US3029364A - Electric discharge tube - Google Patents

Description

April 10, 1962 apt-1 KLEPP ELECTRIC DISCHARGE TUBE 2 Sheets-Sheet 1 Filed Aug. 18, 1955 Inventor G. F KLEPP April), 1962 G. F. KLEPP ELECTRIC DISCHARGE TUBE 2 SheetsSheet 2 Filed Aug. 18, 1955 7 m 7 fl29 5 3 omm B /3 7 VOLT 5 /2O l OLTS lnuenfdr G. F KLEPP A Home y Unite States ate 3,029,364 EI EKITRIC DISCHARGE TUBE George l raneis Klepp, London, England, assignor to in ternatronal Standard Electric Corporation, New York,

N. a corporation of Delaware F led Aug. 18, 1955, Ser. No. 529,255 Claims priority, application Great Britain ept. 2, 1954 8 flaims. (Cl. 315-336) The present invention relates to electric devices for switching circuits and the like utilizing cold cathode trigger tubes.

A typical cold cathode trigger tube comprises, within a gas-filled envelope, electrodes defining a main discharge gap and a trigger gap which primes the main gap. The striking voltage of the main gap is arranged to be consrderably greater than the voltage needed to maintain glow discharge thereat, while the trigger gap has a much lower striking voltage; discharge at the trigger gap primes the main gap in the sense that in the presence of such discharge the main gap fires at the interelectrode voltage supplied by a source of lower voltage than that required for striking without priming. In general, firing of the main gap does not occur simultaneously with establishment of discharge at the trigger gap. A number of factors determine the time interval required between the application of a pulse to the trigger gap electrodes and the firing of the main gap, one such factor is the amplitude of the trigger pulse. One may say that with most trigger tubes, to fire the main gap it is necessary to apply to the trigger gap a pulse whose width and amplitude both exceed certain minima. These two minima are, however, intercorrelated such that a greater pulse Width will reduce the corresponding pulse amplitude and vice versa. The delay in subsequent firing of the main gap then varies as some function of the pulse amplitude, the main gap firing at some time during the pulse.

in a switching circuit the application of a pulse to the trigger gap and the firing of the main gap may be likened to the giving of an order and its subsequent execution. What may be required is that the order should be completed before the subsequent action, or, for the switching circuit, that the firing of the main gap should occur at the end of the trigger pulse. If the trigger pulse has corresponding minima of Width and amplitude this will generally occur, but, naturally, it is undesirable to have to limit the trigger pulse to minimum values. Various circuit expedients have previously been proposed to delay the firing of the main gap of a trigger tube until the end of a trigger pulse, but, so far as the present applicant is aware, the delay means has not previously been inherent in the construction of the tube and the direct connections thereto, but rather additional rectifiers or time constant circuits have had to be employed.

According to the present invention there is provided a device comprising electrodes defining, within a gas-filled enclosure, a main glow discharge gap and a trigger gap to prime the said main gap and means for applying a trigger pulse to the trigger gap electrodes and for maintaining glow discharge across the main gap, characterised in this that at least one additional electrode is situated outside the gaseous atmosphere of the said enclosure so that its potential may yet affect the electric field therein and that the said additional electrode is connected to be substantially at cathode potential, the arrangement being such that the main gap fires after the end of the said pulse.

It is to be understood, of course, that in the above statement and in the appended claims the said trigger pulse is not a minimum in respect of amplitude and time.

Embodiments of the invention will be described with reference to the accompanying drawings'in which:-

FIG. 1 shows, in partial cross section, a trigger tube and circuit connections thereto in accordance with the invention; I

FIG. 2 shows a similar view of another embodiment;

FIG. 3 shows a similar illustration of an embodiment combining features of the embodiments of FIGS. 1 and 2; and FIG. 4 shows curves illustrating the results obtained with the present invention. y

In FIGS. 1 to 3 a trigger tube 1 is shown having a glass envelope 2 provided with a press 3 through which are sealed lead wires 4, 5 and 6 connecting, respectively with a ring-shaped cathode 7, a trigger electrode 8, held on a rod projecting through the cathode, and a rod-shaped main gap anode 9 located beneath the plane of the cathode. An extension of the trigger electrode support carries a conventional getter holder lit. The arrangement of the electrodes so far mentioned and the general characteristics of the trigger tube are described more fully in the specification of British Patent No. 701,307. In the present invention an additional electrode is provided whose potential influences the electric field of the main and trigger gaps but which is arranged so that it'cannot take part in a glow discharge to any of the other aforementioned electrode. In FIG. 1 this additional electrode is a conductive coating 11 on the outside of the envelope 2 located just below the cathode 7. In FIG. 2 the additional electrode is in the form of a rod 12 projecting up towards the cathode through the glass press 3, but covered with insulating material-in the present case a glass sleeve 13-to prevent glow discharge thereto.

In the circuit arrangements of FIGS. 1 to 3, which have been simplified as much as possible to illustrate the invention, the cathode 7 is connected through a resistor 14 to the negative pole of a source of main gap supply rep resented as a battery 15. The resistor 14 is of low value and does not affect the operation of the tube; it is included as a convenient means of measuring the cathode current Waveform by virtue of the potential drop across it. The main gap anode is taken to the positive pole of this source through a current limiting resistor 16. An output terminal 17, labelled OUT, is connected to the anode through a DC. blocking capacitor 18. The values of the resistors 14 and 16 and the voltage of source 15 are such that glow discharge may be maintained at the main gap between cathode 7 and anode 9 but cannot be started in the absence of discharge at the trigger gap be tween trigger electrode 8 and cathode 7.

To fire the trigger gap a positive pulse is applied to pulse input terminal 19, which is connected to the trigger electrode 3 through a current limiting resistor 2%).

In F368. 1, 2 and 3 the respective additional electrodes 11 and 12 are connected directly to the cathode potential. It has been found satisfactory to connect them to any convenient point whose potential is substantially that of the cathode, and varies, if the latter varies, in phase with the changes of cathode potential.

With the ordinary trigger tube from which the additional electrode Ill or 12 is omitted, the measured relation between trigger pulse amplitude and the time of firing of the main gap, at constant pulse width of micro- Patented Apr. 10, 1952 3 was 100,000 ohms and the cathode resistor 14 was 100 ohms.

Approximate time of firm" I main zreu Trigger pulse amplitude.

The 75 volt pulse was just sufiicient to fire the main gap.

In PEG. 4 there is plotted as ordinate the voltage V appearing across the cathode resistor 14 of the arrangement of FIG. 1, the time t, measured from the leading edge of the trigger pulse, being plotted as abscissa, the pulse amplitude used being marked on the curves. In each case it will be seen that the voltage due to the trigger gap current drops to zero before the main gap current commences, the voltage due to the main gap discharge rising sharply to the constant level marked A at the end of the C- sec. interval occupied by the trigger pulse.

When the additional electrode 11 is connected to the trigger electrode instead of to the cathode, it is found that virtually the same results are obtained as in the unmodified tube and circuit to which the foregoing table relates. In the arrangement of FIG. 2, with the additional electrode connected to cathode, for the same pulse width of 100 used, the main gap fires on conclusion of the trigger pulse for a range of trigger pulse amplitudes extending from 94 to 155 volts.

In the arrangement of FIG. 3, with both additional electrodes connected to cathode, similar results are obtained, but the permissible range of pulse amplitudes extends from 94 to 210 volts. Over this extreme range the time of firing of the main gap varied, in accordance with the trigger pulse amplitude, by only 3 sec.

It will be seen that the present invention affords a simple and convenient means of delaying the firing of the main gap of a trigger tube until the end of the trigger pulse without the need for additional diode and time constant circuits external to the tube. Similar results are found to obtain with both greater and lesser pulse widths than the 100 sec. width used to obtain the figures quoted above.

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 in vention.

What I claim is:

1. A discharge device comprising an envelope containing a gaseous atmosphere and a plurality of electrodes therein, said electrodes defining a main glow discharge gap and a trigger gap thereamong, one of said electrodes common to both said gaps, means for applying a discharge-maintaining potential to the electrodes defining said main gap means for applying a trigger pulse to said trigger gap, additional electrode means situated outside said gaseous atmosphere, means for applying a potential to said additional electrode means, said potential having a value substantially equal to the potential applied to said common electrode whereby said additional electrode means afiects the electric field within said atmosphere thereby to inhibit firing of said main gap until the cessation of said trigger pulse.

2. A device according to claim 1, wherein said additional electrode means comprises a conductive coating on the said envelope in the neighborhood of the said common electrode.

3. A device according to claim 1, wherein said additional electrode means comprises a conductor covered with insulating material projecting into the said envelope in the neighborhood of the said main and trigger gaps, but isolated from said atmosphere.

4. A device according to claim 1, wherein said additional electrode means comprises a pair of electrodes, 8. first of said pair being on the outside of said envelope and the other projecting into said envelope but isolated from said atmosphere.

5. A cold cathode trigger tube comprising a glass envelope filled with a suitable gas for glow discharge and a plurality of electrodes comprising, a cold cathode in the form of a ring, a trigger electrode supported by a rod projecting through the said ring and spaced therefrom, a rod-shaped anode electrode parallel to the trigger electrode support rod and spaced both from the plane of the cathode and from said support rod, and additional electrode means separated by insulating material from the gaseous atmosphere within the said envelope situated in the neighbourhood of the cathode anode space.

6. A tube according to claim 5, in which the said additional electrode means comprises conductive material placed around the outside of said envelope,

7. A tube according to claim 5, in which the said additional electrode means comprises a rod covered with insulating material projecting within the said envelope, but isolated from said atmosphere.

8. A tube according to claim 5, wherein said additional electrode means comprises a pair of electrodes, a first of said pair being on the outside of said envelope and the other covered with insulating material projecting into said envelope but isolated from said atmosphere.

References Cited in the file of this patent UNITED STATES PATENTS 1,604,986 Garity Nov. 2, 1926 1,915,019 Ewest June 20, 1933 2,004,585 Pirani June 11, 1935 2,015,885 Dallenbach Oct. 1, 1935 2,027,399 Ostermeier Jan. 14, 1936 2,051,601 Hobart Aug. 18, 1936 2,103,439 Swart Dec. 28, 1937

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