US2000642A - Photoelectric device - Google Patents

Description

IMay 7., 1935. A. H.' LAMB 0 Y 2,000,642

PHOTOELECTRIC DEVCE Filed July 14. 1932 'Patented May 1, 193sv UNITED STATES y amsn ruo'romc'rmc nevica Anthony n. Lamb, Elisabeth, N. '.r., signor o Weston Electrical Instrument Corporation, Newark, N. J., a corporation of New JerseyY Application July 14, 1932, Serial No. 622,531

type including an actinoelectric material such as cuprous oxide, solenlum, tellurium, selenides, tel- -lurides and the'like.

Photoelectricycells of this type have been designed and used as current-change devices for the operation, either directly or through amplifiers, of current-response devices since, in general,

the maximum voltage generated is too low to actuate satisfactorily a static amplifier, or to actuate directly a dynamic amplifier. Photocells of the'evacuated tube type are essentially voltagechange devices ln that the current output is so minute as to be of no practical use, vwhereas the voltage change resulting from wide variations in illumination is of substantial magnitude. The phototubes are not, however, sensitive to small changes within the range` of relatively low illumination.

An object of the -invention is toprovide photoelectric devices of the voltage-change type, and which are characterized bya higher sensitivity than the .known phototubes. A further object is to provide photoelectric devices of high voltage output, and of the type including a layer of actinoelectric material disposed between two electrode terminals. A

These and other objects and advantages of the invention will be apparent from the following spec'fication, when taken with the accompanying y drawing, in which:

Fig. l is a somewhat diagrammatic sectional view of a photocell of the current generating type,

Fig. 2 is a diagram oi.' a' circuit including a plurality of such cells,

, Fig. 3 is a plan view of a device embodying the invention,

Fig. 4 is a sectional view on line 4-4 of Fig. 3, and

' Figs.'5 to' 8, inclusive, are somewhat diagrammatic plan views of other mountings for cascaded cell units.

In the drawing, the reference numeral I ident'fles the actinoelectric layer of material that is arranged between a collector or grid electrode 2 and a second electrode 3 to forma photoeleetric cell CI The layerll may consist of selenium that was applied'in molten state to the backing electrode 3, and then heat treated to produce a crystalline structure. The collector electrode 2 is shown as a. grid with relatively large openings but it is to be understood that this showing serves only for purpose of illustration as the collecting electrode may have other known forms, that of a translucent film of metal.

Whether the actinoelectric layer be crystalline selenium or one of the other materials noted above, a photo-electric device such as shown 1n Fig. 1 has the property of generating a voltage between the electrodes 2, 3 when.the collecting electrode face of the layer i is exposed to light and its opposite face is dark. 'I'he voltage so developed is 'of a very low order of magnitude but 10 a substantial ilow of current may be established in an external circuit between the electrodes. l The absolute values of the voltage and current .will be diierent, of course, for the diiferent actinoelectric materials, the collecting'electrode con- 15 struction and the intensity of the illumination but in all cases the action will be of the type indicated graphically in Fig. l. If appropriate voltage and current measuring instruments are employedfas indicated diagrammatically by instruments V and A, respectively, it will be found that -the maximum voltage obtainable under strong illumination is quite small but the current output is appreciable. In view of this characteristic of the devices, they have been uniformly employed withauxiliary equipment that respondcd to changes in current flow.

As indicative of the low voltages developed, it has been impossible to obtain potentials greater than from '75 to 150 millivolts as the relatively rapid variation in voltage which results from variations in relatively low illumination does not extend over the entire range of illumination, a saturation effect preventing any increase in voltage with increasing illumination.

Voltages of the order stated are ltoo low to operate satisfactorilythe voltage-response devices that are employed with photo-electric devices of the vacuum tube type.

I have discovered that cells of the currentchange type may be cascaded to develop a voltage, when working into a circuit of such highlresistance as to substantially prevent all current flow, that is substantially the sum of the voltages developed by the individual cells, and that the size of the cascaded cells may be but fa smallfraction of the size of the cells commonlyfformed of the same materials and for use as currentchange devices. Thecurrent output of currentchange cells of the solid type is dependent upon the exposed area of the cell but I have found that the desired voltage 'addition effect may be obtained by' cascading a plurality of current-change cell units which are each of such small size as to develop only a negligible current.

such asv light or to open .As shown in Fig. 2, a plurality oi' cells C may be cascaded by connecting the collecting electrode of one cell to the back electrode of the adjacent cell. The terminals of the cascaded cells may be connected to a thermiomc amplifier 4 or other voltage response device, the number of cells being so chosen that the voltage developed between the terminals is suilicient to actuate the amplifier. as indicated graphically by the measuring instruments V, A, in Fig. 2, the input resistance oi the amplifier is ao high that there is no current iiow. but the open-circuit voitage produced upon enh posing the cells to iight is relatively high. The

open-circuit voltage ci the cascaded cells cannot be measured by (a sensitive millivoltmeter connected ...cross the terminals, since the instrument winding will short-circuit the cells and the voltage will iall appronimately to zero, and it is to be understood that the showing of the voltmeter V indicates only the magnitude of the open-circuit voltage, and not a circuit for measuring that voltage. With ten cascaded cells, for example, over 30u millivolts were developed at 5 footcandles and over lVZ volts were developed at 25u foot-candles. The high millivolt sensitivity at low illumination is thus rendered available for control purposes as the absolute value of the voltage change corresponding to a given change in illumination may be stepped up to any desired magnitude by choice ofthe number of cascaded cells.

One practical arrangement for a device comprising a plurality of cascaded cells is shown in Figs. 3 and 4. An'insulating base 5 is recessed to provide seats for receiving a plurality of small cells C and the lower ends of approximately Z-shaped connecting strips 6; the upper ends of the strips overlying an adjacent recess, whereby the strips make contact between the collecting electrode of one next cell. A glass cover plate l is secured to the b'ase 5 by a screw 0 and holds the outer ends of the connecting strips 6 in contact with the respective collecting electrodes. Terminal strips 9 extend from opposite faces of the two end cellsr to points beyond the base i5.

It is to be noted that the size oi' a multiple cell potential-generating device is not directly related to the size of the known current-generating cells employing the same materials. The individual cell units C' may be, and preferably are, quite small and the dimensions and shape of the complete multi-cell device may be the same as those of a single cell C of the current-change type, thus facilitating the manufacture ci mountings and auxiliary equipment by one construction available for use with cells of both the voltage-change and the current-change types.

It will be apparent that there is considerable latitude in the choice of the materials of the individual cell umts, and in the physical arrangements of the cascaded cells.

As illustrated in Fig. 5, a plurality of individual' cells C are alined and carried by a narrow strip I of insulating material. This form of mounting is particularly desirable when a comparatively extended region is to be protected by a light-sensitive alarm or control system. The` for example, be mounted along" strip Il may, the side of an elevator door to energize a signal a circuit-breaker when any object cell and the base electrode of the -is in such position as to be injured by closing the door or starting the elevator.

The mounting plate i I may be oi annular form, as shown in Fig. 6, or a circular mounting I2 may support s plurality oi unit cells C2 which are of sector shape. Or. as shown in Fig. 8, a plurality oi unit cells C" may be compactly arranged on a square mounting plate iii.

The number oi cascadcd cells and their arrangement muy, ofcourse, be varied to suit the particular design requirements in any given case.

I claim:

l. A photoclectric device of the voltagechange type comprising a base ci insulating material having recesses in one face thereoi, a current-generating photoelectric celi snugly received within each oi said recesses, each ci said cells being of disk form and comprising a layer of actinoelectric material between a baci: electrode and an upper light-transmitting electrode, conducting strips connecting said cells in cascade, each strip having an end extending,r to the bottom oi one recess and an opposite end overlying the upper electrode oi a cell in an adjacent recess, a glass plate overlying said cella and connecting strips, and means clamping said plate to said base to retain said strips in electrical contact with the several cells.

2. A photoelectric device as .claimed in claim 1, wherein the actinoelectric material of said cells is selenium, whereby said cells have a high resistance when not illuminated.

3. A photoelectric device of the voltagechange type comprising a base of insulating material, a plurality of connecting strips on said base and each having an outer end overlying and spaced from the inner end of an adjacent strip, a photoelectric cell unit of the current-generating type between each set of opposed inner and outer ends of adjacent strips, each cell unit comprising a layer of actinoelectric material between a back electrode and an upper light-transmitting electrode, and means securing said cells to said base and retaining the respective ends of said strip in electrical contact with the cell electrodes adjacent thereto.

fi. A photoelectric device as claimed in claim 3, wherein each cell unit is below the size capable oi developing an appreciable current output.

5. A photoelectric device of the voltage-change type comprising a recessed base of insulating material, a plurality ot photoelectric cell units of the current-generating type mounted on said base and with the outer surface thereof substantially flush with the surface of said base, each cell unit comprising a layer of actinoelectric material between and united to a back electrode and an outer light-transmitting electrode, a pair oi terminals electrically connected to electrodes oidlierent types `oi' two of said cell umts, a plurality of conducting members vconnecting the said cell units in cascade between the said pair of terminals, each connecting member having one outer end overlying the light-.transmitting electrode of one cell unit and an inner end in contact with the back electrode of an adjacent cell unit, and means securing said cell umts to said base and retaining said connecting members in electrical contact with their associated cell unit electrodes.

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