US2351305A - Discharge lamp base and starter - Google Patents

Description

June 13,- 1944. THAYER 2,351,305

DISCHARGE LAMP BASE AND STARTER Filed Feb. 14, 1942 Fig.1.

Invencor: Richard N. Thager, by m/ His A++orneg.

Patented June 13, 1944 DISCHARGE LAMP BASE AND STARTER Richard N. Thayer, Cleveland Heights, Ohio, assignor to General Electric Company, a corporation of New York Application February 14, 1942, Serial No. 430,894

2 Claims.

This invention relates to the basing of lamps and discharge devices, including fluorescent tubes or lamps of the positive column discharge type, and also to the startin control of discharge devices of this character. .An important object of the invention is to provide for incorporating a starter in the lamp structure, and for also including associated accessories, particularly the usual capacitor or condenser for assisting starting and minimizing radio interference as well as arcing. The invention is hereinafter explained with reference to a lamp base containing a starter and a condenser.

Various other features and advantages of the invention will become apparent from the description of a species and form of embodiment, and from the drawing.

In the drawing, Fig, 1 is a diagrammatic view of a fluorescent tube or lamp equipped with a base or terminal structure embodying my invention,

this base structure being partly broken away and in section, and suitable circuit connections being diagrammatically illustrated.

Fig. 2 is a tilted inside or rear view of the starter-equipped base shown in Fig. 1 with part of its skirt or shell broken away, and with a diagrammatic showing of certain circuit connections.

Fig. 3 is a fragmentary tilted or perspective view, partly sectional, showing one end of a lamp tube with the parts of an associated base, and illustrating a stage in the basing of the lamp according to my invention.

The drawing shows an ordinary fluorescent lamp L (of positive column electric discharge type) with a tubular envelope in having the spaced-apart, activated thermionic cathodes ll, 12 in its ends, which may be specially heated cathodes of usual coiled filament type, and are shown connected through bipost lamp base or terminal structures B, C across a power supply circuit P including the usual ballast H, which also serves as a starting inductance, and the manual make-and-break switch IS. The envelope it] may contain a low-pressure atmosphere of starting gas. such as argon at a pressure of 2 to 5 mm. of mercury, and also a vaporizable and ionizable working substance such as mercury. A supply of mercury, which may exceed the amount that will vaporize during operation of the lamp L, is indicated by a drop ll inside the envelope In, and an internal coating of fluorescent material or phosphor ii on the envelope walls is also indicated. A starting and electrode-heating circuit H is shown connected across the circuit P through the contact terminal biposts I9 01 the bases or terminal structures B, C, the filamentary cathodes I I, I2 which may be connected between these biposts, and the starter S which is interposed between one of the biposts and the filament II. A capacitor or condenser K of suitable capacity (e. g., 0.006 microfarad) may be connected across the switch S, to minimize radio interference as well as arcing when the switch S opens and breaks the circuit H, and to assist in starting.

The general mode of operation in starting the lamp L with this circuit arrangement is that when the switch I5 is closed to turn on the lamp L, the switch device S permits flow of current through the circuit H and the cathode filaments ll, l2 in series therein for a sufficient length of time to preheat the cathodes to an adequate emissive temperature, and then suddenly opens the circuit H; and the resulting voltage kick between the cathodes ll, I2 sufiices to initiate discharge between them-or, in other Words, starts the lamp.-

As illustrated, the starter-equipped terminal or base structure B of the lamp L comprises as its main structural element (Figs. 2 and 3) a transverse insulative wall, web, or disc 20 through which the hollow bipost contacts I 9, I! are riveted, and which serves as a base for the starter switch S, mounted at the inner side of the disc next to the lamp envelope in. In the particular lamp L here illustrated, the end wall of the tubular envelope I0 does not involve the disc or web 20, but is formed by the usual glass stern and flare 2| sealed into the end of the envelope 10. Besides the web or disc 20, the base B comprises a deep sheet metal shell or skirt 22 attached to the disc. As shown, the shell or skirt 22 has one end or margin internally shouldered at 23 and crimped around the edge of the disc 20 at 24, and has its other end secured around the end of the glass envelope ID by cement 25. The central portion of the disc 20 is augmented in thickness or reinforced at its inner side, as by means of a double-ply disc 26 riveted to the disc 20 by means of the biposts l9, 19. The other base structure C may be similarly constructed, but not so deep. As thus far described, these bases B, C resemble those already in use, though the base B is considerably deeper than usual.

As shown in Fig. 2, the starter switch S is of thermal type, comprising a thermostatic strip member 30 which extends parallel to the disc 20 closely adjacent its inner side and may be heated by a resistance heater 3|, here shown as consisting of fine wire coiled around the member 30 over an insulative covering or wrapping 32 of suitably refractory material, such as asbestos paper. At

one end, adjacent the heater 3| the thermostat 30 is fixedly anchored by being welded to a supporting stud 33 upstanding from the disc 20. This stud 33 may consist of one end of a U-bent wire inserted from the other (outer) side of the disc through suitably spaced holes therein, and secured by bending its end 34 down on the inner side of the disc. The thermostatic member is connected by a wire lead to a hollow rivet or eyelet 36 that is riveted through the disc 20. As shown in Fig. 2, the free end portion of the thermostatic strip 3|] is bent back at 31 in an arc of 180 so as to extend toward its anchored end at 33. Upstanding from the disc 28 at a suitable position is a fixed switch contact stud 38 which coacts with a movable switch contact 39 afforded or carried by the free end of the member 30. As here shown, the switch cont-acts 38 and 39 consist of (silver) wires extending at right angles to one another and welded or soldered into one of the hollow biposts l9 and to the free end of the thermostat 39, respectively-the wire 39 considerably extending the retroverted end of the bar 3|] toward its anchorage at 33. The retroversion of the bar at 31 largely compensates for the general rise of temperature inside the base B due to the heater 3| and to the operation of the lamp L and the heating of the cathode II, and is also helpful in other respects, as explained hereinafter. To the other bipost I9 is soldered or connected one end of the heater coil 3|, and the other end of this coil is welded or connected to a hollow rivet or eyelet riveted through the disc 20.

The matter of ambient temperature compensation by the J-bentthermostat strip 30 is of particular importance in the case of a starter S intimately incorporated in the lamp structure. This is because of the wide range of fluctuation of ambient temperature inside the base B, as between the condition when the lamp L has not been in operation for an hour or more and the condition when the lamp L has just been switched off after operating for some time and becoming thoroughly heated up above atmospheric temperature by the discharge and the heating of the cathode II close to the thermostat 38. As the ambient temperature variations in the base B affect the-whole thermo-responsive length of the member 38 alike, the unbending flexure of the retroverted portion at 31 with rising ambient temperature throws the shorter J-arm with its extension 39 forward toward the contact stud 38, thus acting to offset the bodliy backward motion of the portion 31 away from the contact 38 due to the concomitant bending back of the longer arm of the strip 38, and tending to maintain contact at 39, 38. A similar but reverse action occurs with falling ambient temperature inside the base B. On the other hand, the local heating of the longer arm of the thermostat strip 38 adjacent its anchorage at 33 by the surrounding heater 3| substantially without directly heating the retroversion 31, bends this portion of the strip 30 backward and so shifts the whole free portion of the J-bent strip 3|] (including its extension 39) away from contact 38, thereby breaking contact at 39, 38. A similar but reverse action occurs when the circuit H is opened and heater 3| and the portion of member 3|! within it cool ofi".

The lead Wires 4|, 4| to the cathode coil H are soldered into the hollow rivets or eyelets 36, 40, thus connectingthis coilinto acircuit of the base B and lamp Lthat may be traced from circuit H and one bipost l9 through the switch contacts 38, 39, the thermostat 39, lead 35, rivet 36, one lead 4|, coil other lead 4|, rivet 49, heater coil 3|, to the other bipost I9 and circuit P. The condenser K is shown with its leads 42, 42 connected to the bipost I9 that carries the fixed switch contact 38 and to the wire 33 that supports the thermostatic member 30, and as located to one side of the switch S, being thin enough not to project above the upper edge of the member 38 and its heater 3 I.

Basing cement commonly used for attaching bases B, C to the ends of the lamp envelope ID as indicated at 25 in Figs. 1 and 2 requires a considerable degree of heat to cure or harden it properly after application. This temperature, however, would be liable to affect unfavorably some of the parts of the switch mechanism S, and especially the condenser K, which usually comprises sealing and insulating compounds that might be fused by the curing heat, with the result of virtually destroying the condenser. To overcome this difliculty, I do not fabricate the complete base .3 by union of disc 20 and shell 22 as usual, but instead make them up and keep them on hand as separate parts: the disc 29 with the biposts |9, |9, the switch mechanism S, and the condenser K mounted and fully connected thereon; and the shell 22 with the shoulder 23 formed therein, but without the edge crimping 24. After completion of the lamp L in other respects, I cement the still uncrimped shell 22 on one end of the envelope ID, as shown at the left of Fig. 3, and then add the disc 28 and attach it to the shell. To do this, I-may simply place the disc 20 with its attached parts in the end of the shell 2| on the shoulder 23, inserting the cathode leads 4|, 4| through the disc rivets or eyelets 36, 49; crimp over the shell edge 24 as shown at the right of Fig. 3, as by working'around the shell with any suitable'means; and solder the lead wires 4|, 4| into the eyelets (this is done from the outer side of the disc) and cut oil the ends of these wires.

The operation of the switch S will be readily understood from the foregoing description, but may be briefly outlined. When the switch I5 is open and the whole system is deenergized and has cooled off to ambient temperature, the switch S is closed, with the contacts 39,38 resiliently pressed together by the springy bimet'al 30, and the starting circuit H and the cathodes I, I2 are connected across the discharge circuit P, ready to be energized by closure of the switch l5. When this happens, current flows through the circuits P and H, the switch S, and the cathodes I I, I2 in series, heating the cathodes. At the same time, current flows through the heater 3| of the thermostat 39. which is connected in circuit in series with the contacts 38, 39, gradually heating th heater 3| and the thermostat 38. The transmission of heat to the resilient thermostatic member30 is slowed by the thermoinsulation 32, which also increases the thermal capacity of the thermostat. As the bimetallic member 38 gradually heats up, it bends backward, Fig. 2, away from the fixed contact 38, and the contact 39 pulls away from the contact 38 and opens the circuit H through one of the biposts I9, while leaving the circuit P energized through the other bipost l9 and the heater 3| to the cathodes I I, I2. The voltage kick consequent on breaking the circuit starts the discharge between the cathodes. The discharge current now flows through heater 3|, and the thermostat 30 is thus kept flexed to hold the switch S open as long as the circuit P remains energized. When the circuit P is de-energized as by opening the switch I5, the heater 3| and the thermostats 30 cool off and the switch S closes, ready for a repetition of the starting cycle as described.

Certain features of the switch S which have only been glanced at heretofore ar of considerable importance in its operation. It has been usual, heretofore, to provide thermal starting switches with condensers of about 0.05 microfarad capacity-about eight times the 0.006 microfarad capacity of a condenser K such as there is room for in the base B alongside the switch S--in order to delay the opening of the switch on a hot restart of the lamp L (when it is turned oil? and then at once turned on again), to give time for proper reheating of the cathodes ll, [2. This is needful because the cathodes ll, l2 cool off far more quickly than does the switch S, when the current to the lamp is shut off. A condenser of 0.05 microfarad produces adequate delay by causing a minute spot-weld between the contacts 38, 39 when it discharges through them as they come together on the turning off of the current; but a condenser of only 0.006 microfarad produces such a very minute weld that the reopening of the switch S follows almost instantly when the current is turned on again quick1ybefore the cathodes H, I! have time to reheat properly. In my switch S, the inadequacy of the very small condenser K in this respect is compensated for (in part, at least) by thermal inertia due to the thermal insulation 42; the heat developed in the winding 3i is transmitted but slowly through the asbestos 32 to the bimetal 30, giving time for reheating the cathodes II, I! before the switch S reopens. Any delay in the separation of the contacts 38, 39 when the member 30 heats that is produced by its retroversion at 31 (as already mentioned) also tends to compensate for the small capacity of the condenser K.

For the convenience of those desiring to use my invention, I give illustrative particulars of a switch S suitable for a 40 watt fluorescent lamp he usual positive column discharge type, op-

g with a discharge current of some 0.42 ampere and with a cathode preheat current of some 0.42 to 0.65 ampere, and having a tube ill inch internal diameter. Assuming a base- Ol 1 2 disc 20 of 1% inch diameter as usual, the anchorage stud 33 may be spaced about 12 to 13 mm. on centers from the contact stud 38 mounted in the bipost I9, and may be located nearly /4 iii-ch from the other bipost IS, on centers. The thermostat member or bar 30 may consist of a strip of the bimetal commercially known as Chace #2400 Bimetal, composed of laminae of invar, an alloy 01' 64 per cent iron and 36 per cent nickel, and of chrome iron, an alloy of 75 per cent iron, 22 per cent nickel, and 3 per cent chromium, in equal thicknesses, welded together; it may be 0.004 inch thick, /8 inch wide, and 20 mm. long before bending. Its dimension from the anchorage 33 to the bottom of the 180 bend at 31 may be 16 mm., and the radius of this bend 31 may be 0.95 mm. The contacts 38 and 33 may be of 25 mil coin silver wire. and the overall length of the contact 39 may be about '7 mm, with about 1 /2 mm. of its length overlapping the end of the member 30 at the weld between them. The heater 3! may be constructed to have a cold resistance of 6 ohms, and may be made of 8 2 turns (plus straight lead ends) of heating resistance wire such as hereinafter indicated, wound '75 turns per inch around an asbestos-paper wrapping 32 on a /8 inch mandrel and then removed from the mandrel, flattened sufficiently, and then slipped on the bar 30. The wire for this heater 3i may consist of about 3% to 4 inches of 6 mil heating resistance wire such as is known commercially as "Nichrome V," which is an alloy of per cent nickel, 12 per cent iron, 11 per cent chromium, and 2 per cent manganese. The condenser K may have a capacity of about 0.006 microfarad, and may be about inch long, /2 inch wide, and 1; inch thick, or slightly more.

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

1. A base or terminal structure for an electric discharge device having therein a discharge electrode, said structure comprising a disc provided with contact terminals exposed at one side of the disc, switch means comprising a contact and a flexible bimetallic strip anchored by one end at the other side of said disc and exposed to the ambient temperature there, and having its free end retroverted and extending back toward the anchored end for coacting with said contact, said strip being arranged to flex toward said contact at its retroversion with rising temperature there while flexing away from said contact adjacent its anchorage with rising temperature there, an electric heater for locally heating said bimetallic strip adlacent its anchorage substantially without directly heating its retroversion, and means for connecting said switch means, said electrode, and said heater in circuit between said contact terminals.

2. A base or terminal structure for an electric discharge device having therein a discharge electrode comprising electric heating means, said structure comprising a disc provided with contact terminals exposed at one side of the disc, switch means comprising a flexible J-bent bimetallic thermostat strip anchored at the other side of the disc by its longer arm, a contact on said disc at the side of the shorter strip arm remote from the longer arm, said strip being arranged to flex outward toward said contact at its retroversion with rising temperature there while flexing away from said contact adjacent its anchorage with rising temperature there, an electric heater for locally heating the longer thermostat strip arm adjacent its anchorage substantially without directly heating the retroversion of the strip, and means for connecting said switch means, said electrode heating means, and said thermostat heater in circuit between said contact terminals.

R'ICHARD N. THAYER.

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