multi-electrode counting tubes*

J O U R N A L O F T H E B R I T I S H I N S T I T U T I O N O F R A D I O E N G I N E E R S

MULTI-ELECTRODE COUNTING TUBES*by

K. Kandiah, M.A., B.Sc.f and D. W. Chambers!A Paper presented during the Industrial Electronics Convention held in Oxford in July 1954

SUMMARYThe paper considers possible uses of hot and cold cathode decimal counters in systems other than

straightforward counting. It deals with their uses for adding and subtracting, for counting a predeterminednumber, and for dividing by numbers less than ten. The principles of a pulse-amplitude analyser usingtrochotrons and dekatrons in a matrix system are outlined. References are also made to other possibleuses where they are expected to be more reliable than more conventional methods.

1. IntroductionMulti-electrode counting tubes such as the

Ericsson Telephones GC10B, the Mullard E1T,and the L.M. Ericsson RYG10, have made itpossible to count in decimal figures in a mannerwhich is considerably simpler than in thosesystems which use a multiplicity of thermionicor cold cathode tubes. It is now possible to use.these new tubes in equipment for countingnuclear events and for various counting appli-cations in industrial process control, with theadvantage of direct indication of the numberstored, high counting speeds, and simple zeroresets. The reliability of these tubes hasencouraged their use in further applications.It is the purpose of this paper to assess featuresof these tubes which make them suitable forsome unusual applications.

The characteristics of these tubes have beendescribed in detail in the literature.1-2-3'4-5

2. Counting in Decimal FiguresMost of the tubes available at present are

designed to count in decimal figures and theyare all suitable for connection in a cascadesystem providing a store of as many digits asdesired. The complexity of such a completeunit depends largely on the type of pulsesrequired to drive the tubes. These are singlepulses, or pairs of pulses, having fairly widepermissible tolerances for the gas-filled tubes, andpulses of defined amplitude and shape for theE1T and RYGlO-type tubes.

* Manuscript first received June 11th, 1954, and infinal form on August 3rd, 1954. (Paper No. 310.)

t Atomic Energy Research Establishment, Harwell,Berkshire.

U.D.C. No. 621.387 : 621.374.32.

All tubes available at present in this countryprovide an output pulse which is of smallerenergy content than that required to drive asucceeding counting tube. It is thereforenecessary to provide a driving stage, using atleast one thermionic valve, or cold cathodetrigger tube between the stages of a cascade. Agas-filled counting tube has been described6 inwhich the necessary coupling element in theform of a trigger tube is built into the envelopewhich contains the counting tube.

The Ericsson Telephones GC10B has theadvantage of being completely symmetrical, andcan therefore be driven in either direction. It isonly necessary to reverse the connections to thetransfer guides in order to reverse the directionin which the glow transfers. If, however, it isnecessary to make the tube add or subtract whenan input pulse is applied to one of two alterna-tive points, it is necessary to have independentdriving circuits which apply transfer pulses inthe correct sequence. When a cascade ofGC10B stages is required to add or subtract, theproblem becomes mor£ involved, and onemethod of providing this facility has alreadybeen described.7 A disadvantage of this methodis that ambiguity in reading the digits maysometimes be experienced, and it will then benecessary to determine the digit stored byreference to the position of the glow in theprevious tube.

An advantage of the method8 of driving acascade of GC10B stages by utilizing a com-bination of a common pulse generator andgating tubes as coupling elements is that itreadily lends itself to a reliable method ofaddition and subtraction. In its simplest form,the circuit of one stage of a cascade is as shown

221


•A1 PULSE O+400

BIAS

Fig. 1.—One stage of a cascade.

in Fig. 1. In this system, the discharge rests ona "B" cathode of the counting tube and the "A"and "K" cathodes are used as transfer guides.All the stages in the cascade are identical and"A" pulses and "quench" pulses from a commonpulse generator are applied to all the stages ofthe cascade whenever an input pulse is receivedinto the first stage. The waveforms in the firsttwo stages in such a system for addition areshown in Fig. 2. Although pulses are appliedto all the "A" transfer guides, the glow willadvance by one digit in only those stages whichhave received a pulse into the trigger tube.

In principle, a cascade of stages using thecircuit of Fig. 1 can be made to subtract if thecommon pulse generator delivers the pulsesshown in Fig. 3 which also shows the appro-priate waveforms in the first two stages whenthey count backwards from 10. It should benoted that in this method the first trigger tubereceives a pulse which is delayed by about200 [xsec on the input pulse and that all "A"transfer guides receive a negative pulse from thecommon pulse generator during this delay.

The realization of a practical unit which willadd or subtract, working on the principlesoutlined, will require some changes to thecircuit shown in Fig. 1 and to the waveformsfrom the common pulse generators.

During the period of the negative pulse to all"A" transfer guides, the discharge in the count-ing tubes will move from the "B" guide to anadjacent "A." This will result in the loweringof the cathode potential of the trigger tubeassociated with each stage. The tube may there-fore fire even in the absence of an input pulseto the trigger electrode and the unit will mis-count. It is therefore necessary to modify the

222

cathode circuit of the trigger tubes so that theywill fire only when an input pulse is applied tothe trigger electrode and not when the associatedcounting tube momentarily passes current to aguide other than the "B" guide.

Another difficulty arises from the delaybetween the positive-going back edge of the"A" pulse to a GC1 OB—which results in that

IN0ICAUD COUNT 0 I - 2

INPUT PULSE ! |

ALL A'S -H20

ANODES OFTRIGGER TUBES

'CARRY'PULSE + 9 0

U LT

B'S OFSECOND STAGE

Fig. 2.— Waveforms for addition.

NDICATEDCOUNT 10

NPUT PULSES

9 8

FIRST TRIGGERTURF INPUT 1

ALL A'S

' 3 0

ANODES OFTRIGGER TUBES

+ 120

B'S OFFIRST STftCE ft

CARRY PULSE

B'S OFcrrrwr, <;TIC,F

| 1

u u

Fig. 3.— Waveforms for subtraction.

April 1955

K. KANDIAH& D. W. CHAMBERS MULTI-ELECTRODE COUNTING TUBES

particular stage counting to 10, and the firing ofthe subsequent trigger tube. This delay ispartly due to the trigger tube, and in the caseof a fast trigger tube, mainly due to the rate ofrise of the GC10B anode voltage and the rateof transfer of glow to the output guide Ko. Itis possible to keep this delay down to about10 fzsec per stage of the cascade. In a 5-stageunit the delay may therefore be 40 [xsec." Theresulting waveforms on the 1st and 5th stagesduring addition and subtraction are shown inFig. 4. In the case of addition the effect of thedelay can be completely overcome by increasingthe delay between the input pulse and thenegative-going front edge of the "A" pulse.For subtraction, however, it is necessary toensure that the back edge of the "A" pulse isreturned to the + 120V line only when thetrigger tube of that particular stage has fired.If the trigger tube does not receive an inputpulse, the "A" guides are returned to + 120Vwhen the quench pulse is applied to all the triggertubes.

being slightly greater than the current throughthe GC10B. Guides "A" and "K" of theGC10B are at + 60V.

A-o

B-oQUENCH

INPUT

BIAS

-20V

Fig. 5.—Typical stage of cascade for addition orsubtraction.

B'S OFFIRST STAGE'

B'S OFFIFTH STAGE

SUBTRACTION

Fig. 4.—Effect of cumulative delay in five stages of acascade.

The circuit diagram of a typical stage of acascade capable of adding and subtracting,with the modifications necessitated by the aboveconsiderations, is given in Fig. 5. The wave-forms for addition and subtraction are given inFig. 6. Let us first .consider the quiescent stateof the typical stage shown in Fig. 5. The triggertube VI is not conducting and the anode voltageon this tube is at the recommended value forthe tube. The cathode of VI is held at earthpotential by the rectifier MR1, there being asmall current through Rl to — 20V. TheGC10B is passing current to a guide "B"which is held at the potential of the cathode ofVI by rectifier MR2, the current through R2

When the unit is required to add, a triggerpulse is applied to VI and after about 200 fxsec,the common "A" pulse is applied to the A +line as shown in Fig. 6. At the end of this pulse,the quench pulse is applied to the anodes of allthe trigger tubes. The GC10B then transfersforward via a guide "K" and a guide "A" tothe following guide "B." The waveforms in the5th stage of the cascade are shown in Fig. 6,where it is seen that the positive-going frontedges of the pulses on guides "A" and "B" ofthis stage have the cumulative delay through thefour preceding stages. This does not result inerratic counting provided that the delay betweenthe positive-going edge of the "B" pulse and thenegative-going edge of the "A" pulse in thisstage is greater than 80 (j.sec. It should be notedthat, when VI is fired, current flows throughR2 and R3 to the B — and A — lines respectively.Since the number of trigger tubes that are firedby a pulse at the input to the cascade can varyfrom 1 to 5, it is important to ensure that theA — and B — lines do not change their potentialsby more than about 5V as a result of this, sinceit may lead to erratic counting. It is alsonecessary to ensure that the pulse applied to theA + Hne from the common pulse generator iscapable of taking this line to 0V notwithstandingthe current that will flow through the resistorsR4 of each stage in which VI has fired.

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J O U R N A L OF THE B R I T I S H I N S T I T U T I O N OF R A D I O E N G I N E E R S

When the unit is required to subtract, pulsesfrom the common pulse generator are appliedto the A —, B —, and quench lines as shown inFig. 6. Also, the pulse that is applied to thefirst trigger tube is delayed by about 100 fxsecon the input pulse. The sequence of events inthe various stages will now be described. Onreceipt of the input pulse, the glow is made totransfer to the guides "A" immediately preced-ing the guides "B" that were glowing. When thedelayed input pulse fires the first trigger tube, theguides "A" and "B" are taken to + 120V withthe result that the guide "K" immediatelypreceding will now glow. When the quenchpulse is applied, the glow will rest on guide "B"which is one digit earlier than it was at thebeginning of the cycle. If the glow passed to aKo guide during the above sequence a "carry"pulse will have been produced which willhavefired the succeeding trigger tube, and the

associated GC10B will have moved back onedigit. In the case of those stages where a "carry"pulse is not received from the previous stage,the glow will return to the original guide "B"at the end of the cycle. It can be seen from Fig. 6that the effect of the time delays due to thetrigger tube and the rate of rise of the outputpulse from the GC10B tube will result in ashortening of the duration of the glow on aguide "K" in the later stages of the cascade.The duration of the common A — and B —pulses and hence the delay to the front edge ofthe quench pulse from the input pulse mustbe made long enough to avoid erratic counting.It should be noted that, as in the case of addi-tion, the common pulse generator should becapable of maintaining the correct potential atthe A —, B — and A + lines irrespective ofthe number of trigger tubes in the cascade thathappens to fire for an input pulse.

B'SOF FIFTHSTAGE

A'S OF FIFTHSTAGE

- 6 0

+ 60

Fig. 6.— Waveforms for addition and subtraction usingcircuit of Fig. 5.

224

3. Frequency Division and Counting a Pre-determined Number

The use of the new counting tubes for divid-ing the repetition frequency of a train of pulsesby factors of 10 is a further application of theirnormal scaling circuits. Some important in-dustrial uses are: the accurate measurement ofan unknown frequency using standard timingpulses as a reference; measuring the timebetween two events; and the provision offrequency signals which are sub-multiples of astandard frequency.9-10 In general, the totalnumber of components for each divider usingone of the new counting tubes will be greaterthan that needed by one of the monostabletrigger circuits which are normally used wherethe pulse spacing is fixed. However, oneimportant advantage of the circuits using thenew tube is that the number of close tolerancecomponents in each dividing stage can be smaller,and further, the dividing factor is completelyindependent of pulse spacing. It is expectedthat the circuits using these tubes will give longperiods of trouble-free operation.

One advantage of the monostable triggercircuits is the ease with, which the dividingfactor can be changed from 1 up to about 10.Provided that the input repetition frequencydoes not vary by more than say 5 per cent.,this method of frequency division is probablythe simplest. Where, however, the dividingfactor has to be independent of the input

April 1955


frequency, it is necessary to use a countingcircuit. It is possible to alter the dividing factorin a circuit using the E1T counting tube from1 to 10 in a relatively simple way. It is seenfrom the characteristics of the E1T shown inFig. 7 that the 10 stable positions of the beamcorrespond to 10 voltage levels at the right-hand

Fig. 7.—Typical characteristic of the El T.

deflector, with a mean separation of about 14Vbetween two adjacent points. The "0" positioncorresponds to about 240V and the "9" positionabout 100V. When pulses are applied to the left-hand deflector, the beam moves from onestable position to the next, and after passingposition "9," the beam is normally reset to the"0" position by momentarily cutting off thebeam current. This makes the right-handdeflector return to the highest potential whichgives a stable beam position. If the right-handdeflector is caught at an intermediate potentialby a diode, then the beam can be made to resetto any one of the other stable positions. Thisreduces the number of stable positions availableand consequently allows division by any numberup to 10. The use of the EIT in a counting unitto provide an output at the end of a pre-determined number of counts, N follows fromthe above method of setting the beam to anyone of the 10 stable positions. If a cascade ofsay five stages is used, then the stages areinitially set up to the number 100,000 — N bymomentarily arranging to "catch" the right-hand deflectors at suitable potentials whilstcutting off the beam currents. If, now, N pulsesare applied at the input, the unit counts in thenormal manner and the last stage will give anoutput pulse at the Mh input pulse. It can thenbe again set to the original 100,000 — TVposition by resetting as above.

It is also possible to arrange for the trochotronRYG10 to divide by any number less than 10.

Let us first consider the normal operation of thetrochotron in the arrangement which allowsdivision by 10. The basic circuit diagram isgiven in Fig. 8, and the waveforms in Fig. 9.Normally the spade resistors Rl , R2 — R10are all equal, and so are all the spade capacitorsCl, C2 — C10. A negative pulse whose dura-tion is approximately 0-8 CK//(where C is thetotal capacitance at the spade, V is the spadevoltage, and / is the cathode current) is appliedto the anode in order to shift the beam fromone stable position to the next. If the negativeinput pulse on the anode moves the beam fromspade one to spade two, the voltage on spadeone rises with the time constant CJ.RI whereasthe voltage on spade two falls much more rapidlysince the current flowing to this spade duringthe input pulse is the full cathode current ofabout 10 mA. The quiescent current on thespade which passes current is usually less than1 mA. The waveforms for this condition are asin Fig. 9a. If the duration of the negative pulse

+ 25OV

I5K

Fig. 8.—Basic circuit for trochotron RYGiO.

on the anode is increased, the beam will movepast spade two after the potential of this spadehas fallen by about 80V. By increasing theduration of the driving pulse to 2 x CVjI'xt ispossible to make the beam miss every otherspade and therefore divide by five. Suppose itis necessary to divide by nine. If one of thespades, say spade two, has a larger load resistanceand a much smaller capacitor the beam willalways miss spade two, and the waveforms will beas shown in Fig. 9b. If this technique is usedon many spades, the value of the cathode

225

JOURNAL OF THE BRITISH INSTITUTION OF RADIO ENGINEERS

(a) EQUAL C'S AND ft'SON ALL SPADES

(b)SPADE Z HAVING MUCHSMALLER C AND LARGER R

Fig. 9.— Waveforms in trochotrons.

resistor R l l will become critical at high repeti-tion frequencies. An alternative method ofmaking the trochotron divide by a number lessthan 10 is to join the requisite number ofspades together, and connect them to a commonload resistor and capacitor. If more than threespades are joined together for this applicationthe anode and spade supply voltages willrequire re-adjustment.

In the gas-filled counting tubes, the digitstored in the tube can be identified by the guideto which current is passing. In order to be ableto set the tubes to any required number, it isnecessary to bring the 10 guides correspondingto the numbers to separate connectionsoutside the tube. By then applying suitableinitial potentials to these guides, these tubes canalso be used in a predetermined counter. Thesetubes require a large negative pulse to a guidein order to bring the glow to that guide. In thecase of the GC10B, a negative rectangular pulseof at least 200V amplitude with a duration of afew milliseconds is necessary to reset the glowto an arbitrary guide. A pulse with an ex-ponential decay is also effective provided thatthe time constant is more than 10 milliseconds.The faster gas-filled tubes can be reset withslightly shorter pulses, but it is generally truethat the time necessary to reset in this manner

226

is much greater than the resolving time of thetubes.

It will be seen from the preceding statementsthat the use of tubes other than the E1T or theRYG10 for frequency division by a factor otherthan 10 will result in more complicated circuitsassociated with each tube. There are twoexceptions corresponding to division by 2 or 5.If we connect together K0, K2, K4, K6 and K8of a GS10B, in which all cathodes K are broughtout to separate leads, and derive the "carry"pulse from this common point, it will be seenthat this stage will divide by 2. Similarly, if wetake the "carry" pulse from K0 and K5 con-nected together then we can divide by 5. Ingeneral, by connecting together any number Nof cathodes K in a 10-position tube, we candivide by the number 10/iV, but the outputpulses from such a stage will not be equallyspaced except in the cases of division by 2,5 or 10.Where regular pulse spacing is unnecessary, forinstance, when calibrating ratemeters, then thecircuit of Fig. 10, giving a variable dividingfactor from 1 to 10* is very economical incomponents.

In certain cases of frequency division such asin the generation of standard time signals froma quartz crystal oscillator,11 it is necessary tomaintain the least possible time delay betweenthe output pulse and the associated input pulse.In the case of the trochotron RYG10 and theE1T this time delay can be made less than1 (xsec per stage, using the circuits recom-mended for those tubes. With slight modifi-cations to the circuits, this delay can be made lessthan 0-3 fjisec, but this will in general lead tocloser tolerance for some of the componentvalues. Using negative-driving pulses, the timedelay between input and output pulses for theGC10D and the G10/241E will be 20 \xsec ormore, and for the GC10B it will be more than160 (xsec per stage. By driving the gas-filledtubes with positive pulses as in the system usinga common pulse generator, this time delay canbe made less than 2 (Asec per stage for theGC10D and 10 fxsec per stage for the GC10B.

4. Switching ApplicationsAll of the counting tubes discussed earlier

with the exception of the E1T are capable ofbeing used as 10-way switches. A modifiedversion of a tube similar to the E1T, and otherswitching tubes of the trochotron type have beendescribed10 recently. One possible application

April 1955


I 10 20I 1 1 I I 1 I I I I I I I I 1 I I I I I I I I I I

JUUl JUUl JUUl

(a)

• 400 V

DIVIDEDOUTPUT

+-50V

(b) .

Fig. 10.—Method of obtaining calibrating frequencies.(a) Waveforms with K\, K2, K3 connected together.(b) Switching arrangement.

of switching tubes is in communications wherenormal audio or radio frequency signals areused. A prime requirement for such applicationsis that the switch should not introduce spurioussignals or distort or attenuate the signal beingtransmitted through the switch. The gas-filledtubes have the disadvantages of being able toswitch only at relatively low speeds and trans-mitting satisfactory signals only at audiofrequencies. If the signal is fed into the anodeof a gas-filled tube and taken out of one of theguides the voltage and current gains are equalto 1. The signal can therefore be transmittedthrough a number of tubes without appreciableattenuation. The noise in the tubes is generallynot greater than a few millivolts r.m.s. betweenanode and guide, and in the case of good tubesmay be as small as a few hundred microvolts.The maximum signal that can be transmittedthrough the tubes is about 10V r.m.s. with thecurrent being limited to about 100 jzA r.m.s.

At the other extreme of switching speeds thetrochotron of the RYG10 type can change overfrom one spade to the next in about 0-3 [/.sec.

Signals applied to the cathode can be switchedto one of the 10 spades. The voltage gain of thetube is slightly less than 1, and the current gainis less than 0-05 for the RYG10. In the case ofthe tubes with separate collectors10 such as theTR-SR-11, the current gain is about 0-2 and thevoltage gain can exceed unity. It is seen thatthese tubes attenuate the signal considerably andthe use of tubes in cascade for switching purposesinvolves amplification of the signal and will resultin additional valve circuits in series with eachsignal. The greatest disadvantage of these tubeslies in the high noise level which can be as highas 10 (JLA r.m.s. for a mean spade current of1 mA. It should be observed that the completeshot noise given by

I2 = 2ef8Ffor a current of 1 mA is 0-018 JJLA assuming6/to be 106 c/s. In tubes such as the TR-SR-11where the collectors are not in any way con-nected to the spades, the noise current isexpected to be a smaller fraction of the meancollector current although it will still be con-siderably higher than the true shot noise.

The use of various counting tubes as codersand decoders in pulse code modulation systemsand as decimal-to-binary converters is expectedto lead to a reduction of the total number ofvalve elements in such systems. An interestingimmediate application is in a system whereinformation is converted from an analogue to adigital system. One particular case is the pulse-amplitude analyser. In this instrument the pulsesin the amplitude range 0 — E volts are countedin n channels each of which accepts pulses in

E E E E Ethe range 0 to —, — to 2—, 2— to 3 — , . . . and

n n n n n£

(n — 1) — to E respectively. In one method, acapacitor is charged to the peak voltage of eachsignal pulse as it arrives, and at the same timean accurate linearly increasing voltage and apulse train of fixed spacing is generated. Thefirst pulse of the train opens the first channel,the second pulse closes the first channel andopens the se'cond channel, the third pulsecloses the second channel and opens the thirdchannel and so on. When the linearly increas-ing voltage reaches the voltage of the capacitor,which remains constant at the peak signal pulsevoltage, a pulse is applied to all the channelsand only the channel which i.s open at that

227


instant will register this pulse. Some form ofdigital counting system is used in each channeland the number of pulses of a particularamplitude range is therefore counted ia onechannel. As soon as the pulse is counted in achannel the capacitor is discharged and thesystem is ready to accept another pulse.

NPUTii—<

P U L S E

OF CHANGEVOLTAGEGENERATOR

CAPACITORCHARGINGCIRCUIT

PULSE TRAINGENERATOR

VOLTAGEEQUALITYSENSINGCIRCUIT

f

R I N GOFM

* RING OF N

UT\ FTMI In-1

liiil V

-ftl-fiwl •1*J Lp JiLJ -EJ LJ

• + • 4 4J COUNT PULSE

1

S

Fig. 11.—Block schematic of analyser.

A novel method14 of reducing the total numberof valves in a multi-channel pulse analyser ofthe above type is to use two counting circuitsconsisting of a ring of m and a ring of nrespectively and to connect them in a matrix asin Fig. 11. Every complete circulation in thering of m moves the ring of n by one stage.There are mn combinations of states in the tworing circuits in which one stage of each ringcircuit is in an odd state. In order to use this ina pulse-amplitude analyser of the type justdescribed, the pulse train is applied to the inputof the ring of m. Each channel of the analyserconsists of a triple coincidence arrangementwhich receives an input from one stage of thering of m, an input from one stage of the ringof n, and a counting pulse, which is common toall channels. The pulse train, which starts whenthe capacitor is being charged to the peak inputpulse, is counted in the ring circuits until thelinearly increasing voltage reaches the voltageon the capacitor. When this state is reached thepulse train is interrupted'and the counting pulseis applied to all channels. Only that channelwhich is connected to the odd stage in the ringof m and the odd stage in the ring of n willregister the pulse. This is therefore a pulse-amplitude analyser with mn channels, where themnth channel counts all pulses above a certainlevel.

228

An interesting system has been worked outon the above general principles but usingRYGlO-type tubes in place of the ring countersand using GC10B tubes to perform the combinedfunctions of the coincidence unit and the digitalcounter of each channel. In the proposed systemthere are no components in each channel other

than one GC10B, the anode load ofthe GC10B and the output cathoderesistor. The pulses out of theGC10B in each channel can becounted in further counting stagesof any desired type.

The block schematic of the new100-channel pulse analyser is shownin Fig. 12 and one of the two ringcircuits and gates is shown in Fig. 13.The ring circuits are identical toeach other. The main differences infunction are that ring A receives itsdrive pulses directly from the pulse-train generator, and the pulsesthrough the gating valves V2, V 4 . . .V20 are fed to the "A" guides of

the GC10B tubes; whereas the ring B receivesits drive pulses from the "carry" pulses out ofring A, and the pulses through the gating valvesare connected to the "B" guides of the GC10Btubes. The RYG10 has the usual cathode resistorR4 and spade resistors R5, R8 . . . R32. The ninespades that are not passing current are caughtby the corresponding diodes VI, V3 . . . VI9 at+ 250V. The spade that is conducting will be atabout lOVbelowthepotential of thecathodeof theRYG10. The grids of the left-hand sections ofthe gating valves V2, V4 . . . V20 are connected tospades 1, 2 . . . 10 respectively of the RYG10.The grids of the right-hand sections of the valvesare connected together and returned to thejunction of R2 and R3 which is about 20Vabove the potential of the cathode of theRYG10. The anodes of the right-hand sectionsare connected to the GClOB's, those from ringA being connected to the "A" guides and thosefrom ring B to the " B " guides as shown in Fig.12.

In Fig. 13, the valves V22 and V24 are normallycut-off. Hence the cathodes of VI, V3 . . . V19are held by diode V23 at + 250V and thecathodes of the gating valves V2, V4 . . . V20are at about + 275V, there being no currentthrough any of the gating valves. One of thegating valves, corresponding to the spade of theRYG10 that is conducting, has its left-hand

April 1955


INPUTPULSE

DISCHARGE

PULSESTRETCHING

CIRCUIT

CONSTANT RATEOF CHANGEVOLTAGEGENERATOR

w START

PULSETRAIN

GENERATOR

VOLTAGEEQUALITYSENSINGCIRCUIT

ZERORESETCIRCUIT

' 8 'PULSE

GENERATOR

'RESET-PULSE

'COUNT'PULSE .

'CARRY1

PULSE

'RESET*PULSE

'A1

PULSEGENERATOR

'COUNT'PULSE

RING B

RING

DRIVEPULSE

nGUIDES B OF DEKATRONSI—10 11-20 91-100

GUIDES A OF DEKATRONS10,20,30, ... 100

2 , 12, 22 , . . . 92

I , 11 , 21, . . . 91

Fig. 12.—Block schematic of pulse analyser using trochotrons and dekatrons.

DRIVEPULSES•

TO

DEKATRONSI , I I , 21 , . . . 91

>R5

jI

TROCHOTRON•

R7:

DEKATRONS2,12.22, . . .92

•Fi—Pr

V2

C3 <R6

35OV

RESET

PULSE

Fig. 13.—Ring circuit and gates for pulse analyser using trochotron RYG10.

229


grid at about + 120V, whereas the left-handgrids of all the remaining gating valves are at+ 250V. The right-hand grids of all valves areat about + 150V. If the valve V24 is nowbrought into conduction there will be a negativepulse out of the right-hand anode of that gatingvalve which is connected to the conducting spade.

The operation of the complete pulse analysercan now be described with reference to Fig. 12and the waveforms as shown in Fig. 14. Thewaveforms refer to a signal pulse of an amplitudecorresponding to channel 25. The signal pulseis fed through a diode to a capacitor which istherefore charged to the peak value of the signal.The capacitor remains charged to this voltageuntil the information corresponding to thissignal is stored in the appropriate channel.When the capacitor is charged, the constantrate voltage and pulse-train generators arestarted simultaneously. The pulse train whichcan have a spacing of about 2 fzsec is fed toring A and the carry pulse from ring A is fed toring B. When the constant rate voltage reachesthe voltage stored on the capacitor the level-sensing circuit stops the pulse train. Immediatelyafter this a positive rectangular pulse of about100 (zsec duration is fed to V24 of ring A whichtherefore applies negative transfer pulses ofabout 120V to the "A" guides of the GClOB's5, 15 . . . 95 in the case of this particular pulseamplitude since ring A will be stopped onposition 5. Immediately after the "A" pulse, asimilar positive "B" pulse is applied to thecorresponding point in ring B which will there-fore apply a negative transfer pulse to the "B"guides of GClOB's 21 to 30. Since the onlyGC10B which received both an "A" and a" B " pulse is tube 25, this tube and no other willtransfer by one digit. At the end of the "B"pulse a positive reset pulse is applied to thegrids of the resetting valves V22 in the two-ringcircuits. This causes the cathodes of the diodesVI, V3 . . . VI9 to come down to nearly earthpotential and recover slowly to the normalpotential of + 250. Spades 1 to 9 will recoverfaster than spade 10, as shown in Fig. 14, sincethe recovery of spade 10 will be determined byR37 and C15, which is made longer than therecovery of the normal spade circuits.

In a complete analyser it is necessary to havecertain ancillary circuits in order to avoid errors.It will be appreciated that in the system describedabove, any pulse larger than E volts in amplitude

230

will be counted in one of the channels as if itwas a pulse of amplitude less than E volts.It is therefore necessary to have a circuit which

~STRETCHED PULSE

CONSTANT RUNDOWN

OUTPUT OF LEVELSENSING CIRCUIT

UNIFORM PULSE TRAIN

'A' PULSE TO RING A

'B 'PULSE TO RING

GUIDES 'A 'OF DEKA-

TRON GCI0 6 5,I5,...95

GUIDES ' B ' OF DEKA-

TRON GCIOB 21 TO 30

SPADE 10

•Fig. 14.—The waveforms in the pulse analyser of Fig. 12.

ensures that each gate shall be open once onlyduring each cycle. It is also necessary to intro-duce a gate which prevents pulses entering thestretching circuits while a previous pulse isbeing analysed by the unit.

The simplicity of the above system can beappreciated by comparing the total number ofcomponents in the circuits associated with thesorting of the pulses into the various channelsin different types of analysers. In one of theearlier types of analyser13 there are approxi-mately 80 valves and 400 components in thesorting circuits for a 30-channel unit. For thepurposes of this estimate, double valves in oneenvelope have been counted as two valves andthe valves and components which perform

April 1955

K. K A N D I A H & D. W. C H A M B E R S M U L T I - E L E C T R O D E C O U N T I N G T U B E S

functions common to many units are notincluded. The scaling and counting circuits inthe individual channels are not included in theabove estimate. On the same basis the analyserdescribed in this paper uses 72 valves and 100components in the two ring circuits and 100GC10B dekatrons and 200 resistors in the 100channels. It will accept signal pulses with aresolving time of about 500 fj.sec, whereas the 30-channel analyser referred to will resolve signalpulses which are 150 (jisec apart. It can be saidthat the new analyser provides 100 channelswith fewer valves and much fewer componentsthan the 30-channel analyser.

Another comparison can be made with theslow analyser14 working on similar principles.In this unit, which will resolve signal jpulses100 msec apart, there are approximately 160valves and over 200 components. It should benoted, however, that no further components arenecessary to store the number of pulses in eachchannel since mechanical registers which canstore four digits are used. In the unit describedin this paper it will be necessary to use 100 valvesin order to work the registers following thedekatrons, and there will be five componentsassociated with each valve. The main improve-ment that has been obtained is the resolvingtime of 500 (j.sec as opposed to 100 msec in theslow analyser.

Another important instrument for the studyof the interaction of neutrons with nuclei is thetime-of-flight spectrometer.12 In this instrumenta pulse of neutrons of short duration but ofvarying energies is allowed to travel a knowndistance, and the time delay in the arrival of theneutrons at the detector is measured in orderto give information on the energy of the neutron.

The number of neutrons arriving with timedelays of 0 to t, t to It, It to 3>t . . . 99/ to 100?are counted in 100 separate channels. It isseen that the ring circuits and associatedGClOB's in the analyser described above, canbe used directly for this purpose. It is onlynecessary to use the pulse-train generator whichis started when the neutrons leave the source,and stopped when a neutron is received at thedetector. This system will only permit therecording of one neutron during each completecycle; but in those instances where the neutronsource transmits one neutron in the directionof the detector for every few pulses at the sourcethis does not lead to serious error in themeasurement.

The above instrument can be used for anyapplication in which a delayed signal is generatedfrom some main event and where the exact timedelay is not known and where there is a fluctua-tion in the time delay. A simple decimal count-ing unit with two decades is sufficient to measurea time delay of up to 100 units only where thereis one time delay involved.

5. ConclusionsThe counting tubes discussed have shown

great promise not only in simple circuits wherethe total number of events of one type is to becounted, but also in complex equipment suchas pulse-amplitude analysers and time-of-flightspectrometers. In every application whereinformation in a digit form has to be analysedor stored, these tubes provide a means ofobtaining- accurate information of a complexnature in relatively small and simple equipment.The life of these tubes has been found to becomparable to normal valves and since one ofthese tubes performs the functions of manyvalves the ultimate reliability of equipment isexpected to be improved considerably. Thisshould lead to the use of these tubes in industrialmeasurements and process control of complextypes in which combinations of valve circuitshave lacked the necessary simplicity andreliability.

6. References1. J. R. Acton, "The single-pulse dekatron,"

Electronic Engineering, 24, p. 48, 1952.2. R. C. Bacon and J. R. Pollard, "The

dekatron—a new cold-cathode countingtube," Electronic Engineering, 22, p. 173,1950.

3. G. H. Hough and D. S. Ridler, "Multi-cathode gas-tube counters," ElectricalCommunication, 27, p. 214, 1950.

4. A. J. W. M. Van Overbeek, J. L. H. Jonkerand K. Rodenhuis, "A decade countertube for high-counting rates," PhilipsTechnical Review, 14, p. 313, 1953.

5. H. Alfven and L. Lindberg, "Theory andapplication of trochotrons," Ada Polytech.Elect. Eng. Ser., 2, No. 2, p. 106, 1949.

6. P. S. Peck, "A ten-stage cold-cathodestepping tube," Electrical Engineering, N. Y.,76, p. 1136, 1952.

7. J. L. W. Churchill, "New trigger circuitsfor use with cold-cathode counting tubes,"/ . Brit.I.R.E., 11, p. 497, 1952.

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8. K. Kandiah, "A scaling unit employingmulti-electrode cold-cathode tubes," Proc.Instn Elect. Engrs, 101, Part II, p. 237,June 1954.

9. W. R. Bland and B. J. Cooper, "A high-speed precision tachometer," ElectronicEngineering, 26, p. 2, 1954.

10. S. Kuchinsky, "Multi-output beam-switch-ing tubes for computers and general-purposeuse," Record of National Convention of theI.R.E. 1953, Part 6, p. 43.

11. H. M. Smith, "Quartz clocks of the Green-wich time service," Monthly Notices of theRoyal Astronomical Socy, 113, No. 1, 1953.

12. F. S. Goulding and others, "The develop-ment of a neutron spectrometer for theintermediate energies," Proc. Instn Elect.Engrs, 101, Part II, p. 248, June 1954.

13. E. H. Cooke-Yarborough and others, "Apulse-amplitude analyser of improved de-sign," Proc. Instn Elect. Engrs, 97, Part III,p. 108, March 1950.

14. D. H. Wilkinson, "A stable ninety-ninechannel pulse-amplitude analyser for slo"counting," Proc. Cambridge Phil. Soc, 46.Part 3, p. 508, July 1950.

DISCUSSION*N. Armitage: I am interested in protection

problems on power lines and in these circumstancesreliability is most important. We have begunexperiments with cold cathode tubes for variousswitching relay circuits. We have no operatingexperience of the life of these tubes and I wouldtherefore like to ask if Dr. Taylor can give usactual figures of their life ? We have been unableto get any information from the manufacturersapart from "several thousand hours."

I would also like to ask a question of Mr.Kandiah. We may use cold cathode tubes forcounting fault incidence. When the tube comes toand end of its useful life, is that end indicatedrapidly; or does the valve gradually becomeunreliable, and, if so, in what manner?

Dr. D. Taylor (in reply): I do give one figure inthe paperf for the life of cold cathode tubes.Replying to the question further, the type oftrigger tube used in the monitor described byStephens^ has a failure rate of the order of \ percent, per annum. We have used the multi-electrodetube that Mr. Kandiah describes in one of ourdigital computers, and the life figures are of thesame general order as the better-type thermionicvalves.

K. Kandiah (in reply): I would like to make onefurther comment in addition to what Dr. Taylorhas said about cold cathode switching tubes. I feelthat there has been some conflict in the generalopinion on the life of cold cathode trigger tubes.When it is stated that reliability is poor, I am

•Part of this Discussion has already been published in theNovember 1954 issue of the Journal, following the paper by Dr.Taylor. Jt is repeated here for the sake of completeness.

M.Brit.I.R.E., 14, p. 568, November, 1954.tJ.Brit.l.R.E., 14, p. 377, August, 1954.

232

certain that this is due to lack of appreciation ofthe limitations of these tubes, which are of quite adifferent character to thermionic valves. Takingthose limitations into mind there is no doubt thatthe life of these tubes is very long.

Multi-electrode tubes and switching tubes do notfail catastrophically. If a particular characteristic ismeasured, it is extremely unlikely that this will havechanged appreciably in the next few days except in afew special cases. The few special cases are those inwhich the characteristic is a function of the natureof the surface inside the tube, such as in some typesof activated tubes or when the tube containshydrogen or similar gases. Some of those tubes canchange their characteristics in a few hours, but ingeneral it is a very slow process and this sort ofdefect can very easily be overcome by marginal testbefore the tubes are put into use.

W. Nock: We have been using switching tubesof the type described by Mr. Kandiah since theirintroduction in 1950; our primary use is in timemeasurements, although in recent years we haveused them for batching and control purposes. Wehave had very reliable results except for the firstversion of the GC10D (20 kc/s tube) which became"sticky" after a short time in use. We haverecently obtained a modified version of this tubeand this is giving very promising results. We havehad a timer using one in use for four months.

Mr. Kandiah mentions the use of selector tubeswith ten cathodes, GS10B, to give fixed countsof 2 and 5. Using the GS12B with 12 cathodes, itis also possible to produce stages with counts of2, 3, 4, 6 and 12. In addition we have used aGS10B with forced reset to give stages countingin any number up to 10 at speeds up to 2 kc/s.

April 1955

multi-electrode counting tubes*

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