811,461. Fluid-pressure servomotor control systems. B.-I.-F. INDUSTRIES Inc. May 7, 1956, No. 14057/56. Class 135. [Also in Group XXXVIII] Apparatus for weighing fluid material continuously comprises two hoppers which are filled alternately, the rate at which the one hopper is being filled controlling the rate at which the other hopper is being emptied, the change-over occurring when the weight of the filling hopper reaches a predetermined value. Electrical embodiments.- Material is supplied via a conveyer duct 14 (Fig. 1) alternately to hopper 10 or 12 as determined by a gate 16 operated by a solenoidcontrolled air pressure valve 18, while the other hopper is emptied by a rotating valve 20, 22. The hoppers are supported at 27, 29 on weighing beams 28, 30 attached via rods 36, 38 to scale beams 40, 42 each carrying a lead screw 48, 50, along which counterpoise weights 52, 54 are driven in opposite directions by a reversible motor 66 through shaft 64 and gears. The motor is reversed by switches 88, 90 operated by counterpoise 52 at the ends of its travel. As shown, hopper 10 is being filled, so that counterpoise 52 has operated switch 88, simultaneously opening switch 90, thereby operating gate 16 by energizing coil 18b of valve 18, and energizing coil 112 to draw shaft 76 down and prepare switch 74, reversing the feed to motor 66, switch 86, releasing valve 20 and preparing valve 22 for emptying hopper 12, and switch 128 which responds to the balance condition of beams 40, 42. As hopper 10 is filled, beam 40 tilts to close switch 96, causing energization of motor 66 whereby counterpoise 52 rebalances beam 40, whilst counterpoise 54 unbalances beam 42, closing switch 102 and energizing valve 22 to empty hopper 12. Thus the rates of emptying and filling are correlated by the intermittent action of motor 66 and valve 22, until counterpoise 52 operates switch 90 and the filling and emptying functions are reversed. The total weight of material passing through the apparatus is registered by a counter 150 which is given one impulse for each revolution of shaft 64. In a modification (Fig. 2, not shown), the control switches 90, 102 are replaced by fluid pressure switches, and the counterpoises are driven by a continuously running motor through a reversible clutch. In another electrical embodiment (Fig. 3) the weight of each hopper 410, 412 and its contents is determined by a strain gauge resistor 504, 506 forming one arm of a bridge 500, 502, having two fixed resistor arms, and a fourth arm constituted by a potentiometer 455, 455<SP>1</SP> whose slider 457, 457<SP>1</SP> is driven by a motor 466 through speed controller 453 and reversible clutch 467. As shown, the rate of feed. to hopper 410 determines the unbalance current of bridge 500, which is fed to controller 453 to adjust the speed of motor 466. This motor also controls the unbalance current of bridge 502 via potentiometer 455, and is used to control the rate of emptying hopper 412 at valve 422. Limit switches 488, 490 at the ends of travel of potentiometer slider 455<SP>1</SP> reverse the filling and emptying operations, and switch the bridges 500, 502 to the appropriate hoppers. Pneumatic embodiment (Fig. 4). As shown, material is supplied via a conveyer duct 614 alternately to two hoppers 610, 612 as determined by a gate 616 operated by a solenoidcontrolled air valve 618 associated with an air cylinder 617, which also controls a gate 621, whereby the hoppers are alternately emptied at a rate determined by a control valve 620. The weight of the hoppers 610, 612 with their contents is determined by pneumatic transducers 628, 630 whereby proportionate pressures are fed to pressure gauges 640, 642, the pointers 657, 657<SP>1</SP> indicating on the appropriate annular scale the weight in the hoppers. Associated with the pointers are air nozzles 714, 714<SP>1</SP> and the relative position of each nozzle and its pointer determines the pressure in the feed pipes 715, 715<SP>1</SP> to controllers 641, 643. The nozzles 714, 714<SP>1</SP> are mounted on discs 709, 711, which are rotated in opposite directions by a motor 666 operating through a speed controller 653 and a reversible clutch 667. The apparatus operates cyclically over a range determined by limit switches 688, 690, any change in the speed of delivery of material being sensed by the nozzles and operating through pneumatic controllers 641, 643 to control the rate of emptying the hoppers via valve 620.