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July 26, 1938. o. D. KNOWLES 2,125,073 LIGHT SENSITIVE SYSTEM Filed April 25. 1930 W: O Ek [ZI DP 1M m f” W ww p4 a.E W0.WK n T Y, AT‘TORNEY I. Patented July 26, 1938 2,125,073 UNITED STATES PATENT OFFICE 2,125,073 LIGHT- SENSITIVE SYSTEM Dewey D. Knowles, Wilkinsburg, Pa., assignor to‘ Westinghouse Electric & Manufacturing Com pany, a corporation of Pennsylvania Application April 23, 1930, Serial No. 446,482 9 Claims. (Cl. 250-415) My present application is a continuation, in part, of my pending application, Serial No. 149,290, filed Nov. 19, 1926, and assigned to West inghouse Electric 8: Manufacturing Company, 5 that deals, in particular, with electronic relays. The present invention relates to improvements in light-sensitive apparatus of which an elec tronic relay forms an essential element, and it has particular relation to devices of this type 10 wherein means is provided for varying the sensi According to one modi?cation of my inven tion, I provide a light-sensitive system compris ing an electronic relay, a plurality of photo-cells and a variable impedance. The principal elec trodes of the relay are connected to the terminals 5 of a power source, the photo-cells provide a po tential conductive path between one principal electrode and the control electrode of the relay, and the impedance is connected between the re maining principal electrode and the control elec- 10 tivity. trode. The impedance is, furthermore, respon Light-sensitive apparatus, of this nature, con structed according to the teachings of the prior art, with which I am familiar, comprises, chie?y, varies therewith, thus varying the illumination 15 an electronic relay actuated from a source of power and controlled by a plurality of light sensitive cells. ‘ It often happens that apparatus is used in localities where the power supply is not constant 20 but has comparatively large periodic and random ?uctuations. These variations seriously impair _ the utility of the apparatus, since account of them must be taken in designing the apparatus, and, as a result, a comparatively large margin 25 must be provided over which the system does not operate. In the present tra?ic-control sys tems, wherein equipment of this nature is pro vided as the operating element, a variation of i 48% in the light ?ux eii'ecting the photo-cells 30 is required. It is, accordingly, an object ‘of my invention to provide light-sensitive apparatus the vsensi tivity of which is adjustable. Another object of my invention is to provide,‘ 35 in light-sensitive apparatus, means for compen sive to ?uctuations in the power source and required to actuate the relay. ' In a more speci?c application of my inven- 15 tion, the variable impedance comprises a photo cell energized by a source of light heated from the same power supply that yields the voltage for the electronic relay. The novel features that I consider character'- 20 istic of my invention are set forth with particu larity in the appended claims. The invention itself, however, both as to its organization and its method of operation, together with additional objects and advantages thereof, will best be un- 25 derstood from the following description of spe ci?c embodiments, when read in connection with the accompanying drawing in which; Figure 1 is a view, partly in elevation and partly in section, of the discharge tube described 30 in my copending application to which reference was hereinabove made. Fig. 2 is a schematic drawing showing a cir cuit from which my invention has been devel sating for variations in the operating potential. Oped. Fig. 3 is a schematic drawing showing the gen An additional object of my invention is to pro vide a gaseous relay, the response of which is, eral form that a circuit comprising my invention within predetermined limits, independent of the Fig. 4 is a schematic drawing showing a gen eral form of my improved apparatus, Fig. 5 is a graph that will be utilized in de 40‘ value of the difference of potential supplied be tween the electrodes thereof. It is still another object of my invention to provide an electronic relay wherein the value of the potential difference required to cause a dis 45 charge between the cathode and the anode in creases as the potential dl?erence between these two electrodes is increased. More speci?cally stated, it is an object of my invention to provide, in light-sensitive apparatus 50 of the type incorporating an electronic relay, an impedance disposed between the control elec trode and one principal electrode of the relay, and responsive to variations in the electromotive force applied to the principal electrodes of the 55 relay. 35 takes, 40 scribing the theoretical basis of my improvement, and Fig. 6 is aschematic drawing showing a spe cific form of my improved apparatus. 45 The apparatus shown in Fig. 1 comprises a glass envelope l having a press 2 mounted there in from which are supported a cylindrical cath ode 3 and a central anode 4. The anode 4 is surrounded by a glass tube 5 which is either 50 continuous with, or is welded to, the material of the press 2. A metallic screen element 6 surrounds the glass tube 5 and fits closely over the upper end of the anode 4. The tube contains an inert gas, such as argon 55 2. 2,125,074;~ or neon, at a pressure oi’ approximately 2 milli meters of Hg, and the screen element 6 is sepa rated from the anode by a distance preferably less than the mean-free-path of an electron in the gas, at this pressure. _ Suitable conducting leads ‘I, 8 and 9 extend from the various electrodes to the exterior of 6 and the anode 4 is less than the mean-free path of the electrons in the gas, and, consequent ly, the collisions that take place in the gas be tween these two electrodes is not su?lcient to cause a disruptive discharge between these elec-. trodes. The tube is then virtually non-conduc tive. ‘ ‘ - the tube and are connected to a plurality of If, however, Zc'iS large and Z9. is small, the drop contact posts l0, H, I! carried by a base ele in potential between the cathods 3 and the grid 6 is large, and the drop in potential between the 10 ment 13 into which the tube is cemented. The cathode 3 and the anode 4 are customarily . anode 4 and the grid 6 is small. It Zc is large designated as the principal electrodes of the dis chargetube, while the screen element 6 is termed the control electrode or grid. It is well to mention here that the separation 15 between the screen element 6 and the anode 4 is more than an academic matter related to the kinetic theory of gases, in this connection, and has distinct physical signi?cance. It is a well enough, su?icient drop in potential may exist be— tween the cathode 3 and the control electrode 6 to cause a discharge therebetween. 25 minimum value for a certain distance between the control electrode 6, necessary to cause a The gas column through which the discharge 15 takes place is now in a highly ionized state and, consequently, theimpedance between the oath ode 3 and the grid, 6 is relatively small. Virtually, the total electromotive force E is, therefore, now 20 established experimental fact that the electro- ‘ applied between the grid 6 and the anode 4 and, motive force required to cause a disruptive dis as a result, the insulating gas between the grid charge between two electrodes of a gaseous dis and the anode breaks down, and a heavy current charge is not a permanently decreasing function flows through the tube. ' of the distance between the electrodes but has a The impedance Zc between the cathode 3 and the electrodes and rapidly increases, thereafter, as the distance between the electrodes is de creased. Quantitative comparisons between the electrode spacing at which the break-down volt 30 age begins to increase, and values of the mean free path of an electron in the gas between the electrodes, determined from independent physical considerations, have established the prediction 35 trons. By decreasing the probability of collision, the contribution of molecular ionization toward e?‘ecting a break-down of the tube is decreased collect on the control electrode 6 and establish that the two values are approximately equivalent. The explanation of the phenomenon from the and, consequently, the difference in potential that must be applied between the principal electrodes to cause a discharge is correspondingly increased. In view of the above explanation, it is seen that, in a discharge tube of the type described herein } above, the drop in potential, between the cathode and- the grid 6, that is required to cause a disrup tive discharge, may be considerably smaller than the corresponding drop in potential between the . 55 grid 6 and anode 4. In operation, impedances l5 and I6 are con nected between each principal electrode and the 85 70 75 cause a discharge in the tube decreases. It should be noted that, if the control elec trode 6 is entirely insulated from the anode 4 and the cathode 3, the ?rst ?ow of electron cur rent from the cathode results in an accumulation 35 of electrons on the control electrode and causes it to block the ?ow of further electron current. In Fig. 2, an arrangement of the apparatus is shown whereby a discharge tube I may be op erated. In this case, the control electrode is, 40 under normal circumstances, insulated from both the anode and- the cathode. That is to say, the impedances between the electrodes are very large. standpoint of the kinetic theory of gases is simple. Physically, the mean-free path is simply some form of the mean distance between two successive collisions of a random electron in the gas. One 40 of the principal active elements in producing a disruptive discharge is the ionization eiTected by the collisions between the molecules and the elec 60 discharge in the tube, depends on the drop in potential between the principal electrodes 3 and 4 and on impedance Zc. As the drop in poten tial between the principal electrodes increases, the value of impedance Zc that is necessary to 30 control electrode of the tube, and a di?erence of potential is applied by a generator ll between the principal electrodes of the tube. Let Za be the impedance l5 between the anode 4 and the control electrode 6, and Zc be the im pedance l6 between the cathode 3 and the con trol electrode 6. The drop in potential between each of the principal electrodes 3 and 4 and the control electrode 6 is dependent on Za and Zn. If Z3 is large and Zn is small, the drop in poten tial between the anode 4 and the control electrode 6 is large, while the drop in potential between the cathode 3 and the control electrode 6 is small. As a result, the electron current drawn from the cathode 3 to the control electrode 6 is small, and a disruptive discharge does not take place be tween the two electrodes 3 and 4. 0n the other hand, the distance between the control electrode Electrons ?owing from the cathode 3, therefore, a negative potential blocking the ?ow of further electrons therefrom. To provide for the leakage of the electrons from the control electrode 6, a photo-electric cell I9 is connected between the electrode 3 and the 50 ground 20. The anode 2| of the cell I9 is con nected to ground 20 and the cathode 22 to the grid 6 of the tube. The grid circuit is completed through the distributed-capacity-to-ground 23 of ‘the secondary 24 of the transformer 25, which supplies the voltage between the principal elec trodes 3 and 4. When the photo-electric cell I9 is energized, the blocking charge continually leaks away from the grid 6, and a permanent difference of poten 60 tial is established between the grid and the‘ cathode 3 which results in a break-down of the tube I. As shown in Fig. 2, the discharge cur rent excites a relay 21 which, as a matter of fact, may symbolize any signalling device. In the apparatus shown in Fig. 3 and other apparatus constructed according to the teach ings of the prior art, of which I am aware, pro vision is not made for taking care of variations in the impressed voltage. As a result, when the tube I is not operating, the photo-cell 28 must be under the in?uence of a light flux determined by the maximum value of the voltage and not by its average value. The di?e-rence between the light ?ux necessary to operate the tube and 2,125,073 \ the light ?ux under which it does not operate is. therefore, materially increased. In Fig. 4, the apparatus that I provide to remedy the situation is shown in detail. The apparatus shown in the drawing comprises, in addition to the electronic relay I and the source of potential I'l connected to its electrodes 3 and 4, 3 source rather than to the principal electrodes 3 and 4 of the tube. In Fig. 6 a speci?c form of my improved system is shown thabhas particular application in tra?lc control apparatus. In the system shown in the drawing, the photo-electric cell or cells 28 that operate the tube I is under the action of a source a photo-electric cell 28 connected between the of illumination 31 that is operated from the same grid 8 and the anode 4, a variable impedance 28 transformer 48 that supplies the voltage for the 10 connected between the grid 6 and the cathode 3, tube. A second photo-cell 32 is disposed be and an impedance 30 connected in series with the .tween the control electrode 8 and the cathode 3 source of. potential II. and is under the in?uence of a second source of The function of the impedance 38 in the power light 38, also operated from the transformer 48. line I1 is simply to limit the current that ?ows It is to be noted that, in apparatus of this na 15 through the tube I. The variable impedance 28, ture designed according to the teachings of the on the other hand, is responsive to variations in prior art, the second photo-cell 32 and the lamp the impressed potential, and decreases as the 38 are replaced by a constant impedance. In this electromotive force of the source I‘I increases. case, an increase in the voltage in the primary 4| It is representative of a ballast tube or a photo of the transformer 48 results not only in an in 20 cell 32 connected as shown in Fig. 6 that will crease in the voltage between ‘the principal elec presently be explained. trodes 3 and 4 of. the tube I, but also in a large In ‘Fig. 5, the relation between the illumina increase in the light intensity of the operating tion on the photo-cell and the impressed voltage,’ lamp 31. As a result, the margin between the necessary to cause a discharge in the tube relay, illumination required to operate the tube and the 25 is shown graphically. The curve on the left 34 illumination at which it does not operate must is plotted for a certain value of impedance 28 be be rather large. tween the cathode 3 and the control electrode 8, The secondlamp 38 and the second photo-cell and the curve» on the right 35 _is plotted for a 32 may be of such structure that they are more smaller value of the impedance 29. It is seen sensitive to variations in the voltage than the 30 that the voltage E1, necessary to cause a discharge ?rst lamp 31 and the ?rst photo-cell 28. Con in the tube, at a given intensity of illumination sequently, an increase in the voltage supplied to Io, increases as the impedance decreases. A the primary 4| of the transformer 48 causes a potential difference E2 greater than E1 must be decrease in the impedance between the electrodes applied between the principal electrodes of the 2| and 22 of the second photo-cell 32 that is rela " tube to operate it with the smaller impedance tively larger than the decrease between the elec 29 between the grid 8 and the cathode 3. trodes 2| and 22 of the ?rst photo-cell 28. It is seen then that, if. the impedance 28 is Hence, the voltage required to cause a discharge responsive to the voltage ?uctuations between in the discharge tube I is increased, and thus the principal electrodes 3 and 4, the character the ?uctuations in the power supply are at least 40 istic of the tube I itself becomes responsive to partially compensated. the variations in the voltage, and compensation I have found that while, in the earlier tra?ic of the irregularity of the source I1 is effected. control systems, the decrease in illumination of It is thus possible to operate my improved light the operating light 31, necessary to actuate the sensitive apparatus between considerably smaller system, is 48%, my-improved system operates sat 45 limits of intensity of the illumination e?ecting isfactorily for a decrease in illumination of only the photo-cell 28 than is possible with the earlier 24%. apparatus. In addition to the‘ above discussed advantages, It is to be noted that, in the apparatus shown the apparatus shown in Figs. 3 and 4, and, to an in Fig. 4, the tube I is active when the photo even greater degree, the apparatus shown in 50 electric cell 28 is in an energized state. If the anode 2| of the photo-cell is connected to the grid 8, instead of the anode 4 of the tube, and the cathode 22 is connected to the cathode 3 of the tube, a system is obtained wherein the dis charge I is inactive when the photo-cell 28 is energized. In this case, the impedance 29 is connected between the grid 8 and the anode 4 and responds to the voltage E by increasing therewith. A system of this type is within the 60 scope of. my invention. Also within the scope of my invention, is a system wherein a plurality of cells 28 are used instead of a single cell 28. These cells may, of course, have any predetermined arrangement in the circuit. Furthermore, I may point out that my system is operable with direct current as well as with alternating current. The condenser 28 in the drawing, which represents the impedance is, therefore, to be regarded as only symbolical. Finally, it should be noted that it is within the province of my invention to connect the anode 2| of the photo-cell 28 and the lower terminal of 75 the impedance 28 to the terminals of the power Fig. 6, involve certain features which are of con siderable importance. This aspect of the situa tion may be discussed with reference to the modi 20 25 30 35 40 50 ?cation shown in Fig. 6. In the apparatus shown in this view, the anode of the photo-cell 28 is connected to the junction point of the anode 4 of the discharge device I and the resistor 30. When the discharge device I is deenergized, the total potential of the source 48 is impressed between the cathode 22 of the cell 32 and the anode 2| of the cell 28. How 60 ever, when the discharge device I is energized current flows through the resistor 30 and the potential drop across the photo-cells 28 and 32 is decreased by the drop across the resistor. The latter potential drop is in general of considerable magnitude and the decrease is therefore com paratively large. By reason of the decrease, the photo-cells are protected against disruptive dis charge and the injuries resulting therefrom at the very instant that such protection is necessary, namely, when the discharge device I is energized, It is to be noted that the resistor 30 is an im portant element in producing the advantage dis cussed above. Where the current source is of the usual constant-voltage type, the desired result 75 4 9,125,073 . is produced by reason of the voltage absorbed by the resistor as current is transmitted through the discharge device I. Hereinafter, I shall refer to a '_‘voltage absorbing device" when discussing or ' claiming the feature. This expression is used with the understanding that it may apply to any , 4. Translating apparatus comprising an elec tric-discharge device having a control electrode and a plurality of principal electrodes immersed in a gaseous medium, said device having an ener it may be taken as calling for an element such gized condition and a deenergized condition and being capable only of abrupt transition from one as the resistor 30 or the load 21. condition to the other, a source of electrical ener Although I have shown and described certain speci?c embodiments of my invention, I am gy for impressing potentials between the elec 10 trodes of said device to maintain said device in fully aware that many modi?cations thereof are one or the other of said conditions, a ?rst photo possible. My invention, therefore, is not to be 1. Translating apparatus comprising an elec tric discharge device having a control electrode and a plurality of principal electrodes immersed sensitive device coupled between the control elec trode and a principal electrode of said discharge device, means energized from said source for sub 15 jecting said ?rst photo-sensitive device to radia tion, a second photo-sensitive device coupled be tween the control electrode and another principal electrode of said discharge device and a second in a gaseous medium, said device having an ener means energized from said source and having a 20 general element which absorbs voltage. Thus, 10 trical condition of said discharge device are neu tralized. restricted except insofar as is necessitated by the prior art and by the spirit of the appended claims. I claim as my invention: gized condition and a deenergized condition and di?erent radiation characteristic from said means being capable only of abrupt transition from one. last named for subjecting said second photo-elec condition to the other, a source of electrical tric device to radiation. energy for impressing potentials between the electrodes of said device to maintain said device 5. An electric discharge device having a control electrode, an anode and a cathode, means for im pressing a potential di?erence between said anode in one or the other of said conditions, a photo _ and cathode, impedances connected between said sensitive device coupled between the control elec trode and a principal electrode of said device, means for energizing said photo-sensitive device to vary the condition of said electric discharge device, another photo-sensitive device coupled be tween the control electrode and another principal electrode of said electric discharge device and control electrode and each of the other said electrodes and means, responsive to a variation in the terminal potential di?erence of the ?rst said 30 means to decrease the ratio of the impedance connected to the cathode to the impedance con~ ’ means, to be energized from said source, for nected to the anode when said potential di?er energizing said last named photo-sensitive device ence rises. 6. An electric discharge device having a con- , , to suppress variations in the condition of said electric discharge device that tend to arise by trol ‘electrode and a. plurality of principal elec trodes, said principal electrodes being immersed in reason of variations in said source. a gaseous medium, means for impressing a poten 2. Translating apparatus comprising an elec 40 tric discharge device having a control electrode and a plurality of principal electrodes immersed in a gaseous medium, said device having an ener gized condition and a deenergized condition and being capable only of abrupt transition from one condition to the other, a source of electrical energy for impressing potentials between the elec ' trodes of said device to maintain said device in one or the other of said conditions, a ?rst photo sensitive device energized from said source coupled between the control electrode and a principal electrode of ,said discharge device, a second photo-sensitive device energized from said source coupled between the control electrode and another principal electrode of said discharge 55 device, said photo-sensitive devices having differ ent voltage-sensitivity characteristics. ' 3. Translating apparatus comprising an elec tric discharge device having a control electrode and a plurality of principal electrodes immersed 60 in a gaseous medium, said device having an ener gized condition and a deenergized condition and being capable only of abrupt transition from one condition to the other, a source of electrical en ergy for impressing potentials between the elec trodes of said device to maintain said device in one or the other of said conditions, a ?rst photo sensitive device energized from said source cou pled between the control electrode and a principal electrode of said discharge device, a second photo-sensitive device energized from said source coupled between the control electrode and another principal electrode of said discharge de vice, said photo-sensitive devices having diilerent voltage-sensitivity characteristics, whereby the 75 e?ects of variations in said voltage on the elec tial diiierence between said principal electrodes and also between said control electrode and one 40 of said principal electrodes and light responsive means to be energized in response to variations in the terminal potential difference of the ?rst said means to compensate for the eiiect of said variations‘in producing variations in the poten-' tial di?erences impressed between said principal electrodes and in the potential di?erence im pressed between said principal electrodes and said control electrode. '1. An electrical circuit comprising a source of electrical energy, a tube connected to receive current from said source and equipped with a con trol electrode, an anode and a cathode, and a plu rality of photo-cells provided each with a cathode and an anode, the cathode of one of said photo cells being connected to the cathode of said tube, the anode of said photo-cell being connected to said control electrode and the cathode of another of said photo-cells being connected to said con trol electrode and the anode of said cell being 60 connected to the anode of said tube, and means to decrease the ratio of the-resistance of the ?rst mentioned photo-cell to that of the last-men tioned photo-cell as the voltage of said source rises. 8. An electrical circuit comprising a source of electrical energy, a device of the glow discharge type connected to receive current from said source and equipped with a control electrode, an anode and a cathode, a plurality of impedances one of which is a photo-cell provided with a cathode and an anode, one of said impedances being connected between the anode of said device and said con trol electrode, and the other said impedance be ing connected between the control electrode and 76 2,125,073 the cathode of said device, and‘means to cause the ratio of the last-mentioned impedance to the ?rst-mentioned impedance to decrease when the voltage of said source rises. 9. An electric discharge device having a con trol electrode, an anode and a cathode, means for impressing a potential di?erence between said anode and cathode, impedances connected be 5 tween said'control electrode and each of the other said electrodes and means, responsive to a varia tion in the terminal potential difference of the ?rst said means to decrease the ratio of the im pedance connected to the cathode to the imped ance connected to the anode when said potential difference rises. DEWEY D. KNOWLES.