US3009077A

US3009077A - Gas discharge tube sensitive to a.c. signals

Info

Publication number: US3009077A
Application number: US215042A
Authority: US
Inventors: Carlyle W Jacob
Original assignee: Individual
Current assignee: Individual
Priority date: 1951-03-12
Filing date: 1951-03-12
Publication date: 1961-11-14
Anticipated expiration: 1978-11-14

Description

c. w. JACOB 3,009,077

GAS DISCHARGE TUBE SENSITIVE TO A.C. SIGNALS Nov. 14, 1961 Filed March 12, 1951 FIG. 4.

DE TONA 70R FIG.2.

CARLYLE W. JACOB 3nventor ia' w II IIII lw h bun l h I W IU will \1 l/|||| k 7 I l B I; J if nw h M. G R l Z H llllllll ll llllllllllllllll l .llilllulillnnllllllillll attorney Unite tates This application relates to electron tubes and particularly to gas-filled discharge tubes.

Gas-filled grid-controlled discharge tubes are utilized in radio proximity fuzes for ordnance projectiles to initi ate the explosion of the bursting charge of the projectile upon the application to the grid of an operating signal of predetermined amplitude and duration. The grid of such a tube has heretofore been conventionally biased considerably more negative than the starting voltage, i.e., the critical firing voltage, as a safety precaution against premature detonations caused by decay during the flight of a projectile of the output voltages of the deferred action type battery that conventionally provides the grid-bias voltage. Biasing the grid well beyond the starting voltage diminishes the sensitivity of the gas-filled discharge device in that a strong firing signal is required to raise the grid above the starting voltage.

It is an object of the invention to provide a stable gasfilled grid-controlled discharge device which is sensitive to weak A.C. firing signals and substantially immune to drifts in D.C. bias voltage.

It is a further object of the invention to provide a stable gas-filled grid-controlled discharge tube and circuit therefor which exhibit differential sensitivity to rapidly varying and to slowly changing signals.

It is a still further object of the invention to provide a stable gas-filled grid-controlled discharge tube and circuit therefor which can be fired by weak A.C. signals and which prevents accidental firings due to drift in grid bias over a range of voltage considerably larger than the peak voltage of the A.C. signal required to fire the tube.

Still another object of the invention is to provide such a gas-filled grid-controlled discharge tube which, without danger of accidental firing of the tube, can be safely operated at lower grid bias voltages than have heretofore been utilized.

The objects of the invention are attained in a gas-filled grid-controlled discharge device by providing a balancing fourth electrode positioned in the electron path through the apertures in the control grid to compensate for changes in electron flow due to drift in the C bias voltage on the control grid. In operation, a source of potential positive relative to the cathode is connected to the balancing electrode through'a high resistance. A gradual decrease in the cont-r01 grid negative bias voltage allows a few electrons to emerge through the apertures in the grid. Practically all of the electrons are collected by the balancing electrode and flow through the high resistance. The increased voltage drop across the high resistance drives the balancing electrode more negative and thus increases its shielding action. The balancing electrode voltage E, is thus dependent inversely upon the control grid bias voltage E For a given anode voltage the tube has a critical flash point function (i.e., control characteristic) of E and E wherein any combination of such voltages on the non-flash side of the function prevents the establishment of the arc. The control grid C bias source and the source of positive potential for the balancing electrode are selected so that the combination of E, and E determines a point just on the non-flash side of the function, and E balances, i.e., varies inversely with, drift in E to maintain the combination of voltages on the non flash side of the function, i.e., to limit the anode electron atent current to a value below the minimum required to establish the arc, over a wide range of variation of E Differential sensitivity to A.C. signals and to drifts in control grid bias voltage is obtained by providing a time delay in the variation of E, when an A.C. signal is impressed on the control grid. In the preferred embodiment of the invention, this difference in sensitivity is provided by connecting a capacitance to the balancing electrode in parallel with the high resistance. The capacitance offers a substantially infinite impedance to slow variations in electron flow and presents an impedance path to rapid fluctuations of electron flow which decreases with frequency. A momentary delay greater than the ionization time of the tube is required to charge the capacitance when an A.C. signal is impressed on the control grid, thus preventing a change in the shielding action of the balancing electrode until after the electron current to the anode has increased beyond the minimum required to establish the arc. Increased electron flow due to an A.C. signal on the control grid divides between the resistance and capacitance paths, and consequently the voltage drop across the resistance is not as great (and thus the balancing electrode is not driven as far negative) as when E varies gradually. Alternatively, an A.C. firing signal of suificient magnitude impressed directly on the balancing electrode immediately increases the anode electron current above the minimum required to start the arc. Thus the A.C. signal may be applied to either electrode while the tube compensates for, and remains relatively insensitive to, DC. drift. I

The various features of the invention will be more clearly understood from the following detailed description in connection with the accompanying drawings in which:

FIG. 1 is a perspective view of one embodiment of a discharge tube made in accordance with the invention with a portion of the enclosing vessel and the anode broken away to show the internal elect-rode structure;

FIG. 2 is a diagram of the firing circuit of a radio proximity fuze utilizing the novel tube;

FIG. 3 is a diagram of a circuit alternative to that 0 FIG. 2; and

FIG. 4 is a typical control characteristic curve of the novel tube.

Referring to the drawings, a gas-filled grid-controlled discharge tube according to the invention is provided with the usual subminiature type radio tube glass envelope 10 containing an ionizable gaseous medium, for instance, one of the rare inert gases exemplified by neon and argon, or mercury vapor. The envelope 10 terminates in a press 11 in which are sealed both'the lead-in conductors for the electrodes and upwardly-extending rigid rods 12 adapted to support the electrode structure. Each rod 12 fits into a depression '13 provided in, and engages the outer surface of, a metallic cylindrical anode 14. The rods 12 and a lead-in conductor 16, which conductor engages and provides partial support for the anode 14, extend through snug apertures provided in

circular discs

17 and 18 of suitable insulating material, such as mica, in planes transverse of the axis of the cylindrical anode 14. Another lead-in conductor 20 extends through the press 11 and through apertures in the discs 17 and 1 8, and a hook 21 fastened to the upper end of the leadin conductor 20 above the insulating disc 18 supports a filament cathode 23 which extends through apertures in the

discs

17 and 18 along the axis of the enclosing vessel 10. A separate lead-in conductor 26 extending through the press 11 connects to the lower end of the cathode 23 below the insulating disc 17. The filament cathode 23 is coated along the length between the

insulating discs

17 and 18 with thermionically-active material such as barium and strontium oxides to insure a copious supply of electrons.

A rigid rod 27 and a lead-in conductor 28 extending upward from the press .11 and through apertures in the insulating discs *17 and 18 engage a generally tubular metallic control grid B1 disposed coaxial with the cathode 23 between. the

insulating discs

17 and 18. The

insulating discs

17 and 18 thus close the upper and lower ends of the control grid 31 and also fixedly position the lead-in

conductors

16 and 28 and the

rods

12 and 27 to. maintain the anode 14 and the control grid 31 coaxial with the cathode 23. By the Word tubular in this connection is meant any form having a substantially perimetrically complete contour whether such contour be circular or noncircular. In the preferred embodiment of the invention illustrated in the drawings, a rectangular contour is utilized. A plurality of apertures 33 are provided in the grid 31 aligned along the length, of the cathode 23.

My invention is particularly concerned with a balancing electrode 34 positioned in front of the apertures 33 in the path of electronic flow between the cathode 23 and the anode 14. The balancing electrode 34 comprises two spaced rigid rods 35 disposed between the control grid 31 and the anode 14 and extending parallel to the cathode 23 through apertures in the

insulalting discs

17 and 18. One rod 35 is an extension of a lead-in conductor extending through the press 11 and is soldered to the second rod 35 below the insulating disc'17.

While the particular structure of the. tube as illustrated in the drawings is the preferred embodiment of the invention, other elements of the electrodes relative to one another, as regards spacing and configuration, which perform the functions explained are within the scope of the invention. It is obvious that the balancing electrode may comprise a single, or any desired number, of rigid rods 35 in the path of electron flow between the anode and cathode.

The utility of such a gaseous device is shown in the circuit of: FIG. 2, which represents a conventional firing circuit of a radio proximity fuze. The. electrodes of the tube in FIG. 2v bear the same reference numerals as those of FIG. 1 and are schematically represented as though a horizontal sectional view were taken through the electrode structure. After a projectile containing a radio fuze is fired, a source of filament voltage is connected to the cathode 2 3 and a source of anode potential of approximately 90 volts positive with respect to the cathode 23. is connected to the anode 14v through an arming resistor 40, conventionally from the A and B sections respectively of, a deferred action type battery (not shown) contained; the. fuze. An, arming condenser 41 connected to the anode 14 is in series with an electric detonator 44 to, ground. The arming condenser 41 pro-- vides, the energy to fire the electric detonator 44 when the discharge device of the invention fires and conducts current. The arming resistance 40 and the arming condenser 41in combination provide a time delay to prevent the bursting charge from exploding until the projectile is. well away from the gun and from, firing personnel. In order to prevent breakdown of the gas-filled tube of the invention in. the absence of an operating signal, a source of bias voltage negative relative to the cathode 23 is connected. to the control electrode 31. The operating signal from the amplifier (not, shown) of the fuze is coupled. to the control, grid 31 through a condenser 43.

Conventionally, the source of negative grid bias for the control grid 31 is the C section of the deferred action type battery of the fuze. As hereinbefore explained, this C section is subject to decay in output voltage during the flight of the projectile, and in order to eliminate any possibility of premature detonation, it was necessary to maintain the control grid of gas-filled discharge tubes heretofore used considerably more negative than'the starting voltage. Consequently an operating signal of considerable amplitude was required to overcome the negative bias and cause discharge of the gas-filled tube.

To provide a gas-filled device which is sensitive to AC. signals and at the same time prevent any possibility of accidental discharge, the balancing electrode 34 is connected through the parallel arrangement of a resistor 46 and a condenser 47 to a source of potential positive relative to the cathode .23. For every anode potential the discharge device of the invention has a critical fiash point function (i.e., control characteristic) of control grid voltage E and balancing electrode voltage E A- typical control characteristic curve 50 for a given anode voltage is shown in 'FIG. 4 of the drawing plotted with values of E, as abscissae and values of E as ordinates. Any combination of E, and E that determines a point above and to the right of the flash point function 50 indicates that the shielding action of the control grid 31 and balancing electrode 34 are insufficient to limit the anode electron current to a value below the minimum required to establish the arc; but if the point is determined below the flash point control characteristic 50, the shielding action of these two electrodes is suflicient to limit the anode current below this minimum. That is, the arc starts as electrode potentials 'pass across curve 50 from the lower left to the upper right.

The balancing electrode 34 acts to compensate for changes in electron flow due to drifts in the voltage of the control grid C bias source by limiting the electron current to the anode below the minimum required to start the are even though E may drift from its preferred negative value to an excessively low negative value, i.e., drift in a positive direction, due to a defective deferred action type battery. As E slowly becomes more positive due to drifts in the voltage of the C bias source, a few electrons emerge through the apertures 33 in the control grid 31 and are drawn primarily to the balancing electrode 34.

. Substantially all the electrons flowing through the apertures' 33 are collected. by the balancing electrode 34 and flow through the resistor 46, thereby lowering E by an amount equal to the voltage drop across this resistor 46. The increased shielding action of the balancing electrode 34 thus prevents increased electron flow to the anode due to gradual changes in 13;.

The voltages of the control grid C bias source and the balancing electrode source are selected so that the combination of E and E are just below, i.e., on the nonfiash side of the control characteristic 50 of the tube. E and E are balancing voltages in that E, is inversely dependent upon E so that the combination of voltages determines points which are on the non-flash side of the critical flash point function 50 even though the output voltage of the C" bias source may vary over a wide range. The dotted curve 51 in FIG. 4 is drawn through points determined by such combinations of E and E,;. It will be noted that all points on this dotted curve 51 are below, i.e., on the non-flash side of, the control characteristic 50 for a considerable range of variation of E As E drifts positively it drives E less positive so that both move along the curve 51.

It is apparent that if means are provided to momenta-rily raise either E or E i.e., make either more positive, without significantly changing the voltage of the other, the combination of voltages will then determine a resistor 46 which in turn varies E and thus the shielding eifect of the balancing electrode 34. If the decrease in E, is gradual, the increase in electron current is gradual, and the shielding action of the balancing electrode '34 increases substantially simultaneously with changes in electron current and prevents the anode current from increasing above the minimum required to start the arc. The capacitance 47 offers a substantially infinite impedance path to gradual changes of electron flow. However, if a rapidly changing signal is impressed on the control grid 31, the sudden increase in electron current does not cause an instantaneous drop in B The 500 micromicrofarad condenser 47 offers a path to alternating electron current flow of decreasing impedance with increase of frequency. This impedance decreases below the 20 megohms of the resistance -47 at frequencies above 50 cycles. The increase in electrons collected by the balancing electrode 34 is momentarily absorbed in charging the condenser 47, thus providing a momentary delay in the decrease of E, until the electron flow to the anode 14 increases beyond the minimum required to ionize the gaseous medium and thereby distort the electric field and cause the tube to discharge. The time delay provided in changing E, is greater than the ionization time of the tube. The alternating electron flow divides between the parallel resistance and capacitance paths, and the magnitude of the current through each path is dependent upon the frequency. The voltage drop across the rmistance 46 is thus never as great, and the balancing electrode 34 is thus never driven as far negative, as when comparatively gradual changes of voltage are impressed on the control electrode 31. A source of positive potential for the balancing electrode 34 may conveniently be obtained from a tap on the B voltage section of the deferred action type battery.

7 FIG. 3 illustrates an alternative radio fuze firing circuit utilizing the novel tube of the invention and characterized by a high impedance input. A source of bias voltage in the C section of the deferred action type battery is connected to the control grid 31 in exactly the same manner as in the circuit shown in FIG. 2, but the operating signal is impressed through a coupling condenser 48 onto the balancing grid 34 instead of onto the control grid 31. Changes in voltage drop across the resistor 46 vary E and thus compensate for changes in electron current fiowdue to drifts in the output voltage of the C bias source in exactly the same manner as hereinbefore explained for the circuit of FIG. 2. Likewise, changes in the shielding action of the balancing electrode 34 balance changes in E and the combination of voltages limits the electron current to the anode below the minimum required to start the arc over a comparatively wide range of drift of the C bias voltage source in exactly the same manner as hereinbefore explained. However, it is unnecessary to provide a time delay in the change of the shielding effect of one of the electrodes in order to fire the tube on a relatively weak A.C. operating signal. The firing signal is impressed through the coupling condenser 48 directly onto the balancing electrode 34. When E, is driven positive by an AC. firing signal of sufiicient amplitude, the electron current to the anode is immediately raised above the minimum required to establish the arc. Peak values of the AC. signal required to start the are are represented by the vertical distance between the dotted curve 51 and the control characteristic 50 in FIG. 4 of the drawing. It is apparent that the C bias voltage source may vary over a voltage range many times larger than the AC. voltage required to fire the tube without causing accidental detonation. E is inversely dependent upon E and gradual changes in E are compensated for, or balanced, byvarying E and thus the shielding action of the electrode 34. Rapidly varying signals impressed on the balancing electrode 34 immediately raise the anode current above the minimum required to establish the arc.

It has been found that satisfactory compensating action is obtained with a source of potential connected to the balancing electrode 34 considerably less positive than the anode potential, e.g., over a range of voltages of from 16 to volts positive relative to the cathode dependent upon the anode potential and the value of the resistance 46. For the application herein described it has been found desirable to bias the control grid 31 nega tive relative to the cathode, although by decreasing the spacing, the size of the grid apertures 33, and the number of rods 35 in the balancing electrode 34 it is possible to construct positive-grid-potential discharge device, i.e., a tube which prevents the establishment of the are even though a source of potential positive relative to the cathode is connected to the control grid 31. The control characteristics of such a discharge device are more toward the positive region than the typical control characteristic curve illustrated in 'FIG. 4. With the circuit of 'FIG. 3 operated at an anode potential of 90 volts and with a positive potential of 16 volts connected through a resistance of 20 megohms to the balancing electrode 34, it has been found that the negative grid bias on the control grid 31 may drift positive as much as 8 volts without establishing the are, yet if an AC. signal of 0.15 volt R.M.S. is impressed on the balancing grid 34 through the condenser 48, the discharge device is triggered. With the circuit of FIG. 2 operated at similar voltage values for the anode 14 and for the source of potential for the balancing electrode 34, the control grid voltage may drift in a positive direction as much as five volts without firing the tube, and yet if an AC. signal of only 0.5 volt R.M.S. is impressed on the control grid 31, the discharge device definitely fires.

' It is apparent from the foregoing description and the drawing that a gas-filled discharge device has been described that is substantially immune to drifts in control grid bias voltage and sensitive to weak A.C. operating signal voltages. While I have indicated only the preferred embodiments of the invention, it will be apparent that the invention is by no means limited to the exact forms illustrated or to the use indicated, but that many variations may be made in the particular structure used and the purpose for which it is employed without departing from the scope of the invention as set forth in the appended claims.

I claim:

1. LAD electron discharge device comprising an enclosing vessel containing an ionizable medium, a cathode extending along the axis of the vessel, a tubular control electrode coaxial with and surrounding said cathode and provided with a plurality of apertures aligned along the length of said cathode, a balancing electrode consisting of at least one rod parallel to said cathode and in front of, and in the path of electronic flow through, said apertures, a cylindrical anode surrounding and in substantial parallelism with said cathode, said control electrode, and said balancing electrode, insulating disks extending in planes coincident with the ends of said grid and centering said cathode coaxially with said grids, and a plurality of lead-in conductors extending through said vessel respectively from said anode, cathode, control electrode and balancing electrode.

2. A circuit for an electron discharge device in accordance with claim 1 adapted to be triggered by an AC. signal, comprising a source of potential for said anode, a source of bias voltage for said control electrode, and a source of positive potential connected through a high resistance to said balancing electrode of low enough voltage for the combination of said anode and said bias potentials to prevent suflicien-t electron flow to said anode to establish a discharge are, whereby changes in the number of electrons collected by said balancing electrode due to slow variations in said bias voltage change the voltage drop across the high resistance, and thus the shielding action of the balancing grid, sufficiently to maintain the electron current to the anode below the minimum required to establish the arc, and means including a condenser connected to. said balancing electrode for providing a time delay in the change of the voltage of said balancing electrode when an A.C. signal is impressed upon said control electrode, said time delay being of greater duration than the ionization time of said electron discharge device.

3. A circuit for a gas-filled electronic discharge tube adapted to be triggered by an A.C. signal, comprising a gas-filled tube having an anode, a cathode, and two control grids, one grid being an apertured shield between the cathode and the anode and the other grid being a balancing grid generally aligned between the aperture and the anode, a source of potential for said anode, a source of bias voltage for said shield grid, means for applying an A.C. signal to said shield grid, means in cluding a source of positive potential connected to said balancing grid through a high resistance 'and a capacitance also connected to said balancing grid for compensating only for changes in electron current due to gradual variations in the voltage .of said bias source, whereby variations in electron current due to an A.C. signal onsaid control 'grid will not be compensated for.

4. A circuit for a gassfilled electronic discharge tube adapted to be triggered by an A.C. signal, comprising a gas-filled tube having an anode, a cathode, and two control grids, one grid being an apertur ed shield between. the cathode and the anode and the other grid being a balancing grid generally aligned between'the aperture .and the anode, means for applying a potential to the anode positive relative to the cathode, means for applying a D.C.bias voltage to said shield grid, means for applying to the, balancing grid through a high resistance a voltage positive relative to the cathode, whereby said balancing grid assumes a voltage depending inversely on the grid current through the high resistance which current in turn is greater for more positive values of said bias voltage, and means for applying an A.C. signal to said balancing grid.

5.. A circuit for a gas-filled electronic dischange tube adapted to be triggered by an A.C. signal comprising a gas-filled tube having an anode, a cathode and two control grids, one grid being an apertured shield between the cathode and the anode and the other grid being a balancing grid in the path of electronic flow through said aperture, a source of potential for said anode positive relative to said cathode, means for applying to said' shield grid a bias potential E means for applying to said balancing grid through a high resistance a potential positive relative to the cathode, whereby said balancing grid assumes a positive voltage E depending inversely on the flow of electron current through the high resistance which current is greater for more positive values of E said tube having a critical flash point function of E sand E for said anode potential wherein all values of E and E .on the nonflash side of said function prevent the establishment of a discharge are, potentials E, and E being balancing potentials on said nonflash side of said function and remaining so for gradual changes of E and means. for applying said A.C. signal to one of said grids with-, out significantly changing the potential of the other grid.

6. An electron discharge device comprising an enclosing vessel containing an ionizable medium, a cathode, a control electrode surrounding the cathode except for atleast one aperture, a balancing grid in front of, and in. the path of electronic flow througln said aperture, and a cylind-rical anode encompassing said control electrode and said,

balancing electrode, whereby said balancing electrode when connected to a voltage positive relative to said cathode tends to collect electrons flowing through said aperture. I

7. A circuit for an electron discharge device in accordance with claim 6 adapted to be triggered by an A.C. signal, comprising means for applying a potential to said anode positive relative to the cathode, means for applying to said control electrode a DC. bias potential E means for applying tov the balancing electrode through a high resistance a potential positive relative to the cathode whereby said balancing electrode assumes a positive value E depending inversely on the electron current I flowing through the high resistance which 1,, in turn is greater for more positive values of E said tube having a control characteristic curve for said anode potential with E and 15,, as coordinate axes wherein all combinations of E and E which determine points to the left of the curve are insuflicie'nt to establish a discharge arc, said E and E being balancing voltages just on said left side of said curve and remaining so for gradual change in E and means for applying said A.C. signal to one of said grids without significantly changing the potential of the other grid.

References Cited in the file of this patent UNITED STATES PATENTS 1,921,004 Samuel Aug. 8, 1933' 1,995,176 Glaser u Mar. 19, 1935 2,061,254 Rockwood NOV. 17, 1936 2,460,794 Selvidge Feb. 1, 1949 2,491,425 Stutsman Dec. 13, 1949