US3238475A

US3238475A - Transmission line arc detecting and eliminating system wherein the energy source is continually disabled and enabled

Info

Publication number: US3238475A
Application number: US256857A
Authority: US
Inventors: Vita Alphonse J De; Mangiapane Rosario
Original assignee: Raytheon Co
Current assignee: Raytheon Co
Priority date: 1963-02-07
Filing date: 1963-02-07
Publication date: 1966-03-01
Anticipated expiration: 1983-03-01
Also published as: DE1463491A1; NL302267A; GB1038409A; SE307605B; NL132571C

Description

March 1, 1966 Filed Feb. 7, 1963 A. J. DE VITA ETAL TRANSMISSION LINE ARG DETECTING AND ELIMINATI SYSTEM WHEREIN THE ENERGY SOURCE IS GONTINUALLY DISABLED AND ENABLED 2 Sheets-Sheet 1 @y WMMQM ATTORNEY Much l, 1966 A. J. D vrrA ETAL ,238,475

TRANSMISSION LINE ARC DETECTING AND ELIMINATING SYSTEM WHEREIN THE ENERGY SOURCE IS GONTINUALLY DISABLED AND ENABLED 2 Sheets-Sheet 2 Filed Feb. 7, 1965 NHT FQ QSNH /NVENTOHS ALPHONSEJ DEV/TA ROSSMNG/APA/VE By M2M l UwO A II ATTORNEY United States Patent O M TRANSMISSION LINE ARC DETECTING AND ELIMINATING SYSTEM WHEREHN THE EN- ERGY SQURCE IS CONTNUALLY DISABLED AND ENABLED Alphonse J. De Vita, Chelmsford, and Rosario Mangiapane, Burlington, Mass., assignors to Raytheon Company, Lexington, Mass., a corporation of Delaware Filed Feb. 7, 1963, Ser. No. 256,857 14 Claims. (Cl. S33-17) This invention relates to high power radiation systems and, more particularly, to arrangements for detecting voltage breakdown arcs and purging the cause of said arcs which often occur in such systems.

One of the major problems incident to the operation of high power microwave systems, and particularly high power continuous wave transmitters or microwave generators, resides in the fact that after voltage breakdown arcs form, they often walk in the interior of the output waveguide circuits towards the microwave generator which is used to provide energy to said output waveguide circuit. Even though the power normally employed in the system may be much lower than the nominal breakdown value for the waveguide employed, local conditions such as the appearance of some lossy foreign matter in the guide will raise the temperature of the air in the guide to its breakdown voltage, thereby causing arcing. Generally speaking, an arc initiated anywhere in a continuous wave system, if not extinguished, will walk back along the waveguide toward the microwave generator, such as a magnetron or other tube generator having an evacuated interior and a window, and destroy or burn the generator window. Furthermore, the speed of travel of the arc is a function of power applied by the microwave tube generator and, therefore, for high power continuous wave systems providing output powers greater than one kilowatt, some sort of arc detection and cleansing of dirt or lossy material is required, particularly in field operations where lthere is a tendency for dirt to enter and accumulate in the interior of the output waveguide circuits. Systems available today primarily rely on the shutting olf of the microwave tube generator after the detection of the presence of an arc and then cleaning the waveguide by blowing air through the waveguide to blow out the dirt or lossy material so as to preclude the reinitiation of au arc upon returning the microwave generator to full power. Furthermore, the arc detection and suppression systems available today do not provide complete protection of the microwave tube output window due to their inability to recognize an arc without intercepting the arc.

Therefore, it is an object of the present invention to eliminate damage to high powered generators such as may be caused by the existence of voltage breakdown arcs.

It is an additional object to provide a system which purges the cause of the initiation of a voltage breakdown arc in the output waveguide circuits coupled to an energy generator.

In accordance with this invention, means are provided for detecting the presence of an arc within a transmission medium such as air or in a transmission line as a waveguide and purging the cause of the initiation of the arc before damage can be done to a generator supplying electromagnetic energy to said medium or transmission line. For this purpose, a plurality of energyk detectors or sensors are positioned such that the presence of an arc in the transmission line will be detected due to the reduction in power caused by the energy absorption and reflection of the arc. A detection device responsive to the unequal energy intercepted by said sensors in the presence of an arc in said waveguide provides a signal to actuate 3,238,475 Patented Mar. 1, 1966 a control circuit. The control circuit provides an output signal to reduce the power being provided to the transmission line. The control circuit further operates in such a manner as to provide means for the transmission line to purge itself of the lossy material causing the arcing. Additionally, a probe arc detection system is arranged in combination with the above-mentioned t0 provide a self-purging arc detection system in combination with a probe arc detection system.

Other objectives and features of this invention will become apparent from the following description taken in conjunction with the following drawings wherein:

FIG. l is a schematic diagram of a self-purging arc detection system including a microwave generator, waveguide, and sensors and detection and control circuitry according to the invention; and K FIG. 2 is a schematic diagram of a self-purging arc detection system in combination with a probe arc detection system.

Referring now to FIG. l, which shows a self-purging arc detection system including an energy generator, a rectangular waveguide circuit, and a pair of detectors or sensors in combination with detection and control circuitry according to the invention. High frequency oscillator 1l), such as a klystron, is shown for providing an actuating high frequency microwave signal through a waveguide circuit 11 and an isolator 12 to the high power output section of the system. Isolator 12 provides isolation of the oscillator 10 from high power amplier 16 of the system. Isolator 12 is a ferrite isolator which operates on the gyromagnetic resonance principle and provides isolation by absorption of reflected energy. The energy then flows from the isolator through the waveguide 13 to a power switch 14, which could be of the ferrite, ferroelectric or other types. The ferrite switch 14 shown herein is used to control the flow of energy from the high frequency oscillator 10 to the high power amplifier 16 of the system. The ferrite switch operates on the faraday rotation principle. In response to an actuating signal applied to switch 14 a 90 rotation is imparted to the E vector of the energy being applied from waveguide 13. In the absence of a signal being applied to the switch 14, a 0 rotation is obtained and approximately all of the power provided by waveguide 13 is reflected and absorbed by isolator 12. With ferrite switch 14 in the energized condition, energy from the high frequency oscillator 10 will flow through the waveguide 15, to drive high power amplifier 16. Waveguide 15 is positioned orthogonal to waveguide 13 and is coupled to switch 14, thus providing a reflective mismatch condition between

waveguides

13 and 15 in the absence of an actuating signal being applied to switch 14. High power amplifier 16 could be of the klystron, magnetron or other high power energy generator types. The power amplifier 16 which is shown herein as an evacuated tube is shown having an output section or port 17 with a transparent window 18 for permitting energy generated by the power amplifier to be forward coupled to an output waveguide circuit 20. The transparent window 18 could be of a dielectric material, such as ceramic, which is transparent to microwave energy. Power amplier 16 is also provided with a waveguide coupling section 21 which is shown coupled to the output port 17 and positioned so as to extract and sample a portion of the forward coupled or transmitted energy prior to the passing of such energy through the transparent window 1S. Coupler 21 is connected to the output port 17 through a plurality of dielectric window filled waveguide orices 23, which are incorporated in the wall of the waveguide and are of suicient diameter at the operating frequency to permit a small portion of the energy to be sampled or extracted from the energy passing through the output port. The

energy entering the coupler section 21 is then attenuated by an attenuating device 32 which is of a microwave absorbent material, such as a carbon material, and is shown with an adjustable arm 24 for controlling the amount of attenuation. The attenuation is controlled by adjusting attenuating device 32 so that it intercepts a great amount of the energy section as shown herein. The power thus sampled is detected by a microwave detector or sensor, such as a microwave rectifier 25, inserted across the coupler 21 having an output terminal 26. The microwave detector is inserted through the top and bottom wall portions of the coupler so as to detect the sampled power from power amplifier 16. In this instance, detector 25 is of that type of microwave rectifier which produces a negative voltage signal at its output terminal 26 upon the interception of microwave energy, and is designated as the ER type of microwave detector, by the microwave industry.

The forward coupled microwave power from high frequency power amplifier 16 passes from port 17 through transparent window 1S to output waveguide circuit 20 and is shown, in this instance, as coupled to a load such as an antenna 27 by way of a waveguide output coupler 28. Positioned along the length of the waveguide in proximity to the load 27, a second coupler is shown physically connected to waveguide 20 to extract and sample a portion of the energy passing through the waveguide 2t) which is being supplied to the load 27. The coupler 29 is physically connected to waveguide 2t? by way of a plurality of orifices 33 of a size such as described in connection with coupler 21 which permit the forward coupled power to be sampled and detected by a microwave detector 3G, such as a microwave rectifier, having an output terminal 31. Microwave detector 30 is shown in FIG. l as being inserted into coupler 29, similarly as described in relation to detector 25, so as to rectify the sampled microwave power and produce an output signal at terminal 31. In this instance, microwave detector 30 is of the E type, as known by the microwave industry, and provides a positive output signal at terminal 31 in the presence of detectable microwave energy in the proximity of load 27.

During normal operation of the system, high power microwave energy is being supplied to the output waveguide circuit from the power amplifier 16. For purposes of explanation, assume that during operation of the systern, a piece of lossy foreign matter 70, such as dust, enters and deposits itself in the waveguide somewhere between the sampling orifices 23 and 33 which supply sampled forward coupled microwave energy to microwave detectors and 30, respectively. The presence of this lossy foreign material '76 in the waveguide will absorb energy passing through the waveguide and become heated. This heating, by way of the absorption of energy, will cause the air temperature present in the waveguide 20 in the vicinity of the foreign material to be raised to its breakdown voltage. When the air, in proximity to particle 7d, reaches its breakdown voltage, an arc will be formed within waveguide 2l. It has been experimentally observed that when an arc discharge occurs within a waveguide, the arc formed will dissipate or absorb approximately 75 percent of the power incident to the arc and will reflect the remainder of the energy towards the `generator 16. The absorption percentage of the arc is variable and is dependent on the microwave energy power level in the waveguide, the waveguide size, the temperature, and the air pressure within the waveguide.

Once struck across the guide 20, an arc will travel toward the microwave power source 16 and will, if not impeded, impinge on the dielectric window 18. The arc will continue to dissipate and absorb microwave energy until it punctures either the ceramic window or the seal surrounding the ceramic window and thus destroys the power amplifier 16. Due to this characteristic of energy f-iabsorption by an arc, it is possible to sense the difference in forward coupled transmitted energy through waveguide 20 by detectors 25 and 30, and thus prevent damage and ultimate destruction of power amplifier 16.

Referring again to FIG. 1, there is shown an unbalance detection circuit 40 Connected to detectors 25 and 3d at terminals 26 and 31 so that differences in sampled microwave energy levels, caused by the presence of an arc in the waveguide 20 can be detected. In the absence of arcing in waveguide 2t), detector 3@ provides a positive output voltage in response to sampled microwave energy, but due to the initiation of arcing in the waveguide circuit 2t) and the subsequent absorption of microwave energy by the arc, the positive output voltage signal provided by`detector 3f) will drop towards a zero voltage level. Thus, by sensing the difference between the negative output voltage at terminal 26 of detector 25 and the normally positive voltage at terminal 31 of detector 30, it is possible using unbalancing or nulling circuits to detect the presence of an arc in the waveguide In this instance, terminal 26 of detector 25 and terminal 31 of detector 30 are connected across a nulling circuit comprising resistors 41, ft2, 43, and 44. Arcing in the waveguide causes the nulling circuit to produce a negative going output signal. The nulling circuit sums the voltages produced by the sensors and provides a signal to actuate duotriode 45, upon the sensing of an arc in waveguide circuit 20. Duotriode 45 has one section with a cathode 46, grid 47 and plate 48 which henceforth will be referred to as section A and another section having a cathode 56, grid 57 and a plate '58 which henceforth will be referred to as

section B. Cathodes

46 and 56 are connected together and are biased negative through a resistor 49 by a battery 5t). Grid 47 of section A is connected to respond to voltage signal changes provided by the nulling circuit, comprising resistors 41, d2, 43, and 4d. Grid 57 is connected to ground. Plate 4S is connected through a load resistor 51 to a B+ voltage source 52 and is also connected through output voltage dividing resistors 53 and 54 to biasing voltage source 55. Plate 58 is connected through a load resistor 59 to a B-lvoltage source 60. Additionally, plate 58 is connected through voltage divider resistors 61 and 62 to a biasing voltage source 63. Normally, both sections A and B of the duotriode are in the on or conducting condition since grids 47 and 57 are normally biased at zero potential. Therefore,

plates

48 and 58 of the duotriode sections A and B are normally above ground but quiesced somewhere below the voltage source potential of 52 and 60, respectively.

In response to the detection of an arc in the waveguide Ztl, a negative signal will be applied from the nulling circuit to the grid 47 of section A. Plate 48 will then become more positive due to the application of the negative voltage to grid 47 driving duotriode section A towards cutoff. Therefore, a positive voltage will appear at the intersection of divider resistors 53 and 54 and will cause a positive actuating signal to be applied to turn on thyratron 71. Thyratron 71 comprises a plate 72, grid 73, second grid 74, and a cathode 75. Grid '74 is connected to input resistor 78, plate 72 is connected through a load resistor 76 to an alternating source of voltage 77, such as a 400 cycle A.C. supply voltage, and

r grid 73 is directly connected to ground and cathode 75 is connected through an output cathode resistor y94 to ground.

Additionally, a second thyratron 80 is shown as a part of unbalance detection circuit 40 having a plate S1, a first grid 82, a second grid 83 and a cathode 84. The grid 83 is connected through input resistor to the junction of dividing resistors 61 and 62. Plate 81 is connected through a load resistor S5 to an alternating source of voltage 86, such as a 400 cycle alternating supply voltage. Grid 82 is connected to ground and cathode 84 is connected to the junction of cathode 75 and outlput resistor 94.

The application of the positive signal from the divider resistor network 53 and 54 to the grid 73 allows thyratron 71 to be turned on upon application of the next positive voltage cycle from voltage source 77 to plate 72. Therefore, on the next positive cycle of alternating voltage from voltage source 77, thyratron 71 will turn on in the conventional manner and produce a positive signal output across resistor 94 and ground. This output signal is then applied to actuate control circuit 88. Thyratrons 71 and 80 are used to provide an actuating signal to a circuit which controls the energy being applied to waveguide circuit 20. Section B of duotriode 45 is shown adapted to detect a failure of detector 25. The failure of detector 25 will cause a positive signal to be applied through the nulling circuit to the grid 47 of section A of duotriode 45. This will cause the duotriode section A, comprising cathode 46, grid 47 and plate 48 to conduct more heavily and thus the section B, comprising cathode 56, grid 57 and plate 58 will not conduct as fully, therefore, producing a positive signal at the plate 58. This positive signal at the plate 5S is then applied through divider resistors 61 and 62 and input resistor 87 to grid 82. Thyratron 80 then conducts on the next positive half cycle applied to plate 81 by alternating voltage source 86 in the same manner as described with relation to thyratron 71. Due to the initiation conduction of thyratron 80, a positive going output signal is then provided across resistor 94, which then can be used to actuate a switch control circuit 88. Thyratrons 71 and 30 both turn off in the conventional manner upon application of the negative voltage cycle being applied to plates 72 and 81 from 400 cycle voltage sources 77 and 06, respectively.

The positive output signal provided by unbalance detection circuit 40 across resistor 94 in the event of an arc in the waveguide or of a failure in detectors 25 and 30 is transmitted to actuate switch control circuit 8S. Control circuit S8 comprises a lirst controlled rectifier 90 having an anode 91, cathode 92 and a gate 93. Control rectifier 90 provides a negative pulse to the anode and gate of a controlled rectifier 120, which causes controlled rectifier 120 to extinguish and remain extinguished for a predetermined period of time. Cathode 92 is connected to ground and gate 93 is connected to the output load resistor 94 of unbalance circuit 40. Anode 91 is connected through a load resistor 99 to a biasing voltage source 100. A clamping circuit comprising series connected resistors 96 and 97 is connected to a voltage source 98 and is shown connected at the junction of resistors 96 and 97 through a clamping diode 95 t0 anode 91.

A transistor 101 of the N-P-N type is shown having a collector 102, a base 103 and an emitter 104. Collector 102 is shown connected through a load resistor 105 toa voltage source 106. The base 103 is shown connected to the anode 91 of controlled rectifier 90 and through a switching diode 107 to the emitter 104. The emitter 104 is connected through an emitter circuit charging capacitor 108 .andan emitter resistor 109 to ground. Additionally, emitter 104 is connected through another emitter charging capacitor 110 `and resistor 111 to ground.

A sec-ond controlled rectifier 120 having an anode 121, cathode 122 and a gate 123 is shown. Anode 121 is shown connected through output

divider load resistors

124 and 125 to a voltage source 126. Cathode 122 is :shown connected to ground; the gate 123 lis shown connected through a charging capacitor 115 to ground and through a biasing resistor 116 to a source of biasing voltage 117. Additionally, gate 123 is shown connected through a switching diode 113 to the junction of capacitor 108 and resistor 109. Furthermore, anode 121 is shown connected through an isolating diode 112 to the junction of capacitor 110 and resistor 111.

In the absence of an .arc in waveguide 20, no input signal will appear across output resistor 94 of the unbalance detection circuit 40, therefore, because of biasing, controlled rectifier and transistor 101 will be in the off condition and controlled rectifier 120 will be in the on condition. Capacitors 108 and 110 will be charged positively on the sides connected to emitter 104 of transistor 101. The capacitors 108 and 110 are charged positive-ly by transistor 101 conducting for .a short time after the initial connection of voltage sources and 106 and is then cut off yas its emitter 104 becomes more positive than its base 103. The conduction of controlled rectifier 120 causes `a current to flow through resistor 124 and produce a voltage drop ac-ross resistor 124, which is used to maintain ferrite switch 14 in the on condi-tion, thus permitting microwave actuating energy from oscillator 10 to energize high frequency power amplifier 16. Upon the sensing of an arc -in waveguide 20, a positive output voltage will appear across resistor 94 and be applied to the gate 93 to turn on controlled rectifier 90. The turning on of controlled rectifier 90 produces a negative signal -at anode 91 which is applied through an isolating diode 107, capacitor and an isolating diode 112 to anode 121 of controlled rectifier 120. Additionally, this 4negative signal at the lanode 91 `of controlled rectifier 90 is simultaneously applied through diode 107, capacitor 108, -an isolating diode 113 to gate 123 of -controlled rectifier 120. The application of this negative potential .to the vanode 121 of controlled rectifier 120 turns off controlled rectifier 120, thus causing switch 14 to be placed in the off condition. Switch 14 will no longer permit high frequency actuating energy to be applied to keep high frequency power amplifier 16 in the on condition. Therefore, there will no longe-r be provided a .source of forward coupled microwave power to the output waveguide circuit 20 to sustain the arc. Additionally, the simultaneously negative pulse applied to the gate 123 will charge capacitor 115 to a 4negative potential so that controlled rectifier 120 will not turn on once again until capacitor 115 discharges through resistor 116. When controlled rectier 120 once again initiates conduction, switch 14 is placed in the on condition by voltage developed across resistor 124 so as to faince again permit power to be generated by power ampli- After controlled rectifier 90 is turned on by the :positive pulse yat its gate 93, it will conduct for a short predetermined period ot` time. This predetermined time lis less than the time it takes for capacitor to discharge through :resistor 116 to turn on controlled rectifier 120 -to set up the circuit in :a ready condition to turn off rectifier should an arc occur. The c-ontrolled rectifier 90 as shown in FIG. l is biased in its anode circuit in a starved condition. This starved condition is brought about by the fact that resistor 99 is of such Ka magnitude that it will not allow sufiicient current to fiow from voltage source 100 to sustain conduction of controlled rectifier 90. Therefore, in order to sustain controlled rectifier 90 for a `short period of time .so that turning on of controlled rect-ifier 90 will take place, capacitors 110 and 108 discharge through diode 107 and provide sufcient current for a limited period of time, determined by the time constant of the-ir discharge, :so Kas to sustain conduction of controlled rectifier 90. After the capacitors 108 .and 110 have discharged, controlled rectifier 90 will turn off, inasmuch as the current being provided from voltage source 100 through load resistor 99 can no longer sustain conduction. Transistor 101 will then turn on due to its emitter 104 becoming lmore negative than its base 103, and thus positively recharge capacitors 10S and 110 at their ends connected to emitter 104.

Summarizing the operation of control circuit 88, controlled rectifier 90 lis turned on by a positive pulse being applied to its gate 93 and thus provides a negative pulse to the gate and anode circuits of controlled rectifier 120 to turn off controlled rectifier 120. After capacitors 108 and 110 have discharged, controlled rectifier 90 will turn off .and transistor 161 will turn on to recharge capacitors 108 and 110. Controlled rectifier 1211 will then turn on after capacitor 115 has discharged through -resistor 116. The turn-ing on of cont-rolled rectifier 12'@ causes current to `flow through resistor 124 and thus provide a signal to place switch 1li in the on position so as to permit energy from oscillator 1@ to reinitiate operation of power amplifier 16. Thus, it is seen that controlled rectifier 919 due to thesequence of operation, is in a recycled state such that is capable of immediately turning controlled rectifier 12@ off again and hence, the output power, should an arc occur in waveguide 2t).

Upon reactivation of power amplifier 16, forward coupled microwave energy may once again initiate an arc in the waveguide due to some part of the lossy material which was not completely oxidized remaining in the waveguide. It is to be noted that lossy material will gradually dissipate itself due to normal oxidizing caused by microwave energy absorption of the lossy material. If upon reinitiation of the arc, which in this instance should take a longer period of time due to the smaller amount of lossy foreign matter remaining in the waveguide, detectiton circuit d and control circuit 88 will once again turn off power amplifier 16. This turning on and off operation will continue until the lossy material is oxidized to the point where it no long is capable of initiating an arc. This continuous turning on and off operaiton provides the self purging feature in this system. The term self purging is given for this oxidation of the lossy Inate rial, inasmuch as it can `be seen t-hat with this system there is no requirement that the system be shut down after arcing takes place in order to clean out the waveguide by an external means such as a vacuum cleaner. It can also be seen that with this system, due to the lossy material being gradually oxidized, the average power supplied to the load will increase exponentially in time since it takes longer each time for the arc to reestablish itself. Thus, the power amplifier 16 will remain on for greater and greater periods of time until lossy material 70 is burned out or oxidized, thereby exponentially increasing the average output power supplied to the load. It is to be noted that detector provides in effect a reference voltage, the reference voltage being a measure 4of microwave energy being forward coupled to the waveguide -circuit 20.

Referring now to FIG. 2, there is shown the combination of a sel-f purging arc detection system and a waveguide probe arc detection system. The self purging arc detection system is similar to the arc detection system shown and described in relation to FIG. l. More particularly, the unbalance detection circuit MP and the switch control 88 of FIG. l are shown in block diagram form, and the rst coupler 21 is shown physically positioned along the waveguide circuit 2t) external to the tube. Coupler Z1 samples forward coupled microwave power provided from the high power amplier 16 to the waveguide 20 in the same manner as described with relation to coupler of FIG. l. The coupler 21, with the detector 25 inserted therein, is mounted on the waveguide to provide a self purging arc detection system when power monitoring within the power amplifier 16 is not desirable.

The self purging arc detection system as shown in FIG. 2 operates Iin the same manner as described with relation to the circuitry shown in FIG. 1 except that sensors 2.5 and 31 are mounted on waveguide 20 so that there is a possibility of an arc being formed between the transparent window 1S of the port 17 and the first coupler 21, which could conceivably destroy the transparent window 18. There-fore, in order to protect the waveguide Window and to sense the presence of an arc between the transparent window 18 and the coupler 21, a separate arc detection circuit is provided which has a probe mounted to protect against arcs which might occur 'between the coupler 21 and the transparent window 18.

Probe 130 is shown inserted in the waveguide and preferably is physically positioned by splitting the small dimension of the waveguide 2t) and is perpendicular to the small dimension wall to insure minimum interference with the transmission of microwave energy from the high power amplifier 16. The operation of the probe arc detector takes advantage of the fact that when a microwave arc comes -in contact with an electrode which is negatively charged, it will draw electron current from that electrode. The impedance of arcs in waveguides have been observed to vary with the amount of power sustaining the arcs and is a function of the power being supplied to the system by the high power amplifier 16. By using a high impedance probe of a value much greater than the impedance of any arc which is expected to occur within the waveguide, it is possible to measure the loading effect of an arc on the probe, so as to provide a control signal to shut off the power amplifier and thus extinguish the arc. Incorporation of the probe detector and a probe arc detector circuit 132 with the couplers 21 and 29 permits overall arc detection capability, even when sensing within the power amplifier is not feasible.

High impedance probe 131) is shown with a terminal 131 which is connected across a voltage divider network in probe are detection circuit 132 and comprises a divider resistor 133 which is connected to a `biasing voltage source 134, a `resistor 135, and a combination divider circuit comprising a bypass capacitor 137, a pair of

resistors

136 and 138, a source of biasing voltage 142, a resistor 139, a resistor 141, and a diode 141). Probe terminal 131 is connected between the junction of resistors and 133 and is at a negative potential due to the action of the divider network.

Assume, for purposes of explanation, that during the operation of power amplifier 16, a lossy material 200 somehow ent-ers the waveguide 2t) and deposits itself 'between the transparent window 18 and the coupler 21. After a period `of time the material by absorption of energy will begin to oxidize and heat up the air in its immediate vicinity, and thus at the power levels provided by high power amplifier 16, produce an are which will creep towards the transparent window 18. Due to the position of the negatively charged high impedance probe 130, the `arc will come in Contact with the probe and will draw current from the probe. The combination divider circuit acts as a clamp device s-o `as not to allow junction of

resistors

136 and 135 to become too positive. This loading down of the high impedance probe will effectively short out the divider network, and thus the intersection of

resistors

135 and 136, which was initially at a negative potential will go positive, thus causing a positive pulse to be applied through input resistor 143 tot turn on thyratron 150. Thyratron is initially in the off condition due to a negative biasing potential applied to grid 153 via the resistor 143 which is connected to the junction of

resistors

135 and 136. Thyratron 150 is shown having a cathode 151, a first grid 152, a second grid 153 and `a plate 154. Grid 152 is shown connected to the input resistor 143; plate 154 is shown connected through a load resistor 156 to a voltage network comprising a charging capacitor 155, a resistor 157 and a voltage source 161. Grid 153 is connected across a biasing network comprising a biasing resistor 158 connected between the grid 152 and the junction of resistors 156 and 157 and through a biasing resistor 159 to a source of biasing voltage 160. The biasing network adjusts the tuning potential of thyratron 150 to a predetermined level. Cathode 151 is shown connected to the input circuit of the switch control circuit 83, `and provides a positive going signal to actuate the control circuit to insure that the window 18 of the high power amplifier will be protected. Therefore, upon the detection of an arc by probe 130, a positive signal will be applied via input resistor 143 to turn on normally off thyratron 1511 and thereby cause a positive signal to be applied via cathode 151 to actuate the switch control circuit 88. Discharging of capacitor turns off the thyratron 150 so that the circuit is ready for the next actuating signal. The switch control circuit 88 functions in the same manner as described in relation to the description given in FIG. l.

Other embodiments of the invention utilizing the technique `as described with relation to the systems shown in FIGS. l and 2 can be employed and may vary in accordance with the application to be made of the invention. -For example, it would be possible to provide a switch control circuit which would turn off the direct current power provided to the high power amplifier 16 in the presence of an arc. It is to be noted that the use of such a system would operate much slower and provide less protection than the embodiments shown in FIGS. 1 and 2. Accordingly, it is desired that this invention not be limited except as defined by the `appended claims.

What is claimed is:

l. An arc eliminating system including a source of energy and a transmission line circuit associated therewith, means for detecting an arc in said transmission line circuit comprising a pair of microwave energy sensors one of said pair operative to sense the energy provided to an input of said transmission line circuit and the other of said pair operative to sense power supplied to `an output device coupled to said transmission line circuit, and arc purging means coupled to said detecting 4means and being responsive to the difference in energy in said pair of sensors for eliminating the cause of said arc by continually disabling and enabling said energy source until the cause of said arc is removed. y

2. In a system including a source of energy and `a transmission line circuit associated therewith, means for detecting a voltage breakdown arc in said transmission line circuit comprising a plurality of energy sensors to distinguish between the magnitude of the energy on either side of said arc, yand means for disabling said source of energy in response to said energy sensors distinguishing between the magnitude of the energy on either side of said arc, said means for disabling including a means for purging the cause of the initiation of a voltage breakdown arc in said transmission line circuit by continually disabling and enabling said energy source until said cause is removed.

3. In a system including a source of microwave energy and a transmission line circuit associated therewith, means for detecting a voltage breakdown arc in said transmission line circuit comprising 4a plurality of energy sensors to distinguish between the magnitude of the energy on either side of said arc, means for disabling said source of energy in response to energy sensors distinguishing between the magnitude of the energy on either side of said arc, said means `for disabling including a means for purging the cause of the initiation of a voltage breakdown arc in said transmission line circuit by continually disabling and enabling said energy source until said `cause is removed, said means for detecting a voltage breakdown arc having at least one of said sensors positioned to sense the energy within the source of energy prior to the transmission of said energy to said transmission line circuit.

4. In a high power microwave system including a source of microwave energy providing forward coupled microwave energy to a waveguide output circuit associated therewith, means for detecting the existence of voltage breakdown arcs in said waveguide comprising a plurality of energy sensors positioned to sample forward coupled microwave power within said waveguide, means responsive to a signal provided by said energy sensors to provide an output signal to a control circuit, said control circuit comprising a plurality of controlled rectiers cooperating to provide a signal to reduce the amount of energy being provided by said power amplier to said waveguide output circuit, and said control circuit additionally including means for permitting said waveguide output circuit to automatically purge itself of the cause of the initiation of said arcs in said output waveguide circuit.

5. In an arc detection system including a source of energy and a waveguide circuit associated therewith, means for sensing the presen-ce of an arc within said waveguide circuit, said means for sensing comprising a plurality of microwave energy sensors, at least one of said microwave energy sensors positioned so as to internally sample a portion of the microwave energy being supplied from said microwave source to said waveguide circuit, means responsive to the energy intercepted by said microwave detectors and connected in circuit with said 4microwave sensors, a control circuit responsive to said circuit resp-onsive to the sensing of microwave energy, said control circuit providing microwave energy to said output waveguide circuit, and said control circuit providing means for periodically disabling said microwave source upon reinitiation of an arc in said waveguide circuit until arcing in said waveguide circuit can no longer be initiated.

6. A combination sensor and probe arc detection systern including a source of microwave energy and wav-eguide circuit 'associated therewith, means for .sensing the presence of an arc within said waveguide circuit, means for intercepting an arc within said waveguide circuit coacting with said means for sensing the presence of an arc in said waveguide, said sensor and said probe both independently providing an actuating signal to permit disabling of said source of energy if arcing is initiated within said waveguide circuit, and control circuit means responsive to said actuating signal for disabling said microwave energy source upon detection of an arc and periodically disabling said microwave energy source upon reinitiation of said arc in said waveguide circuit until arcing in said waveguide circuit can n-o longer be initiated.

7. In an arc detection system including a source of energy and a waveguide -circuit associated therewith, means for sensing the presence of an arc within said waveguide circuit, said means for sensing comprising a probe for intercepting an arc within said waveguide circuit, a control cir-cuit responsive to the interception of said arc by lsaid negatively charged probe for providing an output signal to disable said source of energy, and said control circuit providing means for periodi-cally disabling said energy source upon reinitiation of an arc in said waveguide circuit until arcing in said waveguide circuit can no longer be initiated.

8. In a system including a source of energy and an energy transmission line circuit associated therewith, means for detecting a voltage breakdown arc in said transmission line circuit comprising a probe mounted in said transmission line circuit to intercept a voltage breakdown arc, said probe being of a relatively high impedance in comparison with the magnitude of the impedance of said arcs expected within said transmission line circuit at the energy levels present in said transmission line circuit, and control means for detecting the loading of said pro'be by said arc and for continually disabling and enabling said source of energy until the cause of Isaid arc is removed.

9. A system -comprising a source of energy, a transmission line circuit associated therewith, and means for detecting ion and electron densities in a voltage breakdown arc within said transmission line circuit comprising a probe mounted in said transmission line circuit to intercept said voltage breakdown arc, said probe comprising a negatively charged electrode from which current is drawn by said arc, and control means for detecting the loading of said probe by said arc and for continually disabling and enabling said source of energy until the cause of said arc is removed 10. In a system for measuring ion and electron densities of a plasma arc occurring within a power transmission line circuit being fed by a source comprising a probe mounted in a transmission line circuit to intercept a voltage breakdown arc, said probe comprising a negatively charged electrode from which current is drawn by said arc, and said probe being of la relatively high impedance in comparison with the magnitude of the impedances of said arc at `the power levels expected within said transmission line cir-cuit, and control means for detecting the loading of said probe by said arc and for continually disabling and enabling said source until the cause of said arc is removed.

11. In an arc detection system .including a source of energy and an output waveguide circuit associated therewith, an energy sensor located in proximity to the terminus of said output waveguide circuit, said energy sensor providing a signal `indicative of the amount of microwave energy flowing in the vicinity of said terminus of said output waveguide circuit whereby an arc can be detected in said output waveguide circuit, a comparison circuit for comparing said output signal of said energy sensor with a reference signal, said reference signal being indicative of the energy which would be flowing within said transmission line circuit in the absence of an arc in said transmission line circuit, and means for disabling said energy source in the presence of an arc within said waveguide circuit, said means for disabling responsive to the comparison of said signal from said energy sensor and said reference.

12. In a high power microwave arc detect-ion system including a source of microwave energy providing forward coupled microwave energy to a waveguide output circuit associated therewith, means for detecting the existence of voltage breakdown arcs in said waveguide caused by the presence of a lossy material in said waveguide, comprising a plurality of microwave energy sensors positioned to sample forward coupled microwave power, control means responsive to the detection of microwave breakdown arcs by said microwave energy sensors, said con-trol means provid-ing a signal to reduce the amount of forward coupled microwave energy being provided to said waveguide output circuit, and said control means comprising means for periodically reducing the amount of microwave energy being provided to the waveguide output circuit until the lossy material present in said vol-tage breakdown arc can no longer initiate an arc.

13. In a system including a source of energy and a transmission line circuit associated therewith, means for detecting a voltage breakdown arc in said transmission line circuit comprising a plurality of energy sensors positioned in circuit with said transmission line circuit to distinguish between the magnitude of the energy on either side of said arc, said energy sensors providing an output signal indicative of the amount of energy sensed, means for nulling in response to said sensor ou-tput signals, means for :sampling a signal provided by said means for nulling, control means responsive to said sampling means for reducing the energy provided by said source of energy to said -transmission line circuit, said control means including means to prepare said control means for the possible reinitiation of an arc in said transmission line circuit prior to said control means returning said source of energy to full power.

14. In a system including a source of energy and a transmission line circuit associated therewith, means for detecting voltage breakdown arcing in said transmission line circuit comprising a plurality of rectifying energy sensors positioned in circuit with said transmission line circuit to distinguish between the magnitude of the energy on either side of said arcing, said rectifying sensors pro* viding an output signal indicative of the magnitude of energy sensed, an unbalance circuit responsive to said output signals provided by said plurality of energy sensors, controlled electrical discharge means in circuit with said unbalance circuit and responsive to said unbalance circuit for cyclically sampling an output signal from said unbalance circuit, con-trol means responsive and in circuit with said electronic discharge means for disabling said soure of energy upon the reinitiation of an arc formed within said transmission line circuit, said control means comprising means for permitting said transmission line circuit :to be purged of the lossy materal causing initia- Ition 4of said arcing.

References Cited by the Examiner UNITED STATES PATENTS 1,896,856 2/1933 Traver 317-42 2,344,261 3/1944 Mortlock 317-44 2,493,720 2/1950 Wild 331-62 2,498,719 2/1950 Spencer 331-62 2,557,180 6/1951 Fiske 333-98 2,860,244 11/1958 Crowley 3 25-150 3,028,507 4/1962 Sacks 307-885 3,081,438 3/1963 Levy 1533-242 HERMAN KARL SAALBACH, Prz'maly Examiner.

W'. K. TAYLOR, P. L. GENSLER, Assistant Examiners.

Claims

2. IN A SYSTEM INCLUDING A SOURCE OF ENERGY AND A TRANSMISSION LINE CIRCUIT ASSOCIATED THEREWITH, MEANS FOR DETECTING A VOALTAGE BREAKDOWN ARC IN SAID TRANSMISSION LINE CICRUIT COMPRISING A PLURALITY OF ENERGY SENSORS TO DISTINGUISH BETWEEN THE MAGNITUDE OF THE ENERGY ON EITHER SIDE OF SAID ARC, AND MEANS FOR DISABLING SAID SOURCE OF ENERGY IN RESPONSE TO SAID ENERGY SENSORS DISTINGUISHING BETWEEN THE MAGNITUDE OF THE ENERGY ON EITHER SIDE OF SAID ARC, SAID MEANS FOR DISABLING INCLUDING A MEANS FOR PURGING THE CAUSE OF THE INITIATION OF A VOLTAGE BREADOWN ARC IN SAID TRANSMISSION LINE CIRCUIT BY CONTINUALLY DISABLING AND ENABLING SAID ENERGY SOURCE UNTIL SAID CAUSE IS REMOVED.