USRE21372E

USRE21372E - R gunn

Info

Publication number: USRE21372E
Authority: US
Publication date: 1940-02-27

Description

R. GUNN Re. 21,372

APPARATUS FOR THE DETECTION OF DISPLACEMENTS Feb. 27, 1940.

Original Filed Dec. .4, 1936 3 Sheets-Sheet 1 m mu 6 wx IO 8 'I'I'L'I'I'I mi mil mvznron Ross Gunn (LMH ATTORNE Y Feb. 27, 1940. GUNN Re. 21,372

' PFARATUS FOR THE DETECTION OF DISPLACBNBNTS OriginaLI-iled Dec. 4, 1936 :s Shoots-Sheet 3 EVZZN INVENTOR Ross Gunn' ATTORNEY Reiuued Feb. 27, 1940 UNITED STATES PATENT OFFICE APPARATUS FOR THE DETECTION OF DISPLAOEMENTS Itoss Gunn, Washington, D. 0.

8 Claims.

(Granted under the act of March 3, 1883, as

amended April 30, 1928; 370 0. G. 757) My invention relates to an apparatus for de tecting displacements and more particularly to a simple, rugged and eilective electrical apparatus for the remote and substantially instantaneous detection or measurement of mechanical displacements which maybe either large or small in magnitude.

In carrying out my invention, I employ a space discharge device which includes at least a cath- I ode and a movable anode and provide means responsive to the displacement to be detected or measured for imparting movement to the said anode. Any movement imparted to the anode results in a change in the average internal'resistance between the anode and cathode with at tendant change in the space current through the space discharge device. By connecting the space discharge device in a proper circuit and providing suitable indicating or recording means, a displacement of any desired character or magnitude may be detected or measured. Various types of novel space discharge devices and circuits may be advantageously employed in carrying my invention into efiect all of which will be pointed out more in detail hereinafter.

The apparatus of my invention is capable of detecting or measuring high frequency periodic or non-periodic mechanical displacements,

other structures; for detecting or recording earthquakes, either natural or such as are produceduas incidental to geo-physical exploration; for detecting or measuring elastic deformation such, for example, as would occur in a ships structure or a propeller shaft; for detecting or measuring angular displacements; and for detecting or measuring instantaneous liquid or gaseous pressures. Many other uses will readily occur to those skilled in the a'rt..

With the foregoing preliminary discussion in view, it is an object of my invention to providea simple, rugged and effective electrical apparatus for detecting or measuring periodic or. nonperiodic mechanical displacements of either large or small magnitude.

It is another object of my invention to provide -an electrical apparatus for detecting or measuring mechanical displacements wherein any change in the value of an electro-motive force incorporated in a balanced electrical circuit of the apparatus or any change in the electron emissivity of a cathode of a space discharge device incorporated in a like circuit and forming part of the apparatus will not affect any indication of the indicating means.

It is another and further object of my invention to provide an electrical apparatus for detecting or measuring angular displacements.

It is'another and still further object of my invention to provide new and novel space discharge 1! devices for incorporation in my detecting or measuring apparatus but which, however, are susceptible of being advantageously used in other environments.

Other objects and many of the attendant advantages of this invention willbe readily appreciated as the same becomes better understood by reference to the following detailed description when considered in connection with the accompanying drawings, wherein:

Fig, 1 discloses one embodiment of my invention;

Fig. 2 discloses an alternative embodiment of my invention employing a difierent space discharge device and circuit arrangement; .30

Fig. 3 depicts a further modification of my invention dlfiering over that of Fig. 2 principally in Fig. 6 is a sectional view taken on the line G6,

Fig. 5;

Fig. '7 shows another modification of my apparatus employing two cathodes in the space discharge device thereof and an amplifier for amplifying any voltage diiiferential of the bridge cir- 4,5 cult;

Figs; 8 and 9 represent different embodiments of my invention wherein the displacement of the movable electrode or electrodes of the space discharge device is controlled by suitable external magnetic means; and I 4 Fig. 10 depicts a modification of my invention suitable for the detection or measurement of fluid pressure. 1

Before proceeding with a detailed description oi. the various embodiments of my invention it is deemed advisable at this point in the interest of clarity and in order to avoid needless repetition in the subsequent description to make certain general remarks concerning the space discharge devices and circuits employed in my apparatus. As pointed out hereinbefore, each space discharge device includes at least one cathode which serves as a source of electrons. A cursory examination of the drawings will show that all cathodes have been depicted therein as of the thermionic type, the heating thereof to insure electron emission being accomplished either directly or indirectly by a suitable source of electro-motive force. I

wish to emphasize in this connection, however,

that I do not desire to be restricted to this type of cathode since cathodes which emit electrons due to bombardment by rapidly moving ions, electrons, or metastable atoms and are said to be secondarily emissive, or photo-electric cathodes, or cold or non-thermionic cathodes which spontaneously emit electrons due to treatment thereof by a radioactive substance, all will serve the purpose of my invention equally well. As for the thermionic cathode, it may be fabricated of a pure metal, be oxide-coated, be of a metal provided with an adsorbed monatomic film of one of the electro-positive metals or be of any other type known to the art. The envelopes of my space discharge devices which are fashioned from any of the materials known to the prior art and serve to enclose the electrodes may be evacuated to'produce a high vacuum and thus insure a substantially pure electron discharge or may alternatively be provided with a suitable filling measured serve to impart movement to at least one of the said three electrodes to cause simultaneously thereamong a decrease in electrical resistance'between the first and second electrodes and an increase in electrical resistance between the first and third electrodes, thus causing an unbalancing of the bridge circuit which is indicated by a suitable indicating or recording device. It is, of course, apparent that the indicating device may besuitably calibrated to indicate not only the magnitude of the displacement but also its direction.

The basic principle underlying my invention I may be best appreciated by considering the embodiment disclosed in Fig. 1 of the drawings.

There is shown depicted in this figure an envelope i of a space discharge device which includes as part thereof a flexible bellows-like me tallic or glass extension 2 to the end of which is rigidly secured the anode 3 by means of the lead-in wire 4. A cathode 5, which may be of a thermionic type, is heated to an electron emissive temperature by the source of electro-motive force' 8. The plate circuit of the space discharge device includes the source of electromotive force I and an indicating device I which may be. a milliammeter. jlhe force, pressure or displacement to be detected is represented schematically by the arrow 9. A small spring and anvil ii) are arranged to return the extension 2 of the space discharge device to its initial and desired position of rest upon removal of any actuating force or pressure. It is evident that the mounting of the anode 3 is such that the application of a force or displacement 9 as shown 'will change the mean spacing between the anode 3 and cathode 5, this displacement of the electrodes being made possible by reason of the flexible bellows-like extension 2.

It is well-known in the vacuum tube art that with a given plate potential the space current density varies in a non-linear manner with the electrode spacing and increases rapidly as the spacing between the anode and cathode structures is reduced. This fact was first established by Child and is known as Childs law. Thus, the average internal resistance between the anode 3 and cathode 5 is a definite and reproducible function of the spacing between these electrodes, which spacing is controlled by displacing the end of the flexible extension 2 by a force or pressure 9. It is therefore evident that any change in.

spacing between the electrodes 3 and 5 will result in a change in space-current, the indicating device 8 reading more or less depending upon whether the spacing between the electrodes is decreased or increased. Hence, any departure from a predetermined and initial reading or reference point of the milliammeter serves to detect a displacement, the magnitude of which is easily ascertainable by suitable calibration of the milliammeter or indicating means 8.

While the apparatus of Fig. 1 is an entirely operative and useful structure it does, nevertheless, possess certain inherent disadvantages. If, for example, the emissivity of the cathode 5 is in any manner impaired or the value of the electromotive force of either sources 6 or I changes, this will be evidenced by first order changes in the plate .current indicated'by the milliammeter I. If, then, the indicating means has been previously calibrated for a fixed electron emissivity and flxed'values of electromotive forces, it is evident that the indicating means 8 will now give inaccurate and false readings because of a changed reference point. In order to minimize any such difliculty as might be encountered in using the apparatus of Fig. 1, I provide different tube structures and circuit arrangements as will be pointed out hereinafter.

In Fig. 2 of the drawings there is shown a space discharge device and circuit arrangement which minimize the difllculties that may be en countered with-the apparatus of Fig. 1. In this figure Ii denotes the envelope of the space discharge device which like that of'Flg. 1 has al one end thereof a flexible metallic or 'glass bellows-like extension ii to which are secured and insulated from each other the two anodes I! and I4 supported by their respective lead-in wire: IS, IS, The cathode l'l which may be of a thermionic type is heated'to an electron emissive temperature by the battery It. The insulated leadin wires l5 and ii are connected in a bridg circuit which includes the two bfla'ncing re sistancesl9 and Ill. It is thus seen that $111 bridge circuit includes four arms or branches two of which are constituted by the resistance between the anodeil, cathode H, and anode l4 cathode IT with the resistances l8 and hereto fore mentioned forming the remaining tw' branches. The indicating device 2! which ma;

Me milliammeter is placed across one diagonal of the bridge and the plate potential or source oi electromotive force 22 connected across the remaining diagonal. A small spring and anvil 28 again serve to return the extension or projection l2 thespace discharge device to its initial v and desired position of rest upon the removal of any actuating force. Ii. now the end or the extension or projection I2 is displaced in any manner, such as for example by the indicated micrometer 24, the anode l2 will move toward the cathode ll while simutaneously the anode l4 will move away from the cathode, this movement of the electrodes occurring due to the fact that the anodes l8 and I4 are rigidly secured to the endofthe projection or extension l2 by means of the lead-in wires l5 and I8. The former electrode movement tends to decrease the internal resistance between the anode l2 and cathode l1 and the latter has a. tendency to increase the resistance between the anode l4 and cathode ll. Ii, then, the bridge be balanced by a suitable adjustment oi the variable resistances l8 and 2|] prlor to the application of a force by the micrometer 24, the bridge will now be unbalanced in both its arms by the displacement oi the micrometer. It is at once evident that any unbalancing of the bridge circuit will be indicated by the milliammeter 2i and that the direction of the indication of the milliammeter 2| will indicate the direction of the displacement. 'The apparatus of Fig. 2 possesses important advantages over that disclosed in Fig. 1. For example, ii the emission oi the cathode i1 is in any manner impaired or if the values of the electromotive forces l8 and 22 change, these changes or variations in emissivity and voltage will aflect the plate circuits in the bridge equally and to the first order at least. These variations or changes. however, will not be indicated by the milliammeter 2| provided the bridge is balanced as indicated in Fig. 2 of the drawings. Hence, the

electrical balance or zero reierence point willrunain fixed under varying conditions of plate plate voltage and emissivity. This is a distinct advantage and improvement over the apparatus 01 Fig. l in that any correction to the meter reading can now be easily made when based upon a fixed reference point; whereas corrections to the meter in the apparatus of Fig. 1 are extremely dimcult because of its uncertain reference point occasioned by any change in emissivity or voltage. It is thus clear that the apparatus of Fig. 2 provides a very rugged and practicable structure for indicating or measuring displacements.

The apparatus shown in Fig. 3 is a variation of that shown in Fig. 2. In this figure the envelope 25 of the space discharge device is provided at one end thereof with a flexible metal seal 28 sealed to it inany manner known to the prior art, the said seal 24 having secured thereto the tubular metallic member 21 supporting the anode leads 28 and 28. The anode lead 28, as shown, supports the anode 88 and is hermetically sealed to and insulated from the tubular member 21 by means of the insulating plug 8|. The metallic' tubular member 21 besidesserving to im part movement to the

anodes

88 and ,82 serves also as a current conductor. The cathode 38, which may be of a thermionic type, is heated to an electron emissive temperature by the battery 34 and is surrounded by a grid 38 which is connected to a suitable source of biasing voltage 88.

The space discharge device 28 as in the preceding figure is connected in a bridge circuit to form two branches thereof, the remaining two branches being constituted by the

variable resistances

81 and 38. Any convenient source of electr'o-motive force 39 serves to supply the current for energizing the bridge circuit. The tubular member 21 with the

anodes

38 and 82 rigidly secured thereto is moved by any means such as the indicated micrometer 48. An oscillographic element 4! is shown in the bridge circuit to emphasize the fact that periodic or rapid displacements of the small projecting tube may be indicated and recorded by photographic or other methods. The essential diiierence oi the apparatus of Fig, 3 over that of Fig. 2 resides in the employment of a grid structure 35 and a biasing battery 36. This arrangement can be made somewhat more sensitive than that of Fig. 2 and balancing of the bridge is somewhat more convenient. The apparatus of Fig. '3, however, also employs the fundamental principle of a change in plate resistance attending the simultaneous movement of the

anodes

38 and 32 as a result of the application of a. pressure or force to the tubular member 21. I

Fig. 4 shows another modification of my apparatus wherein 42 denotes the envelope enclosing the anodes 43, 44 and the thermionic cathode 45 which is heated to an electron emissive temperature by the battery 46. A tubular member 41 supports the anodes 43 and 44 for movement within the envelope and is identical in construction and mounting with that shown in Fig. 3 of the drawings. It is to be clearly understood that the space discharge device of Fig. 4 is identical in construction and operation with that 01' Fig. 3 except that the grid has been omitted. A diiierential galvanometer 48 with an appropriate balancing resistance 49 is connected in the plate or bridge circuit of the space discharge device, a source of electromotive force 50 serving to energize the circuit. Thewindings 5| and 52 of the differential galvanometer are, oi course, connected so that they annul each other and if the current increases in one coil and decreases in the other, the deflection will be increased due.

to both causes. The balancing resistance 49 connected across the coil 5| permits the employment of the differential galvanometer as a null instrument. Again, a spring and anvil are schematically represented at 53 to return the tubular member 41 to its initial and desired position of rest upon the removal of any actuating i'orce.

Anvils

54 and 55 and a test object 58 suggest one use of the apparatus which is applicable to the modifications previously described and to be described hereinafter. Thus, for example, it the test object 56 is a standard test piece and is introduced between the

anvils

54 and 58 as shown the bridge may be balanced so thatthe galvanometer 48 will read some predetermined value. Then as object 56 is removed and comparison objects are introduced in place thereof, the galvanometer or indicator 48 will read more or less than the value established for the standard test piece, thus showing that the object under test is greater or less in diameter than the standard. The galvanometer' 48 is readily calibrated and standardized with the result that the exact amount of departure of any test piece from that of the standard can be easily and quickly determined.

Figs. 5 and 6 illustrate a still further modification of my apparatus which is especially designed for indicating or measuring angular displate structures GI] and GI are alsoeach made of a plurality of conductors which parallel to those of the grid and substanti ly parallel to the cathode and are so arranged that when the conductors of the anode 60 (see Fig. 6) are behind the grid conductors and thus substantially fully shielded from the cathode, the conductors of the anode 6| are substantially fully exposed to the cathode. The envelope of the space discharge device includes an insulating portion 62 to which is sealed a metallic portion "having a part thereof terminating at 64 which is fiexible and to which twisting or torsional movements may be imparted. Rigidly secured to the part or extension 54 is a tubular metallic member 65' in which the lead-in wires of the anodes l and Bi are 'insulatingly supported and hermetically sealed by the insulating plug 66. It

. is evident that any angular movement of the extension 64 will result in rotary or angular movement of the anodes 60 and BI. A suitable source of electromotive force 61 serves to bias the grid while the remaining electrodes of the space discharge device are connected ina bridge circuit which includes the variable resistances 68 and 69 and the voltage source Ill for energizin the same. As in the previous embodiments of my invention a suitable indicating device H is provided for detecting any differential voltage in the bridge circuit. The manner of operation of the apparatus in Fig. is believed to be clear. Thus it any torsional movement is imparted to the flexible extension 64 by any means whatsoever rotary movement of the anodes ill and BI will result. Assuming that the initial positions of the anodes 60 and GI are shown in Fig. 6 if the movement is in the direction indicated by the arrow the conductors of the anode 60 will be exposed more and more to the cathode 58 while simultaneously the conductors of the anode 6| will be moved progressively from their exposed positions to the cathode to positions where they are shielded by the grid conductors. If the bridge be balanced prior to the initiation of any movement it is clear .that the angular displacement of the anode 60 will result in an increased current flowthereto while the current to the anode II is decreased. Since movement of the anodes causes a variation '-in the tube resistances with attendant variation oi currents in the bridge circuit it is evident that the bridge is now unbalanced and that any difierential voltage thus caused is indicated by the indicating device II. In this manner it is possible to indicate or measure angular displacements.

In the modification of Fig. '1, 12 indicates the envelope of the space discharge device to which is sealed the flexible metallic cap I! for movably mounting the anode 14. The anode as shown is interposed between two cathodes l5 and I6 01' the indirectly heated type which are heated to an electron emissive temperature by the resistance units 11 and It energized by the battery It. A small spring and anvil 80 serve to return the anode to its initial and desiredposition of rest, movement being imparted to the anode, for example, by the test piece Bi which is shown interposed between the anvil 82 and micrometer 83.

The space discharge device of Fig. 'I has certain advantages over those previously described in In this embodiment 51 designates that it is not necessary to insulate two moving lead-in wires for the anodesand as in the previous embodiments is connected in a bridge circuit which includes the variable resistances 84 and 85 and a suitable source of electro-motive force 86.

over those previously described in that any dif-. ierential voltage produced in one diagonal of the bridge circuit is amplified, this being accomplished by connected parts of the bridge circuit as shown to grid 86 and an indirectly heated cathode 81 of an amplifier tube 88. .This amplifier tube in turn forms one branch oi a second or auxiliary bridge circuit, the remaining three branches of which are constituted by the variable resistances 89, BI! and 9| and energized by a suitable source 0! electromotive force 92; This scheme insures amplification of any differential voltage in one diagonal oi the first bridge circcuit which is indicated or recorded by any proper indicating means such as, for example, an oscilograph 93. It is to .be emphasized that this arrangement for amplifying any differential voltage may be employed in any other modification of my invention and that any convenient number of stages may be employed.

A further modification of my invention is shown in Fig. 8 in which the anodes It and I! are made 0'! a magnetic material which can be magnetized by induction or maybe permanent magnets with poles as indicated. The anodes are secured to relatively flexible lead-in wires 96 and 81, a cathode 98, which may be of a thermionic type. being interposed between the said anodes. The electrodes oi! the space discharge device are connected in a bridge circuit to form .two branches thereof, the remaining two branches being formed by the variable resistances l8 and Ill and encrgized by a suitable source of electro-motive force Ill. As in the previous modifications an' indicating device I02 serves to indicate or measure any displacement of the anodes M and 5 with respect to the cathode 98. The position of the anodes within the space discharge device is controlled by any suitable external magnetic means such as, for example, a permanent magnet I". The position of the magnet I03 is controlled by The apparatus depicted in Fig. 7, however, diflers the displacement which it is desired to detect or measure, it being apparent that the magnet may be moved in a, desired manner. Thus, for examf pie, rotation of the magnet I about its axis a! symmetry will produce a displacement of the magnetic anodes within the tube in such a way that angular displacements may be readily indicated on the milliammeter or ibdicating device Fig. 9 illustrates another form which my apps.- ratus may take. In this embodiment two thermionic cathodes are employed, one 01' which is designated in general by the numeral I and made in two portions I04 and Ill", the remaining cathode I05 being similarly constructed and consisting of the parts It! and IN". The cathodes I and I" are heated to an electron emissive temperature by the respective sources of electro-motive force I" and ill. The anode is shown at I08 as a magneti'zedbody and is interposed and mounted for rotation between the cathodes. The space discharge device as in the preis indicated by a suitable indicating device II2. As in the modification of Fig. 8 the position of the anode I08 is controlled by any suitable external magnetic means such as, for example, the magnet II3, the position of the said anode with re- II! and H6 and transversely of which there extend two flexible partitions H1, H8 which may be of metal to thus provide upper and lower chambers II9, I20 and an intermediate hermetically sealed chamber I2I. Anodes I22 and I2! are electrically connected to and supported by the respective diaphragms or partitions H1, H8 a thermionic cathode I24 being interposed between the anodes for cooperation therewith. As in many of the preceding embodiments the electrodes within thehermetically sealed chamber I2I are connected to form two branches of a bridge circuit of which the remaining two branches are constituted bythe variable resistances I25 and I26. Any suitable indicating device I2I serves to indicate any diiferential voltage in the bridge circuit which is energized by the source of electro motive force I28. The chambers Ill and I2Il serve as receptacles for the fluid the pressure of which is to control the displacements of the diaphragms III and Ill. It is evident-that any pressure applied to the diaphragm ill will cause a displacement thereof thus decreasing the spacing between the anode I22 and the cathode I24 with attendant unbalancing of the bridge circuit as evidenced by an indication of the indicating means I21. The indication of the indicating means I2I will of course be proportional to the displacement of the diaphragm Ill. The diaphragm IIB which is electrically connected in the bridge circuit and to the anode I23 is introduced for two reasons. It serves as a means for balancing out irregularities in emission of the cathode or any voltage variation in the sources of electro-motive force under balanced circuit conditions but is primarily intended to correct for any changes in barometric pressure. As pointed out herelnbefore, if the dia-' 1 phragm II 'I is subjected to fluid pressure the displacement of the diaphragm will'be proportional to the pressure exerted upon it. If, for example, the apparatus is employed as a fuel gauge in aircraft, operations at high altitudes will reduce the displacement of the diaphragm II! and in order for the indicating device I2I to read the proper pressure-head the anode I23 must be displaced a distance equal to the distance displaced by the anode I22 due to the increased altitude. To insure a displacement of the anode I23 and hence a correct and accurate reading of the indicating device I21 the diaphragm H8 is provided. It is clear that the apparatus of Fig. 10 may be used to indicate diflerential pressure.

All novel features of my system or apparatus as a whole are claimed in this application, the features of novelty of my space discharge devices, however, being claimed in application Serial Number 114,111 filed concurrently herewith.

According to the provision of the patent statutes I have set forth the principle and'mode of operation of my invention and have illustrated and described what I now consider to represent its best embodiments. However, I desire to have it understood that within the scope of the appended claims the invention may be practiced otherwise than as specifically illustrated and described.

The invention herein described and claimed may be used and/or manufactured by or for the Government oi the United States of America for governmental purposes without the payment of any royalties thereon or therefor.

I claim:

1. An apparatus for detecting mechanical displacements comprising in combination an envelope enclosing at least three electrodes, at "least one of which is electron emissive and at least one of which is movable, means responsive to the mechanical displacement to be detected for imparting movement to at least the movable electrode, and means associated withv said electrodes for indicating any detected displacement.

2. An apparatus for detecting mechanical displacements comprising in combination an envelope enclosing two spaced anodes and an electron emissive cathode interposed therebetween, at least one of said anodes being mounted for movement relatively to the envelope, means responsiveto the mechanical displacement to be detected for imparting movement to at least the movable anode, and means associated with said electrodes for indicating any detected displacement.

which are arranged'such that when'the conductors of one' anode are substantially, fully shielded'by the grid conductors ffom the cathode the conductors of the other anode are substan-'- tially fully exposed to the cathode, means responsive to the angular displacement to be detected for imparting rotational movement to said anodes to thereby vary the positions of the anode conductors with respect to the grid conductors, a bridge circuit in which the aforementioned cathode and anodes are connected to form two branches thereof, a grid circuit for suitably biasing the grid, and means for indicating any detected displacement.

5. An apparatus for detecting displacements comprising in combination an envelope enclosing two spaced electron emissive cathodes and an anode interposed therebetween, means responsive to the displacement to be detected for imtity comprising in combination an envelope ene closing at least three electrodes, at least one of which is electron emissive and at least one of which is movable, means responsive to the mechanical displacement to be converted for imparting movement to at least the movable electrode and a bridge circuit in which three electrodes are connected to form two branches thereof. 1

7. An apparatus for converting a mechanical displacement into an appropriate electrical'quantity comprising in combination an envelope ene closing at least three electrodes, at least'one of which is electron emissive and at least one off which is'movable, means responsive to the mechanlcal'displacement to be converted for imparting movement to at least the movable electrode, a normally balanced circuit in which threea v electrodes are connected to form two branches thereof and means associated with said circuit for indicating a condition of unbalance.

8. An apparatus for converting a mechanical displacement into an appropriate electrical quantity comprising in combination an envelope enclosing at least three electrodes, at least one of which is electron emissive and at least one of which is movable, means responsive to the mechanical displacement to be converted for imparting movement to at least the movable electrode; a bridge circuit and an electrical instrument connected across one diagonal of the bridge circuit for energization thereby, three electrodes being connected in the bridge circuit to form two branches thereof and the remaining two branches thereof being constituted by a plurality of balancing elements.