US2958011A - Gas tube circuit - Google Patents

Description

Oct. 25, 1960 H. P. RAAB, JR., ErAL 2,958,011

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oct. 25, 1960 H: P, RAAB, IR1 ETAL 2,958,011

GAS TUBE CIRCUIT Filed June 2o, 1945 2 Sheets-Sheet 2 lwlia v BY @QM ATTORNEY.

United States Patent() GAS TUBE CIRCUIT Herman P. Raab, Jr., and Robert L. Haynes, Indianapolis, Ind., assignors, by mesne assignments, to the United States of America as represented by the Secretary of the Navy This invention relates to gas tube circuits and has for one of its objects the provision of an improved method of and means for rendering a gas tube circuit unresponsive -to microphonic and similar undesired signals due to mechanical shock, while permitting signals possessing desired characteristics to actuate the circuit.

Another object of the invention is the provision of an improved gas tube circuit capable of distinguishing between signals caused by mechanical shock and signals due to other causes.

The invention was conceived in the design of a firing circuit for submarine depth charges and will be described, by way of illustration, in its application -to such a circuit. It is therefore a further object of the invention to provide an improved firing circuit highly sensitive to signals of very low intensity caused by a varying magnetic field, but unresponsive to signals due to mechanical shock. It will become apparent, however, from the following description that the invention is of general application, and it is not intended to limit the invention to -the illustrative example described.

The Iobjects of the invention are achieved by delaying a firing potential applied for any reason to a gas tube, igniting an auxiliary gas tube in response to mechanical shock, and preventing the first-mentioned tube from firing by a signal derived from the ignition of the auxiliary tube.

The invention together With the aforementioned and other `objects and advantages may be better understood from the following description of an embodiment thereof when read in conjunction with the accompanying drawings, in which:

Fig. l is a schematic diagram of a circuit embodying the invention,

Fig. 2 is a schematic diagram of a firing circuit for submarine depth charges and including the circuit of Fig. 1,

Fig. 3 is a graph illustrating the form of the signal api pearing at point a of Fig. l,

Figs. 4, 5, 6 and 7 are graphs on the same time base showing variations in voltage caused by signals at different points under different conditions of the circuit of Fig. 1, and

Fig. 8 is a view in elevation of Ia switch used in the circuit of Fig. 1.

The circuit of Fig. 2 is intended Yto be installed in depth charges which are dropped or projected into water to destroy submarines. `During the descent of such a depth charge it may pass close to a submarine without actually hitting i-t. The circuit is designed to respond to the varying or non-uniform magnetic field in the neighborhood of the submarine and to fire the charge when it is at close range thereby increasing its'eiectiveness.

Depth charges are not always used singly, but are frequently dropped in defined groups or patterns. Mechanical shock which may be caused, for example, by the 2,958,011 Patented Oct. 25, 1960 explosion of a nearby depth charge, or by the depth charge hitting bottom, sets up microphonics in the various elements of the circuit, and particularly in the amplifier which forms a part thereof. For each depth charge to perform its allotted task it is necessary to render the device unresponsive to microphonic and similar false signals dueto mechanical shock.

The circuit of Fig. 2 includes pick-up coils 10 connected to input terminals 2 and 3. When the depth charge passes through a non-uniform magnetic eld, a signal which may have an amplitude of no more than one-half a millivolt and a frequency of one or two cycles per second is induced in ,the pick-up coils and applied to the input terminals. The comparatively weak, low frequency signal thus produced is converted by an input capacitor C2, a chopper schematically indicated -at 12, and an input transformer 14 into a series of high frequency pulses which are amplified by a two-stage vacuum tube amplifier comprising tubes V1 and V2 to a Value suicientV to fire a gas tube V3 connectedV in cascade with tubes V1 and V2. A circuit associated with the tube V3 is arranged to deliver a delayed firing signal to a gas tube V5 which is provided with an output circuit including a capacitor C11. This capacitor is normally charged tov Volts, and firing of tube V5 discharges the capacitor and sends a heavy pulse of current through a detonator 16 which is connected between output terminals 4 and 5, thereby ring the depth charge.

The portion of the circuit of Fig. 2 with which the present invention is more immediately concerned has been redrawn for greater clarity in Fig. l, and the elements common to both figures have been given the same reference indicia in each figure. Fig. l also shows, by way of illustration, the values chosen for the various circuit elements in one practical embodiment of the invention.

The circuit of Fig. l includes a third gas tube V4, in addition to the tubes V3 and V5 already mentioned. The three tubes may be identical and in the embodiment described were of a type known as SA-782-B having the following characteristics:

A battery 18 or other source of direct current is provided with terminals 20a, 20b, 20c, and 20d connected to the anode, filament and grid of each tube to operate the filament and provide anode and grid bias potentials of 90 vol-ts and -3 volts respectively for each tube. The anode and lamentary cathode of the tube V3 are connected by a resistor R16 and capacitor C10 in series with a resistor R15 common to the three filament circuits. From the junction point b of R15 and C10, resistors R17 and R21 connect to terminal 20a of the battery 18. Similarly the anode-lament circuit of the tube V4 comprises a series-connected resistor R20 and capacitor C12, the three resistors R17, R21 and R20 and capacitor C12 being all connected at point e. Y

The capacitor C11 in the anode-filament circuit of the tube V5 has already been mentioned, and from the junction point of this capacitor and the anode of V5 a resistor R23 connects to the high voltage terminal 20a of the battery 18.

Resistors R14, R12 and R22 are connected in the grid circuits of each of the tubes V2, V4 and V5 respectively, tothe terminals 20c and 20d of the battery 18 which provides in conjunction with the common filament resistor R15 a total effective bias of 3.3 volts on each grid.

A capacitor C15 has `one terminal connected to the grid of the tube V5 and the other terminal to the common point b between R and C10. The combination which comprises the three resistors R15, R17 and R22 and the two capacitors C111 and C13 constitutes a time-delay network connecting the anode of V3 to the grid of V5.

A voltage divider comprising resistors R18 and R25 is connected across the terminals 29a and Ztlc of battery 18, and a capacitor C11 connects the junction point of these two resistors with the grid of the tube V4. A normally closed switch S2, shown in Fig. 8, is connected in shunt with the resistor R25. The switch may comprise a lirmly mounted contact A and a second contact B mounted on a member D which is shown in Fig. 8 as a leaf spring, but may be constructed in any other appropriate manner to provide spring tension between contacts A and B. An additional mass M may be attached to the contact B. The construction is such that with sufiicient acceleration even a microscopic displacement resulting from mechanical shock will open the contacts momentarily. Accurate construction is not essential, as would be the case with a normally open switch.

The operation of the circuit described is as follows: In a steady state condition, the three capacitors C10, C12 and C14 are each charged to 90 volts from the battery 18. The charge on the capacitor C12 may be regarded as providing the necessary operating anode potential for the tube V5. The form of the amplified signal appearing on the grid of V2 is illustrated in Fig. 3. This signal may be caused by mechanical shock as before related, or may be due to a non-uniform magnetic ield relative to the pickup coils 10 caused by the presence of, say, a submarine. When this signal reaches a value of at least 1.5 volts, V5 fires and C10 is discharged through R15 and V3 until the charge is reduced to approximately 30 volts, whereupon V3 is extinguished and C10 is recharged exponentially from the direct current source 18 through R21 and R17. Fig. 4 shows how the anode voltage 0f V3 varies upon ignition of that tube, while the solid curve of Fig. 5 shows the variation of voltage with time at point b of Fig. l which is effectively the terminal of the capacitor C111 shown uppermost in that figure.

The voltage variations at point b illustrated in Fig. 5 and caused by ring of V3, produce a transient voltage at point d (the grid of V5). The variations of this transient voltage are shown in Fig. 6. The zero line in Fig. 6 represents the situation before V3 is fired, and it will be remembered that thegrid of V5 is then biased t0 -3.3 volts with respect to its cathode. On tiring of 'V3 the grid voltage of V5 falls sharply by about 60 volts, and then rises as shown in Fig. 6 until it reaches a point more than 1.8 volts in excess of the steady state condition, whereupon the critical voltage is attained, and V5 fires. With the circuit elements concerned having the values shown in Fig. l the period of delay between ring of V3 and V5 is approximately .025 second.

Now if the signal which caused firing of V3 was due to mechanical shock that shock will have caused at least a momentary opening of the switch S2. This opening will have been elfected instantaneously upon the occurrence of the shock and will have applied a transient voltage pulse to the grid of V4. R25 and R18 are so related in value to each other and -to the 90 volt source 18 that this pulse will have a peak value of approximately 8 volts, which is more than suicient to raise the potential of the grid of V4 from the -3.3 volts to which it is normally biased to the 1.5 volts necessary to tire it. V4 therefore tires substantially instantaneously upon the occurrence of mechanical shock, and C12 discharges through R and V4 until its potential is reduced to about 30 volts. V3 however gets its anode potential from the charge on C12, and when that potential is less than about 70 volts, V2 cannot produce suflicient signal to fire V5. Firing of V4 therefore serves to limit the signal applied to the grid of V5 to a value insufficient to fire it. This acti-on takes place almost instantly, and owing to the time constant of C12-R21 it takes about one second to recharge C12 to the 70 volts necessary to reignite V3. During that period V5 cannot be fired. When therefore a microphonic signal is generated in the circuit because of mechanical shock, the tiring potential applied to the grid of V5 in response to that signal is delayed, and in the meantime the shock produces a train of electrical events which inhibit tiring of V5. In colloquial terms the countermine action of S2, V4 and C12 gets there first.

The broken line of Fig. 5 shows the effect on the Voltage of point b of the countermine action of V4, and Fig. 7 shows that with the countermine action, V5 does not attain its critical firing voltage.

There has thus been described a circuit in which a gas tube is red at the end of a predetermined period of delay in response to tiring of a second gas tube which is in turn ignited by signals generated within the system of which the circuit forms part. If these isgnals are caused by mechanical shock, a third gas tube is red substantially instantaneously in response to and upon occurrence of the shock, and this reduces the anode potential of ythe second gas tube to such a point that it cannot provide suiiicient signal to fire the gas tube irst mentioned.

We claim as our invention:

1. In a device which includes a gas tube, the combination with said tube of a second gas tube provided with an anode, a source of potential for said anode constituted by a source of direct current having a capacitor shunted thereacross; one terminal of said capacitor being connected to said anode, a time delay combination connecting said anode and said first mentioned tube, signalresponsive means for tiring said second tube, a third gas tube connected across said capacitor, and means substantially instantaneously responsive to mechanical shock to elements of said device for firing said third tube whereby to discharge said capacitor and thereby to prevent the potential of said anode from rising to a value sufficient to tire said first tube in response to false firing of said second tube as a result of mechanical shock.

2. A combination according to claim 1 wherein the means for firing said third tube include a normally closed switch adapted to be opened substantially instantaneously in response to mechanical shock thereto, and connections for applying a transient pulse of energy to said third tube in response to opening of said switch.

3. In a control circuit, a first gas tube, means for normally tiring said first tube at the end of a predetermined period of delay in response to the firing of a second gas tube, means for firing said second gas tube in response to signals generated within a system of which said circuit forms a part, a third gas tube adapted, when tired, -to prevent normal tiring of said lirst gas tube in response to the firing of said second gas tube, and means including an element actuatable by a mechanical shock to cause said third gas tube to tire before the end of said period of delay, in response to a mechanical shock of suflicient magnitude to actuate said element.

4. In a control circuit, a rst gas tube having a control electrode, means for normally applying to said control electrode after a predetermined delay period a potential of suicient magnitude to tire said tube in response to the tiring of a second gas tube, means for ring said second gas tube in response to signals generated within a system of which said circuit forms a part, a third gas tube adapted, when tired, to prevent the application of said potential to said controly electrode, and means actuatable by a mechanical shock of sucient 5 6 magnitude to cause spurious signals to be generated 1,382,374 Maxim June 21, 1921 Within said system -to cause said third gas tube to re be- 1,919,977 Fitzgerald July 25, 1933 fore the end `0f said delay period. 2,284,850 Smith June 2, 1942 2,404,739 Mumma `uly 23, 1946 References Cited 1n the le of this patent s 2,406,870 Vacquier Sept 3, 1946 UNITED STATES PATENTS 1,310,568 Heap et al. July 22, 1919

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