US2446553A - Electrometer vacuum tube - Google Patents

Description

2 Sheets-Sheet 1 A. L. M. A. ROUY ELECTROMETER VACUUM TUBE Filed Sept. 6, 1944 MM w. m- R 6 Aug. 1o, 194s.

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Aug. 10, 1948. l A. L. M. A. RouY i 2,446,553

ELECTROMETER VACUUM TUBE Filed Sept. 6, 1944 2 Sheets-Sheet 2 Patented Aug. 10, 1948 ELECTRQMETER VACUUM TUBE Auguste Louis Marie Antoine Rouy, New York, N. Y., assigner to L. L. H. Company, Erie, Pa., a partnership comprising Hugh C. Lord, Thomas Lord and Blanche M. Hartman Application September 6, 1944, Serial No. 552,892

Claims. (Cl. Z50- 275) My inventionV relates broadly to electrometer vacuum tubes and more particularly to an improved construction of electrometer vacuum tube for facilitating mass production of such tubes and obtaining a high degree of efficiency in op eration.

One of the objects of my invention is to provide a construction of electrometer vacuum tube in which the electrodes are arranged for decreasing the ratio of grid current to plate current; effecting an increase in plate current; increasing the ratio of plate current to grid voltage; and decreasing the positive ion current.

Another object of my invention is to provide an arrangement for mechanically mounting the electrodes of an electrometer vacuum tube by which the mechanical rigidity of the different electrodes is insured.

Still another object of my invention is to provide a special arrangement of lament electrodes for electrometer vacuuin tubes by which oompensation for relative displacement of the filaments with respect to the other electrodes of the tube is obtained.

Still another object of my invention is to cornbine a construction of elecrtometer vacuum tube in which multipoint supports are provided for the tube electrodes and so related as to permit simultaneous uniform displacement of the electrodes relative to each other under conditions of mechanical vibration for minimizing changes in operating characteristics of the tube over such periods of vibration.

Other and further objects of my invention reside in the mechanical arrangement for mounting the filament grid and plate electrodes of electrometer vacuum tubes as set forth more fully in the specification hereinafter following by reference to the accompanying drawings in which:

Figure 1 is a theoretical plan view showing the relative arrangement of the filaments, plate and grid in the electrometer vacuum tube of my invention; Fig. 2 is a plan view of an arrangement of grid lament and plate electrodes used in prior art types of electrometer vacuum tubes over Which the instant invention is a very substantial improvement; Fig. 3 is a curve diagram showing the characteristics of the electric fields plotted with respect to the function of the instantaneous position of an electron between the grid and plate electrodes comparing' two structures of Figs. 1 and 2; Fig. 4 is a curve diagram illustrating the advantages obtained in the tube construction of my invention where greater field strength is secured in a position which increases eiiiciency in the tube operation; Fig. 5 is a schematic plan View showing the arrangement of lament electrodes in the tube construction of my invention by which uniform operation of the electrometer vacuum tube is maintained independently of mechanical vibration; Fig. 6 is a vertical sectional view through an electrometer vacuum tube constructed in accordance with my invention with the plate electrode broken away andv illustrated partially in section to more clearly show the arrangement of laments and grid electrodes; Fig. 'I is a transverse section taken on lines 'i-l of Fig. 6; Fig. 8 is a transverse section taken on lines 8-6 of Fig. 6; Fig. 9 is a perspective View illustrating the upper support for the filament electrodes; and Fig. 10 is a perspective view illustrating the manner of supporting the plate electrode of the electrometer vacuum tube.

When it is necessary to measure very small currents or rather voltages in circuit where the total amount of energy is extremely low, like for instance in the case of voltages produced by pressure on a piezo electric quartz crystal cell, it is of the utmost importance to avoid any losses of the minute electric charge through leakages in the voltage measuring devices.

Several types of vacuum tubes have heretofore been proposed in which the grid current is kept as low as 10X10-14 amperes. These tubes are generally characterized by a very low plate current of the order of 200x106 microamperes in order to reduce the grid current. Some of them use a grid made with a plate on the opposite side of the iilament arranged for accelerating the electrons toward the plate in function of its negative potential. Some others are made with the grid surrounding the plate which is made in that case out of a mesh grid and then this grid has a decelerating function on the electrons in function of its negative potential.

In either case the mechanical construction is such that the operation of these vacuum tubes is affected by even the smallest mechanical vibrations producing some variations of the mechanical distances between the different electrodes therefore causing the plate current to vary with these minute relative displacements.

My improved construction of electrometer vacuum tube includes a number of advantages summarized as follows:

a. Decrease of the ratio of grid current to plate current;

b. Increase of the plate current;

C. Increase of the ratio of plate current to grid voltage;

d. Decrease of the positive ion current;

e. Increase of the mechanical rigidity of the several electrodes;

f. Special arrangement of the iilaments compensating their relative displacement in respect to the coacting electrodes.

Referring to the drawings I have shown a cross section of the electrometer vacuum tube in Fig. 1 in which P` represents the plate, F1, F2, F3 represent the iilaments and G represents the grid. The plate P and the grid G are concentric and the laments F1, F2, F3 are located on a concentric circle with P and G, at angular distances of 120 or 60.

Fig. 2 shows the customary arrangement of the prior art types of electrometer tubes with grid G and plate P constituted by two plates extending parallel to each other.

In order to clearly distinguish the difference between my improved construction and the prior arrangement, the distance between grid and Plate electrodes has been indicated the same in both instances.

In Fig. 1 it will be understood that any electron emitted by the filament F1, for instance, will be obliged to hit the plate P or the grid G if its initial velocity is high enough. The electrons cannot escape outside of the space limited by the plate P and the grid G. However, in the arrangement of the prior art in Fig. 2 it will be seen that any electron following a path 3 will escape the attraction of the plate P and may hit the glass bulb or envelope of the tube which in turn will become negative and disturb the functioning of the tube.

The structure of the tube of my invention is such that no electron emitted by the filament can escape hitting the plate. Thus the structure of my invention produces a decrease of the ratio of grid current to plate current.

This ratio is further decreased by the fact that the surface of the grid seen from the filament is far smaller `in the case of Fig. 1 than in Fig. 2. In Fig. 1 the half dihedral angle a is approximately whereas in Fig. 2 this half dihedral angle is approximately 70 as shown at a. The angle is bounded by the surface of gri-d G or G' and extends between theoretical angular-ly disposedA planes from the iilament as a boundary edge. The amount of electrons discharged at the same velocity and able to hit the grid is proportional to the dihedral angle. In accordance with my invention the ratio of grid current to plate current will be only of the case of Fig. 2. This serves to distinguish the structure of my invention as depicted in Fig. 1 from the prior art as shown in Fig. 2.

Further study of the iield strength in these two different cases will show .the advantages of my construction. In Ithe case of plane electrodes parallel to each other the value of the electric eld strength is given by In this equation Eb represents instantaneous field strength in volts at a selected reference position and X1-Xn represents the increment of distance over which the measurement is taken. This field is constant in intensity all along the paths from the grid to the plate. In order to compute the field strength between-two coaxial. cylinders (grid and plate), the following equation is used:

Fp= volt/cm.

which gives the eld strength for any point p at a distance r from the axis of the cylinders; ra and Tlc being the radii of the plate and of the grid. The comparison between the two cases will be easily understood by using instead of the value of the field strength for any given point, the value of the mean average value of this field when the electron is going from rn to r1. The mean average value is then given by Consider an example in which (for Fig. l), the radiu-s of the grid rlc=.15 cm., the radius of the plate ra=l75 cm., distance between grid and plate in the two cases is d=.6 cm.

Fig. 3 shows the value of the different elds plotted in function of the position p of the electron between grid and plate for the two' cases, that is the arrangement of Figs. 1 and 2.

For the plane electrodes, Fig. 2, the eld is constant and its value is Fp--EX 1.666 volt/cm.

For the cylindrical electrodes, Fig. 1, the field decreases from Fe=E 4-14 to F .=E` .8`27 passing at FC=E 1-38 at midway between the electrodes. And in the same time the mean value of the eld strength varies from Fm=E 4-14 to the minimum value of Fm=Fp=E 1.666. This fact is very important which leads to a substantial improvement in the reduction of the ratio of the grid current to the plate current.

Assuming, for example, that one electron is coming toward the grid in either case with a velocity such that it can overcome the repulsion produced by the eld strength oi value Ep=EX 1.666

and the energy of the same electron will not be enough to drive it to the grid.

The greater field strength in the neighborhood of the plate has the result to push back toward a positive grid the beginning of the grid electronic current; at the same time the slope of the curve of the grid current will make a smaller angle with the abscissa as a consequence of the reduction of the surface of the grid.

The curves in Fig. 4 show the result very clearly. If the origin of grid current starts in M2 for plate electrodes at a voltage Vg=-1.75 volts, for the same electron condition the grid current will start only at M1 where the grid voltage is only Vg- .-1.28 volts. The angle a1 of the tangent in M1 to the grid current curve is greatly reduced in comparison with the former type. Values of grid bias volts are indicated by the abscissa as -Z.

I locate several laments F1, F2 and F3, etc., intermediate the grid and plate and this serves to improve the electrometer tube operation by decreasing the ratio of grid current to plate current and increasing the plate current by the same amount when the filaments are maintained at constant temperature. The radius of projection of the electrons is in the direction F101; F202; and F303. I further improve the characteristics of the tube by increasing the electric eld strength in the region of the grid which is far more important than such a cld in the region ofthe plate electrode. By increasing the lament temperature, the density of emitted electrons is increased in the arrangement of my invention. It is possible to produce per filament an electronic plate current averaging 600 microamperes, the total output being 1.8 milliampere for a three filament set up giving a voltage amplification factor of about 2.25 volts per volt against .6 for prior types of electrometers. By using a six filament set up the-se last values are nearly doubled. v The next advantage obtained by the type of electrometer tube of my invention is the decrease of the positive ion currents. This result is obtained by using for the plate and the grid a material like tantalum which While being heated up during the vacuum build up is freed of all included gases and which provides a gas free tube during normal operation as a consequence of the tremendous absorption of gases by the tantalum.

In certain ca-ses the heat treatment of the tantalum affords a large reduction of the secondary emission which is always of a deleterious nature in the vacuum tubes especially in this case.

One of the main sources of disturbances created by the mechanical vibrations acting upon a vacuurn tube is the relative displacement of the lament with respect to the other electrodes due to the inertia forces. Such displacement changes the internal characteristics of the tube and therefore produce certain variations of current as a function of the relative displacements, In order to understand this feature of my invention, reference is made to Fig. 5 which shows a cross section arrangement of the electrometer tube of my invention in which F1,Fz, F3 designate the filaments located on the same concentric circle of radius 1' at an angular distance between each other equal to 129.

Now suppose that the tub-e is submitted to an inertia force directed along XX1 which will produce therefore minute relative displacement A of all the filaments, parallel to the axis XXl. Each displacement A will modify the electronic current in accordance with the value of its projection onthe radius extending from the center of symmetry and going through the original location of the filament.

The value of the modification of the electronic current can be represented by: dI=AK cos a, a being the angle of the displacement with the radius of projection. In my invention the filaments are located at an angle of 120 then the total action of the minute displacements is the vectorial addition of` all of them, that is,

e,=AK cos x e2=AK cos (a4-2%) e3=AK cos (owl-4%) centric circle and with such angular distance from each other that the vectorial sum of their moments in respect with the center is equal to zero, the system cannot be influenced by mechanical vibrations. The conditions of symmetry in respect with av point require that the laments must number a minimum of three or any multiple of three or any multiple of four. This gives the following possibilities:

Number of filaments.; l

each combination being formed by N 4 or N 3 or (N V 4+N1 3) and so on.

The structural arrangement of the electrometer tube is illustrated more clearly in Figs. 6-10, from which it will be seen that thelament and anode elements are arrangedV within the tube-on tripod supports illustrated at FZ and Pa which project through the envelope of the electrometer tube and provideelectrical terminals as well as mechanical supports. i

The grid G is formed from a thin hollow metallic cylinder such astantalum. A reduced section forming an annular groove s is provided in one end ofthe cylinder sleeve by which the glass of the envelope shown at V rigidly Supports the grid-like cylinder. An electrical connection Ge is extended from the end of the grid-like cylinder as illustrated in Fig. 6.

The ymaterial of the bulb fused quartz. This material has highly desirable insulating properties for this class of equipment. The bulb is shown'at M-N formed in two parts transversely uniting through the circular periphm eral contact lips L1 and L2.- vThe periphera1 contact lips are Vfused together during the evacua tion process of the tube after assembly of the electrodes within the tube in which the tripod supports FZ spaced 120 degrees for supporting the may be transparent but that whatever the value of a is, the following relation exists:

then the total mechanical disturbance of all the filaments so located is:

I=e1+2+3=AKX 0:0

and the conclusion is that as long as the filaments are located around the grid cylinder on a con- The conditions of con,V

zegge-,essai if, bers H; in welded relation to each of the angularly disposed members FZ and extending over and within the circular ring member R. The hook members H serve as supports for the upper ends ofi the filaments Fi, F2 and F3.

The lower ends of the laments Fi, F2 and F3 are supported by a tripod member that I have indicated at T having a connecting stem portion which is sealed through the end of the envelope N in a position axially of the envelope as represented at Fc. It will be observed that ring memberR has a diameter larger than the diameter of plate electrode P and is spaced away from the end of the plate electrode P and is concentrically related to thegrid electrode G.

The peripheral lips L1 and L2 meet in iace to face contact on opposite sides of the radially extending supports Fz and Pe which are alternately arranged as represented more particularly in Fig. 8. That is considering the arrangement illustrated in Fig. 8 clockwise the disposition of the supporting means for the laments and the plate in the same transverse plane and reading in a clockwise direction is FZ Pa, FZ Pa., FZ and Pa.

, These supporting means are spaced sixty degrees from each other and are electrically insulated through the material of the envelope M-N and are mechanically mounted with very substantial rigidity. Any displacement, however, due to shock vibration tends to produce similar displacement with respect to the filament electrodes and the plate electrode as set forth in Fig. thereby avoiding changes in ion current. The arrangement of the symmetrically disposed filaments spaced at equidistant positions intermediate the grid and plate electrodes serves to decrease the ratio of grid current to plate current and increase the plate current and also increase thev ratio of plate current to grid voltage.

For a further understanding of other applicationsr of the principles of the electrometer vacuum tube of my invention reference is made to my copending application Serial Number 569,403, led December 22, 1944, for Electrom'eter vacuum tube, said application being a continuation-inpart of the instant application.

While I have described my invention in certain preferred' embodiments, I realize that modiiications may be made and I desire that it be understoodthat no limitations upon my invention are intended other than may be imposed by the scope of the appended claims.

What I claim as new and desire to secure by Letters Patent of the United States is as follows:

1. An electron discharge tube comprising an envelope of insulation material, a control element pendently supported axially of said envelope, a filament support comprising a ring member concentrically disposed with respect to said control element, a plurality of supports for said ring member extending radially therefrom and; Y

supported at spaced intervals by the wall of said envelope, means carried by said ring member supportingv the ends of filament elements, a filament mounting device disposed in one end of said envelope, filament elements mounted between said means and said mounting device, a plate element concentrically disposed with respect to said control element with said iilament elements disposed between saidcontrol element and said plate element and radially extending members attachedv to said plate element and projecting into said envelope supporting said plate element with respect to said filament elements and said control element.

2. An electron discharge tube comprising an envelopev of insulation material, a filament support mounted in one end of said envelopey a transversely disposed ring member, means extending through the side walls of said envelope and connected to said ring member and spring arms extending radially inwardly from said ring member and aligned with the filament support in the end of said envelope and filament elements mounted between said spring arms and said filament support.

3. An electron discharge device comprising an envelope of insulation material, a filament support extending through one end oi said envelope, a filament support positioned transversely of said tube and supported through the Iwalls thereof, filament elements suspended between each of said filament supports, resilient means carried by the transversely positioned lament support continuously subjecting said filament elements to tension under varying conditions of temperature of the filament elements.

4. An electron discharge tube comprising an insulated envelope, a iilament support extending through one end of said envelope, a second support disposed adjacent the opposite end of said envelope, means extending through the side walls of said envelope mounting said second support, a plurality of inwardly directed radially extending resilient hook members carried by said second support, and filament elements supported between said first mentioned filament support and said second filament support, said filament elements being maintainable under tension independently of varying conditions of temperature of said filament elements.

5. An electron discharge device comprisingV an enclosing vessel, a grid electrode supported axially within said vessel, a cylindrical plate electrode surrounding said grid electrode, a ring-like member concentrically disposed with respect to said plate electrode and disposed in spaced relation with respect to one end of said plate electrode, resilient supports extending radially inward from said ring-like member to equidistant positions intermediate said grid and plate electrodes, filament electrodes carried by said resilientsupports and means supporting said ringlike member and said plate electrode through the walls of said enclosing vessel for minimizing relative displacement of said filament and plate electrodes under conditions of vibration.

AUGUSTE LOUIS MARIE ANTOINE ROUY.

REFERENCES CITED r,The following references are of record in the ile of this patent:

f Number Name Date 1,478,087 l/Vilson Dec. 18, 1923 1,716,142 Little June 4, 1929 1,980,804 Koch Nov. 13, 1934 1,991,174 Rose, Jr Feb. 12, 1935 2,092,667 Knoll May 28, 1935 2,039,187 Salzberg Feb. 11, 1936 2,269,852 Hummel Jan. 13, 1942 2,277,858 Skellett Mar. 31, 1942 2,284,547 West May 26, 1942

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