Weighing apparatus of the electromagnetic load compensation type including protective shield means

Claim 1

In a weighing apparatus of the electromagnet load compensation type including stationary pot-type permanent magnet means containing at one end an annular air gap which is open at one end; an annular compensation coil arranged asymmetrically relative to said permanent magnet means concentrically within the open end of said air gap; a movable pan carrier member connected for movement between normal no-load and load positions relative to said magnet means; means connecting said compensation coil with said pan carrier member; and means operable when the pan carrier member is displaced from said no-load position relative to said permanent magnet means for supplying compensation current to said compensation coil to return said pan carrier member to its no-load position; the improvement which comprises protective shield means connected with said permanent magnet means and extending in spaced relation completely across the open end of said air gap and the compensation coil contained therein for shielding said coil against the effects of stray magnetic flux and particles of impurities, said protective shield means being formed of a ferromagnetic material and being connected in flux transmitting relation with said permanent magnet means; and further wherein the axis of said permanent magnet means is arranged vertically, said permanent magnet means including spaced parallel horizontal upper cover and lower base plates, one of said plates containing said annular air gap; and further wherein said means connecting said compensation coil with said pan carrier member includes a dish-shaped coil carrier member having an annular flange portion which extends within the open end of said air gap and upon which said compensation coil is mounted, said coil carrier member being arranged in protected relation between said protective shield means and said permanent magnet means.