GB987108A - A circuit arrangement for control purposes - Google Patents

Abstract

987,108. Control of motors. ELECTRIC CONSTRUCTION CO. Ltd. Feb. 26, 1962 [Feb. 24, 1961], No. 6882/61. Heading H2J. As a lift begins to accelerate on moving away from a floor, a switch 11 is actuated to charge capacitor 10. Actuation of a stop-button for a selected floor energizes a relay which is associated with a switch located on a model which copies the operation of the main lift, the said switch being positioned adjacent to a point corresponding to the selected floor and being closed when a movable member of the model reaches the switch. The movement of such member is synchronized with that of the lift-car. Closure of the switch causes change-over of switch 11 so that capacitor 10 discharges at a linear rate through pentodes 15. A signal derived from the capacitor is supplied to the grid of valve 25 which energizes relay 30 for continued acceleration of the lift. A second valve 26, whose grid is supplied from a tachometer generator driven by the lift, remains non-conducting until the increasing speed-responsive signal becomes equal to the decreasing signal from the capacitor 10. When the two signals are balanced, the current through common cathode resistor 28 switches from valve 25 to valve 26 and thereby de-energizes relay 30. This serves to initiate lift retardation to bring the lift to its levelling speed adjacent to the selected floor. Potentiometer 12 is adjusted to provide a voltage representing the normal full speed of the lift, whilst potentiometer 18 is adjusted so that the rate of discharge through pentodes 15 is comparable with the retardation rate of the lift. Potentiometer 37 permits adjustment of the magnitude of the speed-responsive signal. Two pentodes are provided for the sake of safety. For the same reason, valves 45, 46 are connected in parallel with the pair 25, 26.