US2545997A - Radio apparatus - Google Patents

Description

March 1951 R. H. HAGOPIAN RADIO APPARATUS Filed Dec. 7, 1948 V INVENTOR Richard H; Hugopion.

Patented Mar. 20, 1951 RADIO APPARATUS Richard H. Hagopian, Baltimore, Md., assignor to Westinghouse Electric Corporation, East Pittsburgh, Pa., a corporation of Pennsylvania Application December 7, 1948, Serial No. 64,013

18 Claims.

This invention relates to automatic voltage controls for radio ferquency generators, and relates more particularly to controls for maintaining constant the radio frequency voltages of generators having variable loads, such as those used in induction and dielectric heating systems.

In systems using radio frequency generators such, for example, as induction and dielectric heating systems, it is desirable to maintain a constant power density in the load regardless of changes in the projected area of the load. This is especially important in dielectric heating systems using conveyors where large load changes frequently occur.

Load changes cause changes in the radio frequency output voltages of the generators. If a generator has been adjusted to supply a predetermined power into its load, then if the load is reduced, the radio frequency voltage of the generator will increase. By maintaining the radio frequency voltage of a, generator constant, the power supplied to its load can be maintained constant.

Prior systems for maintaining the output voltages of radio frequency generators constant have used relays which were energized in one'direction upon increases in the radio frequency voltage of the generators to actuate contacts for closing circuits for decreasin the voltages, and which were energized in the opposite direction upon decreases in the radio frequency voltage to actuate contacts for closing circuits for increasing the voltages. Such system have had the disadvantages that control over a wide range could be accomplished only in steps, and that hunting sometimes occurred. 7

This invention provides a voltage stabilizer which is continuous in action over a wide range and in which relays are not used.

In one embodiment of this invention, radio frequency current from the output circuit of a generator is rectified and used to bias a thyratron tube which supplies a direct current, the average value of which varies with variations in the radio frequency voltage, to the armature winding of a reversible motor which adjusts the filament voltage of the oscillator tubes of the generator. Current from a constant voltage, direct current, supply source is applied in opposite polarity to the armature winding. Undesired decreases in the radio frequencyvoltage of the generator, caused by increases in its load, cause the thyratron tube to supply currents to the armature of the motor which are smaller than that supplied by the direct current source, causing the motor to be energized to rotate in a direction to increase the voltage supplied to the filaments of the oscillator tubes, and to thereby increase the radio frequency voltage of the generator. Undesired increases in the radio frequency voltage of the generator, caused by decreases in its load, cause the currents supplied by the thyratron tube to the armature of the motor to be larger than the current supplied by the direct current source, causing the motor to be energized to rotate in the opposite direction to decrease the voltage supplied to the filaments of the oscillator tubes, and to thereby decrease the radio frequency voltage.

An object of the invention is to maintain a constant voltage in the output circuit of a radio frequency generator.

Another object of the invention is to provide a voltage stabilizing system for a radio frequency generator which will operate over a wide range of voltages. v

Another object of the invention is to provide a voltage stabilizing system for a radio frequency generator which will operate without hunting.

The invention will now be described with reference to the drawing which is a circuit schematic illustrating one'embodiment of the invention.

The radio frequency generator, the output voltage of which is to be maintained constant, comprises the push-pull connected oscillator tubes 10 having their grids connected together through the inductor I I, the center point of which is connected through the resistor I2 to ground. The plates of the tubes are connected together by the tank inductor I 3, the center point of which is connected to the positive terminal of a conventional, plate voltage, supply source I4. The plates of the oscillator tubes are also connected to a load I5 which may be a dielectric heating load, an induction heating load, or any other form of load with which radio frequency generators are used.

The filaments of the oscillator tubes ID are connected together and to the secondary winding of the filament transformer I6. The primary windin of the transformer has one end connected to one end of the conventional autotransformer I1, and its other end connected to the slider I8 of the auto-transformer. The autotransformer is connected to a conventional alternating current source, and its slider I8 is arranged to be adjusted by the rotation of the armature I9 of the electric motor 20 for varying the voltage supplied to the filaments of the oscillator tubes.

The plate of one of the oscillator tubes In is connected through the series connected voltage dividing capacitors 2| and 22 to ground, the junction point of the capacitors being connected to the plate of the diode rectifier tube 23. The plate of the tube 23 is connected to one end of the radio frequency choke 24, the other end of which is connected to one. end of the resistor 25, and

the other end of which terminates in the contact 26. The slider 2'! of the resistor 25 is connected to the contact 28. The cathode of the tube 23 is connected through the resistor to ground.

The switch 36 which is adapted to contact either the contact 26 or 28; isconnected to "the:

cathode of the thyratron tube 3!, and'through the capacitor 32 to ground. The selenium rectifier 29 is shunted across the capacitor 32- The plate of the tube 3i is connected tothe slider 33 of the resistor 34, and its grid is connected tothe slider 35 of the resistor 34. The resistor 34 is shunted across the secondary winding of the transformer 3'5, the primary Winding of which is connectedto the alternatin current source.

The resistor 34 is tapped at 38, the tap being.

tated'in onedirection by direct current supplied from the tube3l as will be described.

The ungrounded side of the armature 43 is also connected through the selenium rectifiers43 tothe tap 44 on the'resistor'45, oneend of which is connected to the grounded side of the armature winding 46, and the other end of which. is con-' nected through the series connected resistor: 46'

and filter choke 47 to one output side'of the rectifier 48 which includes: the fourseleniumrectifiers 43 connected in aiconventional bridgecircuit, theother-output side of the rectifier'48 being connected to the grounded end of the resistor 45. The input side of the rectifier 48 is :connected to the secondary winding of the transformer 51 the primary winding of'which is .connected to the alternating current source.

The capacitors Hand 52 connected tothe-01%- posite ends of the choke 41 and to'ground, are filter condensers. is connected across the resistor 45.

The rectifier 48 is a source of constant voltage; direct current, which supplies current of opposite polarity to that provided by the'thyratron tube: 3!, to the armature winding of the motor 20;

for causing its armature I9 to rotate in the opposite direction to that caused by the'current:

from the thyratron tube as will be described;

The selenium rectifiers 2'9 and 43 provide unidi.-'

rectional current flow in their respective circuits.

In operation, the rectifier tube 23 rectifies radio frequency current from the tank circuit'of the oscillator *tubes, and supplies the rectified current through the radiofrequency choke 24 and the resistorr25xand switch 36, to charge the capaci' tor 32 which is connected to the cathode of the thyratron tube'3l, negatively. The. tube 3 lis so biased'from resistor 34 so' that it does not conduct until its cathode becomes sufficiente 1y negative withrespect to its grid as the charge inthe capacitor 32 increases. At a predeter mined-negative charge in the capacitor, thetube" 3| conducts, and rectified current from its'plate The voltage regulating tube -53 circuit flows through the armature winding 40 of the motor 20. Current of opposite polarity from the rectifier 48 also flows through the armature winding l9. It is understood that, if desired, instead of obtaining the bias for tube 31 from resistor 34 a separate fixed bias may be provided for tube 3|.

The time required for the capacitor 32 to charge up to the'firing voltage of the tube 31 depends upon the equation C (RH-R2) Where C is the capacity of the capacitor 32 in farads; R1 is the. resistance of the resistor 25 in ohms, and R2 is the resistance of the resistor 30 in ohms. Variationcof theradiofrequency current from the radio frequency generator supplied to the rectifier tube 23, causes'variation of the current flow through the- resistors 25 and 30 which, in turn, varies the time required for the capacitor 32 to charge up to the firing voltage of the tube 31. The discharge time of the capacitor 32 is, however,-. the. same: at all times.

After each firingof the tube 3!, the capacitor 32- is discharged.so'thattheztube 3| is blocked by its grid voltage until the. capacitor 32 is again charged tothe firing voltageof the tube, this cycle being repeated.. In. this way, radio frequency voltageyariations cause) corresponding variations in: theerectifiedccurrent through the tube 3| Although the pulse-of rectified current is the same each time, the average current will depend vupon the time requiredto charge the capacitor 32.

Assuming that the. radio frequency generator has been adjusted to supply a constant power, which,-iby way. of example may be kilowatts, intotheload .I 5, andthe currentfrom the tube'3l hasbeen adjusted by adjustment of the sliders 33 and'35 alongthe resistor 34-, untilit is-equal to the current of I oppositepolarity from the rectifier 48, thenno :current will flow through the armature winding 40-, and the motor 2il-will not operate.

Now assume that the load on the generator decreases .so thaththe radio frequency voltage increases. above its normal value. Then the rectified radio frequency current from the tube- 23 will charge the capacitor. 32 at. afaster rate causing the tube 3 l to conduct at .a corresponding faster rate, and :to supply an average current to :the armature. winding, it-which is greater than that supplied by therectifier. 48. This will provide-acurrent flow through the armature windingin a directionto adjust the slider l3 along-the auto-transformer I! for decreasing the voltagelsuppliedby the transformer It to the filaments of the oscillator tubes I0. This-reduction in filament voltage willcause the tank radio frequency voltage to 2 decrease, and will consequently cause the power: supplied to the reduced load to .be decreased .to normal.

When the load on the generator increases, its tank radio frequency voltage willdecrease below normal,. causing.the current supplied by the thyratron.tube:3l tothe armature. winding 40 to be less than that supplied bythe rectifier 43, so that current will flowxthrough. the armature winding 40 in a direction to'causeits armature torotate to-move thesliderlBof the auto-transformer to increasethe voltagessupplied by the transformer l6 to the filaments of the oscillator tubes ID; This increasein: the. filament. voltage of the oscillator tubes will cause anincrease in the radio frequency voltage andaresulting increase in the power. output. of. the generator.

Thus withan increasein therradio frequency voltage from the generator, the rectified current from the rectifier tube 23 increases and decreases the charging time of the capacitor 32. This causes an increase in the average rectified current through the thyratron tube 3|, and causes current flow through the motor armature winding 40 in a direction to cause the motor to act to decrease the voltage supplied to the filaments of the oscillator tubes I 0. With a decrease in radio frequency voltage, this process is reversed.

The slider 21 of the resistor 25 and its contact 28 are provided so that more than one range of radio frequency voltages may be maintained. By placing the switch 36 on the contact 26, 20,000 volts, by way of example, may be maintained. By placing the switch 36 on the contact 28 and by adjusting the slider 21 along the resistor 25, radio frequency voltages of 10,000 volts and lower may be maintained.

I claim as my invention:

1. A voltage stabilizing system for a radio frequency generator, comprising means for varying the voltage of the radio frequency output current of the generator; a reversible motor for adjusting saidvoltage varying means; means for rectifying radio frequency current from the generator; means utilizing variations in the rectified current for providing a direct current which varies conformably therewith; a direct current source of constant voltage, and means conducting said first mentioned direct current and conducting current from said direct current source in opposite polarity to said motor for energizing same to rotate in one direction when said first mentioned direct current is greater than the current from said direct current source, and for energizing said motor to rotate in the opposite direction when said first mentioned direct current is smaller than the current from said direct current source.

27 A voltage stabilizing system for a radio frequency generator including an oscillator tube having a filament and a plate; a source of current for said filament; means including a reversible motor for varying the voltage supplied by said source to said filament; means for rectifying radio frequency current from the generator; means utilizing variations in the rectified current for providing a direct current which varies conformably therewith; a direct current source of constant voltage, and means conducting said first mentioned direct current and conducting current from said direct current source in opposite polarity to said motor for energizing same to rotate in one direction when said first mentioned direct current is greater than the current from said direct current source, and for energizing said motor to rotate in the opposite direction when said first mentioned direct current is smaller than the current from said direct current source.

3. A voltage stabilizing system for a radio frequency generator, comprising means for varying the voltage of the radio frequency output current of the generator; a reversible motor for adjusting said voltage varying means; a rectifier connected to said generator for rectifying radio frequency current therefrom; an electron tube; a power supply source connected through said tube to said motor; means utilizing the rectified radio frequency current from said rectifier for impressing upon said tube a potential causing it to conduct and to supply direct current from said source to said motor, and a direct current source of constant voltage, connected to said motor in polarity opposition to the current from said tube, said motor being energized to rotate in one direction when the current from said tube is greater than the current from said source, and being energized to rotate in the opposite direction when the current from said tube is less than the current from said source.

4. A voltage stabilizing system for a radio frequency generator, comprising means for varying the voltage of the radio frequency output current of the generator; a reversible motor for adjusting said voltage varying means; a rectifier having an anode; means for supplying radio frequency current from said generator to said anode; a capacitor having one side connected to said anode; a gaseous electron tube having a grid, a cathode, and an anode, means connecting the cathode of said tube to the other side of said capacitor; a power supply source connected to said grid and anode of said electron tube and to said motor, said electron tube conducting and supplying direct current to said motor when said capacitor has been charged to a predetermined voltage, and a direct current source of constant voltage connected to said motor in polarity opposition to the current supplied by said tube to said motor, said motor being energized to rotate in one direction When the current from said tube is greater than the current from said source, and bein energized to rotate in the opposite direction when the current from said tube is less than the current from said source.

5. A voltage stabilizing system for a radio frequency generator, comprising means for varying the voltage of the radio frequency output current of the generator; a reversible motor having an armature winding for adjusting said voltage varying means; means for rectifying radio frequency current from said generator; means utilizing the rectified current for supplyin pulses of direct current the frequency of which is proportional to the value of the rectified current, to said armmature winding, and a direct current source of constant voltage connected to said winding in opposite polarity to said direct current pulses, said motor being energized to rotate in one direction when the average value of the said pulses is greater than the direct current from said direct current source, and being energized to rotate in the opposite direction when the average value of said pulses is less than the current from said direct current source.

6. A voltage stabilizing system for a radio frequency generator including an oscillator tube having a filament, comprising a source of cur rent for said filament; means including a reversible motor having an armature winding for adjusting the voltage supplied to said filament by said source; means for rectifying radio frequency current from said generator; means utilizing the rectified current for supplying pulses of direct current the frequency of which is proportional to the value of the rectified current to said armature winding, and a direct current source of constant voltage connected to said winding in opposite polarity to said direct current pulses, said motor being energized to rotate in one direction when the average value of the same pulses is reater than the direct current from said direct current source, and being energized to rotate in the opposite direction when the average value of said pulses is less than the current from said direct current source.

7. A voltage stabilizing system for a radio frequency generator, comprising means for varying the voltage of the radio frequency output current greater:

of; the generator; a reversible motor havlngan armature winding for adjusting said voltage varying means; a rectifier for rectifying radio frequency current from said generator; means including which is proportional to the value of the rectified current; and adirect currentsource of constant voltage connected to 'said winding in opposite polarity'to said direct currentpulses, said motor being energized to rota-tein one direction when the average value of the said-pulses is greater than the directcurrentfromsaid direct current source, and'being energized to rotate-in the opposite direction whenthe average value of said pulses is less than the current from said direct current source.

8. A voltage stabilizing system for a radio frequency generator including an oscillator tube having a filament, comprising a'source ofcurrent for said filament; means including a reversible motor having an armature winding for adjusting the voltage of thevcurrent supplied by said source to the filament; a rectifier for rectifying radio frequency currentfrom said generatorymeans including a gaseous electron tube for supplying direct current to said winding; means utilizing the rectified current from saidrectifier forcausing said tube to intermittentlyconduct and tosupply-directcurrent pulses to said winding at a frequencywhich is proportional to the value of 'therectified 'current,and a direct current source of constant voltage connected to said winding in opposite polarityto said direct current pulses, said motor being energized to rotate in one direction when the average value of said pulses is greater than the direct-current from said direct currentsource, and being energized to rotate in the opposite direction when the average value of said pulses is less than the current from said direct current source.

9."A voltage stabilizing system for a radio frequency generator, comprising means for varyinginthe voltage 0f the radio frequency output current ofl'thegenerator; a reversible motor having an armature' for adjusting said voltage varying means; a rectifier for rectifying radio frequency current from said generator; means including'a gaseous-electron tube for supplying direct current to said armature winding; means including a capacitor connected to said rectifier and'to saidtube forbiasing said tube to inter- I in opposite polarity to said direct'current pulses;

said motor being energized to rotate in one direction when the averagevalue of said" pulses is greater than the direct current fromsaid direct current source, and being energized to rotate in the oppositedirection when the average value of said pulses is less than the current from said direct current source.

10. Avoltage stabilizing system for a radio frequency generator, comprisingmeansfor varying the voltage of v the radio frequency output current of the generator; a reversible motor' havingan armature windingfor adjusting said voltage varyingmeans a -rectifier having an anode-for rectifying radio frequency-' current from said generator; a capacitor: having one side oonnected to saidanode a gaseous electrontube having a cathode; a grid and ananode; meansconnecting-"theother side of said capacitor to said cathode; a powersupplysource for'saidtube, 'a resistor shunted across said source;-means connecting saidgrid and said anode"of""said tube todifferent-points along said resistorj means for supplying-direct current from said tube when it conducts to said armature winding, and

adirect current source of constant voltage connected-to said armaturewinding in opposite polarityto-the current from said-tube, said motorbeing energized to rotate in one direction-when the current from the said tube 'tosaid Winding is greater than the current from said direct current source to said winding, and being energized to rotate inthe opposite direction when the current from said tube to said winding-isless thanl the current from said direct current source :to said winding.

11. A voltage stabilizing'system for a radio frequency generator including an oscillator tube havinga filament, comprising asource of current for said filament; means including a* reversible motor having an armature winding for adjusting the voltage of the current supplied by said-source to said filament; arectifier-having an. anode.v forlrectifying radio frequencycurrent from. saidlgenerator; a capacitor having one side connected'to said anode; a.gaseous electron tubehaving a cathode,a grid and an anode; means. connecting the-othersidezof said capacitor to said: cathode; a power supply source for said tube, a resistor shunted across said source; means lconnectin said grid andlsaidranode of saidltubetodiiferent points alongsaid resistor; means. for supplying direct current from said tube'when it conducts to said armature windingyand a direct current source of constant voltage-connected to said armature windinguin opposite polarity to the current from said tube,

said motorbein energized to rotate in one direction'when the current from the said tube to said' current from said generator, and having a cathode; a resistor connected to said cathode and toground; a gaseous electron tube 'having a grid,- acathode and-an anode; a-capacitor hav-- ingr one side connected to ground and having its other side connectedto said cathode of said gaseous tube; means includin a resistor con-' necting said other side of said capacitor to said anode of' said" rectifier tube; a power supply source" for said tube, a resistor shunted across said source, means connecting said grid and said anode-of'saidtubeto different points along said resistor; means for'supplyingdirect current from said tube when it conducts to said armature winding, and a direct current source of constant voltage connected to said armature winding in opposite polarity to the current from said tube, said motor being energized to rotate in one direction when the current from the said tube to said winding is greater than the current from said direct current source to said winding, and bein energized to rotate in the opposite direction when the current from said tube to said windin is less than the current from said direct current source to said winding.

13. A voltage stabilizing system for a radio frequency generator including an oscillator tube having a filament, comprising a source of current for said filament; means including a reversible motor having an armature winding for adjusting the voltage of the current supplied by said source to said filament; a rectifier tube having an anode connected to receive radio frequency current from said generator, and having a cathode, a resistor connected to said cathode and to ground; a gaseous electron tube having a grid, a cathode and an anode; a capacitor having one side connec.ed to ground and having its other side connected to said cathode of said gaseous tube; means including a resistor connecting said other side of said capacitor to said anode of said rectifier tube; a power supply source for said tube, a resistor shunted across said source; means connecting said grid and said anode of said tube to different points along said resistor; means for supplying direct current from said tube when it conducts to said armature winding, and a direct current source of constant voltage connected to said armature winding in opposite polarity to the current from said tube, said motor being energized to rotate in one direction when the current from the said tube to said winding is greater than the current from said direct current source to said winding, and being energized to rotate in the opposite direction when the current from said tube to said winding is less than the current from said direct current source to said winding.

14. In combination a thermionic oscillation generator, an electric discharge valve having principal electrodes and a control electrode, connections between said generator and said control electrode for varying the conductivity of said valve in accordance with the oscillatory voltage of said generator, and connections between said principal electrodes and said generator for varying the oscillatory voltage of said generator in dependence upon the variation of the conductivity of said valve.

15. In combination a thermionic oscillation generator, an electric discharge valve having principal electrodes and a control electrode, connections between said generator and said control electrode for varying the conductivity of said valve in accordance with the oscillatory voltage of said generator, and connections between said principal electrodes and said generator for varying the oscillatory voltage of said generator in dependance upon the variation of the conductivity of said valve in a sense such as to tend to restoring said oscillatory voltage to a magnitude from which it varies.

16. In combination a thermionic oscillation generator including a first electric discharge valve having a cathode to be heated; a second electric discharge valve having principal electrodes and a control electrode; connections between said generator and said control electrode for varying the conductivity of said second valve in dependence upon the variation in the oscillatory voltage of said generator; and connections between said principal electrodes and said cathode for varying the temperature of said cathode in dependence upon the varying conductivity of said second valve.

17. In combination a thermionic oscillation generator including a first electric discharge valve having a cathode to be heated and an output load circuit; a second electric discharge valve having principal electrodes and a control electrode, said second valve being of the gaseous type; connections including a capacity coupling to said load circuit between said generator and said control electrode for varying the conductivity of said second valve in dependence upon the variation in the oscillatory voltage of said generator; and connections between said principal electrodes and said cathode for varying the temperature of said cathode in dependance upon the varying conductivity of said second valve.

18. In combination a thermionic oscillation generator comprising a pair of push-pull connected electric discharge devices and an output tank circuit, each of said discharge devices having a cathode to be heated, a gaseous discharge device having principal electrodes and a control electrode, connections between said output tank circuit and said control electrode for varying the conductivity of said gaseous discharge device in dependence upon the variation in the oscillatory output voltage of said generator, and connections between said principal electrodes and each of said cathodes for varying the temperature of said cathodes in dependence upon the varying conductivity of said gaseous discharge device.

RICHARD H. HAGOPIAN.

REFERENCES CITED The following references are of record in the file of this patent:

UNITED STATES PATENTS Number Name Date 2,175,694 Jones, Jr Oct. 10, 1939 2,318,948 Koch May 11, 1943 2,415,799 Reifel et a1. Feb. 11, 1947 2,431,902 Albin Dec. 2, 1947 2,439,816 Marshall Apr. 20, 1948

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