US2291960A - Discharge lamp and circuit - Google Patents

Description

Aug. 4, 1942.. D. s. GUSTlN ETAL 91,

i DISQHARGE LAMP AND CIRCUIT Original Filed April 23, 1938 :NvENToR R5. 70577 IETF an; m.

mmwwz ATTO R N EY Patented Aug. 4, 1942 DISCHARGE LAMP AND CIRCUIT Daniel S. Gustin and Robert F. Hays, Jr., Bloomfield, N. J., assignors to Westinghouse Electric & Manufacturing Company, East Pittsburgh, Pa., a corporation of Pennsylvania Original application April 23, 11938, Seriai No. 203,757. Divided and this application May 25, 1940, Serial No. 337,156

((31. flit-122) 4 Claims.

The present invention relates to discharge lamps and particularly to a starting arrangement therefor which prolongs the useful life of such lamps, and constitutes a division of our application Ser. No. 203,757, filed April 23, 1938, and assigned to the same assignee as the present application.

Discharge lamps at the present time are well known to the art, and one of the characteristics of lamps of this type is the difficulty in starting a discharge between the electrodes. In the majority of cases discharge lamps employ electrodes of the type known as cold electrodes, that is to say, electrodes which are heated to the point of emitting electrons solely by the resulting discharge. This requires a comparatively high starting voltage, and since lamp life is dependent more on the number of times the lamp is started, rather than on the number of hours burning, such lamps have had a comparatively short useful life.

To facilitate starting and thus to prolong useful life, it has been suggested in the art to employ hot electrodes which are heated to an electron-emitting temperature prior to the imposition of a voltage across the electrodes of the lamp. In instances of this kind, the heating elements for the electrodes are usually connected in series and some switching device is employed to interrupt the flow of current through the heating elements after the initiation of a discharge,

'since the electrodes may then be heated by the discharge itself.

Despite the employment of heated electrodes to lower the starting voltage, it nevertheless has heretoforebeen higher than the customary domestic source of supply of 110 volts. Moreover, the switching device for interrupting the fiow of current through the heating elements for the electrodes has been a power consuming device, which is objectionable from the standpoint that the average consumerpays for electrical energy which is not converted into visible light.

It is accordingly the primary objectof the present invention to provide a starting arrange ment for discharge devices which is operable from the customary domestic source of supply.

Another object of the present invention is the provision of a starting arrangement for gaseous discharge lamps having a low starting voltage, enabling them to be readily energized from the usual commercial source of supply.

Another object of the present invention is the provision of a starting arrangement for gaseous discharge lamps wherein starting of the device which has a negative temperature coefiicient so that upon the initiation of a discharge between the electrodes, current flow through such device is negligible.

Another object of the present invention is the provision of a thermal relay for interrupting the flow of current through the heater element for the electrodes of a gaseous discharge device, which relay has a negative temperature coefiicient so that after the initiation of a discharge between the electrodes of the lamp, current flow through the relay is substantially negligible, thus eliminating any loss of power.

Still further objects of the present invention will become obvious to those skilled in the art by reference to the accompanying drawing wherein:

Fig. 1 is a schematic diagram of a starting circuit for a gaseous discharge device in accordance with the present invention;

Fig. 2 i a schematic diagram of a starting circuit for a gaseous discharge device showing still another form which the present invention may take;

Fig. 3 is a side elevational view showing one form which the relay shown in the circuit of Fig. 2 may take in accordance with the present invention;

Fig. 4 is a sectional view taken on the line lV-IV of Fig. 3 looking in the direction indicated by the arrows;

Fig. 5 is a side elevational view of still another form which the relay, as shown in the circuit of Fig. 2, may take in accordance with the present invention, and

Fig. 6 is a sectional view taken on the line VI-VI of Fig. 5 and looking in the direction indicated by the arrows.

Referring now to the drawing in detail, in Fig. 1 a gaseous discharge device is shown comprising an evacuated envelope 5 provided with filamentary electrodes 6 and 1 consisting of a refractory metal, such as tungsten or the like, and which may be coated with a material which emits a copious flow of electrons when heated, such as the oxides of barium, strontium, or the like.

The envelope is provided with an ionizable medium such as mercury, sodium, or other readily volatile material, as well as an inert gas, such as argon, neon, etc., to facilitate starting. The electrodes 6 and 'I are connected to a suitable source of electrical energy 0, such as the customary domestic source of 110 volts, and a selfinductance 9 is connected in series with the electrodes and the source 8.

These electrodes 8 and l are also connected in series through a resistance device it and a capacitor I! of approximately 6 microi'arads with the capacitor l2 and self-inductance 9 being of such dimensions that they are in or near resonance for the fundamental frequency of the alternating current source. The resistance element II) has a negative temperature coeflicient so that when cold, the resistance thereof is comparatively high; and, conversely, when hot, the resistance thereof is low. This device may comprise a glass tube filled with silicon crystals or the device may be formed of a solid rod of zinc oxide or similar material, so long as it has a negative temperature coefllcient.

When the lamp is connected to the 110 volt source 8, upon the closure of a suitable switch (not shown), the total reactance of the lamp circuit is low and the resistance is high, with the result that a small current initially flows. This current gradually heats the electrodes 6 and l to an electron-emitting temperature and at the same time gradually heat the resistance element Ill. As the resistance element heats up, its resistance gradually decreases with a corresponding increase in current. The increase of current through the resistance device I0 is gradual enough that the increase of the electrode temperature doe not lag appreciably.

By the time the current flow through the device IO increases to substantially maximum, the voltage across the capacitor l2 rises to a value sufficient to strike an arc between the electrodes 6 and 1. Upon the initiation of the discharge, the resistance element l0 and capacitor l2 are practically disconnected from the circuit, since the current will follow the path of least resistance across the arc, and any current flowing through the resistance l0 and device I2 is very inappreciable.

Inasmuch as the resistance device Hi practically disconnects the capacitor due to its high increase in resistance, the possibility of surge current flowing through the lamp is substantially eliminated. Moreover, the voltage available for starting the arc is actually higher than the voltage across the condenser, which voltage is not dangerously high, reaching a maximum of only approximately 150 volts.

The various elements of the circuit just described may be so adjusted that in case the lamp fails to start for any reason, the current will not be abnormally high, which thus dispenses with the necessity of other protective devices, such as fuses or the like. Also the inductance element 9 may be of comparatively small size, ince it decreases the voltage between the line voltage of 110 to approximately 60-65 volts across the elec trodes or the lamp.

Referring now to Fig. 2, the circuit differs from that of Fig. 1 in that the various elements thereof are not necessarily selected to make the circuit at or near resonance for the frequency of the supply source. In addition, what has been termed a thermal silicon relay I5, or'the like, has been substituted for the resistance device IU of Fig. 1.

However, this relay is ve y 81111118! to the sistance element ill in that it has a negative temperature coeflicient and diilers from the resistance element 10 solely in the provision of a coil l6 surrounding the device, which is heated by the flow of current through the device. One end of this coil I6 is connected to one end of the tubular portion of the device i5 and one side of the capacitor 12, which latter in this particular modification may be of much smaller size of approximately 2 microfarads.

The coil l6 consists of a metal responsive to temperature changes, and its opposite end is provided with a small contact II which, when the device is cold,'establishes a connection with a stationary contactor IS, the latter of which is connected by means of a conductor I! to the opposite side of the capacitor l2.

In this circuit the capacitor I2 is used to produce a high voltage for starting the lamp 5 and is of such size as to impress a high enough starting voltage across the electrodes with the filaments hot to initiate a discharge, but which does not draw enough current to heat the filaments. Consequently, the thermal relay I5 is utilized to connect the electrodes in series and to short-circuit the capacitor l2 until the electrodes have reached an electron-emitting temperature, at which time the relay opens, thus connecting the capacitor again in the circuit for impressing a sufficiently high starting voltage across the electrodes.

In the normal or "cold position of the thermal relay IS, the contacts I! and it are closed. Upon closure of the switch (not shown), energy will be supplied from the source 8 which will flow through the inductance element 9, electrodes 6 and I and thermal relay l5. This flow of current heats the electrodes 6 and I to an electronemitting temperature in the same manner described relative to Fig. 1 and at the same time causes a gradual increase in the temperature of the thermal relay l5.

As the temperature of this latter device gradually increases, it heats the coil l6, causing the contacts I I and I8 to open due to the thermal characteristics of the material oi which the coil is composed, thus connecting the capacitor II in series with the electrodes in the same manner as previously described with reference to Fig. 1.

Frequently the transient voltage flowing through the inductance 9'is sumcient to give a voltage kick higher than the line voltage and initiate an arc, but in order to assure a sufliciently high enough starting voltage, the capacitor i2 is nevertheless included in the circuit. This allows the voltage to build up across the capacitor to the value required to initiate a discharge between the electrodes 8 and I. Again, as in Fig. 1, upon the initiation of a discharge, the current through the device i5 is inappreciable, since current flow is across the path of least resistance, namely, the discharge.

The thermal relay IE will accordingly decrease in temperature and again close the contacts l1 and I8. However, as the resistance of the device I5 is very high when cold, practically no current will flow therethrough, since the voltage across thet lamp has decreased to approximately 60-65 vo s.

By reference to Fig. 3, one form of thermal relay is shown wherein the core may consist of a glass tube filled with silicon crystals, or a solid rod of carborundum or zinc oxide as herelnbeiore mentioned. This core is surrounded by a hellcal metallic winding or coil having a suitable thermal expansion so that when cold, its free end flexes laterally to make and break contact with the stationary terminal or contact l8, as shown more clearly by the full and dotted lines in Fig. 4.

In Fig. a slightly different modification of the thermal relay forming a part of the present invention is shown. In this embodiment, the stationary contact I8 is of angular configuration and disposed adjacent one side of the core IS. A metallic strip 20 responsive to temperature changes is supported in a saddle 22 so that when no current is flowing through the core i5, and hence the relay is cold, the strip 20 sags inthe center so that a laterally extending pin 23 secured thereto, and corresponding to the contact l1, engages the stationary angular contact l8.

When current flows through the core l5 and the temperature thereof increases, the strip 20 expands and rises to the position shown by the dotted lines in Fig. 5, thus opening the contacts i8 and 23 with the result as previously described with reference to Fig. 2.

It thus becomes obvious to those skilled in the art that a starting circuit for a gaseous discharge device 'is herein provided wherein the device may be operated from the customary domestic source of supply. Moreover, a resistance device is employed having a negative temperature coefficient which, when cold, has a high resistance to the flow of current. This device, being connected in series with a capacitor and the electrodes of the lamp, allows the gradual flow of current therethrough' until the electrodes are raised to an electron-emitting temperature.

Shortly after the electrodes reach an electronemitting temperature, the resistance device enables an increased flow of current so that a starting voltage may be built up in the capacitor, which then delivers a sufficiently high starting voltage to initiate a discharge between the electrodes. Upon the initiation of the discharge, the resistance device cools off, automatically increasing its resistance to a high enough value as to substantially preclude the flow of current therethrough, thus operating to interrupt the flow of heating current through the electrodes, enabling the latter to be sustained at an electron-emitting temperature solely by the heat generated by the discharge.

In addition, a thermal relay has been herein shown and described, which relay has a negative temperature coemcient. This device may be incorporated in the starting circuit for a gaseous discharge device and operates to connect a capacitor to the circuit for the purp se of supplying a voltage in excess of the normal line voltage for initiating a discharge, after which the capacitor is again shunted from the circuit.

In both the modifications herein shown and described, the device utilizedior interrupting the flow of heating current through the elec trodes is such as to consume no power during operation of the device.

Although several embodiments of the present invention have been shown and described, it is to be understood that other embodiments thereof may be made without departing from the spirit and scope of the appended claims.

We claim:

1. A thermal relay having a negative temperature coefficient comprising a pair of supports, a core of a material suspended between said supports and having a high resistance to the flow of electrical current therethrough when cold which gradually decreases as said relay becomes heated by the flow of electrical current, a stationary contact terminal carried by said relay, and a movable contact terminal supported independently of said core but normally engaging the latter and said stationary contact terminal and operable to disengage said stationary contact terminal upon said relay becoming heated.

2. A thermal relay having a negative temperature coefiicient comprising a pair of supports, a core of a material suspended between said supports and having a high resistance to the flow of electrical current therethrough when cold which gradually decreases as said relay becomesheated by the fl0w ef electrical current, a stationary contact terminal carried by said relay, and a bimetallic contact terminal supported independently of said core but normally engaging the latter and said stationary contact terminal and operable to disengage the latter as said relay becomes heated.

3. A thermal relay having a negative temperature coemcient comprising a hollow core of vitreous material filled with silicon crystals hav ing a high resistance to the flow of electrical current therethrough when cold which gradually decreases as said relay becomes heated by the flow of electricalcurrent, a stationary contact terminal carried by said relay, and a movable contact terminal normally engaging said core and said stationary contact terminal and operable to disengage said stationary contact terminal upon said relay becoming heated.

4. A thermal relay having a negative temperature coefiicient comprising a core formed of zinc oxide having a high resistance to the flow of electrical current therethrough when cold which gradually decreases as said relay becomes heated by the flow of electrical current, a stationary contact terminal carried by said relay, and a movable contact terminal normally engaging said core and said stationary contact terminal and operable to disengage said stationary contact terminal upon said relay becoming heated.

DANIEL 5. opens. ROBERT F. HAYS, JR.

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