GB424075A - Improvements in or relating to controlling systems for electrically operated lifts - Google Patents

Abstract

424,075. Control of D.C. motors. GENERAL ELECTRIC CO., Ltd., Magnet House, Kingsway, London, and CHUBB, A. A., c /o General Electric Co., Stoke, Coventry. Oct. 12, 1933, No. 28163. [Class 38 (iii)] In a control system for an electrically operated lift, comprising a Ward-Leonard motor generator set in which the field current of the generator is controlled by a triode VA, the generator H is so connected to the grid circuit of the triode that a change in generator terminal voltage, after a predetermined value has been reached, causes a change in the anode current of the triode tending to restore the generator voltage to the predetermined value. In the arrangement shown, the triode VA is supplied with anode potential and grid bias from a transformer MT, and control potentials are applied to the grid from apparatus of the kind described in Specification 423,805. The anode circuit is connected through reversing contacts r1, r2 to the field coil FC of a generator G, which is rotated at constant speed by a motor M and supplies current to the field coil FD of the generator H. A second triode VB also receives anode and grid bias potentials from the transformer MT, the grid bias being of opposite phase to that applied to the triode VA. The grid circuit of the triode VB also includes reversing contacts r3, r4, and a section of a potentiometer D connected across the terminals of the generator H. The anode circuit of the triode VB includes a contact p1 of a voltage relay P, a contact e1 controlled by a relay which operates to initiate retardation, and a transformer J in the grid circuit of the triode VA. When the voltage of the generator H reaches the value at which the relay P operates, the grid circuit of the triode VB is connected to the potentiometer D, and any subsequent variations in the generator voltage, which may be due to variations in the load of the lift, vary the anode current of the triode VB which in turn influences the grid potential of the triode VA and varies the excitation of the generator in a manner tending to restore the voltage to the desired value. Specification 423,806 also is referred to.