Patent GB-394444-A (GB)
Title: Improvements in or relating to speed regulators for electric motors
IPC: H02P5/48
Filed: 1932-03-11
Abstract: 394,444. Maintaining proportional speeds of motors. IGRANIC ELECTRIC CO., Ltd., 147, Queen Victoria Street, London.-(Assignees of Stansbury, C. ; Wauwatosa, and Brown, G. C. ; West Milwaukee, both in Wisconsin, U.S.A.) March 11, 1932, No. 7309. Convention date, March 12, 1931. [Class 38 (iii).] The speed of a motor 4, Fig. 1, is maintained at a desired value in relation to that of a standard motor 1, by means of a control system comprising a gaseous discharge tube 7, the discharge through which is intermittently stopped by temporarily reducing the potential of its anode 7b, and is restarted after an interval determined by the subsequent duration of a potential impressed on its grid 7c, the ratio of duration of the discharging and non-discharging periods varying with variations in the phase relation of two commutators 22, 22a, driven respectively by the controlled and standard speed motors, and determining the operation of controlling means for the controlled motor. When lines L1 .. L4 are energized, a discharge tube 8 discharges before the tube 7, on account of the inductive lag of the field 5 of the motor 4, and by means of a condenser 35 interconnecting the plates of the tubes 7, 8, prevents discharge through the tube 7 until the discharge through the tube 8 attains a steady value. When the tube 7 discharges, the plate and grid potentials of the tube 8 are affected through condensers 35, 36, to stop its discharge, until charges on condensers 35, 36 have leaked off through resistances 11, 12<1>, respectively, whereupon the tube 8 again discharges and acts through condensers 35, 37, in the same way as tube 7 acted through condensers 35, 36, to stop the tube 7: Thus a resistance 6 in series with the field 5 of the motor 4 is alternately cut in and out of circuit, and the field attains an average value depending upon the relative time intervals during which the tubes 7, 8 are alternately conducting. When the speeds of the motors 1, 4 are approximately the same, a switch 34 is closed, and the first time commutators 16, 19, driven by the motors 4, 1, respectively, are in phase the negative grid potential of a discharge tube 9, due to a battery 14, is removed, and the tube discharges to energize a relay 10, which connects potentiometer resistances 24 .. 27 and 29 .. 32 in the discharge circuits of the condensers 36, 37. ' These potentiometer resistances are acted on by the commutators 22, 22a, driven by the motors 4, 1, and if the desired speed relationship does not exist the rates of discharge of condensers 36, 37 and, therefore, the relative times of discharge of the tubes 7, 8, are varied in accordance with the magnitude and direction of a potential which appears between conducting rings 23, 28, to produce the necessary correction on the field of the motor 4. Instead of using the voltage across the conducting rings 23, 28, to detect deviations from the desired speed conditions, the voltage across a Wheatstone bridge may be used, the commutators driven by the motors 1, 4 varying resistances in the bridge arms. In a modification, Fig. 5 (not shown), the plate potential of a discharge tube connected across the resistance 6 is temporarily reduced by a commutator driven by the standard motor, and its grid potential is affected by a commutator driven by the controlled motor. In the arrangement shown in Fig. 6, the standard motor 1 drives a coil 212 cooperating with two coils 215, 216, driven by the motor 4. The coils 215, 216, which have a common connection with a point between the field 5 of the motor 4 and its controlling resistance 6, are connected to the grids of discharge tubes 206, 207, the plates of which are energized from the ends of a centre-tapped secondary 202, 203, of a transformer 200 supplied from an A.C. source. The coil 212 driven by the standard motor is energized from a secondary 204 on this transformer. The intervals during which the tubes 206, 207 are conducting are thus determined by the phase relation of the coils 212, 215, 216, and the instant at which the grid potentials of the tubes 206, 207 allow discharge vary with variations in speed of the motor 4 from its desired relation with that of the motor 1. A modification of the arrangement shown in Fig. 6, in which the coils 215, 216 are separate, and are connected to auxiliarv anodes and to the grids of the tubes 206, 207, and in which the grid potential of each tube prevents discharge for a time, depending upon the rate at which charges leak from condensers, is described with reference to Figs. 8 and 9 (not shown).