Abstract:
The invention is directed to an improved hollow cathode lamp ( 15 ). In the preferred embodiment, the lamp is comprised of a stem ( 23 ), a cathode lead ( 18 ) which passes through the stem, and a getter ( 26 ). The improvement includes a flash shield ( 28 ) positioned between the getter and the stem, whereby the flash shield will limit the deposit of getter metal on the stem when the getter flashes. The flash shield may be a circular disk and composed of nickel. The flash shield may include an evacuation passage ( 46 ). The flash shield may also be capable of being heated to about 1000° C. during flashing, whereby the flash shield may be heated so as to convectionally repel the getter metal when the getter flashes.

Description:
This application is a continuation of Ser. No. 09,235,021 filed on Jul. 21, 1999, now abandoned. 
    
    
     FIELD OF THE INVENTION 
     The present invention relates generally to the field of hollow cathode lamps and, more particularly, to an improved hollow cathode lamp which limits the deposition of flashed getter metals on the stem and cathode leads of the lamp. 
     BACKGROUND ART 
     A variety of designs are known for hollow cathode lamps. Hollow cathode lamps used in extreme conditions are often designed such that two cathode leads and two anode leads carry electrical energy from the power supply, through the glass stem of the lamp, to the cathode and anode inside the lamp. It is known that hollow cathode lamps which must operate for extended periods of time and from which a high-quality spectrum is required (i.e., spectra calibration lamps for satellite instruments) should include a getter to collect contaminant gases after the lamp is sealed. It is known that a getter can extend the service life of the lamp by assuring that the spectra of the lamp will not become contaminated with hydrogen, oxygen, or water vapor that diffuses from the internal components. The getter, composed of a reactive metal such as barium, is heated until the metal vaporizes, or flashes, inside the lamp, thereby trapping any foreign gases in a location where they cannot enter the spectra. 
     In the prior art, some of the vaporized or flashed getter metal will form a film on the cathode leads. This contact produces a negative potential in the getter film. As an unfortunate result, the electrical discharge of the lamp may occur between the anode and the getter film, rather than between the anode and the cathode. In effect, the getter film will operate as the cathode. Because it is necessary to have the cathode metal produce the emitted spectra, rather than the getter metal, a discharge between the anode and the getter-metal film renders the lamp useless. Hence, it would be useful to provide a hollow cathode lamp with a flash shield that limits the deposition of the getter metal on the cathode leads and stem so as to prevent the getter metal from obtaining a negative potential and, thereby interfering with the proper operation of the lamp. 
     DISCLOSURE OF THE INVENTION 
     With parenthetical reference to the corresponding parts, portions or surfaces of the disclosed embodiment, merely for the purposes of illustration and not by way of limitation, the present invention provides an improved hollow cathode lamp ( 15 ) having a stem ( 23 ), a cathode lead ( 18 ) which passes through the stem, and a getter ( 26 ). The improvement comprises a flash shield ( 28 ) positioned between the getter and the stem, whereby the flash shield will limit the deposit of getter metal on the stem when the getter flashes. 
     The flash shield may be a circular disk and composed of nickel. The flash shield may include an evacuation passage ( 46 ). The flash shield may also be capable of being heated to about 1000° C. during flashing, whereby the flash shield may be heated so as to convectionally repel the getter metal when the getter flashes. 
     Accordingly, the general object of the present invention is to provide an improved hollow cathode lamp with a flash shield which limits the deposit of getter metal on the stem and cathode leads of the lamp when the getter flashes. 
     Another object is to provide an improved hollow cathode lamp with a flash shield which is capable of being heated so as to convectionally limit the deposit of getter metal on the stem when the getter flashes. 
     Another object is to provide an improved hollow cathode lamp with internal supports which provide stability to the internal components of the lamp. 
     Another object is to provide an improved hollow cathode lamp which prevents the getter metal from obtaining a negative potential. 
     Another object is to provide an improved hollow cathode lamp with a flash shield which allows for unrestricted evacuation of the bulb when sealing the lamp. 
     Another object is to provide an improved hollow cathode lamp with a flash shield which allows for high pumping speeds during evacuation. 
     These and other objects and advantages will become apparent from the foregoing and ongoing written specification, the drawings, and the appended claims. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     FIG. 1 is a view, partially in verticle section and partially in elevation, of the improved hollow cathode lamp. 
     FIG. 2 is a right side view, partially in verticle section and partially in elevation, of the improved hollow cathode lamp shown in FIG.  1 . 
     FIG. 3 is a perspective view of the flash shield. 
     FIG. 4 a  is a fragmentary view showing the bottom marginal end portion of a hollow cathode lamp known in the prior art and indicating the vectors of flashing getter metal in the prior art. 
     FIG. 4 b  is a fragmentary elevation showing the bottom marginal end of the improved hollow cathode lamp and indicating the vectors of flashing getter metal. 
     FIG. 5 is a horizontal sectional view of the hollow cathode lamp shown in FIG. 4 b , taken generally on line  5 — 5  of FIG. 4 b.   
    
    
     DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     At the outset, it should be clearly understood that like reference numerals are intended to identify the same structural elements, portions or surfaces consistently throughout the several drawing figures, as such elements, portions or surfaces may be further described or explained by the entire written specification, of which this detailed description is an integral part. Unless otherwise indicated, the drawings are intended to be read (e.g., cross-hatching, arrangement of parts, proportion, debris, etc.) together with the specification, and are to be considered a portion of the entire written description of this invention. As used in the following description, the terms “horizontal”, “vertical”, “left”, “right”, “up” and “down”, as well as adjectival and adverbial derivatives thereof, (e.g., “horizontally”, “rightwardly”, “upwardly”, etc.), simply refer to the orientation of the illustrated structure as the particular drawing figure faces the reader. Similarly, the terms “inwardly” and “outwardly” generally refer to the orientation of a surface relative to its axis of elongation, or access of rotation, as appropriate. 
     Referring now to the drawings and, more particularly, to FIGS. 1-2, this invention provides an improved hollow cathode lamp, of which the presently preferred embodiment is generally indicated at  15 . Lamp  15  is shown as broadly including a cathode  16 , an anode  20 , a getter  26 , a flash shield  28 , a glass stem  23 , and a glass bulb  24 . Cathode  16 , anode  20 , getter  26 , flash shield  28 , stem  23 , and bulb  24  are annular members generated about verticle axis x—x. Stem  23  is an annular glass disk. Bulb  24  is a cylindrical member which is attached at its bottom marginal end to stem  23  along the outer diameter of stem  23 . 
     Four electrical leads  18 ,  19 ,  21  and  22  carry electrical energy from a power supply (not shown) to cathode  16  and anode  20 . Two opposed anode leads  21 ,  22  supply electrical energy to anode  20 , and two opposed cathode leads  18 ,  19  supply electrical energy to cathode  16 . As shown in FIGS. 1-2 and FIG. 5, anode leads  21 ,  22  and cathode leads  18 ,  19  pass through stem  23  at equal radial distances from axis x—x. Leads  18 ,  19 ,  21 ,  22  are metal conductors with circular cross-sections. Cathode leads  18 ,  19  extend up through stem  23  and parallel to axis x—x to axial positions just below cathode  16 . 
     As shown in FIGS. 1-2, cathode  16  is a solid cylindrical member elongated along axis x—x. Cathode  16  is attached at the center of its downwardly-facing annular surface to support rod  38 , which, in turn, is supported by connections to upper cathode strap  35  and lower cathode strap  36 . Straps  35 ,  36  are rectangular cross-bars strung between cathode leads  18 ,  19  and perpendicular to axis x—x. Support rod  38  is attached to strap  36  at its lower marginal end and is attached to strap  35  near its upper marginal end. 
     Anode  20  is a cylindrical ring-like member, the outer diameter of which is connected to the upper marginal ends of opposed anode leads  21 ,  22 . Anode leads  21 ,  22  extend parallel to axis x—x and up through stem  23  to axial positions higher than the upper ends of cathode leads  18 ,  19 . Consequently, anode  20  is positioned above cathode  16 . The inner diameter of anode  20  is greater than the outer diameter of cathode  16 . 
     Four circular mica support disks, severally indicated at  33 , are arranged around cathode  16 . Disks  33  are elongated along axis x—x and are ring-like members. The outer diameter of each support disk  33  is slightly less than the inner diameter of bulb  24 . The inner diameter of each support disk  33  is slightly larger than the outer diameter of cathode  16 . Anode leads  21 ,  22  pass through two opposed circular holes in each support disk  33 . Support disks  33  are evenly spaced, with the bottom disk positioned near the lower marginal end of cathode  16  and the upper disk positioned slightly higher than the top surface of cathode  16 . Four ceramic sleeves, severally indicated at  34 , insulate anode leads  20  and provide spacing between the individual support disks  33  and between the top support disk and anode  20 . Support disks  33  assist in maintaining the internal structure of hollow cathode lamp  15 . 
     A barium getter  26  is used to collect contaminant gases after the lamp is sealed. As shown in FIG. 2, getter  26  is a cylindrical ring-like member elongated along axis x—x and having an outer diameter less than the transverse distance between cathode leads  18  and  19 . Getter  26  is oriented downward and is mounted to and below lower strap  36 . It is know in the prior art that a barium getter can extend the service life of the lamp and help guarantee that the lamp&#39;s emitted spectrum will not become contaminated with hydrogen, oxygen or water vapor that may diffuse from the internal components after the lamp is evacuated and sealed. Getter  26  is heated by coupling with an RF field until the metal vaporizes onto the inside of the lamp. The barium getter manufactured by Toshiba America, Electronics Components, at 290 Donald Lynch Blvd., Marlborouth, Mass. 01752, part number N-1350M(6), may be employed in the preferred embodiment. As shown in FIGS. 4 a - 4   b , getter  26  is directional and positioned to flash downward, as indicated by vectors  29 . In the prior art designs, as shown in FIG. 4 a , the barium metal flashes and forms a film on the lower inside portion of bulb  24  and the inside of stem  23 . However, this design often allows and results in the flashed barium making electrical contact with the cathode leads, which in turn produces a negative potential in the barium. This unwanted electrical connection occurs predominantly at cathode outlets  25  and  27 , where cathode leads  18 ,  19  pass through stem  23  and into the interior of the lamp. 
     As shown in FIGS. 1 and 4 b , the improved device incorporates a flash shield  28  to limit the deposition of the barium getter metal on stem  23  and outlets  25 ,  27 . As shown in FIG. 3, flash shield  28  is a circular disk elongated along axis x—x, and is bounded by an upwardly-facing annular horizontal surface  39 , a downwardly-facing annular horizontal surface  40  (not shown), an outwardly-facing cylindrical vertical surface  41 , and inwardly-facing rectangular vertical planar surfaces  42 ,  43 ,  44  and  45 . Surfaces  42 ,  43 ,  44  and  45  define a rectangular evacuation passage  46 . Evacuation passage  46  allows for unrestricted evacuation of the bulb. As shown in FIG. 3, in addition to evacuation passage  46 , flash shield  28  also contains two co-axial cathode lead through-bores, severally indicated at  47 , and two co-axial anode lead through-bores, severally indicated at  48 . In a preferred embodiment, flash shield  28  is composed of nickel and is approximately 0.008 inches thick. 
     In addition, flash shield  28  is capable of being heated to 1000° C. before the getter flashes. When heated, flash shield  28  provides not only a physical barrier to the barium getter metals, but also a thermodynamic one. When getter  26  flashes, the vaporized barium will tend to move towards lower temperatures and away from the heated flash shield  28 , thereby limiting the contact of barium below flash shield  28  and on stem  23  and cathode outlets  25 ,  27 . 
     As shown in FIG. 4 b , stem  23  includes glass protrusions, severally indicated at  50 , at cathode outlets  25 ,  27  and anode outlets  49 . Cathode leads  18 ,  19  and anode leads  21 ,  22  are chemically bonded to glass stem  23  at their contacting surfaces. Glass protrusions  50  provide added surface area to facilitate an airtight chemical connection between the leads and the contacting glass stem. Four ceramic sleeves, severally indicated at  51 , insulate leads  18 ,  19 ,  21 ,  22  as they exit from stem  23 . Sleeves  51  also act to support flash shield  28 . As shown in FIG. 1, flash shield  28  rests on the upwardly-facing annular horizontal surface of cylindrical sleeves  51 . To provide additional stability, an adhesive may be used between flash shield  28  and the upwardly-facing annular vertical surfaces of sleeves  51 . Flash shield  28  is also held in place by anode sleeves  31 , which insulate anode leads  21 ,  22  between the top of flash shield  28  and the lowest support disk  33 . Cathode sleeves  32  insulate cathode leads  18 ,  19  between the top of flash shield  28  and an axial position just above getter  26 . 
     FIG. 5 is a sectional view of the hollow cathode lamp shown in FIG. 4 b , taken generally on line  5 — 5  of FIG. 4 b . FIG. 5 shows the opposed co-axial orientation of cathode leads  18 ,  19  and anode leads  21 ,  22 . This orientation provides mechanical stability to hollow cathode lamp  15 . FIG. 5 also shows sleeves  31  and  32 , getter  26 , flash shield  28 , rectangular evacuation passage  46 , and axial through-bore  53 . 
     As shown in FIG. 4 b , an exhaust tube  52  extends from and below stem  21 . Tube  52  is a cylindrical glass member. An axial through-bore  53  is cut through stem  21  and has a diameter equal to the inner diameter of tube  52 . Upon evacuation of bulb  24 , tube  52  is melted to form a frusto-conical seal of axial stem through-bore  53 . 
     As illustrated in FIG. 4 b , flash shield  28  limits the deposit of barium metal on stem  23  and cathode outlets  25  and  27 . Because the barium does not contact the cathode leads when it flashes, it does not become charged, does not achieve a negative potential, and does not act as the cathode when the lamp discharges. Consequently, the desired spectra is emitted during discharge of hollow cathode lamp  15 . 
     Modifications 
     The present invention contemplates that many changes and modifications may be made. The particular materials of which the various body parts and component parts are formed are not deemed critical and may be readily varied. The shape and dimensions of the component parts, including the flash shield, may also be readily varied. 
     Therefore, while the presently-preferred form of the hollow cathode lamp has been shown and described, and several modifications discussed, persons skilled in the art will readily appreciate that various additional changes and modifications may be made without departing from the spirit of the invention, as defined and differentiated by the following claims.