Patent GB-576117-A (GB)
Title: Improvements in and relating to electric remote control systems
IPC: G05D3/12
Filed: 1940-10-03
Abstract: 576,117. Remote-control systems. BRITISH THOMSON-HOUSTON CO., Ltd., WHITELEY, A. L., and LUDBROOK, L. C. Oct. 3, 1940, Nos. 14847/40 and 9603/41. [Class 40 (i)] In a selsyn system in which an error-voltage controls the field current of a Ward-Leonard generator, as described, for example, in Specification 527,768, hunting is prevented by combining the error-voltage with a voltage obtained from the Ward-Leonard generator, when its output changes, in the input circuit of an amplifying valve, the A.C. output of which is converted into a direct current of which the polarity and magnitude correspond, for small errors, to the phase and amplitude of the combined error and anti-hunting voltages, and using this current to excite the generator field. A further voltage, varying with the speed of the controlling selsyn, may be combined with the error-voltage to minimize lag or to produce a small lead in the response of the controlled apparatus. This voltage may be produced by a mechanical displacement of the transmitter stator. Specification 430,014 also is referred to. Detailed operation. In the arrangement shown in Fig. 1 (Comp.), the receiver rotor 1 is fed from the A.C. supply and the error voltage developed in the transmitter rotor is limited by a potential divider 4, 25, which includes a non- linear resistance of the kind described in Specification 292,110, [Class 37], or a diode valve, and fed in series with an anti-hunting voltage developed across a resistance 24, to the grid of a valve 3. The output of the valve is converted, with the aid of two rectifier bridges operating as described in Specification 527,768, to a suitable direct current for energizing the field of the Ward-Leonard generator 11. The output circuit of the latter is connected to a resistance-condenser combination 21, the charge or discharge current of which when the generator output is increasing or decreasing varies the condition of a bridge of saturable reactors and so causes A.C. of suitable phase and magnitude to be applied across the resistance 24. The initial phase of this current is determined by transformers 22. 23. The bridge reactors may have separate biassing windings or the bridge may be replaced by a pair of valves as shown in Fig. 4 (14847/40), with the supply connected to their inner grids and the control circuit from the Ward-Leonard generator to their outer grids. The resistancecondenser combination may have the condenser shunted by a resistance or may be replaced by an inductance and resistance in series. In this case the anti-hunting voltage has a component depending on the output as well as the rate of change of output of the generator. In a modification, Fig. 1, (9603/41), the anti-hunting voltage is given a component proportional to the speed of the transmitting selsyn. This is derived from a generator G, fed from the same A.C. supply as the selsyns, to make the arrangement independent of variations in the supply voltage, and geared to the transmitter, with the aid of a bridge of metal rectifiers and is adjusted by means of a potentiometer R to reduce the lag in response of the controlled element or to produce a slight lead. In an alternative arrangement with the same object, the transmitter stator is displaced against a spring by an amount proportional to the rotor speed with the aid of a magnet and copper disc. The magnet is preferably energized from the same source as the selsyns to compensate for variations in the supply voltage. Coarse and fine selsyns may be provided, one being brought into action and the other cut out when the error exceeds a given amount bv the operation of a relay. If the valve V is a high impedance pentode, the anti-hunting action is improved since when the transmitter is accelerating a higher output voltage is produced than that corresponding to the momentary displacement. The error voltage may be obtained from the receiver instead of the transmitter and the functions of rotor and stator may be interchanged.