US2911569A - Electric discharge lamp starting device - Google Patents

Description

Nov. 3, 1959 E. F. HUTCHINS ELECTRIC DISCHARGE LAMP STARTING DEVICE Filed March 4. 1958 IN VEN TOR Z8 [KW/N E HUI'C'H/NS A TI'OR/VEY United States Patent 2,911,569 ELECTRIC DISCHARGE LAlVlP STARTING DEVICE Erwin F. Hutchins, Waldoboro, Maine, assignor, by mesne assignments, to Sylvania Electric Products Inc., Wilmington, Del., a corporation of Delaware Application March 4, 1958, Serial No. 719,061 3 Claims. (Cl. 315100) This invention is concerned with gaseous discharge electric lamps and particularly with an improved starter relay for regulating the preheating cycle of such lamps.

In a typical gaseous discharge lamp, illumination is provided through excitation of a fluorescent coating on the inner surface of the lamp by an arc discharge through an atmosphere of inert gas or mercury vapor ionized by electrons emanating from thermionically emissive filaments. During the starting cycle of the lamp, in order to prevent the shock of the relatively high (eg 200 volt) starting potential from being applied suddenly to cold filaments, it has been the practice to provide a starting relay in shunt across the lamp. This relay presents a temporary current path through the filaments until they have become sufficiently heated to support an are discharge. U.S..Patent- 2,343,262 may be referred to for description of a thermostatic glow lamp adapted to regulate the starting cycle in this manner.

Later improvements, demonstrated for example by US. Patent 2,243,262, provide for a cut-out switch in series with the starting device to protect against strain on its circuit components or unsightly intermittent glow at the lamp electrodes resulting from a prolonged or indefinite starting cycle if the lamp fails to strike "or maintain a satisfactory discharge are. It has been common practice to combine the starting and cut-out devices in a single package. Generally, the cut-out has comprised a heat-sensitive, bimetallic armature and a current-sensitive, heat producing element in series connection across a holding resistor in the starting circuit, arranged so that excessive or unduly prolonged starting current causes the heat-sensitive armature to open the circuit, and the resulting current through the holding resistor retains the armature in its protective open circuit position.

Hitherto, in such devices the cut-out armature has generally been bent into a somewhat semicircular shape embracing the holding resistor. Consequently, when the heated armature flexes to break contact it pulls away from the resistor, making it necessary as a design requirement, because higher wattage resistors are unusable due to limitations of size, to lower the value of the resistor in order to generate sufi'icient heat to penetrate the resulting air gap and maintain the armature in its flexed position. This decreasing the value of the holding resistor has resulted in overload dangers and the possibility of circuit failure if the cut-out is operative for an extended period of time.

An objective of the present invention is to overcome this deficiency of discharge lamp starters and provide a cut-out with a more eflicient holding circuit. Another objective is to provide an improved starter for such lamps.

Accordingly, a discharge lamp starter having a starting switch and a current-sensitive cut-out switch in series connection, with the cut-out. switch having: a heat-sensitive armature; a heat generating resistance element in series connection with said armature; and,-a holding resistor connected in shunt across the circuit of said series connected switches,

one embodiment of the invention features base 18 of of light emission when excited ert gas at low pressure, e.g. neon at the armature being bent to encircle, completely, the holding resistor.

Other objectives and embodiments of the invention will be apparent from the following description and reference to the accompanying drawings, in which:

Fig. l is a side view of a starting device embodying the invention;

Fig. 2 is a front view of the device of Fig. 1;

Fig. 3 is a front view of the cut-out armature of the device of the other figures; and,

Fig. 4 is a schematic representation of a starting device, embodying the invention, connected in circuit with a gaseous discharge lamp.

The starting device of the drawings includes, in a package H, a glow lamp 12 serially connected to a cut-out switch comprising a thermally sensitive armature 13 in series connection with a heating element 14. A filter condenser 15 and holding resistor 16 are also provided, with the armature 13 being so bent as to completely encircle the resistor 16 for a purpose to be explained below. The entire assembly is carried by a supporting board 17 which may be of Bakelite and is mounted on a similar insulating material. Terminals 19 and 20 are provided for connection to a lamp in conjunction with which the device is to be operated.

ig. 3 shows the starting relay connected to the cathodes 21 and 22 respectively of a gaseous discharge lamp 23 of the well-known flourescent type which comprises a glass enevlope 24 filled with an inert gas such as argon or a mercury vapor and has its inner surface coated with a fluorescent material 25 characterized by the property by a discharge arc. The circuit is energized, via switch 26 and inductive ballast impedance 27, from an AC. source 23. Ballast 27 functions in the customary manner for a discharge lamp to offset the negative resistance when a conductive arc is produced between filamentary electrodes Hand 22.

Operation of a gaseous discharge lamp of the fluorescent type is well known to those skilled in the art of electrical illumination, and need not be described in detail here. Briefly speaking, when switch 26 is closed A.C. energy from source 28 is applied to cathodes 21 and 22 of lamp 23. Upon initial closing of the switch, however, a shunt path across the lamp is provided by the starting relay of package 11. After elapse of a time interval sufliciently long to insure proper heating of cathodes 21 and 22, the starting relay is open-circuited to permit full potential to be applied across lamp 23. This results in a discharge are through the gaseous atmosphere enclosed within the envelope 24 and an excitation of the phosphor coating 25 with resulting illumination. "Should lamp 23 fail to start in the first instance, the starting cycle is repeated until it does. If, however, after a number of starting cycles, the lamp still fails to maintain an arc, the cut-out open-circuits the starting device to prevent resulting deleterious and unsightly flashing of the lamp. In more detail, the starting relay 0perates as follows:

Upon initial closing of the switch 26, a conductive path is provided between the filaments 21 and 22 in shunt with the lamp 23.

element 14; terminal 20.

US Patent 2,277,708, referred to above, may be consulted for information concerning glow lamp 1 2. It comprises a glass envelope 30, a heat-sensitive bimetallic armature 31, an armature contact 32, and an output contact 33. Envelope 30 contains an atmosphere ofin- 8mm; and, armature 31- has a normally open position with a gap between contacts 32 and 33.

armature 13; contact 29; glow lamp 12; and,

This conductive path, starting at terminal 19, includes the series connection of: heater the gap between contacts 32 and 33.

v quently, cools.

proper thermal time constant so that it cools enough to :return to its normal open-contact position upon the of a current-passing interval of sufficient duration to bring When switch 26is closed, a discharge results between contacts 32 and 33 to complete a circuit through device 12. This circuit, however, has sufficient resistance to produce enough heat to cause the bimetallic armature 31 of device 12 to flex in the direction of arrow 34 and close Thus, a closed circuit is provided through the filaments 21 and 22 of the lamp 23 in shunt with its operational discharge path. This auxiliary starting circuit permits the filaments to heat and emit sufiicient electrons to support an arc discharge through the gas or vapor enclosed in the lamp before full voltage is applied.

During this preheating cycle, because the contacts 32 which caused the armature 31 to heat and thereby close the contact, is eliminated; and the armature 31, conse- Armature 31 is so designed with the elapse filaments 21 and 22 to proper operating temperature.

This return of armature 31 to normal position opens the circuit between terminals 19 and 20, and applies full operating potential across the lamp 23 and resistor 16. Lamp 23, under normal operating conditions will provide a low resistance conductive path, so that current flow through resistor 16 will be negligible and the starter circuit through glow lamp 12 will be inoperative because, due to the voltage drop across ballast 27 resulting from the negative resistance of lamp 23 in operating condition, there is not enough potential across contacts 32 and 33 to strike an are.

If the lamp 23 fails to start during the period when contacts 32 and 33 are closed, a new discharge arc is produced in glow lamp 12 to heat armature 31, close contacts 32 and 33 again, and thus repeat the starting cycle. If a succession of starting cycles should fail to strike a conductive arc across the cathodes 21 and 22 of lamp 23, the cutout portion of the starting relay in package 11 goes into operation to prevent prolonged operation from damaging the relay, producing undesirable flashes in the lamp 23, etc.

The operation of the cut-out portion of the circuit is explained in U. S. Patent 2,343,262 referred to above.

In brief, the starting current to glow lamp 12 is conducted through the series connection of heater element 14, armature 13, and contact 29; and, a prolonged current flow will cause the element 14 to generate and transfer enough heat to the thermally sensitive bimetallic armature 13, which has its bottom end fastened to support 17, to cause it to break contact at its upper end with contact 29, thus opening the circuit to glow lamp 12.

When the starting circuit is thus opened, the sole conductive path for the AC. energy from source 28, since the lamp 23 is not conducting, is through resistor 16; and current through this resistor causes sufficient heat dissipation to hold the armature 13 in flexed, open circuit, position thereby preventing initiation of further starting cycles until switch 26 is first opened long enough for armature 13 to cool and return to its normal position, and then closed again to initiate another cycle.

The operation of the cut-out component of the circuit depends upon efficient cooperation of heater element 14,

armature 13, and resistor 16. The heater element 14 must be capable of carrying sufficient current to operate the starting device in glow lamp 12, and yet must be properly sensitive to this current and dissipate sufficient heat to armature 13 to cause the uneven expansion of its bimetallic components to flex the arm and thereby open the circuit after it has conducted current for a given period of time. Thus, a critical balance must be accomplished between current conductive and heat dissipative characteristics in the element 14. This may be accomplished with a resistance coil having a 5 to 9-ohm (depending upon the characteristics of the bimetallic armaand 33 are closed, the resistance of the discharge are,

ture 13) resistance and a current carrying capacity of 1 ampere or higher. The coil 14 is connected directly between terminal 19 and armature 13; and, in response to the current it supplies to glow lamp 12, beats armature 13 by both direct conduction and radiation.

The ability of the cut-out to protect the lamp and relay by retaining the starting circuit in an inoperative condition is a function of the interaction of holding resistor 16 and bimetallic armature 13. Previously, the armature 13 has been bent in a more or less semi-circle around the holding resistor. Consequently, when heat from the resistor raised the armature to open the circuit, a physical separation between the resistor 16 and the armature 13 resulted; and it was necessary, as a matter of circuit design, to lower the value of resistor 16 in order to supply sufficient heat to penetrate the resulting air gap and maintain bimetallic armature 13 in its raised position. With this relatively lower value of resistance, resistor 16 has a tendency to become overloaded and prone to failure when called upon to hold the starting circuit inoperative for an extended period of time; and, the size limitation of the relay package has restricted the substitution of higher wattage resistors.

The illustrative embodiment of the invention, however, overcomes this difiiculty by providing that armature 13 be bent into a loop completely encircling resistor 16. Thus, when the armature, in response to uneven thermal expansion of its component metals, breaks from contact with terminal 29 it does not move away from the resistor, but comes closer to it so that there may actually be a physical contact between the low expansive side of the bimetal and the resistor, thereby causing the armature 13 to enclose the resistor 16 more tightly and make for more efficient heat conduction from resistor to armature.

Because of the complete bimetallic loop around it, less of the resistor surface is exposed to waste the generated heat. Also, having the loop of armature 13 encircle resistor 16 increases its total length with a consequent increase in the effective leverage of the armature and the amount ofdeflection at the end which contacts terminal 29. This physical arrangement of armature and resistor has made it possible to increase the resistance value (of the same wattage resistor) from approximately 33,000 ohms to from approximately 47,000 to 56,000 ohms with a consequent increase in the safety and reliability of the holding circuit.

A preferred embodiment of the invention has been described with reference to a gaseous discharge lamp of the fluorescent type and in combination with a particular glow lamp starter. Such description has been for illustrative purposes only and not by way of limitation, e.g. the cut-out switch of the invention may be used in combination with other types of discharge lamps and different glow lamp or other starter circuits.

What is claimed is:

1. A relay for regulating the preheating period in the starting cycle of a gaseous discharge lamp having a thermal time constant starting switch and a current-sensitive cut-out switch in series combination, in which said cutout switch comprises: a heat-sensitive armature; a heat generating resistance element in series connection with said armature; and, a holding resistor connected in shunt across the circuit of said series connected switches, said armature being bent to encircle completely said resistor.

2. A cut-out for the starting circuit of an electric discharge lamp which comprises a current-sensitive switch having a heat-sensitive bimetallic armature, .a first heatgenerating resistive element in series connection with and v arranged for heat transfer to said armature, and a second a pair of contact pins extending from one side of said in a heat transfer relationship with said armature being base; a pair of lead-in Wires each connected to one of Wrapped in a complete encircling loop around said rcsaid contact pins and extending from the other side of sistor. said base; a switch assembly mounted on said upright in connection with said lead-in Wires and including a heater 5 References Cited in the file of this Patent element, a thermally responsive armature, a contact mem- UNITED STATES PATENTS her and a thermal time constant switch in series connec- 1 2,355,476 Smith et al. Aug. 8, 1944 tron, and a holding resistor in snunt across said series con- 2,398,682 Whiteside et a1 Apr. 16 1946 nection, said armature and shunt resistor being arranged.

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