US2432488A - Glow starter for electric discharge devices - Google Patents

Description

9 1947' A. L. PEACOCK ETAL 2,432,488

snow STARTER gar; wacwnzc mscmmea DEVICES filed March 27, 1944 \a V Pi 4: P-

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Amvow L. PEACOCK I CHARLES Lear/m JnvczA/R ATTORNEY Patented Dec. 9, 1947 s PATENT OFFICE GLOW STARTER FoaELEc'rmo DISCHARGE DEVICES .Arnold L. Peacock and Charles Lester Sinclair, 9 Danvers, Mass., assignors to Sylvania Electric Products Inc., 'Salem. Mass, a corporation of Massachusetts Application March 27, 1944, Serial No. 528,306 3 Claims. (01. zoo-113.5)

'This invention relates to an automatic time interval switch of the type commonly termed a glow switch and used in connection with the starting equipment for gaseous discharge'lamps. It may, however, be used in connection with other; devices requiring a measured time interval in their cycle of operation.

The invention relates particularly to the construction and operation of the contacting elements of the switch. Much difficulty has heretofore been experienced in producing a switch of the type suggested whichis positive in action and accurate in timing and which will maintain its efliciency for an extended period of time.

It is an important object of the invention tov produce a switch of the type indicated which overcomes the above-stated difliculties.

A further advantage of the invention'resides in its ability to provide fast and'positive action coupled with extreme simplicity of structure.

A further object of the invention is to provide a switch capable of effecting a closed circuit interval of substantially long and accurately g measured duratiom A further object of the invention is to provide a switchin which a single unitary moving element. opens and closes its contacts. v

Still another object of the invention is to provide a switch having resilient rapid action make and break contact elements which function with an efllcient wiping action at their contact areas thereby maintaining them automatically in effective working condition.

Afurther object of the invention is to provide a thermally operated switch in which at least one of its contact members has inherently in- 'corporated therein means operable upon a change in temperature/to cause a snap action change or distortion of its position thereby to establish or interrupt electrical contact therebetween.

' An upward extension of one of the lead wires serves as a "fixed switch conta'ct' member while the other lead wire has secured thereto a bimetallic member divided lnto at least two' 1on-.

gitudinally extending temperature responsive strips connected together at their end portions. Each stripis curved lengthwise, the curvature of one differing a' calculated amount fromthat of the other. The variance in the curvature in the strips results in accurately controlled fast acting snap-over movement of the contact element into closed or'open circuitposition when its temperaaure passes through certain critical,

temperature ranges.

To present a better understanding of preferred embodiment of the invention;

Figure 2 is a side elevation of the contacting elements ofth switch showing their open circuit position in full lines and their closed cir= cuit position in dotted lines;

Figure 3 is a diagrammatic view illustrating manner in which the switch an example of the is used; Figure 4 is the bimetallic member; Figures5 and 6 are diagrammatic illustrations of different phases in the operation of the switch.

The principles of the invention are shown as v ment of the member l8 tends to move the ele- Otherpbjects and features ofthe invention will appear more fully in the following specification taken in connection with the accompanying drawings and will b'e particularly pointed out in the claims.

The active elements of the switch are enclosed in an evacuated envelope having an ionizable atmosphere. The active elements act both as electrodesand as current carrying contact members. The contact members are providedwith lead wires passing through the envelope and connecting them inseries with the filaments of a hot cathode gaseous discharge lamp-which'in turn is connected to a supply of electric current.

ment i5 away from the contact ll. One of the functions of the element I8 is to compensate for excessive movement of the member 15 during the process of sealing the stem l4 in its correct position in the envelope l2. At this time a relatively high degree of heat must be applied to effect the seal btweenthe body of the envelope and the stem. In so doing the element I5 is strongly affected and bent an excessive amount in the direction of the contact Ii. This excessive movement of the member i5 would tend to bend the member I I so far from its normal position that it might assume a permanent set out of its proper alignment. However, the element the invention particular embodiments thereof will be described in connection with the accompanying A drawings in which: v

Figure 1 is a general view in perspective of a' an illustrationof anotheriorm ofi8 partially neutralizes this excessive movement thereby'preventlns permanent distortiono: the

By correctly proportioning the strips and forming.

them to the correct curvature, the element l when raised to a predetermined critical temperature is caused to move with a snap action which results in closing the circuit'to the lamp filaments.

After a measured interval of time the bimetal coolsto a lower critical temperature at which time it snaps back to its initial position.

Upon the application of h at to the member I5 the strips l6 and i1 enlar their radius of curvature and approach a flat p e. Since the strip It has a longer peripheral ength than the strip i! it increases in length ore rapidlyas they both become flatter. Inasmu has their ends are rigidly tied. together a stress accumulates in the bimetal member as its temperature increases and when the critical predetermined temperatureis approached the strips start to assume a reverse curve at which time the accumulated stress therein is released and acts rapidly to produce a pronounced reverse curvature in the bimetal which causes the sudden and firm engagement of the contact shoe on the. member IS with the contact element ll. thus-closing the circuit.

1 After the heating means is cut ofl in a manner to be described hereinafter, the element i5 cools,

the forming of the strips l6 and i! may be accomplished by stamping a small indentation 22 in one of the strips thereby lengthening its pefrom a supply line 28. The lamp is provided with a pair of electron emitting filaments 28 and 21 at the ends thereof. The glow switch as described is connected in series with the illaments'in a manner to'control flow of current from the line 25 thereto.

The contact elements ill and II are enclosed in an evacuated envelope l2 containing an ionlzable atmosphere. The contact member i-I may desirably be rigidly connected to or integral with its lead wire l3 which projects through and is sealed in the envelope 12 at the stem I4 thereof.

. The contact ii is made of 'a rod of any suitable electrically conductive material and is slightl resilient at its upper unsupported end.

The other contacting member ID is composed .chiefiy of a bimetallic element l5 which is divided into at least two relatively narrow temperature or otherwise secured to a supporting and compenripheral length the required amount. The varlancein curvature between the strips i6 and 11' may also be obtained by a die forming operation without forming the indentation 22. A bimetal element formed in this manner is shown in Figure 4. e

It has been determined that when the switch is employed ina circuit containing 'a' capacitive characteristic, as is sometimes thecase when it is desired to reduce stroboscopic effects in a two lamp fixture, that there is an excessive delay in opening the circuit after the lamp filaments have reached their proper electron emitting ,temperature. To overcome this undesirable delay a plate or flag 24 is secured by welding or otherwise to the. element ii at a position opposite to the element i 8. This construction provides the required alteration in the circuit characteristics to'insure that the cycle of operation of the switch will be equivalent to that of a starting switch connected to the lamp having an inductive circuit. a

As herein suggested an important use of the switch described is in the operating circuit of a fluorescent lighting unit. Such a circuit is illustrated diagrammatically in Figure 3 of the draw-' ings in which a hot cathode gaseous discharge type lamp 24 'is supplied with alternating current sating element l8 which in turn is rigidly secured to the lead-in and supporting wire l9 extending to. the external circuit. The complete contact member in is thus rigidly supported at itsbottom and free to move at its upper end when a change of temperatureoccursin the bimetal.

The strips i6 and I! are slightly laterallyseparated to provide free and independent movement thereof. Acontact shoe 2i is secured to the upper portion of the bimetal member i5 in position to engage the contact member I I. The shoe 2i may desirably be made of Nichrome wirewelded to the bimetal.- It has been found that Nichrome metal functions with a high degree of efiiciency since its peculiar property of relatively high electrical resistance reduces the tendency to spark when the, switch opens or closes its circuit.

In the form of the invention shown in Figures 1', 2 and 3 the strips" i6 and ilare curved convexly from the contact member ll, one of the strips having a greater radius of curvature than the other or at least having a shorter peripheral length than the other. As shown in the drawings the strip l 8 presents a flatter curvature than the. strip l1 and is consequently less in peripheral length.

To operatethe lamp a line switch 29 is closed which applies line potential between the contacting members in and ii of the glow switch which starts a glow discharge between. them. The heat v measured time interval it snaps into open circuit position and finally'assumes its initial position. The time intervalis adjusted to provide suflicient time to permit the filaments to attain their necessary electron emission temperature.

In connection with the operation of the device there are certain vital factors'in the construction a y and operation of the compensator which shouldreceive particular attention. In this connection a further function of the compensator l8 will be set forth as above suggested. In following the 7 opening and closing cycles of. the contact members as the bimetal i6 heats up due to the glow discharge its curvature starts to straighten out thus trate its action. Itis apparent aaaa'eae moving'its contact shoe 2| toward the contact member llbeforethecriticaltemperature of approximate 150 C..is reached'atwhich timerapid snap overmovement of the shoe}! occurs. It is during this warming up period thatthe compensator plate 18 exerts itscontrolling function. The reactive movement of the element I8 upona rise in temperature being opposite to that of the member l5-causes the contact shoe 2! to move away. from the contact member. The resultin .movement of the combined action of the two 'bimetal elements causes the contact shoe 2| to remain substantially stationary until the snap over movement of the member l5 takes place, at which time the bimetal assumes a reversed curvature. In this manner, excessive movement of the contact element and consequent premature closing of the contacts is .prevented. matic illustration of .A diagramthe position of the elements at the instantbefore snap over occurs is shown 2 in Figured. In this figure the distortion of the member i8 is shown exaggerated to better illusthat the action described constitutes a highly efficient. circuit closing operation because matically prevents premature'engagement of the. contacts. By premature is meant engagement-of the contacts due to the slow movementof the upper end of the bimetal l6, occasioned by its rise in temperature and not due -to snap. action. Such slow motion if and when it results in contact would be a relatively poor contact, since at the instant of engagement the pressure of the coritact would be extremely light and probably have Q a momentary high resistance. These char-- acteristics are undesirable and are overcome by the action of the compensator'element which prevent engagement until snapover occurs.

After makingcontact the glow discharge discontinues and the contact It is at this time that the contacts must remain a closed for a measured period of time during which tact shoe 2| firmly 'til snap over occurs.

open the circuit.

the filaments heat up to their electron emission temperature. This measured period ends when the bimetal l5 cools to a predetermined temperature at which time it snaps into opencircuit position. During this preliminary cooling oflyperiod the compensator functions to provide maximum efliciency in maintaining consistently'accurate timing of the internal andrapid and positive opening of the circuit. As soon as the bi- .metal l5 starts to cool, its reversed curvature begins to straighten out, thus tending to move away from the fixed contact II and prematurely However, the compensator also starts to cool and in so doing tends to move the contacts into firmer engagement thus overcoming their tendency to separate as shown diagrammatically in Figure 6. The compensatin action of the member ID is aided by reason of the fact'that it tends to cool faster thanthe element [5 not only because it 'is of smaller area but because it is secured'to the supporting lead wire 19 which carries away the heat by direct conduction. This Figure 6 illustrates ina somewhat exaggerated manner the position of the elements just prior to the instant when the bimetal l5 snaps into open circuit position. The compensating bimetal [8 has assumed a curvature toward thecontact ll thus holding the conin-closed circuit position un- The compensator thus controls the action of the switch rendering its function accurate and reliable over a long period .of time;

The snap the compensator autoelements start to cool. 40

. over action providing fast and positive-make and break operation of the switch and moreover such snap action causes the contact areas to engage with substantial pressure at the instant of can tact and right up to the instant of separation. Such firm contact also causes a slight degree of wiping action between the contacting areas on the two contact members I0 and II. This wiping action arises from the fact that not only is 10 the member l5 inherently resilient but the contact member II is also resilient. -When snap over occurs, therefore, the contactshave a slight relative movement which acts to keep the en gaging areas clean, thereby maintaining a desirable low resistance between the switch contacts. Among the other important beneflts resulting from "the manufacture of.--.-switches of the'type herein presented having e compensator laincorporated .in their simm iiS the fact that switches so made possessconsistent and reliable operating characteristicswhicl r" are not as dim- 'cult to maintain when they are manufactured switches not having the In the manufacture compensation.

relative 3 with or without the compensator element. x The stem portion ll of the envelope I2 desirtype and the exhausting op- I bly is of'the wafer .eration is performed through an exhaust tube- It is also desirable at the top of the envelope.

that the stem M be dished slightly as shown in of switches having the compensator it is important to determine the r sizes of the bimetal members l5 and II toproduce a predetermined time interval. Once. I

the proper ratio and mainvention, however, apply equally well to switches Figure 2 with its concave surface facing toward the switch elements. Furthermore, it is desirable\that theestabllshing oi the discharge between the elements ill and H be facilitated to insure that the arc discharge will not fail to start even when the exciting voltage is at a minimum. To aid in starting the discharge a layer of an especially prepared material is coated uponthe central area of the inner face of the stem.

o A suitable coating material has been found to havethe following ingredients.

. Parts by weight Aluminum 1 Zinc Magnesium Thesematerials if available in commercial Y powder form should be further reduced in particle size by at least ninety-six hours treatment in alcohol in a ball mill. A suitable vehicle is added on to provide the necessary binding for the particles and insure their adherence to the envelope.

What we claim is: 1. An automatic interval timing thermal switch comprising .an envelope having an ionizable atmosphere therein,

envelope, one of said contact members being an active thermally actuated bimetallic member di vided into two sections of unsymmetrical curvature adjusted to cause the member to snap closed circuit and open circuit positions at predetermined temperatures, a support for said active bimetallic member, a bimetallic compensator element secured at one end to said support and at its opposite en to said bimetallic snap action member, said c pensator having a reverse thera pair of contacts in said into mal reaction acting to prevent premature closing of the contacts before snap .over occurs and to maintain firm engagement of the contacts prior to the open circuiting snap over action'thereof, Y

and lead wires connecting said contact members to an external circuit. 1

2. An automatic interval timing switch for starting gaseous discharge lamps comprising an envelope having an ionizable atmosphere therein, a pair of contact members in said envelope one of which is thermally actuated to close the contacts and the other is fixed, lead wires connected to said contact members and extending out of said envelope, said thermally actuated contact member having a fixed supporting base portion ripheral length than the and a bimetallic moving element fixed at one end to said support, said moving element being divided into two sections rigidly secured together at'their ends, said sections being formed in a curve departing from a common plane and presenting different degrees of curvature and having equal chordal lengths whereby when the temperature of said bimetallic member is raised to a predetermined degree it unsupported end will snap into closed circuit position'engaging said fixed contact member and an auxiliary compensating' bimetal member operably connected to said movable bimetal member and acting to prevent premature engagement and disengagement of the contacts prior to the instant of their snap over action.

3. An automatic interval timing thermal switch comprising an envelope having an ionizable atmosphere therein, a movable and a fixed contact in said envelopeeach having a lead wire extending out of said envelope, a main bimetalelement divided into two temperature respon sive strips each strip being curved convexly from a common plane one strip being ofshorter peother but of substantially equal chordal length, an auxiliary compensator member of bimetal operatively connected to said main bimetal and having a reverse thermal reaction, said auxiliary bimetal member acting to prevent premature engagement and disengagement of said contacts, and a metallic -plate of substantial area secured to said fixed contact member in generally parallel relation to said bimetallic element.

ARNOLD L. PEACOCK. c. LESTER SINCLAIR.

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

' UNITED STATES PATENTS

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