Patent GB-421707-A (GB)
Title: Improvements in or relating to weighing apparatus
IPC: G01G13/285
Filed: 1934-04-06
Abstract: 421,707. Automatic-feed weighers. BLAW KNOX, Ltd., New Oxford House, Hart Street, Holborn, London. April 6, 1934, No. 10521. Convention date, March 29. [Class 143] An apparatus for automatically weighing out predetermined batches of different kinds of material for example crushed stone gravel and sand for cement, comprises means responsive to the weight of material in the weigh hopper for closing the feed hopper gate and subsequently repeatedly opening and closing the gate to a slight extent before final closure. The system is placed in readiness for a weighing operation by closing a circuit breaker connected to phase conductors thereby establishing a circuit through a relay. This circuit cannot however be closed unless the discharge gate 24 of the weigh hopper 14 is closed. The operator now initiates the first weighing operation by turning and pushing-in a selector knob to close selectively a predetermined set of contacts. This closure operates a further relay and energizes beam-lifting magnets 41, 42 so as to remove the influence of two beams 36, 37 from the weighing system; a lock-out magnet at the same time locks the selector knob, and a contactor is operated through a further relay to connect up a motor which then moves the feed gate of the first supply hopper 12<a> to the open position. On reaching the full open position a cam on the feed gate operates a limit switch thereby operating the circuit of the contactor and stopping the motor. When the main charge of material has entered the weigh hopper the scale beam 35 dips a contact finger 39b into a mercury cup and by means of a second contactor interlocked with the first-mentioned contactor starts the motor rotating in the reverse direction to close the feed gate the limit of the closing movement opening a contact to stop the motor. A relay is simultaneously de-energized and the original circuit for the first contactor is thereby restored so as again to start the motor and open the feed gate. After a small movement an adjustable pin on the feed gate operates two contacts controlling the reversal of the contactor and the motor is again reversed to close the feed gate after which the action is repeated to produce small back and forth movements of the gate during the dribble feed. When the weigh hopper has descended sufficiently, a finger 39<a> is withdrawn from a mercury cup resulting in a final closure of the feed gate and the unlocking of the selector knob. If an excess of material enters the weigh hopper a third contact finger 39<c> dips into a mercury cup and completes the circuit of the lock-out magnet to prevent the operator from moving the selector switch until the contact finger has been withdrawn from the mercury by removing the excess material from the weigh hopper. The weighing of the first ingredient is thus completed. In order to add the second ingredient the operator rotates the selector to a second predetermined setting thereby adding the loading effect of the beam 36 to the weighing system, bringing the mercury contacts to the original position and coupling the feed motor of the second supply hopper 12b to the system of relays and contactors referred to above. The second weighing operation then proceeds in the same manner as the first. Similarly the third ingredient is added from the supply hopper 12<c> after a third setting of the selector, the third weighbeam 37 being operative ; if the operator in error sets the selector to the first position instead of the third the operation of the relays causes the scale beams 36, 37 to be removed from action and the system to be locked against further operation until the mercury contact mechanism is manually re-set. If the selector is improperly set for the first weighing operation the relays prevent the opening of the feed gate. On completion of the charge the discharge gate of the weigh hopper is released by advancing the selector to its fourth position, the selector being locked by its lock-out magnet until the weigh hopper has completely discharged and its discharge gate again closed. The movements of the selector may be made automatic by means of automatic electric control mechanism. Specification 225,025, [Class 106 (v)], is referred to.