The vertical displacement Δz is recorded continuously for each track with the help of a contactless laser measuring system. The measuring system is based on the triangulation principle.
With the help of a laser beam incident at a certain angle on the road surface, a spot of light is produced, which is received through a lens on the surface of a light-sensitive photodiode. Depending on the angle of incidence of the laser beam, the spot of light on the surface of the photodiode shifts as illustrated. This movement is proportional to the vertical distance between the point of reference and the road surface. It can hence be converted into a measuring signal.
The measurement of the displacement of the vehicle body zB is managed by accelerometers fastened to the vehicle bodywork perpendicularly over the points of reference for distance measurement.
The low-pass effect of the vehicle suspension system results in accelerations of max. 1 to 2 g, and so sensitive acceleration sensors can be selected accordingly, which record low-frequency body accelerations with sufficient accuracy.
The displacement of the vehicle body zB is determined continuously by the double integration of the vehicle body acceleration . The characteristic of unevenness h(t) or h(x) results from the addition of the displacement of the vehicle body zA and the change in distance z.