US2802968A - Electric discharge tube - Google Patents

Description

g- 13, 1957 G. KNOTT ET AL 2,802,968

ELECTRIC DISCHARGE TUBE Filed Jan. 24, 1951 1 2 Sheets-Sheet l IN VEN TORS GEORGE KNOTT NORMAN WRIGHT ROBINSON AGENT g 1957 G. KNOTT ET AL 2,802,968

ELECTRIC DISCHARGE TUBE Filed Jan. 24, 1951 2 Sheets-Sheet 2 fig LM A ,5 3

{J it IN V EN TORS GEORGE KNOTT- NORMAN WRIGHT ROBINSON 5+ fiw7 AGENT United States PatentO ELECTRIC DISCHARGE TUBE George Knott, Epsom, and Norman Wright Robinson, Carlshaiton, England, assignors, by mesne assignments, to North American Philips Company, Inc., New York, N. Y., a corporation of Delaware Application January 24, 1951, Serial No. 207,592

Claims priority, application Great Britain January 25, 1950 3 Claims. (Cl. 315-235) This invention relates to electric discharge tubes for producing flashes of light of short duration and of sufficient brightness for photographic purposes.

Electric discharge tubes, so called electronic flash tubes, are known having an associated electric circuit in which a high potential builds up across a condenser until it has a suflicient magnitude to operate the discharge tube. When such a tube has once operated, it is necessary to wait until the condenser has charged once more before the tube can be operated again and this limitation renders such an arrangement quite unsuitable in circumstances where a number of photographs is required to be taken in rapid succession. I

It is known to use a number of discharge tubes of this type, each of which provides a single light flash, so arranged in an electric circuit that each of the tubes is, separately triggered, a suitable delay arrangement being provided between each triggering operation so that the tubes in combination give a succession of light flashes.

This arrangement has the disadvantage that it requires a number of tubes, delay circuits must be provided and where the number of tubes is large, the combination cannot be conveniently arranged in a single reflector.

The object of the present invention is to provide an electric discharge tube and apparatus including such a discharge tube for providing a series of light flashes for photographic purposes, the flashes following one another in rapid succession.

According to the present invention, an electric discharge tube for producing a number of light flashes in rapid succession, has a cathode and an anode and a number of intermediate electrodes arranged along the discharge path of the tube between the cathode and the anode, the electrodes being connected to an external elec-' tric circuit such that a discharge is produced using first the anode or the cathode and the adjacent intermediate electrode and then using each of the other electrodes in succession along the tube.

Acocrding to one form of the invention, the electrodes are connected to an external electric circuit such that a discharge is produced first between the anode or the cathode and the adjacent intermediate electrode, and then between the said anode or cathode and the next intermediate electrode and so on in succession along the tube.

According to another form of the invention, the electrodes are connected to an external electric circuit such that a discharge is produced first between the anode or the cathode and the first intermediate electrode which is adjacent to the said anode or cathode, then between the first intermediate electrode and the second intermediate electrode and so on in succession along the tube.

A further form of the invention provides an apparatus for producing a number of light flashes in rapid succession having an electric discharge tube having a cathode and an anode and a number of intermediate electrodes arranged along the discharge path of the tube between the cathode and the anode, the anode being connected to the positive terminal of a high-tension supply and the cathode being connected to the negative terminal of the supply, either the anode or cathode being so connected by way of a resistance, each of the intermediate electrodes being connected through a resistance to one terminal of the supply, a condenser being connected between the anode and the cathode and between that electrode which is directly connected to a terminal of the high-tension supply and each of the intermediate electrodes and means for ionising the gas in the discharge tube being arranged between the said electrode which is directly connected to one terminal of the high-tension supply and the adjacent intermediate electrode.

A still further formiof the invention provides an ap. paratus for producing a number of light flashes in rapid succession, having 'an'electric discharge tube having a cathode and an anode and a number of intermediate electrodes arranged along the discharge path of the tube between the cathode and the anode, one of the outer electrodes being connected to one terminal of a high-tension supply and the other outer electrode being connected through a resistance to the other terminal of the supply, a condenser being connected between one outer electrode and the adjacent intermediate electrode, a condenser be-' ing connected between each intermediate electrode and between the last intermediate electrode and the other outer electrode and means for ionising the gas in the discharge tube being arranged between one outer electrode and the adjacent intermediate electrode.

In order that the invention may be readily carried into etiect a number of examples will now be described in detail with reference to the accompanying drawings, in which:

Figure 1 is a longitudinal section of a form of discharge tube;

Figure 2 is a transverse section of the tube shown in Figure 1; s

Figure 3 is a section view of one of the intermediate electrodes;

Figure 4 is a plan view of the intermediate electrode shown in Figure 3;

Figure 5 is a schematic circuit diagram of anapparatus including a discharge tube of the form shown in Figure 1 in which a discharge is produced first between the cathode and the first intermediate electrode which is adjacent the cathode, then between the first intermediate electrode and the second intermediate electrode and finally between the second intermediate electrode and the anode;

Figure 6 is a schematic circuit diagram of an alternative apparatus using a discharge tube of the type shown in Figure 1 in which a discharge is produced first between the cathode and the adjacent intermediate electrode and then between the 'cathode and the second intermediate electrode and finally between the cathode and the anode, and

Figure 7 is a schematic diagram of an alternative form of discharge tube in which the envelope of the tube is a hollow annulus and the electrodes are arranged in a circle inside the tube.

In Figure 1, a tubular envelope 1 has a cathode 2 fused in the envelope at one end and an anode 3 fused in the envelope at the opposite end and two intermediate electrodes 4- and 5 arranged along the length of the tube between the cathode 2 and the anode 3.

The intermediate electrodes are of the same construc-v tion and one of them is shown to an enlarged scale in Figures 3 and 4. Each intermediate electrode is T-shaped and has a tungsten lead-out wire 6, to the inner end of which is welded a transverse wire 7 arranged parallel to the axis of the tube. The transverse wire 7 extends further in the direction of the cathode than in the direction of the anode. The end of the wire 7 facing the anode has,

a hollow nickel tube 8 slid over it and fastened thereto,

A barium getter pellet 9 is inserted in the tube 8 and the tube end is pinched near its end sufiiciently to retain the pellet 9 in the tube during manufacture.

After the tube has been constructed, the getter pellet 9 is fired in the ordinary way.

Alternatively, a quantity of a mixture of barium and strontium carbonates, or a quantity of any of the usual cathode plates used in the manufacture of indirectly heated thermionic valves, may be inserted in the hollow space of the tube 8. After the tube is constructed, the mix ture is fired to convert the carbonate into the corresponding oxides.

In either case, the part of the intermediate electrode facing the anode in the completed tube is, in this way, enabled to serve as an intermediate cathode, either with the anode-of the tube or with ,theadjacent intermediate electrode, whereas the portion of the intermediate electrode facing the cathode serves as an anode either with the cathode of the tube or with the cathode portion of the adjacent intermediate electrode.

It, will be understood that a greater number of intermediate electrodes than the two shown. as 4 and S in Figure 1 may be used and will, in fact, be required for most practical'applications of the tube.

In Figure a discharge tube of the form described with reference to Figure 1 has its cathode 2 connected to the negative terminal 10 of a high-tension supply and the anode 3 connected through a resistance 12 to the positive terminal 11 of the high-tension supply. A condenser 13 is connected between the cathode 2 and the first intermediate electrode 4, a condenser 14 is connected between the intermediate electrode 4 and the intermediate electrode 5 and a condenser 15 is connected between the electrode 5 and the anode 3. A trigger coil 16 is wound around the outside of the tube 1 between the electrodes. 2 and 4 and is connected to a trigger circuit, knownper se and not shown in the drawing.

The condensers13, 14 and 15 are conveniently of equal capacity, and are charged through the resistance 12 to the high potential applied between the terminals 10 and 11. There are, therefore, a series of voltage gradients across separate sections of the tube 1.

In operation, a discharge is first produced between the cathode 2 and the first intermediate electrode 4 by means of a transient discharge through the trigger coil 16.

This first discharge extends beyond the electrode 4, so that the gas in the section of the tube between the electrodes 4 and 5 is ionised land a discharge then occurs in this section of the tube. This discharge similarly initiates a discharge in the section of the tube between the electrode 5 and the anode 3.

If the condensers 13, 14 and 15 are of equal capacity, the light output will consist of three flashes of equal brilliance spaced at equal intervals. The interval be tween the flashes is determined by the potential across the condensers, since the etfect of any discharge on the adjacent section of the tube depends upon the velocity with which ionised atoms travel during the discharge. If the potential between the terminals 10 and 11 is too high, there is a tendency for the flashes to overlap.

In one practical circuit according to Figure 5, the following data was obtained:

Interval Between Flashes (Peak to Peak) Duration of Flash From to Max.

Relative Peak Intensity of Flashes Total Potential Mz'crosec. Iviicroser.

The duration of each flash and the intervals between flashes can be varied over wide limits by the geometrical designs of the tube, by the choice of the gas filling of the tube and its pressure, the capacity of the condensers used and the potential applied between the terminals 10 and 11.

In an arrangement which is very similar in operation to that shown in Figure 5, the cathode is connected to the negative terminal 10 of the high-tension supply through the resistance 12 while the anode 3 is directly connected to the positive terminal 11. In this arrangement, the trigger coil is arranged between the anode 3 and the adjacent intermediate electrode 5 and the first discharge occurs between the anode 3 and the electrode 5, the second discharge between the electrodes 5 and 4 and the final discharge between the electrode 4 and the cathode 2.

An alternative mode of operating the discharge tube is obtained by the circuit arrangement shown in Figure 6, in which the cathode 2 of the tube 1 is connected to the negative terminal 10 of the high-tension supply and the intermediate electrodes 4 and 5 and the anode 3 are connected respectively through resistance 1'7, 18 and 19 to the positive terminal 11 of the high-tension supply. Condensers 20, 21, and 22- are connected respectively between the cathode 2 and the electrodes 4, 5 and 3. The trigger coil 16 is arranged between the electrodes 2 and 4 as in the arrangement shown in Figure 5.

In this arrangement, the condensers 29, 21 and 22 are charged through the resistances 17, 18 and 19 respectively to the full voltage of the high-tension supply, so that the electrodes-4, 5 and 3 are held at the same potential and a voltage gradient exists initially only in the section of the tube between the electrodes 2 and 4.

The first discharge, between the electrodes 2 and 4, is initiated by a transient voltage in the trigger coil and, in consequence of this first discharge, the condenser 20 is discharged so that the potential of the electrode 4 falls rapidly. The voltage gradient is thereby established by the condenser 21 between the electrodes 2 and 5 and this change together with the ionisation existing along the discharge path of the tube between the electrodes 2 and 5 causes a discharge to take place between these two electrodes. In the same manner, a further discharge occurs between the cathode 2 and the anode 3 of the tube by reason of the voltage across the condenser 22.

In a practical circuit arrangement of this sort, flash durations of 20 ,uS. at intervals of 25 ,us. have been obtained with condensers each of capacity 33 pi. charged to a potential of 1.5 kv.

A similar mode of operating the tube may be effected by connecting the anode directly to the positive terminal 11 of the supply and connecting the electrodes 2, 4 and 5 to the negative terminal 10 of the supply through resistances. The condensers are then connected between the anode and each of the other electrodes and the trigger coil is arranged between the anode 3 and the electrode 5. The first discharge then occurs between the anode 3 and the electrode 5 and subsequent discharges follow between the anode 3 and the electrode 4 and the anode 3 and cathode 2.

In Figures 5 and 6, the trigger coil 16 is shown wound round the outside of the tube between the cathode 2 and the adjacent intermediate electrode 4. This is the preferred arrangement but other arrangements are practicable. Any other suitable triggering arrangement may be used and it may be situated at either end of the tube between either the cathode 2 and intermediate electrode 4, as shown, or between the anode 3 and the intermediate electrode 5. However, the former arrangement is preferred because, in the first discharge, the electrons will overshoot the section containing the discharge, thereby ionising the gas in the adjacent section, with better effect than will the positive ions in the case of the latter a1- rangement.

Figure 7 shows an alternative construction of discharge tube 23 having a hollow annular gas-filled envelope, a cathode 24, electrodes 25, 26, 27, 28 and 29 spaced in a circle around the tube of the second cathode 30. A trigger coil 31 is arranged between the cathode 24 and the electrode 25 and it is between these electrodes the first discharge occurs. The second cathode is used to prevent ionisation in the part of the tube between the electrodes 24 and 25 ionising the gas in that part between the electrodes 24 and 29 and thereby setting up discharges which proceed in an anti-clockwise direction. The second discharge uses the electrodes 26 and so on round the tube using the electrodes 27, 28 and 29 in succession. The discharge tube may be made in other forms such as a linear tube folded in the form of a planar grid or folded about a cylindrical.

What we claim is:

1. An electric discharge tube of the gas-filled type for producing a plurality of light flashes in rapid succession comprising an envelope, an ionizable gaseous medium contained within the envelope adapted to glow upon the discharge of an electric current therethrough, cathode and anode electrodes spaced apart Within the envelope, and a plurality of serially-arranged spaced electrodes intermediate the anode and cathode electrodes and spaced therefrom, each of said intermediate electrodes constituting jointly a cathode and an anode and comprising a solid metal rod facing said cathode electrode and a hollow metal sleeve portion containing an electron emissive alkaline earth material facing said anode electrode, whereby with a potential applied between one of said intermediate electrodes adjacent one of the anode and cathode electrodes and the latter electrode a discharge is initiated therebetween and with potentials applied to the remaining intermediate electrodes further successive discharges are initiated in said tube.

2. An apparatus for producing a plurality of light flashes in rapid succession constituted by an electric discharge tube of the gas-filled type comprising an envelope, an ionizable gas medium contained within the envelope adapted to glow upon the discharge of an electric current therethrough, cathode and anode electrodes spaced apart within the envelope, a plurality of serially-arranged spaced electrodes intermediate the anode and cathode electrodes and spaced therefrom, each of said intermediate electrodes constituting jointly a cathode and an anode and comprising a solid metal rod facing said cathode electrode and a hollow metal sleeve portion containing an electron emissive alkaline earth material facing said anode electrode, a source of potential, means for applying a potential between said cathode electrode and the intermediate electrode adjacent thereto, means for applying a potential between said anode electrode and the intermediate electrode adjacent thereto, means for applying potentials between each pair of adjacent intermediate electrode, and means for initiating a discharge between a pair of adjacent electrodes.

3. An apparatus for producing a plurality of light flashes in rapid succession constituted by an electric discharge tube of the gas-filled type comprising an envelope, an ionizable gaseous medium contained within the envelope adapted to glow upon a discharge of an electric current therethrough, cathode and anode electrodes spaced apart within the envelope, a plurality of seriallyarranged spaced electrodes intermediate the anode and cathode electrodes and spaced therefrom, each of said intermediate electrodes constituting jointly a cathode and an anode and comprising a solid metal rod facing said cathode electrode and a hollow metal sleeve portion containing an electron emissive alkaline earth material facing said anode electrode, a source of potential, a first capacitor connected between said cathode electrode and the intermediate electrode adjacent thereto, a second capacitor connected between said anode electrode and the intermediate electrode adjacent thereto, a third capacitor connected between each pair of adjacent intermediate electrodes, means to connect said capacitors in series relationship, a current-limiting resistor connected in series relationship with said capacitors, means for applying a potential across said series-connected capacitors through said current-limiting resistor, and means for initiating a discharge between two adjacent electrodes in said tube.

References Cited in the file of this patent UNITED STATES PATENTS

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