After installing the axle load sensors, it is required to calibrate them. Calibration requires a vehicle platform scale or a weighing pads for individual wheel weighing.

Платформенные весы / Platform scales

Подкладные весы / weighing pads

Lets consider the example:

The truck vehicle is equipped with 2 Eurosens DPS pressure sensors (one each in the left and right air suspension circuits). Also, two Eurosens DPS pressure sensor is installed in the left and right air suspension circuits of the trailer.

We need to measure the actual axial loads on all axles.

We drive the front axle of the tractor onto the scales  and measure the load on the front axle N1 (kg). We write the output value of the sensor of the left circuit Sens1L and the sensor of the right circuit Sens1R.

Первая точка калибровки переднего моста / First point of the front axle calibration

2. Next, we measure the paired axles of the tractor. We cannot place only one of these axles on the scale due to the dimensions of the scale and the vehicle. Therefore, we measure the total load N2 on the paired axles. Due to the impossibility of measuring the individual load on each of the paired axles using platform scales, we will assume that they are the same.

Первая точка калибровки задних осей тягача / First point of calibration for rear axles

3. Next, we measure the axles of the trailer. Again we cannot place only one of these axles on the scale. Due to the impossibility of measuring the individual load on each of the axles using a platform scale, we will assume that they are the same. Measure total weight N3.

Первая точка калибровки осей прицепа / First point of the trailer calibration.

Now we create sensors in the GPS tracking software and add the first points to their calibration tables.

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

Axle 1 (right side): Sens1R; N1

Since we separately measure the value of the load on the left and right sides the axle load is considered as the average of the load values .

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

For axles 2 and 3, the actual measured load is divided 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

To create a calibration table for each of the sensors, at least one more point is required. While the first measurement is usually taken in the “Empty” state, when there is no load in the vehicle or trailer, the second mandatory calibration point is the loaded state. The closer the load is to full, the better.

If during operation the vehicle will drive on the scales and make similar measurements, then additional calibration points  can improve the accuracy of the axle load measurement.

Calibration tables for calculating axial loads can be programmed either on the server side  (for example, in the sensor properties in Wialon) or directly into the sensor.

After that, the current value of the detector is entered into the table along with the measured axial load. The table can be filled in several steps, saving intermediate results to the sensor.

Features of the use of platform scales with a long platform.

Platform scales that can weigh an entire truck-trailer combo are a little more difficult to use for calibration. Measuring the load on the front axle will not cause problems – we can, as before, drive onto the scales only with the front axle. To measure the axle loads on the remaining axles of the tractor, we will have to weigh the entire vehicle.

And then subtract the axle load on the front axle. And then measure the axle loads on the trailer axles

For calibration, it is desirable to use platform scales installed at the same level with the road. High ramp will increase an error in the measurement of axial loads when the car partially enters the scales