US2645680A - Pulse distributor, including electric discharge devices - Google Patents

Description

July 14, 1953 A. H. REEVES 2,645,680

PULSE DISTRIBUTOR, INCLUDING ELECTRIC DISCHARGE DEVICES Filed 001?. 5, 1947 3 Sheets-Sheet l 345678 Q/O/l/Z Inventor -ALEC H-REEVES A ilorney July 14, 1953 R E 2,645,

PULSE DISTRIBUTOR, INCLUDING ELECTRIC I DISCHARGE DEVICES Filed Oct. 5, 1947 s Sheets-Sheet 2;

- /3 75 /4 /a F/ G .2 f I K 2 MASTER a 4 5s 7 s even/2 PULSE GENERATOR {v0 36 I T- A0072 AUDIO 2 ifs/ TPU 7 OUTPUT Attorney July 14, 1953 A. H. REEVES 2,645,630 PULSE DISTRIBUTOR, INCLUDING ELECTRIC DISCHARGE DEVICES Filed Oct. 5, 1947 1 3 Sheets-Sheet 3 46 MASTER 45 PULSE GENE/PATCH SAW 700m 1 PULS 75o film/O SHAPE/P INPUT B SBAP Inventor ALEC l-LRgEV ES Attorney Patented July 14, 1953 PULSE DISTRIBUTOR, INCLUDING ELEC- TRIC DISCHARGE DEVICES Alec Harley Reeves, London, England, assignor f to lnternational Standard ElectricCorporation,

New York, N. Y., a corporation of Delaware Application October 3, 1947, Serial No. 777,818 In Great Britain October 3, 1946 This invention relates to pulse distributors of the type which distribute individual pulses in a pulse train between a number of individual circuits.

The object of the invention is to apply novel means to this purpose.

According to one of its aspects the invention consists of l a pulse'distributor comprising a plurality of gaseous electric discharge gaps adapted ;to fire in succession in' a predetermined order in response to incoming pulses of electrical energy applied in common to the said gaps and individual circuit being connectedto each gap for the transmission of an outgoing pulse when the associated gap fires in response to an incoming pulse. a I

According to another of its aspects the invention consists of a pulse distributor comprising a cold cathode gaseous discharge tube having a plurality of gaps adapted to fire in succession in a predetermined order in response to incoming pulses of electrical energy applied in common to the said gaps, an individual circuit being connected to each gap for-the transmission of an outgoing pulse each time the associated gap fires in response toan incoming pulse.

Certain embodiments of theinventicn will now be described in relation to the accompanying drawings in which:

Fig. 1 is a circuit diagram of a simple form of distributor, using a multi-gap gaseous discharge tube, suitable for distributing the individual pulses of a train of pulses amongst a number of individual circuits. v

Fig. 2 is a circuit diagram of a more elaborate form of distributor performing function analogous to those of the distributor illustrated in Fig. 1. V

Fig. 3 is a c'ircuitdiagram of a distributor suitable ,for generating a repeated pulse train, each pulse of a train being'under the control .of an individual circuit.

These three embodiments make use of gaseous discharge tubes of the type having a number of gaps adapted to fire in succession in response to being separately ledout of the tube, so that an individual circuit can be associated with each gap though the saidpulses are applied to all in common.

Tubes'oi this type are described in specification -No. 763,655 filedJuly 25,1947of Reeves 25 8 Claims. (01. 17915) there wouldbe no guarantee that the starting gap scription thereof will now be given.

forGaseous Discharge Tubes and a brief de- In this specification there is described cold cathode gaseous discharge tubes having a number of discharge gaps which fire in succession in a predetermined order, on application of pulses to the said gaps in common, due to ionisationbf an unfiredgap caused by the discharge in an ad joining fired gap. A first pulse applied to the tube will fire only a predetermined gap called the starting gapand various alternative measures to ensure this include the closer spacing of the electrodes of the starting gap in comparison with the other gaps, a bias potential applied to the starting gap only,

or the provision of a a permanently discharging gap, called a pilot gap, adjoining the starting gap, causing this gap to be permanently ionised.

After a sequence of discharges of the gaps of.

the tube, and when the last gap' in the predetermined order) hasfired, all discharges are extinguished and the tube isallowed to deionise before the commencement of another firing cycle.

If it is required to operate such a tube from a continuous sequence of regularly spaced pulses, a limit is set to the permissable frequency of pulse repetition by the need for a time interval between pulses, long enough to allow the gaps to become deionised (except the starting gap when a pilot gap is provided as previously described) If gaps (except aforesaid) remained ionised,

would fire first, in preference to the others, in a second or subsequent cycle of pulses nor that the predetermined firing order would be maintained.

To enable'higher pulse rates to be used, measures to reduce deionising time may be taken and this may be done by the use of special gas atmospheres in the tube.

Alternatively it may be-arranged to ensure that one or more pulses succeeding that which fires the last gap,.are prevented fromfiring any gaps in the tube so that a time longer than the interpulse interval is allowed for deionisation of the gas in the gaps. 7

Methods of doing this are described in-U. S. Patent No. 2,516,915issuedAugust 1, 1950 ,of A. H. Reeves 29 for Gaseous Discharge Device where (inter alia) the reduction of. the inter electrodevoltage, so that pulses do not reach first pulse of the next cycle.

decay of the memory effect will pass down the gaps of the tube in the predetermined firing order,

, With such a potential applied, gaps once fired will continue to discharge and at the end .ofa

' cycle, all will be discharging and must be extinguished'before the next operation cycle of the tube. There are various ways of doing this, one of which is used in the embodiments of the in'-' vention to be described. I

If no such discharge-maintaining potential is applied, discharges will collapse between pulses, during the firing cycle of thetube and the interval between pulses must not be so long that the ionisation can fall below the level necessary to secure sequential firing.

This involves the use of pulse rates such that the tube has not time to become deionised between consecutive pulses at the end of the firing cycleafter extinguishment of the discharges, and measures such as those described in said U. S. Patent No. 2,516,915 become essential.

A phenomenon occuring in multi-gap tubes of this type, is called the'Memory effect.

This effect consists of a rise in the voltage required to fire a gap, which follows an extinguished discharge in that gap. when certain electrode materials and gasses are used in the construction thereof.

If tubes possessing this feature, are supplied with pulses to their gaps, in common, and with no constant discharge-maintaining potential, a gap once fired, will ionise the adjacent unfired gap and extinguish at the end of the pulse which firedit. The next pulse will fire the ionised adjacent unfired gap but will not refire the extinguishedgap owing to the said rise in its critical firing voltage, it being arranged that the pulse amplitude is below such critical voltage.

This memory effect persists long enough to ensure that gaps once fired, will not again fire during the firing cycle ofthe tube, but when all gaps have fired and all possess the memory effect the first gap to recover will be that which has been extinguished for the longest time, i. e. the starting gap, and this alone will fire on the in advance'of'the firing sequence so that all in turn are ready to fire from successive pulses.

4 l3 to the positive pole ofa battery l4 which may be regarded as representing any" convenient source of direct current supply. r

The various cathodes are separately led out of the tube and each is externally connected through an individual resistance and transformer in series to a common connection leading to the negative .pole of battery I4. Only one such resistance and transformer l5 and I8 respectively are nected to the secondary winding of the transformer.

A correspondin 7 A small bias may be applied to the starting gapto male quite sure that the sequence starts with that gap in cycles afer the first but this bias must not be large enough to leave the starting gap permanently discharging. It is also an advantage to insert a relatively'large resistanceload in series with one of the common pulse feed connections to the gaps so that immediately on the firing of one gap, the increased voltage drop in the re sistance makes it impossible for another gap to fire from the same pulse; p Y,

I This enables the'tube' to be worked at a lower level of discrimination due to memory effect between gaps and still secure the correct firing order.

In Fig. 1 a gaseous discharge tube I has a common anode 2 consisting of a straight bar or strip" and a series of individual cathodes in the form' of rods or strips at right angles to the anode and spaced therefrom at one end of each cathode,

so as to define'disch'arge gaps, the tube illustrated having ten cathodes and ten gaps 3, 4, 5, 6, I, 8,

9, l0, u and I2.

Anode! is connected through an impedance shown in the drawing terminal 19 being con- All cathodes are connected to similar individual circuits. The potential applied to the gaps of the tubes by battery i4 is such that it cannot by itself initiate a discharge in any of the gaps but is sufficient to maintain a discharge, once initiated.

vPositive pulses are applied to the anode of the tube through feed condenser Hi from a common busbar l1. 7

- The pulses from If! consist of repeated trains of l consecutive pulses and the gaps fire in turn from successive pulses until all are fired.

A gap once fired, continues to discharge till all have fired, due to battery I4.

When all gaps have fired, they must be extinguished and allowed to deionise before the next firing cycle can commence; V

There are various ways of extinguishing the discharges but it is proposed in this and theother embodiments to be described, to provide a pulse (hereinafter called the quenching pulse), of

the opposite polarity to that of thepulses (hereinafter called the firing pulses), which fire the gaps.

These quenching pulses will oppose battery l4 and reduce the inter-electrode potential-to that which produces the requiredspeed of deionisa- "be some variation in the output as between the different transformers and where this is important, a differentiating network maybe introduced so that only the inception of the discharge is recorded.

It is contemplated that the individual pulses from the busbar, may carry modulation of .some kind, and it has been found that, with pulse rates such that a gap fires at rates up to about 1000 times per second, and; its corresponding firing pulse is modulated at some frequency, a low frequency transformer will give an output consisting substantially of such modulating frequency, the pulses component being lost in' the transformer, and this irrespectiveof the different discharge duration of the difier'ent cathodes.

' For higher frequencies it is preferable touse A Similar tubeto that illustrated in Fig. l is 'usedandcorresponding items of thetube and its associated circuits are given the same reference numerals in bothfigures.

The cathodes of the tube have separate individual circuits as before, though here two of them are shown (those of the first and last cathodes) and one consists of resistance I and transformer 'a gate to permit the passage of one pulse in each cycle of a continuous pulse sequence, and to dea continuousconducting path and may be made through condensers for instance. It is possible to separate the gate and busbar circuits from the modulate that pulse, where it is-modulated, give an output at the modulating frequency. 7

The associated gap of the tube provides the gating impulse.

The discharges in the tube are controlled by pulses from a master pulse generator 45 WhlCh is synchronized with the pulses from the busbar 46 and, in certain circumstances, both may be derived from a common source, though it only necessary to have a distinctive feature 1n one pulse of the pulse trains from the busbar (such as the quenching pulse on ll in Fig. 1 for 1nstance) to enable a separate pulsegenerator 45 i to be kept in step with the pulses from the busbar.

' sociated gaps, and all simultaneously pass a negative pulse on the quenching of the tube. This negative pulse is ignored by the gate'devices as they incorporate a rectifier and in any event,

there will probably be no pulse from the busbar at these moments and the devices need pulses from both sources to actuate them. I

Eachgate device has a condenser 25 and a resistance 26 which improve the pulse shape delivered by the associated cathode transformer and also decouple the transformer circuit from the busbar.

The busbar is also connected to each gate device through an individual condenser 34 and resistance 35 whichare generally chosen so as not to alter the wave form of the busbar pulses.

Outlets to gate devices associated with intermediate gaps of the tube are indicated by the arrows 31, 38, 39, '40, .42, and 44, these gate devices and the details of the cathode circuits of y the associated tube gaps being omitted to simplify the drawing. v

.In each gate device there is a closed circuit consisting of a rectifier 21, the primary winding of a low frequency transformer 36, a battery 3 I and a and 28.

In a working circuit, of course there will be a common point, probably earthed to which will be connected the negative side of master pulse generator 45, the negative pole of battery I4 in the tube circuit, and the junction o'f'28, 29 and 3|. in the gate device and a second conductor of the busbar. Theseconnections need not provide battery 3|.

cient to open the rectifier 21.

would have a similar effect.

tube circuits by using-separate earths for each by taking two leads from the secondary windings of the cathode transformers (20-22 etc.) instead of earthing one side of these secondaries.

Rectifier 2'! is normally 'biassed to cut ofi by Pulses from the busbar are of positive polarity tending to open the rectifier but being of insufficient amplitude to do so by themselves. When the associated gap fires the pulse from 26, added from the pulse from 35 is sufii- It is arranged that the pulsefrom a cathode slightly leads the corresponding pulse from the busbar and only on the inception of the latter, is

.the rectifier opened. The pulse overlap is arranged to terminate with the end of the tube pulse- The busbarpulse may be modulated in time or duration, but the tube pulse has constant timing, so that theperiod during which. the rectifier is open commences at the varying time of the busbar pulse and ends with the constant trailing edge of the tube pulse, so that a pulse flows in the closed circuitmodulated in duration in conformity with time of duration modulation the fundamental and lower harmoniesof the pulse repetition frequency of the pulses in the closed circuit. Time or duration modulation of the busbar pulses, in either case appears as duration modulation of the pulses in the closed circuit. This modulation can be regarded as a variation in the on-off ratio of these pulses and it is well known that a variation of this ratio varies the amplitude of thefundamental component of the pulse-waveform.

The transformer used is preferably one with a frequency characteristic such that it attenuates the harmonies more than this fundamental, and

theaddition of a low pass filter 32, between the secondary winding of 30 and terminals 36, produces an output at terminals 36 containing sub stantially themodulating frequency only. I

Amplitude modulation of the busbar pulses The embodiment illustrated in Fig. 3 is very similar to that in Fig. 2 corresponding components are given the same reference numerals in the two figures.

The differences consist of the addition of a transformer 4'! in series in the gate device, closed circuit and the substitution in place of the connection through 34 and 35 from the busbar of a connection through condenser 49 and resistance 48, from a saw tooth pulse shaper 50 which modifies the pulses of the master pulse generator 45, to saw tooth waveform. The busbar is connected to the secondary of transformer 41.

A modulating frequency is applied to terminals 36 instead of being taken therefrom.

Three potentials are simultaneously applied to the rectifier 21, first pulses from the associated cathode of tube I, secondly the saw tooth pulses from 55 and thirdly the instantaneous amplitude of the modulating wave from terminals 36. At a certain point in the potential rise of the saw tooth waveform, a potential suflicient to open rectifier 21, will be applied to the closed circuit, and current will flow in the circuit. It will generally be arranged that the current will always stop at a constant time coinciding with the end of the saw tooth pulse since the cathode pulse Will be of longer duration in the case of earlier firing cathodes.

The time at which the rectifier opens will of course be influenced by the contribution to the total voltage across the rectifier, of the modulating wave from 36, and the leading edge of the resulting pulse in the closed circuit, will be modu-' lated in time at the modulating frequency.

The output of 41 applied to the busbar will tend to be differentiated by the transformer 41 to produce a pulse at the beginning of the closed circuit pulse and a pulse of opposite polarity at the end of the closed circuit pulse. If it is necessary to modify this wave form either to reshape the first pulse in the busbar or to eliminate the reverse pulse following'it, or both, a single pulse shaping circuit on the busbar can perform this function for all pulses, and separate pulse shaping circuits for all gate devices are unnecessary.

Taking Figs. 2 and 3 together therefore, the former provides a means of taking repeating trains of pulses from a common source (the busbar) and distributing them amongst various individual outlets (connected to terminals 36 of the various gate devices associated with various vidualpulse in pulse trains applied-to the busbar.

It is envisaged that such devices may be used in a communication system enabling several physical channels to communicate with a corresponding number of physical channels, over a common connecting link (the busbar with or without intermediate apparatus) on a time division pulse multiplex basis. In specification No. 794,724 filed December 30, 1947 of D. H. Ransom- W. L. Roberts-R. H. Taplin 14-1-1 for Pulse Time Position Switching System a system of this nature is described wherein physical circuits are connected to scanned elements of a distributor, on the scanning element of which, the various physical channels are represented by individual pulses in a repeating pulse train. After passing through linefinder circuits and selection circuits, the common output appears again on the scanning member of a second distributor whose scanned elements are connected to individual physical channels. The devices illustrated in Figs. 2 and 3 could be used in the role of the distributors mentioned in that specification.

Tubes of the type described having the memory elfect may be used with advantage in the embodiments described and have the advantage, since each gapof the tube extinguishes, at

the end of the pulse which fires it and fires once only during a firing cycle of the tube, that pulse shaping measures and measures to suppress the end-of-pulse output are unnecessary.

It also has other advantages including increased tube life since all gaps fire only once per firing cycle of the tube, for the duration of their firing pulses only, instead of continuing to discharge during the whole firing sequence of the tube.

The omission of the maintaining potential .with a non-memory tube is possible but presents .the difliculty that a gap fires repeatedly from each pulse subsequent to that which first fired it, during each firing cycle of the tube and measures are required to enable only the first firing to be recorded by the individual gap circuits.

The use of the expedients outlined in said U. S. Patent No. 2,516,915 where one or more pulses are prevented from affecting the tubeafter the completion of a firing cycle, to allow extra time for deionisation, present no complication in the embodiments described, but of course, potential channels in the pulse cycle time are waste'd'to the extent of the pulses prevented from affecting the tube. Actually in the arrangements described, these pulses would preferably not be generated by the master pulse generator.

There are applications where such a pause at the end of a pulse train is necessary for other reasons and where this is the case, the expedients in that specification may be used with advantage to enable any given design of tube to cope with a higher pulse rate than it could handle if it had to become deionised during the normal interpulse interval.

It will have been observed that, whilst the arrangement of Fig. 2 has a corresponding simple or basic equivalent in the arrangement of Fig. 1 no such equivalent has been'shown for Fig. 3.

Such an equivalent may be simply devised by applying a saw tooth pulse sequence, such as that derived from 50 in Fig. 3, to the pulse feed condenser l6 in Fig. 1, in place of the pulses from the busbar.

A transformer capable of passing pulses would then be substituted for l8, with its primary winding in series with the cathodec'ircuit; and its secondary connected to the busbar'through suitable decoupling components to prevent interaction amongst the transformers associated with other cathodes, similarly connected to the busbar.

' Modulation could be impressed upon the pulses applied to the busbar by the use of low frequency transformers, one in series with each cathode circuit, the modulating signals being applied to the primaries of these transformers.

It should be arranged that the interelectrode potential across each gap reaches the critical value at which the gap will fire, at some time during the rising voltage of the saw tooth pulse applied to the gap, the exact instant of firing being determined by the modulating voltage in the secondary of the said low frequency transformer which according to its instantaneous value will delay or accelerate the attainment of the critical firing potential of the gap.

It is possible in certain circumstances to apply rectangular pulses to the gaps of the tube instead of saw tooth pulses and still achieve modulation of the output pulses by means such as that just described.

This arises from the fact, explained in said specification No. 763,655 that there is a time element in the firing of a gap by a given applied voltage. If the voltage is raised the time lag is shortened and vice versa if the voltage is lowered. Raising and lowering the voltage in conformity with a modulating signal thus enables the firing time lag to be varied.

This may only be done effectively when the firing time lag, which can only be varied within certain limits, is a substantial proportion of the pulse duration and therefore at the low pulse frequencies for which these simple arrangements are most suitable, a saw tooth pulse shape is generally preferable.

What is claimed is: i 1. A pulse distributor comprising an envelope, a plurality of electric gaseous discharge gaps each gap including two electrodes one of which is parallel, each pulse firing a successive gap, and a separate utilization device connected in series with each gap. 7

2. A pulse distributor according to claim 1 wherein said gaps include a plurality of cathodes each forming said one electrode of a separate,

gap, and separate leads extending from each of said cathodes through said envelope.

3. A pulse distributor according to claim 2 wherein a separate output transformer is connected in series to each of said leads.

pulses are produced.

4. A pulse distributor according to claim 1 gence channels and separate demodulating means arranged in the utilization device associated with separate gaps to demodulate the pulses distributed to their respective gaps.

7 A pulse distributor according to claim 1, further comprising a local pulse generator synchronized with the pulses applied to the gaps, and coupled to said gaps, 'a plurality of gate circuits each associated with a separate one of said gaps and adapted to give an output only when a pulse derived from the firing of the associated gap coincides with said local pulses.

8. A pulse distributoraccording to claim 7 further including a sawtooth pulse shaper associated with said .local pulse generator and actuated thereby, means for impressing an intelligence signal on each of said gate circuits for combination with the sawtooth pulses, each of said gaps being adapted to fire when the sawtooth and intelligence signals together reach a predetermined amplitude and to cease firing at the end of each sawtooth pulse whereby variable width output ALEC HARLEY REEVES.

References Cited in the file of this patent 550,856 Germany May 23, 1932

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