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Development of a PC-Based Eight-Channel WIM System

1. Date Time Err Des 15 17 50 Err 104 Loop in wrong order 15 17 50 Err 110 axle Sensors 1n wrong Order rae J0 Err 104 Loop in wrong Order Frrr y9 Err lld axle Sensors In wrong order 15 18 36 Err 109 Zero axle found by upstream WIM Figure 71 Error file format For remote data downloading and remote desktop access two different software packages are used Both software packages are in the public domain and have been widely used For the remote desktop view Real VNC Viewer Free edition 4 1 1 is used This software is installed in the remote computer as a server VNC Since the remote server 1s built based on a standard TCP IP stack connections from a client can be made using a variety of means For example dial up Ethernet wireless etc as long as those services are available Presently the server remote WIM site computer is equipped with a phone line and a modem providing a remote dial up connection A standard Windows dial up connection wizard is used for the connection Figure 72 After Real VNC server is installed on the remote PC the incoming connection options should be enabled on that PC A step by step process in graphical view for creating incoming connection is provided After opening the Network connection from the Control Panel click on the create a new connection tab on the left top portion of the wizard as shown in Figure 72 Network Connections Fie Edit View Favorites Tools Advanced Help
2. Start Stop Button In Figure 48 it 1s located at right hand top of the screen with the label Start Acquiring Data and is used to start or stop the program When the computer is powered on or restarted the program starts automatically and the label of the button is changed to Stop Acquiring Data Once the program starts acquiring data it begins to plot real 64 time WIM signals and translates the analog signals into WIM data Figure 49 shows the two states of the Start Stop button Figure 49 Start Stop Button Graph hold release Button The Graph hold bottom is used any time the user wishes to hold and see the current graph in the plot window It is commonly used when the user wishes to carefully inspect the signals such as the signal level structure of the signal noise levels etc This is a toggle button and when the Graph hold button is pressed the button is changed to a Release graph hold button Figure 50 The user should press the Release graph hold button to set the display to the regular mode of real time signal plots Release Graph Hold Figure 50 Graph hold release button Status Status shows the current status of the data acquisition process Figure 51 This is not actually needed or useful for general users However it can indicate that the system is not running if the index and the count values are not increasing In that case the user should press the Start Acquiri
3. Save this username and password for the following users Me only O Anyone who uses this computer Dial 2185251374 Figure 78 Dialup connection wizard After a dial up connection is made to the server the user may run the Real VNC Viewer to start accessing the remote desktop of the WIM system Figure 79 The VNC allows control of the remote computer as 1f the user was actually on a local desktop Once a VNC viewer is connected the user has a full access to all of the WIM software functions such as viewing the current vehicle signals starting stopping the WIM software setting changing parameters etc The VNC also allows access to nearly all of the PC functions For example the user could configure the modem and add more users client user etc If necessary the user could even restart the site computer YMC Viewer Connection Details ry Server TEE C Encryption Figure 79 Connection to the Real VNC Viewer The IP address is automatically assigned to the connecting computer after authentication is approved from the remote WIM computer Any FTP program can be 83 used for downloading the WIM data files The site computer acts as an FTP server to any client computer 84 5 6 Final WIM System Development of the WIM system proposed was successfully completed The final system is shown in Figure 80 The system consists of a fan less PC a standard LCD monitor a keyboard with trackball a modem an analog si
4. Unclassified Unclassified 102 Development of a PC Based EKight Channel WIM System Final Report Prepared By Taek Kwon Bibhu Aryal Department of Electrical and Computer Engineering University of Minnesota Duluth October 2007 Published by Minnesota Department of Transportation Research Services Section Mail Stop 330 395 John Ireland Bld St Paul Minnesota 55155 This report represents the results of research conducted by the author and does not necessarily represent the view or policy of the Minnesota Department of Transportation and or the Center for Transportation Studies This report does not contain a standard or specified technique The author and the Minnesota Department of Transportation and or the Center for Transportation Studies do not endorse products or manufacturers Trade or manufacturers names appear herein solely because they are considered essential to this report Acknowledgements The authors would like to thank the Office of Transportation Data and Analysis at the Minnesota Department of Transportation Specifically the researchers acknowledge George Cepress retired Mark Novak Mark Flinner Bill Martinson and Matthew Oman for participation in TAP meetings and for providing invaluable inputs to this project In addition the Office of Materials allowed the research team to use the MnRoad facilities for collection of analog WIM signals which were critical to this project We thank their gene
5. elog ght Technical Report Documentation Page 1 Report No 2 3 Recipients Accession No MN RC 2007 45 4 Title and Subtitle 5 Report Date Development of a PC Based Eight Channel WIM October 2007 7 Author s 8 Performing Organization Report No Taek Kwon and Bibhu Aryal 9 Performing Organization Name and Address 10 Project Task Work Unit No Northland Advanced Transportation Systems Laboratories 11 Contract C or Grant G No University of Minnesota Duluth 1023 University Drive Duluth Minnesota 55812 12 Sponsoring Organization Name and Address 13 Type of Report and Period Covered Minnesota Department of Transportation 395 John Ireland Boulevard Mail Stop 330 St Paul Minnesota 55155 15 Supplementary Notes http www Irrb org PDF 200745 pdf 16 Abstract Limit 200 words Weigh in Motion WIM data provides vital information for pavement design and maintenance The purpose of this research project was to improve the present piezoelectric WIM technologies through a better system design and signal processing algorithms Present WIM systems are only available as proprietary systems 1 e the internal system design and algorithms are highly guarded making it difficult to compare and improve the underlying technology Therefore the second objective was to develop a WIM system based on an open architecture utilizing a standard PC and off the shelf components and to publish the details of the design to promote a
6. Err 113 Vehicle too Slow This message is generated if a loop detects the presence of a vehicle more than three continuous seconds This error message also appears at the first time of failure of any loop When this error message appears the system discards the data collected and no weight output is reported 5 3 4 ESALs Equivalent Single Axle Loads or ESALs indicate the relative damage to a pavement structure compared to a standard axle The accepted standard is an 80 kN 18 000 Ib single axle load with dual tires The ESAL concept was developed at the American Association of State Highway Officials AASHO Road Test that was conducted from 1958 1961 in Ottawa Illinois Two similar equations one each for flexible and rigid pavements exist and were used for calcualation in the UM8 PCI system For ESAL calculation axles are classified into three axle groups where different multiplication factors are applied for each group Axle group means two or more axles where an individual axle is spaced less than 8 feet and 1 inch from any other axle as measured from the centers of the axles The axle groups are 1 steering and single axle group 2 tandem axle group and 3 tridem axle group Single axle group An assembly of two or more wheels whose centers are in one transverse vertical plane not less than 8 feet and 1 inch from another axle and extending across the full width of the vehicle 58 Tandem axle group Two or more consecuti
7. Lane 4 upstream Lane 4 downstream The call outputs of loop cards are provided as open collector outputs from the C924 Since the ADC inputs require a 5 voltage range a 5V regulator was included and connected to a 4 7K pull up resistor that produces the open collector call outputs The circuit diagram of loop detector connections is shown in Figure 29 37 Loop Input Loop Input 3 4 kP RGST AU GGW xY ez eee 3M Board Figure 29 C924 card connections In Figure 29 Loop Input 1 Loop Input2 etc correspond to the pair of wires coming from the loops installed in the pavement The O1 O2 O3 and O4 are the call output signals for loops 1 4 connected to the ADC channels as specified in Table 5 The lane numbers correspond to the site diagram shown in Figure 22 Table 6 summarizes the edge card pin assignments of the C824 card WHAT IS THIS CARD This table should be used for the Figure 29 connections The finalized internal components and connections of the WIM signal interface box is shown in Figure 30 38 Table 6 C924 Card Edge Connector Assignments Function Common of VDC 0 VDC VDC 10 8 VDC to 38 VDC Channel Loop Input A Channel 1 Loop Input B Channel 1 Switch Call Output C Channel 1 Switch Call Output E Channel 2 Loop Input A Channel 2 Loop Input B Channel 3 Loop Input A Channel 3 Loop Input B Channel 3 Switch Call Output C Channel 3 Switch Call Output E Channel 4
8. Parameters Ins Figure 63 Sampling options Graph Menu The third column of the Menu is Graph all of the graph related functions are included under this menu Data Table Under the Data Table item the user has an option to hide or display the data table i e Figure 64 This option may be used if the user wants to see only the signal plots WIM STSTEM 6 File Settings Meier Data Table y Show Table Graph Hide Table Legend Y Oxis Range Figure 64 Data table 75 Graph Under the Graph option the user can hide or show the graph window WIM SYTSTEM 6 File Settings leper Data Table Show Graph Legend d Hide Graph Y xis Range F Figure 65 Graph table Legend When the Show Legend option is selected the legends of the plot area lines are displayed Figure 66 The user can select this option to view only the upstream signal downstream signal or both WIM SYSTEMY File Settings WEEmE Data Table Graph show Legend Y Axis Range amp ow Hide Legend Figure 66 Legend options Y Axis Range The user may adjust the range of y axis using this option The maximum viewable range is from 5 V to 5 volts Other choices are shown in Figure 67 76 WIM STSTEMy 6 File Settings leper Data Table Y 4xi5 Range io To 15 Figure 67 Y Axis range Help Menu At this time the help option only shows the developer s name and the development
9. uniform distribution Since the tire footprints are the only area that touches the road surface and the inflation air inside the tire interacts to evenly distribute the load it is reasonable to assume that weight loads are uniform on the footprint In reality the edges should have slightly lower loads than the center As a Staring point of constructing the axle signal the peak of the axle weight profile 1s computed from an actual axle load or user supplied axle load Since the signal generated by the piezoelectric WIM strip is a one dimensional signal as a function of time the peak force received by the sensor is determined by the ratio between the footprint length of tire and the sensor width as shown in Eq 14 Axle _load N Sensor _ width 14 Footprint _ length Peak _ sensor _ force N It was assumed that the footprint length is longer than the sensor width which is the case for all commercially available piezoelectric WIM sensors If the footprint length is longer than the width of the sensor the peak sensor load is simply equal to the axle load It is also assumed that all loads are measured in Newton Next the peak sensor load must be converted to an equivalent voltage It is known that the load actuated on the sensor produces an electric charge signal that is converted to a voltage through a charge amplifier Let this converted voltage be called Peak_sensor_voltage then its computation can be done using Eq 15 Pea
10. 45 Typical Typisch e 230 V arrester Ableiter 350 V arrester Ableiter Two 2 electrode arresters wel 2 Elektroden Ableiter a Tip b Ring Arrester _ ii Ableiter 7 Protected device Gesch tztes Ger t Ground Erde Figure 35 Schematic diagram of surge arrestor connection 5 2 6 Loop Splice Panel In the old loop connections the coaxial cables of the loop wires were connected through Din Rail mounted terminal blocks cage clamp type One problem experienced with that type of connector was that the contact problems inside the clamp could not be visually identified To eliminate this issue visually verifiable connectors were designed using barrier terminal blocks The fork type splice ends provided more reliable contacts In addition surge arresters were added to protect against events such as lightening The part chosen was a 2pin 230V Gas tube surge arrester Digikey Part No 495 1471 ND The modified splice panel for loop wires coming from the pavement is shown in Figure 36 46 Figure 36 Loop wire splice panel The loop cables at the Highway 61 site are numbered from 1 to 8 Each cable consists of three contacts two loop wire ends and one ground Since each lane has two loops six contacts per lane are spliced to the panel with clearly marked lane numbers The detailed connections from the loop wires to the splice panel are shown in Figure 37 Installation to the existing panel is shown in Fig
11. Check if Upstream WI detect the vehicle or not artie secondary loop erk at the present data size 32 726 Error 3 Upstream and downstream Loop Sensors are not working Unable to calculate parameters Figure 42 WIM computation flowchart 1 of 3 53 Vehicle is too slow lf Loop3 detect the vehicle presence Yes Prasence of vehicle detected fe more than 2 5 seconds long Ti the Upstream WIM detect the vehicles _ Yes Start storing data in an array2 WIM data Error 1 Failure of 4 Upstream Loop Loops Detect Vehicle Presence more Faure of Downstream Loop Sheck if Upstream WI detect the vehicle or not Yes Gat the size of detected loop length and store data until the second imaginary loop size is same as first No Error 3 Upstream and downstream Loop Sensors are not working Unable to calculate parameters amp Figure 43 WIM computation flowchart 2 of 3 ls the Secondary loop is terminated 32 726 54 G First lane Loop data fram Array Error 5 Vehicle is too light Error 6 Idle Signal Level is too high i hack for detected le level is in between rS to 0 5 then No I Second Lane Same gt steps Pull the WIM data and discard the Error 10 Vehicles axle mismatch Get data of each axles of Channel 1 and ls axle is detected from
12. E 16 SI Veme laS CaN OM saeir s a a E A T eels 16 CHAPTER 4 WIM HARDWARE IN LOOP SYSTEM 2 cccessesccccccescecs 18 Ze INTRODUCTION htt sees here ad Eee eae ne chan as iatat SE Nee ee Oe nis Ait atta ae each 18 4 2 WIM HARDWARE IN LOODP cccccececcecccecescececcscecescecscecsescecescececcecesescesescecasees 18 4 3 CONSTRUCTION OF WIM SIGNAL Q cccceccecceccccecceccscsceccsceccecescescesescesctscesescscuces 19 BaD PMLCL ONAL svcd anise a a a a op tecrudete atl woes 19 PAA AKC NALEN a T aanesawi eames 21 4 3 3 Comparison between Simulated and Real WIM Sign ccccccccccceeseeeeeeeeeees 24 A A CONSTRUCTION OF LOOP SIGNAL miraia Das cietilis ede cede ats eos es 27 4 5 SIMULATION OF FAILURE CONDITIONS ceccececcsceccsceccscececcsceccscecescececescesescececees 28 CHAPTER 5 WIM SYSTEM DEVELOPMENT BASED ON PC 00 30 5 1 SYSTEM COMPONENTS AND SITE DESCRIPTION c csccscececcececcececcececcscecescecesesceses 30 Dds WIM Sensors and Loop Detectors cisccsccchctivszeisecarateaciveeckedias Biaeecee RR 32 Sdz ANaloe Signal Interac BOX oysir enoii a Ea E EN E EEEE 32 Dell GANG NIWOT ornen a a a ala eansiaaes 33 52 HARDWARE DESCRIPTION akanena a E A A 34 2A Char C AMDT EVS oE e T E E AT S N T 34 5 2 2 Analog to Digital Converter ADC Board cccccccccsccccccccsseeeccecceeaeeeeecsenaanseees 35 Pas LOON DE ETOT aE E E EE E E 37 PL AABNCS PI E BD ON pa Ea a E E E 40 D212 SUS AV
13. Finally the A D converter is attached to a PC that processes the digital signals to produce axle loads and separation distances According to the axle loads and separation distances the system reports the vehicle type The system is designed to collect data for a long period of time 1 e until the hard disk space is filled Two files are created daily by the WIM system One contains the vehicle records collected throughout the day while the other summarizes the error conditions encountered on that day The file containing error information is very helpful for troubleshooting the system Error information also reflects the data quality during that period since the data is highly influenced by the hardware error conditions 3 3 WIM Signal Analysis The purpose of WIM signal processing is to convert the voltage outputs of the charge amplifier signals to axle load and axle spacing data for each vehicle Since axle spacing determination is simple and done based on peak signal voltages of the upstream and downstream piezoelectric sensors the focus of this section is on axle load computation There are two principles that must be considered in the axle load signal processing The first is the tire footprint The length of the footprint controlled by the diameter inflation pressure and load on the tire is always wider than the width of the piezoelectric sensor Scm Consequently the peak of the signal does not represent the whole wheel load but rat
14. Loop Input A Channel 4 Loop Input B Channel 2 Switch Call Output C Channel 2 Switch Call Output E Channel 4 Switch Call Output C Channel 4 Switch Call Output E 39 Figure 30 Internal components and connections of the WIM signal interface box 5 2 4 BNC Splice Box It was found that existing T connectors of BNC cables created frequent contact problems This led to critical errors during axle weight computations such as missing or partial weights In order to correct the problems and create reliable BNC connections a splice box was designed and constructed At the Highway 61 site a total of 32 BNC connectors come from the Kistler Lineas sensors that must be spliced from two or four lines into one In order to facilitate the original IRD connections a toggle switch is connected to combine either two or four BNC inputs connected in the same column Figures 31 and 32 illustrate the top view and side view of the BNC splice box 40 Figure 31 BNC Splice Box Top View y lt 4 i 4 h 5678 910 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 a F Q L x 7 qi d A S y o LANE4 O REA J A 5 4 B a 34 78 14 42 BA 15 16 23 24 27 28 34 82 P d x J Xx A N y d A N A UPSTREAM DOWNSTREAM UPSTREAM DOWNSTREAM UPSTREAM DOWNSTREAM UPSTREAM DOWNSTREAM y Figure 32 BNC Splice Box Front View The complexity of this arrangement is due to t
15. been written and tested at Mn DOT s Highway 61 WIM site MP 16 4 northeast of Duluth The site diagram is shown in Figure 22 This diagram is referred throughout for identification of each WIM component Subsections in this chapter describe the UM8 PCI WIM system 30 AARARAR ARAB A Loop CHA a era WIM sensor 6 teet 5 feet WIM sensor WIM sensor CH4 5 10 ft 3 Inch Prepared By University of Minnesota Duluth UMD WIM Cabinet Figure 22 Site diagram Highway 61 MP16 4 Duluth MN 31 5 1 1 WIM Sensors and Loop Detectors One group of inputs to the UM8 PCI WIM system are signals from Piezoelectric Lineas Sensors The sensors are embedded in the pavement and produce a charge signal that is proportional to the deformation induced by the axle loads on the pavement Figure 23 shows this sensor Figure 23 Kistler Lineas Sensor 9195C1 The Highway 61 site is outfitted with Lineas sensors in all four lanes with two sensor arrays one for upstream and the other for downstream in each lane Each sensor array consists of four Kistler Lineas sensors two 9195C1 and two 9195C2 to fully cover the width of a single lane 12 feet In addition to Lineas sensors each lane is also equipped with two inductive loop sensors one for upstream and the other for downstream The positions and identifications of the WIM and Loop sensors at the Highway 61 site are shown in Figure 22 5 1 2 Analog Signal Interface Box The analog
16. button serves as the next step As shown in Figure 73 the Next button is highlighted 80 New Connection Wizard Advanced Connection Options Which type of connection do you want to set up Allow other computers to connect to this computer through the Intemet a phone line or a direct cable connection Connect directly to another computer nect te ather computer using vou c New Connection Wizard Devices for Incoming Connections You can choose the devices your computer uses to accept incoming connections Select the check box next to each device you want to use for incoming connections Connection devices O gt Agere Systems AC 97 Modem Figure 74 New connection wizard c and d Figure 74 d shows the current modem installed on the computer The user needs to place a check mark on the space provided before the modem name or select the modem before proceeding to the next step Incoming Virtual Private Network VPN Connection Another computer can connect to yours through a VPN connection Virtual private connections to your computer through the Intemet are possible only if your computer has a known name or IP address on the Intemet F you allow VPN connections the system will modify the Windows Firewall settings to allow your computer to send and receive VPN packets Do you want to allow virtual private connections to this computer Allow virtual private
17. date VIM SYSTEM 6 File Settings Graph Waele HE About University of Minnesota Duluth Minnesota All right Reserved 2006 Close Figure 68 Developer s name and developed date TI 5 5 Data Downloading remote desktop view Two files are created by the WIM system each day One contains the vehicle records collected while the other summarizes the error conditions that occurred during that day A new file is created at 12 00 AM in a new folder where the folder name is the current year followed by month and day YYMMDD CJ 4007 0531 an 007060 J a 2007 0603 00 0604 20070605 Figure 69 Daily created new folder folder name based on date The vehicle record file is in an ASCII format txt and contains vehicle index time stamp number of axles each axle spacing each axle weight the gross vehicle weight the vehicle classification and any associated error codes An example vehicle record file and an error file are shown in Figures 70 and 71 P 20070917 001 txt Notepad File Edit Format View Help veh Lane Time Axle speed axledist Ax lweight 00 00 42 00 02 59 2 00 03 40 00 04 36 00 06 17 00 06 53 00 09 58 00 10 46 00 11 59 64 1 7 5 0 9 2 5 1 8 16 7 16 6 15 9 16 7 5 1 1 0 1 4 64 1 3 8 2 16 4 Class 5 1 2 3 4 5 6 7 8 9 PR EaRR REAR COHNFOBREN ocooccococo Figure 70 Data file format 78 E Err151745 txt Notepad File Edit Format View Help Lane
18. design and maintenance and accurate data is essential The purpose of this research was to improve the current piezoelectric WIM technologies through an improved system design and better signal processing algorithms to increase measurement accuracies and while lowering the cost of WIM systems This research demonstrated that high quality WIM systems can be built using a common desktop PC and off the shelf components The main innovation introduced in this research was the new HIL WIM simulator that can generate analog axle signals through software control Generally development of anew WIM system or calibration of an existing WIM system requires repeated driving of trucks with known weights to verify the algorithm and measurement accuracies This traditional approach is expensive in terms of both time and resources but the fundamental problem lies in inherent errors associated with the discrepancies between static and moving weights First a known weight of a heavy truck has an inherent error mainly due to static scale and manual measurement errors Second the weight of moving vehicles is affected by environmental effects such as winds the road slope spring effect of the suspension system and pavement roughness Thus a direct conversion of moving weight into static weight includes effects that could produce an error The proposed HIL WIM simulator solves these difficulties using software generated ideal axle signals of known weights which effectiv
19. inside the pavement and a signal processing computer in a roadside cabinet A typical setup is shown in Figure 5 This is a single lane application that includes two rows of piezoelectric sensors and two loop detectors Presently all of Minnesota WIM stations follow this setup Variations exist such as placing a single loop detector between the two rows of piezoelectric sensors Speed is an important parameter for computing weight which is the main reason that the sensors are installed as two rows of parallel lines The inductive loop detectors are augmented to trigger the processing of axle signals More specifically the upstream loop detector detects the entry of a vehicle into the detection zone and the downstream loop detector detects the exit of the vehicle A typical dimension of loop wires follows a standard six feet by six feet The WIM sensors cover the entire width of the lane and are mounted flush with the pavement surface The system developed in this research contains eight channels and is capable of capturing four lanes simultaneously in real time Eight loops upstream and downstream at each lane and 32 WIM sensor inputs are fed into the WIM system Data Processing Analog to Application Digital weight ae SS Converter Axle Distance Reporting Speed Database Planning Classification Analysis Loop x Sensor N WIM Sensors WIM Sensors Figure 5 Overall WIM system block diagram 3 2 Overall System Archite
20. of downstream loop failure the WIM system fails to recognize the correct end of a vehicle signal Another common type of error observed was human error The eight channel WIM system consists of a total of 40 wires 32 piezoelectric sensor wires and 8 loop wires that are connected to the WIM system box A common error was connecting the sensor wires in the wrong position specifically swapping of upstream and downstream lines Additional signal failures encountered frequently was caused by a contact problem between the WIM system and the sensor cables For a single lane eight BNC connectors are combined into two BNC connectors through H and T BNC summing connectors Often H or T BNC summing connectors use mechanical break away sockets and caused electric contact loss from one or more sensor lines The challenge to engineers is to design the WIM system in a way that failure conditions are immediately detected and reported via an error message Upon detection of an undesired condition the raw analog signal was recorded If an undesired condition was missed the raw data was not recorded the observed conditions were documented in a note In the lab each failure condition was first created as an independent module and then numerous combinations of the failure conditions were processed through the HIL WIM simulator control module The WIM system was repeatedly tested and debugged until the WIM software correctly detected the failure conditions and a prop
21. of lower cost piezoelectric WIM sensors Unlike traditional single load cell installations which require a large excavation at a high cost piezoelectric sensors require only small cutouts in the pavement In addition maintenance costs are much less since mechanical parts are not directly involved However there are some concerns with piezoelectric sensors The first is the sensor s sensitive to heat and the consequential effects on the accuracy of measurements Secondly it is difficult to isolate the vertical forces from the moving vehicles to measure the true weight of the vehicle These two concerns were addressed with the introduction of quartz piezoelectric sensors developed by Kistler 9 that include a vertical force isolation design A study has been done on the development of a two channel single lane WIM signal diagnostic system 8 This system collects and analyzes raw data from the WIM site and produces a report however the system can handle only two channels of data at a time In the system developed in this research and the project associated with it the system runs on two operation modes a signal analysis and a data collection mode In the signal analysis mode the raw analog signals of eight WIM channels are simultaneously analyzed and analysis results are reported The report includes faulty channel conditions and signal health states This information indicates data quality so that any relevant maintenance can be activa
22. one second delay Figure 53 Loop calls Plot Window In the plot window the user can observe the WIM activity of one chosen lane at a time The software draws box plots of the upstream red in color and downstream signal green in color condition of the WIM sensors The horizontal axis represents data for one second sampling rate 4096 samples sec or the signal fluctuation at a one second interval The vertical axis represents the voltage level of the signal and can be adjusted accordingly up to the maximum of 5V as shown in Figure 54 Data Table Graph Legend 4 5 To 15 0 5 To 3 0 To 2 OTo 3 b To 5 Figure 54 Y Axis Range 67 WIM Outputs The computed parameters are displayed in the table located below the plot window see Figure 55 The table includes parameter headings in the first row which are described in Table 10 Each column is elastic which means the user can place the cursor at the boundary of the column at the top row and can drag to adjust the width of the column Figure 55 Output table 68 Table 10 WIM Output Parameters Table Column Description Veh Count of vehicles from the start time It is reset to 1 at 12 00AM midnight Lane Lane number 1 2 3 or 4 Time Time stamp when vehicle passed through the site hr min sec Axle Number of axles on the vehicle Speed mph Speed of the vehicle 66 99 Axle Spacing Axle spacing The axles are separated usin
23. signal interface box contains charge amplifiers loop detector cards power supply units I O circuit boards and an ADC analog to digital converter board The ADC board is connected to a PC through a PCI bus from which the digitized raw sensor data is transferred to the computer memory This digitized data is converted to axle weight data using a WIM signal processing algorithm Since the system has eight WIM channels it supports up to four lanes providing two channels per lane The picture of this box is shown in Figure 24 32 Figure 24 Analog signal interface box 5 1 3 PC and Software A Pentium D PC was provided by Mn DOT for this project but it was replaced with a more reliable fan less industrial thin PC The software was developed using VB NET 2003 Framework 1 1 The role of the software is to acquire the digitized raw signals and calculate all required parameters of WIM data In addition it utilizes loop signals to determine the boundary of vehicles in the WIM signal The WIM signals are plotted on a graphical user interface in real time while simultaneously computing and storing the required WIM data The software is capable of generating speed axle spacings gross axle weight gross vehicle weight GVW vehicle classification and error notification in real time In addition the user can save the raw signal data to analyze the signal quality or to review the sensor activities in the future The industrial fan less ITX PC is
24. signals sent by physical components and the simulated signals HIL provides a verification platform not only for the software but also for the hardware In many manufacturing companies the systems that are being developed are initially verified with a mathematical model and then verified with software simulation The design engineer runs simulations of the new components in conjunction with models of the rest of the existing components to study the behavior of the overall system and to optimize the algorithms and routines before building prototypes 25 26 HIL systems are also commonly used for fault tolerance shorted or open signals etc and reliability or endurance tests of new components Additionally HIL simulators are used by companies designing new vehicles parts of airplanes and rockets 16 Also it has been used in the development of automotive anti lock braking systems From the simple to complex design HIL simulations have been widely used as development platforms 4 2 WIM Hardware in Loop Two general purpose PCs are used to set up a HIL WIM development environment as shown in Figure 11 For this setup the WIM system is developed using a general PC platform that is equipped with a multi channel analog to digital converter ADC However other platforms of WIM systems can also be used The charge amplifiers must be disconnected from the ADC before the WIM system is connected to the HIL simulator In Figure 11 the left side of t
25. simulator are the front axle weight of 1 2 Kips the rear axle weight of 0 7 Kips vehicle speed of 70 mph and the axle spacing of 9 4 feet From the original WIM signal the tire footprint length was computed to be 45 cm The generated vehicle signal from the HIL simulator was fed into the WIM system and the result is shown in Figure 20 Notice that the WIM system detects a Class 2 vehicle with a 12001b front axle weight and a 700 lb rear axle traveling at a speed of 70 mph which is identical to the original vehicle data The signal length of the simulated waveform was an almost exact match to the original the difference was less than 1 The correct detection of weight verifies that the area under the waveform of the simulated signal matches the area of the real signal the objective of simulation 0 05 Upstream axle signals T ooo tt Downstream axle signals 0 05 0 10 Voltage 0 15 0 20 0 100 200 300 400 500 600 700 800 900 1000 1100 Time samples Figure 18 Class 2 axle signals generated by HIL simulator 26 Front axle signal load 1200 Rare axle signal load 700 HE p vlag i 20 Lf 60 a0 t00 t23 140 160 180 200 220 20 a i d i t t0 i80 200 220 Time sanrples sec Time Samples sec Figure 19 Class 2 axle signals generated by WIM HIL simulator Lane Time Avle Speedimph Axle Dieffeet Veh Lenffeet Axle Weight King yi Kips Yeh Class Toke 2 be 201
26. takes more than three seconds to pass the sensor the constant speed assumption cannot be met In most cases it is likely the loop is in a stuck on failure state Consequently loop signals longer than three seconds are considered as failures Under this condition red color appears on the corresponding square in the loop calls of the display This error can often be easily corrected by making a firm connection on the loop splice panel and resetting the loop card Err 102 Downstream Loop Failure The downstream loop failure message is generated if the system cannot detect the downstream loop signal This problem may be corrected using the aforementioned remedy in the upstream loop failure case Err 103 Upstream and Downstream Loop Failure The upstream and downstream loop failure message is generated if the system cannot detect both the upstream and the downstream loop signals This generally occurs when both loops have bad contacts to the splice panel Err 104 Loop in Wrong Order This message is generated if the upstream and downstream loop connections are swapped It can also occur if a vehicle passes the site in the wrong direction For instance during a lane closure on a four lane segment or simply when a vehicle passes another at the WIM site on a two lane road It should be pointed out that if the loop is swapped with one in another lane only failure of upstream or downstream message 1s generated 56 Err 105 High Low Idle Lev
27. to cover the full width of a single lane The quartz sensor consists of an extruded metal frame aluminum alloy that supports multiple pre loaded quartz disks The quartz elements are wired together and arranged such that a uniform output is produced regardless of where the force is applied along the length of the sensor The sensor is isolated from side forces by a special elastic material The sensor is installed perpendicular to the traffic flow by cutting a slot in the pavement and using a special epoxy grout to hold the sensor in place These are typically installed flush with the surface on either existing or new asphalt or concrete pavement surfaces 23 Lineas sensor Type 313501 im a Sensor Type 9195C1 source ref 9 b Sensor installed on pavement Figure 3 Kistler lineas Sensor The Lineas sensor utilizes quartz crystal force sensing technology With the piezoelectric quartz measuring elements in the sensor the output of the piezoelectric sensor is an electric charge Qy that is proportional to the applied vertical force F Wheel load 45 000N Velocitiy 80km h Inflation pressure 8 bar Figure 4 Vehicle passing over WIM sensor and the corresponding axle signal waveform source ref 9 As a tire passes over the lineas sensor it generates horizontal vertical and lateral forces between the tire and sensor Figure 4 Due to the special sensor design only vertical forces Fz are measured Lateral and hor
28. vehicle is determined purely from the axle signal itself which may lead to an incorrect output Axle distance calculation ee i l F ris i l Upstream loop signal Upstream axle signals Scale 0 1 5 Y Downstream axle signals w m m Li of Downstream loop signal Scale 0 5 Y speed calculation Vehicle detection period Figure 10 Vehicle detection period The signal conditions upon the detection of a two axle vehicle are shown in Figure 10 Each sensor signal is plotted on a separate vertical axis ranging from 0 to 5 V to visually identify the signal shape The vehicle detection period time is entirely dependent on its speed and total length 14 3 4 2 Axle Detection While the loop signals are used to detect the length of a vehicle the piezoelectric sensor signals are used to detect the axles A nominal axle signal is a positive voltage and the idle level no load on the sensor is near zero volts However the idle level often varies Over time which requires an adaptive procedure to keep track of the slowly varying idle level The adaptive idle level is determined using an average of recent signals when the loop signals indicate that no vehicle is present The signal is flagged as a potential axle signal if the level is 0 1 V threshold volt higher than the idle level The threshold 0 1 volt was determined through experimentation and corresponds to about 150 pounds of load change Finally the algorithm c
29. where the peak voltage generated by the same vehicle does not change for different speeds However this assumption is incorrect since the peak will change if tire inflation pressure is not constant as illustrated in Figure 6 Using the simplified method the accuracy is compromised in favor of simplicity One advantage of this method is that a speed measurement is not required Thus this method could be used in applications where accuracy of weight is not important such as taffic volume counting and or classification Method 2 Area under the signal This axle load computation method was originally recommended by Kistler and has been used in many commercial products 9 This method computes the axle loads using the area under the signal curve and the speed of the vehicle traveling The weight is calculated using W ae O bw 3 11 where Lis the sensor width S is the speed of the vehicle x t is the load signal and b t is the slow varying idle level Equivalently it is written in digital form as w a b 4 Notice from Eqs 3 and 4 that accurate measurements of weight are directly proportional to the measurement of speed Thus an accurate speed measurement is essential for this method which is the reason why two rows of sensors are used This method requires calibration like the Peak voltage method to determine a Method 3 Re sampling of area proposed method This method was originally conceived by Dr Taek Kwo
30. 0 0 0 0 Max 32767 0 178 0 3 2767 0 AXLE WEIGHTS Min 0 0 0 0 0 0 Max 32767 32767 32767 32767 32767 32767 GROSS VEHICLE WEIGHT Min 0 Max 100000 Figure 46 Classification Format provided by Mn DOT 62 HEAVY TRUCKS FHWA VEHICLE CLASSIFICATION DESCRIPTION ALL CARS CARS NO OF AXLES 2 3 CARS W 1 AXLE TRAILER CARS W 2 AXLE TRAILER PICK UPS amp VANS 1 amp 2 AXLE TRAILERS ali ea BUSES 2 AXLE SINGLE UNIT 3 4 4 5 5 ee ee o ANY 7 OR MORE AXLE UNKNOWN VEHICLE TYPE 3 AXLE SINGLE UNIT 4 AXLE SINGLE UNIT 2 AXLE TRACTOR 1 AXLE TRAILER 2 amp 1 2 AXLE TRACTOR 2 AXLE TRAILER 2 amp 2 3 AXLE TRACTOR 1 AXLE TRAILER 3 amp 1 3 AXLE TRACTOR 2 AXLE TRAILER 3 amp 2 3 AXLE TRUCK W 2 AXLE TRAILER TRACTOR W SINGLE TRAILER S AXLE MULTI TRAILER 6 AXLE MULTI TRAILER Figure 47 FHWA Vehicle Classification 63 7 or more 5 4 Graphical User Interface and Operations 5 4 1 Main Window The graphical user interface of the UM8 PCI WIM system is shown in Figure 48 The design philosophy of the user interface was minimalism and ease of operation The buttons and display windows are described in the following sections WIM SYSTEM 6 Fie Settings Graph Help Eight Channel WIM System Ve Lane Time __ Awle Speed mph Axle Dis feet Veh Lenffeet Axle Weight Kips ESAL Veh Class Error Description Figure 48 GUI View
31. 0 20 0 5 0 15 0 24 0 Class 5 J ERa 2 il 44 44 1 20 7 1 4 Class 2 Hf LH H cL eal Lai Ha 2 fil 44 44 12 1 4 Class 2 Figure 20 Generated Vehicle parameter of the class 2 vehicle Screen capture The main difference between the constructed axle waveform and the real signal is the shape of waveforms The constructed axle waveform has a trapezoidal shape while the real signal has a Gaussian shape This difference is due to the assumption in the weight profile model in the simulator that the weight is evenly distributed on the footprint The real weight distribution is not easy to measure but it appears to have a Gaussian shape On the other hand it should be emphasized that the shape of the signal curve in a WIM system is not important as the calculation is based on the area under the curve A small error exists but it is due to digital to analog conversion from the HIL simulator and analog to digital conversion in the WIM measurement system and cannot be avoid 4 4 Construction of Loop Signal As described in Section 3 1 piezoelectric sensors are installed in conjunction with loop detectors and thus loop signals must be one of the WIM HIL outputs In the configuration shown in Figure 5 the upstream loop is used as a trigger signal for the start of the axle signal computation The downstream loop is used as a mark for the end of a single vehicle WIM signal In addition the loops could be used for measuring the overall vehicle length an
32. 0 2500 3000 0 500 1000 1500 2000 2500 3000 Time samples sec Time samples sec a Constructed loop signals b Captured loop signal Figure 21 Loop signal comparison 4 5 Simulation of Failure Conditions By taking advantage of software controlled output signals in HIL simulations many realistic failure signal conditions can be constructed and fed into the test WIM system If the WIM system was designed correctly it should recognize the failure conditions Frequent failure conditions encountered by WIM systems in the field include locked stuck on zero or one piezoelectric signal absence of loop signals idle level fluctuation high noise level and or a combination of these conditions The significance of the HIL WIM simulator is that the failure conditions can be recreated and used repeatedly for testing the system an unlimited number of times For any real time system it is extremely important to test and debug the design errors before the system is installed in the field This vital process is addressed by the HIL simulator Several failure conditions encountered during the development of the eight 28 channel WIM system are discussed When piezoelectric sensors fail the signal was typically a clean DC dropping to 5V but in few cases it remained at OV Such DC signals are interpreted as absence of loop signals or events Absence of upstream loop events causes loss of axle data because the system is never triggered In the case
33. 46 Figure 44 Figure 48 Figure 49 Figure 50 Figure 51 Figure 52 Figure 53 Figure 54 Figure 55 Figure 56 Figure 57 Figure 58 Figure 59 Figure 60 Figure 61 Figure 62 Figure 63 Figure 64 Figure 65 Figure 66 Figure 67 Figure 68 Figure 69 Figure 70 Figure 71 Figure 72 Figure 73 Figure 74 Figure 75 Figure 76 Figure 77 Figure 78 Figure 79 Figure 80 Figure 81 Connecting cable and back PC connection cc ceeeeeeeeeeeeeeeeeeeeeeeeeeceeenaas 51 WIM computation flowchart O03 esi senarnesien autereieiieeannieatss 53 WIM computation flowchart 2 Of 3 ccccccccccccssssssseeecccceeeaeeeseesceceseeaeeeesees 54 WIM computation flowchart 3 Of soseo a a o ed eies 55 Five axle truck used for ESAL computation example cccccccceeeeeeeeeeees 60 Classification Format provided by Mn DOT cc ecccccccceceesseseeeeeeeeeenaes 62 PTI WAN CHICIE CLASSY LCAION neen sel subvadaesieatuelsaondcestsigs 63 GULNI teste ia eben A 64 Slart Stop BURON sie a ertiantanieaeedce E eae aetia 65 Graph hold release button ciciendcezdaneasedavencsavecrseseseiinndsnetaneesedabandsateandeatdabnatedatedes 65 aS ESTA Ici diS 0 heme Ge a ee eer rere ee een eer NneT 65 BV Loh Yad 10 cee Mee et ast ne Pee eee Pea ne E eer eet eee 66 LOODE Nt ican eee meen tee enone ee ene ae rec enrneen er mn nr ee nena ae re rE Te een 67 MP SIR AN OC ie ia err tO SE eile aaa Re a Aw Sneed 67 Otura Dle i rea ae
34. 998 32 Bahman Izadmehr and Clyde Lee On Site Calibration of Weigh in Motion Systems Transportation Research Record 1123 Pavement Management and Weigh in Motion 1987 pp 136 144 33 LTTP Long Term Pavement Performance Program Protocol for Calibrating Traffic Data Collection Equipment FHWA Pavement Performance Division Washington D C April 1998 34 NCHRP On Site Evaluation and Calibration Procedures for Weigh in Motion Systems NCHRP Research Results Digest 214 1996 35 Peter Davies and Fraser Sommerville Calibration and accuracy testing of weigh in motion systems Transportation Research Record 1123 1987 pp 122 126 36 Bullock D and T Urbanik Hardware in the Loop Evaluation of Traffic Signal Systems In Proceedings 10th International Conference on Road Transport Information and Control London 2000 pp 177 181 91 37 R J Engelbrecht C M Poe and K N Balke Development of a distributed hardware in the loop simulation system for transportation networks TRB 78 Annual Meeting CD ROM Washington D C 1999 38 R J Engelbrecht Using hardware in the loop traffic simulation to evaluate traffic signal controller features Proc of the 27 Annual Conference of the EEE Industrial Electronics Society Denver CO 2001 39 R B Wells J Fisher Y Zhou B K Johnson and M Kyte Hardware and software considerations for implementing hardware in the loop tr
35. Berkeley CA June 2002 16 Benjamin Horowitz Judith Liebman Cedric MA T John Koo Alberto Sangiovanni Vincentelli and S Shankar sastry Plattorm based embedded software design and system integration for autonomous vehicles Proceedings of the IEEE VOL 91 NO 1 pp 198 211 January 2003 17 E Kwon S Kim and T Kwon Pseudo real time evaluation of adaptive traffic control strategies using hardware in loop simulation Proc of the 27 Annual Conference of the IEEE Industrial Electronics Society pp 1910 1914 Denver CO Nov 29 Dec 2 2001 18 Abdel Rahim A Z Li and M Kyte Hardware in the loop simulation what s the difference 83rd Annual Meeting of the Transportation Research Board Washington D C 2004 19 Nichols A D Bullock and M Kyte A Laboratory Based Course on Real Time Traffic Signal Control JIECON 01 The 27th Annual Conference of the IEEE Industrial Electronics Society Vol 3 2001 pp 1904 1909 20 R L Singhal Solid State Physics Kedar Nath Ram Nath amp Co Meerut India Sixth edition 1989 21 Donald L Halvorsen Piezoelectric polymer axle sensor National Traffic Data Conference Albuquerque NM May 5 9 1996 22 Tim Stilson Piezoelectric sensors Learning tutorials Princeton University Princeton NJ Oct 1996 23 Emil Bystrom Construction of a portable piezoelectric quartz crystal sensor array for determination of petroleum com
36. C or charge amplifier type This modification would allow calibration of a WIM system without opening the system enclosure 88 REFERENCES 1 AASHTO Guide for Design of Pavement Structure American Association of State Highway and Transportation Officials AASHTO Washington D C June 1993 2 Guide for Mechanistic Empirical Design of New and Rehabilitated Pavement Structures NCHRP 1 37A Washington D C 2002 3 Traffic Data Collection Analysis and Forecasting for Mechanistic Pavement Design NCHRP 1 39 Washington D C 2003 4 Standard Specification for Highway Weigh In Motion WIM Systems and User Requirements and Test Methods ASTM 1318 02 American Society for Testing and Materials ASTM West Conshohocken PA 2002 5 Steve Jessberger Understanding traffic inputs for the pavement design guide North American Travel Monitoring Exhibition and Conference NATMEC San Diego CA June 2004 6 Traffic Monitoring Guide FHWA PL 01 021 Federal Highway Administration Washington D C 2001 7 A T Bergan Norm Lindgren Curtis Berthelot and Bob Woytowich Preserving highway infrastructure using weigh In Motion WIM November 1998 http www irdinc com library pdf highway_preservation pdf accessed July 25 2007 8 Taek M Kwon Signal processing of piezoelectric weigh in motion systems Proceedings of the Fifth IASTED International Conference on Circuits Signals and Systems CSS 2007 Ba
37. CLE 44 AUGUT AD PACER OUT AKCJ TU De PALER OU PO 5 W DA OT 1 CALL Re 29 oad Fialalalelalslalaiaialalalslalsalae Ra T ii Figure 28 Pin outs of the PCI DAS 6013 Single ended mode from datasheet The ADC inputs are labeled as CH IN in the Figure 28 schematic Channels 0 to 7 are used as WIM inputs which are the outputs of the Kistler 5038 charge amplifiers The connection of the ADC channels to the WIM sensors is summarized in Table 4 36 Table 4 ADC Channel Connections to WIM Sensor Signals ADC channel number WIM sensors Lane 1 upstream Lane 1 downstream Lane 2 upstream Lane 2 downstream Lane 3 upstream Lane 3 downstream Lane 4 upstream Lane 4 downstream 5 2 3 Loop Detector The UM8 PCI system requires eight loop detectors and two 3M Canoga C924 detector cards were utilized The same 24V DC power supply used for the charge aplifiers is used to power the C924 cards This card supplies inputs outputs through a 22 44 edge connector at the backthat are connected to loop inputs and call outputs The call outputs of the loop detectors are connected to the ADC inputs for fast and accurate detection The ADC channel allocations for loop call outputs are summarized in Table 5 Table 5 ADC Channel Connections to Loop Call Outputs ADC channel number WIM sensors Lane 1 upstream Lane 1 downstream Lane 2 upstream Lane 2 downstream Lane 3 upstream Lane 3 downstream
38. Changes button followed by the Exit button The change is effective immediately in computations without restarting the software Clicking the Load Default Values button will restore the default settings Each parameter is further described in Table 11 12 F Separation Distance Figure 61 Parameter options Table 11 Parameters Settings Title Description WIM Corresponds lane and each sensor sensitivity positive value as Sensor each lane is equipped with four WIM sensors Sensitivity WIM Distance between the beginning of the upstream WIM sensor to the Sensor beginning of the downstream WIM sensor The value should be in Spacing feet and each lane can be configured with a separate sensor spacing value Loop Sensor The distance between two consecutive loops Spacing A typical KISTLER Sensor is shown in Figure 62 where KISTLER Type Model S N and Sensitivity PC N are shown Typically sensitivity is shown as a negative value but when the sensitivity values are entered in the Parameter window the user should ignore the negative sign and enter only the numbers 73 Figure 62 9195 sensors with sensitivity measure 74 Sampling Rate The default sampling rate is 4 096 samples per second Figure 63 It is recommended to use the default for all cases The 3 000 samples sec option should only be used if the controlling PC is not up to today s speed standards WIM SYSTEM Y6 Sede Graph Help
39. I ESO aisina E O ssa tansilldy 45 IO LOOP SIMCOE FOND ra taak ah E Set Gonadal E 46 5 2 7 WIM Signal Interface Box Cable Connections ccccccccccssseeeeeeececeeeeaaessnseeeess 49 PESONA a Re RA ee ea DZ Dee OV CTV ICW neneetoserntocn E T E S 52 5 3 2 Computation Flow and Implementation cccccccsseccccccseneececceceaesseesseaeesseeeeeas by De TVIOP COGS aisles asian E EE O Seccusacaausuleoswenedeoectets 56 SE E SS EEEE E alae senses ne tee A EEE EEE se acids an oon de Stee eee as eee ae 58 ILICA ORO LSA Lea A a toda ol heh N tes 59 330 VENICIO C LASSI COMIONS neriie Ee KE TE ATE A 61 5 4 GRAPHICAL USER INTERFACE AND OPERATIONS cssccccsececesccceseceeesececseeeeeeees 64 DL VEGI SWING We sist ches Sse hatte Sate aida ah iu S N 64 TLM CHU D A as a kcauasensndnsseud tesa wate usdeasamtadeeadesase 70 De SOULS SII CI EE EENE ab Ate Medals es oie aes hen mus N 72 5 5 DATA DOWNLOADING REMOTE DESKTOP VIEW ccc0cccceecccecscesscceuecseseceesecseeeeees 78 RKOTFINAE WIM SYSTEM eupan eena a a 85 97 SY STEM FIELD DEMO maraa orienta Aue eee eee 86 CHAPTER 6 CONCLUSIONS ainsccinstisistisieisinsitisiicis ities 88 REFERENCES oeeie ina EELEE ENEE NOSE EEE UE S EEAS EESTE 89 List of Tables Table 1 Mn DOT classification scheme source ref 24 c cee cceeccceecceesseeseeee 17 Table 2 Convolved signal sequence digitized axle signal cccceecesccccececeessseeeeeeeeeees 23 Table 3 Axle loads at different speeds of
40. M system used in this research must process 16 channels in real time sampling rate of 4 096 was used as a compromise between the processing time and accuracy 3 4 Vehicle and Axle Signal Detection Detection of a vehicle signal is an important part of WIM software Proper detection of the beginning and end of the vehicle signal leads to more accurate weight computation The detection algorithms are described in this section 13 3 4 1 Vehicle Presence Detection When the upstream loop switches to an ON state it indicates that a vehicle has entered the detection zone which triggers the software to immediately begin storing the WIM signal data The signal data is stored until the downstream loop indicates the departure of the vehicle from the detection zone If the upstream loop fails the software looks for the trigger signal from the axle signals When the axle signal is above the idle level the software recognizes the presence of a vehicle and the data storing process is initiated In the case of a downstream loop failure after a successful detection of the upstream loop one half of the upstream ON time is used to estimate the vehicle exit If the speed changes dramatically while passing from upstream to downstream the software might not properly detect the corresponding axle signal However when both loop signals are present dramatic speed changes do not affect the end point detection If both loops fail the beginning and the end of the
41. Protocol Intemet Protocol The default wide area network protocol Total 254 that provides communication across diverse interconnected networks V Allow calling computer to specify its own IP address g h Figure 76 New connection wizard g and h Figure 77 shows the options from which the user can select an IP range It is always safer to provide the IP address manually rather than DHCP what is DHCP Basically in this wizard IP range denotes that number of users who can log on to a remote computer simultaneously For instance if the IP range in total is 4 then only 4 people can log on to the remote computer at one time New Connection Wizard Completing the New Connection Wizard You have successfully completed the steps needed to create the following connection Incoming Connections The connection will be saved in the Network Connections folder To create the connection and close this wizard click Finish Figure 77 New connection wizard last step The authentication method used on the server side allows only authenticated users to have a access At the UMD lab a 33 3kbps modem was tested for viewing the remote desktop and was provided satisfactory results However a 56kbps modem is recommended for field implementation as better remote desktop resolution should be possible 82 Connect WIM_ site User name Administrator Password Do change foe saved passeord cick pera
42. Q Back 7 wi Search ey Folders Bab Ac sy Network Connections fig Create a new connection _ Incoming Connections f Ea 4 Setup a home or small office network ges Change Windows Firewall E l settings LAN or High Speed Intepm Create new connection Created connection Figure 72 Setup Incoming Connections 79 New Connection Wizard 7 7 New Connection Wizard r Network Connection Type Welcome to the New Connection PER e A Wizard This wizard helps you Connect to the Intemet Connect to the Intemet Connect to the Intemet so you can browse the Web and read email Connect to a private network such as your workplace Connect to the network at my workplace network Connect to a business network using dial up or VPN so you can work from home a field office or another location Set up a home or small office network Set up a home or small office network Connect to an existing home or small office network or set up a new one peeececccesesesccoosoccceceecsssoseseceseessosososeesesossssoseesesossssoseceesssssosossesee ean a r r Connect directly to another computer using your serial parallel or infrared port or set up this computer so that other computers can connect to it To continue click Next b Figure 73 New connection wizard a and b The user needs to follow up the connection wizard to create a new connection where the highlighted
43. This error message is generated when no axle signal is found from the upstream WIM sensor signal after the loop detector senses the presence of a vehicle This condition is acritical error as the vehicle speed cannot be computed using one WIM strip It should be noted that failure of one WIM cable in a strip could lead to a failure of the entire strip Removing the failed WIM sensor from the summed BNC WIM strip can be temporarily fix this problem but a full inspection is necessary to get a correct reading 57 Err 110 Axle Sensor in Wrong Order This error message is generated when the software detects that the downstream axle signal occured earlier than the upstream axle signal This error is caused by swapped connections of upstream and downstream WIM sensors in the same lane It could also indicate that a vehicle traveled in the opposite direction the typical setup It should also be noted that if the WIM sensors were swapped with another lane only failure of the upstream or downstream WIM sensor Err 104 or Err 105 would be generated Err 111 Axle Spacing is Too Short This message is generated if the computed axle spacing 1s less than one foot It is rare but could happen as a result of noise and could lead to an incorrect axle load computation Err 112 Zero Axle Found by Downstream WIM This message is generated if no axle signal is found from the downstream WIM signals after the loop detectors senses the presence of a vehicle
44. _ idle level ls axle is greater than Find out the max voltage of each axle Based on max voltage calculate speed of each axle and average the sum Error 7 Vehicle No not detected number of axles for land ch2 are same No che axle 0 t other way around Error 8 amp 9 Upstream or downstream WIM sensor failure Based on Speed Compute for axle distance Based on speed compute for each axle weight and gross weight Display the result in Screen complete Figure 44 WIM computation flowchart 3 of 3 55 5 3 3 Error Codes An error code is generated as the WIM system encounters error conditions during the signal processing and computations Each condition is encoded with a three digit error code The thirteen conditions are described below Err 101 Upstream Loop Failure The upstream loop failure message is generated if the system does not detect the upstream loop signal When the loop is working correctly and no vehicle is present the loop signal stays at a constant voltage 5V When the loop card detects a vehicle the signal level drops to about 0 62V But when the system finds the voltage level at 0 62V for more than three seconds without any presence of vehicle detected from the axle signal the system identifies a loop failure The WIM computation is based on the assumption that a vehicle moves on the sensor at a constant speed If a vehicle
45. ach data file is limited to 25MB for the convenience of future analysis Figure 58 Indication that recording process is active The purpose of the RAW data collection mode is for users to evaluate the signal at a later time A separate program allows users to monitor the noise level signal quality details and many aspects of the RAW analog signal 71 WIM SYSTEM 6 Settings Graph Help Save Raw Data Start Save Ctrl w Stop Save Figure 59 Save raw data Exit User can exit from the main software by clicking on the Exit option It is recommended that before exiting the main software user should make sure that the real time data acquisition is not running this means that the Stop Acquiring Data button should be pressed before exiting 5 4 3 Settings Menu The second column of the menu is settings items contain in the Setting menu is shown in Figure 60 WIM SYSTEMv6 emacs Graph Help Parameters Ins Sampling Rate Figure 60 Setting options Parameters This is the first item in the Settings menu This option is used to set the WIM sensor and installation parameters used for computation The fixed parameters include WIM sensor spacings and sensitivities axle overweight values threshold values and more Figure 61 Users can set or change the WIM sensor spacing settings loop detector spacing settings and sensitivity of each WIM sensor After changing the parameters the user should press the Save
46. ad difference between static and dynamic measurements W Axle load or gross weight measured by WIM system W Axle load or gross weight measured by static scale simulator input load In a real WIM measurement environment the dynamic load error can be as high as 15 as many factors affect the load applied to the sensors such as wind road slope 23 vehicle suspension spring effects etc To examine how the HIL axle load computation model affects the dynamic load error additional computations were performed at different speeds The same input parameters as the previous example were used The results are shown in Table 3 Note that the dynamic load error tends to increase with the speed but stays below 1 The primary cause of this dynamic load error in the computational model is due to the rounding of the decimal values to the nearest whole number in the digitization process More specifically in the above example Sensor _Signal __length was calculated to be 6 544 but was rounded to 7 to generate a digitized sequence This rounding effect is carried further into the convolution process yet the error stays below 1 This rounding error cannot be avoided since the DAC cannot accept values between two consecutive digital samples However it should be emphasized that the dynamic load error in the axle simulation does not affect the accuracy of real WIM systems when the simulated signals are used for calibration or accuracy checks For examp
47. affic simulation Proc of the 27 Annual Conference of the IEEE Industrial Electronics Society Denver CO 2001 40 Q Lu J Harvey T Le J Lea R Quinley D Redo and J Avis Truck traffic analysis using weigh in motion WIM data in California Research Report UC Berkeley Institute of Transportation Studies Pavement Research Center 2002 92
48. connections e New Connection Wizard User Permissions You can specify the users who can connect to this computer Select the check box next to each user who should be allowed a connection to this computer Note that other factors such as a disabled user account may affect a user s ability to connect Users allowed to connect Administrator CW ASPNET ASP NET Machine Account 0G Bibhu oO Egi Guest O GG HelpAssistant Remote Desktop Help Assistant Account R a SQLDebuaaer SQLDebuacer lt til Ladd Remove nove Properties Figure 75 New connection wizard e and f Figure 75 e f shows the authentication wizard from which a new user can be created or permission to the existing user can be set Only those selected users are able to operate the WIM system remotely 81 New Connection Wizard Incoming TCP IP Properties Networking Software Networking software allows this computer to accept connections from other kinds of computers Select the check box next to each type of networking software that should be enabled Network access for incoming connections TCP IP address assignment Networking software Assign TCP IP addresses automatically using DHCP F Intemet Protocol TCP IP is d2 File and Printer Sharing for Microsoft Networks Specify TCP IP addresses A Deterministic Network Enhancer v From To Description Transmission Control
49. cquired from the ADC board The software is capable of computing the vehicle weight in the absence of one of the two loop signals upstream or downstream The software requires three seconds to update the loop information and it will automatically adjust and start computing the required WIM parameters after failure of the upstream loop The accuracy might be decreased slightly less than 10 percent but if both WIM signals are present the accuracy decrease is negligible In the case of a downstream loop failure the software waits up to three seconds to scan the loop signal and then processes the WIM signal without the downstream loop The accuracy will not be affected in the case of an absent downstream loop but in some cases the software may fail to identify the end point of the vehicle In the above cases one of the loop failures an error message will be generated by the software identifying the upstream downstream or end of vehicle detection problem If the loop cables are connected in an incorrect order the software will detect it and report a corresponding error message It should be noted that the system will not work if both the upstream and downstream loops fail However if the raw data is recorded the software could be made to compute the parameters without the loop information In the absence of both WIM signals no output can be generated This is due to inability to compute the vehicle weights without WIM signals If both the u
50. cture The overall system block diagram is shown in Figure 5 As a vehicle s tire passes over the piezoelectric sensors the force of the vehicle load is applied to the sensors As a result the sensors produce electric charges proportional to the load In the case of Kistler 9195 sensors the single row typically produces 1 8 Pico Coulomb per Newton 9 The level of charge produced per Newton is referred to as sensitivity and is measured at the factory and clearly labeled on each sensor A charge amplifier converts and amplifies the electrical charges generated by the sensor to analog voltages in the range of 5 volts The nominal voltage range is positive but the values can be negative depending on the bias conditions The Kistler 5038 charge amplifier a short name amp is also frequently used among electrical engineers uses 15 to 30 volts DC as its power supply and internally regulates the voltage to produce 7 volts The total consumption of current is less than 25mA The regulated voltages are used as the power inputs of the internal operational or op amplifiers For this WIM system a single 24V 1A switching power supply is used to power all four charge amplifiers Two 3M Canoga C924 cards were used in the developed system for the loop detectors but other detector cards could also be used Each C924 detector card can process up to four loops Since this system requires eight loops two detector cards are necessary The same 24V DC
51. d speed However the accuracy is limited by the low scan rate of signals used in loop detectors The signals obtained from the loop detectors are sampled at the same rate as the piezoelectric signals to reduce the timing problem The output voltage of the loop detector in the absence of a vehicle is 5V and it drops to 0 69V when a vehicle is present The length of the loop signal is calculated using vehicle speed and length and the physical dimension of the loop Itis shown in Eq 22 Zi Total _ vehicle _ length Loop _ signal _ length SamplingRate 22 Speed The signal distance between the upstream and downstream loop is computed using the separation distance between the two loops 1 e Loop _ sensor _ separation Loop _ signal _ separation SamplingRate 23 Speed Figure 21 a shows a loop signal constructed through the above method and Figure 21 b shows the real loop signal collected from the WIM site Note that there is a slight voltage drop from 5V in the captured signal This is due to a pull up resistor in the loop signal output circuit The peak voltage difference does not affect the outcome of vehicle presence detection since a threshold is used Upstream Loop Signal 6 om DownStream Loop Signal Upstream Loop Signal soe Downstream Loop Signa eagene oosssssggesassm os we ove ooooosoa oos oanseg ge sore sonecene o Yoltages Yoltage cu PO eit tater rien m ee 0 500 1000 1500 200
52. e written as x y G w 7 where y is the sensitivity of the piezoelectric signal pC N G is the gain of the charge amplifier V pC and w is the jth slice weight N The total weight of the block is simply a summation of the individual slices as shown in Eq 8 1 N W Sd 4 8 12 Notice from Eq 8 that this method does not require a calibration factor but rather it uses the factory measured sensitivity 7 Over sainple Volt Re sample sensor Measurement period Measurement period Sam Mpling P eriog gt Figure 9 Area under signal Method 2 Vs Re sampling of area Method 3 It should be clarified that the sampling period of the A D converter is different from the measurement period in Eq 5 The sampling rate of the A D converter should be determined based on the required accuracy of speed measurements A reasonable accuracy of speed measurements in WIM applications is less than one mph error with an 80 mph speed Speed measurement accuracy is obtained using the following two relationships Sensor _ sepration _ dis tance Speed Speed Number _ of _ samples SamplingRate 9 Speed _ accuracy _ measurement 10 Number _ of _ sample For sensor rows separated by 12 feet the speed accuracy error for 4 096 samples per second is 0 19mph using the Eqs 9 and 10 Although a higher sampling rate produces higher accuracy it also increases the computation time Since the WI
53. el This message is generated if the idle level of the upstream or downstream axle sensors is not close to zero When the idle signal level increases or decreases significantly particularly more than 1V from zero the load computation accuracy is affected This problem could be due to a charge amplifier that needs time to stabilize after an initial system reboot Err 106 Maximum number of Axles Detected According to Mn DOT specifications the maximum number of axles a vehicle can have is 15 This error message is generated is this threshold is exceeded Err 107 Zero Axle Detected When a loop detector detects the presence of a vehicle but the axle sensors do not respond accordingly this message is generated It could be an indication of failure of both upstream and downstream WIM sensors If the signal levels are too low in reference to the idle level or if the vehicle is too light this message could also be generated If this error appears the connections of WIM cables should be checked and the power of the UM8 PCI should be re circulated do not reset the computer Err 108 Unequal Axle Count This message is generated if the axles counted by upstream axle signal differs from the axles counted by the downstream sensors Noise is a possible cause of this error This problem is usually transient but if it is continuously reported there may be a problem with one of axle sensors or cables Err 109 Zero Axles Found by Upstream WIM
54. ely eliminates the environmental and dynamic effects The flexibility of the software also allows generation of signal anomalies for testing erroneous or faulty conditions To verify the proposed signal generation and weight computation theory various experiments were conducted and verified Based on the experimental results and the theory presented the research team is confident to conclude that the HIL simulator based WIM development environment significantly reduces the development time and cost Additionally a more accurate and reliable system is produced at a low cost Moreover the ideal axle signals generated by the HIL WIM simulator can be used for calibration of WIM systems without measuring a truck of known weight which eliminate the high costs and issues associated with WIM system calibrations The simulation based WIM software development techniques implemented in this research yielded satisfactory results One area of improvement for future study is in the electric form of the axle signals The developed WIM HIL simulator generates analog voltage signals WIM axle signal that are transmitted to the ADC of a WIM system The WIM system software receives the voltage signals and computes the axle load parameters If the analog voltage signals are converted to electric charge signals the test signals can be directly fed into the charge amplifier inputs of the WIM system providing uniform reference axle signals regardless of differences in AD
55. equivalent width varies with the vehicle speed and the sampling rate and is computed as shown in Eq 18 S idth Peak _ voltage _ weight _ profile PELL e Sampling Rate Speed 18 It 1s reasonable to assume that the weight is evenly distributed at each sample point of the sensor width The voltage at each sample point which is referred to as Peak _ voltage _ weight _ profile can be calculated using Peak _ sensor _ voltage Peak _ voltage _ weight _ profile 19 Sensor _ signal _length Based on the calculated Axle_signal_length and the Peak_voltage_weigh_profile a digital sequence representing the axle weight profile is constructed 1 e a sequence number with height equal to the Peak_voltage_weigh_profile and the sequence length equal to the Axle_signal_length Similarly the sensor signal sequence is constructed as a sequence number with the height equal to one and the length equal to the 21 Sensor_signal_length Finally the digital sequence representing the axle signal output of the charge amplifier is generated by convolving the sensor signal and the axle weight profile 1 e Convolved _ axle _ signal Axle _ weight _ profile Sensor _ signal 20 where denotes a convolution operator A numerical example is given below Example Construction of an axle signal The mathematical computation example for constructing an axle signal is provided below This example is based on the front axle of a real vehicle f
56. er action was taken 29 CHAPTER 5 WIM SYSTEM DEVELOPMENT BASED ON PC 5 1 System Components and Site Description The purpose of this project was to develop technology for an eight channel WIM system that uses a standard PC and off the shelf components and can be easily built If successful Mn DOT could produce future systems in house and or the end result could set a new standard for WIM vendors This experimental system was named UM8 PCI where the number 8 signifies availability of 8 channels and PCI Peripheral Component Interconnect denotes the use of a PCI bus The main difference between the UM amp PCI WIM system and the existing commercial systems is that signal processing and analysis capabilities are directly integrated into the system using a graphical user interface GUI This allows diagnostics of the system at the analog signal level by graphically analyzing the signal The system produces real time plots of live signals while continuously processing the regular WIM computation functions During development it was found that poor sensor signals are the major cause of frequent and critical errors in WIM systems and they are hard to detect and correct from the WIM data This new system design allows quick spotting of such conditions through a graphical user interface and daily summary of error conditions This approach provides a means of data quality control at the root of the causes 1 e the signal level The software has
57. ereby significantly reducing the development time and cost The proposed HIL simulator is a new concept and provides an elegant solution to the unavailability of an ideal axle signal CHAPTER 1 INTRODUCTION 1 1 Background on Weigh in Motion WIM Systems Data on weights carried by vehicles is used as a primary input to a number of state highway agency s important tasks For example traffic loading is a primary factor in determining the depth of pavement sections 1 3 It is also used as a primary determinant in the selection of pavement maintenance treatments In addition the new pavement design guide currently distributed as NCHRP 1 37A requires location specific load spectra in which the conventional ESAL Equivalent Single Axle Load is no longer used 4 5 Truck classification and weight information are also the key components in studies that determine the relative cost responsibility of different road users 6 Freight industries use the classification weight information to estimate goods movements freight demands and route planning The total tonnage moved on roads is also used to estimate the value of freight traveling on the roadway system and is a major input to calculations for determining the costs of congestion and benefits to be gained from new construction and operating strategies A linear increase in load magnitude is known to be approximately fourth power exponential increase in the acceleration of road wear 7 Consequen
58. erred to as the fourth power law For example a 36 000 Ib single axle load is only twice as large as an 18 000 Ib axle load but it causes 17 times more loss in pavement life The ESAL concept indicates this damage factor In Eq 24 the axle group load refers to those axles that are less than 8 feet apart The summation of all axle loads is considered as a group axle load The axle group load is calculated in kilonewtons in Eq 24 Steering and single axles with large loads are more detrimental to pavement life when compared to 2 for tandem axle group or 3 for tridem axle group with the same load The calculation of ESALs in the WIM software is based on the above principle For example consider the five axle semi truck shown in Figure 45 There is one single axle group first axle of truck followed by a tandem axle group 2nd and 3 axle from the front and two single axle groups 4 and 5 59 5 axle ruck a7 ft Sin 10f Jin Tit Bin 34 000 Ib 10 000 Ib 10 000 Ib es 4ft 5 lin 12 000 Ib Figure 45 Five axle truck used for ESAL computation example The 1st axle from front of the example truck is a single axle group and its load is 12 000Ib ESAL for this axle is computed by g 4 2 ee 0 182 ESAL _ 1 axle 1 1 80KN where the multiplication factor of 4 448 exists to convert from pounds to Newtons The second and third axles each weigh 17 000 b but are less than 8 ft 1 in apart 4ft 6in so they are c
59. eserve their polarization for a long time even after the polarizing field is removed Figure shows a diagram of the internal structure of electrets In general the alignment of the internal electric dipoles would result in a charge that would be observable on the surface of the solid In practice this small charge is quickly dissipated by free charges from the surrounding atmosphere that are attracted by the surface charges Figure 1 Internal structure of an electret Electrets may be used for generating an electric field without external volatage sources Permanent polarization as in the case of electrets is also observed in certain crystals In these structures each cell of the crystal has an electric dipole and the cells are oriented such that the electric dipoles are aligned Again this results in excess surface charge which attracts free charges from the surrounding atmosphere making the crystal electrically neutral If a sufficient force is applied to the piezoelectric crystal a deformation will take place This deformation disrupts the orientation of the electrical dipoles and creates a situation in which the charge is not completely neutralized This results in a temporary excess of surface charges which subsequently is manifested as a voltage developed across the crystal In order to utilize this physical principle and allow a sensor to measure force the surface charge on
60. flation pressure source ref 9 10 Figure 7 Axle signals on different speeds source ref 8 00 ccccccceetteetteeeeeeeeeees 10 Figure 8 Charge amplifier output signal of single axle or wheel load c ccc00e 11 Figure 9 Area under signal Method 2 Vs Re sampling of area Method 3 13 Preure 1 02 Vehicle detect On penod serra E S E eaaeasementens 14 Figure 11 Logical connection diagram of completed loop of a WIM HIL simulator and WIM system nder ESE ssi searaveitens teat navaacendis eet E N 19 Figure 12 Axle signal generate Dy vehicle esiri irei aaa E Ea 19 Figure 13 Progressive tire footprint positions when a vehicle is MOVING ccc000 20 Fig re 14 Class 2 vehicleov r WIM Sensor asriosciisicariaiii a 25 Figure 15 Computed vehicle parameters by WIM system screen capture 25 Figure 16 Example Class 2 axle signals generated by the TH61 WIM sensot 25 Figure 17 Front and rear axle signals produced by class 2 vehicle ccccccssseeeseeeeees 26 Figure 18 Class 2 axle signals generated by HIL simullator i eeeseeseeeeeeeeeeeeeees 26 Figure 19 Class 2 axle signals generated by WIM HIL simulator o on 2i Figure 20 Generated Vehicle parameter of the class 2 vehicle screen capture 27 Fiure 2 Loops onal Compan ON a a a 28 Figure 22 Site diagram Highway 61 MP16 4 Duluth MN sssseeesssssssseeseeeeessssssssss
61. g signs feet Example If a vehicle has 3 axles it has two axle spacings and will look like 104 12 which indicates that the distance between first and second axle is 10 feet and second to third 1s 12 feet Vehicle Length The total of axle distances In the above example this feet will be 22 For the actual vehicle length the distance front bumper to first axle and rear bumper to last axle must be added by the user Axle Weight Axle weights in kips kilo pounds The axle weights 66 99 Kips are separated using signs Example If a vehicle has three axles and each weighs 1 5 kips then the display parameter will look as follows Lot Lael ESAL Equivalent Single Axle Loads of the vehicle GVW Kips Gross vehicle weight is the total weight of the vehicle load in kips It is the sum of axle weights In the above example GVW is 4 5 kips Veh Class Vehicle classification Class 1 15 is displayed in this column Error Shows the error code along with a description Description 69 Graphical Display The vehicle information is shown in the data table as well as in a graphical display format Figure 56 The parameters displayed graphically in text format are speed mph GWV kips ESALs vehicle class and total spacing between the first and last axle feet Each axle weight and axle spacing is shown graphically an O represents axle the number below O represents axle weight in kip
62. gnal interface box charge amplifier and loop detector and a splice panel for loop wires The software runs as an application program and is loaded from a hard disk The PC provided is a SolidLogic Pentium M GA LOI Fanless Mini ITX System It has multimedia Penttum M main board and a Pentium M processor It has dual PCI expansion slots and a slim line slot loading CDRW DVD drive This system occupies a small space and is specially designed for small form factor applications such as a field cabinet implementation The PC specification is summarized in Table 12 Figure 80 Completed WIM system with a PC and modem 85 Table 12 PC Specifications Parts Specifications Main board Multimedia Pentium M main board with Intel 855GME and ICH4 chipset Memory 1GB of memory Processor Pentium M processor 1 60 GHz Hard Disk Drive 150 GB Dimensions 370 mm x 50 mm x 310 mm wxhxd 14 6 x 2 1 x 12 1 The PC is installed with a Windows XP Professional Edition with Service Pack 2 Microsoft Visual Studio NET 2003 and Teechart Pro Activex 7 developed by Steema Software The Teechart Pro Actives must be installed to successfully run the WIM system software In addition a Real VNC server must be installed and set to server mode for remote access and downloading 5 7 System Field Demo On November n 2006 the research team Taek Kwon PI and Bibhu Aryal RA installed the prototype of UM8 PCI WIM system at the TH 61 WIM site and succe
63. he discrepancy between the IRD system and the UM8 PCI system The IRD system contains twelve BNC inputs as opposed to eight BNC inputs however the toggle switch enabled compatibility between the two systems The numbering scheme in the IRD panel and the original BNC wire numbers correspond to the panel numbers and are specified in Figures 31 and 32 As mentioned above the top part of splice box has the BNC inputs from the piezoelectric sensors corresponding to the lane while front has the BNC outputs that must be connected to the inputs of the ADC The switch is present in front part of the BNC splice box and has a lock for safety This switch can be locked or unlocked by turning the head a half cycle Figure 33 shows the UM8 PCI BNC splice box and Figure 34 illustrates the IRD panel and its cable numbering scheme 4 a oD O 3 Y Figure 33 BNC Splice Box 42 Q Ta gt n O J Figure 34 IRD panel and cable numbering scheme In the BNC box the On up position of the switch connects the four BNC inputs in the same column on the top side to the upper BNC on the side panel of the BNC box When the switch is in the Off down position the first and second BNC inputs in the corresponding column are connected to the upper BNC on the side panel and the third and fourth BNC inputs are connected in the corresponding column on the lower BNC side panel The detailed connections to the Lineas wire numbe
64. he machine is the HIL WIM simulator and is equipped with a multi channel digital to analog converter DAC The channels of DAC are physically connected to the ADC channels of the WIM system through a connection panel also shown in Figure 11 18 Footprint len Digital z To f a Analog Eam a T Digital Connection Panel HIL WIM Simulator WIM Software Figure 11 Logical connection diagram of completed loop of a WIM HIL simulator and a WIM system under test The developed WIM HIL generates axle signals based on user input The parameters needed for construction of WIM signals are speed footprint length of tire axle spacing and weights and total vehicle length As each simulated axle passes over the sensor at a certain speed the WIM system receives an axle signal as shown in Figure 12 Since loop detectors are a part of a WIM system and used for vehicle presence detection the WIM HIL simulator also creates loop signals based on the total vehicle length The WIM HIL simulator software essentially works in reverse to the WIM software In the WIM software the axle weight axle distance and speed are computed from axle signals In the WIM HIL simulator software the simulated vehicle signals are created from axle weight footprint length and speed of the vehicle In other words the WIM HIL simulator acts as a virtual road where traffic flow and vehicle information are controlled by software E A Oa 3 Ve
65. hecks the signal length If the length of the flagged signal is less than 70 of a typical footprint of passenger cars it is considered as a noise and is discarded If both upstream and downstream axle sensors fail to detect an axle an error message is generated Zero axles detected If an axle is detected the segmented axle data is stored for further processing The ending of the axle signal is determined by measuring the time from the initial detection to the time of peak voltage and doubling the difference This method is a solution to a long trail problem 30 that arises when the piezoelectric sensor does not recover in time The final axle load is established by averaging the computed axle loads from the upstream and downstream sensors If the number of axles counted by the upstream and downstream sensors do not match the lower axle count is recorded and the extra is discarded considered as noise 3 5 Vehicle Speed Axle Distances and Weight Computation 3 5 1 Speed Computation Vehicle speed is determined using the known sensor strip spacing and the travel time between the strips The peak voltage time of each axle in the upstream sensors is subtracted from the corresponding downstream peaks and then averaged The speed is computed using g Prensor SamplingRate A peaks 11 where S speed meters second D the distance between upstream and downstream WIM sensors meters Sensor SamplingRate sampling rate
66. her a portion of the total load Figure 6 illustrates the relation between the load and the length of footprint of a passenger car under different tire inflation pressures source Ref 9 Note that lower inflation pressures generate a larger footprint length with a lower peak signal Since any combinations of contact length are possible no assumption can be made for the length of tire footprints However an important relationship between tire footprint and force is that the area under the curve is constant as long as the same load 1s applied ar 38psi 2 0 bar 29psi 5 bar 22psi D bar 14psi T bar 10psi vertical force Fz N A Fi y 7 f y Footprint Area BET k co D 5 10 15 20 25 30 Footprint Length footprint length em Figure 6 Footprint lengths under varying tire inflation pressure source ref 9 A second aspect of the axle load signal is the effect of speed Figure 7 shows an example of axle signals under different speeds Note that the area under the axle signal is approximately inversely proportional to the speed 9 Although this assumption is generally accepted in WIM system designs this relationship only holds while no additional external forces such as winds are influencing the sensor load Area A 32km h 64km h 96km h 20mph 40mph 60mph Figure 7 Axle signals on different speeds Source ref 8 The signal diagram shown in Figure 8 is used to illustrate the axle load computation methods using
67. hicle g Sensor Sensor Figure 12 Axle signal generate by vehicle 4 3 Construction of WIM Signal Generation of precise WIM sensor signals is important for the evaluating the accuracy of a WIM system The signal construction algorithms are described in this section 4 3 1 Axle Signal In order to create an axle signal consideration must be given to how an axle signal is generated by the piezoelectric sensors when a tire footprint of a vehicle passes over the sensor strips Initially the tire contacts a small portion of the sensor strip and gradually advances over the whole sensor width as the vehicle moves forward Eventually the vehicle moves away from the sensor strip and the contact area becomes zero While the footprint is on the sensor the load on the footprint causes the sensor to 19 generate electric charges Figure 13 illustrates progressive footprint positions of a moving vehicle The sensor signal level electric charge 1s approximately proportional to the load on the sensor Conceptually this signal generation mechanism is essentially equivalent to a convolution between the true weight profile i e distribution of weight loads on the footprint and a rectangular pulse with the pulse width equivalent to the sensor width tire tire WIM sensor WIM sensor WIM sensor Figure 13 Progressive tire footprint positions when a vehicle is moving In this research the weight distribution on the tire footprint is modeled as a
68. hicle over WIM sensor Lane Time Age Speedimph Axle Disffeet Yeh Lenffeet Axle Weight Kios GVW Kins Yeh Class I ydagi 2 ll 4 4 4 4 1 2 0 7 1 9 Class 2 Figure 15 Computed vehicle parameters by WIM system screen capture 0 3 O 2 0 1 i 0 0 Ki 0 1 Upstream axle signals coos Downstream axle signals 0 2 oO 10 200 300 400 500 600 YOO s00 9300 1000 1100 1200 Time samples Figure 16 Example Class 2 axle signals generated by the TH61 WIM sensor A close look at the axle signals is shown in Figure 17 The signal geometry depends upon the signal condition or piezoelectric recovery effect The long tail of the signal is not the true weight effect but rather due to the piezoelectric recovery error In the signal processing this error is mitigated by using the signal area only up to the peak and by doubling that area 8 23 Front axle signal load 1200 Rare axle signal load 700 RS ie ak T F T T T T T 20 40 30 dod 12 W0 160 180 20 220 il 2 wo 120 wo t10 150 200 220 Time Samples sec Time Samples sec Figure 17 Front and rear axle signals produced by class 2 vehicle For HIL simulation the WIM parameters of the vehicle obtained from the WIM system shown in Figures 14 17 are used to construct an identical vehicle signal Figures 18 and 19 show the WIM signal generated according to the principles presented in Sections 4 3 1 and 4 3 2 The inputs to the WIM signal
69. hicles pass over the sensor 17 19 The simulated detector actuations are processed by an actual off line traffic controller it was from real detector actuations Research work on HIL application to traffic controllers can be found in 36 39 CHAPTER 2 PIEZOELECTRIC SENSORS Piezoelectric sensors have been widely used as WIM sensors This chapter reviews the working principles and the design used in WIM sensors 2 1 Basic Principles of Piezoelectric Sensors Piezoelectric sensors have proven to be a versatile tool for measurement of various processes Piezo is a Greek word for pressure The piezoelectric effect was discovered in the 1880 s by P and J Curie 20 The piezoelectric effect occurs when energy is converted from the mechanical to electrical form or vice versa When a piezoelectric material is compressed or deformed an electric charge is produced This charge is proportional to the stress or force that is applied to the sensor thus allowing the sensor to be used for weigh in motion applications 21 Piezoelectric microphones serve as another good example of this phenomenon Microphones turn an acoustical pressure into a voltage For certain crystals when an electrical charge is applied to a polarized crystal the crystal undergoes a mechanical deformation that in turn creates an acoustical pressure An example of this type of application are piezoelectric speakers 22 Electrets are samples of dipolar solids that can pr
70. ion specification provided by Mn DOT Mn DOT s classification algorithm is specified based on axle weight axle spacing and gross vehicle weight The software classifies each vehicle record using Mn DOT s supplied text file To illustrate the Mn DOT classification algorithm specification a sample screen shown is in Figure 46 The first and second rows specify the class and the number of axles respectively In the example the definition is for Class 7 with 6 axles Following SPACING are the applicable range of axle spacings expressed in cm centimeter The example has five columns under the SPACGING section since the vehicle has 6 axles After the AXLE WEIGHTS row the subsequent two rows define the weight range of each axle Similarly to the axle spacing the first row specifies the minimum and the second specifies the maximum expressed in pounds Under the GROSS VEHICLE WEIGHT heading the GVW is defined using a minimum and maximum In the example GVW is specified between 0 and 100 000 pounds It should be noted that the numerical values are specified without commas The classification format provided by Mn DOT is slightly different from the classification specified by the FHWA The FHWA classification shown in Figure 47 is more visually identifiable It is based on the number and spacing of axles but does not include a weight parameter 61 Text file format Classification 7 Number of axles 6 SPACING Min 0 0
71. izontal forces Fx and Fy between the road and sensor are decoupled by a special elastic material around the sensor 9 The Kistler Lineas sensors are used for medium and high speed WIM and or vehicle classification applications The accuracy of a WIM site often depends on the pavement characteristics due to the pavement vehicle interaction and the resulting dynamic impact forces Road geometry is another factor that affects WIM accuracy For greater accuracy it is strongly recommended that 50m before and 25m after the WIM site have a longitudinal slope of lt 2 a transverse slope of lt 3 and a radius of curvature gt 1000m 1 e a straight flat road is preferred CHAPTER 3 WIM SYSTEM DESIGN 3 1 WIM Sensor Setup WIM devices are specifically designed to capture and record gross axle loads of moving vehicles WIM systems record instantaneous dynamic axle loads and spacing the number of axles the speed of the vehicle the lane and direction of travel vehicle classification and a timestamp for each vehicle record The accuracy is primarily dependent upon the vehicle dynamics and the inherent variance of the technology used within the WIM system Vehicle dynamics include the forces generated by the suspension system tire characteristics aerodynamic lift etc The variances in WIM system include sensor accuracy different computational algorithms and system noise Piezoelectric WIM systems comprise piezoelectric force sensors embedded
72. k _ sensor _ voltage mV Peak _ sensor _load N Voltage _ sensitivity 15 20 In Eq 15 voltage_sensitivity represents the voltage conversion rate of force by the charge amplifier The sensitivity for the Kistler sensor and amplifier is shown in Eq 16 1 75 5 000 mV Voltage _ sensitivity Y ma A 60 000 pC 0 1458 V 16 Using Eq 16 a weight profile in terms of voltage could be constructed If the sensor width is near zero and the weight distribution on the footprint is uniform a rectangular voltage signal can be constructed with its area under the curve directly representing the gross axle weight In reality the sensor width is not near zero so the signal length is longer and the load must be computed according to the sensor width footprint length and the speed of the vehicle 4 3 2 Axle Signal Length The footprint length and speed of the vehicle are needed to compute the axle signal length Since the signal is generated digitally the signal length is equal to the number of digital sequences and determined by the sampling rate of ADC The signal length is computed based on the time required to pass through the footprint length and the sampling rate 1 e Footprint _ length Axle _ signal _length SamplingRate 17 Speed The width of a typical Kistler WIM sensor is 5 cm the type used in this research The sensor width in terms of number of sampling periods the signal domain
73. le if a vehicle with a speed of 80mph and a 1 200Ib axle load is tested 8Omph row of Table 3 the WIM output should be compared against 1 208 735 Ibs since that is the actual axle load signal generated by the HIL simulator That is if the output of a WIM system under evaluation reported 1 208 735 Ibs when an 80mph speed and 1 200 Ibs signal was sent the system should be considered as 100 accurate This indicates that the HIL generated signals can be confidently used for accuracy measurements of a WIM system or can be used for calibration without driving a known vehicle over the sensor Table 3 Axle loads at different speeds of the proposed computational model Speed Axleload Sum of voltage Samples Computed load Error Vi V mph Ib Ib 0 78019 1 200 992 0 082 0 78144 1 202 916 0 16 0 78522 1 208 735 0 7279 4 3 3 Comparison between Simulated and Real WIM Signal To verify the simulated axle waveforms a real WIM signal waveform from the Mn DOT s WIM site on Highway 61 is compared with a HIL simulator generated waveform The vehicle image for this example was captured by the field video camera and is shown in Figure 14 The WIM system detected that it was a Class 2 vehicle with 1200Ib front axle and 700 lb rear axle The speed was 7Omph Figure 15 is a partial screen capture of the WIM system showing the actual data recorded The axle signals generated by this vehicle are shown in Figure 16 24 Figure 14 Class 2 ve
74. lt to measure This means that even if the weight of the calibration truck is known there is no guarantee that the same load 1s applied with each pass over the sensors during calibration Moreover the accuracy of static truck scales is limited in particular portable scales often produce errors Consequently maintaining a WIM system through regular calibrations is expensive in terms of labor and possibly not reliable It was often reported by maintenance engineers that some WIM stations begin to report incorrect weights the day after calibration In this case the known weight of the truck might have been incorrect or vehicle dynamics may have affected the load on the sensor during calibration What has been found from the current research is that correct installation and proper signal conditioning is more important than calibration 8 That is no amount of calibration would be able to fix the problem of installation or signal deviations Therefore this research focuses on developing a calibration free weight computation algorithm and treatments of signal anomalies and system error conditions through intelligent algorithms This research also presents a HIL approach that creates realistic analog WIM signals for testing and verification of WIM systems This is a new approach and provides an efficient development platform for designing accurate and reliable WIM systems Also ideal WIM signals generated by the HIL simulator facilitate a new efficie
75. n and was used in this research 8 30 A close observation reveals that the area under the signal curve is not a true axle load representation but a convolution of load with respect to the sensor width 8 Suppose that the load is a rectangular block with the same width as the tire footprint and the same weight as the axle load The sensor is mounted flush with the measurement surface Sliding the rectangular block over the sensor should have the same effect as a moving vehicle As the block slowly moves the load on the sensor is clearly overlapping for the duration of the sensor width Consequently the area under the signal is not an exact weight of the block unless the sensor width is nearly equal to zero This method is as an improved version of Method 2 First a measurement period must be determined using the width of the sensor and the speed of the vehicle as TELS 5 The measurement points are then determined as HANFA E st EAEN where t t 2At T L N 6 Second imagine that the block is vertically split into N slices with the block width equal to the sensor width Each slice is then one by one measured independently by precisely aligning to the sensor Each slice denotes the measurement period since it needs to be measured only once as shown in Figure 9 The weight of each slice then becomes reflected in the previous sample within the measurement period If the measurement for the jth slice 1s denoted x volt it can b
76. n open architecture for continuous future improvements by other developers The research team was able to successfully develop a working eight channel WIM system and the details are described in this report c 81655 wo 180 The main innovation introduced in this research is a hardware in the loop HIL WIM simulator that can generate analog axle and loop signals through software control The HIL simulator can create ideal axle signals as well as erroneous signal conditions that can be directly fed into WIM systems The main advantage of using a WIM HIL simulator for developing a WIM system is that the developers may run an unlimited number of signal tests without actually driving a single vehicle through the WIM sensors thereby significantly reducing the development time and cost The erroneous signal conditions generated by the HIL simulator can also identify the error handling capabilities of a WIM system The proposed HIL simulator for WIM system development is new and provides an elegant solution to the unavailability of an ideal axle signal 17 Document Analysis Descriptors 18 Availability Statement WIM piezoelectric hardware in No restrictions Document available from the loop WIM signal processing National Technical Information Services WIM signal generation loop Springfield Virginia 22161 signals charge amplifier ESAL 19 Security Class this report 20 Security Class this 21 No of Pages 22 Price page
77. nce V sequence V V 6 0 079277 26 0 09249 46 0 09249 7 009249 27 0 09249 47 0 09249 i 8 0 09249 28 0 09249 48 0 09249 9 0 09249 29 0 09249 49 0 09249 10 0 09249 30 0 09249 50 0 09249 11 0 09249 31 0 09249 51 0 09249 12 0 09249 32 0 09249 52 0 09249 13 0 09249 33 0 09249 53 0 09249 14 0 09249 34 0 09249 54 0 09249 1s 0 09249 35 0 09249 55 0 09249 16 0 09249 36 0 09249 56 0 09249 17 0 09249 37 0 09249 57 0 09249 18 0 09249 38 0 09249 58 0 09249 19 0 09249 39 0 09249 59 0 09249 20 0 09249 40 0 09249 60 0 079277 In Table 2 the bold numbers represent the samples used for the load computation based on the re sampling method 8 with re sampling taken at every seven samples 1 e Sensor _ signal _length 7 The total of the re sampled sequence 1S gt Vi 0 77955 and thus it is translated into 1 200 0069 Ib of total axle load which was the actual axle weight WIM systems are designed to estimate static load weight at zero speed from the measurement of dynamic load The difference between the static and dynamic loads is referred to as dynamic load error and is define as IW W Dynamic _ load _error 100 21 where Dynamic _load _error Axle lo
78. nff Canada pp 233 238 Banff Canada July 2 4 2007 9 C Helg and L Pfohl Signal processing requirements for WIM LINEAS Type 9195 Kistler Instrumente Corp Amherst NY 10 Weigh in Motion Handbook Center for Transportation Research and Education Iowa State University Ames IA May 17 2007 http www ctre iastate edu research wim_pdf index htm accessed June 25 2007 11 Rob Bushman Andrew J Pratt Weight in motion technology economics and performance North American Travel Monitoring Exhibition and Conference NATMEC Charlotte NC 1998 12 Product Web page Single load cell Weight In Motion scale International Road Dynamics 2007 http www irdinc com its_solutions cvo single_load_cell_wim php accessed June 15 2007 89 13 Ahad Sarif Jazi Simak A Ardekani and Majid Mehdikhani A low cost fiber optics Weight In Motion sensor Strategic Highway Research Program National Research Program National Academy of Sciences November 1990 14 Richard Liu Xuemin Chen Jing Li Lianhe Guo and Jinyang Yu Evaluating innovative sensor techniques for measuring traffic loads Technical Report Project 0 4509 University of Houston Houston TX Oct 2005 15 Q Lu J Harvey T Le J Lea R Quinley D Redo and J Avis Truck traffic analysis using Weigh In Motion WIM data in California Research Report Institute of Transportation Studies University of California
79. ng Data button to start processing the data again Figure 51 Status display View Lane Plotting of real time axle signals is done one lane at a time and the lane can be selected using the drop down combo box shown in Figure 52 If the user would like to view the signal condition of another lane the user can simply select the desired lane at 65 any time The UM8 PCI system is designed for eight channels so the combo box has choices of Lane 1 Lane 2 Lane 3 and Lane 4 Figure 52 View lane Loop Calls The loop activity can be viewed in the loop calls section which is located at the middle right side of the main window As mentioned earlier each lane consists of two loops so the first row of the loop calls represents upstream and downstream loop activity of the first lane Similarly loop activity for lanes 2 3 and 4 are displayed The color code is summarized in Table 9 66 Table 9 Loop call color representation Loop Activity Color Representation No Vehicle Presence No Color Presence of Vehicle Blinking Green Color Loop Failure Continuous Green Color When there is no activity in the loop sensor nothing is diplayed in the corresponding loop calls section It is also possible to verify the loop call LED lights by inspecting the front panel loop section of the UM8 PCI For instance if green light blinks in WM8 PCI system the user will notice a similar blink in loop calls section of the software after a
80. nt way of calibrating existing systems without driving an actual truck of known weight A common problem with present WIM systems is that WIM vendors do not provide any capability of analyzing the raw analog WIM signals Therefore it has been very difficult for maintenance engineers to determine how much the sensor readings can be trusted 1 e correct or problematic since the only available outputs are the final converted weight and axle data In this research work a dual mode system was developed which is capable of displaying and analyzing the raw analog signals while the other mode generates real time WIM measurements Presently the Minnesota Department of Transportation Mn DOT 1s installing all new WIM systems using piezoelectric quartz Kistler Type 9195 technologies after retiring the bending plates and single load cell systems from highways This trend is not only occurring in Minnesota but also in other states in the US In order to advance the present piezoelectric WIM technology and system functionalities Mn DOT awarded the University of Minnesota Duluth a project to develop an open WIM system utilizing off the shelf components This report presents the results of the completed project 1 2 Related Work Significantly less research work has been done in WIM technologies in comparison to other types of traffic sensing technologies such as inductive loop detectors Recently this trend has gradually changed due to the availability
81. of the A D conversion A pax the number of sample periods between the matching upstream and downstream peaks 15 3 5 2 Axle Distance Computation The axle distance is computed using the calculated vehicle speed and the travel time between the consecutive axles The formula used is shown in Eq 12 pn _ gt 12 axle axle axle where D wie AXle to axle spacing meters S speed meters second A the number of sampling periods between the peaks of two consecutive axle axle axle signals 3 5 3 Weight Computation The weight is computed from the summation of re sampled voltage signals v Each voltage is the difference between the actual voltage and the idle level The final computation formula is given in Eq 13 60 000 Axle weight eee is 13 _weig dL 9 845 8 13 9 8 gravitational constant 9 8 m sec to convert from Newton to kilogram 5 maximum charge amplifier output 60 000 maximum charge output 60 000 pC y sensor sensitivity in pico coulombs per Newton The axle load may be converted to pounds Ib or Kilo pounds Kips according to the needs The gross vehicle weight is simply a summation of all axle weights 3 5 4 Vehicle Classification Vehicle classification is established according to Mn DOT s classification scheme Classification is done based on individual axle load axle spacing and the gross vehicle weight An example is shown in Table 1 that dem
82. onsidered as single axle of weight 34 000lb and belong to a tandem axle group Thus the ESALs for 2 and 3 axles is one value and is computed using the tandem axle group value 2 1 e 34 4 448 2 80KN SN 5 pt 2 5 this is 1 09 for a 34 000 tandem 4 2 ESAL 2 amp 3 axle 2 jl 1 578 for a flexible pavement with The forth axle has a load of 10 000 Ib and is apart 27ft 9inch from the third axle and 10ft 3inch from the 5 axle So this axle is considered as a single axle group and its ESAL is computed as 10 4 448 1 80KN Similarly fifth axle has a load of 10 000Ib and is apart 10ft 3 inch from the forth axle So it is considered as single axle group and its ESAL is computed as 4 2 ESAL _ 4 axle 1 0 08497 10 4 448 ESAL _5 axle 1 1 80KN 4 2 0 08497 The final ESAL for the truck is then computed by adding all of the ESALs computed for each axle groups That is ESAL 0 182 1 578 0 08497 0 08497 1 9298 60 It should be noted that this ESAL result is different from the AASHTO table computation More specifically ESAL for a SN 5 pt 2 5 with a 12 000 single two 10 000 singles and a 34 000 tandem AASHTO table produces 1 455 Since ESALs can be recomputed from the vehicle records of WIM data they are only shown on the system screen but not stored as a part of the final WIM data 5 3 6 Vehicle Classifications Vehicle classification is established according to the classificat
83. onstrates the conditions for a Class 7 vehicle The approach implemented in this project is based on the Mn DOT s scheme which differs slightly from the Federal Highway Administration FHWA classification scheme 16 Table 1 Mn DOT classification scheme source ref 24 Classification 7 Number of axles 6 SPACING Min 0 0 00 00 00 0 0 Max 32767 178 2767 178 178 AXLE WEIGHTS Min 0 0 0 0 0 0 Max 32767 32767 32767 32767 32767 32767 GROSS VEHICLE WEIGHT Min 0 Max 100000 17 CHAPTER 4 WIM HARDWARE IN LOOP SYSTEM 4 1 Introduction Hardware in loop HIL is a hardware software hybrid simulator that has been extensively used in the development stage of complex real time systems The main purpose of a HIL simulator is to provide effective development platforms for testing real time systems This simulation produces reliable increase in the complexity during system development by testing and verifying the functionalities under variable complex conditions Instead of testing a system in a real uncontrollable environment the HIL produces an environment with hardware signals generated through software that can be recreated As a result of replacing the complete system with computers running software simulations the size complexity and cost of the development phase is greatly reduced while the flexibility and the rate of generating test scenarios are increased Since the system cannot distinguish between the
84. pounds in contaminated soil Master thesis in Environmental Analytical Chemistry Department of Chemistry UMEA University Sweden 2006 24 International Road Dynamics Data Collection System Version 7 5 0 Weigh In Motion Software user s manual May 2001 90 25 Martin Gomez Hardware in the loop simulation Embedded System Design November 2001 26 NI Developer Zone LabVIEW FPGA in hardware in loop simulation applications Tutorial Feb 2006 http zone n1 com devzone cda tut p id 3567 accessed June 25 2007 27 National Instrument Corporation NI DAC 6723 Microsoft Visual Studio Specification manual for NI 673x board Analog Voltage Output Devices for PCI PXI Compact PCI PCMCIA Bus Computers June 2002 Edition 28 Measurement Computing Corporation MCC ADC 6017 Microsoft Visual Studio User s Guide PCI DAS6013 and PCI DAS6014 Analog and Digital I O Boards Document Revision 5 September 2006 29 Massload Technologies Ultra slim weight pad Ultra Slim with LCD Readout Brochure http www massload com weighpadlopro htm accessed Aug 2007 30 Taek Kwon Signal probe and processing methods for improving WIM data North American Travel Monitoring Exposition and Conference NATMEC Loews Coronado Bay San Diego CA June 27 30 2004 31 FHWA WIM Scale Calibration A Vital Activity for LTPP Sites Publication No FHWA RD 98 104 Federal Highway Administration McLean VA 1
85. power supply which supplies power to the charge amplifiers is used to power the C924 cards This card supplies inputs outputs through a 22 44 edge connector at the back that are connected to loop inputs and call outputs Each call output in C924 indicates presence of a vehicle in a form of open collector output The A D analog to digital inputs require 5 voltage range a 5V regulator was used to generate a 5 volt which is then connected to a 4 7K pull up resistor on the open collector call outputs The actuation outputs of the loop detectors are connected to A D converter inputs for fast and accurate detection In the next stage the voltages from the WIM amplifier and loop detectors are converted to digital signals using A D converters The A D board used in this project was a PCI DAS6013 and was produced by the Measurement Computing Corp This board supports 16 single ended channels or 8 differential channels with a 16 bit resolution in each sample with the collective sampling rate of 200K samples per second For this project the board was configured as a 16 channel single ended mode Sampling rate of each channel was set to 4 096 samples per second for a high accuracy other systems typically use 1K samples per second One of the interesting functions of this board is that the calibration can be done without external reference inputs Calibration of channels is simply done by clicking one button using the software supplied by the manufacturer
86. pstream and downstream WIM signals are present the required parameters are computed by averaging the weight computed from each The software provides the status of loops using color coded squares The square becomes green when a vehicle is detected no color if no loop activity is detected and red if a failure condition is detected 5 3 2 Computation Flow and Implementation The WIM computation algorithm is complex and summarized using a large flowchart shown Figures 42 44 on the subsequent pages 52 Wika data Data collected from WIM sensor i mr Loop 1 Upstream loop of First Lane Array 1 dim Array for first lane Ta Loop Detector Loop sensor data eT f a Loop 2 Downstream loop of First lane Array 2 T dim aray for second Lana Loop 3 Ustream Loon of Second Lane 3 j Loop 4 Downstream Loop of Second Lane Get Eight Channel Data 32 768 Samples 100 ms Plot Samples While Checking Data heck if it ba the middle of data collection No Pe Chack lf Loop1 detect the i vehicle presence osm No VA the Upstream Wil detect the vehicles Start storing data in an array WIM Yes Error 1 Failure of Upstream Loop f Loop 2 Detect Vehict pae Presence the Downstream WIR _ detect the vehicles mor 2 Failure of Downsteam Loop Get the size of detected loop length and store data until the second imaginary loop size is same as first ves
87. rom an actual WIM station The parameters are speed 70 mph axle weight 1 200 pounds footprint length 45cm and voltage sensitivity 0 1458mV N Speed 70mph 3 129 28cm sec Weight 12001b 5 337 86N Footpnt _ Length 45cm Voltage _ sensitivity 0 1358mV N 5 337 86N Peak _ sensor _ force 5cm 593 09621N 45cm Peak _ sensor _ voltage 593 09621 N 0 14584 0 0864V Axle _ signal _ length ee A O096Samples sec 58 90 59 3 129 28cm sec 45cm Sensor _ signal _length _ 4 96 Samples sec 6 544 7 Penner S TII Dona ees 0 086 Peak _ voltage weight _ profile 0 0132 _ voltage _ weight _ profi Peay Total _ signal _length _ after _ convolution Axle _ signal _length Sensor _ signal _length 58 90 6 544 65 The final axle signal for a 1 200 pound load is constructed by convolving the signal length of 59 samples with the corresponding sensor length seven samples The completed digital signal sequence is shown in Table 2 This sequence is sent to a DAC to generate the actual voltage signals Similarly the rest of axle load signals can be constructed The sequence of this voltage signal is equivalent to a signal generated by an actual vehicle with the same weight speed and footprint parameters 22 Table 2 Convolved signal sequence digitized axle signal Convolved Convolved Convolved Convolved Signal i Signal Signal sequence Signal sequence V seque
88. rosity and collaboration Table of Contents CHAPTER T TINTRODU CG TION eaaa aeeiiaii kia aoine aai 1 1 1 BACKGROUND ON WEIGH IN MOTION WIM SYSTEMS cccccsccceesccesceeesceesseeees 1 LARELATE D WOR omina a E a a 2 CHAPTER 2 PIEZOELECTRIC SENSORS cccccccccccccccccccccccccccccccccccces 4 2 1 BASIC PRINCIPLES OF PIEZOELECTRIC SENSORS cccscececccceccececcececcscecescecesescesescess 4 2 2 PIEZOELECTRIC WIM SENSOR cccscosceccccesceccecescestsceecesceceecescecescescesescescesescesceceecs 5 CHAPTER 3 WIM SYSTEM DESIGN ivssccccccccsccccccccccccccccccscsscsccccscsoccscscccccsscsscscescssess 7 Boll WIM SENSOR SEIU Boi coves cect eet eo tome ttn en he eee eee 7 3 2 OVERALL SYSTEM ARCHITECTURE cccecescecescecccecescececcecececcscescececescecscscesescesescecs 8 3 3 WIM SIGNALANAL YSIS sree heen cet eras enlaces Wie Rte Wanclew eee ence este enue 9 3 4 VEHICLE AND AXLE SIGNAL DETECTION c ccccscecescecescecescececcscecescecccscesescesescess 13 3 4 1 Vehicle Presence Detection c ccccccccccccccucuccccccucucuscecucucuscccscucususescececususcscscucusuecs 14 5 Ail AXE DCTCCHON a ieee Rasa a aE 15 3 5 VEHICLE SPEED AXLE DISTANCES AND WEIGHT COMPUTATION 0eceeececeeceees 15 Dab DS PCCU COMPU AON sistas ities Sattulitea tae tase wiinlean a dasu da tiluuusecaudn es esncacatan Soasauwe tine 15 SDL ANE Distance Compil dlon sai shoes ne a a ches e a E 16 De WEIL COMPUTA ON zyn a E E E
89. rs and the numbers in the splice box are shown in Tables 7 and 8 To use the IRD system switches 1 2 7 8 should be at the down off position while switches 3 4 5 6 should be at the up on position While using the UM8 PCI system all switches should be at up positions Table 7 WIM sensor Number corresponding BNC box Number Table WIM Sensor Cable Number Corresponding Customize BNC Box 14 Cable WIM Sensor Cable Number LABEL Red Color Box WIM is BNC Customize Box BOX Number Black Color 44 Table 8 Original WIM cable number corresponding BNC box number Table Cable Number Corresponding to IRD WIM Input ae 12 4 T 3 Note IRD IRD System LABEL Red Color Cable WIM Input Cable Number LABEL Red Color 5 2 5 Surge Arrester A surge arrester 1s used to protect the WIM system from any undesired or unwanted voltage fluctuations High voltage fluctuations can damage the system without warning A spark occurs whenever surge voltages exceed the electric strength of the system s insulation Discharge by a surge arrester limits the surge voltage and reduces the interference energy within a short period of time As the arc with its high current handling capability is ignited a further rise in surge voltage is prevented due to its low internal voltage Gas filled arresters utilize this natural principle of limiting surge voltages The general connection diagram for a surge arrester 1s shown in Figure 35
90. s and the number between two O s represents the axle spacing Ve Lane Time Ale Speedimph Aale Disffeet Veh Lenlfeet Axle Weight Kins ESAL Veh Class Eror Description 1331 OF Patld 225 0 4315 Class 5 13 31 OF 945 4 14 5 OOF Class 2 13 31 OF Tord 21 8 0 3758 Class 5 13 31 OF 385 4 19 6 0 0782 Class 2 Figure 56 Graphical display of vehicles 5 4 2 Menu Bar The Menu Bar is used to view or change various system configuration parameters Menus are located at the top left of the main window Figure 57 It is easy to follow with self explanatory descriptions 70 WIM S STEM 6 Settings Graph Help Save Raw Data Exit Ctrl Figure 57 Menu options File Menu Save Raw Data Each second data collected are saved in a binary bin format and appended to the same file until the Stop Save option is selected Data can be stored continuously and is only limited by the hard disk capacity of the system The software allows a user to save data continuously up to 300 minutes at which point the data saving automatically stops When Start Save is selected a user sees a new line shown in Figure 58 that indicates the status of recording with the time limit When the Start Save option is chosen a new folder is created with a name based on the current year month and day A data file is created in the folder and is named according to the time the recording started The size of e
91. s over the load cell the system records the weights measured by each scale and sums them to obtain the axle load A relatively new WIM sensor is fiber optic sensor which consists of a pneumatic tube filled with an incompressible fluid a diaphragm designed to convert pressure into displacement and an optical displacement sensor 13 Although new fiber optic sensors offer interesting properties They are not responsive to electromagnetic interference such as lightening they can withstand harsh environments and they have low power requirements 14 The accuracy of Gross Vehicle Weight GVW under highway speeds has not been established for fiber optic sensors Most published work on WIM focuses on statistically analyzing the axle loads and GVW records collected by WIM systems For example a study has been done in traffic analysis especially truck traffic where the WIM data collected from different WIM stations was used to determine flow volume and load growth from 1991 to early 2001 15 Other types of work include investigation of axle load spectra for different axle groups and truck types at various locations and time periods Hardware in loop HIL simulation has been used by many large manufacturing companies for more than decade 16 Recently HIL simulation was applied to evaluate traffic signal controllers In this case realistic traffic flow was simulated using a microscopic simulator from which loop signals are generated as simulated ve
92. serctuacesneriats G N 68 Graplicaldisplay Of VENICleS 4 in5 100 sees eeS aos a 70 Ment Options sens caxcssachsstinctvsanchens died TE J1 Indication that recording process is active sssssseerssssssseserrssssssseserrrsssseses 71 e a E E A E E E E T E E A E E E E EE 72 SCI OUI OUS irda A A ES ines we eee phate me se we aad 72 P r ameter ak 0 1 Tc ere mre a ea ra Ree 73 9195 sensors with sensitivity measure cc ceeeeeeccccccceeeeeeesseeceeeeeeeaaeeeseeeeess 74 SAMI MN PAOD MONS srera a en Ea 75 PDO a E E S 75 raph tab reasoner alia eaten untsadaetaadi en eetieattienlemaatiety 76 Legend OPTIONS x5 Sessa denn sew sesedctenstmasus e 76 ASTANO os arsnisteca a hetero etacanet ese eee ce eee ean een een T11 Developer s name and developed date ccccccsssseseeecceceeeeaeeeeeseceeeeeeeaas TI Daily created new folder folder name based on date nnesssseoeeessessseee 78 Data tile TOrmMat yecccaeeansesieue cusses eieeneta a N 78 Pror Tile TOMMAL n E E E EAS 79 SCUD COMINGS Connections ssri a 79 New connection wizard a and D enseri a a a 80 New connection wizard Crand d ienserniie e a Sl New connection wizard e and soenseessensenssessesssessesserserssessesssessesserses Sl New connection wizard 8 and B eceseorerirensan enee aak 82 New connection Wizard last St pp ceccescenntecneccnnaidnn top a a 82 Dialup connection Wizard asseio E EA 83 Connection to the Real VNC Viewe
93. shown in Figure 25 Figure 25 Fan less ITX PC and Software 33 5 2 Hardware Description 5 2 1 Charge Amplifiers The UM8 PCI WIM system is equipped with four Kistler charge amplifiers Type S038A2Y43 each of which takes two piezoelectric sensor inputs Inputs from Lineas WIM sensors BNC coaxial are fed into the charge amplifiers to amplify the electric charges produced by the piezoelectric sensors and convert them into voltage signals The charge amplifier converts the charge to analog voltages in the range of 5 volts The nominal voltage ranges is positive but the values can be negative depending on the sensor line conditions The schematic of the charge amplifier connections is shown in Figure 26 KISTLER 5038 Charge Amp Amplifier CH OUT 1 CH OUT 2 Q 9 Ground Figure 26 Kistler charge amplifier connections The 5038 charge amplifier takes in 15 to 30 volts in DC for the power supply and internally regulates the voltage to produce 7 volts The total consumption of power is less than 25mA The regulated voltages are used as the power inputs to the internal op 34 amps of the charge amplifier circuit For the UM8 PCI system a single 24V 1A switching power supply was used to power all four charge amplifiers The charge amplifier outputs are obtained from the internal screw terminal connections as shown in Figure 26 Pins 4 and 5 correspond to channel 1 and 2 outputs respectively These two outp
94. ssfully demonstrated the working of hardware and software For this demo George Cepress Technical Liaison Mark Novak and Bill Martinson all from Mn DOT TDA came from the Twin Cities and observed the demonstration The field demo was accomplished using live traffic on TH 61 to demonstrate its real time operations The system showed successful detection of vehicles computation of WIM data reporting of error conditions and vehicle classifications all in real time No correctional suggestions were made from the Mn DOT visiting team and approved the system as it was Figure 81 shows the pictures taken during the November 11 site visit and demonstration 86 Oo yon AAY te kek sete rt Se eee lt i T T t r lt Figure 81 Site visit and demo On June J 2007 the WIM research team invited the Mn DOT team and Alan Rindels Administrative Liaison to demonstration remote data downloading and remote desktop access through a dial up connection The system successfully connected to the remote computer site computer and showed a full access to the visual interface of the WIM system software The participants were able to see the real time computation of WIM parameters the axle signals and various other features of the software In the demonstration the research team downloaded the WIM data while browsing the desktop system 87 CHAPTER 6 CONCLUSIONS Traffic load data collected through WIM systems is a primary input to pavement
95. sss 31 Pioure 257 Kistler Lineas Sensor 919 5G Derreneresen in e E 32 Pisure 24 Analog sienal internace DOX tionner iona 33 Fig re 25 Fam less TTX PC and SoftWare etori n E A biases 33 Figure 26 Kistler charge amplifier CONMECTIONS cccccccccccecceceeeeeeeeseeseeeseeeeeeeeeeeees 34 Figure 27 PCI DAS6013 Board taken from the manual cccecceeccccccceeeseeeeeeeeeeeeaes 35 Figure 28 Pin outs of the PCI DAS 6013 Single ended mode from datasheet 36 Prue 29 CI Akcan kenne HONS iste tina enn Dance eas ocecatas aslea eens E 38 Figure 30 Internal components and connections of the WIM signal interface box 40 Pieure 31 BNG Splice Box TOP V 16 W beia a 4 Pisure 52 BNC Splice Box Front Vile Wrists totes eae hee eee 4 Pigute oo DING SpliCe BOX cerren a ate dieastadienatetw E aetna 42 Figure 34 IRD panel and cable numbering scheme cc cece eecccccceeeeseeeeseeeeeeeeeeeeeeeees 43 Figure 35 Schematic diagram of surge arrestor CONNECTION cceececcceeceeeeeeeeeeeeeeeeeeees 46 Pistre 30 LOOP Wile Spice pane lorpenen a O eeeencnoeea nade een tenes 47 Figure 572 12000 CONNECHONS and MUM DOES ena neces tee 48 IQUE 56 Loop CONNECUONS ieie E A a eRe oneiendees 49 Figure 39 WIM cable connection to system esssssessssssssseeereresesssssssssssssseererererreessssssssss 50 Pisure 40 Loopcard Wont anGiCalOr e E TO 50 Figure 41 Figure 42 Figure 43 Figure 44 Figure 45 Figure
96. stream Lane 4 Upsteam Lane 1 Upstream Lane 1 Downsteam Lane 2 Downstream Lane 3 Downstream Lane 4 Downstream Figure 39 WIM cable connection to system Lane 3 Upstream followed by downsteam loop detection Lane 4 Upsteam followed by downsteam loop detection Lane 2 Upsteam followed by t7 downsteam loop detection University of Minnesota Duluth P Lane 1 Upstream followed by downstream loop detection Figure 40 Loop card light indicator 50 The ribbon cable from the UM8 PCI is connected to the ADC adapter on the back of the PC shown in Figure 41 Figure 41 Connecting cable and back PC connection 51 5 3 Software 5 3 1 Overview The development tool used for this project was VB NET 2003 and Teechart Pro ActiveX for signal plotting WB NET was used as it provides full object oriented programming and sophisticated graphical user interfaces The digitized data is collected from the 16 channels of ADC the WIM data from the first eight channels and the loop data from the remaining channels Since the sampling rate is 4 096 samples per seconds a total of 65 536 samples of 16 bit data is produced every second In each frame one second the process looks for vehicle presence from the loop signals If a vehicle is detected the vehicle speed axle spacing and weight and the total gross weight are computed In order to provide sensor signal quality the signals are plotted as each frame of data is a
97. t ccccccccccccceessseeeeeeeeeeeeaeeeseseeeeeeeeeaas 83 Completed WIM system with a PC and modem nneneosesseseenssssssssseerrssss 85 Sle yvbitand de MO cessi n E ES 87 Executive Summary Weigh in Motion WIM data provides vital information for pavement design and maintenance traffic monitoring and management and transportation planning The purpose of this research was to improve the present piezoelectric WIM technologies with an improved system design and signal processing algorithms Present WIM systems are available as proprietary systems which means the internal system design and algorithms are highly guarded This makes it difficult to compare and improve the underlying design and technology Therefore the second objective of this research was to develop a WIM system based on an open architecture utilizing a standard PC and other off the shelf components and to publish the details of the design to promote future improvements The research team was able to successfully develop a prototype WIM system and this report presents the details During the prototype development the research team learned that developing a WIM system using a truck with known weight is not only labor intensive and tedious but also gives an inaccurate weight reference WIM systems translate static weights from the load of moving vehicles which inherently includes environmental factors such as winds the effect of vehicle suspension system pavemen
98. t roughness and slope in addition to the static weight Therefore computational parameters of the WIM system can be tuned to incorrect weight references even if the exact static weight is known To address this fundamental problem this research introduces a hardware in the loop HIL WIM simulator designed as a complete WIM development environment The HIL WIM simulator takes the basic traffic information expressed in vehicle classes speed and volume and produces ideal analog axle and loop signals using a multi channel digital to analog converter and software algorithms It can also generate axle signals for special type of vehicles if the basic vehicle parameters such as axle weights axle distances and the footprint lengths are fed as input In essence the HIL simulator creates ideal WIM sensor signals of moving vehicles with known axle loads and axle separation distances This means that WIM developers can utilize the HIL simulated axle signals to develop measurement algorithms or verify the accuracy of the measurements without driving a single vehicle by using the virtually created WIM sensor environment More important the HIL simulator can produce erroneous signal conditions for testing the error detection capabilities of a WIM system The main advantage of using a WIM HIL simulator for developing a WIM system is that the developers may conduct an unlimited number of tests without actually driving a single vehicle through the WIM sensors th
99. ted In the data collection mode the system has a real time weight translation and recording capability so that it can serve as a WIM data acquisition system for up to eight channels four lanes Weigh in Motion WIM systems have been developed commercially by several US and international companies Among them one of the well known is International Road Dynamics Inc IRD based in Saskatchewan Canada Most of the Minnesota WIM stations are equipped with the IRD system Other manufacturers are Peek Systems and ECM Both systems work on the basis of a calibration constant in contrast to the calibration free approach developed in this research There are several other classes of WIM sensors that have been developed for use and are currently available in the U S and abroad Bending plate WIM systems utilize plates with strain gauges bonded to the underside As a vehicle passes over the bending plate the system records the strain measured by the strain gauge and calculates the dynamic load 10 The static load is estimated using the measured dynamic load and calibration parameters Another type of WIM system available uses load cells A load cell WIM system utilizes a single load cell with two scales that weigh the right and left side of axle loads simultaneously The scale mechanism incorporates patented load transfer torque tubes which effectively transfer all loading on the weighing surface to the centrally mounted load cell 12 As a vehicle passe
100. the crystal must be measured Figure 2 shows a common method of using a piezoelectric crystal as a force sensor Two metal plates are used to sandwich the crystal which creates a capacitor As mentioned previously external forces cause a deformation of the crystal which in turn results in a charge that is a function of the applied force In its operating range a larger force will generate a larger surface charge Figure 2 A sensors based on the piezoelectric effect The voltage which results from the charge is expressed as 1 where Q is the charge resulting from a force f and C is the capacitance of the device Since mechanical stress can be turned into electrical charges piezoelectric crystals act as a strain or force transducer Alternatively if a voltage is applied to the plates of the system described above the resultant electric field would cause the internal electric dipoles to re align which would cause a deformation of the material Piezoelectric strains are very small and the corresponding electric fields are very large In quartz a field of 1000 V Cm produces a strain on the order of 10 20 2 2 Piezoelectric WIM Sensor The Kistler type 9195 piezoelectric quartz Lineas shown in Figure 3 have been most widely accepted by US transportation departments 9 The typical lengths are either one meter or three quarter meters so a standard 12 foot highway lane requires four sensors the sensors can be combined
101. the digitized WIM signal The load signal is detected when the signal amplitude exceeds a preset threshold from the idle level Once the presence of axle load signal is detected the signal between t Aft t At is used for weight computation where Af is a constant proportional to the threshold It should be mentioned that the signal idle level does not remain constant as it is an output of a charge amplifier The output of the charge amplifier should be thought of as two signals the idle signal changing slowly over time and the wheel load signal changing rapidly above the idle level Therefore the idle level b t is determined by separating the slowly changing signal from the overall signal 10 Volt Charge amp output x t Idle level b t Threshold level t AT ti t tat At Figure 8 Charge amplifier output signal of single axle or wheel load There are three methods of axle load computation available for WIM systems Each 1s described below Method 1 Peak voltage This approach is used in some commercial products and is very straight forward The axle load is simply computed using the peak voltage of the signal by w q peak _ signal _ voltage x 2 where POIs Sean VOEE is the peak voltage value of the digitized signal x t and is a calibration factor which must be determined using a known axle load 8 This method is based on the relationship between axle load and speed This is illustrated in Figure 7
102. the proposed computational model 24 Table 4 ADC Channel Connections to WIM Sensor Signals ccccccccccecceeesseeeseeeeees 37 Table 5 ADC Channel Connections to Loop Call Outputs cccccccceeeesseeeeeeeeees 37 Table 6 C924 Card Edge Connector Assignments ccccccccccccceessssseeeeceeeeeeaaaeeeseeeeees 39 Table 7 WIM sensor Number corresponding BNC box Numbet seeeeeeeeeees 44 Table 8 Original WIM cable number corresponding BNC box number 06 45 Table 9 Loop call color ire presenta Ons sicaacsnicensacengsanteesyccnsswanasieat utesteneilaeachoaeeeeeseniadest 67 Table 10 WIN Output Parameters cei icrn oe le rae ie a arate 69 Tabte Parameters Senos waciaicnssicwateationtntiwalesaecnsiunleuisetitiwaliatinsiiatianly 73 Table 12 PC SpeCiliCaMOns tvs ccnasinseczesvessizecaun cetind a aa a 86 List of Figures Figure Ls Internakstruct re Of an Cle Cte be sc sieccusiescacad seuauenesnavauerauaieionddelntauetecckdapuealeeeniniondes 4 Figure 2 A sensors based on the piezoelectric effect eccceccccccccccceeeeeesesseseeeseeeeeeeeeeeeees 5 Foure SIN eUeninea Ss CMG OL aean a ye weunaniicataenstauasnen 6 Figure 4 Vehicle passing over WIM sensor and the corresponding axle signal WavelOr SOULCE Fel 9 haar a dialed at 6 Figure 5 Overall WIM system block diagram cc ceeccecsecceecceceseeseeeeceeeeeaeeeeeeeeeeeeaaas 8 Figure 6 Footprint lengths under varying tire in
103. tly increased load means shorter pavement life and more frequent maintenance and rehabilitative work As early as 1918 highway officials concluded that heavy trucks were critical to the design of highways Today it is well known and accepted that heavy trucks cause the majority of damage to highways Truck weight regulations are firmly in place to protect pavements and bridges from the effects of heavy loads to ensure the safety of all motorists and to maintain manageable traffic operations 7 Traffic weight data is collected through Weigh In Motion WIM systems and it is essential to collect accurate high quality data 3 Many approaches have been proposed to increase the accuracy of WIM systems 30 35 with two schools of approach The first 1s to increase the accuracy of the WIM system through proper on site calibrations of the installed WIM systems 31 35 The second approach is to increase the accuracy through better signal processing algorithms and system designs 8 30 This research mainly follows the later approach and introduces a new calibration technique based on a hardware in the loop HIL simulator which does not require field evaluation of a known truck Accurate WIM calibration is often difficult to achieve due to vehicle dynamics Vehicle dynamics represent the dynamic forces that are applied due to pavement roughness wave loading effects caused by the suspension system of vehicles wind loads etc all of which are difficu
104. ure 38 47 Gnd 1 0 White 2 O Black 3 C Gnd 40 White 5 Black 6 G Gnd 7 O White 8 G Black 9 G Gnd 10 G White 11 Black 12 Gnd 13 O White 14 0 Black 15 Gnd 160 White 17 Black 18 Gnd 19 G White 20 amp Black 21 Gnd 22 0 White 23 O Black 24 GND Loop Cable Label 3 GND Loop Cable a Label 4 i GND Loop Cable Label 1 GND Loop Cable Label 2 GND Loop Cable m Label 7 GND Loop Cable a Label 8 Loop Cable Label 5 GND Loop Cable a Label 6 Figure 37 Loop connections and numbering 48 Figure 38 Loop connections 5 2 7 WIM Signal Interface Box Cable Connections The BNC connections of the Lineas sensor cables to the WIM signal interface box are shown in the Figure 39 Each column corresponds to each lane while the top and bottom rows correspond to upstream and downstream sensors respectively The loop detector shows the status of the loop using LED panel lights as shown in Figure 40 For each loop one green and one red LED light is used for system status identification When 49 a vehicle is detected the green LED turns ON and remains ON while the vehicle is present on the loop If the red light cycles between ON and OFF a faulty condition exists on the corresponding loop When both lights are OFF the loop is active but idle The details of red LED light diagnostic codes are available in the C924 manual Lane 2 Upstream Lane 3 Up
105. uts are connected to the inputs of the ADC card described in the next section 5 2 2 Analog to Digital Converter ADC Board The ADC board used in this project was PCI DAS6013 produced by the Measurement Computing Corp This board supports 16 single ended channels or 8 differential channels with a 16 bit resolution in each sample Its collective sampling rate is 200K samples per seconds It was configured as a 16 channel single ended mode board for the UM8 PCI system The sampling rate of each channel was set to 4 096 samples per second for higher accuracy This sampling rate was determined based on the speed measurement accuracy of 0 14 MPH at 70 MPH One of the interesting functions of this board is the calibration capability without external reference inputs Calibration is simply done using the supplied software The picture of the ADC board is shown in Figure 27 A schematic diagram of the board pin outs is shown in Figure 28 H lg IATE MTL di ig Syn eg LUT a iaie keepin Le E Figure 27 PCI DAS6013 Board taken from the manual 35 ih CTR1 OUT CTR PIE TT _____ tres _30 O Ow m DOS gE tie _ Sr n Oo e _ O aS ne _tr 66 es ee GS i OM H OoOo O ATERA AEE een R es signal Name _ AUXNS AD PACER GATE ALMING DIA START TRIGGER AXING D A UPDATE ALON AD STOF TRIGGER ALA ATD START TRIGSER j ALGUNOS AD CONVERT ALLROUT SOAN
106. ve axles more than 40 inches 3 4 feet but not more than 96 inches apart 8 feet Note that if three axles were within that distance it would be considered a tandem axle for the purpose of Interstate weight limits 40 Tridem axle group Tridem axle group means a group of three axles that are attached to a vehicle with a connecting mechanism with each separate axle located less than 8 feet and inch from the other axles 40 5 3 5 Calculation of ESALs Implemented mathematical formula to calculate the ESAL follows the simplified California model 40 and is given by 24 ESAL n group ao n 80CKN where n is 1 for steering and single axle group 2 for tandem axle group 3 for tridem axle group axle _ group _load LN is the load summation of axle or axles which are less than 8 feet 1 inch apart Note that Eq 24 does not include structural capacity SN or PCC thickness and terminal serviceability pt which are part of the AASHTO methods One of the criticisms for the AASHTO ESAL method is that the load spectra information is buried lost in the ESAL and cannot be restored Therefore Eq 24 was developed based on average across all pavement types all distress mechanisms and ride quality 40 The AASHTO design procedures indicate the effect of traffic loads on pavement condition The effect of a single axle on flexible or rigid pavement increases approximately a fourth power function of the axle load commonly ref

Development of a PC-Based Eight-Channel WIM System

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