US2516915A - Gaseous discharge device - Google Patents

Description

Aug. 1, 1950 A. H. REEVES GASEOUS DISCHARGE DEVICE Filed 001;. 3, 1947 ATTORNEY Patented Aug. 1, 1950 7 7 7 2,516,915 desirous niscnARGE DEVICE .AlecHarley Reeves,iLondonpEngland, assignor -to International Standard Electric Corporation, New York, N. Y., a corporation of Delaware Application OctoberB, 194.7, Serial No. 777,815

UNITED STATES Pints-r *In Great Britain October 3,1946 ioclaims. (01. 315-323) This invention relates to the use of .coldcathode gaseous discharge tubes having a plurality of .discharge gaps such as tubes of the type described in application Serial No. 763,655, filedJuly 25,

Tubes described inthe .said application comprise an arrayof three or more dischargegaps 50 arranged that upon a discharge beinginitiated at one of these gaps, ionisation fromthedischarge lowers the minimum =voltage at whichan adjacent gap will discharge due toionisationof the gas in the latter gap due to ithe discharge inthe former. Whenpulses'are applied in common to the gaps of such a tube, successive pulses cause the firing of successive gaps in the tube till all have discharged. 7 7

A given gap,usually the firstyrnaybe. arranged so that the pulsevoltagecauses it to .fire in the absence ofgas ionisationand a first pulse is applied to the tube when it is de-ionised, causing this gap onlytoiire. 7 7 7 7.Such a gap is called the startinggap and the efiect'may be obtained by various methods of which three may be mentioned:

so that gas ionisation from this discharge permanently primesthe starting gap but not other gaps of the tube. Such an auxiliary gap is called a pilot gap.

In operating tubes of this type a constant standing potential can be applied to all the, gaps sufficient to maintain a, discharge, once initiated, but insufiicient to initiate a discharge by itself, even when ionisation is present.

When pulses are applie to the gaps'of such a tube the gaps will fire in succession and continue discharging throughout the remainder of thesequence of dischargesin the tube.

It is however, possible to operate the tube without a maintainingpotential as willbe described later. L

Where itis' required to apply 'a continuingsuccession of pulsesto the tube itis necessarythat all "discharges in the' tube shallfbe extinguished and thatthe'gas' in the tube' shall become deiorgised before'a further pulse is applied to the ue. This further pulse ;Wil1 then fire, the starting gap and the sequence of discharges will re-commence. Theprocesscan :then be :repeatedagain andiagainn .7 7. 7 7 7 Tubes .01 the typeito whichxthe .invention relates may, bebarranged so that gaps .fired 7 .by. a train of pulses automatically extinguish between pulses, or so that gaps fired by a train of pulses continue todischargebetween pulses.

. .Whena tube is77arrang'edlso 7that .thedischarge is maintained between pulses various 77means 7 of extinguishing theedischarges are possible some of which aredcscribed latch... 7 7 7,

1 After extinguishznent ofithe dischargesitheigas in the, gaps (other thanitheistartinglgap, where a pilotgap is used)- must 77bccome deionised before the application of a further pulse. Ifithis7deionisation has not prooeededto asuflicientextent, 7 there is 77a.;risk .of .gaps other than thestarting gap being fired by the further pulse applied to thetube... 7 7 g 7 ,7

7 Therewill be a;critical .,frequency below which the inter-pulse 77interval -.in.. a777c0ntinu0us sequence of regularlysspaced ipulses inlong enoughgto permit the tube to become deionised between pulses butabove which the tube will fail to operate correctly. 7 77 .7 7

The object of the present invention is to enable pulse .irequencies to77be7 used7.higher than this critical frequency without upsetting the operationofthetuba.

7 According to, its 7 principal, feature therefore, the invention consists. of :7a1deyice.:responsive .to recurring ,pulses iOf; electrical 7-,encrgy which comprises a cold cathodegas discharge :tube having three or more ,dischargegaps adapted to .fire succession in allpredeterminedorder onzthe application of pulses to the,saidgapsincommon, ionisation from a discharge in oneqgap loweringthe voltage necessary to fire the next adjoining unfired gap andso .prirning thesaid adjoining gap, inwhich when all the sapshave been firedin turn, all 7 discharges in these ,gaps' automatically extin guish or are extinguished, and which cornprises means for 7preventing ofnel or'mor'epulses immediately succeedingi the'pulse'7 which causedgthe last of the saidga'ps Ito firefrom firing any of the said gaps 'onth'e gu se in order to provide time for all thesaid gaps fin the tube to extinguishand to deionise to atleast a predetermined extent so that the next pulse allowed to afiect the tube will fire the'first gap in the said predetermined 'order and no other gapi Certain embodiments of the invention will now be described in relation to the accompanying drawings in which:

Fig. 1 is a circuit diagram of one embodiment of the invention.

Fig. 2 is a circuit diagram of another embodiment of the invention. I I

The circuit of Fig. 1 forms part of the subject matter of our co-pending application Serial No. 777,816, filed October 3, 1947, now Patent No. 2,505,006.

In this figure a gaseous discharge tube 1 has a common anode 2 consisting of a, straight rod wire or strip and having eight cathode points adjacent to it forming eight discharge gaps, 3, 4, 5, 6,1,8,9andll3.

Gap 3 is the starting gap and is shown somewhat shorter than the rest. The cathode of this gap is shown as being separately led out of the tube but this is not essential. The cathodes of gaps 4, 5, 6, 1, 8 and 9 are in the form of projections from a common supporting rod. The cathode of gap I is separatel led out of the tube. I

The cathode of gaps B to 9 may alternatively take any of the forms described in my application first above mentioned, for instance a corrugated strip may be used, the peaks of the corrugations towards the anode defining the various gaps.

A voltage is applied across all the gaps in common from battery H, in the case of the anode, through a resistance 12, in the case of the oathode of the starting gap 3, through resistance I3,

in the case of the cathodes of gaps 4 to 9 through resistance [4 and in the case of the cathode of gap I!) through resistance l5, and in certain cases also through apparatus connected to output terminals I6.

Condenser I'll is a feed condenser through which recurrent pulses applied across terminals 18 are fed to the tube.

The startin gap 3 is ensured of striking from a first pulse when the gas in the gap is deionised by being shorter than the rest, and this shortness is exaggerated in the figure so that it may be readily apparent.

If other means of ensuring the firing of the starting gap from a first pulse were resorted to, gap 3 could be the same size as the other gaps, and resistance i3 may be considered as representing a circuit for applying a bias across the gap. In the arrangement illustrated in the Figure 1 resistance 13 could be omitted and the cathode of gap 3 could be fed through resistance 14.

On pulses being applied at i8, first the starting gap 3 and then the remaining gaps, will fire in succession from successive pulses, discharges being maintained after firing by reason of battery ll which is adjusted so that it will not initiate a discharge but will maintain a dischargeonce initiated.

The cathode of gap may have a somewhat larger area than the other cathodes. When this gap fires, a surge of current passes through this gap discharging condenser 19, which at other times is charged to a voltage somewhat below that of the battery H plus the pulse voltage.

This lowers the anode-to-cathode voltage momentarily, below that required to maintain the discharges, which are therefore extinguished.

The time during which the voltage remains lowered depends upon the time constants of condenser 19, resistance I 2, and resistance Hand also, to some extent the circuits if any attached to terminals 16.

Where the frequency and spacing of the pulses applied to terminals i8 is such that the tube can become deionised in the interval between two adjacent pulses, the time constant of the voltage lowering circuit will be chosen to be similar to the pulse interval so that by the time of arrival the next pulse after that which fired gap In, the inter-electrode voltage will have restored to approximately that of battery II.

If, however, with the same circuit values, the pulse rate is increased, the inter-electrode voltage will not have reached that of battery H at the time of the next pulse after that which fired gap l0, and if that voltage at such time is below a critical value, the starting gap will not fire oif this next pulse and may miss several pulses, according to the amount by which the pulse rate is increased. f,

In this way, the tube will measure ofi pulses greater in number than the number of its discharge gaps.

This efiect may be exploited to obtain two advantages; first, to enable a pulse rate to be used such that de-ionisation cannot be completed between successive pulses and secondly, to enable counting to take place to a radix-greater than the number of gaps in the tube.

The circuit of Fig. 1 may be used as a counter, with an external counting circuit connected in series across terminals [6 or in parallel across terminals 2:) (terminals 16 being short-circuited in the latter case) and will record the successive discharges in gap in.

There is sometimes difiiculty in securing a suificiently stable inter-electrode voltage in the tube owing to the varying currents drawn as different numbers of gaps are discharging from time to time.

Accordingly, it is advisable to insert choke 2| and rectifier 22, connected between the anode and a tapping on the battery Hi The tapping is chosen so that rectifier 22 is just non-conducting when all gaps are firing, that is to say, when the voltage drop in [2 is at its maximum.

When fewer gaps are firing 22 is more conducting due to the anode being more positive than the tapping point on H, making a conducting path through 2| and 22 from the anode to the said tapping point which tends to stabilise the anode voltage at a value in the vicinity of that of the said tapping point.

When gap is fires, however, the surge of current causes a further voltage drop in !2 which cuts off the rectifier, so that the drop in voltage required to extinguish the tube, is not defeated by the stabilising circuit 2 I, 22.

The choke 2! is required principally to prevent the bypassing of the pulses through the rectifier and battery, though it is also an additional precaution against the loss of the quenching surge. In the arrangement illustrated in Fig. 2 the prin ciple of preventing the tube from firing from a pulse or pulses after that which fired the last gap, is carried a stage further by switching both pulses and maintaining battery from the tube in question and transferring them to another similar tube which commences a firing sequence where the first tube left off, after the completion of which, the pulses are again applied to the first tube, the two tubes working alternately.

In this arrangement the number of pulses during which a tube is dormant is precisely counted out by anothertube instead of being timed.

aura-e In Fig. 2 atube 23 of the type describedin our copending application, first above mentioned, has an anode 2 4 in theform of a wire, strip or plate, and acathode array at with individual cathodes in the form of rods mounted on a common busbar 26 in the form of a comb. All the array gaps are of equal-length and aseparatepriming gap 2 is included to prime the starting gap. 28 at theleft-hand end: of the array. A separate oath 0de29 is provided at the other end and is spaced similarly to the other array gaps as regards both gap length and separation from its neighbour. Tube 30 is similar in function to tube 23,-but.di-iferent forms of electrode are shownto illustrate an alternative tube construction. Anode 34 is again a wire, strip or plate, but cathode array 32- consists of a serrated metallic strip, coated with alumina or similar substance except at the tips of the saw teeth. At one end, the first tooth on 32 co-operates with a separate anode to provide a priming gap 33 and starting gap 34. At the other end. a separate cathode :35 is provided, similarlyto 23 in tube 23. Cathode arrays 25 and tzare'shown connected to ground and anodes at and Sal are connected via separate leads 3B and i i to the respective side contacts a: of a polarized relay A which has opposed windings and is adjusted to be side stable. Leads 36 and Bl are also connected through individual pulse blocking chokes 38 and 38to the side contacts atohrelay A and through leak resistances til,

to ground. With the armatures of (ti and (1'2 in the position shown, anode 24 is connected through condenser 13.2 to pulse input terminal 43 and through choke at to the positive pole of battery flit, the negative pole of which is grounded. Anode 3:1 is open circuited except for its leak connection to ground. Priming gaps 2'1 and 33 are connected through variable resistances Q5 and 45 respectively across batteries .4! and ill. The output cathodes 29 and 3'5 are connected through the opposing windings of relay A to recording device 49:. It should be emphasized that the functions of relay Aand recording device ct could be carried out b electronic means such as circuits i tubes 23 and 39 without, however, causing any gap to fire (other than the starting gap) even when pulses from terminal it are applied to the respective anodes. Resistances t5 and may be adjusted to control the priming currents of gaps 2i and 33. Assume, now that positive pulses are applied to terminal 63, the relay contacts at a! and a2 being in the condition indicated in the figure. The first pulse will fire gap 28, which Willremain discharging under the influence of the maintaining voltage from battery t l after the pulse has passed. By the time the second pulse arrives, the gas in the next gap is ionised by the discharge recently started at gap 28, and this second pulse added to the voltage from battery id will fire the gap adjacent to 28, the third ulse will fire the next gap, and so on until discharge occurs at cathode 29. The discharge current through cathode 29 actuates relay A and also recording device 49 so that the completion .oflthe firstdischarge-sequence is recorded. Due

to the operationof relay anodeuzlris discom nected from terminal 43 and battery .44: Dis= charge'sat all gaps of tube '23 except the'priming gap 2l will thus collapse, butsome time must elapse before the ionisation levels have returned to their initial values prior tothe discharge sequence. To allow for deionisation in tube 23 without interruption of the pulse recording process, tube 30 takes over until the discharge seiquence reaches cathode 35', when relay. will operate to isolate tube 30 and to reconnect tube 23, and at the same time recording device :49 will beadvanced one count. i I

It would of course be possible to extinguish each of the tubes. of Fig. 2 by means of 311C011- denser circuit of the type used in Fig. 1, these circuits being arranged to transfer the pulses from each tube to the other and temporarilypto reduce the maintaining potential to extinguish the discharges. With this arrangement :the "constant maintaining potential could bepermanently connected to both tubes.

Tounderstancl more fully the operation of :the devices illustratedin Figs. 1 and-2 it isprofitable to consider the working of tubes of the .typendescribed in a little more detail. i

If the circuit of Fig. 1 were to be used with a tube having only three discharge gaps; sequential firing, and a voltage drop for extinguishmentcan be obtained when the cathode surface of'rthe last gap is or thesame dimensions as thezother cathodes;

The level to which ionisation-must be reduced to avoid misfiringof the tube in the next'pulse cycle can be adjusted to some extent by varying the dimensions of the gapsaandrcomposition and pressure of the gas atmosphere. For instance,:it can be arranged that the gaps other thanxthe starting gap require a higher energy level to fire them so that they'will not fire out of turn even in the presence of a fair degree of residual ionisation.

There is however a limit to the extent to which such measures canbe pursuedand a Welldesigned tube-operating on convenient voltages and within practical tolerances will already haveexhaust ed such possibilities.

.A pulserate such that the interpulse interva doesnot leave time for the decay of ionisation to proceed to the required level may be applied to the tube provided that the time constants .of condenser 19 and the resistances l'2eand l5 ar.e chosenso that the voltage across the electrodes is maintained below the level required to start a discharge in the startinggap .for atime sufficient to allow for ionisation decay.

The efiect of this will be that a pulse orpulses after the one whichfired the lastgap will fail to raise the inter-electrode voltage to the firing pointo'f the first gap. The number of pulses missed in this way: cannot be extended; indefinitely since the recovery of the circuit'depends onthe recharging of condenser l9 which will followan 'exp'onentiallaw and "the definition'of thereoovery point inrelation to the pulse cycle-cannot in practice be made accurate enough. unless'the pulse to pulse time'interval is substantial in relation to the'circuit recovery time. Therefore if it is desired to increase the pulse rate to a-point requiring the suppressionof a substantial number of pulses, the arrangementof Fig.2 is-preferable.

As the number of discharge gaps in the tube is increased the problem of obtaining an adequate voltagedropifrom the discharge in the-last gap to extinguish all the discharges becomes more difficult, and necessitates resort to means for increasing the current passed in the last gap. The tube illustrated in Fig. 1 has a larger cathode area for the last gap for this purpose.

A limit is set to the permissible enlargement of the current in the last gap, however, because the considerable ionisation arising from this discharge tends to lower the discharge maintaining voltage of the gaps by the same extent as it decreases the applied voltage, not only defeating the extinction of the discharges but also requiring a longer period for the decay of the increased ionisation to the requisite level.

. This sets a limit to the number of gaps which can be used in a tube connected in the circuit of Fig. 1, and for larger numbers of gaps the arrangement of Fig. 2 is to be preferred.

It is possible to use more than two tubes in a cascade arrangement similar to that of Figure 2.

It is of course possible to apply the principle of the invention in other ways.

For instance an external source of square pulses, synchronised to the discharge of the last gap of the tube can be applied to the tube in opposition to the standing inter-electrode potential so as to hold the tube inert for the requisite time for deionisation, this time being arranged to span an integral number of the pulses to be recorded.

A self restoring flip-flop circuit of any suitable type, for instance an Eccles-Jordan circuit, could be used for the purpose, connected to the external circuit of the last gap so that the discharge in that gap triggered the flip-flop circuit causing it to produce a quenching pulse lasting during the restoring time of the flip-flop circuit.

With such an arrangement the limits to the number of gaps, inherent in the Fig. 1 arrangement could be extended.

The principal advantage of all these arrangements is to enable a tube of a given deionising characteristic to record higher pulse rates.

It has already been indicated, however, that a larger counting radix is obtained than the number of gaps in the tube.

This advantage may not be reaped in cases where discontinuous counting is required, owing to the fact that the tube counts to a radix equal to the number of its gaps on the first pulse cycle applied to it.

When continuous counting is required however, this miscount of the first cycle is unimportant for certain types of the application, e. g. frequency dividing where phase change is not important, whereas the increase of the counting radix may give advantages.

The circuit of Fig.1 for instance using an eight gap tube will count to a radix of ten and without a discharge-maintaining potential when they are used in the manner of this invention provided that the pulse amplitude is raised so that the gaps will fire without the assistance of the constant potential.

With such an arrangement a gap, once fired, will extinguish between pulses but will re-fire -fr'omthe next pulse provided that the inter-pulse 'interval is not so long that the gas in the said gaps and in the next gap required to be fired by the next pulse does not become deionised.

This deionisation will take place and break the sequence of discharges at low pulse rates, but when the pulse rate is such that the period of more than one pulse is required for deionisation, the conditions with which this invention is chiefly concerned, the constant potential may be dispensed with. With such an arrangement since the discharge of the tube as a whole is extinguished by reason of the removal of the last pulse, there is no need to provide special means for this purpose.

Some form of timing means such as an Eccles- Jordan circuit triggered by the discharge of the last gap would of course still be necessary to time the period of one or more pulses and for instance open the pulse circuit to the tube for that period.

What is claimed is:

1. A device responsive to recurring pulses of electrical energy which comprises a cold cathode gas discharge tube having three or more discharge gaps arranged sequentially to fire in succession in a predetermined order on the application of pulses to the said gaps in common, ionisation from the discharge in one gap lowering the voltage necessary to fire the next adjoining unfired gap and so priming the said adjoining gap, means for applying pulses to said gaps, means for automatically extinguishing all discharges in the said gaps when all the gaps have been fired in turn and for preventing one or more pulses immediately succeeding the pulse which caused the last of the said gaps to fire from firing any of the said gaps in the tube in order to provide time for all the said gaps in the tube to extinguish and to deionise to at least a predetermined extent so that the next pulse allowed to affect the tube will fire the first gap in the said predetermined order and no other gap.

2. A pulse responsive device arranged to respond to successive cycles of pulses of a predetermined number comprising a cold cathode gasdischarge tube :having a number of discharge gaps arranged sequentially to fire in succession on the application of pulses to the said gaps in common, the number of the said gaps being less than the number of pulses in an applied cycle, means responsive to the discharge in the last gap for counting the remainder of the pulses of a cycle after all of said gaps have fired once and means for preventing operation of the tube by the said remainder pulses.

3. A device, as claimed in claim 1, in which the last mentioned means comprises another tube or tubes similar to the first mentioned tube, and means responsive to the discharge in the last gap of said first tube for causing the gaps of said other tube to fire in sequence from pulses immediately succeeding that which fired the last gap of the first mentioned tube, and means for preventing pulses from firing gaps of the first mentioned tube during the discharge sequence of the said other tube.

4. A device as claimed in claim 3 in which means is provided for extinguishing the discharge in the said other tube when all gaps have fired and for causing the firing of the said selected gap of the first mentioned tube by the next pulse received and starting a sequence of discharges therein.

5. A device, as claimed in claim 1, in which a source of constant potential is connected across all the said gaps in the tube, such potential being insufiicient to initiate a discharge in the said gaps but sufficient to maintain a discharge, once initiated, and the means for extinguishing all discharges in the said gaps on or after firing of the last of the said gaps in the said predetermined order comprises means for reducing said. potential.

6. A device, as claimed in claim 5, in which the means for extinguishing the said gaps and for preventing one or more succeeding pulses from affecting the tube, comprises a condenser connected in parallel with the electrodes of the last gap of the said tube, the condenser being normally charged by potentials applied to said electrodes, and being adapted to discharge on the firing of the last gap, whereby the potential applied to all the gaps of the tube is maintained below that necessary to fire any gaps in the tube and is maintained at that level so long as the charge in the said condenser remains below a predetermined level.

7. A device, as claimed in claim 1, in which a source of constant potential is connected across all the said gaps in the tube, such potential being insufficient to initiate a discharge in said gaps but sufficient to maintain a discharge, once initiated, and the means both for extinguishing the said gaps and for preventing a succeeding one or more pulses from affecting the tube, is a resistance in series with the connection to one electrode of all gaps in the tube adapted to fire in succession, the increased current through the said resistance, on the firing of the last gap of the said tube, causing the potential across the said gaps of the tube to fall below that required to maintain discharges in the said gaps.

8. A device, as claimed in claim 1, in which the last mentioned means comprises another tube similar to the first mentioned tube, and means responsive to the discharge in the last gap of said 4 first tube for causing the gaps of said Other tubes to fire in sequence from pulses immediately succeeding that which fired the last gap of the first mentioned tube, and means for preventing pulses from firing gaps of the first mentioned, tube during the discharge sequence of the said other tube, said means including a constant source of potential which when applied to all the gap in the tube is insufiicient to initiate a discharge in said gaps, but suflicient to maintain a discharge, once initiated, and means for connecting said potential to the tubes in turn, said means being responsive to the discharge of the last gap in each of the tubes for disconnectin said potential from that tube and connecting it to the other.

9. A device as claimed in claim 8 in which the means for connecting and disconnectinga source of potential simultaneously with the connection and disconnection of the pulse applying means to said tubes are disconnected from a tube at the same time as the said constant potential is disconnected.

10. A device, as claimed in claim 1, in which a source of constant potential is connected across all the said gaps in the tube, such potential being insufiicient to initiate a, discharg in the said gaps, but sufficient to maintain a discharge, once initiated, and the mean for extinguishing all discharges in the said gaps on or after firing of the last of the said gaps in the said predetermined order comprises means for disconnecting the said source of constant potential.

ALEC HARLEY REEVES.

REFERENCES CITED The following references are of record in the file of this patent:

UNITED STATES PATENTS Number Name Date 2,404,920 Overbeck July 30, 1946 2,443,407 Wales June 15, 1948

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