We present a novel velocity and length measuring instrument based on laser-feedback interferometry. Uncertainties down to 10{sup}-4 in length measurement of moving materials can be achieved by combining the measurement signals of two separatesensors. Furthermore the dependence on parameters like the angle of incidence can be eliminated mathematically and no accurate alignment is required. The signal processing unit utilizes a real-time fast Fourier transformation. Thus good signal to noiseratios and very accurate measurements of most scattering surfaces used in industrial production are possible.
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