US2961564A - Pulsating electric discharge - Google Patents

Description

Nov. 22, 1960 c. KENTY PULSATING ELECTRIC DISCHARGE Filed 001;. 2, 195a Inventor Carl, k'ervt b5 5 His A t tovneg.

United States PatentO PULSATING ELECTRIC DISCHARGE Carl Kenty, Cleveland Heights, Ohio, assignor to General Electric Company, a corporation of New York Filed Oct. 2, 1958, Ser. No. 764,812

Claims. (Cl. 313-174) This invention relates to a pulsating discharge in a mixture of mercury vapor and neon.

I have discovered that under certain circumstances pulsations occur in the positive column of a discharge in mercury vapor with neon. The phenomenon may appear as a red wave travelling along an otherwise blue discharge. The general object of the invention is to provide novel electric discharge devices exhibiting this phenomenon.

The pulsing phenomenon occurs in mixtures of mercury vapor in equilibrium with condensed mercury at a temperature in the range from 20 to 40 C., with neon gas at a pressure in the range from approximately 1 to 3 millimeters. The range of currents wherein it occurs is from approximately 0.2 to 3.5 amperes in tubes ranging from approximately to 35 millimeters in internal diameter.

Other objects and advantages of the invention will appear in the following detailed description of representative embodiments read in conjunction with the accompanying drawing. The features of invention believed to be novel will be more particularly pointed out in the appended claims.

In the drawing:

Fig. 1 illustrates in side view a discharge lamp embodying the invention in conjunction with an operating circuit therefor schematically illustrated.

Figs. 2a and 2b illustrate in side and end views another discharge lamp embodying the invention with a simplified mercury vapor pressure control arrangement.

Fig. 3 illustrates another mercury vapor pressure control means which may be used with the lamp of Fig. 1.

Referring to Fig. 1 the invention is embodied in an elongated vitreous tube 1 having enlarged chambers 2, 2' at opposite ends in which are sealed the electrodes 3, 3'. Each electrode comprises a tungsten filament 4 activated by the usual coating of alkaline earth oxides and supported on inleads 5 sealed through the press 6 of a mount 7. The tube is devoid of any internal phosphor coating.

The lamp is operated by a ballast autotransformer 8 comprising a primary winding 9 energized from the usual 115-120 volt A.C. supply at terminals 10, and a high reactance secondary win-ding 11 connected in series therewith. The electrodes are continuously heated by means of auxiliary windings 12.

The envelope has a filling of mercury exceeding the quantity vaporized during the operation of the lamp, and neon gas in the range from approximately 1 to 3 mm. of mercury. The mercury vapor is maintained in equilibrium with the excess 13 thereof which condenses in a tubular extension or appendix 14 extending normally to the envelope 1 near its midpoint. In other words the envelope is filled with mercury vapor at the temperature of saturation T determined by the coolest point of the envelope, such being the appendix 14. In order to maintain the appendix at the predetermined temperature, it

may be immersed in a water bath 15 contained in a double-walled thermos type bottle 16.

By way of example, in the illustrated embodiment of the invention, vitreous tube 1 has an outer diameter of 15 mm., an internal diameter of 13 mm., and a length of approximately 2 feet measured to the shoulder of the expanded end chambers 2, 2'. The autotransformer 8 has an open circuit voltage of approximately 500 volts and provides through the lamp a discharge current of approximately 300 milliamperes. With a neon pressure of approximately 2 mm. and a saturation temperature T as determined by the temperature of the water bath 15 of 35 C. to 40 C., the pulsating effect in accordance with the invention is strongly present.

The pulsation effect is observed as a wave of red light, illustrated by the vertical hatching at 17; the wave travels along an otherwise blue positive column in Hg+Ne, illustrated by the broken horizontal hatching throughout the tube. The wave may travel in the direction indicated by the arrow 18 and is repeated at regular intervals. The red region appears to be of substantially zero Hg density. It is believed that the Hg is cleaned up on the wall in the blue stage of the discharge only to be released again in the red stage.

The salient features of the pulsation phenomenon are as follows:

The pulsation has been found in mixtures of mercury with Ne but not with He, Ar, Kr or Xe.

It has been observed with Ne pressures in the range from approximately 1 mm. to 3 mm.; with Hg appendix temperatures (T in the range from approximately 20 to 40 C.; with tube diameters ranging from approximately 10 to 35 mm. (I.D.); with current from approximately 0.2 to 3.5 amperes, and with AC. or DC.

The pulsation occurs very well with pyrex or lime glass walls, less well with lead glass and apparently not at all with walls coated with a fluorescent lamp phosphor.

Pulse frequencies of 3 to 60 per minute have been observed. The frequency increases with current and with wall temperature; a steady discharge in a lead glass tube was made to pulsate by heatingthe wall externally. The pulse rate increases with decreasing Ne pressure, with decreasing T and with decreasing tube diameter.

The current range for pulsing increases with increasing Hg appendix temperature.

The range of T for pulsing increases with decreasing tube diameter.

Beyond the range of pulsing, the discharge is either all blue, e.g., for currents too low for pulsing, or has a steady red core, -e.g., for currents too large for pulsing (in the latter case the red core being due to radial electrophoresis).

When a discharge is started, some minutes must be allowed for the walls to reach a suitable stage of mercury saturation before pulsing will commence. During this initial stage, the discharge will be essentially red, Hg cleaning up on the wall nearly as fast as it diffuses in from the appendix or reservoir. Gradually the discharge turns blue and then pulsing may commence. Once a pulse pattern has been established, it is very regular and continues for days or indefinitely if conditions remain constant. But with different tubes and different condition-s, a wide variety of pulse patterns have been observed. For example, to mention only two, the red region may develop in the center of the tube and travel as two waves toward both ends; or it may appear at one end and travel toward the other. The direction of the wave appears not to be determined by the direction of current in a DC. discharge; however, it would seem that electrophoresis has some influence on the precise behavior of the pulsation.

Sometimes a slow secondary pattern is superposed-0n the fundamental mode of pulsation, e.g., the waves may slowly increase toward a maximum and then die away again and so on.

Observing with a spectroscope, the red Ne lines are strong in the red region and weak or absent when the discharge is at its bluest. The Hg lines do not appear to change nearly as much in strength through the cycle as do the Ne lines. The phenomenon is most striking as seen through a red filter glass.

The voltage gradient in the red region has been found with floating probes to be to 100% greater than that in the blue stage, depending on current and appendix temperature T Thus when the red wave is at its maximum, the discharge voltage may exceed by 10% or more the voltage in the bluest stage, depending on the extent of the red region; concurrently, depending on the degree of ballasting, the current will be lower. The greater the ballasting, and therefore, the more constant the current, the more pronounced the pulsing is, because as above noted, a decrease in current tends to make a red discharge go blue.

If the current is suddenly increased by external means, a blue discharge will go red, sometimes only for a short time, depending on circumstances; likewise if the current is suddenly decreased, a red tube or region will go blue, sometimes only temporarily.

By introducing a periodic variation in the ballast, pulsing has been induced in an otherwise steady discharge. The effect is greatest at a certain resonance frequency as might be expected. Under these circumstances, the travelling wave nature of the pulse is somewhat subdued, the whole tube swinging more or less from blue to red and back. There is a noticeable time lag between the current and the visual effects.

Indications are that the electron temperature T roughly doubles as the discharge goes from blue to red.

The foregoing observations of pulsing appear to indicate that Hg ions are cleaned up on the wall during the blue stage and there remain, possibly as neutral atoms, until they evaporate naturally or until they are knocked off by the impacts of Hg ions or by Ne ions in the red stage. It would seem that Ne ions are particularly effec tive in dislodging cleaned-up Hg. It is possible that metastable Ne atoms assist in this process. Further additional heating of the wall during the red stage doubtless assists the evaporation. To account for pulsing, a delay mechanism seems necessary and this could be the natural lifetime of the cleaned-up Hg on the wall, the heating of the wall by the Ne discharge, and the ditfusion time of the Hg vapor in getting back into the body of the tube.

A pulsating mercury neon lamp in accordance with the invention lends itself well to novelty lighting effects. Its usefulness for advertising purposes is, of course, apparent. The pulsating effect is most striking when the blue glow from the mercury discharge is cut out and this may readily be accomplished by mounting the lamp behind a red glass or plastic sheet in a display window or advertising device. Alternatively, the envelope of the tube may be made of red glass which cuts out the blue light from the mercury and transmits the pulsing red light from the neon discharge. The lamp may of course be formed to any desired shape, for instance to a rectangular or circular outline for an advertising sign, or else as letter characters or symbols in accordance with advertising sign practice.

By suitable choice of the design parameters, namely the inside diameter of the tube, the neon pressure and the discharge current, the saturation temperature T of the mercury at which pulsations occur may be made to coincide with a given room temperature. In such case the appendix 1-4 is no longer needed and the lamp will pulsate so long as the room temperature is held at the selected value. This may not always be practical to do but other means of maintaining a constant saturation temperature T are available. For instance as illustrated in Figs. 2a and 2b, a small metal radiator comprising several fan-shaped radiating fins fastened to a-curved foot 21 which is held against the body of the lamp envelope 1 by means of a spring 22, may be used to provide a cool spot on the envelope wall. The excess mercury 13' will condense thereat as shown in Fig. 2b, the temperature of this cool spot determining the saturation temperature T The size or eifectiveness of the radiator may be varied by swinging out the fins or sectors 20. Thus compensation may be effected for various room temperatures in order to achieve the desired saturation temperature T for pulsation.

Fig. 3 shows an alternative arrangement for obtaining a constant saturation temperature T despite a variable room temperature. An appendix 14, similar to that illustrated in Fig. l, is provided with a thermostatically controlled electric heater. The heater may take the form of several turns of resistance wire 23 wrapped around the appendix and connected in series with the lamp discharge circuit; a thermostatic switch 24 short circuits the heater winding at the desired temperature to cut out the heating effect. The heater, switch and appendix are preferably enclosed in an insulating casing to maintain all parts at the same temperature.

While certain specific embodiments of the invention have been illustrated and described in detail, these are intended as exemplary and not as limitative of the invention whose scope is to be determined by the appended claims.

What I claim as new and desire to secure by Letters Patent of the United States is:

1. An electric discharge device for producing a pulsating red discharge comprising an elongated vitreous envelope having a pair of electrodes sealed into the ends thereof, said envelope containing an excess of mercury and neon gas at a pressure in the range from approximately 1 to 3 millimeters, said envelope having an internal diameter in the range from approximately 10 to 35 millimeters, and means for maintaining the mercury in said envelope at a pressure corresponding to a mercury saturation temperature in the range from 20 to 40 C. whereby a pulsating red discharge occurs in said envelope upon current flow therethrough in the range from 0.2 to 3.5 amperes.

2. An electric discharge device for producing a pulsating red discharge comprising an elongated vitreous envelope having a pair of electrodes sealed into the ends thereof, said envelope containing mercury in excess of the quantity vaporized at the saturation temperature in the coolest part of the envelope and neon gas at a pressure in the range from approximately 1 to 3 millimeters, said envelope having an internal diameter in the range from approximately 10 to 35 millimeters, and means for maintaining the coolest part of said envelope at a temperature in the range from 20 to 40 C. whereby a pulsating red discharge occurs in said envelope upon current flow therethrough in the range from 0.2 to 3.5 amperes.

3.An electric discharge device for producing a pulsating red discharge comprising an elongated vitreous envelope having a pair of electrodes sealed into the ends thereof, said envelope containing mercury in excess of the quantity vaporized at the saturation temperature in the coolest part of the envelope provided by a laterally projecting appendix and neon gas at a pressure of approximately 2 millimeters, said envelope having an internal diameter of approximately 13 millimeters, and

means for maintaining said appendix at a temperature from approximately 35 to 40 C. whereby a pulsating red discharge occurs in said envelope upon passage of a current therethrough of approximately 300 milliamperes.

4. The method of producing a pulsating red discharge in an electric discharge device in the form of an elongated vitreous envelope having a pair of electrodes sealed into its ends and containing an excess of mercury and neon gas at a pressure in the range from approximately 1 to 3 millimeters and having an internal diameter in the range from approximately 10 to 35 millimeters, which comprises maintaining the mercury in said envelope at a pressure corresponding to a mercury saturation temperature in the range from 20 to 40 C., and adjusting the current flow through said device in the range from 0.2 to 3.5 amperes to obtain the desired pulsating discharge.

5. The method of producing a pulsating red discharge in an electric discharge device in the form of an elongated vitreous envelope having a pair of electrodes sealed into its ends and containing an excess of mercury and neon gas at a pressure of approximately 2 millimeters and having an internal diameter of approximately 13 millimeters, which comprises maintaining the mercury in said envelope at a pressure corresponding to a mer- 15 2,191,507

References Cited in the file of this patent UNITED STATES PATENTS 1,876,083 Spaeth Sept. 6, 1932 1,908,647 Spaeth May 9, 1933 2,009,201 Pirani et a1. July 23, 1935 2,056,464 Jones Oct. 6, 1936 2,103,039 Pirani et a]. Dec. 21, 1937 Spanner Feb. 27, 1940

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