HSWIM Calibration Instruction TEL Equipment_Mikros

MIKROS SYSTEMS TRAFFIC EVENT LOGGING 

HSWIM Calibration Instruction 

TEL EQUIPMENT 

MS001-00006-56 

ISSUE 3 

1 

MS001-00006-56 HSWIM_Calibration_Instruction_Issue_3 17-10-00

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 

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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 

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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. 

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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. 

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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). 

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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 

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7 Procedure to get to calibration reports in TELCOM 

Menu procedure in TELCOM: Logger/MoreOptions/Calibration 

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Loading Cal & Run Files: 

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Viewing the RESULTS panels (Scroll with the Pg Down key) 

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Select the required option: 

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Display the results regression plot: 

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Acrobat Document 

Cal_Reps 

Calibration Report Sample 

14

HSWIM Calibration Instruction TEL Equipment_Mikros

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