Weighing apparatus with electromagnetic force compensation

Claim 1

In a weighing system of the electromagnetic load compensation type including a frame (10), load receiving means (16) movably connected with said frame for vertical displacement from an initial no-load position upon the application of a load thereto, permanent magnet means (27) connected with said frame for producing a stationary magnetic field, load coil means (28) connected with said load-receiving means for vertical displacement in said magnetic field, reference coil means (28) connected with said frame for vertical displacement in said magnetic field from an initial null-position, means (52) for generating a load signal responsive to the displacement of said load-receiving means from its initial no-load position, means (54) for generating a reference signal responsive to the displacement of said reference coil from its null position, compensation current supply means (60) responsive to said load and reference signals for supplying compensating current to said load and reference coils to return the same to their initial no-load and null positions, respectively, and display means (68) responsive to said compensating current for affording a visual indication of the magnitude of the applied load; the improvement wherein said permanent magnetic means comprises (a) a hollow open-ended horizontally arranged sectional yoke housing including a pair of generally identical soft iron components (30a, 30b); (b) a vertical divider wall (32) extending longitudinally between the ends of said housing for dividing the chamber contained therein into a pair of air gaps (48, 49); and (c) at least one first permanent magnet (42a) mounted within a first opening (38a) contained in said divider wall, the polar axis of said magnet being normal to said divider wall; (d) said load and reference coils being arranged in said air gaps on opposite sides of, and parallel with, said divider wall, respectively, whereby the direction of the magnetic flux extending through the lower portions of the coils is opposite to that of the flux extending through the upper portions of the coils.