Measuring instrument with gyro

Claim 1

A measuring system for providing inertial directional reference comprising: A. a main housing, B. an inner housing suspended from the main housing and adapted to function as a directionally stable subsystem, C. a direction measuring gyro mounted on the inner housing for maintaining the inner housing directionally stable, said gyro comprising: C1. a stator fixedly mounted on the inner housing, C2. a rotor mounted around the stator for rotating as a gyro element, the rotor having regions of permanent magnetism thereon, and C3. windings on the stator, adapted, when electrically energized, to cause rotation of the rotor, D. a rechargeable battery mounted on the inner housing and electrically connected to the windings for providing electrical power to energize the windings, E. electrical isolation means for recharging the battery from outside the inner housing, while preventing electric power from the battery from leaving the inner housing, thereby protecting against the effect of electrical sparks in a possibly unsafe environment, F. means for detecting the rotation speed of the rotor, and G. feedback means for controlling the flow of current from the battery to said windings for stabilizing the rotation speed.