tests were not conducted in snow or heavy rain Arrays of two or more infrared light beam sensors can be used to sense vehicle body presence to calculate vehicle speed axle spacing and tire contact patch dimensions to indicate single or dual tires to detect direction of vehicle movement and to sense over height vehicles Off shoulder reflex type infrared sensors with retro reflective raised pavement markers operated for up to three months without cleaning A two sensor array tested in the Houston high occupancy vehicle HOV lane indicated promise as a replacement for loop detector arrays Infrared sensors can supplement weigh in motion systems by indicating off transducer vehicle tires but correlations between infrared light beam sensor measurements and weight were not sufficient to make adequate weight estimates from such measurements practicable 17 Key Words 18 Distribution Statement No restrictions This document is available to the public through the National Technical Information Service Springfield Virginia 22161 infrared light beam sensors retro reflective pavement vehicles speed axle spacing weigh
85. roi module s case around fluid spray or heavy dirt contamination Before deciding on the mounting site and method review the installation and operating information contained in the Mounting Options Using the 6180A Mounting Bracket Wiring All input and output wiring connections are made on a barrier strip inside the control module s case There are two labels that you should find prior to making any connactions The first label is located on the case cover and gives the model number input and output ratings control and terminal designations The second label is located on the inside of the case and graphically identifies input and output terminals The 8882B provides high and low logic levels through a pair of open collector transistor outputs An open collector output functions as an electronic switch between the load circuit sensor head instructlon manual Regardless of the sens ing mode used thru beam reflex or proximity you should provide some flexibility in the mounting setup for align ment purposes For most installations Opcon recom mends the use of its 6180A Universal Mounting Bracket with the 8882B Control Module For specia applications if difficulties are encountered contact Opcon s Applica tions Engineering staff 1 800 426 9184 Opcon will also supply on request user s manual Industrial Photoelec tric Controls PN 102264 Two Axes Mounting Use hex head bolts Rot
86. rray of two pavement level infrared sensors was used to count axles per vehicle and indicate single and dual tires as the basis for classifica tion The two sensor infrared array combined with a loop detector had a 95 percent success rate during peri odic evaluation over a thirty day period at a site where vehicles were traveling between about 50 and 65 miles per hour Experienced human observers were the basis for the accuracy comparison IMPLEMENTATION STATEMENT Arrays of infrared sensors and retro reflectors in both the overhead and roadside arrangements can indicate vehicle presence and direction and thus provide information for counting vehicle bodies and for calculating vehicle speed headway and length In the overhead arrangement vehicles can be counted by lane In the roadside arrangement the height of vehicles can be determined Arrays of infrared sensors and retroreflectors can be used in the pavement level arrangement to calculate axle speed axle spacing tire contact area dimension and lateral position of tires They can also be used to indicate single or dual tires Another sensor either an infrared sensor placed to detect vehicle bodies or an inductance loop detector is required to match tres to the correct vehicle for classification For longer term performance off shoulder mounting of the reflex type infrared sensors with retroreflective raised pavement markers in the center of the outside lane is recommended Senso
87. rs on the edge line work only a few days without cleaning of the lenses and retroreflectors Some infrared sensors are battery powered and have a built in counter with LCD display These units cost about 130 each and are recommended for non recording counter applications perhaps at remote locations where total counts can be recorded by a human observer at appropriate intervals Output signals from infrared sensors can be connected to a counter or classifier which normally accepts road tube loop detector or piezo cable input signals These output signals can also be processed by a software program stored on a single chip microprocessor board Data can be stored on the board or sent to a computer to be displayed and stored In motion tire contact dimensions measured with infrared light beam sensors were not found in this study to be an adequate basis for estimating vehicle weight and tire loads of static vehicles and are therefore not suggested for implementation The reliability of weigh in motion measurements can be enhanced with infrared sensor information which detects off transducer positions of the tires of vehicles being weighed The cost of an infrared reflex sensor and reflector is about 100 while a piezoelectric cable costs over 300 and requires traffic control and pavement cutting to install it TABLE OF CONTENTS IMPLEMENTATION STATEMENT neinna ea aa i a E a a aa a a a a ai aN Gaai ideat v CHAPTER 1
88. sily aligned and adjusted without interrupting traffic Metal cans over the plastic sensors kept off the rain and direct sunlight After two or three days the small retroreflec tors in the center of the lane became covered with road film and the system could not operate After the retrore flectors were wiped clean during a traffic gap the system resumed operation Larger retroreflectors 4 inch square reflectorized raised pavement markers were used to replace the small circular retroreflectors and under regular observation were found to perform reliably without cleaning for three weeks Two temporary markers placed with a liquid primer on the rubberized asphalt adhesive were func tional after more than three months i e at the time of this writing While the larger retroreflectors extended the endurance of the system they also increased the effective size of the infrared light beam and thereby reduced the accuracy of tire contact length measurements Speed counting and classifying accuracy were not affected however The infrared classification system was compared with a piezo cable classification system However the two systems could not be directly compared as the piezo T J 12 ft Shoulder ir Piezo Manual N nm Q e Cc o Axle Counts e e A 2 3 Fifteen Minute Periods Fig 6 17 Comparison of infrared piezo and manual
89. sition and Control Adapter Center for Transportation Research University of Texas at Austin Fig A 8 System layout for three sensor vehicle classification system MC68HC11E9 EVBU SAMPLING SIGNAL GENERATOR SYSTEM LAYOUT OF INFRARED VEHICLE CLASSIFIER FOR MOTOROLA MC68HC11E9 EVBU omm Center for Transportation Research University of Texas at Austin Fig A 9 System layout for two sensor vehicle classification system
90. t arrays traffic weigh in motion systems estimate 20 Security Classif of this page 21 No of Pages Unclassified 80 19 Security Classif of this report Unclassified Form DOT F 1700 7 8 72 Reproduction of completed page authorized INFRARED SENSORS FOR COUNTING CLASSIFYING AND WEIGHING VEHICLES by Joseph E Garner Clyde E Lee Liren Huang Research Report Number 1162 1F Research Project 3 10 88 0 1162 Infrared Detectors for Counting Classifying and Weighing Vehicles conducted for Texas State Department of Highways and Public Transportation in cooperation with the U S Department of Transportation Federal Highway Administration by the CENTER FOR TRANSPORTATION RESEARCH Bureau of Engineering Research THE UNIVERSITY OF TEXAS AT AUSTIN December 1990 The contents of this report reflect the views of the authors who are responsible for the facts and the accuracy of the data presented herein The contents do not necessarily reflect the official views or policies of the Federal Highway Administration or the State Department of Highways and Public Transportation This report does not constitute stan dard specification or regulation There was no invention or discovery conceived or first actually reduced to practice in the course of or under this contract including any art method process machine manufacture design or composition of matter or any new and useful improvem
91. t areas The infrared light beams can be perpendicular or diagonal to the lane edge Di agonal beams are used to measure tire contact area di mensions and the lateral position of tires A presence sensor usually an inductance loop detector is required to match tires with the correct vehicles The next chapter discusses how infrared sensors in these arrangements can be applied for counting classifying and weighing ve hicles Loop Vehicle Presence TIME Bil Fig 4 3 Signal relations CHAPTER 5 APPLICATIONS Infrared sensors can be used for traffic counts over height detection speed surveys and vehicle classifica tion They can also aid weigh in motion measurements by giving the lateral position of tires with respect to tire force transducers The reflex sensing mode can be used in all cases In the direct sensing mode the sensor may be mounted in the roadside position if the receiver is mounted on the opposite side of the lane s The diffuse sensing mode is not currently considered to be suitable for sensing vehicles Infrared light sensors have distinct advantages but visible light sensors can also be used VEHICLE PRESENCE The presence signal required for matching tire sig nals to the correct vehicles can be given by a pair of in frared sensors mounted overhead or on the roadside The first presence sensor should be located upstream from the tire sensors and the second presence sensor should be
92. tector Ps p 1 Effective Beam Diameter are in one j Fleid of 2 Maximum Working Range package j View The effective beam diameter is equai to the reflector s 2 diameter except at very short ranges where the actual Effective beam diameter may be less than that of the refletor It beam will be difficult if not impossible to detect objects Objects whicn cannot diameter smalier than the effective beam diameter in general the beam must be completely blocked at some point for detection to occur The maximum working range varies with the diameter of the retroreflector Within limits increasing the size of the reflector will extend the sensor s working range fully block the beam may not be detected As the range increases the light beam spreads out and the intensi however it will then require a larger object to biock the i is reduced because beam Other factors which affect working range are yp nt of light must contaminants such as dust and steam in the air and or cover a much greater area dirt collecting on the sensor s lens and the surface of the reflector Optimum range information can be ob tained from the excess gain curves given in this manual If possible choose a working range which cor responds to the sensor s peak excess gain point Dirt smoke steam etc have twice the effect on reflex systems because the infrared light must cross the detector region twice
93. terrupting all three beams simultaneously would be classified as dual tires interrupting the first two beams sequentially would be single and vehicles interrupting the first two beams simultaneously would be single or 21 dual depending on the classification of the other tires of that vehicle This proposed system has not been tested Under the Oklahoma Turnpike Authority Classification Schedule axle spacing is not a criterion so a classification system which does not assume constant velocity can possibly be used In the field tests off duty toll booth operators re corded vehicle classifications based on visual observa tions The operators were required to identify the vehicle class and press the appropriate computer key before the vehicles activated the loop detector The operator and in frared system classification errors are summarized in Table 6 4 Ref 10 The operators were 94 7 percent suc cessful while the infrared system was 96 3 percent suc cessful Many of the operator errors were due to ve hicles following too closely which made the time available for pressing the computer key too short The system errors could be reduced by using a three sensor array as described above which could classify small dual tires correctly TABLE 6 4 VEHICLE CLASSIFICATION ERRORS ON OKLAHOMA TURNPIKE Date No of Operator System of Test Vehicies Errors Errors 21 AUG 1990 1 SEP 1990 8 SEP 1990 14 SEP 1990 14 SEP 1990
94. tion and other applica tions where the transmitter and the receiver are mounted on opposite sides of the roadway The diffuse sensing mode is not recommended for traffic applications Either roadside or overhead arrangements may be used for sensing vehicle bodies but the overhead ar rangement must be used for sensing vehicles in lanes away from the roadside To reduce miscounting resulting from gaps between vehicle units sensors with a time de lay may be used For sensing vehicle height an array of sensors at different heights should be used in the roadside arrangement Pavement level sensors should be used for sensing tires The shoulder edge location is recom mended especially for heavy traffic The lane edge loca tion may be used for short term applications of less than about three days duration or when retroreflectors and lenses can be cleaned frequently Corner cube retroreflectors are recommended for all applications Spherical bead retroreflectors should not be used if polarizing filters are used with the sensors Five major field tests were carried out to determine the feasibility of using infrared sensors for counting classifying and weighing vehicles A tire contact area study was performed at San Marcos Texas In motion tire contact area was calculated from infrared sensor measurements and compared with static measurements taken manually Static and dynamic tire contact lengths showed good agreement but because the tire
95. tires just as they contact the ground and have their smallest cross section If the tires were measured closer to their vertical centers the sensors might not have enough time to recover and count a closely following tire separately For this reason only sensors with short response times should be used The through beam sensing mode is not generally recom mended for sensing tires for the reasons discussed previ ously with respect to overhead sensor mounting For the reflex sensing mode the retroreflectors should be placed in the center of the lane so that tires on the same axle straddle the retroreflector and only the tires next to the shoulder break the beam A three sensor pavement level array is shown in Fig 4 2 51 S2 and S3 represent reflex sensors while R2 and R3 represent retroreflectors D1 the distance be tween the two perpendicular beams is used to measure speed D2 is the distance between the center of the lane and the sensors and 6 is the angle used to determine the lateral position and the width of the tires The retrore flectors are inside an inductance loop detector in the cen ter of the outside lane The sensors are on the lane edge or off the shoulder The signals from a two axle vehicle with respect to time are shown in Fig 4 3 S1 S2 and S3 are the signals received from the reflex sensors shown in Fig 4 2 A ve hicle presence signal is necessary for the tires to be matched to the correct vehicle A pr
96. ut The BLACK HOOKUP TO PROGRAMMABLE CONTROLLER sourcing output This diagmam shows bookup of a de VALU BEAM to a programmabis mquiring source using the sensors sourcing QAN put The WHITE 1019 250V ac V de 5 6 SMASTE SMAGTEF SMAN ESA pospan panes pw poum aws w 2 gt a x c d i i ji nii SEU 5105095 S3TW3S NI SHOSNAS 6105095 591199 21 6 5 9B suredeiq dnxyoog fo 4 ON TATIVAVd SIDV LNOD 8 D2 di OVDC C Isolated Solid State Output Collector D Isolated Solid State Output Emitter EE p os Jac J lt 5 J1B D 12VDC R4 R5 10K a Le 470p ry JIC OR OUT J JD D1 J1A J2A O 2N718A oo 9 OR Gate Circuit Diagram of Infrared Sensors DESIGN Huang Liren Jun 4 1990 Center for Transportation Research University of Texas at Austin Fig A 7 Circuit diagram for HOV lane in Houston BI1 IBM MICROCOMPUTER 2 D Sensitivity Adjustment Ojo D 4 BIO POWER SUPPLY CONFIGURATION OF OPCON INFRARED SENSOR SYSTEM LAYOUT OF INFRARED VEHICLE CLASSIFIER for IBM Data Acqui
97. wo more sensors Infrared sensors can de tect wrong direction or over height vehicles They can be used to classify vehicles according to number of axles per vehicle axle spacing pattern and single or dual tire con figuration Infrared sensors can measure tire contact area dimensions and lateral position of tires in the traffic lane These measurements can be used to supplement informa tion from weigh in motion systems The following chap ter discusses field evaluations of several infrared sensor arrangements and applications CHAPTER 6 FIELD EVALUATIONS Five major field tests of infrared sensors were per formed between 1988 and 1990 The objectives were 1 to determine the feasibility of improving or replacing cur rent vehicle counting and classifying systems and 2 to explore the possibility of determining vehicle weight us ing infrared sensors In San Marcos Texas in September 1988 tire contact area dimensions were measured manu ally and compared to infrared sensor measurements of tires on moving vehicles In December 1989 near Junc tion Texas tires were measured by infrared sensors and weighed simultaneously with WIM transducers In May 1990 in Houston a two beam infrared sensor array was field tested as a possible substitute for loop detectors Sensors were installed at Jarrell Texas during the sum mer of 1990 to test their long term performance In Au gust 1990 in Oklahoma City the possibility of using two

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