Short Range Finding using the FM Heterodyne Interferometry with Digital Signal Processing.

An FM heterodyne interferometer using the digital signal processing has been constructed for the measurement of short distance (≥2.5cm). The digital signal processing consists of the signal amplitude correction, the signal frequency measurement by averaging beat periods and the signal phase measurement. In the experiments, the distances from 2.5cm to 10.5cm have been measured with the accuracy less than 76.1μm by the phase measurement. The error in the phase measurement was less than that in the frequency measurement by a factor of 3 to 6. The influences of the digital signal processing on the measurement accuracy have also been discussed.