Patent GB-868823-A (GB)
Title: Improvements in automatic weighing means
Inventor: SETTLE ROBERT NICHOLL
IPC: G01G19/22
Filed: 1956-09-27
Abstract: 868,823. Measuring weight electrically. SIMON Ltd., HENRY, and RICHARDSON SEALE CO. Aug. 28, 1957 [Sept. 27. 1956], No. 29510/56. Class 40 (1). An automatic tare check adjustment means is combined with an automatic weighing machine, as claimed in Specification 779,356, wherein at an initial position of the rotary selector switch of the weighing machine, an electrical element is connected in substitution for the preset adjustable circuit of the weighing machine, which element is adjusted in its electrical characteristics by motor means until a condition of balance is achieved between the characteristics of the electrical element and the progressively changeable circuit controlled by the weigh bucket or scale pan so that the characteristics of the said element are then representative of the weight of the weigh bucket or scale pan with any adherent residue, thereafter during all subsequent stages of the weighing cycle said element in its adjusted condition being connected in series with the preset adjustable circuit of the weighing machine to provide a correction thereto corresponding to the tare weight of the weigh bucket or scale pan with any adherent residue. Potentiometer TB can be replaced by tare tolerance preset resistance TT or can be associated with one or more weighment determining preset control resistances CP1 . . ., CR1 . . . The sequence of operations is controlled by a step-by-step selector switch having four banks of contacts 1, 2, 3 and 4. Rotation of motor TM reduces that part of the resistance of potentiometer TB included in one leg of the bridge circuit until the total resistance in that leg, as determined by the position of contacts 2 and 3 of bank 2, balances the resistance of microtorque potentiometer P in another bridge leg (the variation in resistance of P being proportional to weight. Switch 02 now closes. When relay OA is energized Oa2 opens, so removing the short-circuit across tolerance resistance RO so increasing the resistance of the appropriate bridge leg by an amount within an acceptable negative margin of error. If the setting of potentiometer P is within this margin the bridge is unbalanced so amplifier N normalizes relay O. Relay OA remains energized and the closing of 03 completes a circuit through closed contact Oa3 to energize relay OB which is held energized via Ob1. Ob2 now closes to short-circuit tolerance resistances RO, RU, thus decreasing the resistance of the appropriate bridge by an amount within an acceptable positive margin of error. If the condition of potentiometer P is within this margin, amplifier N operates relay O, so causing 04, Ob3 to close and a circuit to extend through position 3 of bank 1 and interrupter contacts I, so energizing DM and causing contact 4 and subsequently by self-excitation contact 5 of bank 1 to be engaged, contact 5 being that associated with the first weighing operation. After the contacts of bank 4 have reached the fifth position the weighment cycle proceeds as in Specification 779,356 and Specification 839,626 until the weighments of all materials have been made, after which the selector switches of all banks step automatically to the 24th position. If the weighment residue is outside the tolerance limits the bridge condition causes amplifier N to operate relay O and to open O1, so holding the selector arm of bank 1 at the 25th position. In this latter case the fault indicating system indicates that cleaning is necessary. Means can be provided for applying automatic tare corrections to an associated weighing machine by arranging for rotational movements of the secondary shaft of motor TM to be transmitted by gearing to driving elements arranged to move the indicator scale with respect to the pointer.