US2125073A - Light-sensitive system - Google Patents

Description

July 26, 1938. o. D. KNOWLES LIGHT SENSITIVE SYSTEM Filed April 25. 1930 E a p ww T n WK 0 [Z I k W m P D ATTORNEY Patented Jul 26, 1938 UNITED STATES PATENT OFFICE LIGHT- SENSITIVE SYSTEM Application April 23, 1930, Serial No. 446,482

9 Claims.

My present application is a continuation, in part, of my pending application, Serial No. 149,290, filed Nov. 19, 1926, and assigned to Westinghouse Electric 8: Manufacturing Company,

that deals, in particular, with electronic relays. The present invention relates to improvements in light-sensitive apparatus of which an electronic relay forms an essential element, and it has particular relation to devices of this type wherein means is provided for varying the sensitivity.

Light-sensitive apparatus, of this nature, constructed according to the teachings of the prior art, with which I am familiar, comprises, chiefly,

an electronic relay actuated from a source of power and controlled by a plurality of lightsensitive cells.

It often happens that apparatus is used in localities where the power supply is not constant but has comparatively large periodic and random fluctuations. 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 must be provided over which the system does not operate. In the present traflic-control systems, wherein equipment of this nature is provided as the operating element, a variation of i 48% in the light flux eii'ecting the photo-cells is required.

It is, accordingly, an object of my invention to provide light-sensitive apparatus the sensitivity of which is adjustable.

Another object of my invention is to provide,

5 in light-sensitive apparatus, means for compensating for variations in the operating potential.

An additional object of my invention is to provide a gaseous relay, the response of which is,

within predetermined limits, independent of the 40 value of the difference of potential supplied between 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 increases as the potential dlfierence between these two electrodes is increased.

More specifically 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 electrode and one principal electrode of the relay, and responsive to variations in the electromotive force applied to the principal electrodes of the 55 relay.

According to one modification of my invention, I provide a light-sensitive system comprising an electronic relay, a plurality of photo-cells and a variable impedance. The principal electrodes of the relay are connected to the terminals 5 of a power source, the photo-cells provide a potential conductive path between one principal electrode and the control electrode of the relay, and the impedance is connected between the remaining principal electrode and the control elec- 10 trode. The impedance is, furthermore, responsive to fluctuations in the power source and varies therewith, thus varying the illumination required to actuate the relay.

In a more specific application of my inven- 15 tion, the variable impedance comprises a photocell 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 particularity 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 specific 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 circuit from which my invention has been develp Fig. 3 is a schematic drawing showing the general form that a circuit comprising my invention takes,

Fig. 4 is a schematic drawing showing a general form of my improved apparatus,

Fig. 5 is a graph that will be utilized in describing the theoretical basis of my improvement,

and

Fig. 6 is aschematic drawing showing a specific form of my improved apparatus.

The apparatus shown in Fig. 1 comprises a glass envelope l having a press 2 mounted therein from which are supported a cylindrical cathode 3 and a central anode 4. The anode 4 is surrounded by a glass tube 5 which is either 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 or neon, at a pressure oi approximately 2 millimeters of Hg, and the screen element 6 is separated 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 the tube and are connected to a plurality of contact posts l0, H, I! carried by a base element 13 into which the tube is cemented.

The cathode 3 and the anode 4 are customarily designated as the principal electrodes of the dischargetube, while the screen element 6 is termed the control electrode or grid.

It is well to mention here that the separation 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 significance. It is a well established experimental fact that the electromotive force required to cause a disruptive discharge between two electrodes of a gaseous discharge is not a permanently decreasing function of the distance between the electrodes but has a minimum value for a certain distance between the electrodes and rapidly increases, thereafter, as the distance between the electrodes is decreased. Quantitative comparisons between the electrode spacing at which the break-down voltage begins to increase, and values of the meanfree path of an electron in the gas between the electrodes, determined from independent physical considerations, have established the prediction that the two values are approximately equivalent.

The explanation of the phenomenon from the 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 of the principal active elements in producing a disruptive discharge is the ionization eiTected by the collisions between the molecules and the electrons. By decreasing the probability of collision, the contribution of molecular ionization toward eflecting a break-down of the tube is decreased 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 hereinabove, the drop in potential, between the cathode andthe grid 6, that is required to cause a disruptive discharge, may be considerably smaller than the corresponding drop in potential between the grid 6 and anode 4.

In operation, impedances l5 and I6 are connected between each principal electrode and the control electrode of the tube, and a difierence 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 impedance l6 between the cathode 3 and the control 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 potential 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 between the two electrodes 3 and 4. 0n the other hand, the distance between the control electrode anode 4 and the grid 6 is small.

6 and the anode 4 is less than the mean-freepath of the electrons in the gas, and, consequently, the collisions that take place in the gas between these two electrodes is not sufllcient to cause a disruptive discharge between these elec-. trodes. The tube is then virtually non-conductive.

If, however, Zc'iS large and Z9. is small, the drop in potential between the cathods 3 and the grid 6 is large, and the drop in potential between the It Zc is large enough, suflicient drop in potential may exist be tween the cathode 3 and the control electrode 6 to cause a discharge therebetween.

The gas column through which the discharge takes place is now in a highly ionized state and, consequently, theimpedance between the oathode 3 and the grid 6 is relatively small. Virtually, the total electromotive force E is, therefore, now applied between the grid 6 and the anode 4 and, as a result, the insulating gas between the grid and the anode breaks down, and a heavy current flows through the tube.

The impedance Zc between the cathode 3 and the control electrode 6, necessary to cause a 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 potential between the principal electrodes increases, the value of impedance Zc that is necessary to cause a discharge in the tube decreases.

It should be noted that, if the control electrode 6 is entirely insulated from the anode 4 and the cathode 3, the first flow of electron current from the cathode results in an accumulation of electrons on the control electrode and causes it to block the flow of further electron current.

In Fig. 2, an arrangement of the apparatus is shown whereby a discharge tube I may be operated. In this case, the control electrode is, under normal circumstances, insulated from both the anode andthe cathode. That is to say, the impedances between the electrodes are very large. Electrons flowing from the cathode 3, therefore, collect on the control electrode 6 and establish a negative potential blocking the flow 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 ground 20. The anode 2| of the cell I9 is connected 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 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 current 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 teachings of the prior art, of which I am aware, provision 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 influence of a light flux determined by the maximum value of the voltage and not by its average value. The difie-rence between the light flux necessary to operate the tube and the light flux 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, a photo-electric cell 28 connected between the grid 8 and the anode 4, a variable impedance 28 connected between the grid 6 and the cathode 3, and an impedance 30 connected in series with the source of. potential II.

The function of the impedance 38 in the power line I1 is simply to limit the current that flows through the tube I. The variable impedance 28, on the other hand, is responsive to variations in the impressed potential, and decreases as the electromotive force of the source II increases. It is representative of a ballast tube or a photocell 32 connected as shown in Fig. 6 that will presently be explained.

In Fig. 5, the relation between the illumination on the photo-cell and the impressed voltage,

necessary to cause a discharge in the tube relay, is shown graphically. The curve on the left 34 is plotted for a certain value of impedance 28 between the cathode 3 and the control electrode 8, and the curve on the right 35 is plotted for a smaller value of the impedance 29. It is seen that the voltage E1, necessary to cause a discharge in the tube, at a given intensity of illumination Io, increases as the impedance decreases. A potential difference E2 greater than E1 must be applied between the principal electrodes of the tube to operate it with the smaller impedance 29 between the grid 8 and the cathode 3.

It is seen then that, if. the impedance 28 is responsive to the voltage fluctuations between the principal electrodes 3 and 4, the characteristic of the tube I itself becomes responsive to the variations in the voltage, and compensation of the irregularity of the source I1 is effected. It is thus possible to operate my improved lightsensitive apparatus between considerably smaller limits of intensity of the illumination efiecting the photo-cell 28 than is possible with the earlier apparatus.

It is to be noted that, in the apparatus shown in Fig. 4, the tube I is active when the photoelectric 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 discharge 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 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 the impedance 28 to the terminals of the power .tween the control electrode 8 and the cathode 3 and is under the influence of a second source of light 38, also operated from the transformer 48.

It is to be noted that, in apparatus of this nature designed according to the teachings of the prior art, the second photo-cell 32 and the lamp 38 are replaced by a constant impedance. In this case, an increase in the voltage in the primary 4| of the transformer 48 results not only in an increase in the voltage between the principal electrodes 3 and 4 of. the tube I, but also in a large increase in the light intensity of the operating lamp 31. As a result, the margin between the illumination required to operate the tube and the illumination at which it does not operate must be rather large.

The secondlamp 38 and the second photo-cell 32 may be of such structure that they are more sensitive to variations in the voltage than the first lamp 31 and the first photo-cell 28. Consequently, an increase in the voltage supplied to the primary 4| of the transformer 48 causes a decrease in the impedance between the electrodes 2| and 22 of the second photo-cell 32 that is relatively larger than the decrease between the electrodes 2| and 22 of the first photo-cell 28. Hence, the voltage required to cause a discharge in the discharge tube I is increased, and thus the fluctuations in the power supply are at least partially compensated.

I have found that while, in the earlier trafliccontrol systems, the decrease in illumination of the operating light 31, necessary to actuate the system, is 48%, my-improved system operates satisfactorily for a decrease in illumination of only 24%.

In addition to the above discussed advantages, the apparatus shown in Figs. 3 and 4, and, to an even greater degree, the apparatus shown in Fig. 6, involve certain features which are of considerable importance. This aspect of the situation may be discussed with reference to the modification 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. However, 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 comparatively large. By reason of the decrease, the photo-cells are protected against disruptive discharge 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 important element in producing the advantage discussed above. Where the current source is of the usual constant-voltage type, the desired result claiming the feature.

the resistor as current is transmitted through the discharge device I. Hereinafter, I shall refer to a voltage absorbing device" when discussing or This expression is used with the understanding that it may apply to any general element which absorbs voltage. Thus, it may be taken as calling for an element such as the resistor 30 or the load 21.

Although I have shown and described certain specific embodiments of my invention, I am fully aware that many modifications thereof are possible. My invention, therefore, is not to be restricted except insofar as is necessitated by the prior art and by the spirit of the appended claims.

I claim as my invention:

1. Translating apparatus comprising an electric discharge device having a control electrode and a plurality of principal electrodes immersedin a gaseous medium, said device having an energized 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 electrodes of said device to maintain said device in one or the other of said conditions, a photosensitive device coupled between the control electrode 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 between the control electrode and another principal electrode of said electric discharge device and means, to be energized from said source, for

energizing said last named photo-sensitive device to suppress variations in the condition of said electric discharge device that tend to arise by reason of variations in said source.

2. Translating apparatus comprising an electric discharge device having a control electrode and a plurality of principal electrodes immersed in a gaseous medium, said device having an energized 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 electrodes of said device to maintain said device in one or the other of said conditions, a first photosensitive 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 device, said photo-sensitive devices having different voltage-sensitivity characteristics.

3. Translating apparatus comprising an electric discharge device having a control electrode and a plurality of principal electrodes immersed in a gaseous medium, said device having an energized 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 electrodes of said device to maintain said device in one or the other of said conditions, a first photosensitive 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 device, said photo-sensitive devices having diilerent voltage-sensitivity characteristics, whereby the efiects of variations in said voltage on the electrical condition of said discharge device are neutralized.

4. Translating apparatus comprising an electric-discharge device having a control electrode and a plurality of principal electrodes immersed in a gaseous medium, said device having an energized 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 electrodes of said device to maintain said device inone or the other of said conditions, a first photosensitive device coupled between the control electrode and a principal electrode of said discharge device, means energized from said source for subjecting said first photo-sensitive device to radiation, a second photo-sensitive device coupled between the control electrode and another principal electrode of said discharge device and a second means energized from said source and having a difierent radiation characteristic from said means last named for subjecting said second photo-electric device to radiation.

5. An electric discharge device having a control electrode, an anode and a cathode, means for impressing a potential difierence between said anode and cathode, impedances connected between said control electrode and each of the other said electrodes and means, responsive to a variation in the terminal potential difierence of the first said means to decrease the ratio of the impedance connected to the cathode to the impedance connected to the anode when said potential difierence rises.

6. An electric discharge device having a control electrode and a. plurality of principal electrodes, said principal electrodes being immersed in a gaseous medium, means for impressing a potential diiierence between said principal electrodes and also between said control electrode and one of said principal electrodes and light responsive means to be energized in response to variations in the terminal potential difference of the first said means to compensate for the eiiect of said variationsin producing variations in the poten-' tial difierences impressed between said principal electrodes and in the potential difierence impressed 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 control electrode, an anode and a cathode, and a plurality of photo-cells provided each with a cathode and an anode, the cathode of one of said photocells 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 control electrode and the anode of said cell being connected to the anode of said tube, and means to decrease the ratio of the-resistance of the firstmentioned photo-cell to that of the last-mentioned 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 control electrode, and the other said impedance being connected between the control electrode and the cathode of said device, andmeans to cause the ratio of the last-mentioned impedance to the first-mentioned impedance to decrease when the voltage of said source rises.

9. An electric discharge device having a control electrode, an anode and a cathode, means for impressing a potential difierence between said anode and cathode, impedances connected between said'control electrode and each of the other said electrodes and means, responsive to a variation in the terminal potential difference of the first said means to decrease the ratio of the impedance connected to the cathode to the impedance connected to the anode when said potential difference rises.

DEWEY D. KNOWLES.

Images