US2731577A - Stroboscope lamp - Google Patents

Description

Jan. 17, 195 Q H FLOYD STROBOSCOPE LAMP Filed Aug. 28, 1951 United States Patent hce 2,731,577 Patented Jan. 17, 1956 STROBOSCOPE LAMP Oscar H. Floyd, Chicago, Ill., assigner to Kemlite Laboratories, Chicago, Ill., a partnership Application August 28, 1951, Serial No. 243,993

3 Claims. (Cl. 313-116) This invention relates to the stroboscopic art; in particular, it relates to a novel sealed-in stroboscope lamp which is adjustable to provide unusual versatility in application while at the same time possessing physical ruggedness and ease of manufacture.

Stroboscopy is of course, in the broad sense, an old art; its applications in engineering and industry have steadily increased in number and importance since the stroboscope principle was first developed. During the history of the art, many types of stroboscope lamps have enjoyed temporary popularity, but the gaseous-discharge lamp has proved most satisfactory and is now firmly established in stroboscope work.

The gaseous-discharge lamp is popular for stroboscope work primarily because of its extremely rapid ignition and extinction times, which permit the generation of highintensity light impulses of extremely short duration. Such impulses are of course ideal for stroboscopy.

Another property of the gaseous-discharge lamp which makes it useful in stroboscope applications is the fact that it can be triggered by an electric held, the lamp itself drawing negligible energy from the triggering source. This characteristic permits direct control of the stroboscope lamp from engine spark plugs and other such lowenergy electric sources.

Gaseous-discharge tubes used as stroboscope lamps are normally provided with a control electrode (usually called grid) mounted adjacent the terminal electrodes of the tube. The control electrode or grid may be mounted internally or externally of the tube itself, since its function is merely to produce an electric eld in the partially evacuated space within the tube. The tube, as persons familiar with the art will understand, contains at sub-atmospheric pressure an inert gas such as argon, Xenon, or neon. In the absence of the control electrode, the imposition of a sufficiently high potential dilerence between the terminal electrodes will cause ionization of the gas within the tube and current will thereupon ilow between the terminal electrodes. lt is characteristic of such tubes that the potential dierence required to maintain ionization, with resulting current ilow and light emission, is far lower than the potential required to ionize the gas initially.

lThe control electrode or grid, by varying the electric eld within the tube, may be made to control theterminal potential at which ionization occurs.

Thus, to use a gaseous-discharge tube as a stroboscope lamp, one may apply to its terminal electrodes a potential source supplying suicient energy to keep the gas ionized for a short period but having insuicient peak voltage to ionize the gas in the tube under normal conditions (The power source in question will normally comof triggering potential. The trigger potential may comprise any short-duration, high-amplitude, periodic voltage pulses which are synchronized with the moving object whose behavior is to be studied by stroboscopic illumination. For example, in the case of a gas engine, the trigger-voltage source may be a spark plug of the engine.

With such an arrangement, the discharge tube will be normaily dark but will be ignited when a trigger pulse is applied to the control electrode. Once ignited, the gas in the discharge tube will remain ionized and continue to give olf light so long as the potential across its terminals exceeds the extinction voltage. When, as the capacitor discharges, the terminal voltage drops to the extinction level, the gas will resume its normal molecular state and the tube will cease to emit light. The capacitor, of course, will immediately commence to re-cnarge, but the tube will not again re-ignite until the next trigger pulse is applied to the control electrode.

The position of the control electrode in an arrangement of the type just described is frequently rather critical. Often the trigger source will provide an output voltage more or less continuously, varying from instant to instant. The high-amplitude pulses to be used for triggering purposes will t'nus be superimposed on such a continuous background. lt is obviously necessary for stable operation that the discharge tube be designed to ignite positively on the trigger pulses but to remain insensitive to the random voltage peaks of lesser amplitude which may occur between trigger pulses. Thus the position of the discharge electrode may in a given application be quite critical, since the ignition potential of the discharge tube is directly related to the position of the control electrode.

From the foregoing discussion it will be obvious that a particular stroboscope lamp, designed for stable and consistent performance in a given application, would in most cases be unusable in a dierent application, since it is highly unlikely that the new application would have the same requirements, with respect to control-electrode design, as the former application.

This situation has made mass production of gas-discharge stroboscope lamps very difiicult. In general, the lamps have had to be tailor-made to the particular application required.

Sealed-in construction of stroboscope lamps is extremely desirable. Such lamps are usually used in and around engines and other types of rotating machinery, where they are subject to rough treatment. Since the lamps are rather fragile, and particularly since the relative positions of the electrodes are of critical importance, protection of the lamps from the eects of rough treatment is highly desirable.

In the present invention, I have provided a stroboscope lamp which has the popular and desirable sealed-in construction and which is at the same time provided with a control electrode Whose position can be adjusted Within wide limits by a manual operation externally of the Sealedin tube. This novel design achieves the major object of my invention, which is to provide a mechanically rugged stroboscope lamp, well adapted to mass production, wherein means are provided for adjusting the position of the'control electrode to make a single lamp useful in a wide variety of stroboscope applications.

My invention also has the objective of lling the need for a versatile stroboscope lamp providing, in a compact, s ealed package, a gas-discharge tube, an adjustable trigger electrode, a focusing lens for directing the stroboscopic light ina concentrated beam, and a shielding means adapted to protect the discharge tube and the control electrode from the effects of strong stray electric tields which might otherwise cause ignition of the tube at unscheduled times. i

3 Other objects and advantages of my invention will appear as the specification proceeds.

Inthe accompanying drawing I have shown two illus- V'trative embodiments of my invention; in the drawing, lEigure l is a sectional View in the vertical plane of a typical stroboscope lamp made according to my invention; Fig. 2 is a sectional view in the horizontal plane, taken along the line 2-2 of Fig. l; Fig. 3 is a sectional View generally similar to Fig. l but showing an alternative construction; and Fig. 4 is a schematic diagram showing, for purposes of illustration, the manner Vin which my stroboscope lamp might be connected to an external circuit in a typical application.

I shall describe iirst the structure shown in Figs. l and 2. As may be seen from Fig. l, my lamp is mounted in and supported by a base 10, generally similar in appearvance to the base of a vacuum tube and formed of any suitable substance, such as ceramic or plastic material. To facilitate connection of the lamp to an external circuit,

I provide base pins 11, 12, and 13, which are secured t.

rigidly in position by the base and which may be arranged in any desired manner. I prefer, as a matter of convenience, to arrange the base pins in a generally triangular fashion such that the pins are adapted to iit into a standard tube socket.

The base 10 differs from a standard tube socket in one important respect-it contains a central upward extension comprising a hollow annular pedestal surmounted by a tubular top portion of lesser diameter, formed integrally with the pedestal. upper 'portion receives the shaft of a bolt member 16, provided with an annulark shoulder 16a which holds the bolt 16 snugly within the tubular upper portion of member 15, leaving bolt 16 free to rotate but preventing from moving axially with respect to base 10. The hollow interior of the pedestal portion of element 15 provides a recessed accommodation for the head of bolt member 16. The upper end of bolt 16, above shoulder 16a, is threaded.

A gaseous-discharge tube 17 is mounted within base 10, being secured therein by being partially embedded within a mass of material 18, which may be a suitable hardening resin, sealing wax, plastic cement, or Vother material of that sort. (As may be readily observed from either Fig. 1 or Fig. 3, my stroboscope lamp is assembled by mounting all the parts thereof in their proper relative positions while the material 13 is in a soft, plastic state. When the material 18 has hardened, the entire structure is formed into a rigid, unitary body which possesses great physical strength and ruggedness.)

Discharge tube 17 is provided with a pair of discharge electrodes, denoted 18 and 19 respectively, having external wire leads which are respectively joined, as by soldering, to pins 12 and 13.

The gas-discharge tube, as usual, is U-shaped, and is disposed in the lamp structure with its ends downward. Forming a double yoke around the discharge tube is a control electrode member 2i), which may be formed as a stamping from a single piece of metal. The central portion of member 20 is threaded for cooperation with bolt 16, and member 20 is carried thereon, its oppositely extending arms embracing the discharge tube 17 along its, parallel sides. A exible pigtail connector 21 joined at one end to a wire 22 soldered or otherwise joined to pin 11, provides an electrical connection between control.

electrode 20. and pin 11 regardless of the position control electrode 29 may occupy'on bolt 16'. Pigtail 21 is soldered or welded to electrode 2t? at any convenient point and is long enough to permit electrode'Zil a full range of movementV from one end of thev threaded portion of bolt 16 to the other.

Surrounding andl partially enclosing gas-discharge, tube 17 is an insulating sheath 22 formed of insulatingV material such asV sheet mica or a suitable plastic. A metal outer casing 23, lgenerally cylindrical in shape, is carried- The central aperture'in the tubular f within base 10 concentrically with and externally of the l insulating sheath 22, both of saidelements being secured in place by the cementing` material 18.

The upper end of the outer casing 23 is modified 'as shown in Fig. l to provide a receptacle or socket for a lens element 24, the length of the casing 23 and the shape of the lens 24 being coordinated so as to focus into a narrow beam the major portion of the light emitted by discharge tube 17.

An electrical connector is received between the insulating member 22 and the casing member 23, connector 25 being joined to pin 13 by a wire 26.V Thus the Y outer shell 23 is held atall times at the same potential as pin 13 and electrode 19. Normally pin 13 rwill be grounded. Thus thedischarge tube 17 and the sensitive Y accomplished by removing the lamp from its socket and,

with a screw driver, rotating bolt 16. As bolt 16 turns, element 20 is moved up or down the discharge tube 17, and the triggering voltage is accordingly varied. Thus, when a stroboscope is to be used in a new application, the characteristics of the lamp can almost instantly be adjusted to precisely those best iitted to the requirements of the new application. This feature represents a vital improvement in stroboscope lamps and makes mass production of sealed-in stroboscope lampsV commercially practicable. Y

The embodiment of my invention illustrated in Fig. 3 is generally similar in principle to the embodiment of Figs. l and 2, but diiers *structurally in that, the ceramic or plastic base member is extended upward to whollyl enclose the apparatus and to serve as the support for the lens element.

As may be seen from Fig. 3, this alternative embodiment of my invention comprises a body member 110, corresponding to base 10 of the Fig. lembodiment. Body member 11) is preferably molded from ceramic, although Y any suitable plastic material may of courseV be used. Connection to an external circuit isl facilitated by the use of contact pins 111, 112, and 113, which connect respectively' to the control electrode 120, terminal electrode 118, and the other terminal electrode 119. A bolt 116, having an annular shoulder 116e, is carried within a central support member 11S, corresponding to` element 15 in Fig. l. Y Body member 11@ is modi'ed at its upper end to recei'vef the lens 124, and an annular deposit'of ceramic cementv 131, or other suitable cementing material, holds the l'ens 124 in the proper position.

A metal shield 123 protects the tube and the control electrode from stray fields; it is'concentric with the body member and is carried therewithin, sandwiched; be-v tween the body member and the insulating sleeve 122.V

it'V desired, the lower portion ofv the Fig. 3 embodiment may be filled in with a ceramic cement 118; if such matex rial is employed, the entire tube structure isv given a very high degree of rigidity fand mechanical strength. On. the other hand, the ceramic body member 1110 aiords to" this form or" the invention such ruggedness that the cement- 118 may be dispensed with if the Various supporting leads extending from the pins are made sufficiently large and-` external circuit with which my stroboscope lamp will normally be employed. The circuit of Fig. 4 does not form any part of my invention and is shown herein for illustrative purposes only.

As Fig. 4 indicates, electrode 20 is connected to the trigger source, which will normally be a spark plug when a gas engine is being studied. Terminal electrode 19 is grounded, While terminal electrode 18 is connected through a resistor 51 to one terminal of a D.C. source 50, having a potential above the extinction voltage of the discharge tube 17. Capacitor 52 is bridged across the terminal electrodes 1S and 19.

The mode of operation of the circuit is very simple. During periods when the tube 17 is extinguished, capacitor 52 charges through resistance 51 to the voltage of D.C. source 50. Thus, when tube 17 is ignited by a trigger pulse, current will ow from capacitor 52 through the gaseous path within the tube, and the tube will remain ignited for a brief instant. When capacitor 52 has become partially discharged, however, its voltage will drop belo'et the extinction voltage of the tube and the gas in the tube will resume its normal molecular state. (The resistance 51 prevents the maintenance of a steady-state voltage across the discharge tube suiciently high to maintain ionization.)

From the foregoing discussion, it will be obvious to those skilled in the art that the circuit of Fig. 4 will cause tube 17 to emit light for a brief interval following each trigger pulse, being dark at all other times.

While I have herein discussed two embodiments of my invention for purposes of illustration, it is to be understood that those are exemplary only, and that the scope of my invention is to be determined primarily by reference to the appended claims.

I claim:

1. A stroboscope lamp comprising a base member, a gaseous-discharge tube containing ionizable gas, said tube being provided with a pair of terminal electrodes, means rigidly securing said tube in a fixed position relative to said base member, a metal cylindrical shell surrounding said tube, said shell having one end received within said base member and having its other end modiiied to form a lens holder, means sealing said shell Within said base member operative to hold said lens holder at a predetermined xed position relative to said tube, a lens carried in said lens holder for focusing into a beam light emitted by said tube, a control electrode for said tube, said electrode being constrained to movement in a predetermined locus relative to said tube, manually adjustable means carried by said base member, partially external and partially internal thereof, said manually adjustable means being mechanically linked to said control electrode whereby manual adjustment of said adjustable means will cause systematic change in the position of said control electrode without affecting the relative position of the tube and the lens, and circuit means electrically connecting said cylindrical shell and one of said terminal electrodes.

2. Apparatus according to claim l wherein said manuaiiy adjustable means comprises a screw having a head and a threaded shank mounted for free rotation within said base member, said head being carried externally of said base member and said shank extending into the interior of said base member, said screw having also means restraining the same against axial movement relative to said base member, and wherein said control electrode is provided with a threaded portion receiving said shank, whereby rotation of said screw causes movement of said control electrode through a linear locus.

3. A stroboscope lamp comprising a base member, a U-shaped gaseous-discharge tube containing ionizable gas, said tube being provided with a terminal electrode at each end, a deposit of hardened sealing compound within said base member, said tube being mounted within said base member with its terminal ends received therewithin and held rigidly in place relative to said base member by said sealing compound, a plurality of terminals carried on said base member for external electrical connection, conductors joining said terminal electrodes of said tube respectively to two of said base terminals, a bolt rotatably mounted in said base and oriented with its shank disposed between the respective arms of said U-shaped tube, at least a portion of said bolt shank being threaded, said bolt having also means restraining it against axial movement relative to said base while allowing it to ro tate freely with respect thereto, a control electrode for said tube having a pair of oppositely extending members respectively engaging the arms of said U-shaped tube, said control electrode being provided with a threaded p0rtion and said bolt passing through said threaded portion of said control electrode and extending substantially therebeyond toward the curve portion of said U-shaped tube, whereby rotation of said bolt will move said control electrode axially along the arms of said tube, and means for providing external circuit connection to said control electrode.

References Cited in the iile of this patent UNITED STATES PATENTS 1,350,328 Muschenheim Aug. 24, 1920 1,433,982 Cameron Oct. 31, 1922 1,858,497 Hall May 17, 1932 1,976,500 Imaoka Oct. 9, 1934 2,246,486 Blackburn June 17, 1941 2,327,144 Stam Aug. 17, 1943

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