US2502203A - Glow switch - Google Patents

Description

March 28, 1950 w, CARPENTER r' 2,502,203

GLOW SWITCH Filed May 10, 1947 BY UM ATTORNEY Patented Mar. 28, 1956 1 502 UNITED STATES PATENT OFFICE GLOW SWITCH Walter E. Carpenter, West Caldwell, and Charles Wiener, Bloomfield, N. J., assignors to Westinghouse Electric Corporation, East Pittsburgh, Pa., a corporation of Pennsylvania Application May 10, 1947, Serial No. 747,288

3 Claims (01. zoo-113.5) 1 2 The present invention relates to what are now It is accordingly the primary object of the known to the art as glow switches employed present invention to provide a glow switch which for the starting of discharge lamps, particularly operates with a minimum time lapse in performof the fluorescent type and provided with filaing its sequential operations. mentary electrodes adapted to be preheated prior Another object of the present invention is the to initiation of a discharge. provision of a glow switch wherein the spacing In order to start a fluorescent lamp the glow of the electrodes is maintained uniform durswitch must perform a sequential operation of ing fabrication and throughout the life of the first completing a heating circuit for the filaswitch and thus the breakdown voltage necessary mentary electrode of the lamp and, after mainto establish the glow discharge in the switch retaining the circuit closed for a sufiicient period mains uniform. of time to assure the filamentary electrode be- Another object of the present invention is the ing heated to maximum electron emissivity, open provision of a glow Sw Which is exceptionally the heating circuit. Because of this sequeneconomical to manufacture yet positive and rapid tial operation appreciable time elapses before in its operation to start a dischar e With n a minithe lamp actually becomes lighted which time mum of time lag.

varies considerably with individual glow switches. Another Object of the present inv on is the For this reason certain standards have been esprovision of a glow Sw t wherein the Seal f tablished as t maximum allowabl ti 1a i the exhaust tubulation to the envelope is so disthe operation of the glow switch before starting posed relative to the electrodes Of the glOW switch of the lamp, which results in rather high salvage that no mechanical 0 rm Strai is t y for the manufacturer, since the switch must be e i posed on such seal.

completely fabricated and tested before it can be A further object of the present invention is the determined that a given switch meets the standprovision of an envelope for the reception of the ard requirements. One of the salient faults neelements of a glow switch wherein the various cessitating rejection of many glow switches is elements can be accurately aligned and fixed because they are too slow in their operation in during fabrication of the Switch.

closing the lamp filament heating circuit. Such Still further objects of the present invention defect is attributable to the fact that, at the will become obvious to those skilled in the art pressure of the gas employed in the glow switch, w by reference to the accompanying drawings a certain spacing is required between the elecw e n: trodes which required spacing becomes altered Figure 1 is a longitudinal view in cross-section during fabrication of the glow switch and thus of a glow switch constructed in accordance with changes the breakdown voltage thereof. the present invention,

Another factor bearing on the efficiency of the Figure 2 is a View partly in cross-section and glowswitch and its meeting standard requiretaken at an angle of 90 to that of Figure 1. ments is in energy consumption during starting Figure 3 is a cross-sectional view taken on the of the discharge lamp. Inasmuch as a current line III-III of Figure 1, limiting device, customarily in the form of an Figure 4 is a cross-sectional view taken on the inductance, is necessarily included in the cirline IVIV of Figure 1, cuitfor the lamp, the interruption of the heat- Figure 5 is a cross-sectional view showing one ing circuit for the filamentary electrode by the form of apparatus which may be used in connecglow switch causes a high transient voltage or tion with a step in the fabrication of the glow surge from the inductance which is applied across switch of the present invention, the preheated electrodes of the lamp to facilitate 4-5 Figure 6 shows the glow switch in cross-sec starting thereof. Since the glow switch and tion and in another position of the apparatus the lamp are in electrical parallel relation at the dur n a further Step n its fabrication,

moment of the high transient voltage surge, it Figure 7 is a fragmentary view of the glow is essential that the glow switch consume a mini switch of the present invention during its tip-I mum. of energy so that the-full value of high so ping-off. transient voltage be available for the lamp, to Figure 8 is a view of a modification which facilitate more rapid starting and regardless of the completed glow switch of the present invent. the half-waveof the alternating current cycle -tion may take. during which the glow switch opens the fila- Referring now to the drawing in detail the. ment heating circuit. 5 glow switch of the present invention comprises an envelope 5 provided with a pinch seal 6 at one end through which leading-in conductors l and 8 extend to the interior of the envelope. At its opposite end the envelope 5 is provided with a small tribulation 9 circumferentially sealed between its ends to the envelope 5, so that the tubulation projects a short distance intericrly and exteriorly of the envelope, and any strain, either in the tubulation or envelope caused by the seal therebetween, is thus remotely disposed particularly with respect to the inner end of the tuvbulation 9. After exhaustion of the envelope 5 and the filling thereof with a gaseous medium, such as a mixture of approximately 99.6% argon and 0.4% nitrogen, or any other suitable gas to give a break-down ranging from 125 to 145 volts, the tubulation fl is tiped-ofi, by heating with a gas flame Hi or the like, and drawing the 6X- cess tubing, as shown in Figure '7.

As shown, a pair of electrodes in the form of narrow bimetallic strips i2 and 13, having a coating of metal, such as zinc, on their surface, are supported by the leading-in conductors l' and 8 and extend longitudinally of the envelope 5, with their inner ends extending a short distance into the open end of the interiorly projecting tubulation 9. It will also be noted that the pinch press 6 has an inwardly projecting portion M provided with a small recess or crater l5 therein, surrounding the electrodes I2 and 1 3 at their points of emergence from the inwardly projecting portion of the pinch press 3, for a purpose to be hereinafter described. Disposed on the surface of the inwardly projecting portion M, as well as within the crater i5, is a metallic coating, such as aluminum paint it, applied prior to sealing the portion M to the envelope to form the pinch press 6, which coating forms a high resistance conductive path between the leadingin and supporting conductors l and 8, so as to maintain the breakdown voltage of the glow switch during operation substantially uniform in daylight and darkness.

By reference now more particularly to Figures 5, 6 and 7, the method of fabricating the en" velope for reception of the various elements of the glow switch of the present invention is shown. The tubing 20, from which the envelope 5 is formed, may be held in suitable jaws 22 with such tubing resting on a metallic or refractory rod 23. This rod is provided with a central bore 24 which concentrically supports a smaller diameter tubing 25, from which the tubulation S is formed, so that the tubing 25 projects slightly above the line of engagement of the rod 23 with the envelope tubing 20, and thus a short desired distance interiorly of the open end of the envelope tubing 2%. A carbon or other suitable mold 28 telescopically engages the envelope tubing 20 which mold is provided with a recess 2i for engaging the upwardly projecting end of the tubing 25 so as to center the latter within the envelope tubing 2|]. Heat in suitable form such as by gas flames 28, is applied to the lower end of the envelope tubing 20, softening the latter and causing it to flow around the rounded end 29 of the mold 26 and to unite and form an hermetic seal with the smaller tubing 24, as shown by the dotted lines in Figure 5, at a point below the inwardly projecting free end of the tubingljlil.

The mold 2B is then withdrawn from the envelope tubing 20 with the jaws 22 subsequently raising the envelope tubing which withdraws the smaller tubing 25 from the recess 24 thus partially forming the envelope 5 as shown in the inverted position of Figure 6. As will be noted from this latter figure the seal 30, formed between the tubulation 9 and the envelope tubing 20, is somewhat remote from the inner open end of the tubulation 9. This is of importance as hereinbefore mentioned because of the fact that the bimetallic electrodes l2 and It, which project into such open end of the tubulation 9, are subjected to heat during operation of the glow switch. Since the ends of the electrodes l2 and I3 bear against the inner wall of the tubulation some of this heat is conducted to the end of the tubulation 9 but inasmuch as this end is sufficiently remote from the point of seal between the envelope tubing 20 and the tabulation '9, there is no strain upon the seal as would otherwise be the case if the tubulation were sealed at its end to the envelope tubing 20.

After the sealing of the tribulation 9 to the envelope tubing 20, the completed envelope is inverted, as shown in Figure 6, and again held by the jaws 22, for sealing .in of the mountfl; Such mount is preformed and comprises the leading-in and supporting conductors l and 8 and which support the bimetallic electrodes 12 and I3, sealed to a glass head 38 having the aforementioned recess l5 therein and the aluminum coating l 5 on its surface. Asealing-head 34 supports the envelope tubing 20 and is provided with small holes 35 engageable by the leadingin and supporting conductors I and 8 which, together with the electrode ends projecting into the tubulation 9, centers the mount 32 with respect to the envelope tubing '20. The latter is then again heated, such as by gas flames 36, and upon softening a pair of clamping jaws 3'! move in an arcuate direction, as shown by the arrows in Figure 6, to form the pinch press 6, by hermetically sealing the envelope tubing 28 to the glass bead 33, as shown by the dotted lines in Figure 6.

During sealing, the bimetallic electrodes 12 and 13 are naturally also heated and to a higher temperature than during operation of the glow switch. Since the low expansion sides of the bimetals are adjacent each other this causes the ends of the electrodes to engage each other under substantial pressure sufficient to slightly distort the same. Accordingly, upon cooling and completion of the switch, the electrodes l2 and 13 are under a slight tension in an opposite direction, causing them to bear against diametrically opposite sides of the inner wall of the tubulation 9. This results in the maintenance of a uniform predetermined spacing between the electrodes throughout the useful life of the glow switch depending upon the diameter of the tubulation 9. Also during sealing an inert gas, such as nitrogen or the like, is introduced into the envelope tubing 20 to prevent oxidation of the bimetallic electrodes l2 and I3 which would otherwise readily occur, particularly while they are in a heated condition, and efiect their subsequent operation.

The partially completed glow switch then moves to the exhaust position where it flashed to degasify the metallic parts while on the exhaust pump, then filled with the aforementioned ionizable medium and sealed off as shown in Figure 7.

Inasmuch as the breakdown voltage of the glow switch is dependent upon the pressure of the ionizable medium employed and the electrode spacing, it can be appreciated that, since the pressure is definitely fixed at the time of introduction into the envelope, the equally deflriit'etangerine electrodespacing which re.-

upon application of a voltage thereto, in orderv to complete the series heating circuit for the filamentary electrodes of the lamp, so that this time period is invariably below the maximum allowable standard, the crater I is provided in the inwardly projecting portion M of the pinch press 8. The effect of this crater I5 is that it increases the intensity of the discharge at the crater with very rapid accumulation of heat which is quickly conducted to the axis of bend of the bimetallic electrodes l2 and I3, causing them to engage each other with minimum time delay. If desired this crater i5 may be made of appreciable depth so as to surround the bimetallic electrodes l2 and I3 for a greater portion of their length, as shown in the modification of Figure 8. Also, it will. be noted from this latter figure that the electrodes 92 and I3 are provided with contacts 38. This enables a somewhat larger diameter tubulation 9 to be employed when desired while allowing ample passageway for exhaust purposes and yet maintaining constant uniform spacing between the electrodes.

It is also to be noted that the bimetallic electrodes l2 and i3 are very thin and of narrow width in order to increase the transient voltage applied to the lamp upon separation of the electrodes when cooled. As previously mentioned the glow switch is so connected to a fluorescent lamp as to connect the filamentary electrodes in series to the supply source and an inductance element is invariably included in the circuit for the lamp to limit the current supplied to the lamp during operation. Consequently, upon cooling of the bimetallic electrodes of the glow switch and their separation, a high transient voltage or surge is induced in the circuit by the inductance at the instant of separation of the electrodes which is impressed across the preheated electrodes of the lamp for initiating the discharge.

However, this high voltage surge alone is insuilicient to initiate a discharge in the lamp in the absence of sufficient current flow, and, inasmuch as the glow switch is in electrical parallel with the lamp at the instant of this high voltage surge, it must be designed so as not to rob the lamp of current by limiting current consumption of the glow switch to a minimum thus enabling maximum current to be supplied to the lamp. Moreover, this desirable condition must exist at the moment of the high voltage surge and regardless of which bimetallic electrode l2 or l3 happens to be instantaneously cathode. To this end each bimetallic electrode l2 and I3 is accordingly designed to have as small a surface area as is feasible with manufacturing techniques, since the smaller the surface area of the bimetallic electrodes the smaller the current consumption of the arc discharge momentarily formed in the glow switch at the instant of separation of the bimetallic electrodes, and hence the larger the high transient energy available for the lamp to more positively initiate a discharge therein.

It is believed to be obvious from the foregoing that a glow switch is provided by the presentinvention which operates at higheiiiciency" and'th'r'oughout a long useful life because the electrode spacing is maintained uniform. Moreover, the tubulation into which the electrodes of the glow switch extend, so as to maintain this uniform spacing, is sealed to the glow switch envelope in such manner that heat from the electrodes and conducted to the tubulation, in no way places a mechanical or thermal strain upon the hermetic seal which would otherwise cause cracking of the seal and destruction of the glow switch. By the provision of a crater for increas ing the intensity of the discharge, the bimetallic electrodes are rapidly heated and as rapidly cooled, so that the glow switch performs its sequential operations with a minimum time delay in the starting of a fluorescent lamp. Also, by

the provision of bimetallic electrodes of small surface area commensurate with manufacturing technique, the high transient voltage available for starting the lamp is increased which tends toward starting of the lamp on the initial operation of the glow switch and reduces the probability of repetitious operation thereof, before a discharge in the lam is actually obtained thus still further prolonging the useful life of the glow switch.

Although several embodiments of the present invention have been shown and described it is to be understood that still further modifications thereof may be made without departing from the spirit and scope of the appended claims.

We claim:

1. A glow switch operable for the starting of a discharge lamp comprising an envelope provided with an ionizable medium therein, a pair of normally spaced thermal responsive electrodes in said envelope between which a discharge occurs upon the application of a -poten tial to the switch and operable to engage each other when heated by the discharge to extinguish the latter and thereafter separate upon cooling, and an annular member supported by said envelope interiorly thereof and engaging at least the free ends of said electrodes entirely within said envelope to prevent the strain inherent in said electrodes due to heating during fabrication of the switch from causing too great an electrode spacing and to maintain the spacing therebetween constantly uniform throughout a long useful life of said glow switch.

2. A glow switch operable for the starting of a discharge lamp comprising an envelope provided with an ionizable medium therein, a tubulation of insulating material circumferentially sealed to said envelope at a point removed from one end of said tubulation to project a portion thereof interiorly of said envelope, and. a pair of normally spaced thermal responsive electrodes in said envelope between which a discharge occurs upon the application of a potential to the switch and operable to engage each other when heated by the discharge to extinguish the latter and thereafter separate upon cooling, and at least the free ends of said electrodes extending into the projecting portion of said tubulation and each end bearing against diametrically opposite points on the interior wall of said tubulation to maintain the spacing between said electrodes constantly uniform throughout a long useful life of said glow switch.

3. A glow switch operable for the starting of a discharge lamp comprising an envelope provided with an ionizable medium therein, an exhaust tubulation of insulating material of predetermined diameter circumferentially sealed to one end of said envelope between the ends of said tubulation to project a portion thereof interiorly and exteriorly of the envelope and sealed-off at its outer end after evacuation and filling of said envelope with the ionizable medium, and a pair of normalIy spaced thermal responsive electrodes in said envelope between which a discharge occurs upon the application of a potential to the switch and operable to engage each other when heated by the discharge to extinguish the latter and thereafter separate upon cooling, and at least the free ends of said electrodes extending into the projecting portion of said tribulation and the end of each electrode bearing against diametrically opposite sides of the interior wall of said tubulation to maintain the spacing between said electrodes constantly 8 uniform throughout a long useful life of said glow switch.

CHARLES WIENER.

REFERENCES CITED The following references are of record in the file of this patent:

UNITED STATES PATENTS Number Name Date 721,387 Potter Feb. 24, 1903 1,605,911 Banneitz Nov. 9, 1926 2,182,715 Yeske Dec. 5, 1939 2,200,443 Denoh May 14, 1940 2,274,399 Cook Feb. 24, 1942 2,277,708 McCarthy Mar. 31, 1942 2,324,906 Clack July 20, 1943 WALTER E. CARPENTER

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