US2937299A - Capillary spark light source - Google Patents

Description

May 17, 1960 w. J. NOLAN, JR

' CAPILLARY SPARK LIGHT SOURCE.

Filed Nov. 9, 1956 FIG 1 5- IO KY 0.6.

POWER SUPPLY United States Patent 2,931,299 CAPILLARY SPARK LIGHT souncu William J. Nolan, Jr., Norco, Califi, assignor t'o Motorola,

Inc., Chicago, Ill., a corporation of Illinois Application November 9, 1956, Serial No. 621,324

' 3 Claims. or. 313-113) This invention relates to new and useful improvements in electric spark discharge lights and more particularly to. an improved spark discharge light in which the spark electrodes are enclosed within a capillary passage in a transparent member.

In recent years there have been developed improved electric spark discharge lights for producing high intensity flashes of short duration. These spark discharge lights have proved to be very eflective as high intensity light sources'for photographic work, for stroboscopic observation and for optical range finding equipment. In theelectric spark discharge light, a high voltage power supply is used to charge an electrical condenser which is then discharged across'a pair of spark electrodes. In somespark discharge lights a trigger electrode is used to initiate an ionized path for the discharge of a spark between the main spark electrodes. In the development of spark discharge lights as a light source'for optical range measuring equipment one of the problems which has arisen and which has not been satisfactorily solved is that of the'uncertain location of the spark with respect to the electrodes. The spark has a tendency to wander over the electrode surface and produces: an erratic and incomplete illumination of the target. If the electrodes are brought to a sharp point the condition may be improved somewhat, but electrode wear becomes so rapid as to be intolerable and break down voltage varies substantially from pulse to pulse.

It is therefore one object of this invention to provide an improved spark discharge light which is capable of producing a high intensity confined spark.

Another object of this invention is to provide an improved spark discharge light in which spark wander is substantially eliminated and the light is concentrated at approximately half of the sphere to reflect light back to a selected point.

Other objects and features of this invention will become apparent from time to time throughout the specifi- V cation and claims as hereinafter related.

In the accompanying drawing, to be taken as a part of this specification, there is clearly and fully illustrated a preferred embodiment of this invention in which drawings;

Fig. 1 is a view in cross-section of an improved spark discharge light having electrodes discharging in a capillary passage, and showing one possible schematic wiring diagram for the light, and

Fig.12 is a detail sectional view of the quartz sphere and capillary passage therein in which the spark electrodes are positioned,

This invention comprises animproved spark discharge light having a pair of spark discharge electrodes arranged for discharge from a capacitive discharge circuit. The spark discharge electrodes are positioned in a capillary passage through a sphere of a transparent material such as quartz or the like so that the spark is closely confined in the capillary passage and spark wander is thus eliminated. The quartz sphere may, if desired, be provided with a reflective coating over a portion of the surface to concentrate and reflect light back to the light source or any other selected point. 7

Referring to the drawings by numerals of reference and more particularly to Fig. 1, there is shown a spark discharge light assembly 10 which is enclosed and supported within a metal casing 12. Casing 12 has a p1urality of openings 14 around the lower end thereof and has a removable metal plug or end wall 16 at said lower end. A capacitor 18 is positioned within the upper portionofthe casing 12 andhas' a threaded terminal 20 extending through the end wall of the casing and secured in place by a threaded nut 22. At the other end of the capacitor 18 there is a threaded projection 24 constituting the second terminal of the capacitor on which is supported an electrode holder 26 having a spark electrode 28 therein. The electrode holder 26 abuts a spacer member 30 which in turn abuts and secures in place a transparent sphere 32 of glass, quartz, or the like.

I, The sphere 32 has an aperture37 of capillary size therein which receives the lower end of the spark electrode 28. The sphere 32 rests on a ring-shaped support 39 on the removable wall or plug 16. A second spark electrode 341is secured in the re'movablewall or plug 16 and extends in to the capillary opening 37 in the quartz sphere. 32. The quartz sphere 32., as shown in Fig. 2,

may be provided with a reflecting coating 33 of aluminum or other metal which reflects stray light back to the spark zone as indicated by the dotted lines in Fig. 2.

This spark discharge light is energized intermittently from a D.C. power supply 36 which may provide a voltage of the order of 5,000 to 10,000 volts. The power supply 36 is connected as by a lead 38 to the terminal 20 on the capacitor 18 and is also connected to ground as indicated at 40. The power supply 36 is also connected by a lead 42 to a resistor 44 which may have a resistanceof the order of 500,000 ohms. The resistor 44 is connected as at 46 to the other terminal of the capacitor 18. The capacitor 18 may have a capacitance of the order of 0.1 mid. and be rated 5,000 volts.

Operation In operation the power supply 36 is arranged to pro I vide an intermittent source of DC. power to charge the capacitor '18. The capacitor 18 when fully charged will discharge through the electrodes 28 and 34 to produce a spark discharge 35. The spark discharge 35 is confined within the capillary passage 37 in the quartz sphere 32 and thus is not permitted to wander about the surface of the spark electrodes.

The volume occupied by the spark is a function of the energy dissipated and if the energy is not sufficient to create a spark large enough to fill the capillary passage then spark wander may still occur. However, when the energy is increased above that necessary to fill the capillary passage with the spark a substantial increase in brightness is obtained over the brightness produced by an open spark. With very high spark energies, however, it is necessary to use material of substantial thickness to confine a spark within the capillary passage-since the high energy of the spark may shatter the transparent member through which the capillary passage 37 extends.

It is necessary to allow a substantial clearance between the electrodes 28 and 34 and the walls of the capillary passage 37 so that material which is sputtered off the electrodesduring the spark and products ofdecomposition of the glass or quartz will be blown out of the region of the spark gap. If this clearance is not provided, the material sputtered off the electrodes during the spark and products of decomposition of the glass will form on the surface of the passage 37 an opaque film which is electrically conducting and which will short'out the electrodes 28 and 34. This spark light has been successfully operated using electrodes .020 inch in diameter, positioned in a capillary passage, .030 inch diameter, and having spark energies of about 0.5 joule.

While this spark light assembly is illustrated with a spark electrode positioned in a capillary passage through a glass or quartz sphere, it is possible to position electrodes in a capillary passage through a transparent member of other shapes such as a cylinder or prism. The spherical shaped member 32 is preferred, however, for an optical measuring system. Since the usual optical system collects light from only a limited angle, it is possible to increase the brightness of the light source by coating the unused portion of the surface of the sphere with a reflecting material 33 such as aluminum to return the otherwise wasted light to the spark zone. The efiectiveness of this reflector coating of course depends on the absorption characteristics of the spark. While the sphere 32 has been described as being formed of glass or quartz, other materials such as sapphire or other transparent crystalline material may be desired because of considerations of mechanical strength and of light transmittance requirements of the optical system in which this light is used.

I claim:

1. A spark discharge device including in combination, a transparent spherical member having a capillary passage extending therethrough along a diameter thereof, and a pair of spark electrodes positioned in said passage and forming a spark gap at substantially the center of said spherical member, said spark electrodes being adapted to be connected in a high voltage circuit to produce a spark discharge at said gap, with the discharge 5 path being defined by said passage to prevent spark Wander, said electrodes being spaced slightly from the surface of said passage to provide an escape path for erosion products caused by said spark discharge.

2.. A spark discharge device including in combination, a transparent member having a spherical outer surface and a capillary passage therein, a pair of spark electrodes positioned in said passage and adapted to be connected in a high voltage circuit to produce a spark discharge in said passage, said electrodes being spaced from the surface of said passage to provide an escape path for erosion products, and a reflective coating on a portion of said spherical surface of said transparent member for reflecting light radiation and returning the same to said passage.

3. A spark discharge device including in combination, a transparent member having a spherical outer surface and a cylindrical capillary passage therein, a pair of spark electrodes positioned in said passage and adapted to be connected in a high voltage circuit to produce a spark discharge between said electrodes, with the dis charge path being defined by said passage to prevent spark wander, said electrodes being substantially smaller in diameter than said passage to provide an escape path for erosion products, and a reflective coating on a portion of said spherical outer surface of said transparent member for reflecting light radiation and concentrating the same in said capillary passage to increase the temperature therein and thereby increase the brightness of light radiation.

References Cited in the file of this patent UNITED STATES PATENTS 2,154,542 Swanson Apr. 18, 1939 2,222,093 Swanson Nov. 19, 1940 2,391,611 Back Dec. 25, 1945 2,775,718 Dubilier Dec. 25, 1956

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