Pressure measuring apparatus

Claim 1

Measuring apparatus comprising: a force sensing unit mounted for movement in response to a force to be measured and having a rest position from which it is displaced to an extent dependent upon the magnitude of said force; a magnetic structure comprising a permanent magnet component including a core portion and a composite coil component comprising first and second separately energizable coils mounted on said core portion for displacement relative thereto, one of said components being stationary and the other component being movable and interconnected with said force sensing unit for balancing a force applied thereto; means for sensing an initial displacement of said force sensing unit from its rest position and providing a corresponding output current in said first coil which produces a corresponding counter balancing electromagnetic force that restores said force sensing unit to its rest position; and means for sensing the current in said first coil and maintaining an output current in said second coil to hold said force sensing unit in its rest position, the force applied to said force sensing unit being now balanced by the electromagnetic force produced by said second coil so that the current in said first coil drops to zero, whereby subsequent forces applied to said force sensing unit are balanced by an electromagnetic force produced by said first coil and measured relative to the initially applied force by the current in said first coil.