US2769939A - Read-out tube circuit - Google Patents

Description

NOV- 6, 1956 c. R. wxLLiAMs 2,769,939

READ-OUT TUBE CIRCUIT Filed. June 12, 1950 aal/me Poza) United States Patent i READ-OUT TUBE CIRCUIT Charles R. Williams, Hawthorne, Calif., assignor to Northrop Aircraft, Inc., Hawthorne, Calif., a corporation of California Application June 12, 1950, Serial No. 167,571 1 Claim. (Cl. 315-233) extends away from the cathode surface, is inversely proportional to the gas pressure. Hence, if a symbol is to be a cathode formed from a thin conductor such as a Having determlned a preferred gas pressure, then sutiicient current of the tube.

It is an object of the present invention to provide a means and method of greatly reducing, by a factor of from V to 1/100 for example, the current drain required to completely cover an extended area cathode with glow.

It is still another object to provide a means of supporting a plurality of tine wire extended area electrodes in a common envelope.

It is a further object to provide a suitable gas lilling for cold cathode glow discharge tubes to promote the oscillatory tendencies of said glow discharge current.

It is a further object to provide a novel circuit for the indication of a particular symbol electrode in a multielectrode glow tube or a particular cathode in a series of cathode glow tubes by causing a cathode glow to form thereon.

lt is a still further object to provide a means and method of causing an extended area cathode to glow intermittently to produce a visible rate flicker.

In brief, the present invention includes the use of a glow tube having an anode and an extended area cold cathode in a circuit whereby the tube is operated on the negative slope of its characteristic curve to cause the tube 2,769,939 Patented Nov. 6, 1956 to self-oscillate when energized from a D. C. source. An oscillatory circuit of this type has the following advantages over a steady cathode glow current circuit when used for read-out tubes, for example:

A. A smaller supply current can be used to cover a given sized cathode ligure withglow.

B. The cathode glow coverage is less dependent upon supply current. Figures having ditterent sizes and area can be covered by the same value of current; hence, one common current supply circuit can be used for all figures in a series.

C. A thinner cathode glow sheath is obtained by self oscillation, which permits the construction of smaller iigures for a given gas pressure.

Other objects and advantages of the present invention will be apparent from the perusal of the following desc-ription of the gures of the drawings in which:

Figure 1 is a longitudinal sectional view of a preferred form of construction of a multi-symbol cathode glow read-'out tube.

Figure la is a cross sectional View taken as indicated by line liz-1a in Figure l.

Figure 2 is a circuit diagram of a read-out glow tube in an oscillation circuit.

Figure 3 is a chart showing typical voltage-current curves for a glow tube of the read-out type.

Figure 4 is a circuit diagram showing how a read-out tube having a plurality of symbol shaped electrodes can be supplied to form the readout indication of one stage of a decade counter.

Figure 5 is a circuit diagram showing how adjacent symbol shaped electrodes may be used as anodes in a read-out tube having a plurality of symbol shaped electrodes.

A read-out tube 11 is shown in Figures l and la having an envelope 12 with a visually transparent window 13. The envelope 12 supports insulating tubes 14 of glass or ceramic for example, which in turn support the symbol electrodes S1, S2, S3, etc. The electrodes are symbol shaped, formed of tine conducting wire, and each symbol electrode S lies in a separate plane parallel to and suiiiciently spaced from adjacent symbol electrodes for proper operation. The supporting wires connect each electrode through a seal in envelope 12 to a corresponding external lead 15. The envelope is filled with a gas mixture such as neon o, hydrogen 10% for example, at a glow discharge pressure such as 50 mm. Hg. The neon is used for its characteristic bright orange glow, and the hydrogen is included to promote oscillatory characteristics. In addition to the symbol shaped electrodes S the tube may or may not contain an additional electrode 17 to be used as an anode. Normally only one symbol electrode is to be glowed at one time, hence any other symbol yelectrode in the tube can be used as an anode. Figure 5 shows a circuit in which the adjacent symbol yelectrode is used as an :anode and will be referred to later.

nite the tube. A resistor 19 is connected in series with source 21 to limit the supply current drain to a value within theoscillatory range of the tube. lA capacitor 20 is connected across the tube to promote oscillation and to provide suiiicient peak current to cause the glow to Hash over the entire cathode surface. A small value resistor 18 is placed in series with capacitor 20 to limit peak amplitudes of tube current and reduce the tendency to form hot spots and consequent arcing.

In Figure 3, x is a typical voltage vs. steady current characteristic obtained with a neon gas lilled tube. A

point a on this curve indicates the minimum current value with which the tube will conduct stably without shunt capacitance other than inter-electrode capacitance. The addition of a shunt capacitor, such as capacitor 26 in Figure 2, will increase the range of oscillationV to a value indicated by point b. Since the brightness of the cathode glow is proportional to the average current drain, it may be desirable to increase the current drain beyond point b. This can be accomplished by the addition of a small percentage of hydrogen or other suitable gas which shifts' the characteristic to a curve X with maximum unstable current points A and B corresponding to points a and b respectively. In addition to increasing the range of oscillation current, the use of hydrogen also increases the lirin g potential from a value c to a value C for example. This permits greater discharge energies to be obtained from a given size shunt capacitor 2i) and thus extends the range of cathode area which can be covered with glow.

The action of the type of oscillation referred to herein is that glow current in the unstable range will automatically extinguish, whereupon the anode 17 potential rises toward the potential of source 21 thus charging capacitor 2.0. When the tiring potential is reached, the tube restrikes; the anode potential drops sharply permitting capacitor 28 to discharge a high amplitude current pulse through the tube causing a flash of glow over the cathode surface. When the capacitor has discharged, the current falls back into the unstable range and the glow again extinguishes, thus completing the cycle. If the repetition rate of these pulses is sufficiently high, the glow will appear to the eye to be continuous. The repetition rate of the ashcs can be controlled by the value of capacitor 20. A sufficiently large capacitance can cause the glow flashes to be individually distinguishable by the eye thus causing the symbol to appear with a icker which may be desirable, as in an advertising sign for example.

Figure 4 shows a decade read-out tube circuit which may be employed to indicate the state of a counter decade. The ten symbol cathodes S1 to So are connected in series with ten corresponding switches or gates g1 to go. The gates are normally closed and are controlled by the counter such that only one gate corresponding to the state of the counter is open at a given time. A single supply circuit similar `to the circuit of Figure 2 can be used to supply all symbol cathodes regardless of the considerable diierences in surface area of the individual symbol electrodes.

Figure V shows a circuit in which a decimal read-out tube is used to indicate the position of a ten position step switch or stepping relay 23. With this circuit the anode used in Figure 4 is unnecessary, thus an economy of tube components is obtained. The supply circuit is the same as that of Figures 2 and 4. In switching the two poles of switch 23, adjacent symbols are connected to form the anode and cathode of a glow discharge circuit. It is not necessary to use the immediately adjacent electrode as an anode, as a more distant electrode can be chosen for the purpose of obtaining a better l'ing to burning voltage diierential and a resulting better distribution of glow over the cathode. However, if the anode to cathode spacing is too great, an undesirably high potential source 21 will be required so the optimum .anode to cathode distance may be the equivalent of two or three symbol electrode spacings. Anode area is not critical; however, it is desirable to have the anode approximately equi-distant from all parts of the cathode to obtain uniform intensity of glow over al1 parts of the cathode. This requirement is quite well satised by the use of a parallel symbol electrode as an anode. Frequently small glow spots iappear on the anode surface iand conducting paths from anode to cathode are somewhat luminous, therefore, it is sometimes desirable to have the anode behind the cathode as viewed by the observer so that these undesirable sources of glow will have less prominence.

While the invention has been described as using cathodes in the shape of numerals, the invention is equally applicable to the use of multiple cathodes in the form of letters, for example. In this latter case, gates g can be used to cause the letter cathodes to spell words for example, suitable for advertising and similar purposes.

From the above description it will be apparent that there is thus provided 1a device of the character described possessing the particular features of advantage before enumerated as desirable, but which obviously is susceptible of modification in its form, proportions, detail construction and arrangement of parts Without departing from the principle involved or sacrificing any of its advantages.

While in order to comply with the statute, the invention has been described in language more or less specific las to structural features, it is to be understood that the invention is not limited to the specific features shown, but that the means and construction herein disclosed comprise a preferred form of putting the invention into effect, and the invention is, therefore, claimed in any of its forms or modiiicatons Within the legitimate and valid scope of the appended claim.

What is claimed is:

In combination, a tube having a light transmitting portion, an ionizable gas disposed in the tube at a pressure for producing a glow discharge upon ionization, a plurality of cathodes disposed within the tube, the cathodes being shaped to represent different symbols and being superimposed in substantially parallel relationship to one another adjacent to the light transmitting portion of the tube, an anode disposed in the tube, a plurality of switches each associated with a different cathode, a source of direct voltage, a resistance, and a capacitance, the voltage source, the resistance and the switches being connected in series with the capacitance to provide for a charging of the capacitance upon the closure of one of the switches, the Voltage source, the resistance and the switches also being connected in series with the anode and cathodes to provide for an initial iiow of current from the voltage source through the anode and a part'icular one of the cathodes dependent upon the operation of the associated switches, the capacitance being connected across the anode and cathodes to provide at least one discharge between the anode :and the particular cathode upon the initial flow of current from the voltage source through these members.

References cited in the fue of this patent UNITED STATES PATENTS 1,195,239 Laszlo Aug. 22, 1916 1,826,754 Ehrenhaft Oct. 13, 1931 2,054,882 Schlesinger Sept. 22, 1936 2,142,106 Boswau Jan. 3, 1939 2,150,902 Van Bain Mar. 2l, 1939 2,295,869 Seaman Sept. 15, 1942 2,426,209 Hartley Aug. 26, 1947 2,462,781 Schoenbaum Feb. 22, 1949 2,482,266 Goshorn Sept. 20, 1949

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