US2929960A - Electric discharge lamp starting device - Google Patents

Description

March 22, 1960 R. E. PERKINS EIAL 2,929,960

memo nrscwmcs um? swarms nsvxcs Filed March 4. 195a INVENTORS WlLBl A a meow BY R/t/MRDE. FEM/M) Arm/m5) United States Patent M 2,929,960 ELEcrRIc DISCHARGE LAMP STARTING DEVICE Richard E. Perkins and Wilbur D. Bragdon, Waldobor'o, Maine, assignors, by memo assignments, to Sylvauia Electric Products Inc., Wilmington,-Del;,a corporation of Delaware Application March 4, 1958, Serial No. 719,113 1 Claim. (Cl. 315-100) 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 by 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 (e.g. 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 provides a temporary current path through the filaments until they have become sufilciently heated to support an are discharge. U.S. Patent 2,277,708 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 2,343,262, 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 arc. 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 heatsensitive armature to open the circuit, and the resulting current through the holding resistor retains the armature in its protective open circuit position. Hitherto, the heat-sensitive element has generally taken the form of carbon contacts on the cut-out armature, or a heat sink involving: a heater coil, a ceramic chimney, and a metallic holding clip or a cement encapsuled coil. These devices have given satisfactory operation for some purposes, but they have been relatively expensive and difiicult to fabricate and have imposed current limitations on the overall device.

An objective of the present invention is to provide an improved starting relay for electric discharge lamps. Other objectives are to provide a more satisfactory cutiout for use in such relays, and a more eflicient means for making such cut-outs responsive to prolonged current fiow in the starting circuit.

Accordingly, one embodiment of the invention feaures, for a discharge lamp, a starting relay having a 'itarting switch and a current-sensitive cut-out switch in sensitive armature and means for heating the armature comprising a unitary, current-sensitive, heat conducting and radiating element.

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

series connection, with the cut-out switch having a heat-' 2,929,960 Patented Mar. 22, 1960 Fig; 1 is aside view of a'starting device embodying the invention;

Fig. 2 is afront'view of the device of Fig. 1; and

Fig. 3 is'aschematic 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 container' enclosed package 11, a glow lamp 12 serially conneoted toa cut-out switch comprising a thermally-sensitive" armature 13in series connection with a heating element 14 completely exposed to the atmosphere of the container. 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 base 18 of similar insulating material. Terminals 19 and 20 are provided for connection to a lamp in conjunction with which the device is to be operated. The container of package 11 may be provided with an' asbestos or kraft paper liner to prevent heat from being'dissipated outside the container, thereby increasing the efficiency and safety of the device.

Fig. 3 shows the starting relay connected to the cathodes 21 and 22 respectively of a gaseous discharge lamp 23 of the well-known fluorescent type which comprises a glass envelope 24 filled with an inert gas such as argon or a mercury vapor and has its inner surface coated with a fluorescent material25 characterized by the property of light emission when excited by a discharge are. The circuit is energized, via switch 26 and inductive ballast impedance 27, from an A.-C. source 28. Ballast 27 functions in the customary manner for a discharge lamp to oitset the negative resistance when a conductive arc is produced between filamentary electrodes 21 and 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 1 1. After elapse of a time interval sufficiently 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 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 operates 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. This conductive path, starting-at terminal 1 9, includes the series connection of: heater element 14; armature 13; contact 29; glow lamp 12; and, terminal 20. 1 US. Patent 2,277,708, referred to above, may be consulted for information concerning glow lamp 12. 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 of inert gas at low pressure, e.g. neon at 8 mm.; and, armature 31 has a normally open position with a gap between contacts 32 and 33.

When switch 26 is 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 the gap between contacts 32 and 33. 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 sufircient 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 contacts 32 and '33 are closed, the resistance of the discharge arc, which caused the armature 31 to heat and thereby close the contact, is eliminated; and the armature 31, consequently, cools. Armature 31 is designed with the proper thermal time constant so that it cools enough to return to its normal open-contact position upon the elapse of a currentpassing interval of sufiicient duration to bring 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 contact 32 and 33 to strike an arc.

If the lamp 23 fails to start during the period when contacts 32 and 33 are opened, a new discharge are is produced in glow lamp 12 to heat armature 31, close contacts 32 and 33 again, and thus repeat the startingcycle.

If a succession of starting cycles should fail to strike or maintain an arc across the cathodes 21 and 22 of lamp 23, the cut-out 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 US. 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 causes 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 v opening the circuit to glow lamp 12.

When the starting circuit is thus opened, the sole conductive path for the A.-C. energy from source 28, since lamp 23 is not conducting, is through resistor 16; and, current through this resistor causes sufiicient 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 sufiicient current to operate the starting device in glow lamp 12, and yet must be properly sensitive to this current and dissipate sufiicient 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 balance is achieved, in the illustrative example of the invention disclosed, with a resistance coil having a 5 to 9-ohm (depending upon the characteristics of the bimetallic armature 13) resistance and a current carrying capacity of 1 ampere or higher. For a 40 watt lamp drawing approximately .75 ampere in its starting circuit coil 14 is designed for a power rating of approximately 3 watts (depending upon the characteristics of armature 13) to dissipate suflicient heat to flex the armature after a current conducting cycle of a few seconds. The coil 14 is connected directly between terminal 19 and armature 13; and, because it is completely exposed to the atmosphere of the container of package 11 heats armature 13 in response to the current supplied to glow lamp 12 by both direct conduction and radiation instead of by the more cumbersome and less efiicient heat sink methods previously employed.

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: v

For an electric discharge device having a first starting switch for relatively fast repetitive operation in a series of attempts to start said device and including within a container heating means and a thermally responsive switch member in such arrangement that repetitive full energizations of said heating means consistently and continually cause said switch member to close said switch in like repetition, a second switch, separate, distinct, and spaced from said repetitive switch, for relatively slow operation to automatically terminate said repetitive operation of said repetitive switch and thereafter, upon deenergization of said circuit, to automatically reset itself to again permit said repetitive starting attempts, said second switch comprising a contact and a thermally responsive switching arm arranged to remain in closed relation with each other with the switching arm unmoved .during a plurality of said repetitive starting attempts and to thereafter separate to break a lead to said repetitive switch and terminate the operation thereof, and a heating element in operative relation with said switching arm to automatically cause said separation, said heating element comprising a heat dissipative resistance coil with a power rating of substantially 3 watts exposed to the atmosphere of said container and connected in series with and directly to said switching arm to transfer heat thereto by radiation and conduction, said switching arm and coil being so arranged that a portion of the arm overhangs the coil in the path of heat rising therefrom.

2,344,774 Hodgkins Mar. 21, 194

McCarthy Mar. 7, 1944:

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