US2013974A - Electric discharge starting circuit - Google Patents

Description

Sept. 10, `1935. R. MfsoMl-.zRs 2,013,974

ELECTRIC DISCHARGE STARTING' CIRCUIT I Filed Maron 17, i934 T0 A.C. SUPPLY s JN VENTO/e Rza/iard' Mmer BY n i y A TTORNE Y Patented sept. 1o, 193.5y

y UNITED STATES PATENT ori-lcs 2,013,914 ELEc'rmc Discman s'raa'rmo cmcurr Richard M. Somers,

Orange, N. J., alsignor to Thomas A. Edison, Incorporated, Welt Grange, N. J., a corporation of New Jersey Application March 17, 1934, Serial No. 716,038 6 Claims. (Cl. 176-124) This invention relates to electric discharge devices, and more particularly to those of the gaseous or vapor typ with cathodes heated by external means.

The invention is particularly directed to the starting of the main discharge in such a device by the generation of a transient of high voltage and its application between elements within the device. Such a starting method is in general well known, but it is an object of this invention to provide improvements therein and apparatus therefor.

provide for such a device a starting circuit characterized by extreme simplicity, economy and positiveness oi.' operation.

Another specinc object of my invention is to provide, in connection with such a device and the circuit customarily employed for operation thereof from an alternating current source, simple, economical and efficient means for applying a transient of high voltage between the cathode and anodes of the device after the cathode has been heated to substantially i'ull emissivity.

It is another specific object of my invention to provide, in a similar'v connection, an improved starting circuit employing a simple form of switch and arranged to function with minimum impairment of the life of the switch contacts. A

It is still another object of my invention to replace elements frequently employed in starting circuits for discharge devices of the class described with elements customarily provided within the devices for other p Cther and allied objects will more fully appear from the following description and the appended claims: f

In the description reference is had to the accompanying drawing, of which: l

Figure 1 is a partly cross-sectional, partly per-` spective view of a typical discharge device in which the discharge may be started in accordance with my invention;

Fig. 2 is a schematic diagram of the device oi Fig. 1 with typical operating circuits and a slmplied starting circuit therefor as contemplated by my invention; and

Fig. 3 is a diagram generally similar to Fig. 2, but illustrating a modification of the starting t circuit oi that ligure and showing in perspective insteadv of schematically the switch which I prefer to employ in the starting circuit.'

The typical discharge device shown in Fig. 1 may be briefly described as a. tube I having the glass or the envelope 2, the space 2' within the en- It is a more specic object of my invention to4 envelope portions 2".

i auto-transformer, having velope having been evacuated oi air and containing either a gas, for example neon, or a vapor, for example mercury vapor, or a combination oi gases and/ or vapors according to the desired dischargecharacteristics, it being understood that 5 the term gas" and its derivatives are elsewhere in this'speciilcation used to denote any such gas, vapor or combination. Within the space I' may be seen the cathode 3. which is of the thermionic type, i, e., adapted to be maintained in an emis- 10 sive condition by external heating means during the operation of the device. In Fig. 1, I have illustrated thisfcathode as comprising a folded filament which may vbe coated with suitable oxides or'the like to increase its emission. The exl5 tremities of the cathode or filament are secured and electrically connected to the outwardly passing wires or leads I'. At the opposite end of the device from the cathode are seen the anodes la and 4b, respectively secured and electrically cont0 nected to the outwardly passing wires or leads 4a' and lb.

In Fig. 1 will be seen a further element 5. This is in slight spaced relationship to the cathode, and is desirably in the form of a ring essentially surrounding the cathode and interposed between it and the nearest portions 2" of the envelope 2. This element 5 conveniently performs two functions; one is that of a cathode activating element or ring, and the other that of a shield or heat diffuser whereby heat radiated from the cathode is prevented from unduly heating the The second function is of course performed during the operation of the tube, while the ilrst function is performed in the evacuation step in original tube manufacture. It will be understood that in that step the cathode is heated (as by the battery 2| illustrated in Fig'- ure 1) and the ring 5 meanwhile maintained at a potential highly positive with respect to the cathode (as by the battery 22 illustrated in Figure 1) this .procedure serving in well known man ner to activate the cathode by bringing to the surface of its coating a layer of highly emissive material, The activating ring 5 may, for exam- 45 pie, be supported and electrically connected to the U-shaped wire l", and this in turnto the outwardly passing wire or lead 5'.

Reference is now invited to Fig. 2, wherein there appear schematically the envelope 2, the cathode 3, the anodes la and Ib, the activating ring 5 and the leads 3'-, la', Ib and 5' oi' the tube I. There will further be seen the transformer l,.shown by way of illustrationv as an primary terminals lp lrent source through primary switch 9.

adapted for connection to the alternating cur- The cathode heating means is shown in Fig. 2 as the separate secondary winding 'I forming part oi or lamp 8b` to the extreme transformer secondary terminal 6b; and the cathode is vconnected to the central transformer secondary terminal Y6c through the inductance coil I0,

In the operation of the tube the voltage from the transformer secondary will obviously render the anodes alternately positive with respect to the cathode; the main discharge is therefore inof the current cuit. In systems operated from alternating. curte'nded to comprise' a series of alternate discharges between the two respective anodes and l the cathode. While the voltage from the transformer on either anode does not rise to a'high enough value to start one of the alternate discharges in the first instance, each such discharge succeeding the first starts readily if the period of the preceding one be slightly lengthened, and the accompanying ionization of the gas thereby slightly prolonged. function is'performed by the choke or inductance coil I 0; this coil also, together with the ballast resistances or lamps 8a and 8b, serves to limit the average values of the alternate discharges. 'Ihe circuit structure and operation as thus far described will be recognized as conventional.

' To start the main discharge in a system of the type described, it is common practice to generate a transient current of relatively high voltage and to apply this between the anodes and the cathode, thereby producing a transient discharge within the tube which by ionizing the gas per- 4o mits the normal voltage from the transformer terminals to continue-the discharge. It further is common practice to delay the generation of this transient, after current' is first supplied to the system,4for a definite time interval, so that the cathode shall have had time to overcome its thermal inertia and to reach approximately normal operating temperature in response to the operation of its external heating means, e. g., secondary I. This is usually essential, for if the transient be sooner applied between anodes and cathode a discharge may occur therebetween which will be sustained by virtue of ionic bombardment of structure spot heating of the latter.

To generate the transient it is common practice to pass a current through the main discharge period-lengthening inductance, e. g., choke IIJ above-mentioned-and abruptly to break this current; thereupon the desired transient appears across the inductance, and. by virtue of the circuit position of the latter is automatically applied between anodes and cathode. To effect the desired delay of transient generation, it is common to employ in the circuit passing the just'mentioned current through the inductance,

i. e., in the starting circuit, a delay switch` adapted to close at a predetermined time inter` val after current is first supplied to the system. To obtain the most desirable phase or ,polarity ,characteristics of the transient, which is more effective to the extent thatv it renders the anodes positive with respect to the cathode, it is customary to restrict to a single one the direction passed through the starting circathode 3 and the activating ring 5 nection of a single former through the mature I2" This period lengthening ceeds a certain minimum. at least suiiciently to provide normally a satisthe cathode, with attendant de-A stant in the cycle at which the rent sources this is frequently accomplished by the use of a. full-wave rectifier connected-in the starting circuitexternally to the tube.

lI have found that the full-wave external rectier may be replaced with the half-'wave rectifier inherently provided within the tube by the above-mentioned. The operation of the starting circuit with this arrangement is hereinafter described; the circuit itself, however, together with its features of simplicity, is best described as the contap 6d on the auto-transdelay switch I3 and the circuit-breaking switch I2 to the activating ring 5.

-The delay switch, by way of example, is shown as comprising a resistance element I3', and a contact arm I3 responsive to the temperature of the element I3 and adapted to short circuit that element, i. e., to close the delay switch, upon the attainment by the element oi. a predetermined temperature. The circuit-breaking switch I2 comprises a spring arm. I2 carrying the arand. the contact I2a, the arm being biased normally to press the contact I2a against a stationary contact I2b, i. e., to maintain the circuit-breaking switch closed. The armature I2 ispositioned in the field of attraction of the core I0 of the choke I0 and-is adapted to be moved toward the core I0' and thus to open the switch when the attraction of the core I0 ex- The arm I2 is biased factory contact pressure between the contacts I2a and I2b; at the same time the mass of the arm I2' and the armature I2" are kept reasonably low. Consequently the switch I2 is characterized by rapid response to attractions of vthe core I0' for the armature I2".

In simple terms the operation of the system may be outlined as follows: Upon the closing of the primary switch 9 heating of the cathode k3 is initiated and the terminals 6a and 6b and the tap 6d are invested with alternating potential differences from the center-tap 6c. As soon as the cathode has -been slightly heated a discharge occurs every alternate half vating ring 5 to the cathode. The `magnitude of this discharge is at rst limited by two factors: the then sub-normal emissivity of the cathode, and the resistance of the element I3'. The first of these limitations gradually disappears as the cathode attains normal operating temperature; the second is, of course, independent of the cathode temperature and provides a safeguard against spot heating of the cathode which might tend to be produced, under certain possible voltage conditions, as a result of the occurrence of this ringcathode discharge prior to full heating of the cathode. The second limitation also prevents the current through the choke I0 and hence the attraction of the core III for the armature I2" from becoming suflicient to open the switch I2. The temperature of the element I3' at which it will be short-circuited by the arm I3 is preferably that temperature which it will have attained by virtue of the current accompanying the ring-cathode discharge, when the cathode has been heated to substantiallyv When this temperaturehas been attained by the element I 3' the delay switch I3 w' l be closed and the second of the two mentioned limitations removed. Either thereupon, or in the next of the alternate half-cycles during which'the ring-cathode discharge takes place (according to the indelay switch cycle from the acti.

lthe choke will rise to relatively high values. The

high current through the choke will cause the core Il to attract the armature I2" and thus to open the circuit-breaking switch I2. This breaks the starting circuit and the iiow of current through the choke, causing the generation o! the desired transient. 'I'he inmediately ensuing main discharge causes the passage of sufilcient current through the choke to maintain open the switch I2 and hence the entire starting circuit.

The generated transient is required to ionize the gas within the tube, and must therefore not only be of high voltage but must comprise appreciable energy. In general in typical cases, if a current having a peak amplitude of the order of the minimum operating current through the choke be passed through the starting circuit and interrupted when reasonably near its peak value, a transient of ample voltage and energy will be generated. It will be obvious that, by virtue of the far closer spacing of the the cathode than of anodes to cathode, suflicient current will be passed in the' starting circuit upon closing of the delay switch i! Vthere be applied on the activating ring only a minor fraction of the voltage applied to either anode of the tube.

Likewise by virtue of the close spacing of the activating ring to the cathode a voltage not greatly in excess of the ionization potential of the gas in the tube will be sufiicient to start a ring, cathode discharge each alternate half cycle, after the cathode has become slightly emissive. In practice I therefore employ a relatively low voltage between the tap 6d and the center-tap 6c, preterably positioning the tap 6d as close to 6c as is found by test to result in dependable starting at supply voltages slightly below the lowest expected to be encountered in use.. Preferably with any position of tap 6d the bias of the spring arm I2' is maintained at a suflicient value to insure that the switch I2 will open only when the current through the starting circuit is in a peak or near-peak portion of its cycle.

By employing a half-wave rectifier, together with a rapidly acting circuit-breaking switch of simple design actuated only in response to nearpeak current values, I am able to secure with a simplified system wholly dependable operation, wherein the main discharge is invariably started upon the first opening of the switch and without a series of ineffective switch openings tending to impair the life of the switch contacts. It is possible that the dependability of the arrangement is enhanced by the fact that the limitation of the instant of circuit breaking to one of nearpeak current is also a limitation of that instantsimplicity and economy. It is further possiblethat the restriction of the periods of starting circuit current ilow resulting from the gaseous discharge nature of the rectiiier and the small voltage applied thereacross is a factor which, in addition to the adjustment of switch i2, serves to place the period of possible circuit breaking atl a position in the cycle of main anode voltage favorable to the starting of the tube.

Since one of the original limitations of the ring-cathode discharge, i. e., the sub-normal emissivity of the cathode, is a gradually Y'diminishing one and depends directly on the cathode activating ring to i of thev arm I2 of the switch emxssivity, a a passible to uuuze aus dimm V as a measure of the cathode emissivity. and to arrange the starting circuit to break upon the attainment by this discharge of a predetermined magnitude. A circuit for such action is shown as 5 Fig. 3. Therein there is eliminated the del switch il, and consequently there disappears the limitation of this preliminary discharge provided while the cathode is subnormally emissive by the resistance element il' of Figure 2. It is therelo fore particularly desirable that every other available sgfeguard beutili'zed to minimize vtendencies of'the"`preliminary discharge to cause uneven heating of the cathode. I am aware that a circuit oi.' this last described 15 general character has been proposed, in which opposite alternating voltages have been applied respectively to two auxiliary electrodes adjacent the cathode, the combined discharge from these electrodes to the cathode being employed asa measure of the cathode emissivity and as a control oi' the circuit-breaking device. In the proposed circuit, however. choke and circuit-breaking device were each required to bo in a circuit position similar with respect to the two auxiliary 2,5

electrodes, while of course remaining subject to the requirement that the choke only be disposed in the path of main discharge current iiow. This necessitated the expense andA complication of a separate transformer winding for supplying the requisite potentials to these electrodes.

In my simplified circuit as illustrated in Fig. 3, I again employ a ,rapidly acting circuit-breaking switch l2 (in this figure illustrated in perspective by way of alternative showing) and a simple haliwave rectiiier formed within the tube by the activating ring 5 and the cathode 3. I thus avoid the complication and expense of the separate transformer winding and reduce the elements and connections of the circuit to a very simple basis. It is further thought that tendencies of the preliminary discharge to heat the cathode unevenly may be reduced, particularly by virtue of the intermittent nature of the preliminary discharge. It is more particularly desirable in this circuit than in that of Fig. 2, however, that the voltage applied to the activating ring 5, i., e., between the taps 6d and 6c, be kept as low as'possible, the bias i2 being made just low enough to permit opening of the switch by the attractionkof the core Ill'produced at an instant of peak ring-cathode discharge when the cathode is substantially fully emissive. 'I'he voltage in question must obviously somewhat exceed the ionization potential of the gas; but rather than 56 largely to exceed this potential in the adjustment of the .circuit to provide dependably sumcient transient energy for starting any given tube, I prefer if necessary to increase the efiicacy o! the transient generation by the appropriate introduc- B0 tion of capacity into the starting circuit. Such use of capacity is itself well understood; I have illustrated the same by the condenser 2l connected across the choke lil. It is to be noted that such a capacity may, ii desired, be employed in the circuit of Fig. 2, having been dottedly illustrated therein. Y

While I regard the use of the cathode activating ring in particular for an element of the rectifier as a feature of my invention, it is not intended to limit all aspects of the invention by this feature, it being obvious that another element ad' jacent the cathode might be employed in obtain. ing the other benecial advantages of my invennon. Likewise as to other features, I do not in- 76 tend that the invention be limited by the precise details of the embodiments shown and described, but rather that it be gauged in scope by the -following claims. I claim: l 1. The combination with an electric gaseous discharge device having a thermionic cathode and an anode, cathode heating means therefor, a source of current connected between said cath'ode 1 0 and said anode, and a choke interposed between said cathode and said source: of an electrode adjacent said cathode and forming therewitha rec- ,tillen and a starting circuit for said device adapted to generate across said choke a high-voltage 15. transient, said circuit serially comprising said choke, said rectifier, a circuit-breaking switch having a movable portion of relatively low mass substantially instantaneously responsive to current of a predetermined value traversing said cirl cuit, current limiting means operative until said cathode is substantially fully heated, and a source of alternating voltage of value to pass through said circuit when said limiting means is inoperative an intermittent current of peak amplitude 25.: only slightly exceeding said predetermined value. 2. 'I'he combination as claimed in claim 2, wherein said electrode is an electrode substantially surrounding said cathode and formingan activating ring therefor during evacuation of said 30 device.

3. The combination with an electric gaseous discharge device having a thermicnic cathode and two anodes, cathode heating means therefor, a transformer winding adapted for alternating cur- 3 5 rent energization and connected between said anodes, and a choke connecting a central point on said winding to said cathode: of an electrode adjacent said `cathode and. forming therewith a rectier, and a starting circuit adapted to gener- 49 Aate across said choke a high-voltage transient,

' said circuit serially comprising said choke, said rectifier, a. circuit-breaking switch having amovable portion of relatively low mass substantially instantaneously responsive to current of a prede- 4 termined value traversing said circuit, current limiting means operative until said cathode is substantially fully heated, and a single portion of said winding ter ating at said central point t i and of voltage value to pass through circuit when said limiting means is inoperative an in.- termittent current of peak amplitude only slightly exceeding said predetermined value.

4. The combination with an electric gaseous '.5

discharge device having a thermioni'tjl cathode and an anode, cathode heating means therefor, a source of current connected between said cathode and said anode, and a choke lnterposedibetween said cathode and said source: of an electrode adjacent said cathode and forming therewith a rectifier. and a starting circuit adapted to generate across said choke a high-voltage transient, said circuit serially comprising said rectifier. said choke, a source of relatively low alternating'volt- 15 age. and a. circuit-breaking switch having a movable portion of relatively low mass. substantially instantaneously responsive to current traversing said circuit, and biased against response, to substantially less than the peak values of current traversing said circuit when said cathode is substantially fully emissive.

5. The combination as claimed in claim 4, wherein said electrode is an electrode substantially surrounding said cathode and forming an activating ring therefor during evacuation of said device.

6. The combination with an electric gaseous discharge device having a thermionic. cathode and two anodes, cathode heating means therefor, 30. v

a transformer Winding adapted for alternating current energization and connected between said anodes. and a choke connecting a central point on said winding to said cathode: of an electrode adjacent said cathode and forming therewith a rectifier, and a starting circuitJ adapted to generate across Said choke a high-voltage transient, said circuit serially comprising said rectifier, said choke, a portion of said winding terminating at said central point and of relatively low voltage, 40 and a circuit-breaking switch having a movable portion of relatively low mass, substantially instantaneously responsive to current traversing said circuit, and biased against response to substantially less than the peak values of current traversing said circuit when said cathode is substantially fully emissive.

' RICHARD M. SOMERS.

CERTIFICATE OF CORRECTIQN.

.. Patent No. 2, 013, 974.

It is hereby certified that error appears n above numbered patent line 26, claim 2, for Letters Patent should conform to the record of the case Signed and sealed this8th day (Seal) RICHARD M. soMERs.'

september 1o, 1935.

the printed specification of the Page 2, first column,`

and page 4, vfirst column,

read l; and that the sa'd of October, A. D. 1935.

*Leslie Frazer Acting Commissionerof Patents.

tend that the invention be limited by the precise details of the embodiments shown and described, but rather that it be gauged in scope by the -following claims. I claim: l 1. The combination with an electric gaseous discharge device having a thermionic cathode and an anode, cathode heating means therefor, a source of current connected between said cath'ode 1 0 and said anode, and a choke interposed between said cathode and said source: of an electrode adjacent said cathode and forming therewitha rec- ,tillen and a starting circuit for said device adapted to generate across said choke a high-voltage 15. transient, said circuit serially comprising said choke, said rectifier, a circuit-breaking switch having a movable portion of relatively low mass substantially instantaneously responsive to current of a predetermined value traversing said cirl cuit, current limiting means operative until said cathode is substantially fully heated, and a source of alternating voltage of value to pass through said circuit when said limiting means is inoperative an intermittent current of peak amplitude 25.: only slightly exceeding said predetermined value. 2. 'I'he combination as claimed in claim 2, wherein said electrode is an electrode substantially surrounding said cathode and formingan activating ring therefor during evacuation of said 30 device.

3. The combination with an electric gaseous discharge device having a thermicnic cathode and two anodes, cathode heating means therefor, a transformer winding adapted for alternating cur- 3 5 rent energization and connected between said anodes, and a choke connecting a central point on said winding to said cathode: of an electrode adjacent said `cathode and. forming therewith a rectier, and a starting circuit adapted to gener- 49 Aate across said choke a high-voltage transient,

' said circuit serially comprising said choke, said rectifier, a. circuit-breaking switch having amovable portion of relatively low mass substantially instantaneously responsive to current of a prede- 4 termined value traversing said circuit, current limiting means operative until said cathode is substantially fully heated, and a single portion of said winding ter ating at said central point t i and of voltage value to pass through circuit when said limiting means is inoperative an in.- termittent current of peak amplitude only slightly exceeding said predetermined value.

4. The combination with an electric gaseous '.5

discharge device having a thermioni'tjl cathode and an anode, cathode heating means therefor, a source of current connected between said cathode and said anode, and a choke lnterposedibetween said cathode and said source: of an electrode adjacent said cathode and forming therewith a rectifier. and a starting circuit adapted to generate across said choke a high-voltage transient, said circuit serially comprising said rectifier. said choke, a source of relatively low alternating'volt- 15 age. and a. circuit-breaking switch having a movable portion of relatively low mass. substantially instantaneously responsive to current traversing said circuit, and biased against response, to substantially less than the peak values of current traversing said circuit when said cathode is substantially fully emissive.

5. The combination as claimed in claim 4, wherein said electrode is an electrode substantially surrounding said cathode and forming an activating ring therefor during evacuation of said device.

6. The combination with an electric gaseous discharge device having a thermionic. cathode and two anodes, cathode heating means therefor, 30. v

a transformer Winding adapted for alternating current energization and connected between said anodes. and a choke connecting a central point on said winding to said cathode: of an electrode adjacent said cathode and forming therewith a rectifier, and a starting circuitJ adapted to generate across Said choke a high-voltage transient, said circuit serially comprising said rectifier, said choke, a portion of said winding terminating at said central point and of relatively low voltage, 40 and a circuit-breaking switch having a movable portion of relatively low mass, substantially instantaneously responsive to current traversing said circuit, and biased against response to substantially less than the peak values of current traversing said circuit when said cathode is substantially fully emissive.

' RICHARD M. SOMERS.

CERTIFICATE OF CORRECTIQN.

.. Patent No. 2, 013, 974.

It is hereby certified that error appears n above numbered patent line 26, claim 2, for Letters Patent should conform to the record of the case Signed and sealed this8th day (Seal) RICHARD M. soMERs.'

september 1o, 1935.

the printed specification of the Page 2, first column,`

and page 4, vfirst column,

read l; and that the sa'd of October, A. D. 1935.

*Leslie Frazer Acting Commissionerof Patents.

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