GB848330A - Improvements in or relating to methods of and apparatus for dispensing predeterminedweights of material - Google Patents

Abstract

848,330. Electric control systems. UNILEVER Ltd. Oct. 4, 1957 [July 5, 1956], No. 20926/56. Class 40 (1). Apparatus for dispensing a predetermined weight of material comprises a weight-sensitive electrical element (e.g. a resistor strain gauge; a variable inductance) in a bridge circuit; when a first load unbalances the bridge, a first adiustable component thereof is automatically varied to restore balance, a calibrated component having a first setting; the unbalance caused by a second load is automatically corrected by operation of a second variable component, the calibrated component having a second setting; and the flow of material is subsequently controlled by means responsive to the bridge current. As shown, Fig. 1, when an empty container 2 is placed on a platform 1 supported by a load-carrying member to which is secured a multiple resistor strain gauge 3, comprising four strain gauges 17-20 (Fig. 2) connected in a modified Wheatstone bridge arrangement, a detector (not shown) energizes the bridge circuit and causes a switch 8 to connect the bridge output to a servo-system 9, which drives, via a clutch 10, the wiper of a calibrated potentiometer 7 to one end of its path, representing zero, and then drives a variable resistor 5, shunted across strain gauge 18, to rebalance the bridge. Switch 8 operates a motor 16 to rotate a cam 15 to suspend a standard weight 13 from the load-carrying member, the bridge signal thereby produced operating, via servo-system 9 and clutch 10 to drive the potentiometer wiper to the other end of its path, and then to restore balance by altering a variable resistor 6 which is shunted across the potentiometer. The standard weight 13 is lifted from its suspended position, and the bridge output is now fed to a flow controller system 11 which operates to dispense material into the container 2 until balance is restored, the weight of the dispensed material being between zero and the standard weight, depending on the pre-set position of the potentiometer slider. Conveyer mechanism (not shown) then replaces the filled container with an empty one. The range of the apparatus can be increased by moving the potentiometer slider over only a fraction of its path between the first and second balancing operations. The resistance of variable resistor 6 should be high relative to that of the potentiometer 7, so that the first balance condition is not substantially upset by the second balancing operation. The apparatus may be used to allow a predetermined weight of material to be dispensed from a container, which may form part of the load-carrying member.