US2646533A - Light sensitive gaseous electron discharge device and circuit therefor - Google Patents

Description

July 21, 1953 2,646,533

G. G. CARNE LIGHT SENSITIVE GASEOUS ELECTRON DISCHARGE DEVICE AND CIRCUIT THEREFOR Filed July 2'7, 1949 INVENTOR GERALD GLEN CARNE BY W TT NEY Patented July 21, 1953 LIGHT SENSITIVE GASEOUS ELECTRON DISCHARGE DEVICE THEREFOR AND CIRCUIT Gerald Glen Carne, Rockaway, N. J.', assignor to Radio Corporation of America, a corporation of Delaware Application Jul 27, 1949, Serial No. 107,044

My invention relates to electron discharge devices of the gaseous type and more particularly to a light sensitive gas tube.

It is often desirable and necessary to initiate a train of events Whenever the ambient light in a particular area decreases below a predetermined intensity or is entirely out ofi. In the past, light sensitive device which responded to decrease or cut oif of light have generally included one or more phototubes and trigger tubes so arranged in a circuit that the trigger tube fired when the ambient light falling on'the phototube was decreased or completely out off. Such devices are relatively expensive as well as costly in operation because of their complexity.

Thus, the principal object of my invention is the provision of a light responsive gas discharge tube so constructed that a discharge may be initiated when the ambient light falling thereon is reduced below a predetermined intensity,

Another object is the provision of such a device having a photo emissive member and a conductive member capacitatively coupled thereto and to which a suitable biasing voltage may be applied such that when the light falling on the photo emissive member is diminished or cut oil" altogether a discharge is initiated between the oathode and anode.

'Yet another object is the provision of such a light sensitive gas tube which is inexpensive and at the same time has a simple, rugged construction which is highly stable in operation.

A Still further object is the provision of a new and improved control circuit.

' Another object of my invention is to provide an improved control circuit wherein the conductivity of the gaseous glow discharge device is controlled by the intensity of the ambient light falling thereon.

In the embodiment exemplifying my invention I provide a cold cathode gas tube of the glow discharge type having an anode of small effective area and a large area cathode coated with suitable emissive material. I preferably providev a photo emissive member in the form of a coating applied to an interior portion of the envelope wall adjacent the anode, while on the exterior of the envelope and overlying the inner coating I preferably provide a conductive member also in the form of an adherent coating. The anode and cathode are connected across a current source and a source of biasing voltage is connected to the exterior coating. With suitable applied potentials the tube does not fire while ambient light is falling on the tube and the load circuit, as for example a solenoid remains de- 4 Claims. (Cl. 315--150) 2 energized. When the ambient light is cut off from the device a discharge is initiated through the tube and the load circuit is energized.

The novel features which I believe to be characteristic of my invention are set forth with particularity in the appended claims, but the invention itself will be best understood by reference to the following description taken in connection with the accompanying drawing which is a sectional view of an electron discharge device and circuit therefor, shown schematically, constructed in accordance with my invention.

The gas tube shown in the drawing has an envelope it closed at the bottom by a glass stem portion and, has a gaseous filling of neon and argon at a pressure of the order of mm. of mercury; neon constitutin 98% and argon 2% of the mixture. Other suitable gases may also be used. Projecting up from the stem portion is a press I 1 upon which aremounted cathode I2.

and anode i3, dis-c shaped cathode l2 has its rim turned down and a central aperture through which anode l3 extends and is provided with two support members 14 one of which is brought out by conductor I5. The upper or outer surface of cathode I2 is coated with suitable electron emitting material as will be more fully pointed out hereinbelow. Anode I3 is a nickel rod connected to lead-in l6 sealed through the press and is surrounded at all portions except at its upper end by an insulating sleeve I! which may be of glass. A getter loop 24 is also provided.

Envelope I9 carries on its interior surface, adjacent the exposed end of the anode, a floating photo emissive member preferably inthe form of an adherent coating It. The term floating as used herein to describe the coating I8 is meant to designate that it is supported insulatingly on the inside of the glass envelope H) and is not directly connected electrically to any other electrode of the tube or to any of its external terminals. On the exterior surface of the envelope overlying coating I8 and in juxtaposition therewith is a conductive member [9 also in the form of a tightly adherent coating. I

The tube is manufactured in the well known manner except as will be hereinafter described. In the tube illustrated conductive member I9 is formed by applying a coating of stannous -chlo-- ride. The envelope is heated to approximately 500 C. and the area to be coated sprayed with stannous chloride and then allowed to cool. The resulting coating is transparent and conductive. The emitting coating on the upper surface of cathode I2 is formed in the known way, barium and strontium carbonates having been used in the tube illustrated; the cathode being bombarded with high energy ions after exhaust to activate the coating. After activation of the cathode, photo emissive member 18 is formed by sputtering barium and strontium from the oathode and nickel from the anode onto the envelope as indicated forming a somewhat dense semitransparent coating. By applying a sharp 500 volt 60 cycle pulse to the electrodes, the quantity of coating deposited may be readily controlled by varying the duration.

Another highly desirable exterior coating is carbon in a suitable binder; such a coating material being sold commercially under the name Aquadag. Such a coating is not transparent and may be used when sufficient ambient light will still strike photo emission member 58 even when conductive coating (9 is not transparent. Ceasiated silver oxide or ceasiated antimony laid down in the known way also form desirable and highly useful interior photo emissive coatings.

With a suitable current source connected between cathode and anode conductors :5, IE and a biasing voltage connected to conductive member l9, ignition does not take place until the ambient light is reduced in intensity below a predetermined level. As shown the source between the anode and cathode may be a source of D. C. current such as a battery 20 of the order of 150 volts, while the conductive coating and the cath- 1 ode may be connected across an alternating cur rent source 2| of 35 volts R. M. S. I have found such an arrangement to be highly stable, igni tion taking place only when the ambient light is cut off and the tube is in substantial darkness.

With an alternating current source connected between the cathode and anode the tube will fire only when the anode is positive and the discharge is self-extinguishing. With a load such as solenoid 22 connected in the circuit and in position to control switch and circuit 23, the solenoid is deenergized so long as ambient light of at least a predetermined intensity falls on the tube. When the ambient light falls below said intensity, ignition takes place and solenoid 22 is energized. By increasing the voltage applied to coating IS the tube can be made sensitive to different intensities of light.

Although the exact phenomena which take place are not fully known at the present time, I believe that when a positive potential is applied to conductive coating 19, the surface of interior conductive coating I8 capacitatively coupled to conductive member [9 through thewallandfacing the anode assumes a positive charge which is enhanced as a result of the photo emission therefrom. As the conductive coating 1 3 swings negative, the surface of coating i3 facing the anode tends to assume a negative charge which is somewhat positive with respect to the exterior coating l9 as a result of the photo-emission. It is to be noted that the exposed or tip portion of anode i3 is of relatively small area with respect to the upper coated surface of cathode l2, and is uncoated. The gap between the anode and cathode requires a relatively high potential applied thereacross for ignition between the two to take place, while there is a region around the exposed tip of the anode of high field intensity. Now, when the light falling on the exposed surface of coating I8 is reduced below a predetermined intensity or out off entirely, this surface of coating [8 because of the reduction in photo emission assumes a greater charge corresponding to the full negative charge of the exterior coating and of sufiicient intensity which together with the high field intensity around the anode initiates breakdown and ignition between the anode and cathode. This discharge is self-sustaining. It should be further noted that coating 18 is spaced from the exposed tip of the anode at approximately the minimum breakdown potential distance in accordance with Paschens law although no visible discharge appears to take place therebetween.

While certain specific embodiments have been illustrated and described, it will be understood that various changes and modifications may be made therein without departing from the spirit and scope of the invention.

I claim:

1. A light sensitive gas discharge device, comprising a cold cathode and an anode mounted therein and remote from said cathode, a dielectric member having at least a portion thereof extending adjacent said anode, a photo emissive member on the surface of said dielectric member disposed toward and close to said anode, and a conductive member on the opposite surface of said member.

2. A light sensitive glow discharge device, comprising an envelope containing a gaseous atmosphere, a disc shaped cathode and a rod shaped anode mounted therein, all but an end portion of said anode being shielded from said cathode, a photo emissive coating on a portion of the interior of the envelope adjacent said end portion of said anode, and a conductive coating on the exterior of the envelope and overlying said emissive coating and electrically connected to said emissive coating only by electrostatic forces transmitted through said envelope.

3. A light sensitive gaseous discharge device, comprising a large area cathode coated with electron emitting material and mounted in said device, an anode mounted therein and having a small area exposed to the large area cathode and spaced at a distance therefrom, a dielectric memher having a portion thereof adjacent the anode and spaced therefrom a distance less than the distance from the anode to the cathode, a photo emissive coating on the surface of said portion disposed toward said anode, and a conductive coating on the opposite surface of said portion and in juxtaposition with said photo emissive coating.

4. In combination, a load, means for controlling the energization of said load and compris ing an electron discharge device of the gaseous glow discharge type including a cathode and an anode spaced at a distance therefrom with a current source connected therebetween, a photo emissive member in said device adjacent said anode and spaced therefrom a distance less than the distance from the anode to the cathode, a conductive member coupled only capacitatively to said photo emissive member, and a source of gias voltage connected to said conductive mem- GERALD GLEN CARNE.

References Cited in the file of this patent UNITED STATES PATENTS Number Name Date 1,724,872 Case Aug. 13, 1929 2,159,568 Ploke May 23, 1939 2,193,953 Walton Mar. 19, 1940 2,296,269 Craig et a1 Sept. 22, 1942 2,401,736 Janes June 11, 1946 2,525,768 Bruns Oct. 17, 1950

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