US1984449A - Electric discharge tube - Google Patents

Description

D c. 1s, 1934. G. ZECHER 1,984,449

ELECTRI G DI SCHARGE TUBE Filed April 22, 1930 Inventor:

Patented Dec. 18, 1934 UNITED STATES ELECTRIC DISCHARGE TUBE Gustav Zecher, Eindhoven, Netherlands, assignor,

by mesne assignments, to General Electric Gom- Dany, a corporation of New York Application April 22, 1930, Serial No. 446,306 In the Netherlands June 22, 1929 1 Claim.

This invention concerns an improvement in electric discharge tubes with light radiation by the positive column. Discharge tubes of this kind are generally utilized in advertising signs, as light sources for the illumination of buildings and grounds as well as for signalling purposes.

The invention is concerned more particularly with an electric discharge tube of the abovementioned type which has a high emciency and 0 which does not possess the troublesome property of many known tubes consisting in that the-light radiated when,'as is usually the case, these tubes are fed by alternating currents, is not uniform but flickers because of the fluctuations of the feeding current.

According to the invention, a discharge tube adapted to be connected to a source of alternating current of three or more phases, comprises a solid electron emitting electrode and is constructed in such manner that the paths of the discharges produced in the case of feeding with a polyphase current substantially coincide. The electrodes which during operation act as anodes and the number of which is at least equal to the number of phase of the source of current may be located in separate electrode chambers which communicate by means of a common channel with achamber in which an electron emitting electrode is arranged. The electron -.emitting electrode may consist of a metal wire which when heated by an auxiliary current shows a high emission of electrons. However, for causing the wire to emit electrons it is not always necessary to use an auxiliary current: In some cases the discharge current of the tube itself will be sufficient. The electron emitting electrode which during operation acts as a cathode may be constituted, for example by a wire of tungsten or of an alloy of tungsten and thorium or of molyb- 40 denum and the latter metal. Better results are obtained, however, by using a so-called Wehneltcathode, for example a cathode coated with barium oxide. Incandescent cathodes which are indirectly heated may also be advantageously utilized.

According to the invention, the discharge tube has a low starting and operating voltage so that 55 provided in an installation in which, without the interposition of a transformer, the anodes are electrically connected to connecting points for the phase conductors of a polyphase alternating current network of usual low voltage, the cathode being connected to the connecting point for the neutral wire of the network. In this case impedances may be connected in series with the anodes and/or with the cathode.

The expression without the interposition of a transformer obviouslymeans that there is no transformer for feeding the tube. It is evident that a self-inductance connected in series with an anode and fulfilling at the same time the function of a transformer winding (which will hereinafter be discussed more fully) mambe present. In addition, the device may comprise an auxiliary transformer for supplying the heating current for the incandescent cathode.

The invention will be more clearly understood by referring to the accompanying drawing which represents, by way of example, a discharge tube included in a circuit arrangement of the installation as above described.

The tube illustrated has an elongated part 1 which principally serves for the radiation of light and in which at the passage of the current the positive column is formed. Atthe lower end the part 1 terminates in an enlarged portion 2 in which is arranged an incandescent cathode 3 which derives its heating current from a secondary transformer winding 4. As shown in the drawing, the corresponding primary winding 5 is connected between one of the phase conductors of the available polyphase alternating current network and the neutral conductor. It is evident, however, that a transformer suitable for the line voltage may also be utilized. The device has three connecting terminals 6 which are connected to the phase conductors 7 of the network, which via a switch 8 and fuses 9 are consequently connected to the anodes 10, 11 and 12 of the tube. Each of the connections comprises an impedance constituted by resistances 13, 14 and 15. If desired, these impedances may have self-inductance.

The anodes may be made of a refractory metal such as molybdenum but graphite or a similar material is also suitable. They are located in separate chambers 16, 1'1 and 18 which each open into the connecting channel 1. Instead of being located in separate chambers, the three anodes may also be arranged in a common chamber, in which event it is advisable, however, to separate them from one another by means of screens.

netically coupled with each other.

The mid-point of the transformer winding 4 is connected to the terminal 19 which is brought into connection with the neutral wire 20 of the alternating current network. When the circuit is closed by the switch 8, a current flows alternately from the phase conductors of the network via the three anodesof the tube. Owing to the presence of the incandescent cathode the current only passes in one direction, namely from the anodes to the incandescent cathode. In

contra-distinction, however, to the ordinary tubes fed by alternating current, the phenomenon that during a large portion of each alternating current period the discharge current does not pass is suppressed. In fact, there is always one ofthe three discharge paths which is ignited. The current of each phase is not interrupted until the next phase supplies current. This is facilitated by the self-inductances present in the anode-circuits, particularly when they are mag- Since the columns produced in the three separate discharges substantially become manifest in the common tube-portion 1 one obtains a perfectly steady radiation of light, flickering being at any rate practically suppressed.

An additional advantage consists in that it is not necessary that in each period the voltage first attains the value of the starting voltage of the tube before the discharge is established, said value being, as is well known, considerably higher than that at which the tube is operated. This gives rise to a more favourable load and to an increased efliciency.

The gaseous filling of the tube according to the invention depends on the purpose and the shape of the tube. In general, it may consist of such gases as are commonly utilized in positive column tubes. For example, a suitable filling consists of neon under a pressure up to some millimeters of mercury. When use is made of a filling of neon at a pressure of 0.5 to 5 mm. and of carbon anodes, it is possible to manufacture tubes having a length of some meters, which can be directly connected to a three-phase network of 220/380 volts at cycles.

The impedances 13, 14 and 15 have been provided in connection with the falling currentvoltage characteristic curve of tubes working with an incandescent cathode and a gaseous filling and, besides they limit the current intensity if spark-over between the anodes should occur. If these impedances are omitted itis advisable to connect a resistance in series with the cathode.

What I claim is:

An installation comprising an electric luminous tube for positive column discharge and a 220 volt source of alternating current with at least three phases, said tube containing a gaseous filling, a solid incandescible cathode and at least three anodes connected to the respective phases of said source of alternating current, the

installation comprising inductances connected current source.

GUSTAV ZECHER.

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