US2438396A

US2438396A - Electronic device circuit

Info

Publication number: US2438396A
Application number: US651935A
Authority: US
Inventors: Gordon B Jacobs; Oliver I Steigerwalt
Original assignee: US SEC WAR
Current assignee: United States, WAR, Secretary of; US SEC WAR
Priority date: 1946-03-04
Filing date: 1946-03-04
Publication date: 1948-03-23
Anticipated expiration: 1965-03-23

Description

Filed March 4, 1946 FIG.

FlG.2

AUTO. COMP. lNDUCTlQN TYPE POTENTIOMETER AUTO. emu 2 SERVO MOTOR VAR!ABLE v AUTO-TRANSFORMER PWENTIOMETER l. STEIGERWALT ATTORNEY Patented Mar. 23, 1948 UNITED STATES TENT OFFICE Steigerwalt, Chicago, 111.,

assignors to the United States of America as represented by the Secretary of War Application March 4t, 1946, Serial No. 651,935

3 Claims. 1

This invention relates to electronic device circuits, and, more particularly, to a circuit arrangement for regulating or controlling an operating characteristic of a magnetron.

It has been observed that the eiiiciency of operation of a magnetron is afi'ected by variations or change in the temperature of the cathode of the magnetron during the operation of such a device. It is generally intended or desired that the cathode operate at a preassigned normal operating temperature. It has been found that variation from this temperature occurs when, during operation of the magnetron, the cathode is subject to back heating as a result of electron bombardment.

It is an object of this invention to stabilize the temperature of a magnetron cathode during the operation of such a device.

A feature of the invention comprises magnetron cathode-temperature regulating means for stabilizing the cathode temperature in response to changes or variations in the cathode temperature during operation of the magnetron.

In accordance with the invention, a circuit arrangement is associated with a magnetron filament or cathode to regulate the temperature thereof during operation of the device. The regulating circuit is incorporated in the cathode heating power supply, and is responsive to resistance changes of the cathode with temperature change thereof, to vary the heating power input to the magnetron cathode.

A more complete understanding of the invention, of its other objects and features together with their attendant advantages, will be derived from the detailed description that follows, taken in conjunction with the showings of the appended drawing, wherein:

Fig. 1 shows a circuit arrangement embodying the invention; and

Fig.2 shows schematically the mechanical coupling between the control motor and adjustable components included in the circuit arrangement of Fi 1.

There is shown a magnetron H3 comprising a filamentary cathode l2 and anode Hi. The filament is heated by alternating current, through a filament transformer 16. The heating power supply for the filament may comprise a 3-phase alternating current supply, transformed through a Scott-connected type transformer I8 to Z-phase alternating'current, one phase of which is applied throug'h transformer winding 20 to one field windi'ng2-2 of the control or servo motor 2 the other phase of which is applied through trans- 2 former winding 26 to the primary winding of the transformer It. A variable autotransformer 28 is connected across the winding 25 to enable variation, under control of motor 24, of'the voltage furnished to the filament transformer. The primary winding of a voltage transformer fit is connected in parallel with the autotransformer, and a current transformer 32 .is connected in series with the primary winding of transformer id. The transformers 3,0, .32, are so constructed that their secondary voltages are approximately equal when the reflected filament resistance, as given by the ratio of the voltage across and the current flow through the filament transformer primary, is normal indicating thedesired or proper filament temperature. A manually adjustable compensating potentiometer 34 is connected across the secondary winding of transformer 32, and an automatically regulated potentiometer 38, adjustable under control of the motor 2 3, is connected across the secondary winding of the transformer 30. The potentiometers are connected through the primary winding of an input transformer 38 to an amplifier it. Anautomatic gain potentiometer 52 may be connected across the secondary winding of transformerSB, being adjustable under control of the motor 24. The secondary winding of theamplifier output transformer 44 is connected to thesccond field winding it of the control motor 24. The mechanical coupling from the motor 24 to theautotransformer and to the

potentiometers

36, 42 is indicated by the dotted lines in Fig. l. Fig. 2 indicates, schematically, a suitable arrangement inwhich the autotransformer and potentiometers may be driven through a suitable friction clutch 68, and

cam-cam stop 5!] for limiting extreme adjustments of the transformer andpotentiometers.

The operation of the circuit arrangement of Fig. 1 will now be described.

The cathode of a magnetron .is generally designed to operate most efficiently atan approximately constant high temperature. During the operation of the magnetron, however,.the temperature of the cathode may increase beyond the normal or desired value because of back heating of the cathode as a result of electron bombardment. Because of the radio frequency potential between the cathode andanode, not all of the electrons emitted by the cathode reach the anode, but some of them are directed back to the cathode, to change the latters temperature-in-proportion to the number and the intensity of such returned electrons.

For the normal temperature. condition of the above-mentioned network. A fraction of each of the voltages across the secondaries of

transformers

30, 32 is taken from the 'potentiometers. 34, 36 and the difference between these fractions is applied to the amplifier through transformer 38. The difference signal appears at the amplifier input control grid plus or minus 90 degrees out of phase with the voltage applied to the field winding 22 of the motor 24. The input to the amplifier is amplified and applied to the field winding 46 of motor 24, the latter turning in a direction determined bythe phase of the amplifier output, to change the adjustment of the autotransformer, and, hence, the cathode heating power supplied to transformer Hi. When the cathode temperature again becomes normal, the voltages across

transformers

30, 32 will again be of proportions establishing balance in the

network including potentiometers

34, 36. Under the latter condition, there will be absence of signal input to the amplifier, field winding 46 will no longer be energized, and there will be'no further motion of the motor. The gain control potentiometer 42 is varied or adjusted by the motor 24, simultaneously with adjustment of the autotransformer, to maintain constant sensitivity of the arrangement to temperature changes as the absolute values of voltage and current vary with the adjustment of the variable autotransformers setting.

A specific magnetron circuit to which the invention is applicable may include a magnetron in which only a portion of the filamentary-cathode is subject to back heating and, consequently, variation in temperature from this cause. In such a situation, the total resistance of the filament at any time is the sum of the resistance of the back heated 'portion and of the remaining portion of the filament. When the variable autotransformer has been adjusted as outlined here- :inabove, the temperature of the non-back heated filament portion will be changed from its normal temperature, and the total resistance of the filament, therefore, may not be that for proper operation of the back heated portion of the filament. To compensate for this, the potentiometer 36, under control of the motor 24, is adjusted simultaneously with the adjustments of the autotransformer and of the potentiometer 42, t change the proportion of the current and voltage signal input to the amplifier for balance to account for such change in resistance.

Although, in this description, reference has been made to a filamentary type'j cathode for the magnetron, obviously the arrangement is 1. A circuit arrangement for maintaining 'sub-' stantially constant temperature in a magnetron 4 filamentary cathode, that comprises a source of polyphase alternating current, means for heating the cathode from said source, said means comprising an adjustable autotransformer for furnishing one phase of said alternating current to said cathode, and. a multiwinding filament transformer between said autotransiormer and said cathode, a multiwinding voltage transformer connected in parallel with the primary winding of said filament transformer, a multiwindingcurrent transformer connected in series with the primary winding of said filament transformer, a compensating potentiometer connected across one Winding of said voltage transformer, a second potentiometer connected across one winding of said current transformer and manually adjustable for presetting the temperature of said cathode, an amplifier for amplifying any difference voltage developed across said potentiometers, a multiwinding transformer coupling said potentiometers to the input of said amplifier, 'a gain adjusting potentiometer across the input to said amplifier, an induction motor having a pair of field windings, one of said windings being energized with one phase of said polyphase alternating current, means for connecting the output of said amplifier to the second of said motor field windings to energize said second winding for movement of said motor upon development of a difference voltage between said compensat ing and manually adjustable potentiometers on change in temperature of said cathode, and means connecting said motor and said autotransforme-r, compensating potentiometer and gain adjusting potentiometer for adjustment of said autotransformer and potentiometers in accordance with movement of said motor.

2. A circuit arrangement for maintaining substantially constant temperature in a filament comprising a source of alternating current, means for heating the filament from said source, said means comprising an adjustable autotransformer, a filament transformer, a voltage transformer, a current transformer connected in serieswith the primary winding of said filament transformer, said series circuit being connected in 'parallel with said voltage transformer to the output of said autotransformer, a compensating p0- tentiometer connected across one winding of said voltage transformer, a second potentiometer connected across one winding of said current transformer and manually adjustable for presetting the temperature'bf said filament, an amplifier, a transformer coupling said potentiometers to'the input of said amplifier, a gain adjusting poten tiometer acrossthe input to said amplifien a motor, means for connecting the output i 'of said amplifier to said motor for movement/of said motor upon development of afidifierencexvoltage between said compensating and manually Tadjustable potentiometers on changetinitemperature of said filament, and means connecting said motor to the adjusting means of said autotrarisformer, compensating potentiometer and gain'adjusting potentiometer for adjustment; of 1 said autotransformer and potentiometers 'injaccordcomprising said filament transformer and a secfier, means for connecting said amplifier output to a motor to adjust said autotransformer.

GORDON B. JACOBS. OLIVER I. STEIGERWALT.

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

UNITED STATES PATENTS Number Name Date 1,994,076 Kuhle et a1 Mar. 12, 1935 2,149,080 Wolff Feb. 28, 1939 2,262,044 Philpott Nov. 11, 1941