US2539912A - Electrode spacing regulator utilizing reference electrodes - Google Patents

Description

Jan. 30, 1951 D. JOURNEAUX 2,539,912

ELECTRODE SPACING REGULATOR UTILIZING REFERENCE ELECTRODES Filed March 8, 1947 4 Sheets-Sheet l IMVENTOR J m WMW Jan. 30, 1951 D JOURNEAUX 2,539,912

ELECTRODE SPACING REGULATOR UTILIZING REFERENCE ELECTRODES Filed March 8, 1947 4 Sheets-Sheet 2 iNVENTOR Jan. 30, 1951 D. JOURNEAUX 2,539,912

ELECTRODE SPACING REGULATOR UTILIZING REFERENCE ELECTRODES 4 Sheets-Sheet 5 Filed March 8, 1947 INVENTOR 2,539,912 ZING Jan. 30, 1951 D. JOURNEAUX ELECTRODE SPACING REGULATOR UTILI REFERENCE ELECTRODES 4 Sheets-Sheet 4 Filed March 8, 1947 INVENTOR 52am Patented Jam 30, 1951 ELECTRODE SPACING REGULATOR UTILIZ- ING REFERENCE ELECTRODES Didier Journeaux, Milwaukee, Wis., assignor to Allis-Chalmers Manufacturing Company, Milwaukee, Wis., a corporation of Delaware Application March 8, 1947, Serial No. 733,343

' 21 Claims.

This invention relates in general to improvements in electric control systems, and more particularly to means for and methods of regulating 'the spacing of consumable electrodes between which current flows through a gaseous or liquid medium.

Electric current may be caused to flow between a pair of working electrodes through a fluid medrum for different purposes such as electrolysis of salts, fusion and refining of metals, or chemical reaction between gases. The flow of current or discharge may take place over a wide range of spacings between the electrodes, but under a given set of operating conditions it is generally found advantageous to maintain the electrode spacing substantially constant. When the electrodes are of a consumable type, it is therefore necessary to readjust their spacing from time to time.

As it is generally not feasible to measure the spacing between the electrodes, the electrode actuating apparatus is frequently controlled in response to the current intensity through the electrodes. The action of such control is based on the assumption that there is a uniform relation between the current intensity and the electrode spacing, and it is therefore disturbed by fluctuations in the voltage of the source supplying current to the electrodes. In polyphase furnaces the current intensity through each pair of electrodes is also dependent upon the spacings of the other pairs of electrodes, so that inaccurate spacing of one pair of electrodes results in unnecessary and improper readjustments of the other pairs. p

The above disadvantages may be obviated by controlling the spacing of each pair of working electrodes in accordance with the relative values of the voltage across the electrodes and of the voltage of a suitable standard of reference. The latter may consist of any suitable means or combination of means having a volt-ampere characteristic similar to the volt-ampere characteristic of the discharge between working electrodes maintained at the desired spacing. The desired electrode spacing need not necessarily be constant but may vary as a function of the current intensity.

When the discharge between the electrodes has a non-linear drooping volt-ampere characteristic, any type of standard of reference having a drooping volt-ampere characteristic may be utilized over a limited range of currents. To obtain the desired electrode spacing over a wide range of currents, the standard of reference should be a device having a non-linear drooping volt-ampere characteristic, such as a pair of reference electrodes carrying current of intensity in a predetermined relation to the current of the working electrodes. The voltages of the working electrodes and of the reference electrodes are measured by means of suitable indicating instruments or measuring circuits, and the spacing of the working electrodes is varied, either manually or by suitable responsive means, in accordance with the relative values of the measured voltages.

If the voltage measuring connections cannot directly be attached to the points of the working electrodes between which the discharge takes place, the voltage at some other point of the electrode circuit may be measured, and correction may be applied for the voltage drop in the circuit conductors.

It is therefore an object of the present invention to provide a system for regulating the spacing of a pair of electrodes which is unaffected by variations in the voltage of the source supplying current to the electrodes.

Another ob ect of the present invention is to provide a system for regulating the spacing of a pair of electrodes which is unaffected by variations in the spacing of other electrodes connected in the same circuit.

Another ob ect of the present invention is to provide a system for regulating the spacing of a pair of electrodes by which the spacing may be maintained substantially constant at all values of the current intensity through the electrodes.

Another object of the present invention is to provide a system for regulating the spacing of a pair of electrodes by which the electrode spacing may be caused to vary in a predetermined relation to the value of the current flow through the electrodes.

Another object of the present invention is to provide a system for regulating the spacing of a pair of electrodes in which a single standard of reference is utilized at all values of the current flow through the electrodes.

Another object of the present invention, is to provide a method of regulating the spacing of pair of electrodes in which the voltageactually appearing across the electrodes is compared with the voltage which would exist between the electrodes if their spacing had the desired value. 7

Another object of the present invention is to provide a method of regulating the spacingof a pair of electrodes in which the voltage across th the polyphase arcing type.

electrodes is compared with the voltage across a standard of reference having a volt-ampere characteristic similar to that of the electrodes.

Ob ects and advantages other than those above set forth Will. be apparent from the following description when read in connection with the accompanying drawing, in which:

Fig. 1 diagrammatically illustrates one embodi ment of the invention for controlling the spacing of a pair of electrodes of a polyphase arc furnace, in which embodiment a gas discharge device is utilized as a standard of reference for controllingthe electrode hoistmotor through an electric valve;

Fig. 2 diagrammatically illustrates a modified embodiment of the invention differing from the embodiment illustrated in Fig. l in the provision of means for compensating the voltage drop in the circuit supplying current to the working electrodes;

Fig. 3 is a graph of the volt-ampere characteristics of the working electrodes and of the standard of reference;

Fig. 4 diagrammatically illustrates another modified embodiment utilizing the combination of a resistor and of a source of constant voltage as a standard of reference;

Fig. 5 diagrammatically illustrates another modified embodiment utilizing the combination of a reactor and of a source of constant voltage as a standard of reference;

Fig. 6 diagrammatically illustrates another modified embodiment in which a common measuring system is utilized for energizing the grids of electric valves controlling the advancing and withdrawing movements of the electrodes;

Fig. 7 diagrammatically illustrates another modified embodiment differing from the embodiment illustrated in Fig. 6 in the detail of the grid circuits of the valves;

Fig. 8 diagrammatically illustrates another modified embodiment in which the standard of reference controls a field winding of a generator supplying current to the electrode hoist motor; and

Fig. 9 diagrammatically illustrates another modified embodiment in which the standard of reference controls the supply of compressed air or other operating fluid to an electrode hoist motor of the fluid actuated type.

Elements having the same function are designated by the same character of reference in the different figures. It will be understood that elements shown in different figures may also be combined to form further embodiments of the invention.

Referring more particularly to the drawing by characters of reference, numerals l2, I3 designate electrodes of an electric furnace ll of Current is supplied to the electrodes from a suitable source of alternating current represented as a three-phase circuit I5 connected with the electrodes through suitablecurrent limiting means such as reactors IS. The furnace contains a pool of molten metal l1 serving s an intermediate electrode of which different portions cooperate with electrodes ll, l2, l3 to constitute three pairs of electrodes.

Electrodes [2, l3 are severally provided with hoisting means for maintaining the electrodes at a distance from pool II which may be constant or which may vary in dependence upon the current intensity through the electrodes. The hoisting means may be actuated manually, or

iii)

each electrode may be provided with a hoist motor such as an electric motor l8 of the direct current type having an armature l9 connected with the electrode through a shaft 20.

The operation of the hoisting means of electrode H is controlled in dependence upon the relative values of the voltage across electrodes H, l! and of the voltage across a suitable standard of reference. The volt-ampere characteristic of the standard of reference should be generally similar to the volt-ampere characteristic of electrodes II, I! and should therefore generally be drooping when the discharge between electrodes ii, I! is of the type designated as an arc. To obtain a control of maximum accuracy the voltampere characteristic of the standard of reference should further be non-linear.

The standard of reference may consist of a pair of reference electrodes 2| between which current may fiow in the form of an arc discharge through a, gaseous medium. Electrodes 2| may be maintained at operating temperature insuring the emission of electrons thereat by the current flowing therethrough or by the supply of heating current to a pair of filaments 22. Electrodes 2| may be the electrodes of gas discharge device 23 of any suitable known type such as an ordinary fluorescent lamp.

Means are provided to supply to electrodes 2| current of intensity in a predetermined relation to the current intensity through electrodes H, I! and through the working are established therebetween, whereby a reference are is drawn between electrodes 2|. For example, electrodes 2| may be supplied with current proportional to the current of electrodes H, H from the secondary winding of an adjustable current transformer 24 having its primary winding serially connected with electrode II. The voltage across electrodes 2| is measured by a circuit comprising a. rectifier 25 of any suitable known type, suitable current smoothing means such as a, series reactor 26 associated with a shunt capacitor 21, and a voltage divider 28. An adjustable rectified control voltage proportional to the voltage of electrodes 2| is thereby made available between a termizeal and the tap of voltage divider 28. A voltmeter 29 may be connected across voltage divider 25 to obtain a visual indication of the magnitude of the voltage across electrodes 2|.

A similar indication of the voltage across electrodes ll, l'l and an adjustable rectified control voltage responsive thereto may be obtained by means comprising a potential transformer 3| associated with a rectifier 32, a series reactor 33, a shunt capacitor 34, a voltage divider 35 and a voltmeter 36. The reading of the voltmeter includes the voltage drop in the body of electrodes ii, I! and in the portion of the conductors joinme the electrodes to the primary winding of transformer 3|, but such voltage drop is assumed to be negligible compared to the value of the arc voltage.

To control the spacing of electrodes II, II automatically in response to the relative values of the voltages across electrodes ll, l1 and electrodes 2|, armature l9 may intermittently be supplied with rectified current from circuit l5 through a transformer 31 and through an electric valve of any suitable type provided with a control electrode, such as a shield grid thyratron 38. The control grid 39 of thyratron 38' may be connected with the cathode 4| thereof through a circuit comprising differentially connected voltage dividers 28, 35 and a current limiting resistor 42 aasaaia to. render thyratron ll flerentially-responsive to the rectified control-voltages. The: critical potential, above which, control ,grid 39 must be brought to render "conductive, maybe varied by :impressing a suitable potentialon shield grid 41, by means of asuitable source represented as abattery 44.;

in operation, current supplied furnace. l4.

flows from onev of the conductors .ofcircuit- I through one of reactors Iland electrode .II and reaches the adjacent portion of electrode IT in the .form of a working arc. The current returns to, another-conductor of circuit I5 through another are drawn between another portion of electrode I1 and electrode or I3.- in general, the volt-ampere characteristic of the arm drawn be'-' tweenelectrodes- II', II is drooping and nonlinear. It will be assumed that the -character-' istic designated 45 in Fig. 3 is the characteristic of the arc atelectrodes II, I! when the electrode spacing has the desired value. Such spacingmay be constant'or may depend upon the current intensity through the electrodes.

If the electrode spacing becomes too narrow, the volt-ampere characteristic will drop-toa corresponding extent, as shown by curve'46 for example. If the electrode spacing becomes too wide, the volt-ampere characteristic will' 'b'e boosted a corresponding extent, as shown by curve 41' for example; 'It will be assumed that curve 45 is also-the volt-ampere characteristic of the combination of current transformer 24 oi-grid 39 is. therebycaused todrop and, when such potential is again belowcathode potential, thyratron 38 returns to the, nonconductive con-; dition and motor I8 stops. 1 If the voltage. dividers. are properly adjusted. the spacing between. elec trodes -I I l1;will then, have the desiredvaluet The above described control-system"v is 5 operable. only to cause motor: I-8 to lower electrode II, but

- it will. be understood that anothergsimilarz control system may- 'beiprovided toxcause the motor to raise electrode II when the spacing between electrodes I I, r I T is too narrow. :1 Additional motors and associated control-systems will generally be provided for regulating electrodes and.l3. 1-"

It will be understood that device 23 may be 'so' chosen that the voltage drop between electrodes 2| 'difiers invalue from the -voltage drop between electrodes II, II. The-tap 'of'voltage divider 25.

. then should correspondingly be adjusted to main with'electrodes 2i and the circuit e1ementsconnected thereto, including voltage divider 28.

' The voltage appearing across voltage divider is a measure'of the voltage actually present across electrodes II, II. The voltage appearing across voltage divider 28 is likewise a measure of the voltage across electrodes 2|, and is also a measure of the voltage which would exist between electrodes II, I1 if their spacing had the desired value. If the spacing of electrodes II, I! is co!- rectly adjusted, voltmeters 29 and- 36 therefore will always measure equal voltages regardless of the current intensity through electrodes II, I2, I3 and I1 andregardless of the positions of electrodes I2, I3 with respect "to electrode I1. If the spacing of electrodes 1 I I1 is too wide,'voltmeter 29 will have a lower reading than voltmeter 36, and if the spacing is too narrow. voltmeter 29 will have a higher reading than voltmeter 3,6. Ii'thegrid control circuit of thyratron 3a is open,'th e spacing between electrodes II, I! may be adjusted manually in accordance with the relative values. of the voltmeter readings to bring the voltages to equality.' When the control grid circuit o'f thyratron 38 is close'das shown in Fig. 1, the potential of grid 59 with. respect to the potential of cathode 4| is equal to the difference of the voltages of the portions of voltage dividers: 25 and 35 comprised between the tapsthereof. For, the sake of simplicity it will be assumed that the critical potential" of grid 39 is equal to the potential of the associated. cathodej4'I. i

When' thejspacingof electrodes II, I! is too wide, the voltage dividers bring grid 39 to a' po-i tential above the potential of cathode H, and thy'ratron 38 therefore becomes conductive to transmitlrectified'current to armature l9. The armature drives shaft 20 to lower electrode I I; As aresult of the decrease in the spacing betweenelectrodes II, I], the voltage of voltage divider 35 decreases. relatively to the voltage.

of voltagedivider 28 regardless. of the current in-' tensity through electrodes II, II. The potential tain thyratron 38 responsive to differencesabove a predetermined 'valuebetween 'the'reference' voltages impressed onfthe control grid circuit thereof from voltage dividers and 35.} I The connections between transformer 3| and the points of electrodes I 'I 'I'I joined by the working arc include the entire body of electrode I I and sometimes also a substantial portion of the-con nection between electrodeil and the" associated reactor I6, which willbe designated electrode lead. The connections'illustrated in Fig: 1 may then be retainedif thecombination of current transformer '24, electrodes 2I' and voltage divider 28 can be adjusted to have the'same volt-ampere characteristic as the circuit consisting of" electrodes II andl'II, the arc th'erebetwe'en and the electrode leadiportion inserted between thep'rimary terminals of transformerii'ij If thevolt-arnpere charact ristics cannot be matched by a' suitable choice of device '23 and of the circuit elements associated therewith, the voltage drop in electrode I I and in the electrode lead should be compensated. As shown in Fig. 2 the voltage dropcomp'onent due" to the resistance of the electrodebody and of the electrode lead may be compensated by means of fa resistor 48 supplied withcurrent from a current transformer 49 havingits primary. winding serially connected with electrode I l. Anothe 'component due to the self-inductance' of the'electrode body and of the electrode lead maybe compensated by the voltage in 'an inductive reactor ,5I serially connected with resistor 48.

Other components resulting from the mutual inductive action between the circuits of electrodes II, I2, I3 may be compensated by means of cur: rent transformers '52, 53- having' their primary windings serially connected with electrodes I2, I,3., The currentjransformer secondary wind ings are connected across reactors 54, serially connecting resistor 48 and reactor 5| in the'p'rimar-g winding connections of transformer 3|, By suitably adjusting thenportioins of resistor. 48 and of reactors 5I,f5'4,' ',55 serially] connecf fid. with the primary winding .ofltransforr ner 3'I the voltage impressed on-such primary winding may be so corrected as'tobe substantially equal to the; voltage actually, {present between [the points of electrodes I, IIfjoined by the; are dischar e- The system therefore operates substantiallyin the manner abwdeseribed w th espect to the em bodi'ment illustrated in Fig. '1.

The control voltage appearing across voltage divider 35 then 'rna'y be considered a s'jbein g the difference between a component responsive'to the voltage of the circuitsupplyin g currentto elect trode II and a component responsive to the voltage drop in the solid conductors of such circuit.

If the secondary current of current transformer i is higher than the rated current of device 23 even when the current transformer is adjusted for its lowest secondary current, device 23 may be connected in parallel with one or more additional devices of the same type such as device 55. The flow of' current may be caused to divide equally between the parallel devices by means of inductively related windings 51 connected in series with the different devices.

In the embodiment illustrated in Fig. 4, the reference means comprise an adjustable resistor 58 and a source of direct current of suitable voltage and polarity represented as a battery 59 in the connection between grid 39 and cathode 4|. The polarity of rectifier 25 is then reversed with respect to the polarity shown in Figs. 1 and 2.

Thyratron 38 is accordingly responsive to the difference between the constant voltage of battery 59 and the sum of two control voltages proportional to the voltages across electrodes ll I1 and across reference resistor 58.

The volt-ampere characteristic of battery 59 is a horizontal line such as line 6| in Fig. 3. The volt-ampere characteristic of resistor 58 is rising. It is a straight line if the resistor has a resistance which is independent of current and it is curved if the resistor is of a known non-linear type.

Resistor 58 is preferably so adjusted that curve 45, when read with respect to line 6|, is the voltampere characteristic of the combination of current transformer 24, resistor 58 and voltage divider 28. Curve 45, when read with respect to the axis of abscissas, is then also the volt-ampere characteristic of the combination of current transformer 24, resistor 58, voltage divider 28 and battery 59. The potential impressed on grid 39 is then the same as in the embodiment illustrated in Fig. 1 under all operating conditions of the system and the operation remains substantially as above set forth.

As shown in Fig. 5, resistor 58 of Fig. 4 may be replaced by an adjustable inductive reactor 62. As a result of the connections of grid 39, thyratron 48 is again additively responsive to the two variable control voltages, of which one is produced in voltage divider 35 in response to the voltage across electrodes II, II and the other is produced in voltage divider 28 in response to the current flow through electrodes H, H.

The volt-ampere characteristic of reactor 62 is rising and the volt-ampere characteristic of the combination of current transformer 24, reactor 52. voltage divider 28, and battery 59 is drooping. If reactor 62 is provided with a core in which the magnetic flux reaches the saturation range, the volt-ampere characteristic of the combination is rendered non-linear and may be adjusted to approximate curve 45 as in the previously considered embodiment.

Motor l8 may be prevented from moving electrode ll past the desired position by causing the potential of grid 39 to be responsive to the joint action of the current through electrodes II, II, the voltage across such electrodes, and the speed of motor l8. For the latter purpose the terminal voltage of armature l9, or a portion of such voltage, may be introduced into the circuit connecting grid 39 with cathode 4|. As shown in Fig. 6, a voltage divider 63 may be connected across armature l9 and the taps of voltage dividers 35 and 63 may be interconnected to permit adjustment of the relative values of the voltages introduced therefrom in the grid circuit.

Motor It may also be supplied with current to raise electrode l I when the spacing between electrodes II, I! is too narrow by connecting armature IS with an additional secondary winding of transformer 31 through a second thyratron 54. The connections of the control grids of thyratrons 38 and 54 are symmetrical with respect to voltage dividers 28 and 35. The connections of voltage divider 89 with voltage dividers 28 and 35 include rectiflers 65, 68 for preventing the flow of circulating current between the voltage dividers.

When motor 18 is at rest, no voltage is impressed on voltage divider 53. If the spacing between electrodes II, I! becomes too wide, thyratron 38 becomes conductive to supply current to armature I 8 as above set forth with respect to the embodiment illustrated in Fig. 1. Armature l9 rotates to lower electrode II and the armature terminal voltage increases with the armature speed.

When the armature reaches a predetermined speed the potential impressed on grid 39 from armature I9 through voltage divider 53, rectifier 65, voltage dividers 35, 28 and resistor 42 brings grid 39 to a potential below cathode potential and thyratron 38 returns to the non-conductive condition. Armature I9 is thus de-energized and its speed decreases. The armature counter-electromotive force also decreases and the potential of grid39 is thereby caused to rise above the critical values to render thyratron 38 again conductive.

Armature I9 is thus intermittently energized in such manner that its speed is varied in relation to the extent to which the spacing of electrodes II, l1 departs from the desired value. While the electrodes are being returned to the proper spacing the speed of armature l9 gradually decreases, so that electrode ll reaches the desired position at very low speed and does not overtravel.

If for any reacon the electrode spacing becomes too narrow, the voltage of voltage divider 35 becomes lower than the voltage of the voltage divider 28. The control grid potential of thyratron 64 is thus raised above the critical value and thyratron 54 becomes conductive to supply current to armature l9. The armature then rotates in the direction opposite to that above considered, and the operation of the system to raise electrode ll takes place in a manner similar to that above set forth with respect to lowering of the electrode.

During lowering operation of electrode II, if the speed of armature l9 becomes excessive, thyratron 64 will also become conductive to supply current to armature I 9 in such sense as to decelerate the armature. Conversely, during raising operation of electrode ll, thyratron 38 may become conductive to supply decelerating current to armature I9.

In the embodiment illustrated in Fig. 7 the circuit connecting grid 39 with cathode 4| is impressed with'three voltage components. A negative voltage component is supplied from a battery 61. An alternating voltage component of constant magnitude and phase is supplied from circuit l5 through a transformer 58. A second alternating voltage component of constant magnitude but lagging behind the voltage of transformer 68 to a variable extent is supplied from circuit l5 through a transformer 69 and a phase shifting circuit comprising a resistor II and a saturable reactor 12.

The saturating winding of reactor 12 may be supplied with a current component of predetermined magnitude from a battery 13. A variable current component may be supplied to the saturating winding by connecting the latter in series with voltage dividers 28 and 35 across a portion of voltage divider 83. A rectifier 14 may be connected in series with the saturating winding to prevent reversal of the saturating current of reactor 12 in response to decrease of the electrode spacing below the desired value. The grid control circuit of thyratron 84 is similar to that of thyratron 38.

As lOllg as the spacing of electrodes II, II re mains at the desired value, the voltages impressed on voltage dividers 28, 35 remain equal and the current through the saturating winding of reactor 12 remains constant. The grid circuits are so dimensioned that the alternating potential components impressed on grid 39 from transformers 88, 69 are then insumcient to overcome the negative potential impressed thereon from battery 81. The potential of grid 39 is then a periodic negative potential and thyratron 38 remains nonconductive.

If the spacing of electrodes II, I! become too wide and the difference between the voltages of voltage dividers 35 and 28 exceeds a predetermined value, the saturating current of reactor 12 is increased. The voltage impressed on the grid circuit from transformer 89 is thereby caused to advance in phase, and the resultant of the two alternating potential components impressed on grid 39 is thus caused both to advance in phase and to increase in magnitude. Grid 39 is thus caused to become periodically positive to render thyratron 38 periodically conductive. The movements of positive energization of grid 39 are advanced in dependence upon the magnitude of the departure of the electrode spacing from the desired value. Such advance is however subject to being reduced in dependence upon the speed of armature l9 bv the action of the armature voltage through voltage divider 83. The electrode spacing is thereby caused to return to the desired value without overtravel.

If the electrode spacing is too narrow, thvratron 84 is energized to cause motor l8 to return electrode ll to'the desired position in a manner similar to that above described. The thyratrons also control the flow of decelerating current through armature l9 when the armature speed exceeds the speed corresponding to the extent of departure of electrode H from the desired position. In this manner, excess kinetic energy stored in armature l9 may be returned to circuit 15.

In the embodiment illustrated in Fig. 8, armature I9 is assumed to be supplied with current from a direct current generator 15 having a separately excited field winding 16 and a shunt field winding 11 connected across the associated armature 18. A field rheostat 19 in series with shunt field winding 11 may be so adjusted that field I1 alone will induce in armature 18 a voltage which may take indifferently any value consistent with operation of generator 15 within a range below the magnetic saturation range. Any energization of winding 16 with current of one or the other polarity will then cause maximum terminal voltage to be induced in armature 18 with {one or the other polarity. 1', Winding 18 is so connected with voltage dividers 28 and 35 that no current flows through winding I8 when the spacing between electrodes .II, I! is at the desired value. If the electrode spacing becomes too narrow by a predetermined amount, sufficient current will be supplied to field winding 18 to cause armature 18 to operate at electrode H toward the desired position at the maximum speed. Overtravel of electrode H is limited by the action of field 18, which causes reversal of the voltage induced in armature I8 if the electrode overtravel reaches a predetermined value.

In the embodiment illustrated. in Fig. 9, shaft 20 is assumed to be driven by a pneumatic motor 8| comprising a pair of opposed cylinders 82, 83. The cylinders maybe supplied with compressed air from a reservoir 84 through an ordinary magnet valve or through an inverted magnet valve 88. The solenoids of valves 85, 86 are connected across voltage dividers 28, 35 through a battery 59. The weight of the movable elements of the magnet valves is partly or entirely balanced by the current supplied to the solenoids from battery 59. A resistor 81 connected in series with the solenoid of valve 85 causes valve 85 to operate at a slightly higher voltage than valve 88.

As the valve solenoids consume current constantly, they modify the volt-ampere characteristic of the combination of the current transformer 24, electrodes 2| and voltage divider 28. The volt-ampere characteristic may be caused to match that of electrodes II, I! by suitable choice of device 23, by suitable adjustment of the taps of voltage divider 28 and battery 59, and by other adjustments. As shown in Fig. 9 the secondary current of current transformer 24 may be rectifled before being supplied to electrodes 2| to supply thereto a current component proportional to the current of electrodes H, H. A constant current component may then also be supplied to electrodes 2| from a battery 88 through a constant current regulating device such as a device 88 comprising an iron filament in an atmosphere of hydrogen. An additional means is thereby provided for modifying the volt-ampere characteristic of any embodiment of circuit supplied from current transformer 24'.

Voltage dividers 28, 35 and battery 59 are so adjusted that when the spacing of electrodes l I, H has the desired value, valve 86 is in the actuated position shown and valve 85 is in the unactuated position shown. Cylinders 82, 83 are then both at atmospheric pressure, but electrode II is maintained in position by the usual electrode balancing means (not shown).

If the spacing of electrode H, I! becomes too wide, the voltage impressed on voltage divider 35 becomes greater than the voltage impressed on voltage divider 28. The resultant voltage impressed on the solenoids is thereby decreased and valve 86 is de-actuated. Air is admitted from reservoir 84 into cylinder 83 to lower electrode ll. When the electrode has returned to the desired position, the voltage impressed on the solenoids returns to normal value and valve 85 is again actuated to release the air contained within cylinder 83, and motor 8| stops.

Likewise, if the spacing of electrodes H, H becomes too narrow, the voltage impressed on the solenoids is increased and valve 85 is ac- 11 85 is again de-actuated to relieve the air pressure within cylinder 82, and motor 8| stops.

Although but a few embodiments of the present invention have been illustrated and described, it will be apparent to one skilled in the art that various changes and modifications may be made therein without departing from the spirit of the invention or from the scope of the appended claims. Features disclosed but not claimed in this application are claimed in my copending application Serial No. 171,771, filed July 1, 1950.

It is claimed and desired to secure by Letters Patent:

1. In a control system for a pair of working electrodes between which current isflowing in the form of a working arc, the combination of a motor for controlling the spacing of said working electrodes and means for controlling the operation of said motor comprising a pair of reference electrodes, means for drawing a reference are between said reference electrodes, said reference arc producing a reference voltage measurable at said reference electrodes, and means for comparing the value of said reference voltage with the value of the voltage across said working are for varying the magnitude of the voltage impressed on said motor.

2. In a control system for a pair of working electrodes between which current is flowing in the form of a working arc, the combination of a motor for controlling the spacing of said electrodes and means for controlling the operation of said motor comprising a pair of reference electrodes for sustaining the flow of current therebetween, means for supplying to said reference electrodes current proportional to the current flowing through said working electrodes, and means for comparing the va ue of the voltage across said reference electrodes with the value of the voltage across said working electrodes for varying the magnitude of the voltage impressed on said motor.

3. In a control system for a pair of working electrodes between which alternating current is flowing in the form of a working arc, the combination of a motor for controlling the spacing of said electrodes and means for controlling the operation of said motor comprising a pair of reference electrodes for sustaining the flow of alternating current therebetween, means for supplying to said reference electrodes alternating current proportional to the alternating current flowing through said working electrodes, means for producing rectified voltages proportional to the voltages across said working e ectrodes and said reference electrodes, and means responsive to the difference between the values of said rectified voltages for varying the magnitude of the voltage impressed on said motor.

4. In a control syst m for a pair of working electrodes between which current is flowing in the form of a working arc, the combination of a motor for controlling the spacing of said electrodes and means for controlling the operation of said motor comprising an electric valve having main and control e ectrodes, a pair of reference electrodes for sustaining the flow of current therebetween, means for supplying to said reference electrodes a current proportional to the current flowing through said working electrodes, and means for controlling the potential of said control electrode comprising means responsive to the difference between the values of voltages appearing across said working electrodes and said reference electrodes.

5. In a control system electrodes between which flowing in the form of a working arc, the combination of a motor for controlling the spacing of said electrodes and means for controlling the operation of said motor comprising an electric valve having main and control electrodes, a pair of reference electrodes for sustaining the flow of alternating current therebetween, means for supplying to said reference electrodes alternating current proportional to the current flowing through said working electrodes, means for producing rectified voltages proportional to the voltages appearing across said working electrodes and said reference electrodes, and means responsive to the difference between the values of said rectified voltages for controlling the potential of said control electrode.

6. In a control system for a pair of working electrodes between which alternating current is flowing in the form of a working are, the combination of a motor for controlling the spacing of said electrodes and means for controlling the operation of said motor comprising an electric valve having main and control electrodes, a pair of reference electrodes for sustaining the flow of alternating current therebetween, means for supplying to said reference electrodes an alterhating current proportional to the current flowing through said working electrodes, means for producing rectified voltages proportional to the voltages appearing across said working electrodes and said reference electrodes, and means for impressing the difference between the values of said rectified voltages between said main electrode and said control electrode of said electric valve for varying the magnitude of the voltage impressed on said motor.

7. The method of controlling the spacing of a pair of working electrodes between which current is flowing through a fluid medium comprising the steps of serially connecting a pair of reference electrodes by means of a current proportional to the current flowing through said working electrodes, measuring the voltage across said working electrodes, measuring the voltage across said reference electrodes, and varying said spacing in accordance with the relative values of said voltages.

8. In a control system for a pair of working electrodes between which alternating current is flowing in the form of a working arc, said are having a predetermined drooping volt-ampere characteristic, the combination of a motor for for a pair of working controlling the spacing of said electrodes and means for controlling the operation of said motor comprising voltage reference means, means for drawing in said reference means an alternating current reference are having a current intensity proportional to the current intensity of said working are, said reference arc having a drooping volt-ampere characteristic, and means for comparing the value of the voltage across said reference arc with the value of the voltage across said working are for varying the magnitude of the voltage impressed on said motor.

9. In a control system for a pair of working electrodes between which alternating current is flowing in the form of a working arc, said are having a predetermined non-linear volt-ampere characteristic, the combinationeof a motor for controlling the spacing of said electrodes and means for controlling the operation of said motor comprising voltage reference means, meansfor drawing in said reference means an alternating alternating current is g assure current reference are having a current intensity proportional to the current intensity of said working are, said reference are having a nonlinear volt-ampere characteristic, and means for comparing the value of the voltage'across said reference arc with the value of the voltage across said working are for varying the magnitude of the voltage impressed on said motor.

10. In a control system for a pair of working electrodes between which alternating current is flowing in the form of a working arc, the combination of a motor for controlling the spacing of said working electrodes and means for controlling the operation of said motor comprising a pair of reference electrodes, means for drawing an alternating current reference are between said electrodes, said reference are producing a reference voltage measurable at said reference electrodes, and means for comparing the value of said reference voltage with the value of the voltage across said working are for varying the magnitude of the voltage impressed on said motor.

11. In a control system for a pair of working electrodes between which alternating current is flowing in the form of a working arc, the combination of a motor for controlling the spacing of said electrodes and means for controlling the operation of said motor comprising a pair of reference electrodes for sustaining the flow of alternating current therebetween, means for supplying to said reference electrodes alternating current proportional to the alternating current flowing through sa d working electrodes, and means for comparing the value of the voltage across said reference electrodes with the value of the voltage across said working electrodes for varying the magnitude of the voltage impressed on said motor.

12. The method of controlling the spacing of a pair of electrodes between which current of predetermined intensity at any particular instant of time is flowing through a fluid medium, comprising the preliminary step of initially comparing the values of'the voltage actually present across the electrodes only for a certain spacing with the values of the voltage which would exi t between said electrodes if their spacing always had an arbitrarily selected predetermined value and the electrode current retained said predetermined intensity to obtain a certain voltage difference, and the subsequent step of adjusting the spacing of said electrodes to again obtain said certain voltage difference.

13. The method of controlling the snacing of a pair of working electrodes between which a current is flowing in the form of an electric arc having a predetermined volt-ampere characteristic, comprising the step of establishing a second are between a pair of reference electrodes, said second are having a predetermined volt-ampere characteristic substantially identical to sa d pre determined volt-ampere characteristic, the preliminary step of initially comparing the voltampere characteristics of said working arc and said reference are for a certain spacing of said working electrodes to obtain a certain difference in volt-ampere characteristics, and the subsequent step of adjusting the spacing of said electrodes to again obtain sa d certain difference in volt-ampere characteristics.

14. In a system comprising a circuit of solid conductors of substantial impedance connecting a pair of working electrodes to a current source for the flow of current therebetween and through a fluid medium, the combination of a motor for con- 14 trolling the spacing of said working electrodes, means for producing a control voltage responsive to the voltage of said source, means responsive to the magnitude of said flow of current for producing a compensating voltage proportional to the voltage drop. in said solid conductors and said electrodes, reference electrodes, means for supplying to said reference electrodes a current proportional to the current flowing through said working electrodes to produce a reference voltage across said reference electrodes, and means responsive to the difference between said control voltage and the sum of said compensating voltage and said reference voltage for controlling the operation of said motor.

15. The method of controlling the spacing of a pair of electrodes between which current of varying intensity is flowing through a fluid medium, comprising the steps of supplying a reference device with current of intensity proportional to the current intensity through said electrodes, measuring the voltage across said electrodes and a conductor supplying current to said electrodes, variably correcting said voltage in magnitude and in phase for the varying value and phase'of the voltage drop in said conductor and in said electrodes, measuring the voltage across said reference device, and varying said spacing in accordance with the relative values of said corrected voltage and of said voltage across said reference device.

16. In a control system for a pair of working electrodes between which current is flowing in the form of a working arc, the combination of a motor for controlling the spacing of said working el ctrodes, a pair of reference electrodes, means for supplying to said reference electrodes a constant direct current component and a second direct current component proportional to the current through said working electrodes to produce a reference are across said reference electrodes, said reference are producing a reference voltage measurable at said reference electrodes, 9. source of constant unidirectional voltage, and means responsive to the difference between a voltage proportional to the voltage appearing across said working electrodes and the sum of said constant voltage and a voltage proportional to said reference voltage for controlling the operation of said motor.

1'7. In a control system for a pair of working electrodes between which current is flowing in the form of a working arc, the combination of a motor for controlling the spacing of said working electrodes, a pair of reference electrodes for sustaining the flow of current therebetween,

means for supplying to said reference electrodes a current proportional to the current flowing through said working electrodes to produce a reference voltage across said reference electrodes, means for producing a control voltage responsive to the voltage across said working electrodes, 9. source of constant voltage, and means rcsponsive to the difference between said control voltage and the sum of said constant volta e and a voltage proportional to said reference voltage for controlling the operation of said motor.

18. In a control system for a pair of working electrodes between which current is flowing in the form of a working arc, the combination of a motor for controlling the spacing of said electrodes and means for controlling the operation of said motor comprising a pair of reference electrodes for sustaining the flow of alternating current 76 therebetween. means for supplying to-said referauscpra once electrodes an alternating current proportional to the current flow through said working electrodes, means connected with said reference electrodes for producing a reference voltage proportional to the voltage drop between said reference electrodes, and means responsive to the difl'erence above a predetermined value between the value of said reference voltage and the value of the voltage across said working electrodes for varying the magnitude of the voltage impressed on said motor.

19. In a control system for a pair of working electrodes between which alternating current is flowing in the form of a working arc, the combination of a motor for controlling the spacing of said electrodes, and means for controlling the operation of said motor comprising a pair of reference electrodes, means for supplying to said reference electrodes a rectified current component proportional to the current intensity through said working electrodes, means for producing a rectified voltage proportional to the voltage appearing across said working electrodes, and means responsive to the difference between the values of the voltage across said reference electrodes and of said rectified voltage for varying the magnitude of the voltage impressed on said motor.

20. In a control syst:m for a pair of electrodes between which current is flowing in the form of an arc, the combination of a motor for controlling the spacing of said electrodes, means responsive to the current flow through said electrodes for producing a reference voltage, means responsive to the voltage across said electrodes for producing a control voltage, means responsive to the speed of said motor for producing a stabilizing voltage having a polarity dependent upon the direction of rotation of said motor, and means responsive to the difference between said control voltage and the sum of said reference voltage 16 and said stabilizing voltage for controlling the operation of said motor.

21. In a control system for a pair of electrodes between which current is flowing in the form of an arc, the combination of a motor having an armature for controlling the spacing of said electrodes, means responsive to the current flow through said electrodes for producing a reference voltage, means responsive to the voltage across said electrodes for producing a control voltage, means responsive to the voltage of said armature for producing a stabilizing voltage having a polarity dependent upon the polarity of said armature voltage, and means responsive to the difference between said control voltage and the sum of said reference voltage and said stabilizing voltage for controlling the operation of said motor.

DIDIER JOURNEAUX.

REFERENCES orrnn The following references are of record in the me of this patent:

UNITED STATES PATENTS Name Date Sykes Oct. 2, 1917 Smith Nov. 27, 1934 Chapman Jan. 29, 1935 Blankenbuehler et a1. July 16, 1935 Fischer Sept. 20, 1938 Satterlee Oct. 4, 1938 Holslag Oct. 11. 1938 Kennedy et al. Jan. 24, 1939 Freudenhammer Mar. 11, 1941 Adenstedt et al June 17, 1941 Levy Oct. 21, 1941 Andrews July 27, 1943 Grabau Feb. 29, 1944 Reilly Apr. 30, 1946 Number

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