Measurement results with a small cam-driven absolute gravimeter

We describe the design of and first results from a cam-driven portable absolute gravimeter. The cambased design of a dropper allows us to build a compact system that uses 20 mm of free fall for the measurement. The instrument drops a test mass 200 times a minute (a measurement rate of more than 3 times per second). The centre of mass of the apparatus is kept fixed during the entire measurement cycle, thus avoiding ``recoil'' effects that could systematically bias the measurement. Seismic isolation is provided by a passive eddy-current-damped simple spring. Measurement results taken at Table Mountain Gravity Observatory (TMGO, Boulder, Colorado), though reproducible at a level of several microgals (1 µGal = 10-8 m/s2), show a sensitivity to the measurement start and stop points at the 20 µGal level.