Patent GB-843687-A (GB)
Title: Improvements in apparatus for automatically controlling the weight of a batch of material
Inventor: THORSSON MATHEW THEODORE WESLE
IPC: G01G19/30
Filed: 1956-09-21
Abstract: 843,687. Batch weighing. FAIRBANKS, MORSE & CO. Sept. 21, 1956, No. 28927/56. Class 40 (1). A batch-weighing device comprises means for producing a voltage proportional to the weight of material delivered to a hopper, means for setting up an adjustable comparison voltage and means for stopping the delivery when the voltages are in a predetermined relationship. Preferably arrangements are made whereby the hopper is filled rapidly initially and slowly during the final stages. The device may be adapted for feeding several ingredients to the hopper in turn. Circuit details, Fig. 4. As shown, the weight of the hopper and its contents act on a group of strain gauges 12 the output voltage from which is combined with a counterphase voltage from a network 18 for compensating for the weight of the hopper itself, an in-phase voltage from a " dribble " network corresponding to the weight which is to be supplied at a slow rate and a counter-phase voltage from a selected one of a number of networks each of which corresponds to the weight at which the supply of individual ingredients is to be terminated. On the operation of a starting switch 94, relay 172 pulls up and locks and if or when network 18 has been properly adjusted to represent the unladen weight of the hopper, no resultant voltage reaches relay 26 and contacts 80 are closed. In this condition relay 268 pulls up, locks and energizes a selector switch motor 258. The latter drives the switch one step and unlocks 268. In position 1 magnet 234 operates a valve to admit the first ingredient rapidly and the voltage from the corresponding network 198 is connected in the control circuit. When balance is reached again, the switch is moved another step and the first valve is closed. In the new position 244 opens a valve admitting the same ingredient slowly and the voltage from network 158 corresponding to the amount to be fed at a slow rate is short-circuited. When balance is again achieved, the switch moves on and the next ingredient is added in two stages in a similar way. When all the ingredients have been added, the switch is driven to its zero position and relay 276 is operated to unlock 172 and restore the circuit to normal. A further valve is operated to discharge the hopper by a magnet 108. Simpler systems involving only one ingredient are described. Safety arrangements. After the operation of main switch 88, contacts 92 are kept open by apparatus 114 for a time sufficient for the amplifier to warm up. To protect the load cell against overload a circuit 280 is provided involving a number of adjustable resistors ganged to those of circuits 198 . . . 206 and connected to form a bridge with an adjustable resistor 288 and fixed resistors 286 . . . 292. As the voltages of circuits 198 . . . 206 are increased, the output of the bridge is reduced and when the predetermined limit is reached a thyratron 282 which has been paralysed by the bridge output becomes conducting and its anode relay 318 disconnects the power supply from the system.