Patent GB-846715-A (GB)
Title: Weighing systems
Inventor: THORSSON MATTHEW THEODORE WESL
IPC: G01G19/22
Filed: 1957-02-18
Abstract: 846,715. Programmed electrical batchweighing systems. FAIRBANKS, MORSE & CO. Feb. 18, 1957, No. 5423/57. Classes 38(6) and 40(1). Apparatus for weighing the constituents of a mixture in accordance with punched card information comprises a card reader which senses the holes in the card and selectively energizes a group of relays in accordance with contacts made through the holes, the relays controlling the overall value of a series-parallel combination of resistors, the P.D. across the combination being compared with a voltage derived from a strain gauge bridge measuring the weight of material being fed into a hopper, until they differ by a predetermined amount, when either the rate of feed is reduced, or feeding is cut off, the material in transit being sufficient to produce balance. As shown for a concrete mix of cement, aggregate and water, a card 26 (Fig. 3) is punched in a binary-decimal code with details of the required types of materials, weights of materials, and weight at which the feed is to be stopped or reduced. The card is inserted in a card reader, whereby relays 470 (Fig. 6) are selectively energized in accordance with the first entry on the card, i.e. cement Type 1, to select the appropriate type of cement by driving the screw-type conveyer 514 (Fig. 2) with fast motor 500, and cement is fed into hopper 34. The weight of the hopper plus content is indicated directly by a gauge 54, and also determined by a strain gauge bridge 478. Meanwhile the required weight of cement Type 1 has been noted by further relays 472, selected by the weight entry on the punched card, whose contacts adjust the value of a series-parallel combination of resistors 591, 593, 595, 599 (Fig. 9), and a voltage drop across this network is fed in opposition to a voltage derived from the strain gauge bridge 478. The difference voltage is corrected for the empty weight of the hopper by network 480, and opposed by a voltage from network 660 equivalent to the " dribble " value on the punched card 26. At balance, fast motor 500 is replaced by slow motor 502, the dribble weight voltage is removed from the measuring circuit, and balance is again obtained when the cement feed is stopped. An overload detector prevents the weighing process from continuing until the overload condition is corrected. A stepping mechanism is now energized to make a bank of switches, e.g. 580, 582, 588, 590,- move on one step to the next material to enter the hopper 34, and the process is repeated for cement Type 2. Simultaneously the appropriate mixture of aggregate is being collected in hopper 36, and water in hopper 32, when the correct quantities of materials have been collected in these hoppers, they are passed via a gathering hopper 38 to a mixer 40 or 42, with the water in a separate tank 46 for subsequent mixing if desired. An alarm circuit is included for ensuring that the card 26 is correctly inserted in its reader, utilizing a cut-away corner of the card. Relays are also associated with the gates of the hoppers to ensure they are all closed before the automatic sequence can start. Master switches are provided for transferring to manual control of the equipment if required. The weight of aggregate indicated by the punched card is the weight of dry material. Hence the weight as measured by the apparatus cannot be increased by a fraction dependent on the percentage moisture content, separately determined. The read-out relays determining the aggregate weight voltage in the balancing circuit is therefore duplicated, the voltage from the additional resistance network being fed across a potentiometer whose slider is set in accordance with the percentage moisture content. The voltage from this potentiometer is added to that determining the weight of aggregate required, and deducted from that determining the weight of water required. Specifications 846,716, 846,717, 846,718 and 846,719 are referred to.