US3826889A

US3826889A - System for automatic control of electron beam heating device

Info

Publication number: US3826889A
Application number: US00170915A
Authority: US
Inventors: P Yakolvlev; K Gutterman; I Brukovsky
Original assignee: Individual
Current assignee: Individual
Priority date: 1970-10-12
Filing date: 1971-08-11
Publication date: 1974-07-30
Anticipated expiration: 1991-07-30

Abstract

A system is disclosed for automatic control of an electron beam heating device of the type in which a current-stablized powersupply source is coupled to the electron gun and is electrically connected with an automatic reset unit serving to cut off voltage to the electron gun upon an electric breakdown between the electrodes of the gun. The automatic reset system does not operate immediately following the breakdown between the electrodes of the gun, but only after a predetermined time interval to allow the voltage across the electron gun to return spontaneously to the original value when the discharge between the electrodes of the electron gun is unsteady in character. After voltage cut off, if the electrical breakdown still has not been corrected, the automatic reset system successively operates at different time intervals to cut off electron gun voltage. Specifically, and in the preferred embodiment, the instant inventive system is so designed that the time interval between the occurrence of voltage cut off as a result of electric breakdown and the occurrence of the subsequent automatic reset of the apparatus becomes increasingly larger during successive operation of the system.

Description

Kiln-1Z1 ELECTRON BEAM HEATING DEVICE Primary Examiner-J. V. Truhe Assistant Examiner-G. R. Peterson v [76] In enters i gg fir gyfy iigtgsg Attorney, Agent, or Firm-Holman & Stern 2-B, kv. l6; Pavel Borisovich Yakolvlev, ulitsa Tolvukhina, 9, [57] ABSTRACT 5:32; g TJ E 5:53:21??? A system is disclosed for automatic control of an elecumsa 29 kv. 8 a of M 08 c ow tron beam heatmg dev1ce of the type in wh1ch a cur- U S rent-stabhzed power-supply source 1s coupled to the electron gun and is electrically connected with an au- [22] Filed: Aug. 11, 1971 tomatic reset unit serving to cut off voltage to the electron gun upon an electric breakdown between the [21] Appl' 170915 electrodes of the gun. The automatic reset system Related US. Application Data does not operate immediately following the break- [63] Continuation-impart of Ser. No. 80,235, Oct. 12, down between the electrodes of the g but y after 1970, abandoned, which isacontinuation of Ser. No. a p edete i time interval to allow the voltage 836,449, June 25, 1969, abandoned. across the electron gun to return spontaneously to the original value when the discharge between the elec- [52] US. Cl. 219/121 EB, 315/119 trodes of the electron gun is unsteady in character. [51] Int. Cl B231 15/00 After voltage cut off, if the electrical breakdown still [58] Field of Search... 219/121 EB, 121 EM, 69 P, has not been corrected, the automatic reset system 219/69 C; 315/119, 127, 107; 317/141, 157 successively operates at different time intervals to cut off electron gun voltage. Specifically, and in the pre- [56] References Cited ferred embodiment, the instant inventive system is so UNITED STATES PATENTS designed that the time interval between the occur-- 2 619 52s 11/1952 Webb .Q 315/127 x rence of voltage cut off as a result of electric 311931722 7/1965 Opitz 315 30 and the currence of the subsequent automatlc 3,196,246 7/1965 219/69 reset of the apparatus becomes increasingly larger 3,20 ,33 10 19 5 143 5 during successive operation of the system. 3,459,941 8/1969 315/107 X 3,483,347 12/1969 Losey 219/69 P 3 Clalms, 4 Drawlng Flglll'es H POWER SUPPLY f z T BLOCK POWER BLOCK AUTOMATlC SUPPLY CONTROL REPEATED SWITCHING 3 J 4 J DESIGN United States Patent [1 1 Brukovsky et al.

[111 3,826,889 [451 July'30, 1974 SYSTEM FOR AUTOMATIC CONTROL OF PATENTfiijJULS 0 2914 saw 1 er 2 POWER SUPPLY ELECTRON HEATING DESIGN BLOCK AUTOMATIC REPEATED SWITCHING BLOCK POWER SUPPLY CONTROL FIG. 1

U VO LTAGE TIME POWER SUPPY 1 INVENTOR I ELECTRON HEATING DESIGN FIG. 3

ATTORNEY PATBIIEINIIIB A 3.826.889

sIIE 2 IF2 ll. 3 1 I 22 1F HAND. SWITCHING 56 67 74 R T S l W4 AUTOMATIC 24 I7 REPEATED S S -L- sw TC H IN G ARs l T 8 2PB BLOCKING UNDER Ia) 2 9 I. OPENED LINE CONTACTOR 32 I (RK) Q I {34 43 STEADY DISCHARGE 212. DIsCERNING IQ4O 4| CONTAC S .MULTI PLYING 3 Q RELAY 5 44 I 1T" ARS OPERATED CIRCUIT i5 58 EBLOC KING F ID I CONTACTS MuLTIPLY NG Q 47 57 T ME DELAY BEFORE THE 1|' |F* FIRST REPEATED 36 59 Q 64 sw TCH NG TIM DELAY BEFORE THE Q62 5| SECOND REPEATED ll 63 SWITCHING -(NB) 37 3 g TIME DELAY BEFORE THE I IT I THIR REPEATED 8 SWITCHING C69 52 8 S70 ARs OPENING II H A C38 71 72 -1 k INVENTOR F1614 BYM4-V m4 ATTORNEY SYSTEM FOR AUTOMATIC CONTROL OF ELECTRON BEAM HEATING DEVICE This application is a Continuation-ln-Part of copending application Ser. No. 80,235 filed Oct. 12, 1970 now abandoned, which application, in turn, is a continuation of application Ser. No. 836,449, filed June 25, l969 now abandoned.

This invention generally relates to the field of electrothermics and more particularly concerns systems serving to automatically control electron beam heating devices.

As is generally known, electric heating devices having electron guns are supplied from special power sources which comprise commutation means such as a contactor or high-voltage switch to connect the supply source to and disconnect it from the supply network at the end of an operating process or in emergency situations, a step-up transformer and a rectifier comprising controllable or uncontrollable valves or switches and having its negative terminal connected to the cathode of the electron gun, while its positive terminal is connnected to the anode of the electron gun. Such supply sources for use with electron beam heating devices essentially are of two types.

One such supply source ensures a constant voltage value at the output of the rectifier supplying the electron gun with the voltage value being independent of the conductance of the electron gun. When electrical breakdown occurs between the anode and the cathode of the electron gun in an electric heating device supplied from a source of this type, as is frequently the case with industrial apparatus, the conductance of the electron gun sharply rises with the result that a current exceeding many times the rated value flows through the supply transformer, the rectifier and the electron gun. An arc discharge sparks between the cathode and the anode of the electron gun which is likely to melt and put the electrodes of the electron gun out of action.

This mode of operation occurs in emergencies, requiring immediate disconnection of the electron gun by either disconnecting the supply source of the heating device from the network with the help of the commutation means incorporated in the supply source, or by suitably rendering inconductive the valves of the rectifier supplying the electron gun. Subsequently, some time after the disconnection of supply from the electron gun, the electric strength and, consequently, the conductance of the electron gun are restored to the original level due to the recombination of plasma that has formed during the burning of the electric are between the anode and the cathode. To continue the operational process, voltage then is re-applied to the electron gun either manually by the operator or by an automatic reset system through a control unit of the supply source commutation means or the control unit of the rectifier valves.

In cases when the time interval between the cutoff of supply from the electron gun and voltage re-supply by the automatic reset system is insufficient to restore the electrical strength of the interelectrode gap, resetting may result in another breakdown between the anode and the cathode of the electron gun and require a further disconnection of supply from the electron gun to eliminate the emergency operation. Commonly known automatic reset systems for use with electron beam devices supplied from sources maintaining a constant voltage value at the rectifier are characterized by instantaneous (no time delay) disconnection of the supply from the electron gun upon electrical breakdown between the electrodes thereof, and by identical time intervals between each successive reset operation.

A further basic type of supply source serves to maintain a constant current value at the output of the rectifier supplying the electron gun, the current value being independent of the conductance of the electron gun. Supply sources of this type are generally constructed utilizing various resonance circuits, i.e., Boucherot Steinmitz circuits or variants thereof, or utilizing a controlled rectifier which supplies the electron gun to ensure l const. In electron beam heating devices supplied from sources of this type, when electrical breakdown occurs between the cathode and the anode of the electron gun and an electric discharge sparks between them, the current does not change in the circuit formed by the supply transformer, the rectifier and the electron gun. The voltage at the electron gun, however, drops to a value determined by the parameters of the discharge sparking between the anode and the cathode of the electron gun. This electric discharge subsists on the vapors of metal evaporating from the electrodes of the electron gun and on gases dissolved in metals, and it is characterized by low power evolving in the electrodes. For this reason, it can either be steady or unsteady, i.e., last as long as voltage is applied to the electron gun, or spontaneously die out after a certain time interval. In the latter case, the conductance of the electron gun decreases and the voltage across it rises to the value existing before the breakdown.

The character of this discharge, i.e., steady or unsteady, depends on many factors, the most important of which are the material from which the electrodes of the electron gun are made, the value of the discharge current, the extent of vacuum in the interelectrode gap, the relation between the amount of vapors and gases formed during the discharge and the speed vapors and gases formed during the discharge and the speed with which they are discharged from the interelectrode gap. When the discharge is unsteady it is not advisable to cut off supply from the electron gun in an attempt to eliminate the breakdown. But when the discharge is steady, it can be eliminated by disconnecting the supply from the electron gun through the commutation means of the supply source or through the controllable valves of the rectifier connected to the electron gun.

Thereafter, to continue the normal operating process, voltage should not be applied to the electron gun immediately after it has been cut off, but only after a definite time interval which must be sufficient for ionization to take place in the interelectrode gap of the electron gun. If during this time interval the electrical strength of the interelectrode gap has not returned to its normal value, re-applying voltage to the electron gun will result in another breakdown between the gun electrodes.

The instant invention has, as a primary object thereof, the provision of an automatic control device for electron beam heating apparatus supplied from current-stabilized power sources of the type abovedescribed, the automatic control device of the instant invention ensuring automatic restarting of the electron beam heating apparatus after the power supply has been cut off from the electron gun due to an electric breakdown between the electrodes thereof.

A further object of the instant invention concerns the provision of an automatic reset system which will cut off voltage from the electron gun, not immediately following the electric breakdown between the electrodes of the gun, but only after a predetermined time interval. This time interval between breakdown in the electron gun and cut off of the power supply is intended to allow the voltage across the electron gun to spontaneously return to the original value without a forced disconnection of supply when the discharge between the electrodes of the electron gun is unsteady in character, the automatic reset system being effectively utilized only with electron guns supplied from currentstabilized sources.

A further object of the instant invention concerns the provision of an automatic reset system which, upon the presence of recurring electric breakdowns between the electrodes of an electron beam heating apparatus, serves to successively reset the system and re-apply voltage to the electrodes with different time intervals between the successive resets, the duration of each time interval being varied at will. In this respect, the system of the instant invention is contemplated to function such that the time interval between the initial cut off of voltage as a result of the first breakdown and the subsequent automatic reset of the electron beam heating apparatus is smaller than the interval between the cut off occurring as a result of a second breakdown and the subsequent automatic reset of the apparatus, and so on.

A still further object of the instant invention concerns the provision of a system of the type described wherein the overall efficiency and capacity of the electron beam heating device is increased and wherein the life of the switching equipment such as a contactor, an automatic switch or a high-voltage switch incorporated in the supply source of the electron beam heating apparatus and serving to connect and disconnect the supply source to the network, is markedly prolonged. Through the utilization of the automatically reset unit of the instant invention the number of cut outs of the powersupply source is reduced.

These objects as well as others which will become apparent as the description proceeds, are implemented by the instant invention which, as aforestated, comprises a system for the automatic control of an electron beam heating device, the system broadly comprising a powersupply source electrically connected with an automatic reset unit in which, in accordance with the invention, the power-supply source is constructed in the form of a current-stabilized power source. The automatic reset unit of the instant invention is provided with a plurality of time delay elements as will be discussed hereinbelow to ensure prescribed time intervals between the occurrence of short circuits at the interelectrode gap between the electrodes of the electron gun, and subsequent cut off operations of the power-supply in an effort to correct the electric breakdown between the electrodes.

The various advantages of such a system wherein operation of the automatic reset unit occurs only during prescribed and variable time intervals as abovediscussed can perhaps best be understood from the following general discussion.

In this respect, it should be recognized that a chief cause of a short circuit of the electron gun or interelectrode load in an electron gun electric heating device may be an electric breakdown between the electrodes of the electron gun. It the power-supply source is of the type which provides a constant value of supply voltage, such an interelectrode breakdown leads to a heavy current arc discharge.

After breakdown, the time of recovery of the electric strength of the gun to the rated value depends, as briefly discussed above, on the relationship between the amount of vapours and dissolved-in-metal gases entering the interelectrode gap between the electrodes of the electron gun from the working chamber of the device and evolving from the material of the electrodes during the arcing and the efficiency of the vacuum chamber of the electron gun. During the process of melting, the recovery time may change.

If the power-supply source for the electron gun is based on a system providing a constant value of interelectrode current, the current flowing through the power-supply circuit of the device would remain unchanged upon a short circuit between the electrodes. Therefore, the short circuit conditions characterized by a considerable voltage drop at the output of the powersupply source are not emergency conditions which would require an immediate cut off of the device, even though such short circuit conditions do interupt the normal course of the particular technological process being undertaken. This is clear from the following consideration.

During a breakdown of the interelectrode gap, an arc discharge appears between the electrodes of the gun, which discharge is characterized by an insignificant power of the arc. In this event, the power dissipated in the electrodes is not high and, as is found from experience, such dissipated power does not cause notable destruction of the electrodes. Such destruction of the electrodes, i.e., melting or erosion of the material of the electrodes, is a heavy-current discharge sparking took place between the anode and cathode of the electron gun. In the case of a weak-current discharge of the type now under consideration lasting only for a relatively short time, such destruction is substantially absent.

Furthermore, the stability of the discharge burning, whether the discharge be steady or unsteady, is determined by the relationship between the amount of vapours and dissolved-in-metal gases admitted into the interelectrode gap from the working chamber of the device and also evolved from the material of the electrodes and the efficiency of the vacuum system of the electron gun.

In some cases when the arc discharge is unstable, the normal operating duty of the electron gun device is automatically restored after a certain time interval. In such cases, the application of presently known apparatus which serve to cut off the power-supply source immediately after receiving a signal from its output would lead to unjustified disconnections of the device from the power-supply source and thus to a resultant decrease in the device efficiency and to deterioration of the switching equipment utilized therein.

The utilization of the present inventive system, on the other hand, avoids these disadvantages due to the time delay occurring before the first cut off upon detection of an electric breakdown between the electrodes, and through the provision of variable time delays between subsequent reset operations in the event that the electric breakdown between the electron gun electrodes persists.

The present inventive system is thus designed to ensure automatic control of the electron beam heating apparatus and, for this purpose, the instant invention will be seen to utilize a signal which is proportional to the output voltage of the apparatus supply source, which signal is applied to the input of an automatic reset unit. The automatic reset unit itself will be seen to comprise several relays which ensures the required succession of logical operations, the reset unit further including time relays for maintaining preset time intervals between operations. The output of the automatic reset unit of the instant invention is connected to the input of the control unit of the electron gun powersupply source. As the power-supply is automatically cut off by the automatic reset system, the signal from the output of the automatic reset unit is applied to the input of the control unit of the power-supply source so as to influence the operation of the power-supply source in one of two manners depending on the particular design of the supply source for the electron beam heating apparatus.

Specifically, if the rectifier utilized in the powersupply source is constructed of uncontrolled valves, the control unit of the power-supply source would generate a signal to cut off the supply source from the network through the commutation means such as a contactor or high-voltage switch incorporated in the supply source. Alternatively, if the rectifier of the power-supply source is constructed utilizing controlled valves, the control unit of the supply source would generate a signal to the valves such that the valves would assume a non-conductive state.

The invention itself as well as further operational advantages and details thereof will become apparent from the following description of a preferred inventive embodiment, such description referring to the appended sheets of drawings wherein:

FIG. 1 depicts a block diagram of the novel system of the instant invention serving to automatically control an electron beam heating device;

FIG. 2 depicts a time diagram of the operation of the automatic reset system;

FlG. 3 is a schematic diagram of a supply circuit for the electron gun apparatus, the supply circuit comprising a parametric power-supply source serving to maintain an invariable value of current flowing through the supply transformer, and a power rectifier utilizing uncontrolled valves; and

FIG. 4 depicts a schematic diagram of the control unit of the power-supply source, and of the automatic reset unit of the instant invention in an embodiment thereof utilizing contact relays for triple automatic reset cycling as will be explained hereinbelow.

Referring now to the drawings, the overall structure and operation of the novel invention will be discussed and, as is seen from FIG. 1 of the drawings, an electron beam heating device 1 is fed from a currrent-stabilized power-supply source 2 which, in turn, is connected with a unit 3 for controlling the power-supply source 2.

The output of the power-supply source 2 of the device is electrically connected with an automatic reset unit 4 constructed in accordance with the teachings of the instant invention and provided with a plurality of time delay elements such as relays of both the single contact and multiple contact and independently operated variety as will be discussed in more detail hereinbelow. The automatic reset unit 4 is connected with the power-supply source unit 3 so as to operate same to effect cut off of power to the electron beam device in a predetermined manner.

The proposed system operates as follows. If the breakdown in the electron gun of the device 1 occurs at a time moment t (FlG. 2), the use of the time delay element makes it possible to cut off the currentstabilized power-supply source after a definite time interval A I i.e., in the case of appearance of a comparatively stable short circuit.

The first automatic reset of the device I will take place after a time interval At If during the time interval Ar or to the time moment t;, the electric strength of the device 1 is not restored to the rated value, the device 1 will be cut off again within the time interval t The second automatic reset of the device will take place only after a time interval AL If during this time or during the time M the electric strength of the device 1 does not reach a corresponding level, the device 1 will be switched off at the moment 1 and will be switched on again only after the time interval At If the electric strength of the interelectrode gap does not come up to its rated value for the time Ar or M the device will again be switched off within the time period t,,. The automatic reset unit 4 is switched off simultaneously with the device. The subsequent reset of the device 1 can be carried out only by hand.

Thus, the proposed system features a limited number of reset cycles the quantity of which may be determined on the basis of the experience of operation of the device.

If during the time period An; after the first reset or during the period At after the second reset the breakdowns in the device do not occur, the automatic reset unit 4 with the help of the time delay element is set to the initial position corresponding to the time period t The proposed device provides for the possibility of individual adjustment of the time intervals Al At A2 At and At whose optimum values are selected experirnentally.

It should be noted that the selection of the time intervals At At, At ensures a higher stability of operation of the device because the repeated cut off of the device, for example during the time period An, proves that the time interval A1 was insufficient for restoring the electric strength of the device up to the rated value.

The various time intervals At generally are selected to have units ranging from a few hundreths of a second to a few seconds, the differences in the selected units being dependent on the specifics of the operating process carried out in the apparatus and of the parameters and design of the automatic reset system itself.

With the above general operation and structure in mind, the following detailed description of an actual physical embodiment of the invention can be better understood. In this respect, and referring specifically to FIG. 3 of the drawings, the electron beam heating apparatus 1 comprises an electron gun 200 have a cathode 300 and a focusing anode 400. An electron beam 5 shaped in the interelectrode gap 6 passes through an orifice in the focusing anode electrode 400 to the article 7 to be heated which, like the focusing anode electrode 400, is held at ground potential. The filament cathode 300 is fed from a supply transformer 8.

A supply source 9 of the electron beam heating apparatus comprises commutation means such as a contactor, whose power contacts 10 are connected in series to a supply transformer 11 and reactive elements by capacitor 12 and inductor l3, and also a rectifier 14 connected to the supply transformer 11 and having its negative terminal connected to the cathode 300 of the electron gun, while the positive terminal is connected to the article 7 to be heated. When the reactances of the capacitor 12 and the inductor 13 are equal, the circuit formed by the

elements

11, 12 and 13 ensures a constant value of current flowing through the primary winding of the transformer 11 irrespective of the conductance of the electron gun 200 and, with a sufficiently high temperature at the electron gun cathode, this ensures a constant value of current in the electron beam 5.

An additional resistor 15 is provided to allow control of the supply source voltage which may vary with changes in the conductance of the electron gun. One terminal of the additional resistor 15 is connected to the negative terminal of the rectifier l4 and the other, to the coil of a voltage relay 16, whose second terminal is connected to the positive terminal of the rectifier 14. The power contacts 10 of the commutation means of the supply source 9 are controlled by means of the coil of a contactor 17.

Referring to FIG. 4, the control unit of the supply source comprises on on-button 18, on off-button 19,

coils of intermediate relays and 21 and the coil of the contactor 17. When the button 18 is pressed, the coil of the relay 20 is energized and one of its contacts 22 interlocks the button 18 while the other contact 23 supplies the coil of the relay 21. As the latter operates, its contacts 24 and 25 directs supply to the coil of the contactor l7 and, at the same time, the contact 26 feeds supply to the coil of the time relay 27 whose contact 28, having a time delay upon closure, prepares the supply circuit of the coil of a time relay 29 for operation. Since the contact 28 closes with a time delay, the time relay 27 interlocks the operation of the relay 29 in case the coil of the contactor 17 is de-energized.

When the supply voltage of the electron gun decreases, the coil of the voltage relay 16 releases and the relay closes its contact 30 in the circuit of the coil of the time relay 29 which is capable of distinguishing whether the discharge between the electron gun electrodes is steady or not, ensuring a time delay At in accordance with FIG. 2.

If the discharge between the electron gun electrodes and the voltage drop caused by it in the supply source last longer than the time preset in the time relay 29, the latter opens one of its contacts 31, cutting off supply of the coil of the relay 21 with the result that the coil of the contactor 17 is deenergized, while its second contact 32 is closed in the circuit of the coil of the in-v termediate relay 33 serving to multiply contacts. As the relay 33 operates, its

contacts

34, 35, 36, 37 and 38 close.

Upon the closure of the contact 34, voltage is applied to the coil of an intermediate relay 39 which operates and causes one of its contacts 40 to block supply through the contact 34, while the other contact 41 directs supply to the coil of a time relay 42 which unlocks the automatic reset circuits that have operated. If no recurrent breakdowns took place in the electron gun for the time period At, in accordance with FIG. 2, the

relay 42 opens its

contacts

43 and 44 and returns the automatic reset system to the condition corresponding to the time t of the diagram in FIG. 2.

When the relay 20 operates, its third contact 45 directs supply to the coil of the intermediate relay 46 serving to multiply contacts. Upon operation, the relay 46 closes its

contacts

47, 48 and 49, preparing to lock the supply circuits of the coils of the time relays 50, 51, and 52 which ensure time delays Atg, At, and At in accordance with the diagram in FIG. 2.

When the relay 33 operates, its contact 35 directs supply to the coil of an intermediate relay 53 which, upon operation, causes one of its contacts 54 to block supply through the contact 35, while the other contact 55 directs supply to the coil of the time relay 50. Simultaneously the relay 53 opens its contact 56 in the circuit of the coil of the relay 21 with the result that the coil of the contactor 17 is de-energized and the supply source of the electron gun is cut off from the network.

After a time interval At in accordance with FIG. 2, the time relay closes one of its contacts 57, blocking supply of its coil through the contact and opens its contact 58 in the circuit of the coil of the relay 53. The coil of the relay 53 is de-energized, its contact 56 closes and the coil of the relay 21 is again energized, resulting in the first automatic reset of the coil of the contactor 17.

Simultaneously, the third contact 59 of the relay 50 prepares the supply circuit of the coil of the intermediate relay 60 for operation.

If, by a definite time, the discharge between the electrodes of the electron gun has not stopped spontaneously, at that moment the relay 29 operates again, its

contact 31 cutting off supply from the coil of the relay 21 so that the contactor 17 is cut off. At the same time the contact 32 of the relay 29 directs supply to the coil of the relay 33 which, upon operation, causes its contact 36 to direct supply to the coil of the intermedi ate relay 60.

As the relay 60 operates, one of its contacts 61 blocks supply of the coil through the contact 36, while the other contact 62 directs supply to the coil of the time relay 51 which maintains a time delay At, in accordance with FIG. 2. At the time t the relay 51 operates and, with the help of the contact 63, blocks supply of its coil through the contact 62. When the relay 51 operates, it closes its contact 65 in the circuit of the coil of an intermediate relay 66 and opens its contact 64 in the circuit of the coil of the relay 60. As a result, the contact 67 of the relay 60 closes, directing voltage to the coil of the relay 21, thereby effecting a second automatic reset of the contactor 17 at the time time If by the time the discharge between the electron gun electrodes has not stopped spontaneously at that moment the relay 29 operates again, its contact 31 cutting off supply from the coil of the relay 21 after the time interval Al with the result that the contactor 17 is cut off. Simultaneously, the contact 32 of the relay 29 directs supply to the coil of the relay 33 which, upon operation, causes its contact 37 to direct supply to the coil of the intermediate relay 66.

As the relay 66 operates, its contact 68 blocks supply of the coil through the contact 37, while its other contact 69 directs supply to the coil of the time relay 52 which effects a time delay At, in accordance with FIG. 2.

At the moment t,, the relay 52 operates and with the help of a contact 70, blocks supply of its coil through the contact 69. Upon operation, the relay 52 closes its contact 71 in the circuit of the coil of an intermediate relay 72 and opens its contact 73 in the circuit of the coil of the relay 66. As a result, the contact 74 of the relay 66 closes, directing supply to the coil of the relay 21, thereby effecting a third automatic reset of the contactor 17 at the time 1 If by the time t, the discharge between the electron gun electrodes has not stopped spontaneously, at that moment the relay 29 operates again, its contact 31 cutting off supply of the coil of the relay 21 after a time interval At, with the result that the contactor 17 is cut off. At the same time, the contact 38 of the relay 29 directs supply to the coil of an intermediate relay 72 which, upon operation, opens its contact 73 in the circuit of the coil of the relay 20, disconnecting the automatic reset system.

The contactor 17 may again be energized manually be means of the button 18.

Due to the different operation time of the

relays

50, 51 and 52, the present system maintains different time intervals At AL, and At between the disconnection of the supply source from the network and its subsequent automatic resetting.

As should now be apparent, the objects initially set forth at the outset to this specification have been successfully achieved.

What is claimed is:

1. A power supply system for an electron beam heating device having electrodes, said system comprising, in

combination: a current-stabilized power-supply means for providing said electron beam heating device with a substantially constant current; a controllable switching means for selectively disconnecting and reconnecting said power-supply means; sensing means for sensing the output voltage of said power-supply means and for thereby detecting the occurrence of a short circuit between said electrodes; and an automatic reset control unit means responsive to said sensing means for controlling said controllable switching means, said reset unit including time delay logic circuit means responsive to the occurrence of a short circuit between said electrodes for (a) disconnecting said power supply means, (b) reconnecting said power supply means after a definite time interval, and (c) alternately disconnecting and reconnecting said power supply means in succession if the short circuit between said electrodes has not stopped simultaneously, said time delay logic circuit means automatically effecting each successive disconnect and reconnect operation after predetermined and successively different time intervals.

2. A power supply system as defined in claim 1, wherein said time delay logic circuit means comprises a plurality of relays disposed in a logic tree arrangement, said relays having independently adjustable operation times.

3. A system as defined in claim 1, wherein each successive time delay period automatically effected by said time delay logic circuit means is respectively longer in duration.

Claims

1. A power supply system for an electron beam heating device having electrodes, said system comprising, in combination: a current-stabilized power-supply means for providing said electron beam heating device with a substantially constant current; a controllable switching means for selectively disconnecting and reconnecting said power-supply means; sensing means for sensing the output voltage of said power-supply means and for thereby detecting the occurrence of a short circuit between said electrodes; and an automatic reset control unit means responsive to said sensing means for controlling said controllable switching means, said reset unit including time delay logic circuit means responsive to the occurrence of a short circuit between said electrodes for (a) disconnecting said power supply means, (b) reconnecting said power supply means after a definite time interval, and (c) alternately disconnecting and reconnecting said power supply means in succession if the short circuit between said electrodes has not stopped simultaneously, said time delay logic circuit means automatically effecting each successive disconnect and reconnect operation after predetermined and successively different time intervals.