The laser beam is interrupted by a defined object and the time between two signal changes is measured at high resolution.
The object in question could be, for example, a metal element with a precisely defined distance between two sharp edges, which is fixed to the vehicle and driven through the laser beam. The precision is in the region of 0.01 kph, up to a speed of 250 kph. The data are stored on the hard disk with a time-stamp.
Power is supplied directly from the PC. Cables up to a length of 50m are therefore possible.
Besides the laser unit and signal conditioning, the system consists of a stand of adjustable height, the precision measuring element, the measurement PCMCIA board, and the PC or base computer.