GB1227742A - - Google Patents

Abstract

1,227,742. Weighing electrically and photoelectrically. A.R.V. ROBERTS. May 24, 1968, [March 1, 1967], No.9586/67. Headings G1A and G1N. [Also in Division H1] A force balance comprises a panel movable across a magnetic field, electric conductors arranged on a surface parallel to or concentric with the panel and extending through the field, means for applying a force to be measured to the panel and means for passing an electric current through the conductors so as to exert on the panel an electromagnetic force balancing the force to be measured. A weighing machine comprises a flat electrically insulated plate 10 mounted on a pivot disc 13 supported by conductive ligaments 16, 17. The ends 11, 12 of plate 10 have printed on them rectangular spiral conductors 25, 26 electrically connected in series between the ligaments 16, 17. When the weights in scale pans attached at 38 are unequal, the photo-cells 42 are unequally illuminated and the cell outputs vary the current flowing through the coils 25, 26 until the force produced by co-operation with magnets 35 balances the inequality of weights. A plurality of coils may be printed on top of each other with insulation between, or on opposite sides of the plate 10, and the plate may carry a conductive coating for eddy-current damping. In a modification, Fig. 2, (not shown) the weighing machine comprises a rectangular disc with a coil printed on it suspended vertically from four ligaments which permit vertical movement. The disc has a scale pan on top and its position is sensed by two photo-cells co-operating with a lamp through a slot in the disc. The panel may be in the form of a cylinder. The invention may be applied to the measurement of ferromagnetic, paramagnetic, diamagnetic electrostatic or surface tension forces or forces due to pressure or bombardment of particles in vacuum evaporation. The position of the plate 10 may be sensed capacitively instead of photo-electrically.