US3444431A - Electric flash beacon - Google Patents

Description

May 13, 1969 s. GOLDBERG 3,444,431

ELECTRIC FLASH BEACON Filed Oct. 23, 1965 Sheet of 2 Fig.7

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TIMEIMILLISECONDS) TIMEISECONDS) SEYMOUR GOLDBERG INVENTOR A TTORN E YS May 13, 1969 Filed Oct. 23, 1965 S. GOLDBERG ELECTRIC FLASH BEACON LOW VOLTAGE o 0c SUPPLY AC SOURCE MOTOR DRiVE SOURCE Sheet 3 of2 AC SOURCE INVENTOR SEYMOUR GOLDBERG BY (W 4 ATTORNEYS States 3,444,431 ELECTRIC FLASH BEACON Seymour Goldberg, Lexington, Mass, assignor to EG & G, Inc., a corporation of Massachusetts Filed Oct. 23, 1965, Ser. No. 503,948 Int. Cl. Hb 41/34, 41/14 US. Cl. 315200 1 Claim ABSTRACT OF THE DISCLOSURE This invention relates to optical beacons and more particularly to the utilization of electronic flash devices in such beacons.

The prior art has not made full use of electronic flash equipment in beacons because, by its very nature, the flash is of such a very short duration. In identification and warning systems, found in lighthouses and other such locations, the very brilliant light flash from an electronic flashtube can be seen from great distances, but it quenches so quickly that an observer has difliculty in precisely determining an accurate bearing on such a source. For vehicles travelling at great speeds the problem is increased because there may be a substantial change in bearing between flashes.

Many prior art approaches have been tried which combined the high-intensity short-duration electric flash with a low-intensity incandescent lamp. Some of these systems substituted the incandescent lamp for the charging impedance in the capacitor charging circuit. Such systems had a number of disadvantages including a decrease in the light output of the incandescent lamp as the capacitor becomes charged. Another disadvantage was the requirement of two individual light sources to provide one light signal.

The invention disclosed herein has as its primary object to provide a simple and eflicient light flashing system for beacons and the like which combines the advantages of the prior art systems without their inherent disadvantages. This system has a single light source but operates it in a dual mode. In summary, this invention teaches a light producing electric discharge flashtube and associated circuitry to operate it first in its conventional mode in which a brilliant flash of light is produced in response to the discharge of a pulse of energy therethrough. Immediately thereafter, current is passed through a flashtube from a lower potential source for a predetermined period of time to maintain the flashtube conducting. The resulting flash is a very brilliant flash of light for a fraction of a second which does not immediately extinguish but decreases to a substantially constant level of illumination for a longer period of time.

To better understand my invention, the following specifications are presented together with the attached drawings in which:

FIGURE 1 is a schematic drawing of the invention;

FIGURES 2 and 3 are graphs displaying characteristics of the light output; and

FIGURE 4 illustrates schematically another embodiment of the invention.

Referring first to the schematic drawing of FIGURE 1, a light-producing electric discharge device is shown connected to an energy storage element, such as capacitor atent ice 11. A source of potential shown as battery 12 charges capacitor 11 through charging impedance 13. The charging circuit for flashtube 10 comprising the source of potential 12, charging impedance 13 and capacitor 11, must be designed to store substantial energy in capacitor 11 determined by the characteristics of flashtube 10. This energy must be great enough to produce a high-intensity light flash when it is discharged as a pulse through flashtube 10. The voltage to which capacitor 13 is charged must be either insufiicient to cause self-firing thereof in the absence of a triggering stimulus or it must be disconnected from flashtube 10 until the moment of flash. This type of circuit is well known in the prior art particularly in the fields of stroboscopes and flash photography.

There is, of course, a number of configurations and variations that may be employed to trigger flashtube 10 and any of these well-known and widely-used circuits may be used. A trigger electrode 17 may be used to ionize the gas within flashtube 10 in response to the application of triggering impulses as taught by US. Letters Patent No. 2,478,901, issued to H. E. Edgerton on Aug. 15, 1949, and entitled, Electric System. Other useful triggering systems are set forth in US. Patents Nos. 2,677,788, issued on May 4, 1954 to K. I. Germeshausen, entitled, Electronically Controlled Electric System, and 2,722,- 629, issued on Nov. 1, 1955, to K. J. Germeshausen and entitled, Electric System. In fact, any system which discharges a pulse of energy through a flashtube to produce a brilliant flash of light may be employed in my invention.

Also connected to flashtube 10 is a lower voltage, steady state D-C supply 14. Intermediate the source 14 and flashtube 10 is a switch 15 and a check valve 16. Check valve 16 is shown in the form of a diode but it may take the form of any unidirectional device which readily presents a lower impedance path for the flow of current from source 14 to flashtube 10 but prevents flow in the opposite direction. Its prime purpose is to withstand and block the surge of high energy discharged from capacitor 11 through flashtube 10. A plurality of diodes 16 may be used in series for this purpose.

Switch 15 is shown as a transistor with its base electrode connected to terminal 19 through which a biasing potential may be applied to cause the transistor to conduct thereby connecting the battery 14 to the flashtube 10. Any source of such biasing potential available for a predetermined period may be connected to terminal 19.

In operation, the capacitor 11 is charged from a source 12 through impedance 13. The charge on capacitor 11 is insuflicient to cause the flashtube to self-fire. A second source of potential, battery 14, is also connected across flashtube 10 but its potential is much smaller than that of capacitor 11. When, however, a triggering impulse is fed to trigger electrode 17 of flashtube 10, the gas therein is ionized and the impedance reduced so that the energy stored in capacitor 11 can discharge therethrough producing a brilliant flash of light.

The flash is a high-intensity flash on the order of, for example, a millisecond duration. The flash duration may, however, be longer or shorter, the important factor being a high intensity flash and the longer the duration, the lower the peak intensity. When the flash peak has passed but before the flashtube deionizes, a biasing potential is applied to close switch 15 and the potential from battery 14 takes over and current flows through the flashtube keeping the gas therein ionized and emitting a light output of substantial intensity although only a fraction of the peak light produced by the capacitor discharge. Current will continue to flow through the flashtube 10 from battery 14 until switch 15 is opened by removal of the biasing potential to break the circuit. The application of the biasing potential need not be precisely timed. It may be applied 3 while the flashtube is nonconductive and remain'in a standby condition.

The graph of FIGURE 2 shows a typical light output pattern for a beacon made according to the principles of this invention. The high-intensity, short-duration light flashes produced by flashtube 10 as the energy from capacitor 11 is discharged therethrough are represented by the spikes 20. The lower-intensity, longer-duration flashes produced by the current flowing from battery 14 are shown by the line 21. The off-time is indicated as 22. The spike 20 has a duration of only about a thousandth of a second while the lower intensity of flash 21 lasts about a second. This is a typical value selected for the purpose of illustration and may be extended or shortened for particular applications and locations. The characteristics of the flash are shown graphically in FIGURE 3 where the time scale on the left portion of the ordinate is in milliseconds. The peak should be as great as practicable in order to develop maximum observability. For convenience, the peak is shown less than twenty times the intensity produced by the current flow from battery 14. In fact, this ratio would, in a preferred embodiment, be on the order of thousands. The off-time is shown as three seconds but any convenient timing cycle may be followed. It is not essential that the off-time be the same between all flashes. Variations may be used to form flashtime patterns to identify the flash source, particularly in areas where a plurality of such beacons are found. The essential concept is the combination from a single lamp, of a very brilliant light flash and a lower-intensity, longer duration flash.

As an example of typical circuit values, an SO-microfarad, 5 kv. capacitor 11 is charged from a suitable source 12 through charging impedance 13, a K ohm resistor, for example. A long are flashtube for producing a high intensity output is preferred but for convenience the configuration may be helical. Flashtubes having a ionizable gas, such as xenon, are preferred but other electric discharge devices, such as spark gaps and vacuum devices, may be used as long as they produce a bright flash of light. Sintered electrodes of the type disclosed in US. Letters Patent No. 2,492,142, issued on Dec. 27, 1949 to K. J. Germeshausen and entitled, Electric System Embodying Cold Cathode Gaseous Discharge Device are preferred because they are resistant to the severe sputtering and erosion common to ordinary electrodes when operated in a DC mode. 7

A triggering impulse of .several kilovolts is applied to the trigger electrode 17 to initiate the discharge of capacitor 11 through flashtube 10. Other forms of triggering circuits may also be used, such as those patented circuits mentioned above. In FIGURE 4 closure of rotary switch 34 initiates application of the trigger pulse in the wellknown manner. A two-electrode flashtube 10 may be triggered by closing a switch to complete the circuit between the flashtube and the discharge condenser 11 or a triggering impulse may be a source of additional potential to the discharge circuit to raise the voltage across the flashtube 10 to a level above the self-firing potential. All these triggering systems are well known and any of them may be used with my invention as long as they quickly discharge the capacitors energy through the flashtube to produce a brilliant flash of light.

A source of potential 14, shown in the drawing as a battery, may be of 50 to 500 volts and is connected to the flashtube 10 through switch 15 and check valve 16. One or more semi-conductor diodes, connected in series, are preferred as the check valve 16. The switch 15 may be any of a number of well-known sources, such as a transistor, a relay, a mechanical, rotary or electronic switch. The basic requirement for switch 15 is to perform a timed switch function to interrupt the flow of current from battery 14 through flashtube 10 ata predetermined time. It must also close the circuit and apply the potential of battery 14 to the flashtube 10. This may be done at any time after current flow has been interrupted and the tube deionized. When the switch is closed, battery 14 is connected to flashtube 10 but no current will flow until the flashtube is triggered. A useful embodiment of switch 15 is the motor-driven rotary switch 34 shown in FIGURE 4 having a pair of contacts 34 to apply the triggering impulse to trigger electrodes 17 and 34 to connect and disconnect the DC potential on lead 32 from low voltage DC supply 31 by means of the low voltage applied to the base of transistor 15 from lead 33.

Many modifications can be made in the circuit shown, such as variations in the charging, energy storage and discharging of the flashtube and the use of a. single energy source such as the AC source in FIGURE 4 in place of batteries 12 and 14. All such embodiments and variations are deemed to fall within the spirit and scope of this invention.

I claim:

1. A light flashing system comprising:

a light-producing electric discharge device having two main electrodes and a trigger electrode;

a first circuit connected across the main electrodes having:

energy storage means; and

means for charging the energy storage means;

means for applying a triggering impulse to the trigger electrode to initiate the discharge of energy from the storage means through the device to produce a first portion of a flash of light, the first portion having a given first intensity and first duration; and

a second circuit also connected across the main elec trodes having:

a source of potential;

a transistor in series circuit with the source of potential and the main electrodes;

a diode in the series circuit between the transistor and the main electrodes; and

motor-driven rotary switch means connected to the base electrode of the transistor for closing the transistor before the energy is fully discharged through the device and for opening the transistor a predetermined time thereafter to produce a second portion of the flash of light, the second portion having a given second intensity less than the given first intensity ending at the predetermined time and of a second duration longer than the first duration.

References Cited UNITED STATES PATENTS 3,169,212 2/ 1965 Walters 3 l5-223 3,286,128 11/1966 Ward 315241 3,337,755 8/1967 Grabowski et a1 307-106 3,354,351 11/1967 Ward 315240 FOREIGN PATENTS 1,002,884 2/1957 Germany.

OTHER REFERENCES Goncz et al., Double Pulsing Boosts Flash Tube Performance, Microwaves, April 1965.

JAMES W. LAWRENCE, Primary Examiner.

J. R. SHEWMAKER, Assistant Examiner.

US. Cl. X.R.

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