Truck weigh stations calculate weight by using truck scales to measure axle weight, which refers to the weight every axle carries, or gross weight, which refers to the collective weight of all axles, explains HowStuffWorks. Truck scales are capable of handling trucks weighing thousands of kilograms, as they are made of steel, concrete or both. Truck scales operate using load-cell, bending-plate or piezoelectric systems.
Most truck scales use load-cell systems, in which every cell consists of steel or concrete with strain gauges containing wires that deliver small electric currents, reports HowStuffWorks. Putting weight on a cell slightly squeezes the wires, which changes the resistance to the current transmitted through the wires. A junction box receives the signal changes, and its sensors measure the difference in the current and then determine the weight supported by the scale.
In comparison, a bending-plate system consists of metal plates with strain gauges, notes HowStuffWorks. Placing weight on the scale adds pressure to the plates, prompting the strain gauge to measure the amount of stress and the corresponding amount of load.
The piezoelectric sensors in a piezoelectric system calculate a truck's weight by measuring the difference in voltage and amount of load when pressure from the weight alters the voltage of electrical charge passing through a conductor, states HowStuffWorks. One-axle, one-stop and weigh-in-motion are other methods to calculate a truck's weight.