US2234963A

US2234963A - Arc tube system

Info

Publication number: US2234963A
Application number: US284501A
Authority: US
Inventors: David D Coffin
Original assignee: Raytheon Manufacturing Co
Current assignee: Raytheon Co
Priority date: 1939-07-14
Filing date: 1939-07-14
Publication date: 1941-03-18
Anticipated expiration: 1958-03-18

Description

' M r h 18, 1.941. D. D. coFF'm' 2,234 963 ARC TUBE SYSTEM Filed July 14, 1939 a INVENTOR.

DAVID D. Cor-FIN,

ATTY.

Patented Mar. 18, 1941 UNITED STATES PATENT. OFFICE ARC TUBE SYSTEM Application July 14, 1939, Serial No. 284,501

15 Claims.

This invention relates to an arc tube system, and more particularly to such a system in which two controlled arc tubes are connected inversely in order tosupply a controlled alternating our- 5 rent load, such as a resistance welding load.

In alternating current systems of this general nature, particularly in the case of resistance welding loads, it is desirable that if one of the arc tubes fails to conduct current upon the application of an igniting impulse to its igniting electrode, the other are tube shall also be prevented from starting. If this is not done, the current supplied to the load hasa substantially direct current component which is usually disadvantageous, especially when undesired magnetic saturation of magnetic elements in the load circuit may result.

An object of this invention is to devise means responsive to the absence of conduction in either tube for deenergizing the firing circuit of the other tube.

The causes which prevent a tube from firing upon the application of an igniting impulse to the igniting electrode are often temporary in character, and therefore it is often desirable to repeat the application of igniting impulses to the tube which fails to fire. Another object of this invention is to devise means for doing this, which means, however, prevents igniting impulses from being supplied to said other tube as long as the first tube fails to fire.

The foregoing and other objects of this invention will be best understood from the following description of an exempliiication thereof, reference being had to the accompanying drawing, wherein:

Fig. l is a diagrammaticrepresentation of a circuit embodying the present invention; and

Fig. 2 is a curve illustrating the operation of the system shown in Fig. 1.

The embodiment illustrated consists of two are tubes I and 2, preferably of the mercury pool cathode type. These tubes contain

mercury pool cathodes

3 and 4, and anodes 5 and 6, respectively, and are provided with igniting electrodes I and 8. Although these igniting electrodes may be of any type which initiate an are on the mercury pool cathode by means of an igniting impulse supplied thereto, they preferably are of the type which consists of a conductor separated from the mercury pool by aninsulating layer which preferably consists of glass. More particularly these igniting electrodes may be of the form described and claimed in the copending application of Percy L. Spencer, Serial No. 259,355, filed March 2, 1939,

for an improvement in Arc starting devices. In igniting electrodes of this kind, the glass layer on the igniting electrode conductor is in contact with the surface oi. the mercury pool, and the arc tends to form at some such point of contact. The upper ends of the electrodes 1 and 8 may be left exposed to the discharge so as to provide discharge paths in parallel with the respective cathodes and igniting electrodes.

Two alternating current lines 8 and ID are con- 10 nected to supply a suitable alternating current load which may consist of a transformer H having a primary l2, a secondary l3, and a load ll. In the particular system shown, the load Il may consist of a resistance welding load. The are tubes I and 2 are interposed in one of the conductors Iii in order to control the flow of current to the load. In order to permit alternating current to flow through the tube system, the two tubes are reversely connected by means of the 2 crossed conductors l5 and i6. If the tubes i and 2 are conducting, current pulses of one polarity will flow through tube I, and current pulses of the opposite polarity will flow through tube 2, thus delivering alternating current to the load. If, however, tubes l and 2 are non-conducting, the load is deenergized.

Igniting transformers ii and iii are provided to supply igniting impulses to the igniting electrodes i and 8, respectively. These igniting transformers are provided with secondary windings i9 and 28. The secondary winding !9 is connected between the igniting electrode 7 and "the cathode pool 3, While the secondary winding 2b is connected between the igniting electrode 8 and the cathode pool 3. The transformers i! and iii are also provided with primary windings 2i and "2 2 which are supplied with igniting voltage impulses through a control circuit which is energized from atransformer 23 having a primary winding 24 connected directly across'the tubes l and 2. For this purpose the two ends of the primary winding 24 are connected respectively to the two conductors l5 and it. The transformer 23 also has a secondary winding 25 which supplies primary windings 2i and 22 with unidirectional impulses through a rectifying bridge. A pair of control contacts 26 are interposed in one of the conductors leading from the secondary winding 25 to the rectifying bridge. These control contacts may be operated from a control pushbutton or from some suitable timing arrangement.

The rectifying bridge comprises four

rectifiers

21, 28, 29 and 30, preferably of the copper oxide type. The primary windings 2| and 22 constitute two outerlegs of the bridge, while a conductiveconnection 3i, extending from a point between the rectifiers 2i! and 28 to a point between the rectifiers 29 and 3B, constitutes the central leg of said bridge. Included in the central leg ii is a relay armature 32 which normally completes the connection between a pair of contacts 3-333.

The armature 82 forms part of a relay 3% which is provided with an operating coil 35. Said operatins coil 35 is also in series with the contacts 23383 in said central leg 3 l. The polarities of the rectiflers ill-do are such that rectifiers El and 3t allow impulses of one polarity to pass through the primary winding 22, while the

rectifiers

23 and 29 allow impulses of the opmsite polarity to pass through the primary winding 2i.

Connected directly across the tubes 6 and 2 is a series circuit consisting of a resistance 36 and a condenser 87!. This circuit is to enable the incipient arc spots initiated-by the igniting impulses supplied to the igniting electrodes 71 and 8 to progress rapidly into true arc spots irrespective of the nature of the main load. This feature is more fully described and claimed in the copending application of Wilcox P. Over-beck, Serial No. 271,679, filed May 4, 1939, for an improvement in Arc tube systems.

The operation of the system described above can be best understood by referring to the curves shown in Fig. 2. These curves do not purport to show quantitativel the current and voltages involved. However, they do represent ina general qualitative manner the operation of the system. In Fig. 2 the sine wave a represents the line voltage which appears across the corn ductors 9 and id. The curve b represents the load current flowing to the primary winding it. In the systems which are contemplated, particularly resistance welding systems, the current b lags the voltage a, and in the particular instance shown, this lag is about 60 degrees. As the current passes through zero, one of the arc tubes l or 2 goes out, and normally the other tube starts immediately, delivering smooth alternating current to the load. The curve 0, which represents the voltage across the tubes l and 2, shows that when one of the arc tubes goes out, the voltage across said tubes rises very rapidly to the instantaneous value of the line voltage at that particular moment. The system is so arranged that this voltage impulse is transmitted through the firing circuit so as to ignite the previously idle tube, which thereupon immediately starts conducting current so that the voltage across the tube then drops to the relatively low value of the tube arc drop. This operation takes such a short time that the rise in voltage across the tube lasts for a very short time, and therefore these voltage impulses are represented in curve by vertical lines. Of course it is to be understood that this change does occupy some time interval which, however, it is impractical to illustrate in Fig. 2. It will be seen, therefore, that the voltage across the tubes 8 and 2 supplies voltage impulses at exactly the right moment in order to alternatively fire the tubes l and 2 so as to cause the alternating load current b to flow smoothly through said tubes. connected directly across the tubes l and 2 has this voltage wave 0 impressed upon it. This same voltage wave 0 is therefore impressed through the secondary winding 25 upon each or the primary windings 2i and 22 connected in series with their

respective rectifiers

28 and 28.

conductive connection 35,

The primary winding 26 which iswinding 2i, while voltage impulses of the opposite polarity pass through primary winding 22. Thus the impulses of the voltage wave 0 which lie above the zero axis are impressed upon the lgniting electrode 7, for example, while those voltage impulses of the wave 0 which lie below the axis are impressed on the other igniting electrode 8, for example. The polarities of the windlogs on the transformers ii and it are so chosen that the voltage impulses supplied to the igniting electrodes 1 and 8 are primarily positive with respect to the associated

cathodes

3 and 3.

When the control contacts 28 are closed, the igniting circuit is energized and the tubes l and 2 conduct current substantially as described above. If, however, one of the tubes l or 2 fails to become conductive upon an igniting impulse being supplied to its associated igniting electrode or 8, the rela 3G is operated toopen the connection between the contacts 33-33. This action may be described in connection with the curves shown in Fig. 2. It will be seen that during normal operation of the system, the voltage which is impressed upon the operatingcoil 35 of the relay 3i is represented by the complete curve 0, since both polarities of the curve 0 passed by the rectifying bridge pass through the central The only portions of the curve c which have any substantial magnitude are the vertical portions. However, these vertical portions, as previously described, are of very short duration, such that they are insufilcient to cause the coil 35 to operate the relay 36. If, however, upon the occurrence of an igniting impulse at one of the igniting electrodes, the associated tube does not become conducting, the voltage across the tubes instead of falling to the relatively low value represented by the voltage drop of the tube, continues to follow the line voltage a.

Therefore, upon the failure of a tube to become conducting, coil 35 is supplied with a considerable voltage which persists throughout the remaining portion of the voltage wave. The relay 34 is'so designed that if this voltage persists for a sufficient period of time, the coil 35 will operate the relay 34, thus opening the contacts 33-453. The relay 34 is so designed that this operation may occur at some such point as p on the curve a in Fig. 2. When the relay 3 3 is operated and the contacts 33-33 are opened both primary windings 2i an 22 are deenergized, and thereafter no impulses are supplied to the igniting transformers ii and it until the contacts 33-33 are again closed by the armature 32. It will be noted, however, that after the initial occurrence of the voltage impulse to the associated igniting electrode, as represented by the left-hand vertical portion of the curve c, voltage is continued to be supplied to the associated igniting transformer until the point pis reached,

due to the delay-in the operation of the relay 3! In many instances, although a tube may fail to ignite, upon the supply of a short igniting impulse thereto, this failure may be due to a temporary cause, and if the igniting voltage persists until said temporary cause is removed, the tube may then ignite properly. The period of delay between the initial application of the igniting voltage and the point p affords the associated tube an opportunity to ignite under conditions of this kind. In some instancesit may be desirable to provide for a greater increase in flow of current through coil 35 upon the failure of a tube assaoea to fire. For this reason the cores of transformers i7 and II are so proportioned as to become saturated if the voltages supplied to them are substantially larger than a normal igniting impulse. Thus upon the failure of one of the tubes to fire, the associated transformer II or it will saturate, lowering its impedance and permitting a greatly. increased current to flow through coil 8|. This insures a positive and reliable action of the relay 34.

When the relay It has been operated at the point p, it persists in its operated or open position for another delay period which may end, for

period in which the anode of said tube becomes positive. Thus, if the causes which prevented the tube from firing were temporary and existed throughout the previous positive half cycle, the reapplication of an igniting voltage to said tube may permit said tube to fire normally if the tube is then in a condition to do so. If, however, the tube fails to tire, relay 34 is again energized to prevent the other tube from being ignited.

It is usually desirable to provide some adjustment for the periods of delay to which the operation and release of the relay II are subjected. Such an adjustment may be afforded, for exam ple, by a tension spring 38, the tension of which may be adjusted by an adjusting screw 30. The adjustment also may be afforded by an adjustable impedance, such as a variable resistance ll placed across the coil 3!. These periods of delay may be subjected to wide variations and still keep the operation of the system within the principles of this invention as described above.

0! course it is to be understood that this invention is not limited to the Particular details as describedabove as many equivalents will suggest themselves to those skilled in the art. For example, some aspects of thisinvention may be ap plied to tubes having other types of igniting electrodes. Other types of rectifiers and time delay relays may be utilized. Various other changes and additions may be made to the system as disclosed. It is accordingly desired that the appended claims be given a broad interpretation commensurate with the scope of the invention within'the art.

What is claimed is: g

1. In combination, a load circuit, circuit means for connecting said load circuit to a source of alternating current, a pair of inversely-connected arc discharge devices interposed in said circuit means for controlling the flow of current to said load circuit, each of said are discharge devices comprising an anode, a pool type are cathode,

2., In combination, a load circuit, circuit means for connecting said load circuit to a source of alternating current, a pair of inversely-connected arc discharge devices interposed in said circuit means for controlling the flow of current to said load circuit, each of said are discharge devices comprising an anode, a pool type are cathode, and an igniting electrode adapted to initiate an are spot on said cathode, an igniting circuit for supplying each of said igniting electrodes with igniting impulses, and means responsive to the appearance of a substantial voltage across said are discharge devices upon failure of one are discharge device to start conducting current, for deenergising the igniting circuit of the other are discharge device.

3. In combination, a load circuit, circuit means ior connecting said load circuit to a source of a1- ternating current, a pair of inversely-connected arc discharge devices interposed in said circuit means for controlling the flow of current to said load circuit, each of said are discharge devices comprising an anode, a pool type are cathode, and an -igniting electrode adapted to initiate an are spot on said cathode, an igniting circuit for supplying each of said igniting electrodes with igniting impulses, and means responsive to the appearance of a substantial voltage across said are discharge devices, upon failure of one are discharge device tostart conducting current during a half cycle, for preventing the other are dischariedevice from conducting current.

4. In combination, a load circuit, circuit means for connecting said load circuit to a source of alternating current, a pair of inversely-connected arc discharge devices interposed in said circuit means for-controlling the flow of current to said load' circuit, each of said are discharge devices comprising an anode, a pool type are cathode, ana'an igniting electrode adapted to initiate an are spot on said cathode, an igniting circuit for supplying each of said igniting electrodes with igniting impulses, and means responsive to the appearance of a substantial voltage across said are discharge devices, upon failure of one are discharge device to start conducting current during a half cycle, for deenergizing-the igniting circuits of both are discharge devices for the succeeding half cycle, and for reenergizing the igniting circuit of said flrst arc discharge device during the following half cycle.

5. In combination, a load circuit, circuit means for connecting said load circuit to a source of alternating current,"a pair of inversely-connected arc discharge devices interposed in said circuit means for controlling the flow of current to said load circuit, each 'of said are discharge devices comprising an'anode, a pool type are cathode, and an. igniting electrode adapted to initiate an are spot on said cathode, an igniting circuit for supplying each of said igniting electrodes with igniting impulses," means for energizing said ignlting circuits from across said discharge devices, whereby the voltage impulses occurring across said are discharge devices constitute said igniting impulses, and means responsive to the voltage across said are discharge devices for dcenergizing the igniting circuit of one of said discharge devices when the other of said are discharge de-,

vices fails to fire. I

6. In combination, a load circuit having a power factor less than unity, circuit means for connecting said load circuit to a source of alternating current, a pair of inversely connected arc discharge devices interposed in said circuit means for controlling the flow of current to said load circuit, each of said arc discharge devices comprising an anode, a pool type are cathode, and an igniting electrode adapted to initiate an are spot on said cathode, an igniting circuit for supplying each of said igniting electrodes with ignit ing impulses, means for energizing said igniting circuits from across said discharge devices, whereby the voltage impulses occurring across said arc discharge devices constitute said igniting impulses, and means responsive to the voltage across said are discharge devices for deenergizing the igniting circuit of one of said discharge devices when the other oi said arc discharge devices ifails to fire. I

7-. In combination, a load circuit having a power factor less than unity, circuit means for connecting said load circuit to a source of alternating current, a 'pair of inversely-connected are discharge devices interposed in said circuit means for controlling the flow of current to said load circuit, each of said are discharge devices comprising an anode, a pool type arc'cathode, and an igniting electrode adaptedito initiate an are spot on said cathode, an igniting circuit for supplying each of said igniting electrodes with igniting impulses, means for energizing said igniting circuits from across said discharge devices, whereby the voltage impulses occurring across said are discharge devices constitute said igniting impulses, and means responsive to the occurrence of a voltage impulse of substantially longer duration than a normal igniting impulse for deenergizing the igniting circuit of one of said discharge devices when the other of said are discharge devices fails to fire.

8. In combination, a load circuit, circuit means for connecting said load circuit to a source of alternating current, a pair of inversely-connected arc discharge devices interposed in said circuit means for controlling the flow of current to said load circuit, each of said are discharge devices comprising an anode, a pool type are cathode, and an igniting electrode adapted to initiate an arc spot on said cathode, an igniting circuit for supplying each of said igniting electrodes with igniting impulses, means for energizing said igniting circuits from across said discharge devices, whereby the voltage impulses occurring across said are discharge devices constitute said igniting impulses, and a relay havlng operating means responsive to the voltage across said arc discharge devices and circuit-interrupting means operated by said relay for deenergizing the igniting circuit of one of said'discharge devices when the other of said arc discharge devices fails to fire.

9. .In combination, a load circuit having a power factor less than unity, circuit means for connecting said load-circuit to a source of alternating current, a pair of inversely-connected arc discharge devices interposed in 'said circuit means for controlling the fiow of current to said load circuit, each of said are discharge devices comprising an anode, a pool type are cathode, and an igniting electrode adapted to initiate an are spot on said cathode,'an igniting circuit for supplying each of said igniting electrodes with igniting impulses, means for energizing said igniting circuits from across said' discharge devices,

whereby the voltage impulses occurring across said are discharge devices constitute said igniting impulses, and a relay having operating means responsive to the occurrence of a voltage impulse of substantially longer duration than a normal igniting impulse and circuit-interrupting means operated by said relay for deenergizing the ignitmeans for connecting said load circuit to a source of alternatingcurrent, a pair of inversely-connected arc discharge devices interposed in said circuit means for controlling the flow of current curring across said arc discharge devices constitute said igniting impulses, and means responsive to the voltage across said arc discharge devices for deenergizing the igniting circuit of one of said discharge devices when the other of said are discharge devices fails to fire, said means being delayed in its deenergizing action beyond the initialapplication of a normal igniting impulse to said other are discharge device.

11. In combination, a load circuit, circuit means for connecting said load circuit to a source of alternating current, a pair of inversely-connected arc discharge devices interposed in said circuit means for controlling the fiow of current to said load circuit, each of said are discharge devices comprising an anode, a pool type are cathode, and an igniting electrode adapted to initiate an arc spot on said cathode, an igniting circuit for supplying each of said igniting electrodes with igniting impulses, means for energizing said igniting circuits from across said discharge devices, whereby the voltage impulses occurring across said arc discharge devices constitute said igniting impulses, andmeans respon-- sive to the voltage across said arc discharge devices for deenergizing the igniting circuits of both of said discharge devices when one of said arc discharge devices fails to fire, said means being adapted to reenergize the igniting circuit of the latter are discharge device during the next cycle following said failure to fire.

12. In combination, a load circuit, circuit means for connecting said load circuit to a source of alternating current, a pair of inversely-connected arc discharge devices interposed in said circuit means for controlling the fiow of current to said load circuit, each of said are discharge devices comprising an anode, a pool type are cathode, and an igniting electrode adapted to initiate an arc spot on said cathode, an lgniting circuit for supplying each of said igniting electrodes with igniting impulses, means for energizing said igniting circuits from across said discharge devices, whereby the voltage impulses occurring across said arc discharge devices constitute said igniting impulses, and means responsiv to the voltage across said are discharge devices for deenergizing the igniting circuits of .both of said discharge devices when one of said nected arc discharge devices interposed in said circuit means for controlling the flow of current to said load circuit, each of said arc discharge devices comprising an anode, a pool type are cathode, and an igniting electrode adapted to initiate an arc spot on said cathode, an igniting circuit for supplying each of said igniting electrodes with igniting impulses, means for energizing, said igniting circuits from across said discharge devices, whereby the voltage impulses occurring across said are discharge devices constitute said igniting impulses, electro-rnagnetic means included in each ofv said igniting circuits and adapted to become saturated upon the occurrence of a voltage impulse of substantially longer duration than a normal igniting impulse,

I and means responsive to the increased current of alternating current, a pair of inversely-connected gas-filled discharge devices interposed in said circuit means for controlling the flow of current to said load circuit, each of said gasfilled discharge devices comprising an anode, a cathode, and control means for causing a discharge to be started between said cathode and anode, a control circuit for supplying each of said control means with discharge starting impulses, and means responsive to the appearance of a substantial voltage across said discharge devices upon failure of one discharge device to start conducting current for preventing the other are discharge device from conducting current.

15. In combination, a load circuit, circuit means for connecting said load circuit to a source of alternating current, a pair of inversely-connected gas-filled discharge devices interposed in said circuit means for controlling the flow of current to said load circuit, each of said gas-filled discharge devices comprising an anode, a oathode, and control means for causing a discharge to be star-ted between said cathode and anode, a control circuit for supplying each of said control means with discharge starting impulses, and means responsive to the appearance of a substantial voltage across said discharge devices upon failure of one discharge device to start conducting current for deenergizing the control circuit of the other are discharge device.

' DAVID D. COFFIN.