US2405071A - Pulse generating system - Google Patents

Description

PULSE GENERATING SYSTEM Filed Oct. 1, 1943 VOLTAG E Inventor:

Lewi Ton ks,

by 6T JMA I His/Attorne Patented July 30,1946

PULSE GENERATING SYSTEM Lewi Tonks, Schenectady, N. Y., assignor to General Electric Company, a corporation of New York Application October 1, 1943, Serial No. 504,587

11 Claims.

My invention relates to pulse generating systems, particularly to such systems employing spark gaps as a switch mechanism, and has for its object the provision of a new and improved system-of this character which produces a pulse once per cycle of a source of alternating potential, operates at a high charging voltage, and supplies a large amount of instantaneous power of constant voltage and with fair timing precision. In pulse generating systems powered from an alternating current source and using a spark switch it is desirable to have the pulse generating circuit proper effectively disconnected from the alternating current source at the instant of pulse generation to prevent the formation of a power are across the spark gap. It is also advantageous to generate successive pulses at the same voltage so that the instantaneous power transferred by each pulse shall be the same.

In accordance with 'my present invention, earlier difficulties are overcome and the foregoing advantages are attained in a simple manner by the provision of a pulse generating apparatus in which a charged capacitive storage element or network is connected to a load by a spark gap arrangement or assembly providing two sparks in series and in which a predetermined initial apportionmentof the voltages across the two gaps is changed or disturbed at the desired triggering instant thereby to cause breakdown of the spark gap and to initiate the discharge.

According to my invention, an alternating current source is arranged to charge the storage element through a rectifier, and at a predetermined instant in each cycle of the alternating source voltage the spark gap switch means is triggered by a potential derived from the source, thereby initiating the discharge of the storage element through the load. The capacitive storage element is preferably of such character as to produce a discharge pulse. of substantially rectangular wave form. It will be understood that for this purpose, if desired, a suitable section of transmission line may be used. For purposes of illustration, however, I have shown simply a single capacitor as a capacitive storage element.

In one embodiment of my invention, an initial apportionment of voltages across the serially disposed spark gap is disturbed or changed to initiate the discharge by reason of the connection of the intermediate sparking electrode to an intermediate point of a voltage divider connected between points of varying potential in circuit with the alternating current source. By way of example, in circuits where the storage capacitor is charged on alternate half cycles of source' potential and triggered on opposite half cycles,

may be connected either across the transformer secondary winding or across the rectifier connected thereto. In another arrangement where a large auxiliary storage capacitor is maintained permanently charged from one half of a transformer secondary winding the voltage divider may be connected across the other half of the winding.

The novel features which are considered to be characteristic of my invention are set forth with particularity in the appended claims. My invention itself, however, both as to its organization and method of operation, together with further objects and advantages thereof, may best be understood by reference to the following detailed specification taken in conjunction with the accompanying drawing wherein Fig. 1 is a diagrammatic representation of a pulse generating system embodying my invention in one form; Fig. 2 is a graphical representation of certain of the operating characteristics of the pulse generating system of Fig. 1; and Figs. 3 and 4 are diagrammatic representations of pulse generating systems embodying my invention in other forms.

Referring now to the drawing, I have illustrated at Fig. l a capacitive storage element I0 arranged to be charged on alternate half cycles from an alternating current source I I through a charging transformer I2 and a ,rectifier I3, and to be discharged during the intermediate half cycles of the source potential through a desired output or utilization circuit I5 across which may be connected a suitable leakage resistor or reactor I4. The rectifier I3 may be any suitable unidirectional conducting device and, for purposes of illustration, I have shown a two-electrode electron discharge device of the vacuum or gasfilled type. The utilization apparatus I5 may be any suitable radio apparatus employed to generate high power signals of short duration and accurately timed intervals determined by the frequency of the alternating current source I I. For illustrative purposes, I have shown the apparatus I5 as including a magnetron oscillator upon the anode-cathode circuit of which the pulses from the capacitive element I I] are impressed precisely the frequency f the alternating current source II and which is connected to an antenna I6 to transmit therefrom short duration pulses of intense microwave radiation utilized, for ex ample, in the detection of distant objects.

To discharge the storage element l through the load E5, in accordance with the present invention, a switching means is provided comprising a plurality of spark gap members or conductive electrode members ll, I8, and i9. Preferably the electrode members are three in number, as shown in the drawings, thereby to provide two spark gaps 28 and 2| in series between the capacitive storage element in and the load element Ill. The novel constructional features of the sparking electrodes |8, and H! are described in detail and claimed in my copending application, Serial No. 432,009, filed February 23, 1942, and assigned to the same assignee as the instant application. For the purpose of fully understanding the instant invention, it is sufficient to note that the electrodes ll, |8, and iii are suitably supported in predetermined spaced relation and are formed of an electric conducting material. Each electrode is generally elliptical in cross sectional outline, tapering at an angle of approximately 5 degrees from near the. axis of the spark gap towards the opposite ends in order to minimize any tendency to form the. sparks in other than the line of the axis of the gaps. The electrodes H and it are provided with axially disposed sparking points formed by rounded rods 22 and 23 mounted in the electrodes H and I8, ,7

respectively. For cooperation with the points 22 and 23, the electrodes I8 and I3 have formed on those of their faces, which cooperate with the rods 22 and 23, respectively, upraised bosses 2 1 and 25, respectively. To provide for cooling and deionization of the gaps at the termination of a spark discharge, the electrodes ll and |8 are provided with air duct 2t and 21, respectively, having inlet connections 28 and 23 at one side of the electrodes and outlet ports 3! and 3| disposed along the arcing axis and concentrically with respect to the rods 22 and 23, respectively. A suitable source of air under pressure (not shown) is connected to the inlet ports 28 and 29. As shown in the drawing the electrodes ll, l8, and I9 are connected in circuit so that the sparking points 22 and 23 are positive with respect to the bosses 24 and 25, respectively.

A triggering potential for the spark gaps 2!] and 2| of Fig. l is provided by connecting the intermediate electrode l8 to an intermediate point of a voltage divider 33 connected between the terminals of the secondary winding of the charging transformer l2. One terminal of this winding is grounded, and the ungrounded terminal is identified by the reference numeral 35.

Referring now conjointly to Figs. 1 and 2, it will be evi cut that in operation the condenser I9 is charged from the secondary winding of the transformer l2 through the rectifier l3 on each half cycle of negative potential of the ungrounded terminal 35 of the transformer winding. During this half cycle, no current can flow from the condenser ill to the load elements M and I5 because the spark gaps 20 and 2| are maintained non-conductive, as will be explained hereinafter. During the opposite half cycle of potential, when the point 35 is instantaneously positive with respect to ground, no current can flow through the rectifier it to the condenser l9, but during this half cycle the voltage divider 33 acts to initiate a discharge across the spark gaps 2d and 2|, thereby to discharge the condenser |0 through the load elements |4, |5.

Accuracy of timing the firing intervals is en- (ill hanced by irradiating the gaps and 2| from a source of ultraviolet light either continuously or during phases which include at least the firing instants. At Fig. l I have shown such a source of ultraviolet light conventionally as a rectangle 36. The source 36 may, for example, be a quartz mercury lamp or a spark in air.

The above pulsing operation will be clarified by referring to Fig. 2. At Fig. 2, the curve E represents the instantaneous voltage of the transformer terminal 35. This voltage continuously describes a sine wave at the frequency of the alternating current source H. At the time t:0 the voltage E35 is shown at the beginning of the negative half cycle. Since the rectifier I3 is conducting during this half cycle, the instantaneous potential of the electrode l9 follows the instantaneous potential of the transformer terminal 35 to its maximum negative value and then, by reason of the unidirectional conductivity characteristic of the rectifier l3, remains at this maximum negative potential until a pulse discharge is inltiated. The potential of the electrode l9 is represented by the curve E19 at Fig. 2. Furthermore, during the half cycle of negative potential of the transformer terminal 35, the potential of the electrode l8 also describes a negative half cycle by reason of its connection to an intermediate point on the voltage divider 33. Because of its connection to the voltage divider the maximum negative potential of the electrode I8 is less than that of the transformer terminal 35, and this potential is shown by the curve E18 of Fig. During this negative half cycle, the potential of the electrode remains tied to ground through the resistor i l, and is indicated on Fig. 2 as Em. Thus, at a time approximately electrical degrees after the time i=0, the maximum instantaneous potential of the secondary windof the transformer l2 exists between the electrodes Ill and H3 across the gaps 20 and 2| in series. This total potential remains across the two gaps in series as the potential of the transformer terminal 35 again approaches zero during the second quarter cycle, the distribution of potential across the two gaps being controlled by the potential of the electrode l8. During this second quarter cycle the potential of the control electrode I8 also approaches zero by reason of the sine wave of voltage applied to it from the voltage divider 33. At a time electrical degrees after the time i=0 the full potential of the capacitor 18 is applied across the gap 2| between the electrodes i8 and L! and the electrodes H and I8 are both at zero or ground potential. As the transformer terminal 35 now becomes positive on the positive half cycle of potential of the transformer terminal 35, the potential E18 of the electrode l8 also goes positive by reason of the voltage divider connection, thereby to increase the potential across the gap 2| to a value greater than the maximum instantaneous potential of the transformer terminal 35. This gap 2| is So designed that, while it will withstand slightly more than the maximum instantaneous potential of the transformer terminal 35, it will not withstand the scalar sum of the maximum negative transformer potential on the terminal 35 and electrode l9 and the maximum positive potential of the electrode l8 derived from the voltage divider 33 on the positive half cycle. Thus, at some time 151, between 180 and 270 electrical degrees after the time i=0, the potential between the electrodes |8 and i9 becomes sufiicient to break down the gap 2|.

At this time the potential E18 of the electrode I8 falls substantially instantaneously to the maximum negative potential E19 of the electrode l9 because the electrodes I8 and I9 are substantially directly connected by the arc therebetween. This discharge places across the gap 20 alone substantially the full maximum potential of the capacitive storage element II The cap 20 is so designed that, while it will withstand the maximum potential applied across it to ground by the voltage divider 33 during the negative half cycle of the transformer potential, it will not withstand the instantaneous potential now applied to it upon discharge across the gap 2I. Ac-

cordingly, the gap 20 now breaks down and the electrode I'I assumes substantially instantaneously the potential of the electrodes I8 and I9. Thus, at the instant of discharge, the instantaneous potential of all of the electrodes I'I, I8, and I9 is substantially equal to the maximum negative potential of the capacitive storage element Ill. The condenser I now discharges through the gaps and 2I and the load element I5, so that the instantaneous potentials of all three electrodes I7, I8, and I9 decrease toward ground potential as the energy stored in the condenser ID is gradually exhausted. When the energy of the condenser I8 is exhausted at a time t2, the discharge across the gaps 20 and 2I ceases. At this time the electrode I8 is returned substantially instantaneously to control by the voltage divider 33 and its potential again follows the sinusoidal portion of the curve E18 of Fig. 2. The potential Er; of the electrode II remains at ground by reason of its connection through the leakage resistor I4. Similarly, the potential of the electrode I9, having been brought to ground potential by the discharge, remains at ground potential for the remainder of the positive half cycle of transformer potential by reason of the fact that during this half cycle the rectifier I3 is non-conducting and the condenser I0 receives no charge.

In the foregoing explanation it has been assumed by way of simplification that the discharge of the condenser It! continues until all the electrodes I'I, I8, and I9 reach ground potential. In a practical case the discharge may be interrupted shortly before ground potential is reached. In such a case the electrode I8 is returned substantially instantaneously, and at the moment of interruption of the discharge, to control by the voltage divider 33 exactly as in the manner previously described. The potential of the electrode II, if below ground potential at the instant of arc interruption, is quickly brought to ground potential by leakage discharge through the resistor I4. The potential f the electrode I9 may remain slightly below ground potential, but as soon as the rectifier I3 again becomes conducting on the next negative half cycle the electrode I9 will be connected to the transformer terminal and will follow it in potential in the manner already described.

From the foregoing explanation of the operation of Fig. 1, it will be observed that by this arrangement I am able to initiate an accurately timed ulse of energy through the sparking gaps 20 and 2| once during each complete cycle of the alternating current source I I and Without danger of establishing a power are from source II through the load I5. This operation is carried out with a minimum of apparatus, the discharge being timed from the alternating current source itself by-the simpleconnection of an intermediate control electrode to a voltage divider connected across the charging winding of the input transformer. In a practical application of the invention constructed and operated in accordance with Fig. 1 using a simulated load, the transformer I2 was connected to a 60 cycle source of alternating potential having a maximum instantaneous value of approximately 30 kilovolts, the voltage divider 33 had a total resistance of 150 megohms, there being megohms between the transformer terminal 35 and the connection of the electrode I8, and the capacitor It was of .028 microfarad. With this apparatus, I was able to obtain accurately timed high voltage pulses of a few Inicroseconds duration.

At Fig. 3, I have shown another embodiment of my invention which in many respects is similar to that of Fig. 1, and like parts have been assigned the same reference numerals. At Fig. 3, however, the secondary winding of the transformer I2 is provided with a grounded mid tap and terminals 35 and 31 of opposite instantaneous polarity. The transformer I2 of Fig. 3,

has connected across one half thereof, in series with the rectifier I3, an axiliary storage capacitor 6E which is large in relation to the pulse discharge capacitor IIl. Across the other half of the secondary winding of the transformer I2 is connected the voltage divider 33, a predetermined intermediate point of which is connected to the control electrode I8. Also, according to the embodiment of Fig. 3, the pulse discharge capacitor In is connected across the large capacitor 41 in series with a high resistance resistor 4|. The condenser Ill of Fig. 3 may suitably have a capacity of the order of one one-hundredth of the capacity of the condenser 40. Finally, as at Fig. l, the load elements I4 and I5 are connected cross the capacitor I0 in series circuit relation with the two sparking gaps 20 and 2|.

The operation of the circuit of Fig. 3 will now be clear from the following brief description. The capacitor 4!) is so large that the half Wave rectifier !3 is able to maintain the capacitor 40 substantially fully charged at all times. Thus, a continuous unidirectional potential is available at the terminals of the condenser -G. Assuming for the purpose of illustration that the spark gaps 29 and 2| are non-conducting at an instant i=0, the condenser It will now be charged from the condenser 40 to the full unidirectional potential appearing across condenser 49. Let it also be assumed that at this instant the alternating current wave from the source I I is at its zero point so that the opposite terminals of the secondary winding of the transformer I2 are both at ground potential. At this instant, then, the electrodes I I and I3 Will both be at ground potential and the full voltage of the capacitor Ill will be applied across the gap 2I between the electrodes I8 and 9. If, now, the alternating potential of the source begins a negative half cycle in respect to the transformer winding terminal 35, the opposite terminal 3'! of the transformer secondary winding will follow a sine wave of positive potential with respect to ground. As this half cycle proceeds, the potential of the electrode I8 is raised positively by reason of the connection of the voltage divider 33. Thus, the electrode I! remains at ground potential, the electrode I9 remains at the maximum negative potential of the condensers I5 and 40, and the control electrode I8 is gradually raised above ground potential thereby increasing the potential difference between the electrodes I8 and I9 to an amount greater than the potential across the condenser ill. At some point less than the maximum positive potential of the electrode 58, the breakdown voltage of the gap 2! will be exceeded. It will be evident that the gap 2! must be set so that it will withstand slightly more than the maximum potential of the condenser ii! but less than the scalar sum of the potential across the condenser I plus the maximum positive potential of the electrode is. The gap E l may be set for a lesser breakdown voltage, since the maximum voltage applied across the gap 29 is only that portion of the transformer voltage appearing across the voltage divider section between the electrodes I! and [3. When the gap '12! breaks down, the high negative potential of the electrode E9 is conducted substantially instantaneously to the electrode it thereby to place the entire voltage of the condenser l0 across the gap 29 between the electrodes IT and 13. Since this voltage far exceeds the breakdown potential of the gap 25!, the gap 20 will become conducting thereby to establish a discharge path for the condenser Ii! through the gaps 2d and 25 and the load element in series circuit relation. After the stored energy in the pulse discharge capacitor iii has been dissipated in a high current pulse through the gaps 2e! and 2| and the load, the large storage capacitor 4i! tends to continue the discharge through the re- 'sistor 4| the gaps 29 and 2 l, and the load. However, the resistor 4| is of such large resistance that any discharge current from the condenser so alone is small enough to be interrupted by the air blast introduced into the gaps 26 and 2|. Thu the arc is interrupted and the gaps 20 and 2! become non-conducting as soon as the condenser it is discharged. Thereafter, the condenser lil recharges from the condenser 4!! in preparation for the next pulsing operation.

In a practical embodiment of the apparatus illustrated at Fig. 3, which was tested using a simulated load, the transformer l2 was operated at 60 cycles with a secondary voltage of 40 kilovolts peak. The condenser 40 had a capacity of .06 microiarad, the condenser H3 had a capacitance of 600 micromicrofarads, the resistor ti had a resistance of 5 megohms, and the Voltage divider 33 had a total resistance of 159 megoh'ms, the electrode It being connected at a point spaced by 190 megohms from the transformer terminal 3?.

At Fig. l, I have illustrated a still further embodiment of my invention wherein the voltage divider 33 is connected across the rectifier l3 rather than across one of the input transformer windings. In all other respects the circuit of Fig. 4 is similar to that of Fig. 1, and like parts have been assigned the same reference numerals. Although its theory of its operation is not currently fully understood, the circuit of Fig. 4 was tested under simulated load conditions and found to operate quite satisfactorily. In a practical embodiment of the circuit at Fig. 4, the transformer l2 operated at 69 cycles with approximately 8 kilovolts maximum instantaneous potential across the secondary winding, the capacitive element It had a capacity of 0.2 microfarad and the Voltage divider 33 had a total resistance of 150 megohms, the control electrode I8 being connected to the potentiometer at a point spaced by 50 megohms from the transformer winding terminal 35.

While I have illustrated only certain preferred embodiments of my invention by way of illustration, many further modifications will occur to 8 those skilled in the art and I therefore wish to have it understood that I intend in the appended claims to cover all such modifications as fall within the true spirit and scope of my invention.

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

1. An electric pulse generating system comprising a source of alternating potential, a capacitive storage element, means connecting said capacitive storage element to said source to be charged once per cycle of said alternating potential, a load device, means including a multiple gap spark discharge device for periodically discharging said capacitive storage element through said load device, and voltage dividing means for deriving from said source and impressing across one of said gaps a varying control potential difference which exceeds the breakdown potential of said one gap once per cycle of said alternating potential source thereby to initiate a discharge.

2. An electric pulse generating system comprising a source of alternating potential, a capacitive storage element, means connecting said capacitive storage element to said source to be charged once per cycle of said alternating potential, a load device, means including a multiple gap spark discharge device for periodically discharging said capacitive storage element through said load device, said capacitive storage element when charged impressing across said gaps in series the total potential of said capacitive storage element, and voltage dividing means for deriving from said source and applying to said dis charge device a potential such that at a predetermined time after said capacitive storage element becomes fully charged the potential difference across one of said gaps exceeds said maximum charging potential thereby to initiate a discharge of said storage element through said gaps and said load device.

3. An electric pulse generating system comprising a source of alternating potential, a capacitive storage element, means connecting said capacitive storage element to said source to be charged once per cycle of said alternating potential, a load device, at least three spaced electrodes providing two spark gaps in series between said capacitive storage element and said load device, voltage dividing means for impressing upon an intermediate sparking electrode at least a portion of said alternating potential thereby to initiate a discharge of said capacitive storage element through said load device once per cycle of said alternating potential, and means for irradiating said gaps with ultraviolet light at least during the intervals of cyclic discharges.

4. An electric pulse generating system comprising a source of alternating potential, a capacitive storage element, means including a unidirectional conducting device for connecting said capacitive storage element to said source to be charged to a predetermined maximum instantaneous potential once per cycle of said alternating potential, a load device, three spaced electrodes defining two spark gaps in series between said capacitive storage element and Said load device, and voltage dividing means for deriving from said source and applying to the intermediate of said three electrodes a potential such that the total potential difference between said intermediate electrode and one other of said electrodes exceeds said predetermined maximum instantaneous potential of said capacitive storage device once per cycle of said alternating potential thereby to initiate a discharge or said storage element through said load device.

5. An electric pulse generating system comprising a source of alternating potential, a capacitive storage element, means including a unidirectional conducting device for connecting said capacitive storage element to be charged from said source once per cycle of said alternating potential, a load device, a multiple gap spark discharge device comprising at least three spaced electrodes defining two spark gaps in series between said capacitive storage element and said load device, and voltage dividing means associated with said source potential and having an intermediate point connected to an intermediate electrode of said spark discharge device thereby to initiate once per cycle of said source potential a discharge of said capacitive storage element through said load device.

6. An electric pulse generating system comprising a source of alternating potential, a capacitive storage element, means including a unidirectional conducting device for connecting said capacitive storage element to said source to be charged once per cycle of said alternating potential, a load device, a multiple gap spark discharge device comprising at least three spaced electrodes defining two spark gaps in series between said capacitive storage element and said load device, and voltage dividing means connected directly across said source of alternating potential and having an intermediate point connected to an intermediate electrode of said spark discharge device thereby to initiate Once per cycle of said alternating potential a discharge of said capacitive storage element through said load device.

'7. An electric pulse generating system comprising a source of alternating potential, a capacitive storage element, means including a unidirectional conducting device for connecting said capacitive storage element to said source to be charged once per cycle of said alternating potential, a load device, a multiple gap spark discharge device comprising at least three spaced electrodes defining two spark gaps in series between said capacitive storage element and said load device, and voltage dividing means connected directly across said unidirectional conducting device and having an intermediate point connected to an intermediate electrode of said spark discharge device thereby to initiate once per cycle of said alternating potential a discharge of said capacitive storage element through said load device.

8. An electric pulse generating system comprising a source of alternating potential, a first capacitive storage element, means including unidirectional conducting means for maintaining said first capacitive storage element charged from said source to a predetermined substantially constant unidirectional potential, at second capacitive storage element connected to be charged from said first capacitive storage element through an impedance device, a load device, means including a multiple gap spark discharge device for periodically discharging said second capacitive storage element through said load device, and voltage dividing means for deriving from said source and applying across at least one of said gaps a control potential difierence varying with time and arranged to initiate a discharge of said second capacitive storage de- 10 vice through said load device once per cycle of said alternating potential.

9. An electric pulse generating system comprising a source of alternating potential, a first capacitive storage element, means including a unidirectional conducting device for connecting said first capacitive storage element to be maintained continuously charged from said source to a predetermined substantially constant unidirectional potential, a second capacitive storage element connected to be charged through a high impedance device from said first capacitive storage element, a load device, a plurality of spaced electrodes defining at least two spark gaps in series between said second capacitive storage element and said load device, voltage dividing means for deriving a potential proportional to the potential of said source and applying said derived potential across one of said gaps thereby periodically to initiate a discharge of said second capacitive storage element through said load device, and means for interrupting said discharge upon dissipation of the energy of said second capacitive storage device.

10. An electric pulse generating system comprising a source of alternating potential, a first capacitive storage element, means including a unidirectional conducting device for connecting said first capacitive storage element to said source to be maintained continuously charged to a substantially constant unidirectional potential, a second capacitive storage element connected to be charged through an impedance device from said first capacitive storage element, a load device, three spaced electrodes defining therebetween two spark gaps in series circuit relation between said second capacitive storage element and said load device, the full unidirectional potential of said first capacitive storage element being applied across said gaps in series when said gaps are non-conducting, and voltage dividing means for deriving from said source and applying to one of said electrodes a varying control potential such that once per cycle of said alternating potential the potential difference across one of said gaps exceeds said constant potential thereby to initiate a discharge of said second capacitive storage element through said load device.

11. An electric pulse generating system comprising a source of alternating potential, a first capacitive storage element, means including a rectifier for connecting said first capacitive element to said source to be maintained continuously charged to a substantially constant unidirectional potential, a second capacitive storage element connected to be charged through an impedance device from said first capacitive storage element, a load device, three spaced electrodes defining therebetween two spark gaps in series circuit relation between said second capacitive storage element and said load device, means for deriving an alternating potential of opposite phase with respect to said source potential, and voltage dividing means associated with said potential of opposite phase and having an intermediate point connected to the intermediate of said three electrodes thereby to initiate a discharge of said second capacitive storage element through said load device once per cycle of said source potential.

LEWI TONKS.

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