US2601917A - Glow discharge switch - Google Patents

Description

J y 1,952 P. LEMAlGRE-VOREAUX GLOW DISCHARGE SWITCH Filed July 18, 1950 lnv'entor Pierre Lemoigre- Voreuux,

y 47 m, hm

Patented July l, 1952 UNITEDLSTATES "Arsinr OFFICE ill 4' 2 3013131 I I v cr S HAB EI W F- bfi I Pierre Lemaigre-Vo're'aux, Paris, France-,assignorto Societe Ano'n'yme Pour les Applicationsde lElectricite et des .Gaz Rare's-Etablissement's' Claude-Paz & Silva, Paris, France, a company of France Application July18; 1950, scream- 114,500 I In France August '1, 1 949 This invention relates to a glow I discharge switch for starting and operating gaseous elec tricdischarge devices, said switch being of the type comprising twoelectrodes, a part of one of said electrodes being a bimetallic member which controls a connection between said two electrodes and which is coated with thermionic emissive materials.

An object of my invention is to provide a new and improved glow switch which will close when a'rela'tivel'y low voltage is impressed between its terminals and which is easy to manufacture.

Another objectof my invention is to provide a new and improved glow switch, the closing voltage of which varies little in the course of time. 1

A further object of my invention is toprovide a new and improved glow switch of simple design.

A feature of my invention is to connect to the bimetallic member which carries the movable contact of the switch a conductor coated with a substance which, under the effect of a discharge issuing from said conductor, emits thermionic emissive materials; part, at least, of these materials forms a deposit on the bimetallic member and lower the cathode voltage drop of said member.

Further objects and features of my invention will appear from the following detailed description of species thereof.

The accompanying drawing shows an embodiment of the invention designed for controlling, according to the well known method of pre-heating the electrodes, the starting of a gaseous discharge apparatus. The latter may be, for instance, a fluorescent lamp supplied directly from a 110 volt A. C. line, the term directly meaning that the line voltage is not raised or boosted by a transformer or any other device.

The operation of this switch, i. e. its closure under the action on the bimetallic element, of a discharge taking place between the latter or said conductor and the fixed contact, should occur under the lowest value which the line voltage can assume; on the other hand, it should not occur under the voltage existing between the electrodes of the fluorescent lamp during the normal operation of the latter; in the switch described hereinafter, the minimum closing voltage is about 80' volts A. C.

This switch comprises, inside an envelope 3 containing a neon atmosphere with 1% argon, under a pressure of about 25 millimeters of mercury, a fixed contact 5 and a bimetal element 4 acting as a moving contact; when'cold, the minimum distance between the fixed contact 3 Claims. Q (01. 200%1135) denses on the bimetal element.

and the bimetal element is about 0.5 millimeter. The fixed contact 5 is connected directly with the outside circuit by its current supply leadin cl. 'JI'he bimetal'element 4 is connected with the same circuit through the conductor 1 and the current supply lead-in H mounted in series; element is" carried by the support 8 an end of which is inserted in the stem 9 of the envelope, said ste m 'comprisingtan exhaust tube 10 and the currlent leads 1. and II .passing air-"tight through said stem.

.This arrangement makes it possible to use :a stem 9 comprisingonly :two ilead-in passages. Further, the current which, when the bimetal eleme'n'td. touches. the Jflxed contact 5, .passes thr'ough'sthe conductor lfheats up the latter,

I which heats upth'e bimetal'element 4, which delays the moment when the latter moves away from the contact 5. The period of uninterrupted pre-heating of the fluorescent lamp started by means of the switch, is thus lengthened, which decreases the fatigue of the lamp electrodes.

The conductor 1 is a filament of refractory 'metal, in the shape of a double-coiled spiral, coated with alkaline earth oxides and alkaline earth metals, like a so-called hot cathode in a fluorescent lamp. It is, in fact, practically, a hot cathode of a normal design which is used as a conductor 1. The formation of this con- 'ductor, i. e. the transformation of the alkaline earth compounds deposited thereon into a mixture of oxides and metals is effected like that of a usual hot cathode; the current leads for this operation are then, one the normal lead I l, the other one I, that of the fixed contact.

The connection between the latter and the upper end of the electrode 1 is ensured by a heating to about 400 C. of the switch assembly in an oven, a heating which causes a change in shape of the bimetal element 4 which then touches the contact 5. The formation of the conductor 1 consists in heating it by means of the Joule effect, which causes the decomposition of the alkaline earth substances; it is accompanied, towards its end, by a production of alkaline earth metals which evaporate and part of which cong The alkaline earth metals thus deposited on the bimetalelement in a very thin layer 6 have the effect of lowering the starting voltage for the discharge between the bimetal element and the fixed contact. When the cold switch, placed in the preheating circuit of the fluorescent lamp which it should cause to start, is subjected to a voltage higher than volts, a glow discharge occurs between the bimetal element 4 and contact 5 as in usual glow interruptors with bimetallic electrodes, used for the starting of fluorescent lamps by a temporary short-circuiting of the electrodes of the latter.

Normally, the glow does not occur on conductor I, probably because of the high value of the cold resistance of the oxides coating it. When, after a number of operations, the metal deposit 6 activating the bimetal element 4 has disappeared or become insufiicient, the glow discharge occurs on conductor 7 and partly reduces the alkaline earth oxides coating it into alkaline earth metals, a part of which is projected by cathodic atmoization on the bimetal element 4 and re-activates it.

Such a switch can operate tens of thousands times Without any appreciable change in its closing voltage or operating delay. Its manufacture on a production scale is easy since the activation process used involves a technique commonly utilized in the industry of fluorescent lamps.

I claim:

l. A glow discharge switch of the type comprising in an envelope containing a gaseous ionisable medium, a first and a second electrode, at least a part of said first electrode being a bimetallic member for controlling a connection between said electrodes and being coated, at least partly, with thermionic emissive material, said switch comprising in the envelope a conductor, connected with said first electrode and comprising a refractory metal wire winding coated with materials containing at least one alkaline earth metal and the vapor tension of which is negligible at the maximum electrodetempcrature, said conductor emitting emissive material when a discharge starts from it, at least part of the material so emitted depositing on the bimetallic member.

2. A glow discharge switch of the type comprising, in an envelope containing a gaseous ionisable medium, a first and a second electrode, at least a part of said first electrode being a bimetallic member for controlling a connection between said electrodes and being coated, at least partly, with thermionic emissive material, a first and a second lead-in wire, respectively for the first and the second electrode, said switch comprising in the envelope a conductor, connected in series between said first lead-in wire and said first electrode and coated with at least one substance, the vapor tension of which is negligible at the maximum electrode and conductor temperature and which, when a discharge starts from said conductor, emits said emissive material, at least part of the material so emitted depositing on the bimetallic member.

3. A glow discharge switch according to claim 2, the winding being in the form of a helical coil at least singly coiled and being made up of at least one wire, and the materials coating said winding comprising at least one alkaline-earth oxide.

PIERRE LEMAIGRE-VOREAUX.

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

UNITED STATES PATENTS Number Name Date 2,251,278 Hays, Jr., et al Aug. 5, 1941 2,280,550 Smitley Apr. 21, 1942

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