Patent GB-1309552-A (GB)
Title: Synchro systems
IPC: G08C19/48
Filed: 1969-05-23
Abstract: 1309552 Synchro systems SMITHS INDUSTRIES LTD 22 May 1970 [23 May 1969] 26468/69 Heading G1N In a synchro system comprising single phase rotor windings 3, 18 fed from an A.C. source 4 and associated with inter-connected three phase windings in the transmitter TX and receiver TR respectively, and where under conditions of correspondence between the rotors the voltages induced in stater windings 6, 7, 8, counterbalance those induced in windings 12, 13, 14 so that no stater current flows but where under imbalance, the stater and rotor fields provide flux to restore correspondence, and additional winding 22 is provided in the receiver rotor to enhance the torque available to restore correspondence. When correspondence does not exist currents flowing in the windings 12, 13, 14 create a flux causing a voltage to be induced in the winding 22. This voltage is sampled in a control unit 23, which if the voltage is above a threshold value, causes the winding 22 (or some further winding) to be energized transitorily to exert the addition torque, the steps of sampling and energization being repeated until correspondence is effected. One form of control unit 23 is shown in Fig. 2, and comprises an astable trigger 24 whose output waveform is supplied to a gate 26 and a monostable circuit 25. During a first half-cycle of the waveform the gate 26 is opened to pass the induced signal from winding 22 to a demodulator gate 28. This is controlled via a buffer amplifier 29 to be open during alternate half-cycles of the source 4, so that the signal from 22 charges a capacitor 30 to a value dependent in magnitude and sense on the deviation from correspondence between the rotors. This voltage is sampled during the second half-cycles of the waveform from trigger 24 by the circuit 25 operating on a gate 31. The signal therefrom is supplied to a modulator gate 32 which is opened during alternate half-cycles of the supply 4 and whose output (a measure of the deviation) is fed to a high gain amplifier 33. Should the signal exceed the threshold value of this amplifier a power amplifier 34 is caused to energize transitorily the winding 22. Should an extended interval between sampling and energization be unnecessary the gate 31 may be controlled directly from trigger 24, circuit 25 being omitted. A modification Fig. 3, (not shown) provides an arrangement wherein monitoring of the winding 22 is effected during one half-cycle of the source 4 and energization thereof during the subsequent half-cycle. In a further modification Fig. 4 (not shown), concurrent sampling and energization of the winding 22 is disclosed. This is effected by arranging for the energization supply to be 90 degrees phase displaced from the sampled signal, and by making the gating circuitry non-responsive to the quadrature signal. Further modifications suggest that discrimination between sampled and energization signals may be based on frequency rather than phase. Means are also disclosed Fig. 5 (not shown) to avoid rotor displacements which are 180 degrees out of correspondence. A control unit 23 may be shared between two or more synchro systems.