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How to avoid errors when using the Wheel Weigh Pads

The Wheel Weigh Pad system allows many pads to be connected to one indicator at the same time. The wiring goes from one pad to the next so that there is no mess of wiring around the vehicle.

It is very easy to set up the wheel pads to weigh any vehicle. If the vehicle has only two axles then only two pads are needed. The front axle is weighed first, and then the rear axle is moved onto the pads. The indicator will give a printout of the individual axle weights and the total vehicle weight.

If a vehicle has many axles then more pads can be used. For example, take the case of an articulated vehicle with a two axles tractor unit and a two axles trailer unit. To weigh the truck correctly four pads should be used. The tractor unit is weighed by placing all the wheels onto the four pads, and then the trailer unit is weighed by placing all the wheels onto the four pads. The individual axle weights and the total vehicle weight will be printed out.

If an articulated vehicle has three axles on the trailer then it would be correct to use six wheel pads. As previously mentioned, all six pads can be linked together with the signal cables and plugged into one indicator. All the individual weights from the pads can be seen on the indicator, and the axle weights and the total weight will also be shown.

Typical examples of weight shift due to non-level weighing surface

Weight transfer occurs when the Weigh Pad is above the ground.

The closer the axles are to each other the more the weight will transfer from one axle to another. This is because of the shift in centre of gravity of the vehicle.

Vans or trucks that have a long wheelbase will have negligible weight differences between the axles. Weight transfer is most noticeable in close-coupled axles, especially in tri-axle trailers. Even where the pads are only a few millimetres high, large discrepancies may be noticed. To avoid this, one pad should be put under each wheel. A tri-axle trailer would, therefore, require six pads to avoid errors.

Roadway not level

If the road surface is uneven, or if there are changes in gradient in the road, then incorrect axle weights will be recorded. This is most noticeable on articulated vehicles and other large, multi-axle vehicles. The correct way to solve this is to use more pads for large vehicles. This will reduce errors and increase accuracy of weighing.

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