Patent GB-852902-A (GB)
Title: Improvements in and relating to electrically operated hoist or winder equipment
Inventor: PEDLEY DAVID
IPC: B66B3/00
Filed: 1956-02-01
Abstract: 852,902. Electrical weighing. METROPOLITAN - VICKERS ELECTRICAL CO. Ltd. Jan. 18, 1957 [Feb. 1, 1956], No. 3211/56. Class 40 (1). [Also in Group XXXV] A load indicating or recording arrangement for an electrically-operated hoist or winder involves measuring the operating characteristies of the winding motor and applying the quantity so obtained, for a predetermined time or distance travelled by the hoist, to an indicator which gives an integrated reading over the time or distance interval. In the Figure the switch 52 is closed during the predetermined time or distance and thereby applies power to the various circuits via the contacts 12. The armature of the winding motor 1 is supplied at 2, 3 from a Ward-Leonard generator (not shown), and the operating voltage is applied via the transductor 18 to the voltage coil 13 of an A.C. integrating meter 4. The current coils of the meter 14, 15 are supplied via the transductor 22 from the resistor 27, the p.d. across which gives a measure of the current taken by the motor. The power so recorded is not exactly proportional to the load raised and has to be adjusted to compensate for copper losses in the motor, windage loss and frictional loss. The coil 24 is energized proportionally to the motor current and induces a similar current in the coils 29, 30 via the coupling coil 28. This system therefore produces a torque (in opposition to that from coils 13, 14, 15) proportional to the square of the motor current and hence to the copper losses. The speed of the motor is measured by the tacho-generator 44 which energizes the coil 38 in proportion to the speed; as in the previous case the opposing torque due to the coils 38, 48, 49 is proportional to the square of the speed and therefore to the windage losses. The frictional losses are approximately constant and the correcting torque for these is supplied by coils 32, 35, 36 energized by a transformer 33 which is preferably of the constant voltage type. Thus the reading on the indicator 8 (which may comprise dials or a printer) shows the load lifted by the motor corrected for the residual losses. The predetermined interval is preferably a distance equally spaced from the midway position of the hoist and so chosen that no acceleration or deceleration occurs; the effects of variable rope out-of-balance and variable speed are thereby eliminated. According to the Provisional Specification the voltages supplied by transformers 16 and 33 are stabilized by arranging auxiliary windings which can be switched in or out by relays to series aid the secondary voltage. The supply for the relay coils is taken from the phasewindings to which the primary is connected, the supply being rectified and applied to two parallel potentiometers. The outputs of the latter are connected via series neon tubes to the two relay coils, and the sliders are adjusted so that neither tube fires if the supply voltage is 10% below normal and one tube fires if the voltage is 5% below normal. Specification 630,980 is referred to.