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595,141. Automatic control systems. ELECTRIC CONSTRUCTION CO., Ltd., and MILNE, J. C. Nov. 28, 1944, No. 23743. [Class 38 (iv)] Voltage; speed.-In an electronic field regulator for controlling the output of an electric generator or the speed of a D.C. motor, a potential which is a function of the generator output or motor speed is applied to the grid of a gas-discharge valve and operates to vary the ratio of conduction time to non-conduction time of the valve, thereby regulating the anode current which flows through the field of the generator or an exciter therefor, or the field of the D.C. motor. A flat, rising or partly compounded characteristic may be obtained with variations in the load of an alternator. In one example, Fig. 1, a potentiometer 4 is connected across the output circuit of an alternator 14, and a proportion of the voltage across the potentiometer is rectified through a half-wave rectifier 5 and applied across a condenser 6 and resistance 3 connected in parallel, a connection being taken to the control grid of a gas-discharge valve 1 and tending to hold that member biassed negatively. A resistance 2 connected between the resistance 3 and the cathode of the valve 1 has applied across it a constant D.C. potential in opposition to the potential across resistance 3. The anode of the valve 1 is connected through the secondary winding 7 of a transformer to the main field 10 of an exciter 11, which has a smaller winding 12 connected to a constant D.C. source and acting in opposition to the winding 10. The primary winding 8 of the transformer is connected across an A.C. main circuit, and a reservoir condenser 9 is connected across the secondary winding 7 and the cathode of the valve 1. A rise in generator voltage renders the grid of valve 1 more negative, thereby reducing the cyclic period of conduction of the valve and correspondingly reducing the exciter field 10 and the voltage of alternator 14 until stability is attained. In a modification, Fig. 3 (not shown), the regulator is arranged to give either a falling or rising output characteristic with increase in alternator load by applying to the grid of the discharge tube a control potential of a valve which is a fuction both of the alternator voltage and load current, this being obtained by rectifying the resultant of a tapped part of the output voltage and the secondary voltage of a current transformer which is connected either in phase or phase opposition therewith, the former giving a falling characteristic and the latter a rising characteristic with increased load.
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