US2089896A

US2089896A - Rectifier control system

Info

Publication number: US2089896A
Application number: US668498A
Authority: US
Inventors: Journeaux Didier
Original assignee: Allis Chalmers Corp
Current assignee: Allis Chalmers Corp
Priority date: 1933-04-29
Filing date: 1933-04-29
Publication date: 1937-08-10
Anticipated expiration: 1954-08-10

Description

Aug. 10, 1937. D. JOURNEAUX 2,089,896

RECTIFIER CONTROL SYSTEM Original Filed April 29, 1933 3 Sheets sheet 1 ug. 1937. D. JOURNEAUX 2,089,896

RECTIFIER 'CONTROL SYSTEM Original Filed April 29, 1933 3 Sheec Sheet 2 Aug. 10, 1937.

D. JOURNEAUX RECTIFIER CONTROL SYSTEM Original Filed April 29, 1933 3 Sheecs-Sheet 3 %IIIIII ml Patented Aug, 10, 1937 PATENT OFFICE BECTHIER CONIROL SYSTEM Didier Jumeaux, Wauwatosa, Wls., asslgnor to Allis-Chalmers Manufacturing Company, Milwaukee, Wia., a corporation cf Delaware Application April 29,

1933, Serial No. 668,498

Eenewed November 14, 1936 49 Clalms.

This invention relates to imprements in control systems, and more particularly to a system for limiting the current within an electron discharge device to a value which the device is in condition to carry at the instant considered, with out danger of damage thereto or of iaulty operatien thereof.

It is.known that, in an electron discharge device 0! the vapor type in which the vapor is 1 supplied from the cathode material, the arc drop within the device depends upon the conditions of pressure and temperature of the vapor carrying the arc. It is desirable to always maintain the arc drop at a low value because a high arc drop '15 decreases the efliciency of the device, may cause deterloration or destruction et the device by calized liberation of excessive heat, mavcause failu're of the control'electrodes to function and --may also result in oscillations or other disturbances in the circuits associated with the device. The arc drop may reach an excessive value when the walls of the device are too cold so that the vapor produced at the cathode condenses on the walls toc rapidly and does not leave a sufiicieht 5 amount of vapor available for ionization in the arc path. Tire result of such condensation is that the electronic space charge is not sufliiently neutralized by the amount of ionizable vapor present and the arc drop reaches a value inter- 3o mediate that of a normally operating vapor device and that of a device ofathe vacuum type. Such condition may arise -When eooling means assoclated with the device are adJusted for maintaining the temperature-thereoi at tob low a value or else when the device, alter carrying an amount ct current for which its temperature ls adequate,

is suddenly required to carry a larger amount of current for which its temperature is too low. It is then necessary either to disconnect the device from the associated circuits, or to provide a larger amount of vapor wlthin the device, or to reduce the amount of current fiowing therethrough to prevent the continued operation of the device under conditions producing a high arc drop. Such results can be obtained by means of a system responsive to the magnitude ot the arc drop, which prterably utilizes voltage responsive means 'connected between one anode and the cathode of the device over an auxiliary electron discharge device. The connections are then prat- -erabl'such as to; imp'ress the voltage between qde and cathode of the device on the voltage ;,iep0nsive means only while the anode is carryv in: crrent. Under the most favorable operating fl 5 conditions, as in wellknown. the value of the arc drop normally varieswith the amount of current carried by the device and it is therefore advantageous to provide an automatic adjustment of the voltage responsive circuits in response to the amount of current fiowing through the device.

It is thereiore among the objects of the present invention to provide a control system for electron discharge devices which system is responsive to the variations of the magnitude of the arc drop within the device.

Another object of the present invention is to provide a control system for electron discharge devices which system is responsive to the peak value of the arc drop within the device.

Another object of the present invention is to provide a control system for electron discharge devices which system is responsive to the value of the voltage between one anode and the cathode of the device only during the periods when the anode is carrying eurrent.

Another object of the present invention is to provide a control system for electron discharge devices which system employs one or more auxiliary electron discharge devices. v

Another object of the present invention is to provide a control system for electron discharge devices in which the system is automatica1ly variably adjusted in response to the magnitude of the current flowing through the device.

Another object of the present invention is to provide a control system for electron discharge devices for interrupting the fiow of current through the device when the arc drop Within such device reaches a value greater'than the normal operating value thereof.

Another object of the present invention is to provide a control system for electron discharge devices whereby the amount of vapor produced within the device may be increased when the arc drop within the device reaches a value greater than the normal operating value thereof,

Another object of the present invention is to provide a control system for electron dscharge devices operable to regulate the floW of current through the device in response to the variations et the arc drop within such device.

Another object 01. the present invention is to provide a control system for electron discharge devices operaile to variably energize the control electrodes of the device in response to the variations of the arc drop within such device.

-Objects and advantages other than those above set fortin will be apparent irom the.following description when read in connection with the accompanying drawings, in which:

Fig. 1 diagrammaticaily iliustrates one embodiment of the presentinventian operable to disconnect an electron discharge device of the vapor type, which is operable as an alternating current rectifier, from the supply line thereof when the average arc drop within such device exceeds, by a predetermined amount, the value of the arc drop of an auxiliary device having the arc drop therein adjusted in response to the value of the current flowing through the main device;

Fig. 2 diagrammatcally illustrates, the portions differing from the embodiment 01. Fig. 1. of a modified embodiment of the present invention difiering from the embodiment illustrated in Fig. 1 in that the amount of exciting current of the device is regulated in response to the variations of the value of the arc drop and the device is not disconnected from the supply line upon change in the arc drop;

Fig. 3 diagrammaticaily illustrates the modified portions of another modified embodiment of the present invention diflerng from the embodiment illustrated in Fig. 2 in providing means for supplying vapor to the device in response to the 2 variation of the arc drop within such device;

Fig. 4 diagrammatically illustrates another embodiment of the present invention whereby the current within the device is regulated in.re sponse to the variations of the peak value 01 30 the arc drop within the device;

Fig. 5 diagrammatically illustrates another embodiment of the present invention whereby the control electrodes of the device are variably energized, in response to the variation of the average arc drop, to control the flow of current within such device;

Fig. 6 diagrammatically illustrates the modified portions 01 a modified embodiment 01 the present invention diflerlng from the embodiment illustrated in Fig. 5 in the method of connecting the voltage responsive circuits Fig. 7 is a diagram of the voltage relations between one anode and the cathode of the device illustrated in Figs. 1 to 4;

Fig. 8 is a diagram of the voltage between one anode and the cathode and of the voltage of a current transformer receiving the current of the same anode of the device illustrated in Figs. 5 and 6;

Fig. 9 is a characteristic curve oi some of the auxiliary discharge devices utilized in the ditferent embodiments illustrated; and Fig. 10 diagrammatically illustrates another embodiment of the present invention in which the control electrodes of the device are variably energized in response to the variations et the peak value of the arc drop within such device.

Referring more particularly to the drawings by characters of reference, reference numeral il designates an alternating current line, herein shown as a three phase line only for the reason that such type of line is most frequently utilized in practice. Line il is utilized as a supply line for an electron discharge device i6 connected therewith by means of a transformer having a primary winding 12 and a secondary winding fl3. Winding i3 preerably' comprises a plurality of star connected portions severally connected With the anodes E4 015 device l6. Ihe cathode il of of a direct current line having the second conductor l9 thereof .connected with a neutral point 75 66 may be interrupted by means of 8. circuit device i6 is connected with one conductcr i8 breaker 2l heren shoWn as being inserted in the connection between winding [2 and line Il. It will be understood that such circuit breaker could also be inserted in the connections between winding l3 and anodes [4 or in conductors l8 and l9, opening of such circuit breaker resulting, in each case, in interruption of the flow of current within device l6. Circuit breaker 2l tends to open under the action of a spring 22 and is normally retained in the closed position by a latch 23 which may be released by a solenoid or trip coil 24.

For the purpose of obtaining a circuit responsive to the variations of the voltage between one anode M and cathode il, one"of such anodes is connected through a battery 25 with the anode 26 of an electron discharge device 21 having a cathode 28. .Device 21 is preferablv of the gas or vapor type and the operating vapdr therein may be supplied by a drop of mercury 29. Cathode 28 may be of the incandescent type heated by the current of a battery 3l, such current being adjusted by means of a rheostat 32. Cathode 28 is connected With conductor l8 over a rheostat 33, a meter 34 and the coil 36 of a time delay relay 31. Relay 31 is operable to close contacts 38 to connect a battery 39 With trip coil 24; current flowing in rheostat 33 and coil 38 may be fmeasured by the indicating cr recording-instrument 34. As is well known, the arc drop within a device such as device 21 is smaller than the arc drop within device l6, and also varies to a large extent in dependence upon the temperature. The temperature of device 21 is preferably maintained constant by means of a heater 4l receiving 'current from a suitable source such as battery 39, such current being controlled by a thermostat such as a bimetallic strip 42. A. rough adjustmnt of the current in heater 4l may be obtained by a rheostat 43. To 1egulate the flow of current through device 21 in response to the amount of current flowing through device i6, the operation of thermostat 42 may be controlled by a second thermostat 44 maintainedat a variable temperature by heater 46 energized in response to the value of current flowing through device I6 by means of a shunt 41 in circuit in conductor l8.

In operation, assuming the system to be connected as'shown inFig. 1 and line Il to be encrgized, each of the anodes l4 cf device l6 receives an alternating voltage from the associated portion 0i winding l3. Such voltage is represented in Fig. 7 by a curve 48 drawn with respect to line 49 representing the voltage of cathode i1 as the reference line. As will be seen from Fig. 7, the voltage represented by curve 48 is positive and has an approximately constant value during the active period et operation of anode M and ls variably negative during the idling period of such anode. In Fig. 7, the distance between line 49 and line 5l represents the arc drop within device 21 which drop may be considered as substantiaily constant even when such device receives variable currents, provided such currents are limited in value within a predetermined range. When the voltage represented by curve 48 is greater than the voltage represented by line 51, a pulsating current will :flow from anode i4 over bttery 25 and anode 26 to cathode.28 of device 21, over rheostt 33, meter 34, and coil 36 to conductor i8, in parallel with the arc between anode M and cathode il. The magnitude oi? such current is proportional to the cross hatched areas 52 in Fig. 7 and is dependent upon the average value of the arc drop between anode M and cathode i1 represented by the positive ordinates o! curve 48. In the above consideration, the voltage et the battery 25 was not taken into account. By adJusting 5 such voltage at a value substantiaily equal to the voltage drop within device 21 and opposed thereto, the flow of current through device 21 is substantially unaflected by such two voltages and is then substantially proportional to the entire areas bound by the positive portions of curve 48 and also, thereiore, to the average voltage drop withindevice l5. Assuming that for any reason, the arc drop in device l8 increases over the value previoualy considered. such increased arc drop causing application of a higher potential to anode 28, the current flowing from anode l4 over device 21 will increase correspondingiy and, upon reach- Inc a predetermined value, will cause 0011 38 to attract armature of relay 31 to close contacts 88 thereof. Such closure is eflected, however, only if such flow of current is cmtinued over a predetermined period of time necessary for the operation of the time delay mechanism of relay 31. Such time delay is dasirable to prevent closure 01 contacts 38 upon occurrence of a transient increase of the arc drop in device l5 which would' notnecessitate interruption of the operation of device I8.

If the increase of the arc drop considered above is commensurate with an increase in the value of the current carried by device l6, such increase in the current will cause a.larger current to flow through heater 48, thereby causing thermostat 44 to move out et engagement with the contact 5 cf thermostat 42. Thermostat 42 is thereby adjusted to maintain device 21 at a temperature lower than previously obtained. The arc drop in device 21 then increases as the temperature oi such device becomes lower, thereby maintain- 40 ing the flow of current therethrough at a low value and preventing the operation of relay 31. By means of the system illustrated, the flow of current through the device is thus interrupted only when the arc drop within such device reaches 45 a value which is in excess of a value commensurate with the value of the current flowing through the device. As heater 45 and thermostat 44 are however necessarfly endowed with thermal inertia, the heating of thermostat 44 by heater 46 cannot follow rapld variations et the current flowing through device 18 and shunt 41; If such current increases from a relatively low value to a relatively high value, thus causlng the arc drop in device l8 to increase. at first the arc drop in 55 device 21 remains adJusted to the initial value thereof.. 'If the rate of change of the current in device l6 is relatively low, the response of the adjustment of the arc drop in device 21 by the action of heater 4|, although lagging behind the 0 change of current in device [8, is never materiaily diflerent from the steady state adjustment thereoi'. If however the rate et change of the current in device t8 15 relatively high, as the result for example of a short circuit in line i8, l8, the operation cf device 21 is completely readiusted in response to the increased value of such current after a time delay such that, in the meanwhile, relay 81 may operate in response to the increase in 70 the arc drop in device l8. Devie I8 la thus protected against any damage which might be caused therein by the flow of short circuit current therethrough. In a general manner, the opention oi device 21 and, therefore.the operation of 7 relay 81 is variably adjusted in dependence upon the rate of change of the flow of current through device l5.

In the embodiment partially illustrated in Fig. 2, it is assumed that the arc within device [6 is maintained by means of two excitation anodes 53 supplied over fesistances 54 from an excitation transformer 58 energized from line l I. The amount of excitation current flowing through device I5 is regulated by adjusting the amount of resistance in the circuit of such excitation anodes, such resistance comprising a fixed resistance 51 and resistance 58 which may be short circuited over contacts 38 of relay,81. In the present embodiment, when the arc drop in device l8 reaches a value greater than the normal value commensurate with the value of the current flowing through such device, relay 31 closes contacts 38 and thereby short circuits resistance 58. amount of excitation current flowing between excitation anodes 53 and cathode l1 is thereby suddenly increased and results in the production 01 a larger amount of operating vapor from cathode l1. Such increased production of vapor results in an increase of the vapor pressure within device l5 which tends to reduce the arc drop within such device to the normal value thereof.

In the embodiment partialiy illustrated in Fig. 3, device l6 is associated with a heating chamber 59 receiving operating materiai from cathode l1. Chamber 59 is in communication with a vapor distributor 82 conducting the operatlng vapor produced within such chamber to the space adjacent anodes l4, where such vapor escapes through openings 63 in pipe 62. Chamber 59 is preierably heated by a heating resistance 6l energized from battery 39 over contacts 38. When the arc drop within device I5 reaches a value which is excessive according to the standard defined above, relay 31 causes resistance to receive current from battery 39 over contacts 38 thereby causing the production of vapor which is conducted in the space adjacent anodes I4. Such vapor is utilized for the complete'ionization of the arc path, and the arc drop within device 80 is thereby restored to the normal value thereof.

In the embodiment illustrated in Fig. 4, the flow of current through device I6 is controlled by a

plurality cf reactors

18, 19 and 8! which may be given variable values of inductance by saturation of the cores thereof by means of a plurality of direct

current saturating windings

14, 16 and 11. In the present embodiment, the current flowing through device 21 is utilized for charging a condenser 64 connected between cathode 28 and conductor l8. Rheostat 33 is then adjusted to a high Value so that the current fiowing over such rheostat between successive cycles of the voltage of line il does not appreclably decrease the charge of condenser 64. Cathode 28 is connected with the cathode 69 of an electron discharge device of the high vacuum type having the grid 66 thereof connected with conductor l8 over a blas battery 12 and a protective resistance 13. Cathode 69 is preferably of a. type similar to that of cathode 28 and may be energized from battery 3l over a rheostat 1l. The anode 58 of device 61 is connected with cathode 69 over 9. circuit including a plate battery 82, a rheostat 83 and coils 14, 16 and 11. Such circuit may also include the resistance element 86 of a carbon pile regulator 84 having an operating solenoid 81 energized from shunt 41 over a rheostat 89. The action of solenoid 81 is opposed by a spring 88 as is weil known in the art. 1! the voltage between anode I4 and cathode l1 during the idling period of such anode. repre- The sented by the negative portion of curve 48 Fig. 7, is greater than may be safely applied between anode 26 and cathode 28, a suitable device such as a glow tube 91 may be connected between 5 anode 26 and conductor 18. Such device should be so selected as not to conduct current when recelving the arc drop between anode 14 and cathode 11, but to conduct current when receiving the much larger negative voltage of anode 14 during the idling period. The current then flowing through device 91 is preferably limited by a resistance 92. Such resistance does not appreclably affect the charge of Condenser 64 provided that the ohmic drop caused within such resistance by the current flowing over rheostat 33 be maintained at a negligible value.

In operation, during the idling. period of anode 14, device 91 carries current and maintains anode 26 at a voltage which is negative with respect to 30 the voltage of cathode 28 by tfie value of the discharge drop within device 91. Device 21 therefore does not carry current during such period. During the active period of anode 14, neglecting the current flowing over rhostat' 33, it Will be seen that condenser 64 is gradually charged during the successive periods of current flow in anode 14, at a rate depending upon the value of resistance 92. As shown in Fig. 7 the arc drop shown by curve 48 usually presents a maximum or peak 30 value during 9. portion of the current carrying period of the anode. When the arc drop reaches such valuecondenser 64 is charged correspondingly, and as such .condenser cannot discharge over device 21, it will maintain its charge from one cycle to the next. The voltage between cathode 28 and conductor 18 is then represented by the difierence of the ordinatescf line 92 passing .through the peaks of curve 48 and of line 51 representing the arc drop within device 21. As 40 set forth above, the current flowing through resistance 33 is too small to cause condenser 64 to discharge appreciably between peaks of curve 48 but the flow of such current through device 21 tends to maintain the arc drop therein et a 45 stable value. In addition, resistance 33 provides a. path for the partial discharge of condenser 64 when the arc drop within device 16 changes from one value to another and lower value.

In Fig. 9, curve 99 represents the value of the 50 plate current of device 61 plotted against the value of the grid voltage of such device for a predetermined value of the resistance in the plate circuit. In the embodiment illustrated in Fig. 4 it may be assumed that the voltage of grid 66 is negative 55 relative to the voltage of the cathode and is represented in magnitude by the distance 0A consisting oi the negative voltage 0B et condenser 64 plus the voltage BA of battery12. The current fiowing through coils '14, 16 and 11 is 60 then represented by ordinate AC of curve 911.

Assuming that the voltage drop in device 16 increases above the normal value thereof, condenser 64 becomes charged at a higher voltage represented in Fig. 9 by distance 0D and the voltage 85 of grid 66 is then represented by distance 0E. The plate current oi device 61 is thereby reduced 'to the value EF so that the cores of reactors E8, 119 and 81 become substantially desaturated. Such 4 reactors then introduce, in the circuit of device 16, &- voltage drop whlch causes the current flowi ng through such device to be reduced to such an xtent that the voltage drop again decreases to tle 'normal value thereof. If the increase of the voltage drop is dueonly to an increase in the 75 current of device l6, such in crease ci current will .ags of line 11.

"cause solenoid 81 to receive an lncreased cunent from shunt 41 thereby increasing the pressure on carbon pile 86. The resistance in the circuit of

coils

14, 16 and 11 is thereby decreased so that a current of sufliientmle 'to saturate the cores.

nected portions of the secondary winding 96 of a control transformer having a primary winding 94 energized from line 11. .The control transformer 94, 96 may be constructed as a phase shifter to permit regulation of the flow of currentwitlfin device 16. As is well known, such device may then operate as a rectifier to transmit power from line 11 to

line

18, 19, or as .an inverter to transmit power in the reverse direction. The energization of control electrodes 93 ls automatically adjusted by means of a regu-.

lator 98 operable to vary the resistance in the connections of winding 94 with line 11.

The regulator is herein represented as being of the rocking sector type and being actuated by.

an armature 99 mounted on a spindle 101. Ar-

'mature 99, which is movablebetween' the pole pieces of an electromagnet core 102, is provided with a winding 163 which is connected in series with a winding 1114 of the electromagnet to impart a torque to such armature upon energization of the windings. The core also has a second winding 196 energized from shunt 41. The torque imparted to spindle 101 is opposed by a spring 101 which prevents spindle 1111 from rotating continuously and the tension of the spring is adjusted by a screw 168. Spindle 101 canies a hub 1119 serving as fulcrum for a plurality of conductive sectors 111. Ea,ch sector is insulated from hub 1119 and rocks on an arcuate contact path consisting of a plurality cf conductive segments separated by insulation; each segment is connected witha portion of a tapped resistance 112. Tosimplify the drawing each sector is however represented as being directly in contact with the associated resistance. Each resistance 112 is connected between two conductors of line 11 so that each sector 111 serves as a movable tap to impress, on winding 94, voltages of variable phase with respect to the volt- Such connections permit shifting of the phase of energization of control electrodes 93 to thereby regulate the amount of current carried by the associated anodes 14 as is well known in the art.

Assuming that device 16 is operating as a rectifier, curve 113 of Fig. 8 represents the voltage between anode 14 and cathode 11 when the time of operation of anode 14 is delayed by the action of control electrode 93. Curve 113 includes portions GH over which the anode does not carry current although its voltage is positive with respect to that of cathode 11 and portions KL, over which the anode carries current, which are similar to the positive portions cf curve 48 in Fig. 7. The remaining portion LG is similar to the negative portion of curve 48. It will be seen that the system must be made respbnsive to the voltage between anode 14 and cathode 11 over portions KL of curve 113 and not over portions GH, over which such voltage may be of considerably greater magnitude.

To obtain the :oove result grid 88'of device 61 must not be on 1stantly operatively connected with the anode 16 considered, as suchgrid would then receive voltages corresponding to portion 5 GH of curve 113. Such result is avoided by connecting grid 61S, over resistance 13 and bias battery 12, to resistance 92 already utilized in the embodiment illustrated in Fig. 4. In the present embodiment, for the reason that the positive voltage between anode and cathode of device 18 may become very great, it is no longer possible to use a device 91 which would carry current during the positive period of anode 14 corresponding to curveportion GH, and which would 15 thereafter continue to carry current over the period corresponding to curve portion KL. Device 91 is preferably replaced by a device 114 of the same type as device 21, which may carry current only during the negative period of anode 14. During the period corresponding to portion GH, grid 66 receives through battery 12, 8. voltage which is substantialiy the voltage of conductor 18 by the connection of resistance 92 With the anode 124 of a device 121 similar to device 61. The cathode 126 of such device is connected with conductor 18 and the grid 119 thereof is connected with cathode 126 over a resistance 123, a bias battery 122, and 3. portion of a rheostat 11T. Rheostat 111 is energized from a current transformer 116 inserted between winding 13 and anode 14. The plate circuit of device 81 is closed over battery 82, rheostat 83 and colis 183 and 184, so that the position of regulator 98 is determined by the average magnitude of the plate current in device 81.

As is well known the voltage impressed on rheostat 111 from current transformer 119 may be represented by a curve H8 referred to axis 113 in Fig. 8. The voltage between grid 119 and cathode 126 may then be represented, at a dltIer-.

ent scale, by the same curve-118 referred to another axis 128. During the period corresponding to curve portion GH, grid 119 thus has a slightly negative voltage with respect to cathode 128, represented by point A in Fig. 9, and permits flow of current from anode 124 to cathode 128. The voltage between anode 14 and cathode 11 then appears at the terminals of resistance 92 and the only potential applied on grid 68 is that of battery '12, provided that the impedan'ce of device 121 be small as compared with resistance 92. Such voltage may be represented by distance 0M in Fig. 9, corresponding to the lower knee of curve 911. At the time corresponding to point H, K in Fig. 8.-thc voltage of current transformer 118 reverses so that the voltage of grid 119 reached a value represented by point B sufiiciently negative to interrupt the flow of current through device 121. Grid 86 is then energized f 1om anode 14 over resistance 92, battery 12 and resistance '13. The average voltage of grid 86 during interval KL is then represented by distance 0E in Fig. 9 and the current fiowing through windings 1113 and 104 is represented by ordinate EF. If the arc drop within device 18 increases, the average voltage of grid 66 becomesless negative and reaches a value represented by 0A for which the current in windings 193 and 184 is represented by ordinate AC. Regulator 98 therefore rotates in such 70 3. direction as to retard the time of positive energization of control electrodes 93, thereby causing the current within device 16't0 decrease to an extent sufllcient to reduce the average arc drop to the normal value thereof. If the increase of arc drop was caused by an increase of current,

winding 1118 receives an increased current from shunt 41 thereby opposing the e1ect 015 the current increase in windings 1113 and 184. Armature 99 will therefore tend to remain in the position which it occupied previously and the fiow of 5 current will not be afiectedhy the regulator. By suitable adjustment of sprlng 101 bymeans of screw 188, the regulator may also be so adjusted as to move only when windings 1113 and 1114 receive a current corresponding to an excessive arc 10 drop within device 18. Such regulator will then be without e1ect on the fiow of current as long as the average arc drop within device 18 remains normal.

In the embodiment illustrated in Fig. 6, device 15 121 is omitted and device 61 is replaced by a device 129 of the gas or vapor type having the anode 132 thereof connected with anode 14 over battery 25 and resistance 135. The cathode 133 of the device is then connected with conductor 18 over 20 windings 183 and 184. The voltage applied to the device during the idling or negative period of anode 14 may again be applied to resistance 135 by short circuiting device 129 over device 114. During the period corresponding to curve portion 25 GII in Fig. 8, the grid 131 of device 129 is maintained negative with respect to cathode 133, because grid 131 and battery 122 are herein connected wlth rheostat 1 11 in a manner opposite to that illustrated in Fig. 5 to obtain a grid voltage 30 represented by curve in Fig. 8. At a time corresponding to point H, K in Fig. 8, grid 131 then becomes positive with respect to cathode 133 and permits the flow through device 129 o! a current by the same process as the flow of cur- 35 rent through device 21 in the embodiment illustrated in Fig. 1. Such current is again in proportion to the average value of the arc drop within device 18. At the end of each active period of anode 14, the voltage between anode l32and 40 cathode 133 reverses so that device 129 is without current and grid 131 is again capable of retardlng the flow of current through device 129 untll anode 14 again carries current. The control of regulator 98 ls thus obtained in a manner similar to 45 that described with respect to Fig. 5.

In the embodlment illustrated in Fig. 10, winding 94 is directly connected wlth line 11 and the adjustment of the cOntrol electrodes is obtained by means of a variable positive direct current bias 50 voltage. In the present embodlment, anode 14 is no longer connected with grid 68 over battery 12 and resistance 13 but is connected over a battery 139 and a resistance 141 with the grid 138 01 a diScharge device 134 similar to device 81. 55 The cathode 142 of device 1341s connected with conductor 18 over condenser 84, this connection being similar to that 01 device 21 et th embodlment illustrated in Fig. 4. The anode 139 of device 134 is energized from battery 82 over a 60 rheostat 131. The heating circuit of cathode 89 of device 61 includes a regulator 143 similar to v regulator 84 but difieringfrom the latter in that regulator 143 is provided with a solenoid 144 tending to release the pressure applied to the 05 carbon pile 88 by a spring 148.

The operation of

devices

114 and 121 remain substantially as described with respect to the embodiment illustrated in Fig. 5. During the active period of anode 14, grid 138 receives the voltage 70 of battery 139, the arc drop in device 18 and the Voltage condenser 84. When the system is connected as shown, andanode 14 begins to.carry current durlng a cycle of its operation, condenser 64 13 net charged, and and 133 is more positive 75 than the value M of Fig. 9 with respect to cathode 52 so that a comparatively large current flows through device l34 from battery 32 over rheostat l31. The flow of such current gradually charges condenser 64 in such a manner that the condenser plate connected with cathode i42 becomes positive and the plate of such condenser connected With conductor l8 becomes negative. The voltage of condenser 64, being also inserted in the circuit between cathode I42 and grid 538, causes grid l38-to become increasingly negative by the amount of the voltage of condenser G4. Due to such variation of the voltage of grid i38, the current through device i34 gradually decreases and reatzhes a very small value when the device l34 operates on the lower knee of its characteristic at point M in Fig. 9. Such point correSponds to a condenser voltage CE, a bias volt age BP and an arc drop PM. Beyond the point M, device i3 i is not entirely non-conductive and a small current would continue to flow, thereby slowiy changing the voltage of condenser 64. The voltage of the condenser is preierably stabili2ed by permitting the small current represented by ordinate MN in Fig. 9 to lak over resistance 33, thereby maintaining point M as operating point of device i 34. The voltage of condenser M, represented by distance 0B, impressed on grid 66 of device 61 in a manner opposite to that previously described with respect to the embodiment illustrated in Fig. 4. For the particular value PM of the arc drop in device l6, the condenser 64 receives voltage 03 which brings grid 66 to voltage 0E, thereby causing the flow of a predetermined amount '01 current EF through device 67 from battery 82 over rheostat 83. Battery 82 also supplies, over rheostat 83, another=,current which fiows over a resistance Ml. thereby bflngs the neutral point of winding 96 to positive potential with respect 'to the potential of cathode Il. The phase relation between windings 13 and 96 'is so chosen that control electrode 93 becomes positive with respect to cathode il at the desired moment to pemiitfloW of current through anode M. 45 If the arc drop in device l6 increases, the voltage of condenser 64 increases thereby bringing the grid 66 of device 67 to the value 0A less negative with respect to cathode 69. The impedance of device 61 is thus decreased and a .arger cur- 5o rent fiows through such device. The voltage drop in rheostat 83 caused by the flow of such current then increases which results in a decrease of the flow of current in rheostat M! and therefore in a decrease of the voltage drop in such resistance. 55 The positive bias impressed on control electrode 93, which is equal to such voltage drop, is thus decreased and the moment 01 the voltage cycle at which control electrode 93 becomes positive is thereby retarded. As is well known such re- 60 tardation results in a decrease of the current in device l6. If, however, the increase of the arc drop results from an increase in the current carried by device i6, solenoid I receives an increased current from shunt 41. The action of 5 the solenoid causes a lasser pressure to be applied to carbon pile 86 and the resistance of such carbon pile increases. The heating current of cathode 69 is thereby decreased, such action tending to increase the impedance of device 61 7 and thus neutralizing the eiect of the change of Voltage of grid 66. Under such conditions the bias voltage applied to control electrode 33 will not change and the flow of current in device i6 will not be altered. 7 Although but a few embodiments of the preseut invention have been illustrated and described, it will be apparent to those skflled in the art that various changes and modifications may be made therein without departing from the sp it of the invention or from the scope of the appended claims.

It is claimed and desired to secure by Letters Patent:

1. The combination with an electric current supply circuit, an electric current. load circuit, and an electron discharge device comprising an anode and a cathode interconnecting said circuits and constituting spaced electrodes for the flow of current therebetween, of means operable responSive to variations in the magnitude of the voltage drop only between said electrodes for controlling the operation of said device.

2. The combination with an electric current supply circuit, an eleotric current load circuit. and an electron discharge device comprising an anode and a cathode interconnecting said circuits and c6nstitting spaced electrodes for the flow of current therebetween, o! meansoperable responsive to variations in the magnitude of the voltage drop'of unidirection only between,said electrodes for controlling the operation of said device.

3. The combination with an electric current supply, circuit, a load circuit, an electron discharge device comprising an anode and a cathode interconnecting said circuits and constituting spaced electrodes for the flow of current therebetWeen, and means operable to control the said flow of current between said electrodes, of means operable responsive to variations in the magnitude of the potential diflerence of unidirection only between said electrodes for controlling the operation of said device.

4. The combination with an electric current supply circuit, a load circuit. an electron discharge device comprising an anode and a cathode inteonnecting said circuits and coristituting spaced electrodes for the flow of current thereb etween, and means for controlling the flow of current between said electrodes, of means operabie responsive to variations in the average value of the voltage drop only between said electrodes for controlling the operation of the first said means.

5. The combination with an electric current supply circuit, a load circuit, and an electron discharge device comprising an anode and a cathode interconnecting said circuits and constituting spaced electrodes for the flow of current therebetween, of means Operable responsive to variations in the potential diierence of unidirection only between said electrodes for controlling the operatian of said device.

6. The combination with an electric current supply circuit, an electric current load circuit, and an electron discharge device comprising an anode and a cathode interconnecting said circuits and constituting spaced electrodes for the flow of ourrent therebetween, of means connected with said electrodes and operable responsive to the voltage drop therebetween for aiecting the operation of said device, an electron discb.rge device having spaced electrodes includedin said connections of said means operable to limit the response of the latter to periods during which current flows beable responsive to the voltage drop therebetween for afiecting the operation of the first said means, and an electron discharge device included in the connection of the second said means operable to 15 1imit the response thereot to periods during which current fiows between said electrodes.

8. The combination with an electric current supply circuit, a load circuit, and an electron discharge device of the vapor arcing type comprising 20 an anode and a. cathode interonnecting said circuits and constituting spaced electrodes for the flow of current therebetween, of thermal means for producing operating vapor within said device, means connected. with said electrodes and 25 operable responsive to the voltage drop therebetween for afiecting the operation of the first said means. an electron discharge device ci. the vapor type included in the connection of the second said means operable to limit the response 30 thereof to periods during which current flows between said electrodes, means for producing operating vapor within the second said device, thermally actuated means for aifecting the operation of the third said means, and means connected with one of said circuits and operable responsive to and in dependence upon the magnitude of the current fiowing therein for causing actuation of the fourth said means.

9. The combination with a polyphase alternat- -40 ing urrent supply circuit, an electric current load circuit, and an electron discharge device comprising a Diurality oi anodes and a cathode interconnecting said circuits and constituting spaced electrodes for the flow of current through 45 said device from said suppl circuit to said load circuit, of means for regulating the said flow of current comprising a plurality cf inductors having windings severally included in the connections of the conductors of said supply circuit with said 50 device, meansfor variably exciting said inductors to thereby vary the inductance thereoi, means for energizing the second said means, and means comprising an electron discharge device having connections with said cathode and with one cf 55 saida;iodes operable responsive to and in dependence 'on the voltage drop therebetween for controlling the operation of the third said means, Whereby the. inductances of sad inductors are varied and the flow of current through the flrst 60 said device thereby regulated.

10. The combination with a polyphase alternating current supply circuit, an electric current load circuit, and an electron discharge device comprising a plurality of anodes and a cathode 65 interconnecting said circuits and constituting spaced electrodes for the flow of currentthrough said device from said suppiy circuit to said load circuit, of means for regulating the said flow of current comprising a plurality o! inductors 70 having windings 'severally included in the connections of the conductors of said supply circuit with said device-means including a source of current and an auxiliary winding for each of said inductors for exciting the latter. means com- 75 prising an electron discharge device included in the connections of said source with said auxiliary windings operable to control the flow of current through the latter, means for controlling the operation of the second said device, and means comprising an electron discharge device having con- 5 nections with said cathode and with one of said anodes operable responsive to and in dependence on the voltage drop therebetween for controlling the fourth said means, whereby the flow of current through the said auxiliary windings is varied and the flow of current through the first said device thereby regulated.

11. The combination with a polyphase alternating current supply circuit, an electric current load circuit, and an electron discharge device comprising a plurality of anodes and a cathode interconnecting said circuits and forming spaced electrodes for the flow of current therebetween,

. of means for regulating the said flow of current comprising a plurality of inductors having windings severally included in the conn ctions 01 the conductors of said supply circuit wit said device, means for variably exciting said inductors, means for energizing the second said means, means comprising an electron discharge device having connections with said cathode and with one of said anodes operable responsive to and in dependence on the voltage drop therebetween for controlling the operation of the third said means to thereby control the operation of the second said means, and means having connection with said load circuit and with the. third said means operable to control the latter in dependence upon the magnitude of the current flow in said load circuit whereby the flow of current through the second said device is regulated in dependence upon the voltage drop between the cathode and an anode of the first device and in dependence of the magnitude of the current supplied therefrom to said load circuit. 40

12. The combination with an alternating current supply circuit, an electric current load circuit, au electron dlscharge device comprising a cathode, a plurality of anodes and a plurality of control electrodes severally associated with said anodes, means connecting said device with said circuits comprising a transformer winding operable to impress potentials on said anodes during such recurring moments and of such sign and magnitude as to cause the flow of current sequentiaily through said anodes from said supply circuit to said load circuit, means connected with said supply circuit and with said control electrodes operable to impress alternating current potentials on the latter of such phase and during such recurring moments relative to the potentials impresSed on the associated said anodes as to control the moments of initiation of recurring flow of current through the latter, and means for varying the phase angle of said potentials impressed on said control electrodes,

of means connected with one of said anodes and said cathode operable responsive to the voltage drop therebetween during periods oi flow o! current therebetween for controlling the operation of the third said means, and means having connection with one of said circuits and operable in dependence on the current fiowing therein for controlling the operation of the third-said means.

13. In a control system for electron discharge devices, a supply line, an electron discharge device connected with said lime, an output line connected with said device, means responsive to the peak value of the voltage drop in said device, means for controlling the flow of current through said device, and means controlled by the first said means to control the second said means.

14. In a control system for electron dischalre '10 through said device, and means controlled by the first said means to caus operation of the second said means when the voltage drop Within said devlce exceeds a predctermined value.

15. In a control system for electron discharze devices, a supply line, an electron discharge device connected with said line, an output line connected with said device, means responsive to the value of the voltage drop in said device,

means for controlling the operation of said device, and means controlled by the first said means to cause operation of the second said means when the voltage drop within said devlce exceeds a predetermined value.

16. In a control system for electron discharge devices, a supply line, an electron discharge device connected with said line, an output line connected With said device, means responsive to the value of the voltage drop in said device,

' means for controlling the operation of said device,

means co-ntrolled by the first said means to control the second said means, and means responsive to the flow of current through said devlce to adjust the operation of the first said means.

17. In a, control system for electrn discharge devices, a supply line, an electron discharge device connected with said line, an output line connected with said device, means .responsive to the value of the voltage drop in said device, means for controlling the operation ofsaid device, means controlled by the flrst said means to control the second said means, and means responsive to the flow of current through said device to adjust the operation of the second said means.

18. In a control system for electron discharge devices, a supply line, an electron discharge device connected with said line, an output line connected with said device, means responsive to the Value of the voltage drop in said device, a

circuit breaker in said supply line. and means responsive to operation of the flrst said means for causing operation of said circuit breakcr when the voltage drop within said device excceds a predetermined value.

19. In a control system for electron discharge devices, a supply line, an electron discharge device connected with said line, an output line v connected with said device, means responsive to the value of the voltage drop in said device,

means producing operating vapor Within said device, and means responsive to operation of the first said means for causing operation of the second said means when the voltage drop within sa d devise exceeds a predetermined value.

5 20. In a control system for electron discharge devices, a supply line, an electron discharge device connected With said line and having electrodes, an otput line connected 'Wlth said device, means connected With two of said elec- 7o trodes and receiving current only 'When current fiows therebetwecn, and means controlled by said means to 'regulate the flow of current through said device.

21. In a control system for electron discharge 75 devices, a supply line, an electron discharge devalue during periods of flow of current there- 10 between.

22. In a control system for electron discharge devices, a supply line, an electron discharge device connected With said line and having electrodes and current controlling means, an out- 15 put line connected with said device, means connected with two of said electrcdes and receivng current from said supply line only when current -fiows betwecn said two of said electrodes, and means controlled by the second said means 20 to control the operation "of said current. controlling means.

23. In a control system for electron discharge devics, a supply line, an electron discharge device connected with said line and having elec 25 trodes, an output line connected with said device, au electron discharge devlce connectcd Wlth two of the electrodcs of the first said device, the second said devlce receiving current only when current flows between the said two of the 30 electrodes, and. means responsive to the flow of current through the second said device to control the operation of the flrst said device.

24. In a control system for electron dlscharge devices, a supply line, an electron discharge device connected witl: said line and having electrodes, an output lin'e connected With said device, an electron dlscha rge devlce connected with two of said electrodes and receiving current from said supply line only when current flows bein tween the said twooi said electrodes, and means responsive to the flow of current through the second said devlce to regulate the flow of current through the flrst said device.

25. In combination with an electric current 45 supply circuit, au output circuit, and an electron discharge devlce having electrofles constituting arcing terminals for the flow of current through said devlce from said supply circuit to said output circuit, of means for controlling the opera 50 tien of said device. means connected With and responsive to the voltage drop above a predetermined value between two of said electrodes for controlling the operation of the flrst said means,

and an electron discharge devlce included in the 55 said connection of the second said means operable to limit the said responseof the latter to periods during which current flows betvycen the said two of said electrodcs.

26. In combination with 'an electric currentfio supply circuit, au output circuit, and an electron disoharge device comprising electrodes constituting arcing terminals for the flow of current through said device from said supply circuit to said output circuit, means for producing and Ionizing vapor Wlthin said device, means connected with and responsive to the voltage drop above a predetetmird value between two of said electrodes for afiecting the operation of the! flrst said means, and an electron discharge device included in the said connection of the second said means operabIe to limit the response of the latter to periods during which current flows between the said two of said electrodes'.

27. In combination with an electric current supply circuit, au output circuit, an electron discharge device having a plurality of electrodes constituting arcing terminals for the flow of current through said device from said supply circuit to said output circuit, and means comprising an excitation electrode disposed within said device for producing and maintaining ionized vapor therein, of means connected with and responsive to the voltage drop above a predetermined value between two of said plurality of electrodes for afiecting the 'operation of the first said means, and an electron discharge device included in the said connection of the second said means operable to limit the response thereof to periods during which current flows between the said two of said electrodes.

28. In combination with an electric current supply circuit, an output circuit, and an electron discharge device comprising electrodes constituting arcing terminals for the flow of current through said device from said supply circuit to said output circuit, of means for producing operating vapor within said device, means connected with two of said electrodes and responsive to the voltage drop therebetween above a predetermined value for afi'ecting the operation of the flrst said means, an electron discharge device having electrodes included in said connections of the second said means operable to limit the response of the latter to periods during which current flows between the said two. of said electrodes, means for producing operating vapors within the second said electron discharge device, and means connected with said output circuit operable responsive to and in dependence upon the magnitude of the current flowing therein for varying the operation of the third said means.

29. In a system of the character described, an alternatingcurrent supply circuit, au output circuit, au electron dischargedevice comprising a cathode, a plurality of anodes and a plurality of control electrodes severally associated with said anodes, means connecting said device with said circuits comprising a transformer winding operable to impress potentials on said anodes during such recurring moments and of such sign and magnitude as to cause the flow of current sequentially through said anodes from said supply circuit to said output circuit, means connected with said supply circuit and with said control electrodes operable to impress alternating current potentials on the latter of such phase andmagnitude and during such recurring moments relative to the potentials impressed on the associated said anodes as to control the moments of initiation of recurring flow of current through the latter, means for varying the phase angle of the said potentials impressed on said control electrodes, and means connected with one of said anodes and said cathode operable responsive to the voltage drop therebetween during periods of flow of current therebetween for controlling the operation of the third said means.

30. In a system of the character described, an alternating current supply circuit, an output circuit, au electron discharge device comprising-a cathode, a plurality of anodes and a pluraiity of control electrodes severally associated with said anodes, means connecting said device with said circuits comprising a transformer winding operable to impress potentials on, said anodes during recurring periods and of such sign and magnitude asto cause the flow.of current sequentially through said anodesfl irOm' said supply circuit to said output circuit, means connected with said supply circuit and said control electrodes operable to impress alternating current potentials on the latter of such phase and magnitude and during such recurring moments relative to the potentials impressed on the associated said anodes as to control the moments of initiation of recurring flow of current through the later, means for varying the phase angle of the potentials impressed on said control electrodes, means connected with one of said anodes and said cathode and receiving current from said supply circuit in dependence upon the magnitude of the voltage drop between the said one of said anodes and said cathode for controlling operation of the third said means, and an electron discharge device included in the said connections of the fourth said means operable to 1imit the flow of current therethrough to periods during which current flows between the said one of said anodes and said cathode.

31. The combination with an electron discharge device comprising an anode and a cathode constituting spaced electrodes for the flow of current therebetween, of means for measuring the voltage drop between said electrodes comprising an indicating device having connections therewith and responsive to the voltage drop only therebetween.

32. The combination with an electron discharge device comprising an anode and a cathode constituting spaced electrodes for the flow of current therebetween, of means for measuring the voltage drop between said electrodes comprising an indicating device having connection therewith and responsive to the potential difference only therebetween, and means operable to limit the response of said indicating device t0 periods dring which current flows between said electrodes.

33. The combination with an electron discharge device comprising an anode and a cathode constituting spaced electrodes for the flow of current therebetween, of means for measuring the voltage drop between said electrodes comprising an indicating device having connection therewith and responsive to the potential difference only therebetween, and an electron discharge device comprising electrodes included in the said connection and operable to limit the response of said indicating device to periods during which current flows between the first said electrodes.

34. The combination with an electron discharge device comprising an anode and a cathode constituting spaced electrodes for the flow of current therebetween, cf means for measuing the voltage drop between said electrodes comprising an indicating device having connection therewith and responsive to the potential diierence only therebetween,' and means operable to limit the response. of said indicating device to said potential diiierence of unidirection only.

, 35. The combination with an electron discharge device comprising an anode and a cathode constituting spaced electrodes for the flow of ourrent therebetween, of means for measuring the voltage drop between said electrodes comprising an indicating device having connection therewith and responsive to the potential difference only therebetween, and an electron discharge de vice having spaced electrodes included in said connection and operable t0 limit the response of said indicating device to said potential of unidirection only and to periods during which current flows between the first said electrodes.

36. The combination with an electron discharge device comprising an anode and a cathode constituting spaced electrodes for the fiow of current therebetween, of means for measuring the voltage drop between said electrodes comprising an indicating device having connection therewith and responsive to the potential difierence only therebetween, means controlling the response of said indicating device comprlsing an electron discharge device having spaced electrodes included in said connection, and means for regulating the conductivity of the second said electron discharge device.

37. The combination with an electron discharge device comprising an anode and a cathode constituting spaced electrodes for the fiow of current therebetween, of means for controlling the said fiow of current, means for measuring the voltage drop between said electrodes, and means comprising an electron discharge device having spaced electrodes connecting the first said electrodes with the first and second said means and operable to limit the response thereof to the potential diference of unidirection only between the first said electrodes.

38. The combination with an electron discharge device comprising an anode and a cathode constituting spaced electrodes for the fiow of current therebetween, of means for controlling said flow of current, means for measuring the voltage drop between said electrodes, and means comprising an electron discharge device having spaced electrodes connecting the first said electrodes with the first and second said means and operable t limit the response thereof to the potential difierence of unidirection only between the first said electrodes and to periods during which current fiows between the first said electrodes.

39. The combination with an electron discharge device comprising an anode and a cathode constituting spaced electrodes for the fiow of current therebetween, of means for regulating the voltage drop between said electrodes, means for measuring said voltage drop, and means comprising an electron discharge device having spaced electrodes connecting the first said electrodes with the first and second said means and operable to limit the response thereof to the potential difierence of unidirection only between the first said electrodes and to periods during Which current flows therebetween.

40. The combinationwith an electron discharge device comprlsing an anode and a cathode constituting spaced lectrodes for the fiow of current therebetween, 'of means for measuflng the voltage drop between.said electrodes comprising an indicating device having connection with said electrodesand responsivetothe potential .difierence only therebetween, means comprising an electron dlscharge device having spaced electrodes included in the connection of the first said electrodes with said indlcating device and operable to limit the response thereof to periods during which currentflows between the first said electrodesb and means operable in dependence upon theflow of current between the first said electrodes for regulatlng the conductivity of the second said electron discharge device.

41. In a control system for electron dlscharge devlces, a supply fine, an electron discharge device connected with said line, an output line connected with said device,means responsive to the value of the voltage drop only in said device including time delay means operable to retard the response of said voltage responsive means to variations in the said voltage drop, means for controlling the fiow of current through said device, and means controlled by the said voltage responsive means for controlling said current controlling means.

42. In a control system for electron discharge devices, a supply lime, an electron discharge device connected with said lime, an output line connected with said device, means responsive to the value of the voltage drop only in said device, means for controlling the fiow of current through said device, and means controlled by said voltage responsive means operable t0 cause operation of said current controlling means including time delay means for retarding the operation of said current controlling means in response to variations in the value of said voltage drop.

43. In a control system for electron discharge devices, a. supply line, an electron discharge device connected with said lino, an output line connected with said device, means responsive to the value of the voltage drop only in said device, means for controlling the fiow ofcurrent through said device, means controlled by said voltage responsive means for controlling said current controlling means, and time del?.y means responsive to the magnitude of the fiow of current through said device to adjust the operation of said voltage responsive means, wherby said operation is variably adjusted in dependence upon the rate of change of the said fiow of current through said device.

44. The combination with an electron discharge device comprising electrodes operable for the fiow of current therebetween, of means for measuring the voltage drop between said electrodes comprising an indicating device responsive to the potential diffrence therebetween, means connected with said indicating device for controlling the response thereof, and means for controlling the action of said response controlling means to prevent the response of said indicating device durng a period immediately preceding a period Of current fiow between said electrodes.

45. The combination with an electron discharge device comprising electrodes operable for the fiow of current therebetween, of means for measuring the voltage drop between said electrodes comprising an indicating device responsive to the potential difierence therebetween, means connected with said indicating device for controlling the response thereof, and means operable in dependence upon the fiow of current between said electrodes for controlling the action of said response controlling means.

46. The "=cpmbination with an electron dS- charge devicecomprising electrodes operable for the'fiow of currnt"therebetween, of means for measuring the voltage drop between said electrodes comprising an indicating device responslve to the potential difference therebetween, means confprising an auxiliary electron discharge device connected with said lndicating device for controlling the response thereof, and means operable in dependence upon the flow of current between said electrodes for controlling the conductlvlty of said auxiliary electron discharge device.

'47. The combination with an electron discharge device comprisng electrodes operable for the fiow of current therebetween, of means for measuring the average value of the voltage drop between said electrodes comprising an indicatlng device connected with said electrodes and responsive to the potential dlference therebetwn,

48. The'comblnatlon w1th an electron discharge devlce comprising electro des operable for the 110w of current therebetween, of means for measuflng the average value of the voltage drop between said electrcdes comprislng an lndlcating dev lce connected wlth sald electrodes and responslve to the,.

potential dlflerence therebetween, means con: neCted with.said lndlcating device for controlling the response thereof, means comprisflng an auxlllary electron dlscharge devlce connected with sa1d indlcating device for controlling the response theredt, and means operable in dependence upon the flow or current-between safld electmdes for controflingthe conductivity of said auxliary electron diacharge devlce.

49. The oomblnatlon wioh an electron discharge devlce comprlsing lectrodes operable for the flow of current therebtween, of means for measuring the average value of the voltage drop between said electrodes comprising an indicating devlce connected with sa:ld electrodes and responsive to the potential diffrence therebetween, means compfl5ing an a'.uxiliary electron dlscharge devlce connected w1th said indicating device for controlling the response thereot, and means operable in dependence upon the flow of current between said elctrodes for controlling the conductivlty of said auxlllary -discharge device to lim1t the response of sald indicatlng device to periods durlng whlch current flows between said electrodes,

DIDR JOURNEAUX.