US2716719A - Synchronized fluorescent lamp starter - Google Patents

Description

United States Patent O 2,716,719 SYNCHRONIZED FLUORESCENT LAMP STARTER Dewey D. Knowles, Verona,

house Electric Corporation, poration of Pennsylvania Application April 25, 1951, Serial No. 222,818

2 Claims. (Cl. S15- 103) This invention relates to starters and, more particularly, to a starter for a low pressure discharge device of the positive column type, such as a fluorescent lamp.

The conventional glow type starting switch for a low pressure discharge device of the positive column type, such as a fluorescent lamp, consists of two normally open electrodes, one of which is a bimetallic strip, enclosed in a small glass bulb filled with an inert gas, such as neon or argon. When line voltage is applied, a small current ilows through the circuit as a result of a glow discharge between the two electrodes of the switch. The heating effect of the current expands the bimetallic element and causes the electrodes to touch. The closing of the switch stops the glow discharge, but allows a substantial ilow of current to preheat the lamp filaments during the short period of time when there is enough residual heat in the switch to keep it closed. As the bimetal cools, the switch opens and a resultant high voltage surge through a preheat ballast or simple choke initiates the lamp discharge. if the lamp arc fails to strike, the cycle is repeated.

This conventional starter has several undesirable characteristics. Firstly, the high voltage surge through the inductive preheat ballast is often not a maximum when the contact of the switch is opened; so that the lamp fails to start. Secondly, the opening of the contacts of the switch is not synchronized with the current in the circuit. Finally, a gas-lled switch, opening gradually and continuing the discharge until the arc is quenched, does not induce as much voltage as a vacuum switch.

Hence, it has been found advantageous, according to my invention, to employ as a starter for a low pressure discharge device of the positive column type, a temperattire-sensitive normally-closed vacuum switch in conjunction with magnetic eld producing means, to synchronize the opening of the switch when the iield reaches a maximum and hence when the maximum current ows through the field-producing means.

In its general aspect, the present invention has the object of eliminating the disadvantages and defects of the prior art glow-type starting switches for a low pressure discharge device of the positive column type.

The principal object of the present invention is a temperature-sensitive normally-closed Vacuum starting switch for a low pressure discharge device of the positive column type, supplemented by a magnetic eld producing means which will synchronize the opening of the switch when maximum current is tlowing through said device.

Another object is a vacuum starting switch for a low pressure discharge device of the positive column type, to obtain a voltage surge higher than the conventional inertgas-tilled glow switch.

A further object is a normally closed vacuum starting switch for a low pressure discharge device of the posi tive column type, in combination with magnetic field producing means which will automatically cut out the switch from the device circuit after the discharge is initiated in the device.

A still further object is a vacuum switch and magnetic field producing means for starting a low pressure discharge device of the positive column type which, in the event the device becomes defective, will operate to lock out the lamp.

Other objects of the invention will appear to those N. J., assigner to Westing- East Pittsburgh, Pa., a corskilled in the art to which it appertains as the description proceeds, both by direct recitation thereof and by implication from the context.

Referring to the accompanying drawing, in which like numerals of reference indicate similar parts throughout the several views:

Fig. l is an elevational View of a temperature-sensitive normally-closed vacuum starting switch and magnetic field producing means;

Fig. 2 is a sectional View of the vacuum switch on line 2 2 of Fig. l, in the direction of the arrows;

Fig. 3 is a schematic diagram of the vacuum switch and magnetic field producing means in a typical iiuorescent lamp circuit;

Fig. 4 is a force diagram illustrating the principles 0f operation of the invention;

Fig. 5 is a schematic diagram of the vacuum switch and magnetic field producing means and incorporating a locking out feature in said switch.

Referring to the drawings in detail, and rst considering Figs. l and 2, the part designated 1t) is a soft glass tubular envelope of a temperature-sensitive normally-closed vacuum starting switch 11. Sealed in one end of said envelope is element mount 113. This mount 12 consists of a soft glass stem 13, a low resistance filamentary heater 14, a bimetallic strip or bimetal i5, and a soft iron armature 16.

The stem 13 may comprise two three-piece leading-in conductors 17 and 17 and a two-piece dummy lead or support 1S, suitably embedded in but not through a press 19 of stem 13. For purposes of exhausting or evacuating the interior of the switch 11, a suitable exhaust tubulation Ztl is provided.

The sealing portions of leading-in conductors 17 are suitably Dumet Dumet is the trade name for leading-in wires comprising a thin copper sheath about a nickel iron core. The total thickness of said sheath usually does not exceed 25% of the total diameter of the wire. The inner portions of leading-in conductors 17 may be suitabiy nickel, while the exterior portions, for example, may be braided copper cable. Similarly, the sealing portion of dummy lead 18 is Dumet and the inner portion nickel.

The filamentary heater 1liy is suitably horizontally mounted a short distance above the press 1% between the inner nickel portions of the leading-in conductors 17 and the dummy lead 18.

The leading-in conductor 17 terminates at the heater 14. In turn, the portion of dummy lead 18 above heater 14 is bent horizontally and then vertically downwardly for joining, as by welding, to the lower end of bimetallic strip 15 and for securing the strip in close proximity to heater 14. The nickel portion of the other leading-in condoctor, 17 is L-shaped to form one of the contacts for the switch 11.

On the outside of the unsecured end of the bimetal strip 15 is aixed, as by brazing, a soft iron desirably disc-like armature 16. This bimetallic strip 15 is designed to exert a spring force against the contact extremity of conductor 17, and to bend away from said Contact extremity under the iniluence of heat from iilamentary heater 14.

After the usual exhaust which may comprise baking, induction treatment of metal parts, heater treatment and iinal evacuation, the switch 11 is tipped olf at 21.

Also shown in Fig. l, suitably disposed with respect to bimetal 15 and armature 16, is a simple choke or magnetic field-producing means 22. When the starting Voltage required for the low pressure discharge device is not greater than the supply voltage, a simple choke is employed. However, when the supply voltage is not suiicient to start the arc in a conventional iiuorescent lamp, a step-up auto transformer (not shown) to provide the necessary starting potential and the choke 22 are used.

This choke 22 is designed and disposed with respect to armature 16 so that the maximum value of the magnetic eld force 32, as shown in Fig. 3, produced by such choke alone will not open the contact, and also that the magnetic held alone will hold the contact open once the circuit has been broken and the armature 16 has been noved closer to choke 22 by the combined action of forces 31 and 32.

In Fig. 3 is shown a typical iiuorescent lamp 23 having iilamentary electrodes 24 suitably disposed in each end. While a uorescent lamp has been selected as an example of a low pressure discharge tube of the positive column type, the invention is not restricted to use with iiuorescent lamps. One iilamentary electrode 24 is connected through one leg to the leading-in conductor 17 through the choke 22 to one side of a conventional 60 cycle alternating current voltage supply of vacuum switch The other electrode 24 is connected through one leg to conductor 17 of switch 11 and through a suitable switch 2S to tl e other side of said voltage supply.

Referring now more particularly to Fig. 5, a high resistance heating element 40 is disposed between the conductors 17 and 17 and in a shunt circuit with the switch 11. While it draws negligible current, nevertheless sufricient heat is produced after a predetermined number of unsuccessful starts by this high ohmic resistance heater 40 to heat the bimetal 15 and maintain the switch 11 in an open position, thus locking out the lamp 23.

According to my invention, when switch 25 (Fig. 3) is closed, current tlows successively through the electrodes 24 of lamp 23, the heater 14 of vacuum switch 11, and choke 22, thereby preheating electrodes 24, heating the bimetal 15, and producing an electromagnetic field about choke 22.

As the temperature of the strip 15 rises, slowly in comparison with the 1/120 second duration of a half cycle on a conventional 60 cycle/ second alternating current system, the spring force 30, shown in Fig. 4, of the bimetal 15 against the contact extremity of leading-in conductor 17', is counteracted by a gradually increasing opposing force 31, induced by the heating of the bimetal. However, the force 31 alone never becomes large enough before the Contact in switch 11 is broken to overcome the force 30 and thus open switch 11.

From Fig. 4- it will be seen that the magnetic field force 32 reaches a maximum once every half cycle of alternating current or 120 times per second. The force 31 inducted by heat in bimetal 15 on the other hand increases very slowly, in fact, an innitesimal amount from halt cycle to half cycle of operation. ference between the striking spring force 30 of the bimetal 1S and combined opposing induced by heating force 31 and maximum value of magnetic eld force 32 during a particular half cycle 33 were innitely small, since the maximum value of force 32 is constant from half cycle to halt cycle, the innitesimal increase in torce 31 during the next ,alf cycle 34 would be sufficient to overcome the intinitely small force difference. The contact would be broken during this halt cycle 34, but only at or very near the maximum value of magnetic field torce 32 during half cycle 34 and hence at a time when maximum current is ilowing through magnetic field producing means 22 and the lamp 23.

When vacuum switch 11 is opened, the choke 22 provides a maximum inductive surge of sufficiently high potential to start the arc in uorescent lamp 23. If the lamp 23 fails to start, no current ows through the open switch 11 and the bimetal 15 cools, again making contact with the contact extremity of conductor 17. The abovementioned cycle in vacuum switch 11 and choke 22 is then repeated. If, however, the lamp 23 starts and continues in operation, the magnetic field produced by choke 22 by normal lamp current is sufficient to hold the contact 16 which has been moved closer to choke 22 by the combined effect of forces 31 and 32 away from the contact Thus, if the difend of leading-in conductors 17', and thus automatically cutting the switch 11 out of the circuit of Fig. 4 during the operation of lamp 23.

1f the alternative embodiment of Fig. 5 of switch 11 is employed and the lamp 23 fails to start, after a predetermined number of attempts, the high resistance heating element 40 by this time has heated bimetal 1S suthciently to open switch 11 and maintain said switch in an open position, thereby locking out lamp 23.

Thus, it can be seen from the foregoing description that my invention provides a temperature-sensitive normally-closed vacuum switch 11 for a low-pressure discharge of the positive column type operating in combination with magnetic-tield-producing means, such as the simple choke 22, which will synchronize the opening ot the switch when maximum current is ilowing through said device. This vacuum switch 11, which opens faster than the conventional inert gas-filled glow type switch, thus produces a higher voltage surge for initiating the arc in a low-pressure discharge device of the positive-column type, such as fluorescent lamp 23, than said glow switch type.

Although a preferred embodiment of my invention has been disclosed, it will be understood that modications may be made within the spirit and scope of the appended claims.

I claim:

l. 1n combination a synchronized starter for alternating current operation and a low pressure discharge device having two spaced electrodes at least one of which is a directly heated electrode, said starter comprising a coil connected to one end of said directly heated electrode for providing a magnetic eld force and a normally closed vacuum starting switch adjacent said coil for fast opening at the maximum value of magnetic field torce when maximum current is owing to achieve a maximum inductive surge to start the arc in said device, said switch having an envelope, a stem sealed to said envelope and having at least two leading in and supporting conductors connected to said other end of said directly heated electrode and to said other electrode and a dummy supporting conductor, a resilient bimetallic element on said dummy conductor and having a spring force to yieldingly hold said element in normally closed position against the contact end of one of said conductors, an armature on said bimetallic element disposed within said magnetic tield of said coil so that the magnetic eld alone will hold the bimetallic element in the open position once contact has been broken, heating means connected electrically across said other conductor and said dummy conductor and operable to induce by heat a force on said bimetallic eiement tending to produce armature and bimetallic eiement movement to an open position only when the diiference between said spring force on said bimetallic element and the opposed combined induced force and the maximum value of magnetic eld force on said armature on said bimetallic element is infinitely small on a particular halt cycle of alternating current operation and hence only when maximum current is flowing through said coil on the next succeeding half cycle.

2. The combination recited in claim 1 further including a high resistance heating element connected electrically across said leading-in conductors and hence in a shunt circuit with said switch to heat said bimetallic element after a predetermined number of unsuccessful starts and to maintain said switch in the open position.

References Cited in the tile of this patent UNITED STATES PATENTS 2,025,471 Osborne Dec. 24, 1935 2,355,476 Smith Aug. 8, 1944 2,374,315 Whiteside Apr. 24, 1945 2,398,682 Whiteside Apr. 16, 1946 2,410,198 Buckley Oct. 29, 1946 2,557,809 Willoughby June 19. 1951

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