Patent GB-657625-A (GB)
Title: Improvements relating to controlling the phase of electrical oscillation generators
Inventor: WHITE ERIC LAWRENCE CASLING
IPC: H04N5/04
Filed: 1948-04-01
Abstract: 657,625. Automatic frequency and phase control systems. ELECTRIC & MUSICAL INDUSTRIES, Ltd. April 1, 1948, No. 9186 [Class 38 (iv)] In a system for automatically maintaining constant the phase of an alternator, the power output of the driving means is controlled transiently in proportion to alternator output current to minimize transient phase deviation upon variation in load. In a system for maintaining the frequency and phase of an alternator 1, driven by a prime mover 2 and supplying a load 42, equal to that of a reference source 16, a comparison is made through transformers 14, 15 in a phase discriminator circuit which also includes rectifiers 17, 18 and produces across resistances 19, 20 a D.C. voltage which is a sinusoidal function of the phase difference. This voltage is amplified by a triode 23, having negative feed-back through resistance 31, and applied, together with first and second differential stabilizing components developed in networks including condensers 24, 34 respectively, to a push-pull valve amplifier 12 controlling the split field winding 11 of a reversible D.C. servomotor 8 connecting throttle 4 of the prime mover through a cam 6, shaped to give a linear relation between angular setting of the servomotor and prime mover torque. The armature of the servomotor is supplied from a D.C. source through a resistance 10. A potentiometer 35 associated with a D.C. source and a D.C. generator 37 are driven by the servomotor and produce signals dependent on angular position and speed of the servomotor which are applied to the input of amplifier 12 through a condenser 39 so that transient feed-back occurs upon movement of the servomotor to provide temporary opposition to change in speed of the prime mover. The output of a a rectifier 44 supplied from a current transformer 43 associated with the output of the alternator provides a signal which is also applied to the input of amplifier 12 through condenser 39 so that a transient feed-back also occurs upon a change of load to oppose change in speed of the prime mover. There is also provided a frequency discriminator including valves 49, 56 to correct the frequency of the alternator during starting. These two valves are associated with counting circuits of the type described in Specification 471,731, [Group XXXVI], which produce, across condensers 51, 58, D.C. voltages, dependent on the frequency of the reference source and the alternator respectively, which charge in opposite directions a condenser 68, the resultant voltage across which, being representative of the difference frequency, is also applied to amplifier 12 in the appropriate sense to effect frequency correction. A relay or electronic switch 70 may disconnect the phase discriminator from amplifier 12 when the frequency difference exceeds a predetermined value. In a modification, Fig. 3 (not shown), potentiometer 35 is dispensed with and the component dependent on the angular position of the servomotor derived from the output of tachometer generator 37 by a triode valve integrating circuit. Specification 657,626 is referred to in the Provisional Specification.