Laboratory Instruments

Introduction

The FG5 absolute gravimeter (manufactured by Micro-g LaCoste, USA) is mounted on an isolated pier inside the Shibajianshan tunnel laboratory. Based on the free-fall method, it uses a laser interferometer to measure the displacement of a corner-cube prism inside an evacuated drop chamber, and a Time Interval Analyzer (TIA) to record the corresponding fall time, from which the gravity value g is computed.

International Comparison

In September 2005 the instrument was taken to the Bureau International des Poids et Mesures (BIPM) in Paris to participate in the 7th International Comparison of Absolute Gravimeters (ICAG 2005), confirming a national gravity measurement accuracy of the 10⁻⁸ m/s² level.