Magnetic Suspension Balance

An analytical balance is described in which the materials to be weighed are attached to a ferromagnetic body that is freely suspended by the axial magnetic field of a solenoid. The vertical position of the suspended mass is maintained by the automatic regulation of the current through the solenoid by means of an electronic servo‐circuit actuated by a light beam and photomultiplier tube arrangement. The horizontal position of the supported mass is maintained by the symmetrically diverging field of the solenoid. Changes in the nonferromagnetic masses of the suspended bodies are determined by the resulting changes in the current through the solenoid necessary to keep the bodies freely suspended. Masses ranging from 105 grams to 2×10−6 gram have been suspended. The precision of the balance is limited only by the natural fluctuations in the circuit, the photomultipliers and the support system. This balance is especially useful where it is necessary to weigh materials inside of sealed chambers which contain gases, vapors or liquids, or which are evacuated. A method is described for accurately calibrating the balance.