Patent GB-617918-A (GB)
Title: Improvements in or relating to automatic control circuits
IPC: G05D3/12
Filed: 1946-06-28
Abstract: 617,918. Electric control systems. SUBMARINE SIGNAL CO. June 28, 1946, No. 19351. Convention date, Nov. 20, 1943. [Class 40 (i)] [Also in Group XXXVII] In a positional control system the operation of a D.C. servomotor driving an object in accordance with the movement of a controlling member is controlled by a Thyratron type valve operated through an A.C. source, the cathodegrid circuit of the valve being associated with a number of series-connected resistors whereby grid bias. voltage components are derived respectively from the back E.M.F. of the motor, the signal potential, and a constant pulse voltage, the latter being obtained by shunting at least one of the resistances by a condenser charged periodically from the A.C. source through a rectifier. Follow-up devices are provided, and a smooth transition from forward to reverse rotation of the motor is obtained by a reversal of the armature current before the direction of rotation is changed. The armature 1 is connected through reduction gearing 3 to the load 4, such as a radiolocator, submarine signal ranging head, gun turret, &c., which is also connected to.drive the rotor 6 of a selsyn 5 associated in the usual manner with a selsyn 8 provided with a rotor 9 which is positioned by a manual control 11. The system may be associated with a gyro compass through another selsyn unit 12, so that the control signal provided by the rotor 9 will be the resultant component of the three selsyn units 5, 8 and 12. The signal voltage across the rotor 9 is applied to the common grid 16, 17 of a double triode rectifier 18, with anodes 19, 20 connected to the split secondary winding of a transformer 21 and 180 degrees out of phase, the respective anode circuits comprising resistances 23, 24 with their common point earthed and their outer extremities connected to the grids 27, 28 of a pair of triode rectifiers 25, 26. A D.C. source 29 provides anode voltage for the triodes 25, 26 over resistances 36, 35 and these anodes are connected over resistances 58, 71 and 57, 70 to the grids of the Thyratrons 42, 41 respectively. The anodes of the Thyratrons are connected to the secondary windings 60, 61 of a transformer and are phase displaced by 180 degrees, the motor armature 1 being included in the anode-cathode circuit of each Thyratron. The motor field winding 2 is energized by a D.C. source 46 across which is connected a resistance 45 in series with a potentiometer 44 whereby a small negative bias can be applied to the grids of the Thyratrons. Negative grid pulses are also supplied by way of condenser discharge circuits 52, 51 comprising condensers 73, 72 shunting the resistances 58, 57 and connected across transformer secondary windings 56, 55 through rectifiers 54, 53 respectively, these secondary windings being of the same phase as windings 61, 60. Rotation of the armature in a forward direction is obtained when Thyratron 42 is operative due to a resultant positive potential on its grid 40, this being obtained when point B<SP>1</SP> is positive to C\ which occurs when B is positive relative to C due to triode 25 being non-conductive and triode 26 conductive. Triode 25 is non-conductive when its grid is negative due to current flowing in the direction of arrow F in resistance 23, this taking place when the anode-cathode path 19, 15 of valve 18 is conductive. U.S.A. Specifications 2,147,674 and 2,264,333 are referred to.