Proof mass support and sensing system

An accelerometer comprising:

• an elongate proof mass having a sensitive axis and supported by a support system including a pair of alignment coils for controlling the rest position of the proof mass, wherein said alignment coils are constructed to provide a levitation force when they carry electric currents which varies along the length of said proof mass, and the relative strength of said electric currents in sniff alignment coils is tuned to cause said proof mass to take up a predetermined orientation with respect to one or more degrees of freedom defined by said alignment coils;
• and
• at least one sensing coil for monitoring movement of said proof mass due to acceleration of the proof mass with respect to the sensitive axis.

A gravity gradiometer comprising:

• a first accelerometer including a first proof mass and a pair of first alignment coils for controlling the rest position of the first proof mass and wherein said first alignment coils provide a levitation force which varies along the length of said first proof mass and the relative strength of said electric currents is tuned in said first alignment coils to cause said first proof mass to take up a corresponding predetermined orientation;
• and
• a second accelerometer including a second proof mass and a pair of second alignment coils for controlling the rest position of the second proof mass, wherein said second alignment coils provide a levitation force which varies along the length of said second proof mass and the relative strength of said electric currents is tuned in said second alignment coils to cause said second proof mass to take up a corresponding predetermined orientation.