DENSITY MEASURING INSTRUMENT HAVING ELECTROMAGNETIC SUSPENSION WITH A VARIABLE SPRING CONSTANT

摘要

An electric coil is provided for the purpose of carrying alternating current. An electrically conducting sphere placed within the magnetic field of the coil incurs eddy currents resulting in magnetic repulsion between the sphere and the coil which is maintained at a null position by means of an autoregulation or feedback circuit. Voltage or current applied to the coil to maintain the sphere at a null position is an indication of the buoyant forces acting upon the sphere and thus is representative of the density of the gas or liquid surrounding the sphere. The coil and sphere are enclosed in a magnetic enclosure to provide a flux path and the top plate of the enclosure is provided with an opening of a size selected to alter the magnetic field of the coil and thereby the equivalent spring constant of the system.