US2930872A - Glow switch - Google Patents

Description

Mardi 29, 1960 W LAKE 2,930,872

GLOW SWITCH Filed March 25, 1957 F5251. F-: Flzf-#Tw NUMBER 0F STA/@T5- L/Sfd Lil 27/ lm/ervlor;

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GLOW SWITCH william H. Lake, Mayfield Heights, ohio, assignor to General Electric Company, a corporation of New York Application March z5, 1957, snial'N.l 4648,261 t 6 Claims. (C1400-113.5)

`connected to the output circuit of the ballast and the other terminal of each electrode is connected across the switch. The switch comprises a small glass envelope containing an ionizable gaseous atmosphere and a pair of normally spaced apart electrodes, at least one of which is heatdeformable. The heat-deformable electrode, which may be a thermally responsive bimetallic strip, is positioned to flex toward and engage the other electrode when heated.

At starting, the open circuit voltage of the ballast exceeds the breakdown voltage of the switch and starts a glow discharge therein which heats the thermally responsive electrode and causes it to engage the other electrode in the switch. The closure of the switch effectively short circuits the lamp electrodes in series across the ballast;

thereupon the increased current flow through the electrodes raises them rapidly toan electron emitting tem.-

perature Simultaneously, the glow dischargethrough the switch is extinguished and the switch electrodes begin to cool. After a time, the thermally responsive electrode in the switch disengages itself from the stationary electrode and the heating circuit is thereby opened. wA transient voltage surgeor kick then occurs due to the-inductance in the ballast. This surge impressed across theV lamp normally starts the main discharge between the lamp electrodes; if the lamp fails to start, this cycle is repeated until starting is achieved. After the main discharge through the lamp has started,rthe voltage drop thereacross is less than the breakdown voltage of the switch so that the switch does not develop a glow discharge and its electrodes remain disengaged.

`Until recently when glow switches constructed in accordance with my Patent 2,740,861-Glow Type yThermal Switch became commercially 4available-the lead lamp in a lead-lag switch start circuit generally'had `a muchshorter life thantthelag lamp. The cause vthereof was premature'starting ofthe lead'larnp, that is,starting vbefore the lamp electrodes hadvattained the required electron emitting temperature. Such premature starting happens most frequently under high line voltage .con-

ditions or with wellaaged and easy starting lamps. Itftakes place before the glow switch contacts have closed and `may be ycaused by vexcessive ballast peak kkvoltages or atrans'ientvoltage surges or oscillations. In my aforemenftioned patent, I disclose a glow type thermal 4switch which substantially eliminates instant startingr and reduces IUnited States ,Patent the differential in life between the lead lamp and the lag lamp from a former figure in excess of 30 percent to one less than l0 percent. The switch disclosed therein makes use of electrically symmetrical electrodes having approximately equal electron emissive areas. This feature eliminates a voltage doubling effect through the series capacitor of the lead lamp circuit caused by rectification of the current in prior switches having electrically asymmetrical electrodes and which was a facto-r in premature starting. Further by proper correlation of thefilling gas pressure and the relative percentages of neon and argon in the gaseous filling, that switch effectively reduces transient voltage surges or oscillations and excessive ballast peak voltages characteristic ofthe lead branch of lead-lag ballast circuits and which ,are another factor in premature or instant starting of the lead lamp.

The object of this invention is to provide a glow switch which is more reliable in yoperation and which is simpler and more economical to produce than switches heretofore available.

Another object is to provide such a switch having instant starting suppression characteristics.

A further object of the invention is to provide a glow switch having operating characteristics which remain extremely stable' throughout its life.

ln accordance with the invention, the solid ionizing agents which have been used heretofore in glow switches to eliminate dark effect and which formed substantial cost elements and which were laborious to apply, have been eliminated. Instead, a minute quantity of radioactive krypton 36Kr85 is introduced into the switchenvelope to provide a source of ionization to eliminate dark effect. However, the mere substitution of radioactive krypton for the solid ionizing agent is not suicient to achieve stable operation throughout life, as willbe explained more fully hereinafter. It has been found necessary to add a minorproportion of another gas, which will be referred to as a Vgaseous impurity, in order to prevent the breakdown voltage of the switch from dropping with life. Suitable gases for the impurity are hydrogen, carbon dioxide and nitrogen. By proper correlation of the pressures and concentrations of the various gases, the coating of low-.melting point metal such as zinc, magnesium or aluminum on the electrodes and the lengthy seasoning operation formerly required to achieve stable operation characteristics for the switches, may be eliminated.

In appreferred embodiment, the glow switches are provided with electrically symmetrical electrodes at least one of which is heat-deformable and which are made of metal such as an iron alloy not coated with a low-melting point metal. rifhe gaseous filling within the switch .consists for the major part of neon to which may be added a vminor proportion of argon. The radioactive gaseous isotope provided as ionizing agent is krypton 85. A small percentage of hydrogen is added to achieve stable breakdow voltage characteristics throughout life. i

For further objectsand advantages and for adetailed description of a preferred embodiment of the invention, attention is now directed to the following description and accompanying drawing. The features of the invention believed to be novel will be more particularly pointed out in the appended claims. 'v

AIn the drawing:

Figs. 1 and 2 are front and side elevations, respectively, of a glow switch embodying the invention.

, circuit.

lleferrng to Figs. 1 and 2, there is shown a glow swltch comprising a tubular glass bulb 1 having its upper end closed and its lower end perpherally sealed to a glass stem tube 2. Lead-in wires 3, 4 extend through the stern and have intermediate portions 5, 6 of copper clad nickel iron alloy wire commonly known as dumet sealed through the press 7 of the stem. To the inwardly projecting ends of the lead-in wires are welded thermally responsive bimetallic strips 8, 9 which are angled toward each other in order to overlap at their upper ends. Each bimetallic strip consists of two strips of metal having different linear coecients of expansion welded together, for instance a nickel-iron alloy on the lower expansion side and a chrome-iron alloy on the hlgher. expansion side. Other suitable metals or alloys preferably of iron and, in any case, of a relatively high melting point may be used. The two strips are mounted in Such fashion that the sides of lower coefficient of expansion face inwardly, that is in confronting relation. Thus, when the electrodes become heated, they bend inwardly toward each other and make contact at their upper ends. In a commercial form of the instant switch intended for operationpof standard 40-watt switch-start fluorescent lamps, the bimetallic strips have a projected length of approximately 0.31 inch, a width of 0.075 inch and a thickness of 0.008 inch. The overlapping electrode ends are spaced apart when at room temperature a distance from 0.025 to 0.030 inch.

Glow switches as incorporated in commercial fluorescent lamp starters are enclosed in a sheet metal can. yUnder these circumstances, they are subject to dark effect, that is the tendency of the breakdown voltage to rise in the dark after a period of non-operation. This kresults in delay at starting and erratic operation. Various expedients have been resorted to heretofore for elimination of dark effect. One which has been widely used and which is described in my Patent 2,740,861, is to provide a coating of uranium oxide on the inner surface of the end wall of the glass envelope. Another expedient is to provide a coating of aluminum paint on the inner end of the stem and extending onto the lead-in wires at the points where they emerge from the press. It has also been necessary, in order to achieve stable operating characteristics with life, to coat the electrodes with a low-melting point metal such as zinc. Thereafter, the switches have to be seasoned and this involves a period of continuous operation on normal ballast circuits without lamps. For the glow switch designated GS4A incorporated in a starter designated commercially FS- 400 which comprises a metal can having suitable terminals and including a radio interference suppression capacitor, the seasoning schedule required continuous operation of the switch for thirty minutes. The seasoning stabilizes the glow voltage characteristic and also raises the transient impulse, that is, the voltage impulse derived from the switch when the bimetal contacts separate. Probably the low transient impulse prior to seasoning is due to metal arc phenomena inasmuch as the zinc plating has a very low work function (3.5 compared to 4.5 for the bimetal) and a very low melting point (495 C. compared to 1495 C. for the bimetal). Until the bimetal surface is cleaned thoroughly of zinc plating, the transient impulse is low.

With the improved glow switches in accordance with my invention, the solid ionizing material such as uranium oxide or aluminum stem paint for elimination of dark effect are no longer used. Furthermore, the bimetals are not plated with low-melting point metal such as zinc and the need for prolonged seasoning is eliminated. These results are achieved by the provision of a gaseous filling consisting for the major part of neon and if desired with a minor proportion of argon, up to approximately percent, to which there is added a trace of radioactive krypton and a small percentage of a gaseous impurity, preferably hydrogen. The filling is introduced 11t0 the ,4 switch envelope through the exhaust tube 10 which is .then tipped off. y

The gaseous filling within the switch, principally neon, is at a pressure in the range from 45 to 70 mm. of mercury. The current carrying capacity of the switch increases with increasing pressure of neon. For the instant switch intended for the operation of standard 30 and 40-watt fluorescent lamps, a current carrying capacity of approximately 200 milliamperes is desirable in order to reduce peak voltages in the lead branch of the ballast circuit where such circuit is of the lead-lag type; this is achieved at a neon gas pressure of approximately 60 mm. However, neon alone at such a pressure would provide too low a transient impulse upon opening up the switch contact to assure reliable starting of the lamp. Moreover, the American Standards Association specifies a minimum closure voltage for such switches of 128 volts R.M.S., and at the stated ceiling pressure with neon alone the switch has a closure voltage of to 115 volts which is below the specified minimum. This may be remedied, in accordance with the teachings of my aforementioned patent, by introducing a minor proportion of argon to the neon, neon being extremely sensitive to such addition in the determination of its breakdown voltage. The argon may be added in a proportion up to approximately 20%.

According to the present invention, a minute proportion of radioactive krypton is added to the gaseous filling of the switch in order to eliminate dark effect. This eliminates the need for the uranium oxide used in prior art switches. However, when the uranium oxide is left out, other effects are observed, relating to the breakdown characteristic of the switch with life. While the initial breakdown characteristic of the neon-argon switch with radioactive krypton additive is of the proper magnitude, as the switch is operated the breakdown characteristic changes radically. This is illustrated in Fig. 3 wherein the ordinate represents breakdown voltage of the switch and the abscissa represents number of starts, that is the number of times the switch has been operated to start a lamp. It will be appreciated that each start represents several closure cycles, for instance up to 2O closure cycles, depending upon the facility of the lamp for starting. Curve A illustrates the breakdown voltage characteristic of prior art switches having a neonargon filling and uranium oxide within the envelope for elimination of dark effect as per my aforesaid patent. It will be observed that the breakdown voltage is relatively constant with life, showing at most a slight increase. Curve B illustrates the breakdown voltage characteristic of neon-argon switches with radioactive krypton additive alone; it will be observed that while initially, at the beginning of life, the breakdown voltage is close to the desired value, it drops off rapidly with life. While the reasons for this effect are not fully known, an explanation may reside in bimetal contamination and clean-up of minor impurities under the action of the gaseous discharge. Contamination of the bimetal surface results in lowering of its work function and tends to reduce the breakdown voltage. Also elimination of minor gaseous impurities inadvertently introduced into the switch during its manufacture likewise tends to lower the breakdown voltage. The deliberate addition to the gaseous filling of the switch of an impurity gas which cancels or minimizes these effects then provides a suitable operating characteristic throughout life. Sev eral such impurity gases are known which, when added in small percentages, produce the desired result, for instance hydrogen, carbon dioxide and nitrogen. Of these various gases, hydrogen is preferred for the breakdown voltage controlling impurity.

The addition of hydrogen as the breakdown controlling 'impurity in a proportion from 3 to 10 percent relative to the neon or neon-argon mixture substantially stabilizes the breakdown voltage characteristic over the life of the switch, as illustrated by curve C in Fig. 3. -The explanationfor this unexpected result may reside inthe' ability ofathe highly active hydrogen to clean-up the "surface of the bimetal and prevent contamination thereof by other impurities, as mentioned above, and consequent lowering of work function. Also, hydrogen is extremely potent in its direct effect upon the breakdown voltage of the vgaseous filling of the switch in that much smaller amounts of hydrogen than most other impurities, produce a much greater effect on the discharge. By introducing a relatively large amount of hydrogen by comparison with other secondary impurities inadvertently introduced into the switch envelope during manufacture, the effect of such other secondary impurities is overriden so that the cleanup of such other secondary impurities no longer has any appreciable effect on .the breakdown characteristics of the switch. The upper limit to the permissible concentration of hydrogen given above, namely approximately 10 percent, is determined by the effect of hydrogen on other characteristics of the switch such as breakdown voltage., glow current, and transient impulse. With the addition of hydrogen within the stated range, the minor percentage of argon formerly required to achieve the required transient impulse is no longer essential, and in fact, for reasons of simplicity of manufacture, neon alone is nowy preferred as the principal gas.

Radioactive krypton 36Kr5 has a half-life of 9.4 years :and emits beta rays with a maximum energy of .07 mev. (million `electronvolts). The production of. ions in a gaseous medium containing a radioactive'isotope is directly Idependent upon thenumber of disintegrations per second foccurring in the radioisotope. Accordingly, the quantity -of radioisotope required is most conveniently stated in terms of its activity expressed in euries, a curie by defini- -tion consisting of 3.7 l010 disintegrations per second. Generally, an activity no less than 0.1 millicurie per liter of filling gas measured at atmospheric pressure is required to overcome dark effect, and an activity in excess Iof l millicuries is unnecessary and provides no additional benefits. For the switch herein considered, an activity of approximately 1 millicurie per yliter in the filling .gas measured at atmospheric pressure has been found sufiicient to eliminate substantially all dark effect. However, it is desirable to have some excess radioactivity preswatt fluorescent lamps, the proportions of the constituent gases in the filling may be in the following ranges:

Principal constituent-neon or neon-argon mixture, 90 to 97 percent.

Controlling impurity-hydrogen, 3 to 10 percent.

Radioisotope-krypton85, 0.1 to 10 millicuries per liter measured at atmospheric pressure.

Filling pressure-45 to 70 millimeters of mercury.

The preferred proportions are approximately 95 percent neon, percent hydrogen and 5 millicuries per liter of radioactive krypton, the filling pressure for the mixture being approximately 60 millimeters of mercury. Curve C in Fig. 3 is representative of a switch having these preferred proportions of filling gases.

Fig. 4 illustrates diagrammatically a switch-start leadlag circuit for operating a pair of standard 40-watt fiuorescent lamps, 48 inches long and 11/2 inches in diameter, 11 being the lead lamp and 12 the lag lamp. Each lamp comprises an elongated glass envelope having sealed into its opposite ends a pair of filamentary electrodes 13, 14. The lamp envelopes are filled with a starting gas such as argon at a few millimeters pressure and contain a small amount of mercury. An internal coating of phosphor 6 15 emits visible light under excitation by the A25,37 Wavelength radiations produced by the discharge through the mercury vapor.

The ballast for operating the lamp, indicated at 16, comprises an autotransforrner having a primary winding 17 and high reactance secondary windings 18, 19 loosely coupled to the primary. The primary windingis energized from the usual 11S-120 volt A.C. supply at terminals 20, 21 through a manual switch 22. The operating circuit for lead lamp 11 comprises primary winding `17, secondary winding 18 and a ballasting capacitor 23 all connected in series. The reactance of capacitor 23 is in the range of 1.4 to 2.3 times the inductive leakage reactance of secondary winding 18. The ycurrent through lamp 11 is limited by the excess capacitive reactance in the circuit so that the lamp operates with `a leading power factor. The operating circuit for `lag'lamp 12 comprises primary winding 17 and secondary winding 19 connected in series; the current through that lamp is limited by the inductive leakage reactance of the secondary winding so.

that the lamp operates with a lagging power factor. a

The operating circuit for the lamps are made to one side of their filamentary electrodes 13, 14; the glow switches indicated by the symbol S are connected to the remaining or free sides of the electrodes. In the case of lag lamp 12, glow switch 24 is connected directly across the free sides of the electrodes. In the case of lead lamp 11, glow switch 25 is connected across the free sides of the electrodes in series with compensating winding 26 whose function is to offset in part the excess capacitive reactance in the circuit when the switch electrodes are closed whereby to raise the pre-heating current through the electrodes of the lead lamp to the level of that through the electrodes of the lag lamp. In commercial practice, each switch is shunted by a small capacitor 27 for the suppression of radio interference, the capacitor being enclosed along with the glow switch in the metal can of the starter.

When priar art glow switches not having` instant-start suppression characteristics are used in circuits of the type illustrated in Fig. 4, the life of lead lamp 11 is usually at least 30 percent less than that of lag lamp 12. The differential in life was caused by premature starting of the lead lamp. The use of improved switches in accordance with the present invention substantially eliminates instant starting and assures that the differential in life affecting the lead lamp is no greater than 10 percent.

While .a certain specific embodiment of the invention has been shown and described in detail, it is intended primarily as illustrative and not as limitative of the invention. Various modifications for adapting theswitch to other sizes of lamps and to other operatingrconditions provided by different ballast circuits will readily suggest themselves. The appended claims are intended to cover any such modifications coming within the true spirit and scope of the invention.

What I claim as new and desire to secure by Letters Patent of the United States is:

l. A glow switch comprising `a sealed envelope containing a pair of electrodes at least one of which is deformable by heat into engagement with the other, and an ionizable gaseous atmosphere in said envelope at a pressure in the range from 45 to 70 millimeters of mercury and comprising to 97 percent of a principal gas consisting for the major part of neon and containing not over 20 percent argon, 3 to 10 percent of a gaseous impurity for stabilizing breakdown voltage with life and selected `from the group consisting of hydrogen, carbon dioxide and nitrogen, and -a trace of radioactive krypton in a concentration providing sufficient activity to overcome dark effect.

2. A glow switch comprising a sealed envelope containing cooperating electrically symmetrical electrodes at least one of which is deformable by heat into engagement with the other, an ionizable gaseous atmosphere in said envelope at a pressure in the range from 45 to 70 millimeters of mercury and comprising 90 to 97 percent of principal gas consisting for the major part of neon and containing not over 20 percent argon, 3 to 10 percent of a breakdown voltage controlling impurity from the group consisting of hydrogen, carbon dioxide and nitrogen, and radioactive krypton in a concentration providing suicient activity to overcome dark effect.

3. A glow switch comprising a sealed envelope containing cooperating electrically symmetrical electrodes at least one of which is deformable by heat into engagement with the other, and an ionizable gaseous atmosphere in said envelope at a pressure in the range from 45 to 70 millimeters of mercury and comprising 90 to 97 percent of a principal gas consisting for the major part or" neon and containing not over 20 percent argon, 3 to l0 percent lhydrogen for stabilizing the breakdown voltage characteristic with life, and radioactive krypton in a concentration providing an activity in the range of 0.1 to 10 millicuries per liter measured at atmospheric pressure to overcome dark effect.

4. A glow switch comprising a sealed envelope containing cooperating electrically symmetrical electrodes at least one of which is deformable by heat into engagement with the other and consisting of iron alloys devoid of any plating of low-melting point metal, and an ionizable gaseous atmosphere in said envelope at a pressure in the range from 45 to 70 millimeters of mercury and comprising 90 to 97 percent of a principal gas consisting for the major part of neon and containing not over percent argon,

3 to 10 percent hydrogen, and a trace of radioactive krypton in a concentration providing suicient activity to overcome dark elect.

5. A glow switch comprising a sealed envelope containing cooperating electrically symmetrical electrodes mounted in confronting relation, said electrodes consisting of iron alloy bimetals devoid of any plating of low melting point metal and being spaced apart at room temperature and deformable by heat into mutual engagement, and an ionizable gaseous atmosphere in said envelope at a pressure of approximately millimeters of mercury and comprising percent of a principal gas consisting for the major part of neon and containing not over 20 percent argon, 5 percent hydrogen, and radioactive krypton in a concentration providing a radioactivity in the range of 0.1 to 10 millicuries per liter measured at atmospheric pressure.

6. A glow switch as defined in claim 4 wherein said principal gas is substantially all neon and the radioactivity is approximately 5 millicuries per liter measured at atmospheric pressure.

References Cited in the tile of this patent UNITED STATES PATENTS 2,241,240 Chirelstein May 6, 1941 y 2,324,907 Clack July 20, 1943 2,449,632 Admiraal Sept. 21, 1948 2,650,278 Foulke Aug. 25, 1953 2,678,979 Beese May 18, 1954 2,740,861 Lake Apr. 3, 1956

Claims (1)

1. A GLOW SWITCH COMPRISING A SEALED ENVELOPE CONTAINING A PAIR OF ELECTRODES AT LEAST ONE OF WHICH IS DEFORMABLE BY HEAT INTO ENGAGEMENT WITH THE OTHER, AND AN IONIZABLE GASEOUS ATMOSPHERE IN SAID ENVELOPE AT A PRESSURE IN THE RANGE FROM 45 TO 70 MILLIMETERS OF MERCURY AND COMPRISING 90 TO 97 PERCENT OF A PRINCIPAL GAS CONSISTING FOR THE MAJOR PART OF NEON AND CONTAINING NOT OVER 20 PERCENT ARGON, 3 TO 10 PERCENT OF A GASEOUS IMPURITY FOR STABILIZING BREAKDOWN VOLTAGE WITH LIFE AND SELECTED FROM THE GROUP CONSISTING OF HYDROGEN, CARBON DIOXIDE AND NITROGEN, AND A TRACE OF RADIOACTIVE KRYPTON IN A CONCENTRATION PROVIDING SUFFICIENT ACTIVITY TO OVERCOME DARK EFFECT.

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