MIKROS SYSTEMS TRAFFIC EVENT LOGGING. HSWIM Calibration Instruction TEL EQUIPMENT MS001-00006-56 ISSUE 3

MIKROS SYSTEMS TRAFFIC EVENT LOGGING HSWIM Calibration Instruction TEL EQUIPMENT MS001-00006-56 ISSUE 3 1

Table of content 1 Introduction... 3 2 Equipment Needed... 3 3 Methodology... 5 4 Interpretation of the calibration results reports... 5 5 Format of the reports... 7 6 Statistical formulas used... 7 7 Procedure to get to calibration reports in TELCOM... 8 Calibration Report Sample... 14 2

1 Introduction Mikros Systems recommends the following method for calibration and verification of HSWIM installations. To eliminate as many variables as possible the installation must confirm to document MS001-00005-41 (Wim Site Requirements). As a calibration and verification vehicle a two-axle truck with high quality suspension (air suspension preferred) must be used. The detail data capture and analysis procedures are part of the TELSYS suite of programs, the operation of the calibration data capture procedures are described in document MS001-95000-86 (Tel Software Suite Telsys Manual) Alternatively more than one calibration truck can be used. The same procedure must be followed as with one truck. It is of the utmost importance that if multi (more that two) axle trucks are used all of the axle be weighed on the reference scale in one action. Enough scales must be available to do all the axles (wheels) at once. This means that for a five axle (tractor semi-trailer) truck ten wheel scales are five axle scales be used. Should a segmented weigh bridge be used it must be kept in mind that axle weights are not available. 2 Equipment Needed 2.1 Calibration truck Two-axle truck (or multi-axle trucks) with good suspension (air suspension preferred) capable of maintain the average running speeds of trucks over the HSWIM site. The truck(s) should have an evenly loaded with a stable load to at least 75% of the legal axle limits. This axle limit must be the legal road load limit. 2.2 Reference scales The truck must be weighed at a legal static weighbridge. In addition static portable scales conforming to at least OIML No. 76 Class 4 or NBS H44 Class 4. 2.3 Traffic control Adequate traffic control must be provided for the turnarounds. Under no circumstances shall turnarounds be permitted without the required authority and prescribed traffic deviations. Should it be more beneficial to close off a whole lane to allow the truck to reverse back to the start of each run adequate length of lane closure must be provided. 2.4 Trained driver A professional driver must be employed to ensure that the truck will be driven smoothly over the site. No sudden braking or gear changes are allowed over the HSWIM site. 2.5 Data collection team A team of two observers at the Data Logger, observer one to check for the truck arriving at the WIM site and observer two to tag the vehicle on the laptop connected 3

to the Logger. Two-way radios might be needed if the site geometry does not allow for direct communication between the two observers. 2.6 Laptop computer A Laptop computer is needed to tag and collect the calibration information. 4

3 Methodology The calibration truck must first be loaded with a stable load of at least 70% of the legal road axle limits and then be weighed at a legal static weigh bridge (in total and axle by axle). This step can be substituted by only using the weights from the static wheel scales. (minimum of five readings). Close the affected lane and weigh the calibration truck with two static wheel scales, take five readings per axle (pull off and drive on). This must be done at the position of the sensors to allow for local cross fall and camber conditions. Calculate the average of these values and check with the weighbridge values. It may be that due to the local geometry the axle values can be slightly different. Do not accept a difference larger than 1.5%. Place the observers at the running logger. Connect the laptop and select the calibration mode of TELSYS. Observer A (in view of the roadside) must warn observer B (at the logger) of the approaching calibration truck. Observer A must also closely note any abnormal driving behaviour due to traffic conditions or other (sudden braking, swerving or missing the sensors at the site). Any suspect data due to these abnormal conditions must not be taken into account for calibration and verification. The calibration truck must pass over the sensor area at the normal prevailing speed for trucks at the site. The driver should maintain normal lane position and drive smoothly without gear changes or sudden breaking. Turn arounds should be done under approved conditions and traffic control. Collect a minimum of 40 sample runs to allow for the discarding of possible erroneous runs. For proper statistics a minimum of 34 valid runs are needed per lane. The data captured in TELSYS is also analysed in TELSYS. Refer to the calibration part of Document MS001-92000-86. 4 Interpretation of the calibration results reports The TELCOM module of the TELSYS program provides a comprehensive analysis of the calibration results. Results from the calibration are obtained from the run and cal files that are stored by the calibration function of TELCOM. 5

TELCOM provides results for: 1. Weigh sensor calibration factor in terms of: Mean error (μ), an indication of bias 0 means that the result is not skew. Error percentage as the standard deviation (σ) value, this is an indication of the variance between the static and the dynamic weight. The 95 % confidence value (percentage) of the mean error. 3. Front axle factor compensation as a percentage. 4. Temperature correction factor (percentage per degree). 5. Axle spacing correction (speed correction) done as a correction on the loop (sensor) spacing. Static scales normally are either: 1. Wheel or axle scales. Then in the case of wheel scales it is possible to individually calibrate left and right sensors (if this configuration is used). Should axle scales be used half the value is used to calibrate individual wheel sensors. 2. Platform scales. In the case of a full fixed platform scale only gross vehicle mass (GVM) can be used for calibration. If segmented platform scales (or small axle group platform scales) are used axles must be allocated to segments that can be weighed. There are therefore four units that can be distinguished: i. Wheels ii. Axles iii. Segments iv. GVM In the calibration procedure of TELCOM three types of vehicle are defined: 1. CAL vehicles: these are vehicles accepted or chosen as a valid calibration vehicle. 2. ALL vehicles: these all the vehicles that where logged during the calibration procedure. (The rejected plus accepted vehicles for calibration). 3. OTHER vehicles: are the vehicles that are normally rejected for calibration procedure. Where two sensors are used per lane for improved accuracy the calibration results are presented per sensor and for the Physical Lane (PLn). 6

5 Format of the reports For the weigh results the report gives firstly the results per sensor and then per lane (PLn). (Up to 8 sensors and 4 PLn, for dual sensor application). Calibration results are calculated for: Axle Masses, GVM and then Segmented Masses. Each of these calculation are done using the Axles and GVM data of: Cal vehicles All vehicles Other vehicles The axle spacing results are presented in a similar manner but are only per lane. 6 Statistical formulas used Mean % error: 100*(MD-MS)/MS where: MD is the dynamic mass and MS the static mass. Standard deviation: M1=Σ((MD-MS)/MS) M2=Σ(ρ((MD-MS)/MS)) σ=ρ ( ((M1*M1/n)-M2/n)-M2 /(n-1)) n = number of samples. The 95% confidence of the mean: CE95 = t95(n)*σ/ ρ(n) Where t95(n) is the 95% confidence estimate for samples (n) less than 30. At n > 30 assuming a normal distribution t95(30) = 1.960 7

7 Procedure to get to calibration reports in TELCOM Menu procedure in TELCOM: Logger/MoreOptions/Calibration 8