US1972647A - Electric glow discharge tube - Google Patents

Description

' P M. J. DRUYVESTEYN 1,972,647

ELECTRIC GLOW DISCHARGE TUBE Filed May 28, 1931 Patented Sept. 4, 1934 1,972,647 ELECTRIC GLOW DISCHARGE TUBE Mari Johan Druyvesteyn, Eindhoven, Netherlands, assignor to N. V. Philips Gloeilampenfabneken, Eindhoven, Netherlands Application May 28, 1931, Serial No. 540,707 In the Netherlands July 26, 1930 4 Claims. (01. 176-122) This invention relates'to an electric glow discharge tube containing cold electrodes and a gaseous filling. In referring to a gaseous filling it is intended hereinafter to include not 5 only a filling consisting of one or more gases but also a filling consisting of one or more vapours or a mixture of gas and vapour.

As is well known, the voltage to be impressed on the electrodes of such a glow discharge tube in order to start the discharge is higher than the potential difference existing between the electrodes once the discharge is struck. This difference between the starting potential and the operating voltage is frequently very objectionable.

The invention has for its object to lower the starting voltage of a glow discharge tube and thus to decrease the difference between the starting voltage and the operating voltage.

According to the invention, for this purpose a grid-shaped auxiliary electrode is arranged between the electrodes, which auxiliary electrode is electrically connected to the anode. The grid-shaped auxiliary electrode, has the same potential as the anode so that there is between them a space substantially free from any electric field; this is found to bring about a reduction of the starting voltage, also termed the break-down voltage.

Preferably, the distance between the main electrodes, and the composition and the pressure of the gaseous filling are so selected that the voltage necessary for starting the discharge between the main electrodes be a minimum in the absence of the grid shaped electrode. Even in this case, the provision of the grid-shaped auxiliary electrode is found to favourably influence the starting voltage.

The starting voltage of the discharge tube may be given a very low value by causing the 40 active surface of the cathode to be constituted by an alkali metal layer applied to an alkali oxide.

In order that the invention may be clearly understood and readily carried into effect a luminous discharge tube, according to the invention will be described more fully by way of example with reference to the accompanying drawing, the single figure of which is a diagrammatic view of a discharge tube embodying the invention.

Referring to the figure, the tube has a bulb 1 into which is sealed a pinch 2. This pinch has secured thereto three electrodes; namely, an anode 3, a cathode 4 and an auxiliary electrode 5.

The anode is formed by a metal disc, consisting for example of nickel, carried by a pole wire 6.

This pole wire also supports the auxiliary electrode 5. This auxiliary electrode is constituted by a grid-shaped member, for example, a piece of wire gauze. The cathode 4 is constituted similarly to the anode 3 by a small metal .disc secured to a pole wire 7 and coated over its surface with a layer of caesium oxide to which a layer of caesium is applied. This cathode surface may be formed subsequent to the exhaustion of the tube by liberating and depositing a small quantity of caesium from, a capsule 8, for example, arranged within the tube and containing a caesium compound, such for example, as caesium chromate, and a reducing agent, for example zirconium. When this capsule is subjected to high frequency heating the caesium compound is reduced and the caesium is liberated. Thus, the caesium is precipitated on the wall and the component members of the discharge tube. By gently heating the outer wall of the discharge tube, the caesium is expelled from the inner wall and is precipitated on the electrodes. If it is desired to prevent the caesium from being precipitated on the anode, the latter may be formed of a material to which the caesium does not adhere firmly whereas the surface of the cathode is formed for example of nickel, preferably oxidized, to which the caesium adheres well.

After the caesium film is formed on the cathode, a small quantity of oxygen is admitted into the tube.to convert the caesium-film into caesium oxide.

After the excess oxygen has been removed, a small quantity of caesium is again introduced in the tube, for example from a second capsule 9. to the cathode surface where This caesium is applied it is precipitated on the caesium oxide film previously formed to which it adheres very readily.

It is found that such a cathode considerably lowers the starting voltage of the glow discharge.

Subsequent to the formation of the cathode surface, a suitable gaseous filling, consisting, for example, of a rare gas, is introduced in the discharge tube.

Satisfactory results have been oba minimum (Paschens law).

In the use of the gaseous filling described, the most favourable distance between the main electrodes was found to be about 15 mm.

If a grid shaped auxiliary electrode is arranged between the electrodes 3 and 4, the starting voltage of the luminous discharge tube is further lowered. The starting voltage was, in the absence of the auxiliary electrode, 66 volts; the provision of the auxiliary electrode was found to reduce this voltage to 47 volts, the

operating voltage being in either case 36 volts.

and the pressure of said gaseous filling being so selected that the starting voltage of the discharge between said cathode and said anode is a minimum according to the law of Paschen, and a grid-shaped auxiliary electrode arranged between said cathode and anode and electrically connected to said anode said auxiliary electrode reducing the starting voltage of the discharge tube below said minimum.

2. An electric glow discharge tube comprising a cold cathode, an anode and a gaseous filling consisting of neon to which percent argon is added, the pressure of said gaseous filling being approximately 6 mm, the distance between said cathode and said anode being approximately 15 mm, a grid-shaped auxiliary electrode mounted between said cathode and said anode and electrically connected to said anode.

3. An electric glow discharge tube, comprising cold main electrodes, including a cathode and an anode, a gaseous filling, and a grid shaped auxiliary electrode disposed between said cathode and anode and in proximity of said anode, and being in direct electric connection with said anode.

4. An electric glow discharge tube comprising, a cold' cathode and an anode, a gaseous filling, said cathode having an active surface consisting of an alkali oxide layer to which an alkali metal layer is applied, the distance between said cathode and said anode and the pressure of said gaseous filling being so selected that the starting voltage of the discharge between said cathode and said anode is a minimum according to the law of Paschen, and a grid-shaped auxiliary electrode disposed between said cathode and anode and electrically connected to said anode, said auxiliary electrode reducing the starting voltage below said minimum.

MARI J OHAN DRUYVESTEYN.

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