US2062270A - Electric discharge apparatus - Google Patents

Description

Nov. 24, 1936. D. D. KNowLEs ELECTRIC DIS CHARGE APPARATUS Original Filed June' 2l ATTORN Y Patented Nov. 24, 1936 ELECTRIC DISCHARGE APPARATUS Dewey D. Knowles, Wilkinsliurg, Pa.,.a'ssgnor to Westinghouse Electric & Manufacturing Company, a corporation of Pennsylvania Original application .liune 21, 1933, Serial No. 67 6,903. Divided and this application April 22,

1936, Serial N0. 75,759

9 Claims.` (C1. Z50-27) My invention relates to electric discharge apparatus and it has particular relation to relay systems of the type incorporating electric discharge devices generally known as glow tubes.

'Ihe present application is a division of my application Serial No. 676,903, led June 21, 1933, which, in turn, is a division of my application Serial No. 149,290, led November 19, 1926; both of the latter are assigned to the Westinghouse Electric & Manufacturing Company.

An object of my invention is to provide a relay of the type incorporating a glow tube provided with a self-contained discharge-controlling element.

Another object of my invention is to provide a relay of the type incorporating a glow tube capable of handling comparatively large current and controlled solely by potential changes and therefore by small variations in current.

A speciiic object of my invention is to provide a sensitive relay of the type incorporating a. glow tube capable of delivering considerable current 'and controlled solely by a small current.

More concisely stated it is an object of my invention to provide an electric discharge device for greatly amplifying a minute current.

There is, at the present, a large iield of usefulness for a potential-controlled relay capable of handling comparatively large currents. Multistage amplifiers, utilizing the usual three-electrode thermionic tubes have been employed in the past, but they are expensive to build and maintain in operation and are not entirely dependable. In addition, the thermionicampliers are not entirely satisfactory when an attempt is made to supply anode potential from a source of alternating potential.

I have accordingly designed a gaseous relay having two cold principal electrodes incorporated therein between which the output current passes, and a third, or control, electrode so arranged as to regulate the passage of the output current. The relay provided in accordance with my in vention is dependent for its operationin the variation of the current transmitted between the principal electrodes for variations in the potentials impressed between the control electrode and the principal electrodes.

The novel features which I consider characteristic of my invention are set forth with particularity in the appended claims. 'Ihe invention itself, however, both as to its organization and method of operation, together with further objects and advantages thereof, will best be understood by reference to the following description and to the drawing, in which Figure 1 is a view partly diagrammatic and .partly in section showing an embodiment of my invention, and

Figure 2 is a view partly diagrammatic and partly in section showing another modification of my invention.

If a potential is applied between an electrode having a large surface and a point electrode in the presence of an ionizable gas, a discharge will take place. Tubes have been developed for maintaining -a constant voltage across the electrodes, regardless of the current flowing within certain limits and are known commercially as voltageregulator glow-tubes.Y

It is generally known that the drop in voltage near the cathode of a glow-discharge tube is constant until the current is so large that the glow covers the whole cathode. The constant voltage drop at the Vcathode is called the cathode fall of and the electrode material. WhenV the gas is argon or neon and the cathode is made of, or coated with, sodium, potassium, or caesium, this cathode drop will be of the order of 90 volts.

A tube utilizing but two electrodes becomes active as soon as a critical voltage is applied. In

Yorder to adapt glow tubes of this type for use as relays, it was accordingly necessary to provide means for instantaneously stopping or starting the discharge independently of the applied voltage. In'my improved relay I have utilized, for thispurpose, an element somewhat analogous to the grid used in the ordinary thermionic tube.

YReferring specifically to Fig. 1, my discharge device comprises a glass envelope l having mounted therein a press 2 from which are supported a cylindrical cathode 3 and a central anode 4. The central 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 encircles the glass tube and fits closely over the exposed upper end of the anode 4. Suitable con-ducting leads l, 8, and 9 extend from the various electrodes to the exterior of the tube and are connected to a plurality of contact posts I0, Il and I2 carried by a base element i3, into which thev tube iscemented.

The cylindrical cathode 3-may be made of substantially any metal, although I have preferably employed nickel for this purpose. The grid or screen 6 and the anode are also preferably made of nickel. *Y

It is very important that the grid be placed quite close to the exposed end of the wire, a space of 11g therebetween being amply sufficient. f

In the manufacture of the device, the glass envelope carrying the various electrodes is first carefully exhausted while being heated at a temperature of 460 C. The preliminary exhaust should last for at least an hour in order to make sure that all occluded gas and water vapor are drivenout of the electrodes.

Apotential and depends on the kindv of gas used A small amount of argon or neon is then admitted into the tube, sufficient being used to raise the pressure therein to approximately two millimeters mercury. I have utilized helium with fair results, though I prefer argon or neon.

Before removing the tube from the source of gas, an alternating potential of approximately 440 V. is applied between the anode and the cathode, and the gas pressure is adjusted until a glow discharge occurs between these electrodes at a predetermined potential. The tube is then sealed off and may be supplied with a base, as indicated in the drawing, if desirable.

In operation, a source I4 of alternating potential is applied between the anode 4 and the cathode 3. If the grid element 6 is grounded, the gas in the tube will ionize and conduct current at a definite potential, in the same manner as in glow tubes of the usual type. The current is mainly from the wire anode to the cylindrical catho-de, the percentage of inverse current being very small.

Ii the grid is now insulated from ground as shown in Fig. 1, electrons will be accumulated thereby during such times as the electrode 4 is positive. When the polarity changes so that the electrode 4 is negative and the electrode 3 is positive, the previously accumulated charge on the grid remains, and each successive reversal in polarity serves to increase it. This negative charge on the grid lowers the eiective gradient between the grid and the electrode 3 to a value insuiiicient to cause ionization and increases the gradient between the grid and the electrode Il. The distance between the grid and the electrode 4, however, is quite small as compared to the distance between molecules of the gas, so that a glow discharge does not occur between the said electrodes. The insulating property of gases between closely spaced electrodes is qtute well known in the art and is styled the short path principle. It is based on the fact that a gas between electrodes will not ionize if the electrodes are spaced apart by a distance no greater than the mean free path of a molecule of the gas. It is thus apparent that, with the proper alternating potential source I4 impressed beween the electrodes 4 and 3 and with the grid floating, only a very small current will flow when the central electrode is the cathode, and substantially no current will flow when the central electrode is the anode.

If, however, the grid is grounded in order to prevent a charge being accumulated thereon or to conduct away a previously accumulated charge, this grid-eiect is lost, no charge being present to prevent a current flow when the cylindrical element becomes the cathode. The result is that a rectified alternating currentows in the same manner as in any well known point-to-plane rectifier.

When charged, the grid potential is extremely high, making it possible to remove the charge through a. resistance or a megohm or more to ground. In certain instances, it is not even necessary to connect the grid to ground in order to remove the charge, contact with the body, or with any object I6 having an appreciable capacity, being suicient to lower the potential to the point at which the discharge starts.

The sensitivity of the device to the grid charge may be varied by varying the operating voltage on the tube. If the voltage is raised, the grid will charge to a higher potential rand the tube becomes more sensitive. With4 lower voltage, a

better contact with ground is necessary to remove the charge, in order to render the tube conductive.

The device is practically self-adjusting. If the grid is left free and unconnected to ground, or to a capacity area, it will of itself, assume a charge sufficient to block the main discharge in The output of'rectiiied current when the tube is energized from an alternating current source may be as high as 100 milliamperes at 100 volts. This current is amply suiicient to energize a tenwatt incandescent lamp connected directly in circuit with the discharge device.

My relay device is useful in a variety of applications. Asa burglar-alarm-controlling device, an arrangement` could be made in which a door knob would be insulated from ground and connected to the grid, or` the grid could be connected to any other object which an intruder would be likely. to handle. Upon touching .the protected object, the grid charge would immediately be dissipated and the output current of the device could then be utilized to either ring a bell or actuate an indicating device i8 of some other type.

The device would also be useful in connection with recording meters and the like, WhereA a pointer, incapable ofV carrying a heavy current, could be utilized to carry off the grid charge.

It is also feasible to control the leakage of the grid charge by means of aphoto-electric. cell 20 as shown in liig` 2, thus giving an indication when the light reaches a certain predetermined condition.

The photo-cell could obviously be extremely small and inexpensive, inasmuch as it would merely be utilized to vary the conductivity of a leakage path for the grid charge.

By the expression unexcited cathode I mean a cathode that is not, in the normal operation f the apparatus, excited by an external energy source to emit electrons.

Although I .have illustratedV and described a specic embodiment of my invention, obvious modications will be apparent to those skilled in the art. My invention, therefore, is not to be limited except, insofar. as is necessitated by the prior art and by the spirit of the appended claims.

I claim as my invention:

1. In combination, a device comprising an evacuated envelope containing a cathode, a normally completely insulated electrostatic control member, an anode and an inert gas at a pressure sufficient to support an arc-like discharge at the impressed voltage, a source of alternating current for impressing potentials. between said anode and cathode, a load circuit connected between said anode and cathode, a current path between said load circuit and ground, anelectrostatic capacitor and means kfor connecting and disconnecting at will said capacitor between said electrostatic control member and ground.

2. In combination, a device comprising an evacuated envelope containing a cathode, a. normally completely insulated electrostatic control member, an anode and an inert gas at a pressure sufcient to sup/port an arc-like discharge at the impressed voltage, a source of alternating current for impressing potentials between said anode and cathode, a load circuit connected between said anode and cathode and means for connecting and disconnecting at will a capacitor between said electrostatic control member and the circuit between said anode and cathode. 'f f 3. In combination, a device comprising an evacuated envelope containing an unexcited cathode, a normally completely-insulated electrostatic control member, an anode and an inert gas at a pressure suflicient to support an arc-like discharge at the impressed voltage, the distance between said anode and said control member being of the order of the mean-free-path of a molecule of said gaseous medium, a source of alternating current for impressing potentials between said anode and cathode, a load circuit connected between said anode and cathode, and means for removing from said control member the charge accumulated thereon while insulated to energize said device, the last said means including control circuit elements connected between said control member and the circuit between said anode and cathode.

4. In combination, a device comprising an evacuated envelope containing an unexcited cathode of extensive surface area, an anode having a surface area which is small compared to that of the cathode, a normally completely-insulated electrostatic control member and a gas at a pressure such that strong ionization by electron collision is capable of producing a disruptive discharge in said gas, the distance between said anode and said control member being of the order of the mean free path of a molecule of said gas, a source of electrical energy and connections between said source and said anode and cathode for impressing a diierence of potential between said anode and cathode which functions to cause a charge to accumulate on said control member to maintain the ionization in said gas so weak that said device is deenergized and means for removing from said control member the charge accumulated thereon, whereby said gas is so strongly ionized that said device is energized, the last said means including control circuit elements connected between said control member and said anode and cathode connections.

5. Apparatus according to claim 4 characterized by the fact that the means for connecting the control member in such manner that the charge leaks off comprises means for inserting an electrical capacity between the control member and ground in such manner that it is charged by the charge on said control member.

6. In combination, an envelope having a gas therein at a, pressure such that strong ionization by electron collision is capable of producing a disruptive discharge in said gas, an unexcited cathode of extensive surface area and an anode having a surface area which is small compared to that of the cathode in said envelope, a source of electrical energy, connections between said source and said anode and cathode for impressing a difference of potential between said anode and cathode, an electrostatic control member within said envelope, said control member being so closely spaced to said anode that a potential difference between said control member and said anode greater than said difference of potential between said anode and said cathode is necessary to produce suicient ionization for a disruptive discharge between said control member and said anode, means for electrically coupling said control member and said anode and cathode in such manner that the difference of potential between said anode and cathode causes a charge to accumulate on said control member which prevents ionization sufficient to produce a disruptive discharge n the region between said anode and cathode and means for removing said charge from said control member, whereby disruptive discharge is produced in the region between said anode and cathode, the last said means including control circuit elements connected between said control member and said anode rand cathode connections.

7. In combination, an envelope having a gas` therein at a pressure such that ionization by electron collision is capable of producing a disruptive discharge in said gas, an unexcited cathode of extensive surface area and an anode having a surface area which is small compared to that of the cathode in said envelope, a source of electrical energy, connections between said source and said anode and cathode for impressing a difference of potential betweenV said anode and cathode that is large enough, inthe absence of discharge suppressing means, to Yproduce a disruptive discharge between said anode and cathode, means for suppressing said discharge, the last said means including an electrostatic control member within said envelope, said control member being located at a position between said anode and cathode at which the density of electron charge, in the absence of a disruptive discharge, is a maximum and substantially shielding said anode from said cathode whereby an electron charge accumulates on said control member the i'leld of which prevents a disruptive discharge in the region between said anode and cathode, and removing said charge from said control member, whereby a disruptive discharge is produced in the region between said anode and cathode, the last said means including control circuit elements connected between said control member and the connections between said source and said anode andl cathode.

8. In combination, an envelope having a gas therein at a pressure such that ionization by electron collision is capable of producing a disruptive discharge in said gas, an unexcited cathode of extensive surface area and an anode having a surface area which is small compared to that of the cathode in said envelope, a source of electrical energy, connections between said source and said anode and cathode for impressing a difference of potential 'between said anode and cathode that is large enough in the absence of discharge suppressing means to produce a disruptive discharge between said anode and cathode, means for suppressing said discharge, the last said means including an electrostatic control member within said envelope, said control member being located at a position between said anode and cathode at which the density of electron charge, in the absence of a disruptive discharge, is a maximum and substantially electrostatically shielding said anode from said cathode whereby an electronk charge accumulates on said control member the eld of which prevents a disruptive discharge in the region between said anode and cathode, and means for removing said charge from said control member, whereby a disruptive discharge is produced' inthe region between said anode and cathode, the last said means including the elements of an impedance connected between said control member and the connections between said anode and cathode.

9. Apparatus according to claim 8 characterized by the fact that the impedance is a capacity.

DEWEY D. KNOWLES.

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