US2099111A

US2099111A - Gaseous discharge device

Info

Publication number: US2099111A
Application number: US10239A
Authority: US
Inventors: John R Hefele
Original assignee: Bell Telephone Laboratories Inc
Current assignee: AT&T Corp
Priority date: 1935-03-09
Filing date: 1935-03-09
Publication date: 1937-11-16
Anticipated expiration: 1954-11-16
Also published as: GB456402A

Description

' Nov. 16, 1937. H FELE 2,099,111

GASEOUS DISCHARGE DEVICE Filed March 9, 1935 2 Sheets-Sheet l INVENTOR J. R. HEFELE A T TORNEV Nov. 16, 1937. HEFELE 2,099,111

GASEOUS DI SCHARGE DEVICE LAMP CURRENT IN M/LL/AMPERES FIG. 4

6 LIOHT- POWER CURVES V- A CATHODE HEATED CAT/ ODE COLD PHOTO-ELECTRIC RESPONSE IN MICROAMPERES o a z a 4 s a 1 LAMP POWER //v WATTS lNl/ENTOR J. R. HE FELE ATTORNEY Patented Nov. 16, 1937 UNITED STATES PATENT OFFICE GASEOUS DISCHARGE DEVICE Application March 9, 1935, Serial No. 10,239

10 Claims.

This invention relates to a gaseous discharge device and more particularly to a device having a heated cathode.

The prior'art contains a disclosure of a discharge lamp including a cathode adapted to be heated to electron emitting temperature, in which the cathode is directly and continuously heated by electric currentsupplied by the source which supplies energizing potential to the discharge l path or indirectly heated by supplying current from that source to a heating unit associated with a cathode either during the starting period alone, i. e., for a short time preceding the initiationof the discharge across the path between i the electrodes when the heating unit is disconnected from the supply source, or during a starting period and throughout the operating period.

While such a lamp is satisfactory for lighting purposes, it is not adapted for use in signaling 3 systems wherein the energy supplied to the discharge path varies between wide limits of current and voltage, for the reason that at low values of current and voltage the lamp becomes inoperative, because the current supplied to the heat- 5 er is insufiicient to maintain the cathode heated to electron emitting temperatures, with the result that certain signals may be lost or so mutilated that-they are unintelligible. Again, since the heat supplied by the heater unit varies with p the square of the current, the temperature of the cathode and hence its electron emissivity will vary therewith and, as a result, the signal produced will be distorted.

In certain types of signaling, such as in picture I transmission and television systems and in sound recording, it is essential that the light source be maintained in a continuously operative condition in order that the light supplied by it may faithfully follow variations of the signal current and potential, which fluctuate from substantially zero amplitude, representing a dark condition or a minimum intensity, to a large amplitude corresponding to white or maximum intensity. In other words, the operation of the heating unit must be independent of the potential producing the discharge between the electrodes.

An object of this invention is to provide a gaseous discharge lamp adapted to be supplied with variable energizing potential and having a 0 heated cathode, the temperature of which is independent of the potential producing the discharge.

Another object is to provide a gaseous discharge lamp adapted to be supplied with variable ener- 5 gizing potential and having a cathode continuously maintained at electron emitting temperature.

An important feature of this invention relates to a gaseous discharge device having a heating unit exposed to the discharge but protected from bombardment by such discharge.

According to one embodiment of this invention, a gas-filled container or bulb encloses electrodes between which is applied a signal br variable potential for controlling a luminous dis- 1o charge between them. The electrodes comprise an anode having a small aperture, and either a tubular cathode surrounding, or a. cylindrical cathode having a closed end adapted to completely enclose, a heating unit that is supplied with constant current for maintaining the cathode at all times heated to an electron emitting temperature. There is also a discharge directing member provided with a capillary opening, this capillary opening and the aperture in the anode being in line with the longitudinal axis of the cathode, whereby there is provided a low voltage positive column gaseous discharge device which operates to produce light which varies in intensity with the fluctuating signal potentials applied to its electrodes and hence operates to faithfully reproduce the signals without introducing dis-' tortion.

A detailed description of the invention follows which is illustrated in the attached drawings, in which Fig. 1 illustrates a glow lamp, partly in section, having atubuiar cathode surrounding a heating unit;

Fig. 2 shows a glow lamp, also partly in section, in which the heating unit is completely enclosed by a cathode;

Fig. 3 is a graphical representation of the relation between the voltage and the current applied to the lamp; and

Fig.4 is a graphical representation of the relation between the light emitted and the power taken by the luminous discharge of the heated cathode type lamp as compared with a cold cathode lamp of otherwise similar construction.

Referring more particularly to the drawings, Fig. 1 shows a glow discharge lamp comprising a bulb I provided with a press 2. Lead-in

conductors

3 and 4 extend through this press 2, conductor 3 connecting to one terminal of a heating unit or coil 5 while conductor 4 is connected to cathode 6, to which the other terminal I of the heating coil 5 is attached for a purpose which will be more fully explained as the description PIOQQQGSQ The cathode 6 in Fig. 1 comprises an open cylinder surrounding the heating coil I and is formed of or externally coated with a material which is adapted to be heated to electron emitting temperature by that coil.

5 Surrounding the cathode I is a cylindrical member I provided with a conical extension I which terminates in a capillary opening l0 ad- Jacent an aperture II in the anode l2. Aperture II in the anode l2 and the capillary opening I0 are in line with the longitudinal axis of the cylindrical cathode I.

Clamped on the press 2 are a pair of split sleeves II from which rods l4 extend into the lamp away from the base. These rods support the member 8 which surrounds the cathode 8.

Secured to the rods II are a pair of rods II provided at their upper ends with insulators II from which extend short projections I'l. These short projections I! are secured to the anode I2. The elements l6 serve to electrically insulate the rods II from the projections l1 and these three sets of elements combined with the rods I serve as supports for the anode l2. A lead-in wire l8 extends through the base of the lamp and is connected to the anode l2.

The bulb I contains a charge of a rare gas, such as neon, helium, or argon, at a pressure of a few millimeters of mercury. It may be advantageous also to have a charge consisting of a mixture of one of these gases and either nitrogen, hydrogen or mercury. The pressure of the gas charge may be between 5 and 10 millimeters of mercury and, in the case where nitrogen or hydrogen is used, the nitrogen or hydrogen may constitute from 2 to 5 per cent by volume of the charge. When mercury is used a smaller amoun would be suillcient.

The coil 5 is supplied with heating current from any constant current source, such as, for 40 example, the battery IS. The negative terminal 20 of the source I! is connected to the cathode I by means of the lead-in wire 4 and the positive terminal is connected via the lead-in wire 3 to the coil 5. The coil I is thus supplied with constant current of sufllcient value to maintain the cathode 6 heated at all times to electron emitting temperature. This is an important feature of this invention.

The negative terminal of the battery i9 is also connected to the negative terminal of a battery '2l, which has its positive terminal connected through the secondary winding of a transformer 22 and lead It to the anode l2. The primary winding of the transformer 22 is supplied with variable signal current transmitted over the circuit 23, for example, with current varying as the tone values of a picture or object scanned at a transmitting station of a picture transmitting or television system. Battery 2i supplies a steady potential of sufllcient value to cause a luminous positive column discharge of constant light intensity to occur across the space between the surface of the cathode I and the anode l2. This positive ionic discharge occurs between the g5 anode l2 and both surfaces, inside and outside, of the cathode 8. For this reason, the discharge is distributed over a greater area than if the closed end cathode is used. The concentrated beam is consequently more intense. As the heating coil I is in the path of the discharge, means 'which will now be described are provided to prevent the positive ions from causing destructive ent of this coil. The drop across the heating coil I is such that the potential difference between the lower end of the coil I and the anode I2 is less than that across the battery 2| which produces the luminous discharge. This coil, therefore, is not subject to the highly destructive ionic bombardment due to the luminous discharge which would materially reduce the useful life of the lamp as all portions of the coil except the end connected to the cathode are positively polarized with respect to the cathode. If the battery It were reversed in polarity, the potential difference between the lower end of the coil I and the anode l2 would then be greater than that between the anode l2 and the cathode I and most of the discharge would occur between the coil I and the anode l2, thus materially reducing the life of the coil I. By utilizing an electron emitting surface of extended area, a large current carrying capacity is assured, and by concentrating the discharge into the capillary opening It, a positive column of great brightness and constant intensity is produced.

By properly selecting the potential of the battery 2|, signals varying over 'an extremely wide range of values may be supplied by the transformer 22 for superposition on that supplied by the battery without causing the eifective potential applied to the lamp to be reduced below its extinction voltage. However, even if the signals areof such magnitude as to reduce the voltage applied to the electrodes to a value below the extinction voltage of the lamp, the luminous discharge will be immediately restarted upon restoration of the breakdown voltage of the lamp, due to the fact that the cathode is maintained uniformly heated to electron emitting temperature by current from the constant current source I! As shown in Fig. 3, the relation between the voltage and current supplied to the lamp is linear, and the line representing this relation has a negative slope. For an otherwise similar cold cathode lamp the slope would be positive.

Fig. 4 shows light versus power curves A and B, which respectively relate to a heated cathode lamp of the type described herein and to a cold cathode lamp of otherwise similar construction. It will be observed that the shape of curve A for the heated cathode lamp is somewhat similar to curve B for the cold cathode lamp. However, the amount of light produced by a glow discharge lamp having a heated cathode is several times that produced by a lamp of this type provided with a cold cathode, which is identical in design and is operated under exactly the same conditions, and this result is attained with an expenditure of only a fraction of the electrical power used in a cold cathode lamp. Curve A shows only the power taken by the luminous discharge, but the total power curve (tahng into account the power extended by the heater coil) would be parallel to and slightly to the right of A.

The design of lamp shown in Fig. 2 differs from 7 that of Fig. 1 solely in the feature that the cathode I, instead of being an open cylinder surrounding the heating coil, consists of a solid cylindrical body 30 having a central bore 3| which extends from one end 32 thereof to a point intermediate its length, so as to provide an electron emitting element having closed upper end 33.

The heating coil I is secured in this opening so that it is completely enclosed by the cylindrical charge. In this case, the battery l9 may be connected in either direction with respect to the heating coil. As shown, the heating coil is connected between the lead-in wire 3 and the cathode 6, but it may be connected between the two lead-in

wires

3 and 4 or directly to the terminals of battery l9.

' From the preceding description, it will be apparent that this invention provides a low voltage, positive column discharge lamp, designed to have a long useful life, operable with low power input to provide a discharge having high current density to produce illumination of great intensity and controllable by signal potentials which vary over an extremely wide range of values, such as, for example, those used in sound recording and at the receiving station of a picture transmission or television system to control the production of a picture or image, without causing the positive column discharge to be interrupted in such manner that distortion would be introduced.

What is claimed is:

l. A gaseous discharge device comprising electrodes determining a discharge path between said electrodes, a discharge directing member between said electrodes, means for heating one of said electrodes to electron emission temperature, and means for supplying to said heating means constant current, one terminal of said heating means being connected to the heated electrode and the other terminal being positively polarized with respect thereto.

2. A gaseous discharge device comprising electrodes, a discharge directing member between said electrodes, a unit exposed to the discharge between said electrodes for heating one of said electrodes to electron emission temperature, and means for supplying to said unit constant current, one terminal of said unit being connected to the heated electrode and the other terminal being positively polarized with respect thereto.

3. In combination, a transformer, connections from a source of signal potential to the primary of said transformer, a glow lamp comprising an anode, a cathode, and a heating unit for said cathode, a source of direct current in series with the secondary of said transformer and the discharge space between said anode and cathode, and a source'of constant current for said cathode heating unit, one terminal of said heating unit being connected to the cathode and the other terminal being positively polarized with respect thereto.

4. A positive column gaseous discharge device comprising an anode, a cathode having an open end adjacent said anode, a member surrounding a said cathode provided with a capillary opening, an aperture in said anode, said aperture and capillary opening being in line with the longitudinal axis of the cathode, a unit exposed to the discharge between said anode and cathode for heating said cathode to electron emission temperature, and means for supplying to said unit constant current, one terminal of said unit being at cathode potential and the other tenninal being positively polarized with respect thereto.

5. A positive column gaseous discharge device comprising an anode, a cylindrical cathode, a member surrounding said cathode provided with a capillary opening to direct the discharge between said anode and cathode, means within said cathode for heating it to electron emission temperature, a source supplying signal potential between said anode and cathode, and a source supplying constant current to said heating means, one terminal of said heating means being at cathode potential.

6. A positive column gaseous discharge lamp comprising an anode, a cathode, a cylindrical member surrounding said cathode, a conical cap for said cylindrical member, a capillary opening at the apex of said conical cap, an aperture in said anode, said aperture and capillary opening being in line with the longitudinal axis of the cathode, and means exposed to the discharge between said anode and cathode for heating said cathode to electron emission temperature, said heating means having one terminal thereof connected to said cathode and its other terminal pos itively polarized with respect thereto to prevent ionic bombardment of said unit.

'7. A positive column gaseous discharge device comprising an anode, a cathode, a cylindrical member surrounding said cathode, a conical cap for said cylindrical member, a capillary opening at the apex of said conical cap, an aperture in said anode, said aperture and capillary opening being in line with the longitudinal axis of the cathode, means combined with said cathode for heating it to electron emission temperature, a source supplying signal potential between said anode and cathode, and a source supplying constant current to said heating means.

8. A gaseous discharge lamp comprising a glass bulb, a press in said bulb, a plurality of split sleeves clamped on said press, an anode, a cathode, a heating unit for said cathode, an aperture in said anode, a cylindrical member having a conical cap and a capillary opening at the apex of said cap surrounding said cathode, said aperture and capillary opening being in line with the longitudinal axis of the cathode, rods fastened to said split sleeves for supporting said cylindrical member and said anode, leads through said press to said cathode and heating unit, and a lead to said anode.

9. A positive column gaseous discharge device comprising a glass enclosure, a press in said enclosure, an anode having an aperture therein, a cathode, a heating unit for said cathode, a cylindrical member having a conical cap and a capillary opening at the apex of said cap surrounding said cathode, said aperture and capillary opening being in line with the longitudinal axis of the cathode, means on said press'for supporting said anode, cathode, heating unit, and cylindrical member, a source supplying constant current to said heating unit, and a source supplying signal potential between said anode and cathode.

10. An electric discharge device comprising a gas-tight receptacle containing a gas filling, an anode, a cathode, and electrical means adjacent said cathode for heating it to cause it to emit electrons, said anode, cathode and heating element being so disposed that when an electric discharge occurs between said anode and cathode said heating means is exposed to bombardment by positive ions, and means for limiting said bombardment of said heating means comprising means for maintaining the potential of at least the major portion of said heating means more positive than said cathode.

.JOHN R. HEFELE.