Phase meter for a rotating grating goniometer using a personal computer and sound card

Abstract

A sound card and personal computer are used to implement a digital phase meter for a rotating grating goniometer. Inexpensive reflective optical sensors read the goniometer grating and produce sinusoidal waveforms which are continuously acquired and digitized by a personal computer sound card. Digital signal processing algorithms calculate the time-averaged relative phase of these waveforms, enabling the angle between the reference head and moving head to be determined in real time. Comparison with a calibration grade polygon yielded an experimentally measured error of 9 arcsec or better over an angular range of 90°.