Patent GB-709102-A (GB)
Title: Improvements in or relating to automatic weighing apparatus
IPC: G01G7/06
Filed: 1950-04-13
Abstract: 709,102. Automatic feed weighers. THORPE, T. A. W. July 9, 1951 [April 13, 1950], No. 9081/50. Class 143 [Also in Group XL(c)] In an automatic feed weigher, dribble feed, cut off, dumping of the weighed charge and re-setting of the apparatus, are initiated cyclically by an electronic relay circuit on variation of the grid circuit impedance of an electronic valve by a device operable by a moving part of the weighing mechanism. In the preferred embodiment, this device comprises a variable capacitor V1, having a pair of fixed plates 31a, 31b, and a movable plate L connected to either the weighbeam or an indicator; but in a modification (not shown), it may comprise an apparatus in which self or mutual inductances are varied. In the preferred embodiment, material is fed through a vibrating hopper and a vibrating shoot (not shown) driven by vibrators VM3. VM5, to a weighing receptacle 8 which comprises a pair of spring-closed doors pivoted at 12 and carrying soft iron armatures 14 which, when magnets 9 are energized, are attracted thereto and so dump the charge into a shoot feeding a container. As shown, the' mains are connected through a switch S1 to a power pack SPS which feeds a high frequency oscillator HFO in circuit with the variable capacity V1. With the plate L in the position shown in full line. relays R1, R2 are unoperated, and, on closing a switch S2, the vibrators VM3, VM5 are energized over contacts R1a. R2a and material is fed to the receptacle 8. On the capacitor plate moving to an intermediate position M, due to the major part of the charge accumulating in the weigh pan, the voltage applied to the grid of control valve CV through rectifiers DR. MR, is high enough to permit sufficient anode current to flow through this valve to operate relay R1, whereupon contacts R1a open and a variable resistor VR is connected in series with the vibrators which then effect a dribble feed. When the charge reaches the predetermined weight, the capacitor plate moves to a position U and the potential of the grid of valve CV is further raised and consequently increases the anode current which in turn operates relay R2 so opening contacts R2a, to effect cut off, and closing contacts R2b. A capacitor LLC is thus connected to the H.T. supply through contacts R2b and a variable resistor VR1, and, after a time delay determined by the setting of this resistor, the potential applied to,the grid of valve ECV rises sufficiently to allow the anode current of this' valve to operate a relay R3, so closing a circuit through the magnets 9 over contacts R3a, and effecting dumping of the charge from the receptacle 8, and, simultaneously, through contacts R3b, connecting a variable resistor VR2 across the capacitor LLC which, after a time delay determined by the setting of this resistor, discharges and decreases the anode current of valve ECV so de-energizing relay R3 which then opens contacts R3a, R3b and allows the receptacle to close. The return movement of the capacitor plate de-energizes relays Rl, R2 and the cycle is repeated. Indicator lamps LRPL, HRPL, PLB, PLR and PLG are provided to show the condition of the circuit during the cycle of operations.