US2694788A - Circuit and starting switch for electric discharge devices - Google Patents

Description

Nov. 16, 1954 C. H. WALKER ET AL CIRCUIT AND STARTING SWITCH FOR ELECTRIC DISCHARGE DEVICES Filed Feb 12, 1949 IIWVGYTbOTSI Cyril H. WaLker,

Fvederick E. La lge.

by (fizz. JCS

Their" Ai: omeg.

United States PatentO CIRCUIT AND STARTING SWITCH. FORKELECTRIC DISCHARGE DEVICES:

Cyril Hubert Walker and ,Frederick. Edmund Large, .Rugby, England, assignors to. General ElectricCompany a, corporation of'New York Application February lZ, 1949, Serial No. 76,165

. Claims priority, application. Great Britain April 8, 1948.

8 Claims. (CL 315.-10;,0)

This invention relates to the starting and operating of electric discharge lamps.

'Electric dischargelamps of the low pressure type such, for example, as fluorescent lamps in which the predominantly ultraviolet radiation from the dischargeis converted into visiblelight by means of aluminescent materialon the interior of the envelope of the device, generally require relatively complex circuits for their starting and operation. This is due to the fact that it is usually'necessary to preheat the electrodes to an electron-emitting temperature prior to the application of the operating voltage between the electrodes.

In order to control the supply of preheating current to the electrode, use has generally been made of a thermostatic starter switch, the contacts of which are arranged, when the source of supply voltageis connected to the lamp, to connect the electrodes in a series circuit to the source, whereby to supply heating current to the electrodes, the thermostatic switch being so constructed that after a predetermined time period its contacts open, thereby interrupting the series circuit through the'lamp electrodes. As a result of the presence inv series with the lamp of the inductance necessary for stabilizing the discharge, .a voltage pulse is impressed between the electrodes when the contacts of the thermostatic switchopen, whereby the discharge is initiated between thepreheated electrodes.

Two types of thermostatic switch have generally'been employed. In onetype, commonly known as a thermal switch, the contacts are normally closed and'are arranged to.be opened by distortion of the bimetal element of the switch when heated by a heating, element connected in series in the circuit. supplying, the discharge current of the lamp. Whenvoltage is first applied to the. lamp circuit, current flowsthrough the series circuitincluding the heating element of the thermostatic switch, and vthe electrodes of the lamp causing them to heat up and at the endof the preheatingperiod' the contacts ofthe thermostatic switch openand the discharge between thevpreheated electrodes is initiated. Thereafter: the discharge currentflowing through the heating element of the switch is suflicient to maintain its contacts open, andonlyifthe discharge ceases by reason of the supply beingswitched off? or otherwise do the contacts of the switch reclose ready for a further starting operation.

In another well-known arrangement, the starting switch is of the glow discharge type, the contacts beingnormally open and arranged, when closed, to complete the preheating circuit for the lamp electrodes. When-the supply isfirst connected to the lamp, aglowdischarge appears between the contacts ofthe switch and, aftera predetermined period, distortion of the bimetal contact due to the heat of the glow dischargecauses the contacts to close, completing the preheatingcircuit'for thelarnp electrodes. On closure of the contacts, however, the glow discharge ceases by virtue of' there being no potential available betweenithe electrodesofthe switchto maintain it and the contacts reopen after a time periodsufiicient to preheat the lamp electrodes to a desired electron emitting temperature. Thereafter, the voltage, drop between the lamp electrodes is insuflicient to maintain a glow discharge between the contacts of the starter switch and only. if the discharge ceases vwith the lamp connected to the supply voltage will the starting process described above recommence.

Itis an object of the present inventionto providean improvedform of=glow'discharge switchand of starting- '2 and operating circuit arrangement employingsame for electric discharge lamps of the kind, set-forth above.

'Other objects and advantages of our invention will appear from the following description of. species thereof.

In the accompanying drawing, which illustrates the manner in which the invention may be carried into effect, Fig. 1 shows, diagrammatically, one improved formof glow discharge starter switch employed; Fig. 2 is a circuit diagram illustrating the improved starting and operating circuit using the starter switch of Fig. l; and Figs. 3 and 4 are two further forms of starter switch.

In accordance with one aspect of the invention, a glow discharge starting switch is arranged with its main contacts normally closed and is furnished with at least an additional electrode which is connected to a point on the circuit of the discharge lamp. This point is chosen, so that between it and one or the other of the main contact electrodes there appears, when the supply voltage is applied to the lamp, a potentialsutficient to produce a glow discharge in the switch, such glow discharge being suflicient to heat the heat-deformable electrode of the startingswitch to a temperature such as to cause its-,normally closed contacts to open. Thereupon the opening of the electrode preheating circuit of the lamp, the termination of the preheating period, and the initiation of the discharge through the lamp occur.

Thus, after the normally closed contacts of the starting switch have been opened by the heating eiTect on the heat-deformable electrode of the glow discharge, so long as the discharge through the lamp persists, the voltage applied to the additional electrode is sufficient to maintain a glow discharge and hold the contacts in the open position. When the operating voltage is removed, the starting switch contacts reclose in readiness fora further cycle of starting operations.

In some cases, for examplewhen the lamps are used on electric traction systems, the supply is subject to frequent interruptions. The time delay necessary for the cycle of cooling, and subsequent reheating, of the bimetal.

electrode is an undesirable feature of a circuit arrangement using a switch as set forth above, since the lamp remains unlighted for periods materially longer than those of the interruption of supply. According to a further feature of the invention, the starting switch is modified to reduce this time delay by providing at least onefurther contact so disposed as to be contacted in response to a further distortion of the heat-deformable electrode and thereby to enable the circuit for the heating of theelectrodes of the lamp to be completed. This further distortion of the heat-deformable electrode is produced by arranging for the supply voltage to be impressedbetween the main contacts of the starting switch (one of which is carried by the heat-deformable electrode) when the discharge through the lamp is absent, so that a more intense glow is then present in the starting switch. This further distortion may be produced in a shorter time periodthan would be required-for-the necessary cooling of the heat-deformable electrode to enable the main contacts to close. On the closure of the further contact, theglow. in the starting switch ceases so that the reopening of those contacts, and the restoration of. the lamp discharge is then effected.

We may provide in serieswith the additional electrode ofthe starting switch a resistance (which may be constructionally integral with the switch) the purpose of which is to limit the current in the glow discharge from.

the additional electrode. Thus,-by adjustingthe'value of this resistance one can vary the heatingvalue of the glow discharge and consequently the time takenfor the contacts of the startingswitch to open.

Where we have used the term electrodeit is to be.

Fig. Line-main operating member-of theswitch consists ofa bimetal electrode 1 which is conveniently made of U-shapedform. The bimetal'electrode 1 is-supported by one of its limbs upon a lead-in wire 2 and has the free end of its other limb arranged between contact members 3 and 4 supported on lead-in wires 5 and 6, respectively. The free end of the bimetal. electrode 1 may, and preferably does, carry a contact 7 which cooperates with the contact 4, since the main duty of the switch is to make and break the circuit between the contacts 4 and 7. The elements of the switch are enclosed in the usual sealed glass envelope 8, which is provided with a suitable ionizable gas filling to enable a glow discharge to take place between electrode 3 and the bimetal electrode 1 when a suitable voltage, hereinafter specified, is impressed between them.

Referring now to the circuit diagram shown in Fig. 2, contacts 4 and 7 are normally closed and are connected, respectively, to one terminal of each of the thermionic electrodes 9, 10 of the lamp 11, the other terminals of the electrodes being connected to terminals 12, 13 to which the supply of operating current for the lamp is intended to be connected. The lead between terminal 13 and one terminal of electrode 9 includes the usual choke 14 for limiting the current flow through the lamp. The additional electrode 3 of the switch is now connected to that terminal of the series inductance 14 which is remote from the electrode 9, or to any other suitable point on the circuit as will provide, when current flows through the series circuit including the electrodes 9, 10, a voltage drop sufficient to produce a glow discharge between the additional electrode 3 and the bimetal electrode 1 of the switch. Preferably included in this connection is a resistance 15 which may, as indicated in Fig. 1, be included in the base of the starter switch, if desired.

On applying operating voltage to the terminals 12, 13, preheating current flows through the series circuit including the electrodes 9, 10 and the contacts 7 and 4 of the starter switch, heating the electrodes of the lamp to an electron-emitting temperature. Simultaneously, a glow discharge takes place between the bimetal electrode 1 and the electrode 3 of the starter switch, which heats the electrode 1 and causes it to bend away from the contact 4. After a suitable period of time, depending on the pressure between contacts 4 and 7, the time taken for the necessary heating of the electrode 1, and the value of the resistor 15, the electrode 1 distorts sufliciently to open contacts 4, 7 and a discharge is produced in the usual manner between the electrodes 9, 10 of the lamp as a result ofthe voltage pulse produced owing to the presence of inductance 14 in the circuit. Thereafter, a sufiicient glow discharge is present to maintain open the contacts 4, 7 and the contacts will only reclose in the event of the discharge through the lamp failing by reason of the removal of the operating voltage. When the operating voltage is restored, the above-described sequence of operations will be repeated. If, however, the discharge fails by reason of the failure of one or other of the electrodes of the lamp, the operating voltage will still be present between the heatdeformable electrode 1 and electrode 3 of the starter switch, and consequently the contacts 4, 7 will remain open and will not make repeated attempts to restart the lamp. Excessive duty on the contacts 4, 7 of the starter switch is thus avoided.

If desired, an additional element 19 may be provided in the switch to limit the travel of the free end of bimetal electrode 1 or it may be arranged that the heating effect of the glow discharge, when a discharge current is passing through the lamp 11 is only sufficient to distort the electrode 1 to a position midway between electrodes 3, 4.

Referring now to the modified form of starter switch shown in Fig. 3, in addition to the contacts provided in the arrangement shown in Fig. 1 we have provided an auxiliary fixed contact 17 located between the main fixed contact 4 and the fixed electrode 3 and electrically connected with the main fixed contact 4. We furthermore provide an auxiliary movable contact 18 attached to the bimetal electrode 1. This movable contact is so arranged, between the fixed contact 17 and fixed electrode 3, that, when the bimetal electrode 1 distorts sufiiciently to carry the main movable contact 7 into engagement with the fixed contact 17, the auxiliary movable contact 18 will simultaneously engage the fixed electrode 3. This modified form of starter switch is particularly suitable for use in circuits where the supply is subject to momentary interruptions of sufficient duration to prevent immediate restriking of the discharge across the lamp. Under these conditions, when the discharge through the lamp momen-' tarily ceases owing to interruption in the supply, and the supply is thereafter reconnected, due to the presence of the supply voltage between auxiliary fixed contact 17 and the bimetal electrode 1, a more intense glow takes place with the result that a further bending of the bimetal electrode 1 occurs. It will, of course, be understood that the reconnection of the supply, mentioned above, occurs before the glow switch has time to cool sufficiently to restore bimetal electrode 1 to its rest position, wherein it is in contact with electrode 4. The bending which now occurs, as a result of this more intense glow, elfects mutual engagement of contacts 7, 17 and 18, 3. The electrode heating circuit of the lamp is thereupon completed, and, as a result of the consequent removal of the glow discharge, the bimetal electrode 1 cools, opening the circuit at the contacts 18, 3 and 17, 7. The discharge through the lamp is thereby re-initiated and the bimetal electrode is once more heated by the glow discharge between fixed electrode 3 and auxiliary movable contact 18. This heating is just sufficient to maintain the main movable contact 7 in a position midway between fixed contacts 17 and 4. The normal running position of the switch is thereby restored.

Fig. 4 shows a further arrangement, similar in character to that shown in Fig. 3, but in which the fixed electrode 3 and auxiliary fixed contact 17 are arranged to be simultaneously interconnected by a contact element 7 in the form of a transverse wire located on the free end of the bimetal element 1.

The adjustment of the duration of the preheating period for the lamp electrodes may be effected by varying the value of the series resistance 15. An increase in the value of the resistance will diminish the glow discharge current, and therefore increase the period of time required for distorting the heat-deformable electrode 1 and effecting opening of contacts 4, 7.

We preferably connect a radio interference suppression condenser 16 in shunt with the contacts 4, 7 of the starter switch.

While certain specific embodiments have been shown and described, it will, of course, be understood that various modifications may be made without departing from the invention. The appended claims are, therefore, intended to cover any such modifications coming within the true spirit and scope of the invention.

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

1. In combination, an electric discharge device having two cooperating electrodes at least one of which is thermionic; a ballast impedance connected in series with said discharge device in an operating circuit therefor and proportioned to limit the discharge current therethrough; a thermal glow discharge starting switch comprising a sealed envelope containing an ionizable medium, a pair of normally closed main contacting electrodes at least one of which is heat deformable and designed to break contact when heated, and an auxiliary electrode adjacent said heat-deformable main electrode and defining therewith a glow discharge gap; the main electrodes of said switch being connected across the electrodes of said discharge device in a preheating circuit shunting said discharge device and serially including its thermionic electrode; and a connection between the side of said ballast impedance removed from said discharge device and said auxiliary electrode.

2. In combination, an electric discharge device having two cooperating electrodes at least one of which is thermionic; a ballast impedance connected in series with said discharge device in an operating circuit therefor and proportioned to limit the discharge current therethrough; a thermal glow discharge starting switch comprising a sealed envelope containing an ionizable medium, a pair of normally closed main contacting electrodes at least one of which is heat deformable and designed to break contact when heated, and an auxiliary electrode adjacent said heat-deformable main electrode and defining therewith a glowdischarge gap; the main electrodes of said switch being connected across the electrodes of said discharge device in a preheating circuit shunting said discharge device and serially including its thermionic electrode; and a resistanceconnecting said auxiliary thermal switch electrode to the sideof said ballast impedance removed from said discharge device.

3. In combination, an electric discharge device having two cooperating electrodes at least one of which is therm-' ionic; a voltage supply; a ballasting impedance connected in series with said discharge device across said supply to constitute a main discharge circuit during normal operation of said device; a thermal glow discharge starting switch comprising a sealed envelope containing an ionizable medium, a pair of normally closed main contacting electrodes at least one of which is heat deformable and designed to break contact when heated, and an auxiliary electrode adjacent to said heat-deformable main electrode and defining therewith a glow discharge gap; the main electrodes of said discharge device being connected in a preheating circuit shunting said discharge device and serially including its thermionic electrode; and a connection between said auxiliary thermal switch electrode and the side of said supply connected to said ballasting impedance in order to produce a discharge in said gap for causing said heat deformable main electrode to break contact with the other main electrode of said switch.

4. In combination, an electric discharge device having a pair of cooperating electrodes of the filamentary thermionic type; a voltage supply; a ballasting impedance connected in series with said discharge device across said supply to constitute a main discharge circuit during normal operation of said device; a thermal glow discharge starting switch comprising a sealed envelope containing an ionizable medium and a pair of normally engaged and closed main contacting electrodes, at least one of which is heat deformable and designed to disengage and break contact when heated, and an auxiliary electrode spaced apart from said heat deformable electrode and defining therewith a glow discharge gap therebetween; the main electrodes of said switch being connected across the thermionic electrodes of said discharge device in a preheating circuit shunting said discharge device and serially including said thermionic electrodes; and a connection between said auxiliary electrode and the side of said supply connected to said ballastin impedance in order to produce a discharge in said gap for causing said heat deformable main electrode to break contact with the other main electrode of said switch.

5. In combination, an electric discharge device having a pair of cooperating electrodes of the filamentary thermionic type; a voltage supply; a ballasting impedance connected in series with said discharge device across said supply to constitute a main discharge circuit during normal operation of said device; a thermal glow discharge switch comprising a sealed envelope containing an ionizable medium, a main fixed contacting electrode, a heatdeformable contacting electrode normally biased into engagement with said main fixed contacting electrode but movable away therefrom when heated, an auxiliary electrode adjacent to said heat-deformable electrode and defining therewith a glow discharge gap, and an additional contact on said main fixed contacting electrode engageable simultaneously with said auxiliary electrode by a portion of said heat deformable electrode at the limit of movement thereof; the contacting electrodes of said switch being connected across the electrodes of said discharge device in a preheating circuit shunting said discharge device and serially including its electrodes; and a connection between said auxiliary fixed electrode and the side of said supply connected to said ballasting impedance in order to produce, during normal operation of said discharge device, a glow discharge between said auxiliary electrode and said heat-deformable electrode within said switch.

6. A thermal glow discharge switch comprising a sealed envelope containing an ionizable medium, a main fixed contacting electrode, a heat-deformable contacting electrode normally biased into engagement with said main electrode but movable away therefrom when heated, an auxiliary fixed electrode spaced from a portion of said heat-deformable electrode for defining a glow discharge gap therebetween and located in the path of movement of said portion, and an additional fixed contact electrically connected to said main electrode and spaced from said heat-deformable electrode but in the path of movement thereof, so as to be engaged thereby simultaneously with the engagement of said auxiliary fixed electrode by said portion.

7. A thermal glow discharge switch comprising a sealed envelope containing an ionizable medium, a main fixed contact and an additional fixed contact spaced apart but electrically connected together on a common fixed electrode, an auxiliary fixed electrode spaced apart from said fixed contacts, a heat-deformable electrode carrying a main movable contact and an additional movable contact, said main movable contact normally engaging said main fixed contact, said additional movable contact being spaced between said additional fixed contact and said auxiliary fixed electrode to provide a glow discharge gap between itself and said auxiliary fixed electrode, said heatdeforrnable electrode being operable, when heated by a glow discharge between said main fixed contact and said main movable contact, to position said main movable contact substantially midway between said main and additional fixed contacts, and said heat-deformable electrode being further operable, when heated by an additional glow discharge between said additional movable contact and said auxiliary fixed electrode, so that said main movable contact engages said additional fixed contact and said additional movable contact simultaneously engages said auxiliary fixed electrode.

8. A thermal glow discharge switch comprising a sealed envelope containing an ionizable medium, a main fixed contact and an additional fixed contact spaced apart and electrically connected together on a common electrode, an auxiliary fixed electrode spaced apart in side-by-side relationship with said additional fixed contact, a heat-deformable electrode having its free end normally biased into engagement with said main fixed contact and spaced apart from said auxiliary fixed electrode for defining a glow discharge gap therebetween, said heat-deformable electrode being operable, when heated by a glow discharge, to move said free end out of engagement with said main fixed contact to a position intermediate said main fixed contact and said auxiliary fixed electrode, and said heat-deformable electrode being further operable, when heated by an auxiliary glow discharge between said auxiliary fixed electrode and itself, to move said free end further in order to form electrical contact simultaneously with said auxiliary fixed electrode and said additional fixed electrode.

References Cited in the file of this patent UNITED STATES PATENTS Number Name Date 2,212,427 Peters Aug. 20, 1940 2,267,098 Hayes Dec. 23, 1941 2,268,522 Abbott Dec. 30, 1941 2,299,499 Sanford Oct. 20, 1942 2,313,575 Peters Mar. 9, 1943 2,341,520 Babb Feb. 15, 1944 2,372,295 Rubenstein Mar. 27, 1945 2,375,967 Vaughan May 15, 1945 2,423,031 Kurtz June 24, 1947 2,438,557 Hehenkamp Mar. 30, 1948 2,464,748 Hodgkins Mar. 15, 1949

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