APPARATUS AND METHOD FOR FORMING SEGMENTED LUMINOSITY IN GAS DISCHARGE TUBES

Abstract: A gas discharge tube (10) containing gas at a pressure of from 0.5 to 15 mm of Hg and excited by AC power (13, 15, 16) at a frequency of from 1500 to 4000 hz to produce a segmented luminous gas within the tube, in the form of bubbles, and means to provide a net current flow (68, 80, 96) through the tube or waveform asymmetry to cause the bubbles to move.

Description: -OL¬ APPARATUS AND METHOD FOR FORMING SEGMENTED LUMINOSITY IN GAS DISCHARGE TUBES This invention is in the field of illuminated gas discharge tubes. TECHNICAL FIELD Gas discharge tubes, such as the familiar "neon" tubes, are widely used in signs, works of art and for illumination. Such tubes are made by evacuating air from a glass tube, and then introducing a selected gas such as neon inside the tube. The tube is sealed at each ejκl-,.around an electrode with external connection wires. Conventional neon tubes use ordinary 115VAC, 60 Hz electrical power; in order to provide enough voltage to ionize the gas, a current- limiting type of transformer is employed to step up the 115V to the level of usually 2,000 to 12,000V, depending on tube length. The pressure of the gas in the tube is usually from about 1 to about 15 mm Hg. Instead of neon, the' tube may contain other noble gases, mercury vapor or gas mixtures, and the tube may be transparent, translucent, or internally coated with a material that fluoresces when subjected to the radiation of the gas discharge. Different gases and coatings produce different colors and intensities of radiation. All of the familiar gas discharge tubes produce a steady, continuous line of illumination along their lengths. DISCLOSURE OF INVENTION This invention is an apparatus including a gas discharge tube in which the luminosity within the tube is segmented or discontinuous. The luminosity is in the form of a series of closely spaced segments with dark regions between them. The segments of luminosity have the appearance of illuminated "bubbles" in an otherwise dark tube. This invention also includes means to cause the bubbles to move and to contol their movement in order for them to move in either direction along the axis of the tube, or to not move and always occupy a fixed position in the _ tube. The invention includes an ordinary gas discharge tube fabricated by conventional means and having conventional interior rare-gas pressure within the range cited above. The tube is operated by an AC power source having adequate . - potential to produce a discharge and having an operating frequency of from about 1500 to about 4500 Hz. In general, smaller tube diameters require higher frequencies in the range to obtain the discontinuous or segmented luminosity. Operation of the tube at an appropriate frequency 15 within the cited range produces the bubbles; in order to render or maintain them visible it is necessary to control their tendency to "stream" in one direction or the other. This is done primarily in one or both of two ways: Either by slightly adjusting the period- or amplitude-symmetry of the o n a plie AC excitation waveform or by introducing a small DC current into the tube. Secondarily, after the above adjustment(s), a change of frequency can control bubble motion. The bubbles are generally in the form of elongated, 25 oval-shaped segments which may be slightly brighter at their ends and may have their middle portions .slightly necked down. Ordinarily the bubbles are about twice' as long as their diameters. Their size is influenced by the frequency of the excitation energy and the diameter of the containing tube. 30 Their color is determined conventionally as described above. BRIEF DESCRIPTTON OF THE DRAWINGS FIGURE 1 is a schematic electric circuit and a partial view of a gas discharge tube embodying this invention. 3 5 FIGURES 2 and 2A illustrate wave forms useful in the process of this invention. ■-_ FIGURE 3 is a cross-sectional partial elevation view of a tube embodying another form of the invention. FIGURE 4 is a cross-section taken along the line 4- 4 of Fig. 3; 5 FIGURE 5 is a schematic of another electric circuit embodying this invention. FIGURE 6 is a schematic of another electric circuit embodying this invention. FIGURE 7 is a schematic of another electric circuit ■ ] _0 embodying this invention. FIGURE 8 shows a detailed schematic electric circuit for operating the gas discharge tube of this invention. BEST MODE OF CARRYING OUT THE INVENTION 15 The schematic representation of an embodiment of the invention illustrated in Figure 1 includes a gas discharge tube of indefinite length that is generally designated 10. The tube is provided with an electrode 11 and 20 an electrode 12 which are located in opposite ends of the tube. The electrodes are hermetically sealed in the ends of the tube to make a gas-tight interior. The electrodes are placed in the tube which is then evacuated of air, raised to a high temperature so as to evacuate impurities and then 25 filed with a suitable gas, such as neon, at a pressure typically ranging between 1 and 15 mm i_g, after which the ends of the tube are sealed. The manner of making such tubes is well known. An AC power source 13 is connected through leads 15 30 and 16 to electrodes 11 and 12 respectively. Source 13 provides AC power for exciting the gas in the tube to the ionized or luminescent state; it supplies voltage and current generally known to be appropriate in conventional circuits for a discharge tube the length and diameter of tube 10. 35 Source 13 also includes means to limit the magnitude of the tube current e.g., a series reactance either external to a driving transformer within source 13 or a part of that transformer. Such means is also known to the art. Appropriate excitation voltages are those known to the art; in the range of 2000-12000 volts, with currents in the range of 15 to 100 m.illiamperes. Rather than the usual 60 Hz frequency, source 13 in this invention provides a tube excitation frequency in the range about 1500 to about 4000 Hz, with a substantially symmetrical waveform. In addition, the symmetry of the waveform is made capable of being adjusted in any of several ways so that the shape of the waveform above an arbitrary line may be made slightly different from the shape below the line. When source 13 is turned on, the gas in the tube will become ionized and will glow. Segmented luminosity, or bubbles will form, as generally designated 28, but they may or may not be visible since the.train or string of such bubbles may be moving in rapid or slow progression in one direction or ' the other. The symmetry of the waveform may be adjusted in order to slow any rapid drifting of the bubble train until individual bubbles become visible. By appropriate symmetry adjustment and with generally only minor departure from perfect symmetry, the bubble train may be brought to a standstill or caused to move in one direction or the other. Motion may also be controlled by varying the frequency perhaps several hundred Hz after symmetry adjustment. The luminous segments or bubbles, 28, are about as wide as the internal diameter of tube 10 and about twice as long as they are wide. The bubble-like illuminated areas have a slight peanut or dumbbell shape having ends 30 that have about the diameter of the internal diameter of tube 10 and a slightly necked-down center portion 31. Additionally, the regions 30 are slightly brighter than the necked-down region 31. Each of the segments 28 is separated from the adjacent segment 28 by a region 32 which is not illuminated, or is much less illuminated than any portion of bubble 28. The appearance of a tube containing neon is that segments 28 are brilliantly illuminated and have the characteristic red neon color, the brilliance of the illumination blending from very brilliant in regions 30 to slightly less brilliant in region 31 while the regions 32 are almost unilluminated and look relatively dark or take on the character of the background against which the tube is viewed. The bubbles in a moving train of bubbles appear to be provided from a source at or near electrode 11 and to disappear to a reservoir at or near electrode 12, or vice versa. Depending on the individual electrical or mechanical characteristics of tube 10 or electrodes 11 or 12, there may be an appearance of bubbles stretching as they enter tube 10 proper and compressing as they exit at the other electrode. The bulk movement of bubbles through tube 10, however, is one where each bubble appears to be of exactly the same size and shape of each other bubble, they are equally spaced from one another, they have exactly the same brilliance and color and they move at the same speed as one another. In a preferred embodiment of the invention the AC energy is provided in the form of a square wave or a nearly- square wave which is generally illustrated in Figure 2 as 40. One complete cycle of the wave starts at point 41 and extends through a positive portion and a negative portion and ends at point 42. Perfect symmetry of wave 40 obtains when time interval 200 equals time interval 201; asymmetry exists when time interval 200 differs ija magnitude from time interval 201 so that, for instance, right-hand limit of interval 200 is extended to the dashed vertical line 45 while the left-hand limit of interval 201 is equally retracted. A waveform equally satisfactory for production of the bubble effect is generally illustrated in Figure 2A as 202. A typical wave of this general type is a sine wave. Asymmetry of this wave, for the purpose of producing the bubble effect, may be created in the manner described for wave 40 of Figure 2 or may also be effected by clipping, as shown by 203 in Figure 2a. , Although a square wave as shown in Figure 2 is the preferred waveform for the AC power involved in the device of this invention, any AC waveform providing sufficient voltage, current and degree of symmetry and at the proper frequency c may be employed successfully in this invention. A degree of asymmetry in the wave—either in regard to time or amplitude— ill produce movement in one direction or the other of the bubbles 28. If the movement of bubbles 28 becomes too rapid Q they will blur into one another producing effects that depend on their velocity. Some of these effects may be the appearance of luminous dots, moving bands of lesser or greater illumination, or a generally chaotic appearance. As previously stated, the amount of asymmetry required in the 5 waveform is generally slight. It is believed that, if the tube electrodes were exactly identical—which practical ones are not—perfect waveform symmetry would yield a stationary bubble train. Figures 3 and 4 are partial illustrations of o another embodiment of this invention. In Figure 3 tube 10 is only partially illustrated and is connected, as illustrated in Figure 1 for example, to a suitable source of AC power. In the embodiment illustrated in Figures 3 and 4 there is a mid tube current path in the form of a ring 50 made of 5 electrically conductive material that surrounds tube 10 and is connected to 51, a ground or other electrical node electrically referenced to the AC power source, through a lead 52 and a switch 220. When the circuit including tube 10 is adjusted or built to produce a condition where bubbles 28 0 move neither to the left nor to the right, that balanced electrical condition can be changed by closing switch 220. The conducting ring 50 and the conducting gas within tube 10, separated by the glass wall of the tube, form a capacitance through which AC current will flow, causing bubbles 28 to 5 flow in the direction of arrows 53 and 54—or inversely—in opposite directions to or from ring 50. Instead of using an external ring and capacitive coupling, an internal, auxiliary, electrode may be used. This embodiment of the invention produces a striking effect that is useful in advertising or in artwork involving gas discharge tubes. Figures 5, 6 and 7 show in partial schematic form three additional circuits which can be used to control the motion of the segmented luminosity once formed. In Figure 5, an AC power supply generates a symmetrical waveform 61 of voltage, current and frequency as described in connection with Figure 1. The waveform is made substantially symmetrical and its symmetry need not be varied. DC current source 68 is provided, capable of introducing into tube 66 a current of either polarity and variable amplitude, up to typically several hundred microamperes, or zero. Capacitor 67 provides a path for AC current around source 68. With AC source 60 turned on and no DC current introduced from source 68, the gas in tube 66 will become ionized and will glow with the segmented luminosity. Individual segments may or may not be visible because.of their velocity as described in connection with Figure 1. A DC current may now be introduced from source 68 and by appropriate choice of polarity and amplitude the segmented luminosity or bubbles may be rendered visible and controlled as to motion as described in reference to Figure 1 for the case where waveform symmetry was varied. Current source 68 may be configured in several ways known to the art; one such configuration is that of a battery in series with a resistor. The capacitance of capacitor 68 is chosen to allow a negligible AC voltage drop due to the current from source 60, using criteria known to the art. Figure 6 shows another circuit which is the same as in Figure 5 except for the DC current source. In the circuit of Figure 6 a portion of the AC current coming from source 60 is rectified into a resultant DC current for controlling the bubble flow. In this arrangement, connected in series with AC source 60 and tube 66 is a variable rectifier 80 which consists of reverse-connected diodes 81 and 82 and potentiometer 83. The AC current through rectifier 80 is rectified unequally dependent on the setting of potentiometer 83, yielding a net DC current flow through tube 66 which will control bubble flow in the manner described with reference to Figure 5. Figure 7 shows a third circuit making use of a negative feedback loop for controlling bubble motion. The circuit of Figure 7 compensates for any changes in the circuit due, for example, to individual tube characteristics or undesirable miscellaneous current leakages or temperature effects. In the embodiment of Figure 7 an AC power source 90 is used to produce a nominally symmetrical AC wave 91 which is used to drive the system. Capacitor 70 is included in series with AC source 90 and tube 66 to couple the AC signal of source 90 to the tube but block passage of any DC current. It is found that, in a circuit having a series capacitor such as 70, a DC voltage will appear across the capacitor when a tube such as 66 is powered from an AC source such as 90, or 60 in Figure 5. This relatively small DC voltage, on the order of several volts, is apparently generated as a result of the slightly asymmetrical AC excitation and slight electrical and/or mechanical differences between the two tube electrodes. It is further found that change in this DC voltage has polarity and magnitude that are a direct function of change in bubble flow direction and rate of flow. As shown in Figure 7, the described DC voltage across capacitor 70 may be connected back to AC source 90 at 96, in such a manner as to form a negative feedback loop using means known to the art. In this instance, the feedback signal 96 acts to control symmetry of waveform 91, summing its action on the symmetry with the control normally provided within source 90 in the previously discussed manner. If the phase of signal 96 is made such that it opposes any change in symmetry of waveform 91 that would increase signal 96, conventional negative feedback results and the circuit is stabilized against undesirable electrical change of any of the elements within the loop. In the manner described, bubble flow rate and direction may be initially chosen by the primary symmetry adjustment within source 90 and then stabilized against change by feedback signal 96. In any of the embodiments, of course, bubble appearance may be deliberately concealed by suitable asymmetry or net tube current adjustment. Figure 8 shows a detailed circuit diagram of a driving circuit capable of both creating the desired segmented luminosity and controlling its motion. Diodes 100 and 101 are respectively connected to charge capactitors 102 and 103 to opposite voltage polarities from an AC power 5 source 105, typically 115VAC, 60 Hz. Diodes 100 and 101 are rectifier diodes rated at around 2 amperes with breakdown voltage of 300 volts; they need have relatively slow recovery times, operating only at AC power-line frequency. Capacitors 102. and 103 have capacitance of typically 1000 microfarads 0 with voltage rating of 250 volts. Current flowing from power source 105 is connected through a resistor 106 to initiate oscillation by turning on transistor 107 by connection to its base through resistor 113. Transistor 107 is an NPN bipolar junction transistor 5 rated at 200V collector breakdown voltage and a collector current of about 30 milliamperes. The collector of 107 is connected through a resistor 108 to the base of a transistor 110, the collector of which is connected to the base of a transistor 111. Transistor 110 is a PNP transistor rated at Q 1W power dissipation, 300V collector breakdown voltage and 500 milliamperes collector current. Transistor 111 is an NPN power transistor having a gain of 5 to 20 at collector current of 2A and having a collector breakdown rating of 300V. 5 The emitter of 111 is connected to the collector of a similar or identical transistor 112 at electrical node 210. The emitter of 111 is also connected through a resistor 113 to the base of transistor 107. After 107 turns on as previously described, it ~ turns on 110 and 111, causing the voltage of node 210 to swing toward the positive potential of 102. Current also flows from 111 through 113 to act regeneratively to further turn on 107, 110 and 111. Node 210 is also connected through a resistor 115 to the base of a transistor 116 that may have characteristics and specifications identical to those of 110. At this point, 116 is kept turned off because its only base current comes through 115, and at this time the current has the wrong polarity. Node 210 is likewise coupled through a resistor 120 to a low-voltage capacitor 121 with the RC product chosen to yield the desired frequency of operation. Capacitor 121 is connected to the emitter of a transistor 122, the collector of which is coupled to the base of a transistor 123. Transistor 122 is a general purpose PNP low voltage audio transistor such as type 2N3645 and 123 is a general purpose NPN low voltage audio transistor such as type 2N5133. Capacitor 121 now commences charging through 120. When the potential on 121 reaches about +1.4V, 122 turns on regeneratively with 123. Transistor 123 has its collector connected to the base of 107 and thus turns off 107, which in turn switches off 110 and 111. This causes the 210 node voltage to swing toward the negative potential on 103. The 210 node is also coupled through a capacitor 125 to the load including transformer 126, a gas discharge tube 127 and a capacitor 128 connected to one another as previously described. Connected between emitters and collectors of 111 and 112 are respective switching diodes 130 and 131, each having a current capacity of about 2 amperes, a breakdown voltage of about 300V and a recovery time of less than one microsecond. The transformer load coupled through 125, being inductive, causes the 210 node voltage to swing completely toward the negative potential of 103 until 131 conducts to thus clamp the voltage swing so as not to damage transistor 112. 1 Numerous configurations can be devised for transformer 126. In this particular example 126 consists of two transformers 135 and 136 which are connected in tandem. Transformer 126 is a power transformer which takes the 5 incoming 115V signal and steps it down to about 24V. Transformer 136 is an automobile ignition transformer which provides the current limiting and high voltage required for driving the tube 127. Next, current flowing toward the 210 node passes 0 through 115 to turn on 116, whose collector is connected through a resistor 140 to the base of transistor 112 to turn it on. Capacitor 121 now begins charging through 120 toward the opposite polarity (i.e., negative), thus turning off 122 and 123. The current through 113 now has the wrong polarity 15 to turn on 107, while the current through 115 acts regeneratively to hold 116 and 112 on. Capacitor 121 continues charging negatively until its potential reaches about -1.4V, at which time transistors 141 and 142 accomplish regenerative shut-off of transistor 116 in a manner identical 20 to that of 122 and 123. The cycle continuous, with the 210 node voltage again swinging toward the potential of 102, on this half-cycle being clamped by diode 130. Resistors 145 and 146 are connected to capacitor 121 to function as the asymmetry means generally designated 25 148. Resistor 146 is a potentiometer connected between plus and minus supply voltages at capacitors 102 and 103 respectively. By its adjustment, a small current of either polarity may be delivered through resistor 145 so as electrically to offset the charging waveform of capacitor 30 121, thus slightly altering the symmetry of the node 210 waveform, as illustrated in Figure 2, in order to control flow of the segmented luminosity or bubbles in gas discharge tube 127. Tube 127 is driven by high-voltage, high-reactance transformer 126, which receives excitation on its primary 35 winding via capacitor 125 from the 210 node. Capacitor 128 is included in Figure 8 to illustrate the embodiment of this invention shown in Figures 5 and 7. In order additionally to control bubble flow, a DC current, from a conventional DC current source not shown, may be introduced at terminals 152 and 153. Also, 152 and 153 may be connected through conventional circuitry to terminals 150 and 151 (removing the connection shown between 150 and 151) to effect a negative feedback loop. Another means for controlling bubble flow is to incorporate a photoelectric device connected, for example, at terminals 150-151 or at terminals 152-153 or delivering current directly to capacitor 121. A photoelectric device placed adjacent to tube 127 can sense bubble position and motion by responding to the alternate lighter and darker regions within the segmented luminosity * Instead of a photoelectric device, this means may be implemented using a third, auxiliary electrode or plurality of electrodes inserted into the tube. The third electrode will extract a small current flow from the main flow of current through the tube. The magnitude and polarity of this current or currents may be used to control bubble flow.

Claims: • ] _ CLAIMS: I. In a transparent gas discharge tube (10) having an electrode (11, 12) sealed in each end and an AC circuit (13, 15, 16) including said electrodes (11,12) and sufficient 5 potential (13) between said electrodes to ionize sai gas, the improvement comprising: first means to produce an alternating current (60, 90) at a frequency between 1500 and 4000 Hz and second means to regulate the symmetry (68, 80, 96) of the resultant tube current, o 2. The device of claim 1 wherein said second means (68, 80, 96) produces current having a symmetric waveform. 3. The device of claim 1 wherein said second means (68, 80, 96) produces an asymmetric waveform. 4. The device of claim 1 wherein said second means 5 (68, 90, 96) provides a net current flow through said gas. 5. The device of claim 4 wherein said second means comprises a DC current source (68) that includes said electrodes. 6. The device of claim 5 wherein said DC current o source (80) is powered by a rectifier which is powered by said AC circuit. 7. The device of claim 1 including means (96) to derive a DC signal from said AC circuit. 8. The device of claim 7 wherein said DC signal is 5 employed to regulate said second means. 9. The device of claim 1 wherein said means to produce alternating current (60, 90) produces said alternating current in a square waveform (91). 10. The device of claim 1 including a mid-tube 0 current path (50). II. The device of claim 10 wherein said mid tube current path includes an electrically conductive surface in capacitive proximity to said tube. 12. A method for producing segmented luminosity in 5 a gas discharge tube (10) having an electrode (11, 12) at each end comprising maintaining said electrodes in an AC circuit having sufficient potential to ionize said gas and having a frequency of from about 1500 to about 4000 hz, and regulating the symmetry of the current in said tube. 13. The method of claim 12 including maintaining a DC circuit (68, 90) including said electrodes. 14. The method of claim 13 wherein the current • flow of said DC circuit is variable. 15. The method of claim 13 wherein said AC circuit has an asymmetric waveform.

Inventors: HERRICK KENNAN CLARK, HERRICK, KENNAN, CLARK
Applicants: HERRICK KENNAN C, HERRICK, KENNAN, CLARK
Application year: 1986
Main classification: H05B37
IPC codes: H05B41