US2183102A - Mercury cathode discharge tube - Google Patents

Description

Dec. 12, 1939. JURRIAANSE 2,183,102 I MERCURY CATHODE DISCHARGE TUBE Filed April 15, 1938 Patented Dec. 12, 1939 UNITED STATES PATENT OFFICE MERCURY OA'I'HODE DISCHARGE TUBE AppllcationApril 15, 1938, Serial No. 202,333

In Germany April 10, 1937 8 Claims. (Cl. 175-354) My invention relates to mercury-cathode discharge tubes, and more particularly to means for controlling the main discharge in such tubes.

It has been proposed to block the main discharge by applying a negative potential to an electrode located within the discharge space or to a metallic member forming part of the envelope of the tube. This method, however, is comparatively uncertain and it is diflicult to make it sufficiently reliable for practical use.

The main object of my invention is to overcome this dificulty, and for this purpose I locate an extinguishing electrode in the immediate vicinity of the cathode spot, and apply thereto a potential which is positive with respect to the cathode to thereby take over the discharge from the main anode. By locating the extinguishing electrode in the immediate vicinity of the cathode spot, its influence on the portion of the main 29 discharge near the cathode, is considerably greater than that of the anode, and as a result the extinguishment will always be effectuated with great reliability and under constant conditions.

To ensure conditions which are favorable for extinguishment of the discharge, I prefer to provide a cathode-spot anchoring body. However, these conditions can also be attained without using an anchoring body, by reforming the oathode spot during each current impulse. As a result, and because of the short duration of each impulse, the cathode spot can, during the passage of current, move only a short distance from the point at which it is produced. This means that 5 irregularities in the effect exerted by the extinguishing electrode on the cathode spot-in so far as they may be due to variations in the location of the spot-are practically eliminated. For this purpose I may use an internal ignition electrode iii of semi-conductive material, 1. e. an igniter, which is permanently immersed in the cathode mercury, and which at the start of each current impulse forms the cathode spot anew at the point of immersion.

A combination of an extinguishing device according to the invention and the above-described internal ignition electrode may be obtained in a simple manner by using a single auxiliary electrode consisting of a conductive portion arranged so in the immediate vicinity of the cathode mercury,

and a semi-conductive portion immersed in the mercury and acting asthe internal ignition electrode. This greatly simplifies the construction of the tube because only a single electrode and 55 current-supply conductors serves both for extinguishing the discharge and forming the cathode spot.

In such a device a cathode spot is formed each time at the point of immersion but does not attain the required intensity before the semi-con- 5 ductive portion has been bridged by the discharge which climbs up to the upper conductive portion. Owing to its low resistance, the conductive upper portion forms the portion of the auxiliary electrode which is essential for the extinguishing im- 10 pulse with its very high current intensity of short duration, and therefore, in accordance with the invention, this portion must be arranged in the immediate vicinity of the anchoring point of immersion. Thus, I prefer to extend the conduc- 15 tive portion, which acts as a holder and as a current-supply conductor for the semi-conductive portion, along the side of the latter portion and coaxially to the same so that it will extend into the immediate vicinity of the cathode mercury.

In the extinguishing process according to the invention, it can be assumed that when a short positive voltage impulse is applied to the auxiliary or extinguishing electrode, the discharge passes 25 in an extremely short time from the main anode to the extinguishing electrode, and that this discharge must be extinguished at once at this electrode, to prevent it from returning to the main anode immediately after the positive voltage im- 30 pulse. The first part of this process may therefore be improved by making the wave front of the positive voltage applied to the auxiliary electrode as steep as possible, and for this purpose I prefer to apply, by way of a mechanical contact or a controlled gas filled discharge device, a potential obtained from the terminal of a charged condenser, which terminal is positive with respect to the cathode of the tube.

' During the second part of the process, 1. e. the subsequent extinguishment of the discharge after its shifting to the auxiliary electrode, possibly a favorable influence is exerted by the extinguishmg electrode becoming negative during a short 45 moment following the positive voltage impulse. This may result from oscillations in the extinguishingcircuit, for example, due to resonance with the condenser utilized. It is therefore desirable to give the extinguishing circuit a very low resistance, because otherwise, due to the extremely heavy current which is produced during a short time, the greater part of the voltage would be dissipated in this circuit. For this purpose, I prefer to keep the resistance of the extinguishing circuit at a low value for instance below 0.1 ohm.

In order that the invention may be clearly understood and readily carried into effect I shall describe the same in more detail with reference to the accompanying drawing in which:

Fig. 1 is a schematic diagram of a direct current extinguished device according to the invention, and

Fig. 2 is a schematic diagram of a device according to the invention in which the mean value of the direct current in a rectifier is regulated.

The device illustrated in Figure 1 comprises a mercury-cathode discharge tube having an envelope l, a main anode 4, a mercury cathode 2, and a cathode-spot anchoring member 3 for instance of nickel. Partly immersed in mercury 2 is a stationary internal ignition electrode or igniter 5 of a semi-conductive substance such as silicon carbide. Above the member 3 is a cupshaped extinguishing electrode 6, for instance of iron or molybdenum, whose side extends downwardly with its edge in the vicinity of and concentrically to the cathode line formed around the periphery of member 3. In this manner, the entire cathode line can be influenced in the same way.

Anode 4 is connected through a load 8, shown as an ohmic resistance, to the positive terminal of a direct-current supply I, shown as a generator, whose negative terminal is connected to cathode 2.

Electrode 5 is connected through a single-pole single-throw switch Ill and a current-limiting resistance 9 to the positive terminal of supply l. Closure of switch It) applies a positive potential to electrode 5 to thereby initiate the main discharge in a manner which is known per se.

The positive terminal of supply I is also connected through a conductor 3i, to a contact 26 of a single-pole double throw switch i2 having a second contact 21 connected through a conductor 34 to the extinguishing electrode 6. The heel 28 of switch I2 is connected through a conductor 35 to terminal 29 of a condenser whose other terminal 30 is connected through a conductor 36 to cathode 2 and to the negative terminal of source 7. With switch |2 in the position shown, condenser becomes charged from source 7 to make terminal 29 positive, and when switch |2 is moved in the direction of the arrow so as to break contact 26 and make contact 27, electrode 29 is connected to electrode 6. Condenser I I, then discharges through the short discharge path between electrode 6 and mercury 2 with the result that the main discharge is transferred from main anode 4 to electrode 6 and is extinguished at the first change in polarity of the voltage of oscillatively-discharging condenser As has been stated it is advisable to make the discharge circuit of condenser H of low resistance to ensure that the discharge oscillations will be as strong as possible and for this purpose conductors 34, 35, and 36 are made short and of large cross-sections, as indicated by heavy lines.

I have found that the highest current which can be extinguished by a device such as shown in Fig. l is substantially directly proportional to the direct voltage applied to condenser l i. e. to the root of the stored energy 1/2 CV If it is desired to increase the amount of current which can be extinguished, an additional source of direct current may be inserted in conductor 3| so as to charge condenser II to a higher voltage. I have found that when source I had a value of about 130 volts, and condenser II had a capacity of about 10 microfarads, it was possible to extinguish a main anode current of 5 amperes with a condenser voltage of 230 volts, and a current of 10 amperes with a condenser voltage of 460 volts.

In Fig. 2, in which similar parts are given the same reference numerals as in Fig. 1, the main anode 4 is connected through load 8 to one terminal 31 of an A. C. supply l3, shown as a generator, whose other terminal 38 is connected to cathode 2.

In this case an internal ignition electrode l4, of semi-conducting material which is similar to electrode 5 of Figure 1, is partly immersed in the cathode 2 and is secured to a holder l5 of a conductive material, for instance iron or molybdenum. The holder l5 also serves as an extinguishing electrode and for this purpose is provided with a flared lower edge 39 which extends close and concentrically to the circular limiting line of electrode l4 and mercury 2. Electrode |4-|5 is provided with a common terminal 40.

A transformer l6 has a primary winding 32 connected through conductors33 and 34 to terminals 3'! and 38 respectively, and has two secondary windings I! and H3 which serve to charge two condensers 2| and 22. For this purpose winding H has one end connected, through a rectifier l9, which may be a dry or thermionic rectifier, to one terminal of condenser 2| and its other end connected to the other terminal of this condenser. Similarly, winding I8 has one end connected through a rectifier 20 to one terminal of condenser 22 and its other end connected to the other terminal of this condenser.

The discharge of condensers 2| and 22 is controlled by two commutators 23 and 24 mounted on the shaft of a synchronous motor 25 connected across A. C. supply l3. Commutator 23 periodically inter-connects contacts 4| and 42 connected to condenser 2| and terminal 40 respectively, and commutator 24 periodically interconnects contacts 43 and 44 connected to condenser 22 and terminal 40 respectively. In this manner condensers 2| and 22 are discharged at the proper instant through electrode |4|5. It will be noted that, as in Fig. 1, the discharge circuit of condenser 2| is given a low resistance as indicated by heavy lines.

The windings l1 and H), as well as rectifiers l9 and 20, are so arranged that the terminals of the condensers connected to contacts 4| and 43 will be positively charged as indicated, and that the charging will take place during the blocking phase of the discharge tube. Thus it is possible to first apply one positive voltage impulse to terminal 40 by means of commutator 24 and subsequently apply a second positive voltage impulse with commutator 23. In this manner it is possible to control the mean value of the rectified current and to select at will within certain limits the phase of the current impulses with respect to the voltages.

It will be noted that fixed contacts 4| and 42 and fixed contacts 43 and 44 are mounted on insulating rings 45 and 46 which are provided with an angular adjustment in the direction of the double-headed arrows. In this way it is possible to adjust the sequence of and the interval between the closure of contacts 4|42 and contacts 4344 by way of the commutators 23 and 24 respectively.

As shown in the drawing, the commutators 23 and 24 are positioned in a current-carrying phase of the discharge tube. Commutator 24 has just bridged contacts 43 and 44 to apply the positive voltage of condenser 22 to terminal 40 and thereby initiate the main discharge. The main discharge is taking place, and when commutator 23 connects contacts 4| and 42, the positive potential of condenser 2| will be applied to terminal 40 to interrupt the discharge.

After each ignition at the semi-conductive portion I 4, it is impossible for the cathode spot formed at this point to move any appreciable distance away in the short interval before application of the positive potential to portion l5. As a result the extinguishment of the discharge is effected in a very reliable and regular manner.

It will be noted that the single electrode l4-I 5 has two distinct functions, i. e. forming a cathode spot and interrupting the main discharge, which are effected in a similar manner and with similar switching means.

In preliminary experiments on a device such as shown in Fig. 2, I found that it was possible to reduce a rectified current having a mean value of 1.5 amperes and with an efiective voltage of the A. C. supply i3 of 220 volts, to a mean value of 0.5 ampere without the need of delaying the establishment of the discharge. In this case condenser 2| was given a capacity of 6 microfarads and winding l8 produced an eifective voltage of 600 volts. However, with some forms of construction this voltage can be reduced an appreciable amount.

While I have described my invention in connection with specific examples and applications, I do. not wish to be limited thereto, but desire the appended claims to be construed as permissible in view of the prior art.

What I claim is:

1. A current-converting installation comprising a discharge tube having a mercury cathode, a main anode spaced from said cathode to form a discharge space, means to form a cathode spot on said mercury cathode, and an extinguishing electrode above the surface of said mercury cathode and adjacent the cathode spot formed thereon, and means for applying to said electrode, to interrupt the main discharge, a short voltage impulse which is positive with respect to the oathode.

2. A current-converting installation comprising a discharge tube having a mercury cathode, a main anode spaced from said mercury to form a discharge space, a cathode-spot anchoring member partly within said mercury, means to form a cathode spot on said mercury cathode, and an extinguishing electrode above the surface of the mercury and adjacent said member, and means for applying to said electrode, to interrupt the main discharge, a short voltage impulse which is positive with respect to the cathode.

8. A current-converting installation comprising a discharge tube having a mercury cathode, a main anode spaced from said cathode to form a discharge space, an internal ignition electrode permanently immersed in the mercury, and an extinguishing electrode above the surface of said mercury cathode and adjacent the cathode spot formed thereon, and means for applying to said electrode, to interrupt the main discharge, a short broadly as voltage impulse which is positive with respect to the cathode.

4. A current-converting installation comprising a discharge tube having a mercury cathode, a main anode spaced fromsaid mercury to form a discharge space, a body having a semi-conductive portion permanentlyimmersedin the mercury and serving as an internal ignition electrode, and a conductive portion above the surface of the mercury and adjacent thereto, said latter portion serving as an extinguishing electrode, and means for applying to said body to interrupt the main discharge, a short voltage impulse which is positive with respect to the cathode. 5. A current-converting installation comprising a discharge tube having a mercury cathode, a main anode spaced from said cathode to form a discharge space, and a body having a portion of conductive material disposed above the surface of the mercury, and a semi-conductive portion supported by said first portion and extending into the mercury to act as an internal ignition electrode, said first portion extending along the sides of the second portion to the immediate vicinity of the mercury surface, and means including a single conductor connected to said first portion to supply current to said second portion and to apply to said first portion a short voltage impulse which is positive with respect to the cathode to thereby interrupt the main discharge.

6. A current-converting installation comprising a discharge tube having a mercury cathode, a main anode spaced from said cathode to form a discharge space, an extinguishing electrode above the surface of said mercury cathode and adjacent the cathode spot formed thereon, and means for applying to said electrode, to interrupt the main discharge, a short voltage impulse which is positive with respect to the cathode and has a steep front.

7. A current-converting installation comprising a discharge tube having a mercury cathode, a main anode spaced from said mercury to form a discharge space, and an extinguishing electrode above the surface of the mercury and adjacent the cathode spot formed thereon, and means for applying to said electrode, to interrupt the main discharge, a short voltage impulse which is positive with respect to the cathode, said means comprising a condenser having a terminal adapted to be connected to said extinguishing electrode, and a voltage supply source for charging the condenser.

8. A current-converting installation comprising a discharge tube having a mercury cathode, a

main anode spaced from said cathode to form a discharge space, an igniting electrode, and an extinguishing electrode above the surface of the mercury and adjacent the point at which the cathode spot is formed during operation of the tube, and means for applying to said electrode to interrupt the main discharge a short current impulse which is positive with respect to the cathode, said means including an extinguishing circuit, and a source of voltage within said circuit, the resistance of the circuit being less than 0.1

ohm.

TOM JURRIAANBE.

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