US2150770A - Electrical discharge device - Google Patents

Description

March 14,. 1939. K H. KINGDON ELECTRICAL DISCHARGE DEVICE Filed Jan. 26, 1937 gcio all His Attorrwey.

hwverwtor Kenrw eth H. Kim

Patented Mar. 14, 1939 2,150,770

UNITED STATES PATENT ornca ELECTRICAL DISCHARGE DEVICE Kenneth H. Kingdon, Schenectady, N. Y., assignor to General Electric Company, a corporation of New York Application January 26, 1931, Serial No. 122,381

' 6 Claims. (c1. 250-27-5) The present invention relates to electrical (118- the appended claims. The invention itself may charge devices, and more particularly to devices best be understood by referenceto the following which utilize a condensible ionizable medium as description taken in connection with the accoman operating atmosphere. panying drawing, in which Fig. 1 represents a s In the operation of discharge devices of the I longitudinal section of a discharge device suitclass mentioned it is important that the presably embodying the invention; Fig. 2 is a fragsure of the operating atmosphere be maintained mentary view in partial section illustrating. an within predetermined limits. At pressures above alternative mode of application of the invention,

a permissible maximum the device may lose its and Fig. 3 is a view showing in greater detail unidirectional characteristic if it is of the twocertain of the operative parts of Fig. 2. in electrode type, or may cease to be controllable Referring particularly to Fig. 1 I have shown if it is of the three-electrode grid-controlled a threeelectrode discharge device primarily invariety. In stable operation the pressure is custended for high voltage use. The main discharge I tomarily governed by the provision of some conelectrodes of the device comprise an anode l0 densing point which is maintainedat a temperaand a separately heated cathode H, these elel5 ture below that of the remaining parts of the ments being enclosed in. a sealed envelopev l3. device. This expedient limits the pressure exist- In the illustrated embodiment the envelope coning in the discharge space by condensing all vasists principally of metal and is constructed and por in excess of that required to maintain a presarranged to serve as a control electrode for the sure corresponding approximately to the temmain discharge. It should be understood, how- 20 perature of the condensing point. ever, as far as the present invention is concerned, While such a mode of regulation is satisfacthe arrangement of the electrodes is immaterial tory after a condition of stable operation has and that the envelope may be used as the anode, been attained, it is not entirely adequate to solve for example, without affecting the applicability 5 the problems presented in connection with reof the-invention. 5

starting a discharge device after a prolonged pe- The anode I0 is supported and insulated from riod of disuse. After such disuse it is frequently the upper end of the envelope I! by means of a found that by diffusion or otherwise the concorrugated sleeve II, for example, of glass or densed vapor has become more or less uniformly another vitreous insulating material. The distributed on the walls and electrodes in the sleeve may be hermetically sealed to the metal 30 discharge space. Under these conditions, initial of the envelope in a conventional fashion and operation will result in abnormally high presmay be closed at its upper end by means of a sures being produced by rapid vaporization of metal cap l6 joined thereto and to an anode condensed medium from the heated parts. As mounting rod H. The various glass-to-metal 5 a result, imperfect or uncontrollable operation joints may be protected against ionic bombardmay occur and persist for from one to several ment caused by the high electrostatic fields exhours' depending on the amount of time reisting during operation by means of metal shields quired to cause all the excess vapor to be conl8 suitably arranged for that purpose. densed at the normal condensation point. The cathode II is illustrated as being of the 40 It is an object of the present invention to obindirectly heated type in which the principal elec- 40 viate this difliculty by preventing excess contron emission occurs from extended surfaces prodensate from leaving the preferred condensation vided by a plurality of spaced disks I9. These region during periods of disuse of the device. In disks may be coated with an activating substance, one aspect of the invention this is accomplished for example, an alkaline-earth metal oxide and 1.1 by controlling the connection between such reare heated by radiation from an electrical region and the main body of the discharge ensistance heater 20 arranged axially within the velope in accordance with a predetermined condicathode. The cathode structure as a whole is ention of operation of the device. A preferred emclosed in a metal casing (indicated by the leadbodiment includes a valve interposed between line from the numeral II) which casing isprothe condenser and the envelope and thermostatic vided with a plurality of openings 22 to permit 50 or electromagnetic means for controlling the pothe passage of a discharge therethrough. sition of the valve, in dependence on the ener- Around the cathode and interposed between it gization of one of the discharge electrodes. and the walls of the envelope l0 there is pro- The features of novelty desired to be protected vided a metal shield 24 adapted to control the herein will be pointed out with particularity in electrostatic field between the cathode and the 55 envelope and to cause the normal path oi electron travel to be in the direction of the anode.

-The'c'ontrolling function. or the envelope is supplemented by means of a transverse metal barrier 23 interposed between the cathode and anode and'having a suiiicient number oi openings to permit the passage oi'a discharge to the anode.

- The cathode and its heating elements are supplied with current by'means oi conductors '21 and 23 which are sealed through the lower wall of the discharge envelope. Each 0! these conductors .is

insulated from the envelope by means of a glass sleeve, such sleeves being numbered 23 and respectively. The portion of the conductor 23 which is within the discharge envelope is connected to the shield 24 in such a way as to furnish support for the cathode structure as a whole. Additional support is provided by means of a tie rod 32 which rests on the bottom 01' the envelope and is connected at its upper end with the base of the shield 24. The envelope l'3'encloses a quantity of a condensible ionizable medium; for example, mercm, which is capable of supporting a low voltage discharge between'the anode Ill and the cathode Ii. Associated with the main body of the envelope I3 there is provided means for conassociated therewith. In 'the present case such means are illustrated as comprising metal vanes 36 secured in good heat-exchanging relation with the lower end of the container 34 by a mass, 0!

' solder 39 or other heat-conducting material.

- denser.

These vanes preferably have an area materially in excess of the cross-sectional area of the metal tube which connects with the bottom of the envelope.- With this arrangement, which isiully described and claimed in application, Serial No.

19,867, filed May 4, 1935 m the name of Thomas A. Elder, the heat flow to the cooled portion of the condenser is limited, and that portion is enabled to be maintained at a temperature substantially below the average temperature of the The condensate thus collected .in the container 34 is indicated by the numeral envelope walls.

In the normal operation of the device thecon. denser 34 is intended to be in open communication with the interior of the envelope, so that when stable equilibrium is reached, the desired pressure will exist in the discharge space, this pressure-being maintained by the action of the con- If such open communication is allowed to exist during periods of disuse of the discharge device, however, the mercury held in the container 34 may gradually difluse into the main body of the envelope and become more or less uniformly distributed on the envelope walls.

Thereafter in attempting to resume operation of the device the excessive vapor pressure created by vaporization of mercuryirom the high temperature points of the envelope will tend to make normal operation of the device impossible. As previously indicated, this excessive pressure may ,continue until substantially all the excess mer-.

cury has been condensed in the container 34, this procedurebeingas'low andhighlyobiectionableonthataccolmt. r

In accordance with the present invention means is provided'ior interrupting the connection between the container 34 and the main body oi. the envelope during theperiods o1 disuse of the device. Such means may comprise, for example, a valve operable either independently by the operator or automaticallyin accordance with a condition of operation oi! the device. In the particular arrangement illustrated in Fig. 1 a

valve 31 is shown as being positioned to close the opening through which the container. 34 com-' municates with the interior of the envelope II. This valve is adapted to cooperate with a valve seat 31', the opposed faces 01 these two members being so formed as to constituted relatively tight closure. Actuation of the valve 31 is controlled by a thermostatic element 33 which in turn is actuated in accordance with the energization of the cathode ll. Specifically, the thermostatic element 33 is supported on the upper portion of the conductor 21 so that it is in good heat exchanging relation'with the cathode structure, or at least with that portion of the cathode structure which comprises the shield 24. With .this arrangement as long as the cathode is at low temperature, as-it is during its-inoperative periods, the valve 3'l will remain tightly closed-thus substantially preventing the escape of mercury into the envelope interior.

supplied to the resistance heater 20, the resultant flection oi the thermostatic element'will raise the valve 31 from its seat and establish a normal connection between the container 34 and the discharge space. 1

An. alternative mode of application of the invention is illustrated in Figs. 2' and 3 in which for the sake of simplicity there is shown only a portion of the discharge device, such portion comprising the lower end of a glass envelope 4| and a cathode 42 corresponding in essential particulars to the cathode described in connection However, as soon as the cathode heats up as a result of current being with Fig. 1. In this case the cathode 42 is vsupported, and supplied with current by means of lead-in conductors 43 and 44.-sealed through a press .45 formed at the base of the envelope.

Condensing means ior the ionizable medium within the envelope is provided in the form of an offset tubulation 41 terminating at its lower end in an enlarged bulbous portion 48 adapted to receive the condensate 46. The bulbous portion or container 48 connects with the tubulation "and the main body of the envelope only by means of Fig. 3). During periods of disuse of the disan orifice 50 formed in a separating wall 5| (see 55 charge device, this orifice is closed by means of a flattened disk 53 resting against the, upper sur- Iace of the wall 5|. This disk is held loosely in place by means of a retainer 54 but is capable of moving under the action-of a mechanically separate push-rod 56. The rod 56 includes as an intermediate portion thereof a magnetic armature 51, and the rod as a whole is of suflicient length so that its lower end rests on the curved bottom of the container 48. Under normal conditions, that is, during periods of disuse of the discharge device, this rod assumes the position shown in full outline in Fig, 2, T

When the cathode 42 is energized by the ap: plication of voltage to theener z ng transformer 58 preparatoryto using the discharge device, the

armature ,5! is drawn aside by the action of an electromagnet 59 also connected to the transiormer. .Under these conditions the push-rod asin order to permit a normal condition of vapor .sumes the position indicated in dotted outline in Fig. 3. Furthermore, the action of its lower' end in riding up the inclined surface of the wall of the container 48 is such as to cause the disk 53 to be lifted from its seat and to open the orifice II. This operation places the container 48 ,in communication with the discharge space and assures the maintenance of the desired pressure conditions during the subsequent use of the device.

As a result of either of the arrangements [described in the foregoing the escape of mercury or other vaporizable ionizable medium into the main body of the envelope during periods of disuse is substantially prevented. Consequently no appreciable delay in restarting the, device is required equilibrium to be established. 1

The prevention of excessive accumulation of condensed vapor in the discharge space has other advantages in addition to those particularly emphasized in the foregoing. It has been noted, for example, that when mercury is employed as the operating'medium, stripping of active material from the cathode surfaces is frequently caused by the chemical action of the mercury condensing 'on such surfaces when the device is not in operation. By limiting the mercury in the envelope to the relatively small quantity actually vaporized during active periods, this effect is almost entirely eliminated.

While I have shown particular embodiments of my inventio'n, it will be understood by those skilled in the art that many modifications may be made without departing from the invention,

and I aim by the appended claims to cover all such modifications as fall within the true spirit and scope of the invention.

What I claim as new and desire to secure by Letters Patent of the United States is:

1. An electrical discharge device including a sealed envelope enclosing a quantity of condens ible ionizable medium, electrodes including a separately heated cathode within the envelope adapted to be energized during the operation of .the device, a cooling condenser outside the envelope forreceiving' excess ionizable medium, a

connection between the cooling condenser and the interior of the envelope, a valve interposed in said connection,-andmeans including a thermo-,

static element eifective to open the valve upon energization of the cathode and to close the valve upon deenergization thereof.

2. An electrical discharge device comprising a sealed envelope consisting principally of metal and enclosing a guantity of mercury, electrodes within the envelope including a separately heated cathode, a hollow tubulation projecting outwardly of the envelope for condensing excess mercury, a

valve controlling the connection between the tubulation and said envelope and a thermostatic element for controlling the opening and closing of said valve, said element being in good heat-exchanging relation with said cathode whereby said valve is opened only'in response to energization of the cathode. I

3. A discharge device including an envelope enclosing discharge electrodes and a quantity of Ta condensible'medium, means outside the envelope for condensing excess medium during normal operation of the device, a connection between the CODdBDSiDEvIDBBDS and the interior of the envelope, means closing the said connection during periods when the device is not in use, and means including an electro-magnet which is energized automatically in response to energization of the device for opening the said connection.

4. An electrical discharge device including a sealed envelope enclosing a quantity of condensible ionizable medium, electrodes including a cathode, and means for heating the same, a condenser outside of the main body of the envelope for receiving excess ionizable medium. a connection between said condenser and said envelope, avalve controlling said connection, said valves being closed during periods 'when the device is not in use, and means including an electro-magnet. for opening the said valve in response to the energization of said cathode heating means.

5. An electrical discharge device including an envelope, means within the envelope providing terminals for a discharge therethrough, an auxiliary container connecting with theenvelope and enclosing a quantity of mercury, means responsive to an operating condition of the device for maintaining said container in substantially free communication with the interior of the envelope throughout the entire period of normal operation of the device, and means automatically effective in response to deenergization of the device to interrupt the connection between the envelope and the container during periods when the device is not in use.

. 6. Anelectrical discharge device including an envelope enclosing a quantity of condensible ionizable medium, electrodes within the envelope adapted to be energized during the operation of the device, a condensing chamber connected with the envelope for receiving excess ionizable medium, a vapor-conveying connection between the condensing chamber and the interior of the envelope, means closing said connection during periods when the device is not in use, and means operable automatically upon energization of the device for opening said connection and for maintaining it open throughout the operation of the devlce.

KENNETH H KINGDON-

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