US2861218A - Discharge lamp flashing circuit - Google Patents

Description

Nov. 18, 1958 w. P. LOWELL, JR 2,851,218

' DISCHARGE LAMP FLASHING CIRCUIT Filed May 25, 1954 INVENTOR. L WILLIAM F LOWELL,JR.

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ATTORN United States Patent DISCHARGE LAMP FLASHING CIRCUIT William P. Lowell, Jl-., Newburyport, Mass., assignor to Sylvania Electric Products Inc., Salem, Mass., a corporation of Massachusetts Application May 25, 1954, Serial No. 432,205

1 Claim. (Cl. 315-98) This invention relates to the flashing of electric gaseous discharge lamps such as fluorescent lamps, for example in signs and the like, and to apparatus for accomplishing such flashing. In particular, the invention relates to alternate flashing of each of a pair-of such lamps.

Flashing of fluorescent lamps has been deleterious to their life when the filaments were not kept heated continuously by heating transformers and the like, and even with the use of such transformers the life of the lamps has been reduced when too high a voltage surge has been produced across the lamp. The voltage surge has been caused by the interruption of the primary or secondary circuit of the transformer for providing the voltage across the electric discharge, especially when a ballasting choke coil has been used in circuit with each lamp. When the circuit breaking and closing device for the flashing has been put in the secondary circuit, the higher voltages involved have been deleterious to the circuit breaking device due to sparking of the contacts.

My invention overcomes such difliculties by flashing the lamps in pairs, with only one lamp being in operation at a time, that is with one lamp being in operation while the other is out of operation, and vice versa. A single choke is used in the circuit to both lamps, with a circuit changing or commutating device for shifting the connections from one lamp to the other, the commutating device being designed so that the second lamp is connected in circuit before the first lamp is disconnected. The second lamp will not flash until the first lamp is disconnected because the voltage across both lamps will be the same and equal only to the operating voltage of the first lamp, which as with most elongated gaseous discharge devices, is less than the voltage required for starting.

Other features, objects and advantages of the invention will be apparent from the following specification, taken in connection with the accompanying drawing which shows one embodiment of a schematic circuit arrangement for flashing the lamps.

Although the circuit changing or commutating device is shown in the drawing as a rotating commutator, other circuit changing devices can be used, for example, time delay relays, thermal switches, pendulum contactors and the like.

In the figure, the elongated fluorescent lamps 1, 2, which may be for example of the type shown in Patent No. 2,258,158, issued October 7, 1941, to Erwin F. Lowry, have elongated tubular glass envelopes 3, 4, hermetically sealed at each end and containing an inert gas such as argon at a low pressure of say 3 millimeters of mercury, and a small quantity of mercury. At each end of the lamps 1, 2 are the usual filamentary cathodes 5, 6, 7, 8, which will generally have a coating of alkaline earth oxides. Cathodes 7, 8 are connected to the secondary 9 of a filament heating transformer 10 having a primary 11 connected to an alternating current line or other suitable source of power. Although shown See V connected to secondary 9 in parallel, the cathodes 7, 8 can be connected in series, if desired.

Each of the filamentary cathodes 5, 6 at the other end V of each of the lamps 1, 2 is connected to a separate secondary 12, 13 of a filament heating transformer 14 having a primary 15 connected to an alternating current line or other suitable source of power.

Another transformer 16, having a primary 17 connected to an alternating current ,line or other suitable source of power, has its secondary 18 connected at one end to the junction of filamentary cathodes 7, 8 and at the other to the choke coil or inductance 19, and from there through the commutator 20 to the cathodes 5, 6 of lamps 1, 2, so that the particular lamp to which con nection will be made at any instant is determined by choke coil 19 can be a separate reactor, as shown, or

can be simply the leakage reactance of winding 18, if the leakage is made sufficient.

The commutator 20 may have any suitable form, but in the form shown consists of two discs 21, 22 of insulating material bearing the metal conducting segments 23, 24. The conducting metal shaft 25 is electrically connected to the segments 23, 24, on which the brushes 26, 27 bear, each brush bearing on only one segment. The brushes 26, 27 are connected, respectively, to lamp 1 through wire connection 29, and the lamp 2 through a wire connection 28. The commutator is attached to the shaft 30 of motor 31, through the insulating connector 32.

There is a portion 25 of the circumference of discs 21, 22 along which the segments 23, 24 overlap circumferentially although spaced apart laterally. Connection to shaft 25 is made through the bearing 33 or a brush.

In operation, the power source heats the filamentary cathodes 5, 6, 7, 8 through the transformer 10, 14 and produces a voltage across the secondary 18 of transformer 16. The motor can be energized by the same, or another, source of power.

When the discs are in the position shown, voltage is applied across only lamp 1, because only brush 26 is in contact with a segment. Lamp 1 is therefor operating, and lamp 2 is not. When the portion 25 of the segment passes under the brushes 26, 27-due to being rotated by the operation of motor 31, both lamps 1, 2 will be connected to the voltage from transformer 16. However, due to the current flow through lamp 1, there will be a voltage drop in choke 19, so that the voltage across the lamps will be less than the voltage of transformer 19, that is, less than the starting voltage of the lamps 1, 2. Lamp 2, therefor, will not start at this position of the commutator 20.

When the commutator 20 turns further, brush 26 slips off segment 24, thereby interrupting the current through lamp 1 and allowing the voltage across lamp 2 to rise to a voltage suflicient to start lamp 2. The latter lamp will now be operating, and lamp 1 will be out of operation. This will continue until the commutator 20 turns around to the position where brush 27 leaves segment 21; lamp 1 will then be lighted again and lamp 2 dark.

When the commutator 20 breaks the circuit to one lamp of the pair, the voltage that would otherwise produce excessive sparking at the breaking of the contacts will be dissipated in starting the other lamp of the pair. The other lamp will start as soon as the voltage across it rises to the voltage necessary for starting so that the voltage across the lamp'need not rise to the full voltage of the secondary 18, if the latter is above the starting average conditions before the voltage"'ri"ses toi thei full volt-age of" secondary 18-, or to any higher value which could otherwise be'produced by a surgeon "disconnecting The lamp' is thus automaticallypro tected from over-voltage at starting, andglon'ger life is,

one of the lamps.

obtained from the lamps.

Whenthe lamps 1 and 2-are standard; 40-watt commercial rapid-start; fluorescentlarnps, 48inches long and 1 /2 inches'in diameter, containing a drop of mercury and filled-with argonat-about 3 millimeters ofmercury pressure; and having filamentary, oxide-coated electrodes of the type shown in United States Patent 2,530,394, issued November 21', 1950; to E. F. Lowry et al., the filament transformer secondary voltage vcantbe about 3.5 volts per filament and the transformer secondary voltage about 250' volts, the choke coil 18' having'alvalue sul'li-v about 0.4,ampere.

What I claim is:

Flashingapparatus for a pair only'of electric gaseous discharge lamps having filamentary cathodes including a first lamp and a second lamp, the starting voltage of each lamp being greater than its operating voltage, said apparatus comprising: a common voltage supply for said lamp in parallel; a;v common ballasting reactance for saidlarnps .in parallel, whereby the voltage across 'the lamps is reduced below the starting voltage on the passage of current'by one of said lamps; a switch for connecting said voltage. supply through said reactance to the first only of said lamps; then to both lamps in parallel, andthen, to the second only of said lamps, the switching to the second only of said lamps serving to provide a surge of'voltztgeacross,said'second lamp sufficient to start the same, and means for supplying heating current continuously to said filamentary cathodes.

References Citedsini the file of this patent 2,481,714 Ludvigsen Nov. 8, 1949

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