National Highway Institute 5-1 REV-2, JAN 2006 EQUIPMENT FACTORS AFFECTING INERTIAL PROFILER MEASUREMENTS BLOCK 5

National Highway Institute 5-2 REV-2, JAN 2006 Objective l List the different components of the profiler and how these components work l Name the components of the profiler that require calibration and procedures to be used for calibration

National Highway Institute 5-3 REV-2, JAN 2006 Height Sensor l Measures vertical distance from vehicle to road by means of triangulation

National Highway Institute 5-4 REV-2, JAN 2006 Height Sensor Types – In Common Use l Laser –Spot of invisible light projected to road surface l Infrared –K.J. Law profilers –Invisible light projected to pavement surface l Warning: Do not look directly at light emitted by sensor, can damage eyesight

National Highway Institute 5-5 REV-2, JAN 2006 Height Sensor Types – Not in Common Use Now l Optical: –K.J. Law profilers –Slit of visible light –Replaced by infrared sensors l Ultrasonic –Sensor emits sound waves, time for sound waves to reflect measured distance –Variety of problems (repeatability, bias, coarse textured pavements)

National Highway Institute 5-6 REV-2, JAN 2006 Height Sensor – Resolution l Smallest unit of distance that can be measured accurately l Laser sensors typical value 0.04 mm (0.002 inch) l K.J. Law infrared sensors static resolution of mm (0.001 inch) l Ultrasonic sensors typical value 1.5 – 3 mm (0.06 – 0.12 inch) l For computation of IRI and RN required resolution is 0.5 mm (0.02 inch)

National Highway Institute 5-7 REV-2, JAN 2006 Height Sensor – sensor footprint l Area on pavement surface covered by signal l Laser sensors typical value 1 – 5 mm (0.04 – 0.2 inch) l K.J. Law infrared sensors 6 mm x 37 mm (0.2 x 1.5 inch)

National Highway Institute 5-8 REV-2, JAN 2006 Height Sensor – Stand-Off and Measurement Range l Stand-Off: Prevent damage l Measurement Range: Large enough to measure features of interest l High-Speed profilers for construction acceptance 150 mm (6 inch) measurement range

National Highway Institute 5-9 REV-2, JAN 2006 ACCELEROMETERS

National Highway Institute 5-10 REV-2, JAN 2006 Accelerometer l Measures vertical acceleration l Mounted above height sensor l Vehicle must be above a minimum speed to measure acceleration l Need sufficient range of measurement l Bandwidth at least 150 Hz l Acceleration is integrated twice to obtain displacement

National Highway Institute 5-11 REV-2, JAN 2006 Distance Measuring Instrument l Measures distance traveled by profiler l In high-speed profilers measured by pulsar attached to a wheel l Rotation of wheel measured by detection of pulses as wheel rotates and notches pass l Affected by rolling radius of tire

National Highway Institute 5-12 REV-2, JAN 2006 Profile Computation Procedure l Profile computed by combining output of height sensor, accelerometer, and distance measuring instrument l A high-pass filter is finally applied on the data. Typically use a 91 m (300 ft) high-pass filter

National Highway Institute 5-13 REV-2, JAN 2006 Sampling Interval l Longitudinal distance between points that are digitized for computation of profile – can be selected by user l Accurate computation of IRI requires sampling interval < 167 mm (6.7 inch), for RN it is < 50 mm (2 inch) Measurement Roadway Surface Measurement Sampling Interval

National Highway Institute 5-14 REV-2, JAN 2006 Recording Interval l Interval at which profiler stores elevation values l Can be same as sampling interval l If recording interval is > sampling interval, elevation values averaged l IRI recording interval at least 250 mm (10 inch), for RN it should be at least 75 mm (3 inch)

National Highway Institute 5-15 REV-2, JAN 2006 Recording Interval (Cont) Roadway Surface Recording Interval Average of points calculated

National Highway Institute 5-16 REV-2, JAN 2006 Photo-Triggering Device l Automatically initiates data collection at a specified location l Triggered when it detects a change in reflectivity l Mounted either vertically or horizontally in profiler

National Highway Institute 5-17 REV-2, JAN 2006 Photo-Triggering Device (Continued) l Vertical is triggered by a reflective tape on pavement l Horizontal is triggered by a cone with a reflective mark placed on the shoulder l Ensures data collection begins exactly at desired location l Essential when repeat runs are made at a section

National Highway Institute 5-18 REV-2, JAN 2006 Number of Sensors l High-speed profilers usually have two sensors that measure along each wheelpath l Some lightweight profilers equipped with two sensors, some with one l Devices with one sensor have to make two passes to get profiles for the two wheel paths

National Highway Institute 5-19 REV-2, JAN 2006 Lateral Sensor Spacing l This is spacing between two sensors in profiler l Usually can be adjusted l Make sure spacing corresponds to spacing between wheel paths specified in smoothness specification

National Highway Institute 5-20 REV-2, JAN 2006 CALIBRATION OF PROFILER COMPONENTS

National Highway Institute 5-21 REV-2, JAN 2006 Components of Profiler Requiring Calibration l Height sensors l Accelerometers l Distance measuring instrument

National Highway Institute 5-22 REV-2, JAN 2006 Calibration Guidelines l Follow procedure outlined by manufacturer l Frequency between calibrations are recommended by manufacturer l Calibrate equipment if problems are suspected l Calibrate equipment if repairs are performed

National Highway Institute 5-23 REV-2, JAN 2006 Calibration of Height Sensors l Laser sensors (e.g., Selcom) cannot be calibrated by user. However, user can perform a calibration check. l Procedure used for KJ Law Profilers that are equipped with infrared sensors - Blocks of known height placed below height sensor -Readings recorded by data acquisition system are used to compute calibration factors for height sensors -Computed calibration factor saved in computer

National Highway Institute 5-24 REV-2, JAN 2006 Calibration of Height Sensors (Continued) l Calibrate height sensors (check with manufacturer) –Repairs on suspension –Repairs on bumper housing them –Tires are replaced or rotated l Follow manufacturers procedures to ensure center of measurement range coincides with pavement surface

National Highway Institute 5-25 REV-2, JAN 2006 Calibration of Accelerometers l Accelerometers have built-in calibration system that allows them to be calibrated electronically l Performed using the computer system l Calibration factor saved in computer

National Highway Institute 5-26 REV-2, JAN 2006 Calibration of Distance Measuring Instrument l Section of known length laid out l Tire pressure checked and adjusted if necessary l Drive profiler for tires to warm up l Profiler driven over section l Actual distance of section entered to computer l Calibration factor computed by computer

National Highway Institute 5-27 REV-2, JAN 2006 If equipment is not calibrated, incorrect data will be collected

National Highway Institute 5-28 REV-2, JAN 2006 Considerations Related to Calibration l Keep a log book and write date of calibration and calibration factors l Helps in keeping track of calibration factors l Large changes or erratic patterns may indicate a potential problem with component

National Highway Institute 5-29 REV-2, JAN 2006 PROFILER CERTIFICATION l Texas and Pennsylvania have a profiler certification program l Objective is to check data collection capabilities of profiler against a specified set of criteria l Only profilers that are certified can collect data

National Highway Institute 5-30 REV-2, JAN 2006 CERTIFICATION - TEXAS l Two test sections –Smooth IRI < 0.99 m/km (63 in/mi –Medium smooth IRI range 1.50 – 2.27 m/km ( in/mi) l Perform repeat runs and provide data to DOT for analysis l Reference measurements (Walking Profiler) obtained by DOT

National Highway Institute 5-31 REV-2, JAN 2006 CERTIFICATION - TEXAS l Data evaluated for –Profile repeatability and bias –IRI repeatability and bias l Equipment: Static sensor check and check of distance measuring system l If profiler meets all requirements it is certified

National Highway Institute 5-32 REV-2, JAN 2006 Summary of Equipment l Characteristics of height sensor, accelerometer, distance measuring system and profile computation procedure affect quality of data l These are outside operators control l When purchasing equipment, agency should specify requirements and perform “acceptance testing”

National Highway Institute 5-33 REV-2, JAN 2006 Summary (Continued) l Equipment factors within operator control: –Calibrate height sensor (if applicable), accelerometer and distance measuring system –Select appropriate sampling or recording interval –Ensure sensor spacing matches distance specified in smoothness specification

National Highway Institute 5-34 REV-2, JAN 2006 Class Exercise l Name 5 major components of an inertial profiler and their function