US2676249A - Discharge tube isolation circuit - Google Patents

Description

April 20. 1954 P. CROSMAN DISCHARGE TUBE ISOLATION CIRCUIT Original Filed April 28, 1948 FIG. I

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5 3 L .IIDIIR 6 "n 6 m a l J 2 m m J l l lfl lw l l l 60V 1 INVENTOR. LORING P. CROSMAN ATTORNEY aivoltage higher than it's Patented Apr. 20, 1954 DISCHARGE TUBE ISOLATION CIRCUIT Loring P. Crosman,"Darien, Conn., assignor to Remington Rand Inc.,

poration of Delaware New York, N. Y., a cor- Original application April'28, 1948, Serial No. 23,811. Divided and this application August 26, 1949, Serial No. 112,621 I 4 Claims. (01. 250-27) This invention relates to circuits which may be isolated and controlled by gaseous discharge tubes, and is a division of application S. N. 23,811, filed April 28, 1948, now abandoned. It more particularly relates to circuits which may be used for control of communication devices or for calculating machinery. While the circuits to be described can be used in a wide variety of applications, they are especially suited for use with two-element discharge lamps having symmetrical electrodes. One type of lamp which has been used in these circuits is filled with low pressure neon gas, and has an ionization potential of about '75 volts. At potentials below this value, the lamp cannot be lighted and will pass a very small current which is generally considerably less than one microampere. When the lamp issubjected to a voltage higher than the ionization potential, the gas is ionized, and in this lighted condition these lamps present a voltage drop of about 60 volts and pass current within the range of .5 milliampere to 50 microamperes. Neon and other gas filled tubes have been used as voltage indicators and as constant current regulators, but so far as it is known, not been used as a variable impedance element to isolate certain parts of a circuit while other parts are working.

The present invention employs only gaseous discharge tubes which have two symmetrical electrodes. It is well known that prior art tubes hav- 7 ing three, four, and five electrodes have been used purposes well incommunication circuits for switching and for generating oscillations. It isalso known that two electrode tubes with unsymmetrical electrodes have been used extensively for regulation of constant current and constant voltage circuits.

One feature of the invention includes a gasdischarge tube connected to two or more input circuits. A voltage dividing network comprising a plurality of impedances is associatedwith each of the input circuits, certain of the impedances being common to each of the dividing networks. The output circuit consists of an output resistor and a gaseous discharge tube arranged in series and connected across the terminals of the voltage dividers. The application of a predetermined voltage to one of the input circuits is not suflicient to ionize the discharge tube in the output circuit and, therefore, no electrical energy can be passed to the output resistor. However, if two or more input circuits receive input voltages of predetermined values, the discharge tube receives ionizationpotential.

the two-electrode type has 1..-

2 It isthen rendered conductive and energy flows through the output resistor and is available at the output terminals.

For a better understanding of the present invention, together with other and further objects thereof, reference is made to the following description taken in connection with the accompanying drawing.

Fig. 1 is a schematic diagram of the circuit in its simplest form.

Fig. 2 is a schematic diagram of a similar circuit showing a neon discharge tube connected to the output leads of two vacuum tube trigger circuits.

The circuit shown in Figure 1 comprises a gaseous'discharge tube it, an output impedance 26, two potential sources [3 and ll, and the im pedance networks comprising impedances ll, l2, l5 and it. switches I4 and I8 control the application of potentials from batteries is and I1 respectively. Resistors ll, 15 and It in parallel with resistor 82 comprise a voltage dividing network associated with battery l3. When switch hi alone is closed the potential at the junction of resistors I l and 15 will be equal to the potential of battery [3 less the drop through resistor H. The voltage dividing network associated with battery l'l comprises resistors 15, H and it which are in parallel with resistor It. When switch It alone is closed the potential at the junction of resistors l I and i5 will be equal to the poten-- tial of battery illess the drop through resistor i5. Note that resistors ii and I5 are common to the voltage dividing networks associated with both batteries l3 and Il. if the batteries l3 and I! provide equal potentials then the impedance networks can be made symmetrical; otherwise impedance values may be chosen to compensate for the inequality of supply potentials.

If the gaseous discharge tube H3 comprises a neon tube having an ionization potential of '75 volts, then for best operational results the resistors should be arranged so that the voltage across the tube is about 50 volts when either one of the input circuit switches is closed. The output circuit resistor 23 is bridged by conductors and output terminals 2! so that an output voltage may be derived from the terminals and transmitted to a voltage operated device such as a vacuum tube.

In order to disclose the operation of this simplified circuit, let it be assumed that resistors I i and it have a value of 15,000 ohms and that resistors l2 and [6 have values of 5,000 ohms. The

batteries is and I1 have a terminal'potential acraeas 3 supply of 88 volts. If, now, switch [4 is closed, the battery [3 Will send currents through two branch circuits. One branch comprises resistor 12. The other branch includes resistors ll, l5, and I 6 in series, the result being an applied voltage of 50 volts across the output circuit which includes the lamp lit and the resistor 20. This applied voltage is insufficient to light the lamp and no current will pass through the output resistor. Because of the equivalents of the two input circuits, the same conditions will apply if switch [4 is open and switch i8 is closed. Now,

if both switches l4 and it are closed, the same currents will flow through resistors l2 and It. The output circuit, however, will receive the full battery voltage the instant before the lamp is lighted. This value of 88 volts is far above the average ionization value of about 75 volts. In this condition the lamp will be lighted and current will flow through the lamp H) and the output resistor 25, thereby providing a potential diner.-

ence between the two output terminals 2!, which. may be applied to a vacuum tubeto operate other" circuits.

It isclear from theforegoing that the values of the impedances comprising the network associated with each potential source must be so chosen that when only one potential source is operated the'potential across the gas tube'circuit is less then its ionization potential. If the imi pedance values are chosen such that with only one potential source active the potential across the gas tube circuit is less than its'ionization potential but greater than its extinguishing potential, then once the tube is fired it will remain i Fig. 2 illustrates a practical adaptation of, the.

simplified circuit shown in Fig. 1, and represents one of the applications of the basic idea to a high speed computing circuit. In this case, the output circuit is composed of two resistors 2fll and 2e 2. Resistors corresponding to II and in Fig. 1 are reproduced without. change in Fig. 2. The input circuit corresponding to resistor 52 in l is shown in Fig. 2 as tworesistors iZ-J and 5 2-2. In a similar manner,.the input circuit B comprises resistors lS-l and l5-2. Instead of a battery and switch as is used in the simplified version, trigger circuits. C and D are employed. Each trigger circuit comprises two triode electron discharge devices with the well known trigger circuit arrangements so that.

either one or the other triode components are in a conducting condition. The trigger circuits are supplied with an anode voltage supply of 166 volts, and a grid potential supply 3! of 34 volts. The operation of this device is essentially the same as the operation of the simplified circuit shown in Fig. 1 except that the voltage values have a different range of operation. If, for example, the double triodes are similar to the 6SN'7, then the trigger circuits may be easily adjusted so that the anode of the conducting triode has apotential of volts, while the anode of the non-conducting triode has a potential of 160- volts. Under these conditions, the lower resistor 20-2 is connected to a biasing source of potential of 60 volts. Now, if trigger circuit C is conducting on the right hand side, thereby applying a potential of 50 volts to resistor H, and if the other trigger circuit D is also conducting on the right, thereby applying a potential of about 160 volts to resistor IS, the potential of the midpoint between resistors i l and i5 is approximately volts. This voltage minus the 60 volt biasing potential is considerably less than the ionization potential of thelamp and, therefore, the lamp will not light. If, however, trigger circuit C is actuated so that it conducts on the left, then its right hand anode potential will be volts, the same as the left hand anode potential of trigger circuit 1). Under theseconditions, the lamp Ill will have an applied potential at its upper terminal of 160 volts which, minus the 60 volt biasing potential, equals 100volts or considerably in excess of the ionization potential. The lamp will be lighted, current will pass through the output resistors 28-1- and 2il-2, and an operating voltage will be made available to an output triode From the above disclosure it will be obvious that when trigger circuit C is conducting on the right hand side, and trigger circuit D is conducting on the left hand side, the lamp will not be lighted. When either one of the trigger circuitsis actuated, the lamp will still not be lighted, but if both trigger circuits are actuated so that trigger circuit C is conducting on the left, and trigger circuit D is conducting on the right, the lamp lfiwill be lighted and the potential across all or any part of the output resistor 20 can be made available forother circuits to control other operations. Trigger stages 0 and D may be actuated by the application of suitable negative pulses applied to conductors 34 and 35. While, in the embodiment of Fi ure 2, control potentials for the gas tube circuit are taken from the anodes of the trigger circuits, it is clear that control signals could be taken from other points in the trigger circuits such as, for example, the cathode circuits of the triggers. It should be further noted that the same considerations that affect the choice of impedance values in" the embodiment of, Figure 1 also apply in the embodiment of Figure 2. Thus, extinguishing of the gas tube obvious that various changes and modifications maybe made therein without departing from the field of the invention which should be'limited only by the scope of the appended claims.

What is claimed is:

1'. An electronic isolating and gating device comprising in combination, a gaseous discharge diode, a first galvanic impedance connected in series with said diode to form a first seriescircuit, second and third galvanic impedances connected in series to form a second series circuit, fourth and fifth galvanic impedances. connected in. series to formua third series circuit, said first, second and third series circuits being connected in parallel with oneanother, a first and second source of potential, means for selectively applying said first source of potential across said second galvanic impedance, and means for selectively applyingpotential from said second source across said fourth galvanic impedance.

2. An'electronicisolating and. gating device-as set-forthin claim J. wherein: the relative values of the second, third, fourth and fifth galvanic impedances are such that the application of potentials from either of the two sources alone results in the application across the gaseous discharge diode of a potential less than its ionization potential, and wherein the simultaneous application of potentials from both sources results in the application across the gaseous discharge diode of a potential exceeding its ionization potential.

3. An electronic isolating and gating device as set forth in claim 1 wherein the first and second sources of potential and the means for selectively applying potentials from these sources comprise a first and second trigger circuit, the steady state outputs of said trigger circuits being galvanically coupled with said second and fourth galvanic impedances.

4. An electronic isolating and gating device as set forth in claim 3 wherein the steady state trigger circuit outputs are taken from galvanic 6 connections to impedances in the anode circuits of said triggers.

References Cited in the file of this patent UNITED STATES PATENTS Number Name Date 2,103,439 Smart Dec. 28, 1937 2,108,219 Smart Feb. 15, 1933 2,146,576 Haselton Feb. 7, 1939 2,252,? 66 Holden Aug. 19, 1941 2,310,328 Swift Feb. 9, 1943 2,311,543 Horn Feb. 16, 1943 2,448,387 Newall et al Aug. 31, 1948 2,502,443 Dunn Apr. 4, 1950 OTHER, REFERENCES Depp and Holden, Circuits for Cold Cathode Glow Tubes, Electrical Manufacturing, vol. 44, pp. 92-97, July 1949. (Note Fig. 10B.)

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