Axle load sensor calibration using platform scales

Sensor calibration process always raises a number of questions. Below you’ll find a thorough step-by-step calibration guide for any type of Mechatronics axle load sensors: Eurosens DDS, DPS or DSS.

Let’s take a semitrailer truck with air spring suspension as an example. To calibrate the sensors, truck scales are a must: either platform scales or axial weighing pads. The below guide describes the calibration process using platform scales.

The truck has two independent suspension circuits. The same is true for the semitrailer. Thus, they have the same type and number of axle load sensors installed: one Eurosens DPS axle load sensor on each suspension circuit for a truck (two sensors in total), and two Eurosens DPS for a semitrailer – one on each suspension circuit.

To begin with, let’s measure the actual axle load on each axle.

1. Drive the truck front axle on the scales and measure the actual axle load on the front axle N1 (kg). The output value of the left circuit sensor mark as Sens1L. Sens1R will have the output value of the right sensor.

2. Further, we need to measure the actual axle load of the truck rear axle. The axle is paired and one axle can’t be put on scales, so we’ll measure the total load N2 (kg) of the paired axle. Also, we’ll assume that the individual load of each of the paired axle is equal. 3.Let’s move on to the trailer axles. Measure the total axle load N3 (kg) by placing the axle on the platform scales. Here, the individual loads can not be measured too. Thus, we’ll again suppose that they are equal.

Mark the output sensor value of the trailer left circuit as Sens3L and Sens3R for the right. As soon as we are done with the measurements, let’s proceed to the GPS tracking software and create a calibration table adding the first calibration point:

Axle 1 (left side): input value Sens1L; output value N1

Axle 1 (right side)Sens1R; N1

Since the output sensor value for the truck front axle was measured individually, the axle load is calculated as the average of the load values.

Load_axle1=(Axle 1 (left side) + Axle 1 (right side))/2

To calculate the load for the second and the third axles, divide the actual measured load by 2, equally for each of the axles.

Axle 2 (left side): Sens2L; N2/2

Axis 2 (right side): Sens2R; N2/2

Axis 3 (left side): Sens2L; N2/2

Axis 3 (right side): Sens2R; N2/2

Load_axle2=(Axle 2(left side) + Axle 2(right side))/2

Load_axle3=(Axle 3(left side + Axle 3(right side))/2

Follow the same algorithm for the semitrailer:

Axis_t_1  (left side) :     Sens3L;    N3/3

Axis_t_1 (right side):      Sens3R;   N3/3

Axis_t_2  (left side) :     Sens3L;    N3/3

Axis_t_2 (right side):      Sens3R;   N3/3

Axis_t_3  (left side) :     Sens3L;    N3/3

Axis_t_3 (right side):      Sens3R;   N3/3

Axis_trailer_1=( Axis_t_1  (left side)  + Axis_t_1  (right side) )/2

Axis_trailer_2=( Axis_t_2  (left side)  + Axis_t_2  (right side))/2

Axis_trailer_3=( Axis_t_3  (left side)  + Axis_t_3  (right side))/2

To calibrate the sensor, we need to make a calibration table with at least two calibration points: empty and full (fully-loaded). If possible, add more calibration points to increase the accuracy of sensor readings.

The calibration table is programmed either by the sensor itself or on the server side (for example, in sensor properties in Wialon). The server-side calibration can be done remotely, it does not require a direct wired connection to the sensor. The output sensor values​​ (marked above as SENS values) are shown as GPS tracking data. So, to calibrate the axle load sensors, we need to measure the actual axial loads N using the scales as it was described above.

The sensor-side calibration is possible if the axle load sensors are connected to an on-board display, such as Eurosens Display CAN. The display will calculate axle loads values in tons directly onboard.

To perform the calibration onboard:

• Measure the axle loads several times using the truck scales.
• Stay connected to the sensor during the measurements.
• Enter the weight values of the truck scales in the field “Load, kg”.
• After each measurement, add a line to the calibration table by pressing the “Calibrate” button. As soon as you are ready with that, enter the current value of the detector together with the measured axle load to the calibration table. You can fill in the table partly, saving the intermediate results to the sensor.

Calibration tips for using weighing scales with a long platform.

Platform scales with a long platform to weigh the entre road-train are a bit more difficult to deal with. If the front axle load measurement is done as mentioned above, the remaining axles measurement needs the entire vehicle weighing.   