US2433753A - Electric switch - Google Patents

Description

Dec."30, 1947.1 F. P.'GAssER ELECTRIC SWITCH Filed Oct. 7, 1942 .Q f 55.1. o

HL2-95m i l 52 ATToQ/vfy Patented Dec. 30, 1947 ELECTRIC SWITCH Frank P. Gasser, Beverly Farms, Mass., assignor to Harry M. Burt and Guy II. Burt, doing business as The Lloyd Products Company, Providence, R. I.

Application October 7, 1942, Serial No. 461,098

4 Claims.

This invention relates to electric switches of the type which provide a low impedance path when a high potential is applied thereto, automatically change the low impedance path to a high impedance path after a short time lag, and effectively maintain such high impedance path if the applied potential is lowered.

More particularly, the invention is concerned with an improved starting switch adapted to be used with an electric discharge lamp of the type having at least one thermionic electrode which must be heated to an electron emissive temperature before discharge can be initiated in the lamp. The switch connects the lamp electrodes in series.

At the present time, starters for such electric discharge lamps are of two types; the rst having a pair of normally spaced contacts, and the second a pair of normally closed contacts.

Switches of the rst class have at least one contact mounted on a thermal responsive element and are provided with electrically energizable thermal emissive means connected in parallel with the contacts. The thermal emissive means is of such nature that when potential is applied to an unlit lamp, the heat generated by said means will raise the temperature of the thermal responsive element and cause the contacts to move into engagement. Since the switch connects the lamp electrodes in series, closing of the contacts provides a low impedance path between said electrodes and passes a high current through the same, causing the thermionic electrode to be heated to the desired temperature. Engagement of the contacts also bypasses the current which energizes the thermal emissive means, allowing the thermal responsive element to cool off, so that shortly after closing of the contacts they will reopen. If the lamp starts upon reopening of the contacts, its low running impedance so reduces the potential applied to the thermal emissive means that insufilcient heat is generated thereby to again close the contacts. If, however, the lamp does not start, its high idle impedance reduces the current flow and allows a high enough potentialv to again be applied to the thermal emissive means to create sufficient heat to close the contact for a Second time. This second closing and subsequent reopening of the contacts (upon shunting of the thermal emissive means) is known as recycling, and is essential because on occasion, the lamp will fail to start upon the rst starting try, i. e., when the contacts are rst reopened. This failure to start may be due to a variety of causes, such for example, as opening of the contacts at a moment when the potential (Cl. 20G-122) of switches is that, since the switches employ normally spaced contacts, arcing occurs both when the contacts approach and recede from each other before and after engagement. The two arcings cause the starting switch to have a very short life. Also due to the normally spaced position of the contacts and resultant multiple arcings, contact resistance increases rapidly and raises the resistance of the low impedance path through the switch thus lowering the temperature to which the thermionic electrodes are raised. Another detrimental feature of these switches is that recycling is performed on the same contacts as those used fcr'making the rst starting try.

Switches of the second class have-at least one of their contacts mounted on a thermally responsive element and are provided with electrically energizable thermal emissive means in series with the contacts and disposed in the main supply circuit for the discharge lamp. When potential is rst applied, the closed contacts provide a low impedance path between the thermionic electrodes and allow a heating current-l to lilow therethrough. This same current flows through the thermal emissive means and, after a predetermined time, generates sufcient heat to actuate the thermal responsive element and separate the contacts. If the lamp does not light when the contacts are separated, the thermal responsive element cools off, since 'the opening ofthe contacts breaks the series circuit, and recycling occurs. On the other hand, if the lamp does start, suilcient current passes through the thermal emissive means to keep the contacts open. Switches of this latter class, like switches of the first class, recycle on the same pair of contacts as those employed to make the first starting eiort and are thus subject to considerable wear which appreciably shortens their lives. These switches avoid the initial movement of the contacts towards each other and arcing arising from such movement. However, they only avoid this defect by employing four terminals, two for the contacts and two for the thermal responsive element in contrast with the two terminals employed in switches of the rst class. Thus, the gain in longevity of the switch is made at the expense of a more complicated starting circuit and additional switch parts.

It is the primary object of the present invention to provide an improved switch of the character described which incorporates al1 the desirable features ofthe Vabove described types of switches, but avoids theV inherent defects thereof.

More particularly it is an object' of my invention to provide a switch of the character described in which different pairs of contacts are used for the rst starting try and for recycling` A more specic object of my invention is to provide a switch of the character .described-in which a single contact cooperates' with a pair of electrically connected contacts, with one of which it causes an initial starting attempt to be made, and with the other of which it. causes subsequent starting attempts to be made,

An ancillary object of my invention is to provide a switch of the character described in which the vcontact resistanceA iskept.; low, arcing between contacts lessened, andthe escape of fumes upon' separation of the contacts; minimized.` Y

Another object of my inventionistogprovide a switch ofthe character described which employs only two terminals, includesy relatively few and simple parts, is easily fabricated, durable, and in general highlyeflicientin use'.

Otherobjects of this invention will in part be obviousand in partghereinafter pointed out.

The invention accordinglylconsists in' the featuresfof construction, combinations of' elements, and arrangement of Darts which will be exemplilied` in the construction hereinafter described.'

andof which the scope of application will be indicated in the claims. 1

In the accompanying drawings,v in which is shown one of. the various possible embodiments of thisY invention,

Fig.. 1.'i`s a schematic circuit diagram for a fluorescent electric discharge lamp, the starter switch embodying my invention being illustrated inA perspective; l

Fig. 2 isa side elevational View ofsaid` switch showing the contacts in their initial starting position; and

Figs. 3' and 4 are similar fragmentary views thereof showing the contacts in running and recycling vpositions respectively.

Referring now to the` drawings, and more particu-.larly to Figs. 1-4, I have there shown a fluorescent electric discharge tube I of the standard type comprising. an elongate-dy pellucid vitreousy envelope I2 which is internally coated withv suitable phosphore. The 'tube ends are sealedl ofi and the tube iilledwith a gaseousv ionizable medium at a proper pressure. Two spaced lamentary electrodes I4 are enclosed within the tube. `These electrodesY may be fashioned from or coated with material which when raised to an elevated temperature at or approaching incandes'cence will emit electrons.

A. suitable supply of electric energy, such as an alternating' current source,v is. connected' to an end' of each' electrode l4 throughIlead-in wires t6, Il', one of which has "the usual manually operat'ed'switch 20, and the usual ballast coil 22 series-connected therein. The other ends of the electrodesare connected by leads 24, 26- to a l starting switch 28 constructed in accordance with my invention.

Said starting switchcomprises a base disc 30 oi insulating material from which electrically conductive terminals 32, 34 project, the same being adapted to be detachably received in a customary starting socket (not shown). A tubular shell 36 cooperates with the base 30 to enclose the operative elements of the switch.

A conductor wire 38 connected to the terminal 32 projects upwardly from the base 36. A similarly' disposed conductor Wire 46 is connected to the terminal 34. Said two wires have angularly disposed portions 42, 44 received in aperatures in a partition 46 of insulating material whereby to support said partition vertically within the shell 36. Extensions 48, 50 of the conductor wires 38, 46 onthe other side of the partition 46 lead to a condenser 52.

An elongated bimetallic strip 54 is disposed on v the side of the partition opposite the condenser 52` and is held in substantially vertical position by means of a supporting wire 56 welded to the lower end ofthe strip and secured to said partition. The upper end of the bimetallic strip 54 is free and has welded thereto a cylindrical metallic contact 58 which projects laterally from said strip'. The strip 54 is so fashioned that when heated it will move the contact 58 away from the partition 461 Potential is applied to the bimetallicstrip 54 from the terminal 32 and conductor wire. 38 through a low impedance resistor 60 which may take the formV of a short helix of small diameter andlarge pitch. Said helix is disposed immediately adjacent said bimetallic strip near its point of cantilever support on the wire 56.

A second bimetallic strip 62 is connected to the conductor wire 40 by means of a lead wire 64 which retraverses the partition 46 to provide a rm support for said second strip. Saidr second strip is disposed horizontally and transversely of the rst bimetallic strip 54, and is so fashioned that when heat is applied thereto, the free end of the second strip 52 will move away from the partition 46. As is well known, this construction enables the switch to operate uniformly regardless of the room temperature.

The free ends of the two bimetallic strips are disposed in close proximity. The free end of the horizontal strip 62 has welded thereon a U-shaped metallic member 66 including a base 68 which interconnects two vertically disposed, spaced contact legs 10, 'l2 which lie substantially in a. vertical plane perpendicular to the partition 46. Said metallic contact legs 70, I2 are so disposed as to lie in the path of travel of the contact member 58 when the latter` is actuated by movement of Ithe bimetallic strip 54 upon the variation in temperature of the latter relative to the temperature of the second strip 62. Furthermore, the two bimetallic strips and the various contact elements4 58, lI0, I2 are so constructed and arrangedl that when the strips are at the same temperature the contact element 58 will be pressed by the rst strip 54 against the contact element 16 as shown in Fig. 2.

A high impedance resistor 'I4 is connected by wires 16, 18 across the terminals 32, 34, and is thus electrically disposed in parallel with the contacts 58, 10, T2. Said resistor is physically disposed above the low impedance resistor 60 and adjacent the rst strip 54.

In the operation of a fluorescent tube I2 employing a switch 28 embodying my invention, the hand operated switch 20 is first closed. This allows current to flow through the ballast reactor 22, one of the lamentary electrodes I4, the low impedance path through the switch 28, and the other nlamentary electrode I4. Said low impedance path between the terminals 32, 34 includes, in series connection, the conductor wire 38, low impedance resistor B0, bimetallic strip 54, contact element 58, contact element 10, base 68, contact element 12, strip 62, lead wire 64, and conductor wire 40. The resistance offered by this low impedance path is so small that a high current will pass through the lamentary electrodes I4, thereby raising said electrodes to an electron emissive temperature. While the temperature of the electrodes is being thus elevated the heavy current traversing the low impedance resistor 80 generates heat which is applied to the bimetallic strip 54 near its cantilever mounting. Said strip 54 and resistor 68 are so relatively proportioned and arranged that after a short period of a few seconds, during which the filamentary electrodes I4 will have had suflicient time to be raised to electron emissive temperature, the strip 54 will move its contact element 58 away from the contact leg 10. When this occurs the surge potential induced by the ballast reactor 22 will be applied across the electrodes I4 in an attempt to strike a discharge therebetween.

If the discharge occurs, the impedance of the tube I0 is suddenly reduced from the high impedance offered by the non-ionized gaseous medium to the low impedance of the ionized space between said electrodes when the tube is lit. The large illuminating current now flowing will raise the potential drop in the electrodes I4 and reactor 22 and cause a lower potential to be applied to the switch 28. This lowered potential, however, will flow enough current through the shunting, high impedance resistor 14 to generate sufficient heat to keep the bimetallic strip 54 warped enough to maintain the contact element 58 disposed spaced away from the contact leg 18. This amount of heat is not sulicient to warp the bimetallic strip 54 to such a degree that the contact element 58 will engage the contact leg 12. This intermediate or floating position of the Contact element 58 is illustrated in Fig. 3 and represents the disposition of the various operative parts during running operation of the tube I0.

It will be appreciated that during the foregoing first try of the starter switch, the Contact elements 58, only move apart so that an arc is struck but once. It will further be understood that little or no heat is generated in the vicinity of these contacts so that at the time that the arc is struck the contacts are at relatively low temperature and will not be greatly degenerated to increase contact resistance and liberate objectionable fumes. Also, by employing a construction which operates in the foregoing manner, the low resistance path through the switch 28 which makes the iirst try can be held to a very small impedance thereby allowing a maximum heating current to flow through the iilamentary electrodes I4.

If discharge in the tube I0 is not initiated upon separation of the contacts 58 and 18, the impedance oifered by the tube I0 remains high and voltage drop through the reactor 22 small, so that a greater potential will be applied to the switch 28 than when the tube is lit. This potential is applied to the high impedance resistance 14, and because a larger current is passing through this resistance than when the tube is lit, the heat generated thereby will warp the bimetallic strip 54 to a greater extent than indicated in the floating position shown in Fig. 3. The warping at such time is suflicient to press the contact 58 into engagement with the contact leg 12, as

shown in Fig. 4. This is the recycling position of the switch. In this position a low impedance path is again formed between the terminals 32, 34. This path includes conductor wire 38, low impedance resistor 60, bimetallic strip 54, Contact 58, contact leg 12, bimetallic strip 62, and conductor wires 64 and 40. Said low resistance path enables a high heating current to pass through the filamentary electrodes I4 and again heats said electrodes to incandescence. However, the abutting of the contacts 58, 12 forms a low impedance shunt path across the high impedance resistor 14, causing said resistor and the strip 54 to cool and allowing the contact 58 to retract from the contact leg 12. It may be mentioned that the current passing through the low impedance resistor 60 when the contacts 58, 12 are closed does not generate suflicient heat to maintain the strip 54 in the recycling position shown in Fig. 4. In addition abutment of the strip 54 against the resistor 14 in the oating position inhibits further warping of said strip under the innuence of said low impedance resistor. When the contacts 58, 12 separate, a surge potential will once again be applied between electrodes I4 in a second attempt to strike a discharge therebetween.

If the discharge fails to occur upon first disengagement of the contacts 58, 12 from recycling position, an increased potential will be reapplied to the resistor 14, once more distorting the strip 54 and urging the contact 58 against the contact leg 12. The recycling will continue between the contacts 58, 12 until the lamp is lit or until the switch 28 is rendered inoperative.

If the lamp lights after disengagement of the recycling contacts 58, 12, insunicient potential is applied to the resistor 14 to distort the strip 54 suiiiciently to reengage the contacts 58, 1'2, However, enough potential is applied to keep the strip' 54 in such distorted position that the contact 58 lies or floats between the two contact legs 10, 12 as shown in Fig. 3.

The impedance values of the low and high resistors 68 and 14 are so chosen as to effect the above described operation. For purposes of illustration, and without in any way limiting my invention to any of these values, it may be mentioned that on a 110 volt supply circuit and with a li0-watt fluorescent discharge lamp, a resistance of 15,000 ohms for the high impedance 74 and 3.7 ohms for the low impedance will function satisfactorily. It will, of course, be understood that these values may be varied within wide r ranges depending upon the type of bimetallic strips, the spacing of the various contacts, and the spacing and disposition of the resistors relative to the bimetallic strips and contacts.

Various possible embodiments may be made of the above invention and various changes may be made in the embodiment set forth without departing from the spirit of the invention. It will therefore be understood that al1 matter herein set forth or shown in the accompanying drawings is to be interpreted as illustrative and not in a limiting sense.

It will thus be seen that there is provided a device in which the several objects of this invention are achieved, and which is well adapted to meet the conditions of practical use.

Having thus described my invention, I claim as new and desire to secure by Letters Patent:

l, An electric switch adapted to be used for starting an electric discharge lamp having at least one thermionic electrode, said switch comprising a pair of electrically connected spaced con-- tact members, a third contact member normally in contact with one of said pair of members, at least one bimetallic strip for effecting relative movementJ of said third member and said pair of members, said bimetallic strip and said contact members bei -g so constructed that upon heating of said strip said third contact member and the other of said pair of contact members are caused to approach each other, a low impedance resistor electrically connected in series with said contact members and arranged in heat transfer relationship with said bimetallic strip, and a high impedance resistor electrically connected in parallel with said contact members and also arranged in heat transfer relationship with said bimetallic strip, said high impedance resistor being so constructed and positioned that the heat generated thereby when said contacts are open and said lamp is lit will sunice only to maintain said contacts open and that the heat generated thereby when potential is applied to said lamp with the lamp unlit and the contact members open will cause said third member to contact the other of said pair` of members, said bimetallic strip being supported at an end thereof remote from said contact members and said low impedance resistor being disposed closer to said point of support than said high impedance resistor, said bimetallic strip abutting said high impedance resistor when the heat generated by said low impedance resistor causes said third contact member and the first of said pair of contact members to be separated.

2. An electric two-terminal switch adapted to be used for starting an electric discharge lamp having at least one thermionic electrode, said switch comprising a pair f electrically connected spaced contact members permanently electrically connected to a switch terminal, a third contact member normally in contact with one of said pair oi members and permanently electrically connecte-d to the other terminal of the switch, at least one bimetallic strip for effecting relative movement of said third member and said pair of members, said bimetallic strip and said contact members being so constructed that upon heating oi said strip said third contact member will leave said one of the pair of contact members and approach the other of the pair of contact members, a low impedance resistor permanently electrically connected in series in a cornmon circuit for all of said contacts and arranged in heat transfer relationship with said bimetallic strip, and a high impedance resistor permanently electrically connected in parallel with said contact members and also arranged in heat trans-- fer relationship with the same bimetallic strip, said high impedance resistor being so constructed and positioned that the heat generated thereby, when said contacts are open and said lamp is lit, will sunice only to maintain said contacts open and that the heat generated thereby, when potential is applied to said lamp with lamp unlit and the contact members open, will warp said strip to such an extent as to cause said third member to contact the other of said pair of members, said bimetallic strip being supported at an end thereof remote from the Contact members and the low impedance resistor being disposed closer to said point of support than the high impedance resistor, said bimetallic strip abutting said high impedance resistor when the heat generated by said low impedance resistor causes the third contact member and the first of the pair oi contact members to be separated.

3. An electric two-terminal switch adapted to be used for starting an electric discharge lamp having at least one thermionic electrode, said switch comprising a pair of electrically connected spaced contact members permanently electrically connected to a switch terminal, a third contact member normally in contact with one of said pair of members and permanently electrically connected to the other terminal of the switch, at least one bimetallic strip for effecting relative movement or said third member and said pair of members, said bimetallic strip and said contact members being so constructed that upon heating or" said strip said third contact member will leave said one of the pair of contact members and approach the other of the pair of contact members, a low impedance resistor permanently electrically connected in series in a common circuit for all of said contacts and arranged in heat transfer relationship with said bimetallic strip, and a high impedance resistor permanently electrically connected in parallel with said Contact members and also arranged in heat transfer rclationship with the same bimetallic strip, said high impedance resistor being so constructed andpositioned that the heat generated thereby, when said contacts are open and said lamp is lit, will suilce only to maintain said contacts open and that the heat generated thereby, when potential is applied to said lamp with lamp unlit and the contact members open, will warp said strip to such an extent as to cause said third member to contact the other of said pair of members, said bimetallic strip being supported at an end thereof remote from the contact members and the low impedance resistor being disposed closer to said point of support than the high impedance resistor, said bimetallic strip abutting said high impedance resistor when the heat generated by said low impedance resistor causes the third contact member and the iirst of the pair of contact members to be separated, and the heat generated by said low impedance resistor being insufcient to warp said bimetallic strip to such an extent as to maintain said third contact member and the other of said pair of contact members in contact.

4. An electric two-terminal switch adapted to be used for starting an electric discharge lamp having at least one thermionic electrode, said switch comprising a pair of electrically connected spaced contact members permanently electrically connected t0 a switch terminal, a third contact member normally in contact with one of said pair of members and permanently electrically connected to the other terminal of the switch, at least one bimetallic strip for effecting relative movement or" said third member and said pair of members, said bimetallic strip and said contact members being so constructed that upon heating of said strip said third contact member will leave said one of the pair of Contact members and approach the other of the pair of contact members, a low impedance resistor permanently electrically connected in series in a common circuit for all of said contacts and arranged in heat transfer relationship with said bimetallic strip, and a high impedance resistor permanently electrically connected in parallel with said contact members and also arranged in heat transfer relationship with the same bimetallic strip, said high impedance resistor being so constructed and positioned that the heat generated thereby, when said contacts are open and said lamp is lit,

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

Number UNITED STATES PATENTS Name Date McCarthy Apr. 4, 1944 McCarthy Aug. 10, 1943 Bensin Oct. 19, 1943 Abbott Dec. 30, 1941 McCarthy June 9, 1942 Lord Aug. 25, 1942 Gustin et al. Oct. 6, 1942 Hall Dec. 15, 1942

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