US2896122A - Electric discharge tubes - Google Patents

Description

July 21, 1959 T. M. JACKSON ETAL 2,396,122

' ELECTRIC DISCHARGE TUBES Filed Nov. 1a, 1955 I 2 Sheets-Sheet} CDN y 21, 1959 T. M. JACKSON ETAL 2,896,122

ELECTRIC DISCHARGE TUBES Filed NOV. 18, 1955 I F1 *330 F/G.3. ff- I )220 20 25 +50 22 A A Fla L /6 /5 24 27 /5 2 5 lfzoov 1L Inventor T.M.JACKSON- E kFi SELL Attorney 2 Sheets-Sheet 2 United States Patent ELECTRIC DISCHARGE TUBES Thomas Meirion Jackson and Eric Andreas Frederic Sell, London, England, assignors to International Standard Electric Corporation, New York, N.Y.

Application November 18, 1955, Serial No. 547,653

3 Claims. (Cl. 315169) The present invention relates to gas-filled electric glow discharge tubes and to electric circuit arrangements employing such tubes for switching, computing and the like purposes.

In many types of switching or computing circuit it is desired to cause operations to occur when and only when certain specified conditions occur simultaneously. Thus, one of these conditions may be a master pulse whose periodical appearance causes some switching operation to occur provided some other condition or conditions have been set up. It is usually desirable that the operation then initiated should occur at the end of the master pulse, rather than immediately a coincidence occurs. This requirement may be expressed by saying that action in response to a command should be delayed until the command is completed. The present invention enables the use in circuits, as a basic gating relay unit, of a simple cold cathode glow discharge tube in which the required delay and storage is inherent in the operation of the tube rather than in ancillary storage circuits as are required for hard valve systems.

In the present invention this basic unit is essentially a combination of a triode and a diode unit in the same envelope with simple coupling means between the two units. We define a cold cathode triode as an electrode assembly, within a suitable gaseous atmosphere, defining a main discharge gap between a cathode and an anode together with a trigger gap, of lower striking potential than the main gap, between a trigger electrode and the said cathode. Firing of the trigger gap primes the main gap. Similarly a cold cathode diode indicates an anode and a cathode assembly forming a glow discharge gap without any associated trigger gap. It may also be as well to explain the use of the terms priming and firing used in the present specification. A gap is said to be fired when a space charge condition has been set up in the gap such as to permit a glow discharge being maintained indefinitely by the continued application to the gap electrodes of potentials difiering by the maintaining voltage appropriate to the electrode geometry and'the gasfilling. A gap is said to be primed when, by some agency such as discharge at a trigger gap, the first mentioned gap will fire at an inter-electrode voltage sulficient for maintenance of the discharge but too low for initiation of the discharge in the absence of such priming.

According to the present invention there is provided a gas-filled electric low discharge tube comprising within the one envelope electrodes defining a cold cathode triode and a cold cathode diode (both as defined herein), a probe extension of the diode cathode projecting into the anode-cathode space of the triode and shielding means decoupling the triode and the diode from one another except by means of the said probe extension.

The invention further provides an electric circuit arrangement comprising a low discharge tube as above specified and connections to the several electrodes such that discharge in the triode occurs when and only when coincidence occurs between a positive potential-condition applied to the triode trigger electrode and a negative potential condition applied to the triode cathode, while discharge in the diode section is initiated only in the presence of residual ionisation in the triode section after extinction of discharge between anode and cathode of the triode, the arrangement providing an output signal from the diode only when coincidence has occurred between a said positive and a said negative potential condition and the latter has been removed.

The invention will now be described with the accompanying drawings in which:

Fig. l is a diagrammatic view, in part in cross-section, of a discharge tube according to the invention;

Fig. 2 is a circuit diagram showing the basic manner of operation of the tube of Fig. 1; and

Fig. 3 is a circuit diagram showing a counter chain typifying the use of tubes according to the invention.

In the embodiment illustrated in Fig. l a normal type of receiving valve envelope 1, having a glass base 2, houses a triode and a diode electrode assembly secured on opposite sides of a mica sheet 3. The sheet 3 is secured at right angles to a mica disc 4, which contacts the surrounding envelope wall, by means of a pair of eyelets 5 (only one of which is to be seen in the drawing) clamped through the insulator 3 and each welded to a respective wire 6 fixed through the disc 4. The diode assembly consists of an anode 7 and a cathode 8 formed from metal strip so that the discharge surfaces lie in parallel planes normal to the mica sheet 3 while the electrodes are riveted to the same. To avoid trouble due to cathode sputtering, the discharge surface of the cathode is spaced away from the supporting insulator. The triode assembly consists of an anode 9, a cathode 10 and a trigger electrode 11, all fon'ned from metal strip bent so as to be riveted to the sheet 3 with the actual discharge surfaces in parallel planes normal to the sheet. The diode assembly further comprises a wire probe 12 welded to the cathode discharge surface and extending into the anode-cathode space of the triode through a small aperture in the sheet 3.

In order to overcome what is known as the statistical delay of firing in the tubeat least one ionised particle is required in a gap before it will break down, and this is otherwise produced by such random occurrences as the passage of cosmic radiation through the tube-an auxiliary gap is provided between a wire 13 and a covering of wire mesh 14, both secured to the mica disc 4. Since the invention is not concerned with this auxiliary feature, no further mention will be made of it, nor is it indicated on the circuit drawings.

Leads to the several electrodes have not been drawn in Fig. l, but are formed by wires welded to the electrodes and to corresponding pins in the base 2.

For use in the circuit arrangements to be described below, with the component values and voltages there given, an experimental tube constructed as shown in Fig. 1 had electrodes of nickel and a gas filling of 92% neon, 7% hydrogen and 1% argon at mm. pressure of mercury. The principal dimensions were:

reference to Area of diode cathode 8 mm. 4 Anode-cathode gap length (diode) mm 1.5 Area of triode cathode mm. 4 Triode cathode-anode gap length mm 4.5 Trigger-cathode gap length mm 0.25

to ground through .a load resistor and to an output terminal 16. The diode anode is taken through a current limiting resistor 17 to 'the positive terminal of a 330 volt source :of supply potential 18, represented .-in the drawing conventionally as .a battery. The negative terminal of the source 18 is earthed. The triode anode 9 :is :connected through a voltage dropping 1resistor 19 to a .220volt sourceof supply potential, shown as a tapping on the source 18. The triggerelectrode 11 is connected to a terminal .20 to which is applied a positive potential condition represented as .a 50 volt pulse. The triode cathode 10 is taken :to a terminal 21 which is normally biased 50 volts above earth and which'is taken 150 volts below earth potential by negative-going master pulses.

The operation of the arrangement is as follows. In the absence 10f the positive condition .at terminal 20 and .of the negative pulse at terminal 21, the cathode 10 being 50 volts positive with respect to the trigger, no discharge .can occur in the triodesection, the anode potential being well .below the .unprimed striking voltage. In the diode section the anode voltage is also insufficient of itself,sto cause the diode to fire and it is assumed that no discharge is already being maintained. Similarly the unprimed striking voltage between the triode anode and the extremityof the probe 12 exceeds the 220 volts potential difference between these electrodes. The tube geometry, furthermore, is such that no discharge will .take place if, independently, the trigger electrode 11 is raised in potential by 50 volts or the cathode 10 lowered 350 volts ihelow earth. If both these changes in potential occur simultaneously, however, the trigger gap will fire :and will prime the main triode gap.

When, therefore, a negative pulse occurs at terminal 21while a 50 volt positive potential is still being applied to terminal 20, and only then, the trigger gap will fire. With the tube construction described, a formative time .delay of some 4 secs. occurs between the application of the required triggering .conditions and the firing of the trigger gap. This sets the lower limit of pulse width and duration of coincidence for operation of the arrangement. When the trigger gap is fired, the triode anodecathode gap is primed to the extent that it can now fire with the interelectrode voltages available. The ensuing voltage drop in resistor 19 lowers the triode anode voltage -to some 40 volts aboveearth, the current for maintenance of the triode discharge being supplied from the negative pulsesource. .Discharge still cannot occur to the probe electrode, therefore. When, however, the negative pulse at terminal 21 dies away, the anode voltage rises to its :former value of 220 volts and the gap probe- .triode anode ;now fires under priming from the residual ionisation in the triode section. The triode cathode returns to 50 volts positive with respect to earth, so that the cathode-anode discharge is extinguished. The cathodeglow on :theprobe electrode spreads along the-probe, passing through the aperture in the screen 3, and onto the diode cathode 8. The diode gap between cathode 8 and anode 7 is thus primed and fires, producing an out- .put pulse of some 50 volts amplitude at terminal 16. The 'rise in potential of cathode 8 ensures that the discharge from probe 12 to triode anode 9 is extinguished. This output pulse occurs, therefore, when and only when there is coincidence between the two specified potential conditions at terminals 20 and 21 and, furthermore, it then occurs only after completion of the master pulse at terminal 21.

For the above described mode of operation the values of the components shown in Fig. 2 are as follows:

in addition, :the .trigger :pulse current supplied at ter 4 minal 20 should be limited, for example by inclusion .of a 220,000 ohm resistor, not shown in Fig. 2. If used, this resistor can be shunted by a capacitor of 50 microfarads, which capacity will store sufiicient energy to fire the trigger gap.

In the arrangement of Fig. .2 no means is shown for extinguishing the discharge through the diode gap once this has been fired. 'Such means has not been included, as .a tube according to the invention would rarely be used in isolation from other similar tubes, the precise arrangement desired then incorporating means for extinguishing the diode discharge as required. It will be evident to those skilled in the art that with the arrangement of Fig. 2 the diode discharge could be extinguished, for example, by applying a positive pulse to terminal 16 to reduce the diode gap voltage below that needed for maintenance.

In Fig. 3 :anarrangement is shown in which tubes according 'to the invention are connected into a closed chain. Two'tubes, 22 and Bare shown, each connected substantially as in the arrangement of Fig. 2, but with common connections, respectively, to the triode anodes, the diode anodes and the triode cathodes. So far as possible, the circuit components in Fig. 3 are identified by the same reference numerals as the corresponding components of Fig. 2 and are of the same respective values. Any number of tubes may be included in the closed chain .intermediate the .two shown, which may be taken to .represent respectively, the first and the last tube. Alternatively, if only the two .tubes are included in the chain, the arrangement becomes a binary pair such as is commonly used in the computing art but with a different mode of internaloperation.

The diode cathodes are each connected to earth through load resistors 15, as in Fig. 2, but each shunted by .a capacitor 24 of value 0.001 pf. Trigger current limiting resistors .25, shunted by capacitors 26, are inserted, as previously discussed, in series with the trigger electrodes. In order to provide a 50 volt bias on the triode cathodes, the latter, instead of being taken direct to terminal 21, are connected to that terminal through a capacitor 27 of value 0.001 ,uf. and through a rectifier 28 to .a 5.0 volt tapping on the source of potential supply 18. The .diode cathode in-each tube is connected to the trigger electrode of the next tube, this connection being indicated by the dotted connection 29 between the tubes 22 and 23,, it being understood, of course, that if there are more than two tubes in the chain the connection shown would be altered appropriately. On the assumption that tube 22 follows tube 23 in the closed chain, a connection 30 is shown connecting terminals 16 and 20, these terminals, as physical components, being omitted if desired.

To explain the operation of the arrangement, assume that the diode gap of tube 23 is discharging. The associated cathode capacitor 24 will be charged to the output load potential of 50 volts. This potential will be present on terminal 16 and will also appear on the trigger electrode of the next tube in the chain, thus establishing a positive potential condition thereat. With the connection 30 between terminals 16 and 20, tube 22 will be in a condition to operate as soon as a master pulse is applied to terminal 21. On arrival and passage of the master pulse, the operation of tube 22 is exactly as previously described with reference to Fig. 2. The associated diode capacitor 24 is uncharged before firing of the diode, and so the voltage across the diode of tube 22 is greater than that of tube 23. The additional voltage drop in resistor 17 is sufficient to lower the diode anode voltage to extinguish the diode discharge in tube 23, it being remembered that its cathode is held positive by the charge in its cathode capacitor, while the diode cathode potential'of tube 22 hasnot yet risen .to the same value. Thus the diode discharge is transferred from tube 23 to tube 22, and the positive potential condition is transferred fiomzterminals .16 .and 20 .to the trigger electrode ofthe tube following tube 22 in the chain, this next tube then operating at the next master pulse applied to terminal 21.

While the principles of the invention have been described above in connection with specific embodiments, and particular modifications thereof, it is to be clearly understood that this description is made only by way of example and not as a limitation on the scope of the invention.

What we claim is:

1. An arrangement comprising in combination a gasfilled electric discharge tube and a circuit for operating said tube, said tube comprising an envelope containing a plurality of electrodes, a pair of said electrodes comprising a first anode and a first cathode defining a diode gap therebetween, other of said electrodes comprising a second anode and a second cathode defining an anode-cathode gap therebetween, a trigger electrode positioned with respect to said second cathode so as to define a triggercathode gap therewith, said trigger gap included in said anode-cathode gap, means for shielding said diode gap from said other gaps, a probe for coupling said diode gap with said anode-cathode gap, said probe extending from said first cathode electrode through said shielding means into said main gap and defining a probe gap with said second anode, said operating circuit comprising a first source of anode potential, 9. second source of triggering potential, a third source of biasing potential, means for applying said second source to said trigger-cathode gap, means for applying said third source to said anode-cat11- ode gap coincident with the application of said second source to said trigger-cathode gap, means for coupling said anode-cathode gap and said diode gap to said first source, said coupling means including means for reducing the potential applied to said diode gap while said anode-cathode gap is discharging, means for firing said probe gap after extinguishment of said anode-cathode gap, said probe adapted to be primed by residual ionization in said anode-cathode gap after extinction of the discharge therein, said diode gap adapted to be primed by ionization from said probe gap and to be fired by said first potential source, and means coupled to said diode gap for deriving an output therefrom.

2. An arrangement as claimed in claim 1, wherein said means for coupling said anode-cathode gap and said diode gap to said first source comprises a first resistor connected between said second anode and a point of intermediate potential on said first source, said means for reducing the potential applied to said diode gap comprising a second resistor connected between said first anode and a point of higher potential on said first source than said last-mentioned resistor, the values of both said resistors and the voltage of said first source being such that during discharge of said anode-cathode gap, the potential on said second anode is reduced to a value at which discharge between said second anode and said probe extension cannot occur, said values further selected so that after removal of said third source from said anode-cathode gap and the extinguishment of the discharge therein, discharge occurs between said second anode and said probe extension, the discharge adapted to spread along said probe extension to prime said diode gap.

3. An arrangement as claimed in claim 2, further comprising a closed chain of at least two tubes, each of said tubes having coupling means for coupling the anodecathode gap and the diode gap as claimed therein and further comprising parallel connections among corresponding anodes in said tubes, a common connection between said second elecrodes, a connection from the out put means associated with one diode gap to the trigger electrode of the adjacent tube in the chain whereby the discharge of each said diode provides a triggering potential to the trigger-cathode gap of said next tube.

References Cited in the file of this patent UNITED STATES PATENTS 2,096,865 Swart Oct. 26, 1937 2,103,439 Swart Dec. 28, 1937 2,398,772 Cone Apr. 23, 1946 2,577,809 Reeves Dec. 11, 1951 2,635,810 Townsend Apr. 21, 1953 2,741,734 Johnson Apr. 10, 1956

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