A NEW METHOD FOR FRINGE-SIGNAL PROCESSING IN ABSOLUTE GRAVITY METERS

In all modern absolute gravity meters, an interferometer illuminated with a stabilized laser tracks the motion of a freely falling retroreflector. The value of gravity is measured by timing the passage of interference fringes. Typically, the sinusoidal fringe signal is converted to a series of pulses, a subset of which are input to a time digitizer. In our new system, the fringe signal is digitized with a fast analog-to-digital converter and fit to an increasing-frequency sine wave. In addition to being smaller and less expensive, the system should eliminate some potential systematic errors that may result from imperfect zero-crossing discrimination and pulse pre-scaling.