Patent GB-644871-A (GB)
Title: Improvements in and relating to electric regulators
IPC: H03B9/10
Filed: 1947-07-28
Abstract: 644,871. Automatic temperature and voltage control. BRITISH THOMSON-HOUSTON CO., Ltd. July 28, 1947, No. 20316. Convention date, July 29, 1946. [Class 38 (iv)] In order to regulate a temperature variable impedance, for the purpose of maintaining a constant voltage supply, or, in the case of a temperature variable impedance subject to external temperature conditions, maintaining its temperature constant, a voltage inversely proportional to the impedance is compared with a reference voltage, the difference voltage being amplified and applied to a control element which varies the supply to the impedance in such a manner as to restore its temperature to that corresponding to its desired resistance value, thereby maintaining constant either the voltage supply or the temperature of the impedance. As shown in Fig. 1, the variable impedance, the temperature of which is to be maintained constant, comprises a cathode 4, subject to back-heating effects, of a magnetron 1, energized through a transformer 9 from a source 8. Across a low resistance 12 is connected a step-up transformer 14 which develops a voltage E across the secondary 15 which varies inversely with the resistance, and therefore with the temperature of the cathode 4. Under normal conditions the voltage e is equal to a voltage t, with which it is compared, developed across the points a and b, but during deviation, a control voltage e<SP>1</SP>, where e<SP>1</SP>=e-E, is obtained, which is amplified by an amplifier 18 and applied to a control element 17 which alters the supply voltage, thereby altering the power input to the cathode 4 and restoring its temperature to normal. As shown in Fig. 3, the voltages e and E are obtained as D.C. voltages by rectification in diodes 19 and 22 and are applied to a voltage divider 28, the control voltage e<SP>1</SP> being developed across a condenser 27, and applied to the grid of an amplifying pentode 33, the power supply for which is obtained through a rectifier circuit 40, 41. The control voltage e<SP>1</SP>, the magnitude and size of which depend upon the magnitude and sense of the temperature deviation from normal. of the cathode 4 causes more or less anode current to flow so as to operate relays 46 and 47 in such a manner that under normal conditions a reversible motor 62 remains stationary but at other times either one of the fields 63 and 64 is energized, causing the motor to. rotate in a sense to operate an auto-transformer 68 to alter the supply voltage and restore the tem-. perature of the cathode to normal. A generator 44 geared to the motor 62 provides a potential on the grid of the amplifier valve 33 opposing that of the voltage e<SP>1</SP> in order to prevent hunting. In a modification (Fig. 4, not shown), the voltage E is derived from the primary of the transformer 9. In order to maintain a constant voltage supply to a load 77, Fig. 5, a dummy load 78 comprising a temperature variable resistance is connected in series with a low resistance 79 across the supply. A voltage e<SP>1</SP> dependent upon the temperature of the load 78 is obtained as in the previous embodiments, and restores the voltage supply to normal through the control element 17.