US2408004A - Constant voltage field emission arc discharge device - Google Patents

Description

24, 1946. c SLACK A 2,408,004 CONSTANT VOLTAGE'FIELD EMIssIoN-ARc DISCHARGE'DEVICE Filed Sept. 2e,. 1942' -2 Sheets-Sheet 1 Patented Sept. 24, 1946 UNITED STATES. PATENT OFFICE CONSTANT VOLTAGE FIEIlD'EMISSION AR DISCHARGE DEVICE Charles M. Slack, Glen Ridge,-and Clarence E. Dawley and Andrew Pfeiflfer, Bloomfield, N. J

assignors to Westinghouse Electric Corporation, East Pittsburgh, Pa., a corporation of Pennsylvania Application September 26, 1942, Serial No. 459,777

The present invention relates to discharge devices and more particularly to such devices. wherein operation is initiated by a field emission arc discharge as an electron source.

A device of this character is fully shown and described in the copending application of Charles M. Slack et al., Serial No. 412,566, filed Sept. 27, 1941, and assigned to the same assignee as the present invention. As pointed out in this application, in the operation of devices of this character field emission of electrons occurs between a pair of cold electrodes due to the high potential gradient at the cathode. This electrostatic field pulls electrons from one of the electrodes which causes a minute arc discharge to form between the starting electrode and the cathode, apparently due to evolved metallic particles, and the positive ion bombardment caused by ionization of the evolved metal vapor resulting from the are, forms a cathode spot and reduces the impedance of .the device, and an electron discharge between the cathode and anode of the device almost instantaneously occurs following initiation of the arc discharge between the starting electrode and cathode.

It has been found that a certain amount of material will be lost from and transferred between the closely spaced electrodes between which the field emission arc is initiated. This-loss and transfer of material is inherent in the operation of this "field emission arc since, contrary to other high current sources intubes; a device of this character does not depend upon the. ionization of volume gases or vapor within the tube, but is dependent primarily on the positive ions which are the result of the vaporized material fromone of the electrodes interacting withthe field emission electrons. The positive ions arenece ssary to relieve space charge and to increase the field concentration at the cathode spot which in turn produces more field and Schotky electrons.

This loss of electrode material tends eventually to increase the electrode spacing, causing an increase in the voltage, required to initiate the field emission are, finally leading to a condition where operation of the device becomes unsatisfactory because of the high initiating Voltag involved, or the device may stop functioning altogetherbecause of a lack of sufficient voltage. From such characteristics it follows that even though the spacing betweenthe initiating electrodes may not be measured directly, nevertheless, this spacing is a function of the voltage required to initiate the field emission arc and is a definite factor in the useful-life of the device.

acia ms. (01. 315-357 the automatic control In th copendingapplications of Charles M. Slack et al., Ser. No. 459,775, and John H. Findlay et al., serial No. 459,776, both filed concurrently herewith and assignedhto the same assignee as the present invention, various structures are shown and claimed for maintaining the electrode spacing and hence the initiating voltage substantially. constant during the useful life of the device. Although such structures operate satisfactorily, they are subject to the disadvan-.

tage that they are dependent on the human element by requiring manipulation by an operator.

It is accordingly an object of the present invention to provide a discharge device wherein operation is initiated by a field emission arc and the spacing between the ignition electrodes is automatically maintained substantially constant throughout the useful life of the device.

Another object of the present invention. is the provision of a discharge device wherein operation is initiated by a field emission. arc and the voltage required to initiate such, are discharge is automatically maintained substantially constant throughout the useful life of the device, A further object of the present invention is the provision of a discharge device wherein operation is initiated by a field emission arc and the spacing between the ignition electrodes is automatically maintained substantially constant to thus maintain a constancy of the ignitionvoltage despite an inherent tendency for the spacingbetweentheelectrodes to increase due to loss of electrode material during the useful life of the device. i i

Still further objects of the present invention will become obvious to those skilled in the art by reference to the accompanying drawings wherein:

- Fig. 1 is a schematic diagram of the automatic control arrangement of the present invention for maintaining the spacing between the ignition electrodes of a field emission discharge device constant and showing such device partially in cross section;

Fig. 2 is a schematic diagram showing a modification which a portion of the automatic control, arrangement of Fig. 1 may take;

Fig. 3 is a view similar to Fig. 2 but showing a still further modification which a portion of arrangement of Fig. 1 may takej i 1 Fig. 4 is a schematic'diagram of another automatic control arrangement for maintaining constancy of spacing between the ignition electrodes and hence constancy of ignition voltage in accordance with the present invention, and

Fig. is a graphic illustration of the voltage required to initiate a field emission arc with a given electrode, spacing, togetherwith the rela-' tionship' of the ignition voltage for a somewhat greater spacing, as Well as an electrode spacing too great for field emission to occur.

Referring now to the drawings in detail, the present invention as shown in Fig. 1 comprises a discharge device 4 having a vitreous envelope 5 provided with a pair of oppositely disposed ignition electrodes 6 and 1 of substantially rectangu lar configuration with their edges parallel to each other and spaced apart a distance of less than approximately .010 inch. The structural details of the device 4 are set forth in detail in the above noted concurrently filed application of Charles M. Slack et al., Serial No. 459,775, and reference may behad thereto, making further description herein superfluous.

I'It shou-ldsuffice to say that the cathode electrode I is supported by a leading-in and sup porting conductor 8 provided with a bimetallic portion or section 9 and secured by welding, soldering, or the like, to a terminal II). A similar terminal" 12 and leading-inand supporting conductor I3 is provided for the starting electrode .6 and-a terminal [4 and leading-in conductor i5- for the anode [6, except that these latter conductors l3 and 1-5 are not provided witha bimetallic portion. For the purpose of passing a heating current through the bimetallic portion 9 a terminal I! is provided which is connected to the electrode side of the leadingin and supporting conductor 8 by a short support or rod 18 and horizontally disposed conductor l9.

Although the discharge device 4- has a variety of usages, it is here shown as a control tube for supplyingenergy to a load. In such application the secondary winding 29' of a high tension transformer 2-2 has one end connected directly to the load, as indicatedby the legend, while its remaining end is connected to the terminal L0 and hence'tothe cathode 1 andalso groundedat 23. Since the anode l-6= isconnected through its terminal M to the load, energy from the secondary winding 20 is supplied as soon as the device'4 becomes conductive. The transformer 2-2-has its primary winding 24 connected to the customary domestic source ofpotential of 115-230 volts. a

In order to cause the formation of a fieldemission arc between the ignition electrodes 6 neously between the cathode I and anode l6, as hereinbefore mentioned, with the device 4 then becoming conductive, allowing energy from the transformer secondary 20 to be supplied to the loadf The ignition electrodes; as before mentioned, are subject to wear due to theevolution of metallic particles which tends to increase the spacing therebetween, as well as causing an inand 1:, an induction. coil 2-5. is provided, the

primary winding 26 of which. may be connected to a suitable source for supplying an energyimpulse thereto, such as thatshown in the abovernentioned copend-ing application of- Charles. M.

Slack et al., Serial No.- ll'2,566, filed Sept. 27, 1941. The; secondary winding 21- of'this induction coil 25, has one end. connected to the terminal l2, and hence to the starting electrode 6, while its remaining end is grounded at 28; and since the cathode is grounded at 23 as before mentioned, the potential of this secondary winding, resulting from the impulse induced therein by energization of the primary winding 26, is impressed across the ignition electrodes 6' and 1.

'Ahigh potential gradient at the cathode 1 accordingly results, causing the formation of a field emission arc" discharge between the ignition electrodes 6 and 1. Such are in turn causes an electron discharge to occur almost instantacrease in the voltage required to initiate the field emission arc. i i

In order to maintain the electrode spacing and hence the ignition voltage constant, a source of heating current ;is provided for the bimetallic section 9 comprising a transformer 29 having its secondary winding 13.0 connected to the terminals l0 and i1 and thus through the rod l8 and conductor H to the bimetallic portion 9, while the primary winding 32 -is arranged to be connected to a sourceof the customary domestic potential of -230 volts upon attraction of the armature 33' of a relay -34. For the purpose of energizing this relay 34 a further transformer 35 is provided which also has its primary winding 36 connected to the same domestic source as that of the primary windings 24 and 3'2.

The main secondary winding 3! of this transformer 35- has one of its ends connected-to one end of the winding of the relay 34, while the heating current to the bimetallic portion 9 is,

accordingly controlled by the relay 34.

In order-to make the control tube 38 conductive in accordance with variation in ignition voltage due to an increase in spacing between the ignition electrodes 6 and l of the discharge device 4,'t he grid electrode of the control tube 38 is connected through a resistance 42 to an ad'- justable resistance or rheostat 43, the latter of which is connected across a battery 44, with one side of both the rheostat 43 andbattery 44 being connected'to the filamentary cathode of the tube 38 at the mid-point" of the tertiary winding 39. and hence to ground at 40. Such arrangement enables the battery 44, to normally apply a potential to the grid of the control 'tube 38 which is made negative withjrespect t0 the cathode through adjustment of l the. rheostat43 tocause the tube to blockv the flow of energy, in thefila ment-plate. circuit, whiletheresistance 42 operates to.limit thepotent-ial. 'A small direct cur-- rent thusflows from the battery; 44 through the rheostat43.

A potentiometer 4,5 isconnected across thesecondary winding 2.1, and its adjustableiarm 46' is connected totheadjustable arm of the rheostat 43. as wellas tothe grid of the control tube 3.8 through theresistance 42-. The potentiometer 45 is thusdivided by its adjustable arm 46 into what may be considered as two resistances RI andRZ-so that when initially set for a given ignition voltage for the electrodes 6 and 1 of the discharge device 4', a fbucking current is caused to'flow throughthe rheostat 43 of the same magnitude as the. current supplied to the latter-by the-battery 44, 'so that current flow through'the' rheostat 43is neutralized. it y It is a characteristic-of discharge devices operable by field emission that the initial field emission from the initiating electrodeis transformed almost instantaneously into a negative characteristic metallic arc, as hereinbefore mentioned, causing the voltage to fall quickly to a low value. Thus the'spacing of any given electrode determines the maximum voltage independent of the maximum or peak voltage of th supply coil 27. This maybe better appreciated by reference to Fig. 5 wherein the ordinate represents voltage and the abscissa time. The curve A indicates the' ignition voltage required to cause a field emission arc for a given electrode spacing, while the curveB represents the voltage for a somewhat greater electrode spacing. Curve C shows the form of voltagewave when the electrode spacing is too great for field emission to occur.

Accordingly, when the ignition voltage impressed across the electrodes 6' and l tends to rise due togwearing away of the electrodes with an increase in their spacing, the voltage on the potentiometer'also varies, although independently of the voltage of the supply coil, causing a change in current flow through the rheostat 43 which imbalances the neutralized condition resultin from the direct current fiow from the battery 44, and this in turncauses the potential of the grid to becomeless negative with respect to the cathode, thereby making the control tube 33 conductive. Upon this control'tube becoming conductive, energy then flows from the secondary winding 31 'of the transformer 36, thus energizing the winding oi the relay 34. The relay armature 33 is accordingly attracted completing a circuit from the source of domestic supply to the primary winding 32 of the transformer 29, with the result that a heating current is supplied by the secondary winding sci-,0 the bimetallic portion 9 of the leading in conductor 8. Deflection of the latter follows, causing the electrode to move closer to the starting electrode 6, lowering the voltage to which the potentiometer 45 can rise, thus again causing a reconditioning of the arrangement so that the negative bias is restored to the grid of the control tube 38 making it non-conductive. When this occurs, the winding of relay 34 is de-energized, allowing the armature to return to its normally openposition, thus interrupting the circuit to the transformer 29 and hence the supply of heating current to the bimetallic portion 9. i i

The above described operation is intermittent and-occurs each time the ignition voltage tends to rise above the'value for which the electrodes ligand 1 were initiallyset. Moreover, the voltage corresponding to the electrode spacing and at which the system functions may be set by altering the ratio between the sections RI and R2 by adjustment of the arm of the potentiometer 6 secondary winding 21 of: the induction 0011.25, may be employed in lieu of the potentiometer of Fig. 1 if desired, with such elements: being connected to the circuit at the points designated.

a: and y as shown in both Figs. 1 and 2; In the same manner a series connected capacitor 53 and resistance 54 as shown in Fig. 3 may be substituted in the arrangement as shown in Fig. 1, which would also be connected thereto at the points a: andy. In both modifications, however, the operation is substantially the same in its eiiect on the conductivity of the control tube 38.

A still further modification is shown in Fig. 4 and wherein the discharge device 4 is constructed inthe manner as shown and described in the copending application of Charles M. Slack et al., Ser. No. 459,776, filed concurrently herewith. Since reference may be had to such application for structural details of the device 4, it is believed unnecessary that theybe set forth herein. Suffice it to say that one ofthe leading-in conductors is secured to a deflectable terminalor a diaphragm, such as shown at 55, which enables deflection of the leading-in and supporting conductor, together 5 with the starting electrode 6 carried thereby, upon sliding movement of a terminal block 56 so as to decrease the spacing between the ignition electrodes 6 and 1 similar to that hereinbefore de-' scribed with reference to Fig. 1. A

Inthe same manner as shown in Fig. l the discharge device 4 of Fig. 4 controls the supply of energy from the high voltage transformer. 22 to the load and the induction coil 25 also supplies the ignition voltage to the starting electrodes 6 and I. Since the only difierence in the modification of Fig. 4 residesin the apparatus for automatically controlling the electrode spacing, further description of Fig. 4 will be restricted to the'latter. By reference to Fig. 4, it will be noted that a second induction coil 5'1 is provided, the primary winding 58 of which is connected across the secondary winding 2'! and thus in electricalparallel with the ignition electrode circuit, as is the potentiometer 45 of Fig. l.

The low potential secondary winding 59 of the induction coil 51 is connected to a full wave rectifier, shown generally at 60' and comprising the customary two pairs of oppositely connected rectifying valve tubes, and the direct current output side of such rectifier is connected to the magnetic coil 62 of a suitable switch 63. Although this switch may be of any appropriate type, it is shown as being provided with a spring biased rotatable arm 64 which is normally maintained in a central position between a pair of stationary contacts 65 and 66 against the tension of a spring fill, when a small D. C. magnetizing current fiows through the winding 62.

Flow of current through this winding 62 is thus dependent upon the voltage impressed on the primary winding 58 of the induction coil 51, which latter is dependent upon the voltage of the secondary winding 21 of the first induction coil 25 supplying the ignition Voltage to the electrodes 6 and 1. Again, as in the modification of Fig. 1, when the ignition electrodes 6 and i wear away, there is a tendency for the ignition voltage to rise, which thus increases the voltage supplied to the primarywinding 58. This increased voltage causes an increase in the flow of D. C. current through the magnetic winding 62 of the switch 63, with theresult that the rotatable arm 64 moves into contact with the stationary terminal 65, and when the current falls to a low value, the spring 621 causes. thearmtd. to engage the; stationarycontact: tenninallid, V

'Asshown, the rotatable arm 641 is connected to a D. "C. motor .66, while the. contacts: 65.:andi 6.6 are. connected respectively to suitable I); C. sources. of supply, such as batteries; 69; and 10., with the. opposite side of these batteriesin turn connected to the D. C. motor B8; Accordingly, when the: switch arm 64. engages thecontact 65., an energizing circuit is. completed from theb'att-eries 1.0- to'the DC. motor. The motor- 68: is providedwith a worm, 'EZ' engageable with a worm gear 13', the latter of" whichis carried: by a journalled shaft 142 engageable by a threaded shaft 15 loosely secured to the slideable block 56. Consequently, rotation of the motor upon closingv of the ener-- gizing circuit will cause the sliding block 56 to. move to'the left, as shown in Fig. 4, deflecting the leading-in and supporting conductor carrying. the starting electrode 6, thus decreasing the spacing between the ignition electrodes 6 and 1..

Reverse operation is. effected by engagement of the. rotatable switch arm 64 engaging the stationary contact terminal 66 which again closes an energizing circuit. from the batteries 69 to the D. C. motor 68, thereby causing reverse rotation of the D. C. motor, together with the gears 12 and 13 and sliding movement of the block. 56 to the right, as shown in Fig. 4..

It will be appreciated that, as. in the modification of Fig. 1, the arrangement of Fig. 4 isintermittently operable in response to variations in ignition voltage caused by wearing away of the electrodes 6 and 1., so that. again the spacing between the ignition electrodes and l. is automatically maintained constant, as is the ignition voltage, by energization of the motor and attendantmechanical operation to move the! electrodelfi toward the electrode I, thus decreasing the spacing.

It thus becomes obvious tov those skilled in the art that a discharge device is herein shown and describ d wherein operation is initiated by field emission of electrons. and the spacingibetween the ignition electrodes isv automatically maintained substantially constant during the useful life of the device, despite the fact that such electrodes are subject to; deterioration tending to, increase 7 their spacing, due to. the evolution of metallic particles.

Moreover, since any tendency for the ignition electrode spacing to. increase causes a corresponding increase in theignition voltage, such variation in ignition voltage is employed to automatically readjust the electrode spacing, thereby maintain ing the ignition voltage substantially constant.

Although several embodiments of the present invention have been shown and described, it is to be understood that other modifications of the 7 same may be made without departing from the spirit and scope of the appended claims.

We claim:

1. A discharge device wherein operation is ini- 8 trodes: tQiOEt'llSB controlled movement between: the latter and maintain the spacing: between said pair of electrodes substantially constant dining the useful. life-of said device. p

2; A discharge device wherein operation-is initiated. by field emission of electrons comprising a. pair of oppositely disposed spaced electrodes between which a field emission arc'd-ischargeoc curs upon the application of a potential thereto, and subject to deterioration tending: to increase the gap therebetween. during operation, an anode positioned adjacent said pair of electrodes'for supporting; an. electron discharge with. oneof the electrodes of said. pair immediately following the field emission arc discharge between said: pair of electrodes, and means automatically operable; in. response to variations-in. ignition voltage between said pair of electrodes to cause relative movement therebetween and maintain the spacing between;

said pair of electrodes substantially constant de-- spite deterioration of the latter during the useful life of said device. 7 V a 3a A discharge device wherein operation is ini-, hated by field emission of electrons comprising. a: pair of oppositely disposed spacedelectrodes; be-

tween which a field. emission arc: discharge occurs.

upon the application of a potentialthereto-and subject to deterioration tending to increase the. gap therebetween andthe voltage required to. inltiate the field emission are. discharge during op eration of said device, an anodepositioned; adja: cent said pair of electrodes for supporting an. electron discharge with one Of the electrodes of said pair immediately following the field emission arc discharge between saidpair of electrodes,

tiated by field emission of electrons comprising appair of. oppositely disposed spaced electrodes between which a field emission are discharge occurs upon the application of a. potential thereto. and subject to deterioration tending to increase the gap therebetween and the voltage required toinitiate the field emission arc discharge during operation of said device, an anodepositionedadjacent said pair of electrodes forsupportingan electron discharge with one of the electrodes of i said pair immediately following the field emission arc discharge between said pair of electrodeSQa deflectable support for one of the electrodes otf said pair, and means associated with said pair of electrodes and automatically operablein re sponse to an increase in voltage between said-pair of electrodes to cause. deflection of said supp rt andmovementof the electrode supported thereby toward the other electrode of said pair to maintain. the spacing between said pair of electrodes substantially constant during the useful life of said device. 7

5. A discharge device wherein operation is. initiated by field emission of electrons comprising; a pair of oppositely disposed spaced electrodes. between which a field emission are discharge occurs upon the applicationof a potential thereto and subject to deterioration tending-to increase the gap therebetween and the voltage-required to initiate the field emission arc discharge during operation of said device, an anode positioned adjacent said pair of electrodes for supporting an electron discharge with one of the electrodes of said pair immediately following the field emission are discharge between said pair of electrodes, a heat-responsive element in said device and operalble upon heating to cause deflection of one of the electrodes of said pair, and means electrically associated with said pair of electrodes and automatically operable in response to an increase in ignition voltage to cause heating of said heatresponsive element with attendant deflection of one of said electrodes toward the other electrode of said pair to maintain the spacing therebetween substantially constant despite deterioration of said pair of electrodes during the useful life of said device.

6. A discharge device wherein operation is initiated by field emission of electrons comprising an envelope, a pair of oppositely disposed spaced electrodes in said envelope between which a field emission arc discharge occurs upon the application of a potential thereto and subject to deterioration tending to increase the gap therebetween and the voltage required to initiate the field emission arc discharge during operation of said device, an anode in said envelope positioned adjacent said pair of electrodes for supporting an electron discharge with one of the electrodes of said pair immediately following the field emission are discharge between said pair of electrodes, means operable to cause relative movement between said pair of electrodes, an electrical circuit operable upon closure thereof to cause operation of said means, a second electrical circuit for supplying an ignition voltage to said pair of electrodes to initiate the field emission are discharge therebetween including an element subject to variations in voltage corresponding to variations in ignition voltage caused by an increase in spacing between said pair of electrodes, and a third electrical circuit operable in response to voltage variations on the element of said second circuit to cause closure of said first mentioned circuit with attendant operation of said means and relative movement between said pair of electrodes to automatically maintain the spacing therebetween substantially constant despite deterioration of said pair of electrodes during the useful life of said device.

'7. A discharge device wherein operation is initiated by field emission of electrons comprising an envelope, a pair of oppositely disposed spaced electrodes in said envelope between which a field emission are discharge occurs upon the application of a potential thereto and subject to deterioration tending to increase the gap therebetween and the voltage required to initiate the field emission are discharge durin operation of said device, an anode in said envelope positioned edjacent said pair of electrodes for supporting an electron discharge with one of the electrodes of said pair immediately following the field emission arc discharge between said pair of electrodes, a heat-responsive element in said device and operable upon heating to cause deflection of one of the electrodes of said pair, an electrical circuit operable upon closure thereof to supply heating current to said heat-responsive element, a second electrical circuit for supplying an ignition voltage to said pair of electrodes to initiate the field emission are discharge therebetween and including an element responsive to variations in ignition voltage caused by an increase in spacing between said pair of electrodes, and a third electrical circuit operable in response to variations in ignition voltage on the element of said second circuit to cause closure of the heating circuit for said heat-responsive element with attendant deflection of one electrode of said pair to automatically maintain the spacing between said pair of electrodes substantially constant despite deterioration thereof during the useful life of said device.-

3. A discharge device wherein operation is initiated by field emission of electrons comprising a pair of oppositely disposed spaced electrodes between which a field emission are discharge occurs upon the application of a potential thereto and subject to deterioration tending to increase the gap therebetween and the voltage required to initiate the field emission arc discharge during operation of said device, an anode positioned adjacent said pair of electrodes for supporting an electron discharge with one of the electrodes of said pair immediately following the field emission are discharge between said pair of electrodes, electrically operable means mechanically connected to one of the electrodes of said pair and operable when energized to cause deflection of said electrode, and means electrically associated with said pair of electrodes and automatically operable in response to an increase in ignition voltage to cause energization of said electrically operable means with attendant deflection of one of said electrodes to maintain the spacing therebetween substantially constant despite deterioration of said pair of electrodes during the useful life of said device.

9. A discharge device wherein operation is initiated by field emission of electrons comprising an envelope, a pair of oppositely disposed spaced electrodes in said envelope between which a field emission arc discharge occurs upon the application of a potential thereto and subject to deterioration tending to increase the gap therebetween and the voltage required to initiate the field emission arc discharge during operation of said device, an anode in said envelope positioned adjacent said pair of electrodes for supporting an electron discharge with one of the electrodes of said pair immediately following the field emission arc discharge between said pair of electrodes, an electric motor mechanically connected to one of the electrodes of said pair and operable when energized to cause deflection of said electrode, an electrical circuit operable upon closure thereof to cause rotation of said electric motor, a second electrical circuit for supplying an ignition voltage to said pair of electrodes to initiate the field emission arc discharge therebetween and including an element responsive to variations in voltage corresponding to variations in ignition voltage resulting from an increase in spacing between said pair of electrodes, and a third electrical circuit operable in response to variations in voltage on the element of said second circuit to cause closure of the circuit to said electric motor with attendant deflection of one electrode of said pair to automatically maintain the spacing between said pair of electrodes substantially constant despite deterioration thereof during the useful life of said device.

CHARLES M. SLACK. CLARENCE E. DAWLEY. ANDREW PFEIFFER.

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