US2902624A - Discharge tube flashing circuit - Google Patents

Description

P 1, 9 c. s. WRIGHT 2,902,624

DISCHARGE TUBE FLASHING CIRCUIT Filed June 22, 1953 INVENT'OR. 01421.55 Warm/r United States PatentO DISCHARGE TUBE FLASHING CIRCUIT Charles S. Wright, Van Nuys, Calif.

Application June 22, 1953, Serial No. 363,127

1 Claim. (Cl. 315-100) More particularly Blinking signs and lights, for advertising purposes for example, are conventionally caused to flash or turn on and off rapidly by means of simple break and make contact in the input circuit to the light. Flashing the light bulbs in this manner materially diminishes their life, primarily because of the rapid and perpetual cooling and reheating of the filaments. The expansion and contraction of the filaments due to this variation in heating will cause the filaments to break down relatively quickly. It is Well known that a light bulb will actually last longer if permitted to burn continuously as opposed to turning it on and off in rapid succession.

The problem of long life is especially acute in fluorescent type bulbs employing a gaseous discharge for illuminating purposes. the filaments must be heated to a given temperature in order to effect ionization of the gas within the tube. There must also be applied a given voltage across the tube to eflect the discharge. If a simple make and break circuit Were employed at the input terminals, a preliminary glow discharge would have to be effected to commence the ionization before the actual discharge resulted. Upon turning oif or breaking the input circuit, the filaments would cool down thereby permitting the formerly ionized gas particles to become neutral. On again making the circuit, the ionization process would have to be repeated before a suitabledischarge could be efl'ected. As a result, not only have discharge types of tubes had their lives seriously diminished by virtue of blinking them, but in addition the blinking itself'has.

been somewhat erratic due to the pre-ionization period required before the main discharge will take effect.

It is a primary object of the present invention accordingly, to provide an improved flashing circuit for a discharge type of tube in which the filaments of the tube are maintained in a heated state even though the main discharge is not taking place. This results not only in a prolonged tube life since the variation in the filament temperatures are quite small between the olf and on periods, but also the blinking is more uniform in that the initial ionization preceding the main discharge is maintained to a far greater extent than is the case when the filaments are permitted to 0001 during the off period. This latter feature results in the substantial elimination of erratic operation.

A further object of the invention is to provide a 'simplified and completely automatic means for making and breaking the flashing circuit to effect theblinking. A feature in this regard is inclusion of means for adjusting the period of blinking and also means for critically adjusting the current flow through the discharge tube fil- In these types of discharge tubes,

2,902,624 Patented Sept. 1, 1959 ice aments in order to minimize temperature variations of these filaments.

These and further objects and advantages of the invention are attained by connecting the flasher circuit in shunt with the filaments in the discharge tube. The flasher circuit includes a make and break contact in series with at least one resistance. When the contact is made, the current Will be provided with an additional path through the resistance to drop the voltage between the tube filaments momentarily, and thereby terminate the main discharge. With the termination of the discharge, the impedance between the filaments along the discharge path is greatly increased and most of the discharge current will be shunted through the contact and series resistance in the flasher circuit. This current however, will maintain the filaments of the discharge tube in a heated state. When the make and break contact is opened, the removal of the flasher circuit current path will cause a momentary increase in the voltage between the tube filaments thereby immediately starting the main discharge to cause the tube to light. The tube will then not be turned off again until the contact in the .flasher circuit is again closed.

The series connected resistance in the flasher circuit may be adjusted to control the current going through the filaments during the off period of the tube to maintain the current 'at least as great as the current passing therethrough during the on period of the tube. So adjusting the resistance in this manner will minimize the temperature variation of the filaments during the OE and on periods thereby greatly lengthening the life of the tube. If desired a second series connected variable resistance may be provided for this purpose.

The flashing circuit itself includes a 'bitrnetallic strip adapted to break the contact upon being heated. In a preferred arrangement the series connected resistance is wound in a coil type of formation and adapted to radiate heat for actuating the bimetallic strip, which strip itself may be insulatively supported. This particular arrangement is extremely advantageous, since the usual bimetallic strip construction requires much more current to heat it than is available in the conventional fluorescent lamp circuits. In other words, for a given amount of current much more heat can be generated by the resistance coil as described above. This resistance then, serves a dual function: first, it permits an adjustment of the current flowing through the filaments of the tube during the off periods to maintain them in their heated state with a minimum of variation from that when the tube is on, and secondly, this same resistance serves as a heater element for the bimetallic strip.

A better understanding of the invention will be had by referring to the accompanying drawings, in which:

Fig. l is a perspective view of a typical advertising sign employing a blinking or flashing light operated in accordance with the invention;

Fig. 2 is another perspective view of the rear of the sign shown in Fig. l as seen looking in the direction of the arrow 2;

Fig. 3 is a cut-away perspective view of the flasher circuit housing and the various flashing circuit components enclosed therein;

Fig. 4 is a cross-section of the housing showing the terminal connections; and

Fig. 5 is a schematic circuit diagram of a preferred form of the invention.

In Fig. 1 there is shown an advertising sign comprising a translucent plate 14), which may comprise Lucite for example, mounted on an elongated base support 11 provided with a window 12 for displaying further information.

As shoWn in Fig. 2, the base support 11 includes ,a fluorescent type discharge tube 13. An open slot (not shown) is provided along the top of the base support over I which the plate or lucite slab is placed to permit light from the bulb 13 to pass to the plate. A rear housing 14 projecting from the lower support 11 serves to enclose the transformer circuit for the discharge tube.

.In order to attract attention to the sign, it is desirable to flashor blink the bulb 13. This is accomplished in accordance with the present invention by means of an exout of contact with the first terminal strip 24 thereby opentremely simple electrical circuit adapted to fit within a can 15 removably secured within ahole 16 in the housing 14. The flasher circuit may thus be readily removed for adjusting the period of thefiashing or blinking, or for substituting a different simple starting switch should it be desired to operate the sign continuously.

Figs. '3 and 4 show sectional views of the can 15 and the various electrical components therein. As-shown, .the can is providedwith a stifi insulative cover member 17 through which project terminals 18 and 19 adapted to contact two seating terminals within the housing 14 when the cylindrical can 15 is pushed all the way into the hole 16. The terminals 18 and 19 are connected to a terminal block 20 as at 21 and 22. A small condenser 23 may be provided between these terminals.

"Secured to the terminal '21 is a first terminal strip 24 adapted to be engaged by a second terminal strip 25 of bimetallic construction. One end of the second strip 25 is insulatively cantilevered to the terminal block 20, the other end being biased 'to engage the end of the first terrninal strip 24 as shown. Within the housing 15 there is also provided a resistance element 26 in the form of a coiled resistance wire. One end of this resistance is secured to the terminal 22, the other'end being connected to the second terminal strip 25. As shown the resistance 26 is longitudinally disposed adjacent the second terminal strip 25.

Referring to Fig. 5 the components shown schematically are provided with the same reference numerals used to designate the corresponding components in the other figures. The input power to the tube is supplied through a conventional 110 volt A.C. line through a transformer 27 providedwith a primary 28 and secondary 29. In the specific type of sign taken for illustration, the fluorescent tube consumes about 15 watts and the operative voltage for this tube is in the neighborhood of 67 volts. The transformer 27 therefore steps down the 110 volt AG. input to this value.

From the secondary 29 the circuit connects to first and second spaced filaments 3t and 31 provided in opposite ends of the fluorescent tube 13. The other end of these filaments respectively are connected through a make and break contact comprising the terminal strips 24 and 25, and the series connected resistance 26. There may also be provided a second variable resistance R in series as shown. All of these components shunt the discharge path between the filaments 30 and 31. In-order to diminish the tendency for the contacts themselves to spark, there is provided thesmall shunting condenser 23. It wiil .be noted that the resistance 26 is disposed longitudinally adjacent the second terminal strip 25. This arrangement permits heat generated in the resistance 26 to be radiated to the terminal strip 25.

In operation, the contact points of the first and second terminal strips 24 and 25 are in normally closed position whereby a current will be passed through the first filament 30, terminal 21, first terminal strip 24, resistance 26, second terminal 22, resistance R, and filament 31'back to the other side of the secondary of the transformer 27. This current will heat the tube filaments 30 and 31 to a temperature sufficient to commence ionization of the gas within the tube 13, the current value through the ' filaments 30 and 31 being controlled by the combined value of the resistance 26 and the resistance R.

The coiled resistance element 26 will become heated and radiate this heat on the second terminal strip 25 which, due to its bimetallic characteristics, will be bent in the circuit (R removed).

ing the flasher circuit. Opening of this circuit will momentarily cause a slight increase in the voltage between the two filaments 30 and 31 due to the removal of the former current path. This momentary increase in the voltage is suflicient to initiate the main discharge between the filaments, such discharge resulting in the complete or substantially complete ionization of the gas throughout the tube length. Once the discharge has started, the resistance along the discharge path between the filaments 30 and 31 is materially reduced and constitutes the main current path. With the contact terminal strips 24 and 25 separated, no current will pass through the resistance 26 and this resistance will subsequently cool permitting the bimetallic strip 25 to re-engage the first terminal strip 24.

With the first and second terminal strips 24 and 25 once again in engagement there is provided the shunt path for the current in addition to the discharge path 32. This resultsin a momentary decrease in the voltage between the filaments 30 and 31, such decrease being sufficient-to extinguish the main discharge thereby causing substantially all of the current to pass through the contact strips 24. and 25 and the resistance R. This .current will maintain the filaments 30 and 31 in their heated condition while the tube is off until the resistance 26 is again heated by such current to break the contact.

Diiferent bimetallic strips maybe employed to gauge the period of operation. Further the resistance R may be incorporated in the small resistance element 26 which, asnoted, may serve the dual function of providing sufficient resistance in the flasher circuit to prevent the filaments 30 and 31 from overheating when the contacts are closed and to radiate heat to the bimetallic strip 25. In a circuit of. this nature, there is generally not suflicient current to heat the bimetallic strip if it were itself employed as part of the conducting circuit. It is an important featureof the invention that this problem has been overcome by the provision of the resistance elewith substantially 67 volts across the secondary transformer winding 29, it has been found that a value of about 150 ohms for the coil type wound resistance element 26 is satisfactory when there is no other resistance With this value there results sufficient current through the tube filaments 30 and 31 to keep them heated to at least the temperature they have when the main discharge exists but not sufficiently heated to the state of incandescence. This is an important adjustment since it permits the fluorescent tube to turn on immediately when the contacts are broken without the preliminary glow at each end due to initial ionization.

When a resistance of less value, in the neighborhood of -ohms, is used, a slight incandescence is visible at the ends of the tube just vpriorto opening of the strip contacts 24 and 25. However this initial starting glow Would not be of suflicient magnitude to be visible on the sign. 1 *It is therefore preferred touse a resistance in the range of 100 to ohms for the'specific device illustrated. In the case of larger type fluorescent tubes operating at different voltages, a suitable value of resistance may be found by simple experimentation. Where the variable resistance R is employed, its value may be adjusted to determine a current value through the filaments which minimizes thefilament temperature variation betweenthe on and off periods.

By means of the flasher circuit of this invention then, there has been provided a fluorescent'type flashing tube in which the temperature of the filaments are maintained within reasonable limits, thereby greatly prolonging the life of the tube. Also, the blinking of the tube is accomplished without flutter and is accurately timed. The flashing circuit itself, being provided in a conveniently removable type can, can be easily replaced in the event of failure, or an entirely new circuit employing a different bimetallic strip may be easily inserted in its stead to change the blinking period. The circuit itself is extremely reliable, compact, economical to manufacture, and employs a minimum of components and may be readily adapted to be connected into the circuit of any conventional type fluorescent tube.

I claim:

In combination, an arc discharge tube including a pair of filaments having therebetween a discharge path of given electrical resistance during discharge of the tube, said filaments having first terminals for connection to an operating voltage source and second terminals; and an electrical flasher circuit connected across said second terminals comprising thermally operated switch means including a resistance heater, said heater being connected in series with said filaments for energizing of the heater when said switch means are in one position, said switch means normally occupying said one position when the current through the heater is less than a. predetermined value and being operated to another position to deenergize the heater in response to a current flow through the heater at least equal to said predetermined value, the resistance of said circuit in one of said positions of the switch means being substantially less than said discharge path resistance and the resistance of said circuit in the other position of the switch means being substantially greater than said discharge path resistance, said circuit resistance in said normal position of the switch means being such that the normal operating voltage across the tube after starting thereof will produce a current through said heater at least equal to said predetermined value.

References Cited in the file of this patent UNITED STATES PATENTS

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