The absolute gravitation acceleration (g) is generally measured by observation of a free-falling test mass in a vacuum chamber based on laser interference. Usually the free-falling object trajectory is obtained by timing the zero-crossings of the interference fringe signal. A traditional way to time the zero-crossings is electronic counting method, of which the resolution is limited in principle. In this paper, a fringe signal processing method with multi-sample zero-crossing detection based on Digital Signal Processor (DSP) is proposed and realized for the application in absolute gravimeters. The principle and design of the fringe signal processing method are introduced. The measuring precision is evaluated both theoretically and from numerical software simulations with MATLAB®, and verified by hardware simulated free-falling experiments. The results show that the absolute error of the gravity acceleration measurement introduced by the fringe signal processing method is less than 0.5 μGal (1 μGal = 1×10−8 m/s2), and the impact on the standard deviation is about 2 μGal. This method can effectively reduce the systematic error of the traditional electronic counting method, and satisfy the requirements for precision and portability, especially for field ready absolute gravimeters.
Automated Optical Counting of Blood Platelets
