GB1309200A - Scale having a restrained movable balancing member - Google Patents

Abstract

1309200 Weighing apparatus BROOKLINE INSTRUMENT CO 12 Nov 1971 [13 Nov 1970] 52745/71 Headings G1N, G1W A weighing scale comprises at least one hydraulic load cell 14 for receiving the weight W of a body to be weighed, connected to load cells 24 which apply a force proportional to the weight W on a balance beam 18, the displacement of the beam from an initial position being proportionately resisted, e.g. by springs 39 or an air jet (61) Fig. 8 (not shown), and being measured and displayed by read-out means which gives an indication representative of the weight W. In Figs.1, 2, the beam 18 pivots about a knife-edge fulcrum 22 and carries counter-poise weights 38 at one end. The force applied by load cells 24 via a knife-edge 29 is resisted by one or more springs 39, the number and moment arm of which may be changed to suit the load range required. Displacement of the beam from its initial position is sensed by a linear variable differential transformer 47 Fig. 5 (not shown) the A. C. output of which is demodulated in a control box 52 to provide a D.C. signal to a digital display voltmeter 53 and/or a meter 54 which are calibrated to read directly in weight units. The signal may also control a printer. A potentiometer 57 allows zero adjustment of the meters. Instead of the demodulator, a linear phase detector may be used. The circuit may include a thermister to correct the transformer output signal for temperature variations. A further alternative circuit uses a D.C. ammeter as a null instrument, with a first potentiometer for initial zeroing and a second, calibrated potentiometer to bring the reading back to zero under load. In Fig. 8 (not shown), displacement of the beam is resisted by an air jet (61), a control shutter being moved in response to signals from the transformer 47 to increase the jet velocity as the displacement increases. In Fig. 9 the fulcrum 22 is above the beam 18 and the load cells 19 below it. The beam tare weight is taken by springs 39 and 77, the springs 39 also serving to proportionately resist displacement of the beam under load. Stops 75 limit displacement of the beam.