US2871755A - Photo electric cell - Google Patents

Description

Feb. 3, 1959 E. A. PIERRE 2,871,755

PHOTO ELECTRIC CELL Filed oct. 6.1953 2 sheets-snet 1 Feb. 3, 1959 E. A. PIERRE 2,871,755

PHOTO ELECTRIC CELL' Filed oct. 6, 195s 2 sheets-sheet 2 INVENTOR L' 7u-l( f'cled S'. D9/[er ATTORNEY -inside a transparent enclosure-which --is air States This invention relates to photo-electric calls arranged tight and evacuated.

This application is a continuation-in-part of my U. Patent application Serial No. 130,109, led `by me on November 30, 1949, for Photo-electric cells, now abandoned.

As it is well known, photo-electric cells of this kind comprise at least two electrodes, namely an anode generally centrally arranged and a cathode generally peripherally arranged, adapted to be respectively connected to the two poles of a D. C. source. When a luminous beam is projected on the cathode an electric current is generated in the electric circuit thus formed, and the intensity of this electric current is proportional to lthe intensity of the luminous beam. In order to use this electric current which is very weak, it may be amplified for instance by means of a multiple electrode electronic tube according to a well-known technique.

The desired amplifyingfefect may also be obtained by using the device known under the designation oli photomultiplier which is a photo-electric cell comprising several anodes generally arranged facing one another and at gradually increasing potentials as they are located further from the cathode, each anode acting as an electron receiver with regard to the preceding anode and as an electron generator with regard to the subsequent anode.

One object of my invention is to provide a vacuum photo-electric cell which makes it possible, apart from measuring the intensity of the luminous beam, to indicate or localize the position of this beam along a reference axls.

Another object of my invention is to provide a vacuum photo-electric cell which makes it possible, apart from measuring the intensity of a luminous beam, to indicate and to follow the movement of this luminous beam, either along an axis or along any path in a plane with respect to a rectangular coordinate system.

Still another object of my invention is to provide a vacuum photo-electric cell adaptedfor reproducing sound records, by throwing on to the kscreen formed by the cathode of ysaid photo-electric cell, the sound records eiected in clear on a dark background or in dark on a clear background on a suitable support by means for instance of a cathode ray oscillograph.

The vacuum photo-electric cell according to the invention makes it possible to etect measurements according to the so-called Zero method as it will be seen further on.

Other objects and advantages koi. my invention will appear in the course of the following description with reference to the accompanying drawings wherein:

Fig. 1V is a diagrammatical view showing the connections of a two-anode vacuum photo-electric cell according to the invention for the 4localization of a luminous spot along a reference axis.

re l@ Fig. 2 is a diagram used to explain the distribution of the currents issuing from its anodes.

Fig. 3 is a curve of the currents.

Fig. 4 shows the connection of the cell illustrated in Fig. l for the reproduction of sound records.

Fig. 5 shows a generalisation ofthe device illustrated in Fig. 1, for localizing and studying the movement of a luminous spot with respect to two perpendicular reference axes.

Figs. 6 and 7 illustrate diagrammatcally further modiiications of the method according to the invention.

Referring first to Fig. l, a Vacuum photo-electric cell is constituted by an air-tight transparent evacuated enclosure E which contains a planar cathode C and` two parallel rectilinear anodes al and a2 having preferably a constant cross-section and arranged on one and the same side of the cathode' C parallel thereto. The cathode C is coated with a photo-responsive surface adapted to emit electrons upon the impingement of a'beam of light. Moreover the cathode C, on one hand is directly connected to the negative terminal of a D. C. source S and the two anodes a1 and a2, on the other hand, are connected to the positive terminal of this source through two resistors R1 and R2 of equal resistance values, whereas a galvanometer G is connected across said two anodes.

ln the arrangement in this gure, two anodes are symmetrically arranged with respect to a middle plane perpendicular to the plane of the cathode. point of origin O of the cathode is located on the intersection line between said middle plane and the plane of the cathode and will be used as a reference point for localizing the luminous spot.

It may be assumed, to begin with, that the luminous spot is moving over the cathode along the straight line formed by the intersection of the plane of the cathode and of the plane of the ligure. of this spot situated on the right-hand side of point O, the current issued from the anode a2 is stronger than the current issued from the anode a1 since the distance between point P and the `anode a1 is longer than the distance between point P and the anode a2. Consequently, a voltage diieren'tial appears at the terminals of the galvanometer G, by reason of the differential in the voltage drops in the two resistors R1 and R2 respectively. The smaller the distance of P is from the anode a2 (and therefore the further Adistant it is from the anode a1) the greater is the galvanometer deflection. When v point P coincides with point O; the two distances P 'al and P a2 are equal and the voltage drops in the two resistances R1 and R2 being the same, there isno deliection on the galvanometer. 1f point P moves on the left-hand side of point O the distance P a1 becomes shorter than the distance P a2, Vthe current issued from the anode al becomes stronger thanthe current yissued from the anode a2, the differential between the two resistances yR1 and R2 changes its sign `and therefore a deflection of opposite direction may be observed on th galvanometer. f

Thus, may he appreciated that the deflection on the galvanemeter sho-ws in magnitude and direction the distance of the point P from the point of origin 0.

This localization is all the more easy that, as it will be now explained, the intensity of the current which is circulated through 'Sie galvanometer is practically proportional to the distance 0P=X. In fact, referring also to Fig. 2, if it is assumed that the numbers of electrons absorbed by each anode a1 and a2 are designated by N1 and N2 respectively and thatfthe anodes a1 andra?, are spacedfrom the cathode by the same distance b, the distribution of N1 and N2 takes place according to a; law inversely proportional to the second power ofthe distances The center For any positionV P Fig. 3.

` as represented by the curve C2.

d1 and d2, respectively, of point P from the two anodes respectively N2 di'l (Z22 Y u Y Let a be the distance between the two anodesY therefore If we carry this value into the Equation Vl we Vobtain 2 a 2 u b JF 2 M) Nl- (l Z VThe current that is used in the device involved is (N2-N1), let it be i the value ofthis current If Q designates the total number of electrons falling upon both anodes:

Let d be the distance from a1 to 0 0r from a2 to O, therefore d2=0a22.

We have therefore:

Z-Qm (2) The curve which gives the variations in the current i as measured in the galvanometer, (or a value proportional thereto) in terms of the abscissa x of point P is therefore a cubic, as shown at C1 on the diagram in On this diagram, the abscissae represent, like in Fig. 2, the distance between point P and the origin, and the ordinates the intensity i of the differential current issued from the two anodes. The minima and maxima of the curve C1 correspond to abscissae (-d) and (-i-d),

' the distance d being defined as stated above with reference to Fig. 2.

However, as soon as a voltage is applied to the anodes the `maximum and the minimum correspondY to points located at the end portions of the cathode,

since the electrons fall in greater number in the potential area of the nearer anode. This results therefore in the curvature of the curve obtained being actually less marked than that of curve C1, in its inclination being steeper than that of this curve C1, and in the maxima and minima being located respectively facing the anodes; It is appreciated that the substantially rectilinear portion of the curve is practically still longer on the curve C2 than on the curve C1 and that the anode current differential is practically proportional to the distance OP=x along an extent which is about the three quarters of therwidth a=EF on the Y cathode.

In al1 the explanations given above, it has been assumed that thel luminous spot was moving in the plane of Fig. 1 along a rectilinear path over the cathode C, but it is appreciated that for all the spots having the same luminous intensity located on the cathode along a straight line parallel with the anodes al and a2 and passing through point P, the distribution of the currents issuing from the two anodes is the same and that a dilerential current of same intensity is therefore circulated through the galvanometer G.

Moreover, when the luminous spot moves only along the straight line EF, the anodes a1, a2 may havev a. short length, and theoretically they could even be reduced to mere points and practically to spheres of very small dimensions.

In practice it is not possible of course to make use of a geometrically punctual spot which would immediately destroy the cathode, and a spot havinga material surface area should be resorted to all the points of which follow the rectilinear law just explained. This results in the device having a great accuracy, since the quantity which is measured is the resultant radiation emitted by the cathode area stricken by the luminous spot and consequently it is the center of gravity of the spot which is localized, that is to say a theoretical geometrical point without any dimension. The larger the spot the greater is the quantity Q in the Equation 2.

In the present days, it is a common practice to localize optically by means of a good quality microscope, displacements of mechanical parts within an accuracy of the order of a micron, but when it comes to localizing the position of a luminous spot by means of the same procedures it has heretofore not been possible to obtain results with an accuracy better than 1A@ mm. i. e; 100 microns. The device according to the invention allows localizing the position of the luminous spot within l micron.

With this device, an amplifying device may be associated for instance a rotary mirror optical amplier, so that the precision of the final measurement is practically unlimited, apart from the lack of stability of the apparatus due for instance to vibrations, microseisms or variations.

The device suits prefectly Well for eiecting so called zero measurements since a quantity (intensity of an electric current) is available which is adapted to vary not only in absolute value, but which is also able to change each sign (either po-sitive or negative value) according as the current is circulated from a given anode towards the other or vice-versa.

Considering that all the measurements in a broad sense are based upon the measurement of displacements, the disposition according to the invention is universally applicable to all the industrial and scientific measurements.

Now, Fig. 4 schematically shows the use of a photo electric cell of the type represented in Fig. l, for reproducing sound records consisting of curves obtained by means of a cathodic ray oscillograph. Tobeusable these curves are reproduced on a suitable support preferably a 'liexible support upon which they appear either clear on a dark back-ground or dark on a 'clear back-ground, these curves are projected on to the cathode C whiebworks as a screen, by means of a wide luminous beam F either by transparency through said support, or by reflection. The two anodes al and a2 areA respectively connected to the terminals of the primary winding of a transformer T the middle tap of which is connected to the positive terminal that the-curve projected upon the cathode moves in a direction at right angles to the direction of the anodes a1, a2, the currents issuing from the anodes a1, a2 create in the `indicated in my U. S. Patent No. 2,644,857.

primary winding of the transformer T a magnetic flux which induces into the secondary winding a modulated current which follows closely the curve 'being scanned, as In other words, the motion of the support on which the curve is recorded gives rise to a corresponding modulated current fedinto the amplier A1. A loud speaker LS connected to this amplifier is used for reproducing the sound recorded on the curve.

l In Fig. 5, I have shown diagrammatically another. em-

bodiment of a photo-electric cell the basic principle of which has been explained with reference to Fig. l. In this Pig. 5, we see again thevcathode indicated by C, the anodes by a1, a2 and the corresponding connections including the source S, the two resistors R1, R2 and the galvanometer Gx. To this arrangement, however, I have added two other anodes a3, a4 also parallel with each omen-parallel with the plane of the cathode C and located on one and the same side of the cathode, preferably on the same side of the cathode as the iirst two anodes al, a2, these two additional anodes a3, a4 being futhermore at right angles to the iirst two anodes a1, a2 and this requirement constitutes another important feature of the invention. To these two additional anodes a3, a4 is associated an electrical circuit identical with the circuit associated with the two anodes a1, a2 and which, therefore, includes a source S', two resistors R3, R4 and a galvanometer Gy.

it is appreciated that by means of this arrangement, for a given emitting point P on the cathode a deflection is observed on the galvanometer Gx which is proportional to the abscissa of the point P and on the galvanometer Gy a dellection which is proportional to the ordinate of this point, in a Cartesian rectangular system of two coordinates comprising the two oriented axes Ox, Oy. It is use- 'less to give here more detailedY explanations on the reasons Vfor these results, since it has been explained in detail with Vreference to Fig. l how theabscissa of point P may be lmeasured by the use of the two anode cell.

In the arrangement comprising the cell illustrated in'Fig. 5, the measurement Vof the abscissa of point P is effected exactly Vin the same manner. Moreover, the measurement of the ordinate of point Py is effected in the same manner by means of the two anodes a3, a4 angularly shifted 90 with respect to the two anodes a1, a2. Such a disposition makes it possible to localize a point by means of the two Cartesian coordinates thereof.

It is thus possible to plot separately on agraph the coordinates of a point P on the cathode in a system of axes Ox, Oy which is assumed to be scribed onfthe cathode, as shown in Fig. 5 by merely writing down the values of the current asread on the two` galvanometers Gx, Gy, which Vare respectively proportional to the abscissa and to the ordinate of point P as already stated hereinabove. Thus,

if a curve L is scribed on the cathode and if this-curve isV scanned 'by successive spots ,while the indications of the f twogalvanometers are 'each-timeplotted on agraph ,with

rectangular coordinates, the curve L scribedonthe cathode is thus reproduced on the graph on a scale which is a function ofthe lamplifying factor. A sort of electronic pantograph is thus obtained.

Of course the invention is not limited tothe embodii ments' described and shown which have been given merely as examples. Thus, inethecase of several pairs of anodes there may be more thantwo pairs of anodes.

Instead of being located on kone and tne same side of the cathode, the various pairs of anodes may be placed on .both sides of the cathodeand, in this case, useis made For'proper interpretation of the following claims it should be understood that therein the term impedance is being used in its broad generic meaning so that in the case of a circuit to which an alternating potential is applied the term impedance includes the ohmic resistance and the reactance existing inthe particular portion of the circuit. -On the other hand, if a constant potential is applied to the particular circuit then,V in the absence of any reactance, the impedance isv automatically reduced to the ohmic resistance of the particular portion of the circuit.

For the same purpose of proper interpretation, it should Y also be noted that the Vterm indicating includes showing,

for instance by means of a suitable instrument, the existence of a ow of current between two points of an electric arrangement or the existence of a potential difference between such points and, wherever applicable, the magnitude of said current or potential dierence and the direction of tlow of such current. In addition, the term indicating is also intended to include, in the case of application of an alternating potential to the particular circuit, the supply of an audible signal of a frequency related to that of the alternating potential applied to the particular circuit.

What I claim as new and desire to be secured by Letters'Patent is:

l. A photoelectric device comprising in combination an air-tight evacuated envelope, a planar cathode in said envelope, a photo-responsive surface on one face of said cathode adapted to emit electrons upon impingement of a beam of light thereon, two pairs of parallel rectilinear elongated ano-des with a constant cross-Section facing said photo-responsive surface, said two anodes of one pair of anodes being pcsitioned'at right angles to said two anodes of the other pair of anodes, two electrical circuits respectively lassociated-with ,said two pairs of anodes, each of -said two circuits comprising two branches having each one end portion thereof respectively connected to said two v anodes of the associated pair of anodes while theother end portions of said two branches of said circuits, respectively, are joined together atrespective junction points,

iirst means for producing a voltage drop in each of said branches of one of said two lelectricalcircuits depending upon a current flowing through the vparticular branch, second means for producing a voltage drop in each of said branches of the other of said two electrical circuits dcpending upon a, current flowing through the particular branch, two D. C. sources having their negative terminals connected to said cathode and their positive terminals respectively connected to said junction points offsaid two branches of said two electrical circuits, respectively, and means connected in circuit between said two branches of said two electrical circuits respectively, so as to be responsive to any diderence between currents iiowing in said two branches, respectively, of said two electrical circuits.

2. A photo-electric device comprising in combination an Vair-tight evacuated envelope, a planar cathode in said envelope, a photo-responsive surface on one face of said cathode adapted to emit electrons upon impingement of a beam of light thereon, two pairs of parallel rectilinear alongated anodes with a constant cross-section arranged n in a` plane parallel with the plane of said cathode and facing said photo-responsivevsurface, said two anodes of one pair of an'odes .being positioned' at right angles to s aid two .anodes of the other pair of anodes, two electrical circuits respectively associated with said two pairs of anodes, each ofi-said two circuits comprising two branches V,having each one end portion thereof respectively connected-'to said two anodes of the associatedpair of anodes while the other end portions of said two branches of said circuits, respectively, are joined together at respective junction points, two resisters of equal value arranged respectively in said two branches of said two electrical circuits, respectively, two galvanometers respectively connected across said two anodes in said pairs of anodes, respectively, and two D. C. sources having their negative terminals connected to said cathode and their positive terminals respectively connected to said junction points of said two branches of said two electrical circuits, respectively.

3. A photo-electric device according to claim 2, with a photo-responsive surface on both faces of said cathode, at least one pair of anodes being located on one side of said cathode and at least another pair of anodes on the other side of said cathode.

4. A photo-electric device according to claim 3, wherein said cathode is transparent.

5. In a photo-electric apparatus, in combination, a gas-tight evacuated envelope; a planar cathode arranged in said envelope and having a photo-responsive surface adapted to emit electrons therefrom upon impingement of a beam of light thereon; at least one pair of spaced anodes arranged in said envelope and lying in a plane parallel to said planar cathode; direct-current energizing means for energizing the photo-electric apparatus having a negative terminal connected to said cathode and having a positive terminal; rst impedance means connected in a lirst circuit between said positive terminal of said direct-current energizing means and one of said anodes; second impedance means connected in a second circuit with said positive terminal and the other one of said anodes; and indicating means connected in circuit with said rst and second impedance means for indicating any difference between the currents flowing through said rst impedance means, respectively, whereby upon the impingement of a lbeam of light on said photo-responsive surface of said cathode, electrons are emitted therefrom and attracted by said anodes to produce current flow through said first and second impedance means, the indicated difference between said currents flowing through said impedance means indicating the location of the point of impingement of said beam of light on said planar cathode.

6. In a photo-electric apparatus, in combination, a gas-tight evacuated envelope; a planar cathode arranged in said envelope and having a photo-responsive surface adapted to emit electrons therefrom upon impingement of a beam of light thereon; at least one pair of spaced parallel, rectilinear anodes having a constant cross-section, arranged in said envelope and lying in a plane parallel to said planar cathode; direct-current energizing means for energizing the photo-electric apparatus having a negative terminal connected to said cathode and having a positive terminal; first impedance means connected in a iirst circuit between said positive terminal of said direct-current energizing means and one of said anodes; second impedance means connected in a second circuit with said positive terminal and the other one of said anodes; and indicating means connected in circuit with said first and second impedance means for indicating any difference between the currents ilowing through said rst and second impedance means, respectively, whereby upon the impingementy of a beam of light on said photo-responsive surface of said cathode, electrons are emitted therefrom and attracted by said anodes to produce current flow through said rst and second impedance means, the indicated difference between said currents owing through said impedance means indicating the location of the point of impingement of said beam of light on said planar cathode.

7. in a photo-electric apparatus, in combination, a gas-tight evacuated envelope; a planar cathode arranged in said envelope and having a photo-responsive surface adapted to emit electrons therefrom upon impingement of a beam of light thereon; at least one pair of spaced anodes arranged in said envelope and lying in a plane parallel to said planar cathode; direct-current energizing means for energizing the photo-electric apparatus having a negative terminal connected to said cathode and having a positive terminal; first resistor means having a-preselected resistance and being connected in a iirst circuit between said positive terminal of said directcurrent energizing means and one of said anodes; second resistor means having a resistance of predetermined magnitude ratio to said preselected resistance and being connected in a second circuit with said positive terminal and the other one of said anodes, and indicating means connected in circuit with said first and second resistor means for indicating any difference between the currents ilowing through said irst and second resistor means, respectively, whereby upon the impingement of a beam of light on said photo-responsive surface of said cathode, electrons are emitted therefrom and attracted by said anodes to produce current flow through said first and second resistor means, the indicated diference between said curents flowing through said resistor means `being a function of the distance between a preselected point on said planar cathode and the point of impingement of said beam of light on said planar cathode.

8. Apparatus as claimed in claim 7 wherein said indicating means includes a direct-current galvanometer connected directly between said two anodes.

9. Apparatus as claimed in claim 5 wherein said first and second impedance means are opposite halves of the primary winding of a transformer, said transformer having a secondary winding forming part of said indicating means.

10. A photo-electric apparatus, comprising, in combination, a gas-tight evacuated envelope; a planar cathode in said envelope; a photo-responsive surface on at least one face of said cathode adapted to emit electrons upon impingement of a beam of light thereon; at least one pair of anodes arranged in a plane parallel with the plane of said cathode and facing said photoresponsive layer; an electrical circuit associated with said pair of anodes and comprising two branches each having one end portion thereof respectively connected to one of said two anodes while the other end portions of said two branches are joined together at a junction point; impedance means in each branch of said circuit; a D. C. source having its negative terminal connected to said cathode and its positive terminal connected to said junction point of said two branches of said electrical circuit for causing a current to ow between said cathode, when exposed to light, and at least one of said anodes and through the pertaining branch of said circuit; and indicating means connected in circuit between said two branches so as to be responsive to any difference between currents which circulate in said two branches of said electrical circuit.`

References Cited in the nle of this patent UNITED STATES PATENTS 1,470,696 Nicolson v Oct. 16, 1923 2,000,705 Long t--- May 7, 1935 2,015,133 Barsties Sept. 24, 1935 FOREIGN PATENTS 1,045,737 France July 1, 17953

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