Gravimeter

Claim 1

A gravimeter comprising: a. an electromagnet adapted to produce a levitational magnetic field directed downward therefrom; b. first means coupled to said electromagnet to energize same and being responsive to a variable feedback signal to vary the magnetic field intensity, the intensity varying monotonically with variations of said feedback signal; c. an evacuated chamber; d. a magnetic body positioned below said magnet and being subject both to the levitational force of said field and an oppositely directed gravitational force, said body being disposed in said chamber; e. body position indication means rendered responsive when said body is positioned within a predetermined vertical zone spaced apart from and positioned below said electromagnet to generate an output signal varying with upward and downward changes of vertical position of said body within said zone produced by changes of said gravitational force with respect to the gravimeter, said indication means including a device for producing a ribbon of light lying in a vertical plane, the upper and lower edges of this ribbon respectively defining the upper and lower bounds of said vertical zone, said device including a light source of narrow bandwidth disposed on one side of said body, means coupled to said source to modulate the light intensity thereof, a lens system disposed between said source and said body to derive said light ribbon from said source, an electro-optical transducer disposed on the other side of said body in the path of said light ribbon to produce a position signal which varies as the position of said body with respect to said beam varies and demodulator means coupled to said transducer to obtain the output signal from the position signal; f. second means coupled between said indicating means and said first means to obtain said feedback signal from said output signal and to supply said feedback signal to said first means, said feedback signal increasing said field intensity when said gravitational force increases and decreasing said field intensity when said gravitational force decreases to prevent said body from escaping from said zone, the magnetic field intensity being a monotonic function of the gravitational force; and g. third means responsive to said output signal to obtain therefrom a measure of said gravitational force.