US2137299A - Electron discharge tube system - Google Patents

Description

Nov. 22, 1938. N. MINORSKY ELECTRON DISCHARGE TUBE SYSTEM Original Filed June 25, 1926 5 Sheets-Sheet l NICOLA! MINORSKY BY a;

ATTORNEY.

Nov. 22, 1938. N. MINORSKY 2,137,299

ELECTRON DISCHARGE TUBE SYSTEM Original Filed June 25, 1926 5 Sheets-Shet 2 INVENTOR. NICOLAI MINORSKY ATTORNEY.

Nov. 22, 1938. N. MINORSKY ELECTRON DISCHARGE TUBE SYSTEM Original Filed June 25, 1926 5 Sheets-Sheet 5 INVENTOR. NICOLAI MINORSKY BY 'MQ ATTORNEY.

Nov. 22, 1938. N. MINORSKY 2,137,299

' ELECTRON DISCHARGE TUBE SYSTEM Original Filed June 25, 1926 5 $heets$heet4 INVENTOR. NICOLAI MINORSKY ATTORNEY.

Nov. 22, 1938. N. MINORSKY 2,137,299

' ELECTRON DISCHARGE TUBE SYSTEM Original Filed June 25, 1926 .5 ShGQtS-Sheet 5 INVENTOR. NIC Al MINORSKY KMW ATTORNEY.

Patented Nov. 22, 1938 UNITED STATES PATENT OFFICE ELECTRON DISCHARGE TUBE SYSTEM Nicolai Minorsky, Paris, France, assignor to Radio Corporation of America, a corporation of Delaware 9 Claims.

This application is. a division of my copending application, Serial Number 118,508 filed June 25, 1926.

This invention relates to circuits employing electron discharge tubes, and more particularly to such systems for use with direct currents.

It has heretofore been proposed to employ the remarkable properties of such tubes in various ways, but very little progress has been made in 10 their use in direct current circuits, although theoretically, the applications of such tubes in this connection are very attractive, as the tubes would form inertialess relays with very high ohmic'resistance particularly adapting them for series operation in highly inductive circuits, with a low time constant and hence rapid control.

An especial difiiculty encountered with such systems was the necessity for many and very large grid batteries, which are difficult to adjust when several stages of amplification are used.

The present invention resulted from work designed toward eliminating diificulties inherent in former systems, and incidentally provides a tube system with entirely new properties differing from those of an ordinary amplifier. Under certain conditions, the system behaves abruptly,

similar to the action of an electric contact A resistance coupled amplifier circuit is pro- 4 vided having a plurality of electron discharge tubes, in which the tubes receive their space current and grid biasing potentials from a common direct current source, in such manner that the regulation of the tube circuits produces reactions from this common source and its associated elements upon the tube circuits themselves, whereby the cumulative or regenerative eifect is obtained.

A peculiar feature of this invention is the fact, as set forth above, that the tube system has the characteristic of acting, under certain circumstances, as an electric contact switch rather than in the usual continuous or gradual manner of electron discharge tube circuits: this is hereinafter termed the "contact efiect, as by it a discharge tube is associated with circuits in such discontinuous and instantaneous circuit-making and circuit-breaking performance may be produced, similar to the action of an electric contact switch. This phenomenon may be em ployed in controlling and regulating apparatus associated with such a circuit, whereby an in-- stantaneous and decisive action may be obtained at a predetermined and adjustable point, and substantial quiescence or continuity of action at other points. To this purpose, the circuits are provided to establish a single point of stability in the output of the system at each of a plurality of applied grid potentials, and these individual values for stability are separated by graph distances corresponding to a large space current variation in the tube as it passes from one grid potential difiering very little from the first.

This invention may be employed in conjunction with various electrical controlling systems,

in which a supervising instrument such as a bolometer, a thermostat or thermometer, a pressure gage, a Pitot or Venturi tube, a photoelectric cell, or other hydraulic, centrifugal, electrical, mechanical or optical device is employed to govern an electric circuit including a regulator such as a trip-out relay, voltage or current regulator for a direct or alternating current generator, speed controlling device, etc., wherebythe regulation is accomplished.

The invention is illustrated by way of example in the accompanying drawings, which demonstrate the circuits employable and several applications of the phenomena produced thereby, to the regulation of electrical machinery: but it will be understood that these illustrations are not limitations.

In' the drawings: Fig. I is a circuit diagram of the arrangement of a system according to the invention, having three three-electrode electron discharge tubes.

Fig. II is a graphic diagram of a phenomenon which may be produced in the circuit of Fig. I.

Fig. III is another graphic diagram illustrating the principle of the phenomenon.

Fig. IV is a further graphic diagram illustrating the result of the phenomenon when the circuit is associated with a regulator for an electric generator. 1

Fig. V is a circuit diagram similar to Fig. 1, with the tube system employed to regulate a direct current generator.

Fig. VI is a modification of the circuit shown in Fig. V.

Fig. VII is a circuit diagram of the application oi? the invention to the regulation of an alternating current generator.

Fig. VIII is a graphic diagram illustrating the rectifying and regulating effect of the apparatus shown in the diagram of Fig. Vfl.

Fig. IX is another circuit diagram of an arrangement similar to that of Fig. VII.

Fig. X is a circuit diagram resembling Fig. I, in which the speed of an electric motor is supervised and controlled.

Referring to Fig. I, the electron discharge tubes I, 2, 3 have the filamentary cathodes 4, 5, Ii; the grids I, 8, 9; and the anodes III, II, I2. The tubes I and 2 are preferably high amplification tubes, while the tube 3 is a power tube. The filaments 4, 5, 6 are heated by individual sources of electricity, such as the separate secondaries I3, I4, I5 of the transformer whose single primary winding 5| is connected to an alternating current supply main 50.

The potentiometer I! has the end terminals I6 and I8 across which is applied a direct current from a source of such energy, e. g., the generator IS. The cathodes or filaments 4, 5, 8 are connected respectively to the points I6, 20, 2i on this potentiometer by'the respective conductors 52, 53, 54 which, with the illustratedemployment of an alternating heating current, are connected .to the middle points of the secondary windings, I3, I4, I5. The filaments 4, 5, 6 are thereby maintained at negative potentials; filament 4 being at the negative potential of generator I9, while filaments 5 and 6 may have their potentials varied by sliding the contacts 20, 2I along the potentiometer I1. 1

The anode circuits of the tubes I, 2 are connected by wires 55, 56 through the respective fixed resistors 24, 25 to the points 22, 23 which represent sliding contacts on the potentiometer II.

The points 26, 21 intermediate the anodes III, II and the resistors 24, 25 are connected by wires 51, 58 to the grids 9, 9 of the succeeding tubes 2, 3 in their respective relations. The anode I2 of the tube 3 is connected by wire 59 through a coil 28 to the end point I9 of the potentiometer II which is at the positive potential of the generator I9. The coil 28 constitutes theoutput of the system, and may be the field coil of an exciter, the trip coil of a relay, etc:

The staggering of points I5, 20, 22, 2| with regard to each other eliminates the necessity of having biasing batteries, but requires the use of separate sources or heating current.

The grid 1 of the tube I is connected to a terminal 29; and the input potential for the system is applied between points I5 and 29. In order. to explain the operation of the system for the con-' tact effect, these points are shown with the electromotive force of a battery 30 applied across them, as regulated by the potentiometer 3|. since generally the grid I must be biased 'at a certain negative potential with respect to the point I6 or the filament 4. The potential applied across points 29 and I6, by slight variation at the critical condition of the system, produces the phenomenon of the contact eflect, and this potential will therefore be hereinafter called the trigger voltage.

I The tube I is normally at the potential diii'erence between points 22 and It on the potentiom-' eter II; the tube 2 at the potential difi'erence between points 23 and 20; and the tube! at the potential difierence between points I8 and 2|. These potential differences 22-48, 232l, ll-2I are staggered with respect to each other by the amounts corresponding to the potential drops across the overlaps 20I8, 2I20, respectively. By moving the sliding contacts, it is possible to so control these differences as to eliminate the necessity for grid biasing batteries between point 25 and the grid 8 on the one hand, and between point 21 and the grid 9 on the other.

If desired, the current from the generator or source I9 may be kept constant by a ballast device I9a of well known type.

The system shown in Fig. I may be operated in any one of three ways: (1) as a resistancecoupled amplifier; (2) as a regenerative amplifier; (3) as a contact eilect" device, with selfexcitation: which will now be individually described.

1. In this case, the elements of the system are so adjusted that the current through the potentiometer I1 is much greater than the space currents in the tubes themselves. The tubes I, 2 are voltage amplifier tubes and their internal resistance is very high, so that the plate currents therein are generally negligible as compared to the plate current of the power tube 3, which itself must be negligible as compared to the current flowing through the potentiometer II: in such event, changes in the several plate currents, or in any of them, will not cause any apprciable change in the distribution or current along the potentiometer.

In an actual test, the potentiometer II had a total resistance of about 350 ohms; the generator I9 delivered a steady potential difference of about 350 volts. The tubes I and 2 were Western Electric type l02-D tubes, and tube 3 was a Western Electric 101D power tube. The plate resistors 24 and 25 were each oi about 200,000 ohms. The tube I worked under the potential difference between I5 and 22, and tube 2 under that between 20 and 23, which were staggered so that the controlling point 29 of tube I was about 1%; volts below the potential of the filament (point 20) or the second tube, which corresponds approximately to the middle point of the rectilinear part of its characteristic. The alternating current mains 50 where fed by 110 volts, cycle current, Thus the plate currents in tubes l and 2 may be of the order of 1 mllliampereor less; the plate current in tube 3 of the order of 20-30 milliamperes; and the potentiometer current 1 ampere.

Assuming that the potential of the grid 1 of tube I is increased by a small amount in any way, e. g., by moving the sliding contact of the potentiometer 3|; the increased potential of the grid I will cause an increased space current to flow between filament 4 and anode ll of the tube I, with a resultant decrease or the potential of the point 25 and at the grid l of the tube 2. The space current in the tube 2 will decrease, so that a correspondingly increased potential will be applied at point 21 and the grid 9 of the tube I.

that the initial point of performance is approxi- 7 mately at the middle of the rectilinear portion of the characteristic curve of the respective tube. When the points 20, 22, 23 are once adjusted, their potentials remain constant and no further adjustment is needed: the system works as a very stable and reliable amplifier whose amplification may readily be calculated in the known way.

2. If the plate current variations of the power tube 3 are approximately of the same order of magnitude as the current flowing through the potentiometer, for example the current through the potentiometer being about one hundred milliamperes and the plate current variations of the tube 3 around 20-50 milliamperes, the tube 3 constitutes a variable resistance connected in parallel with the section 2I--I8 of the potentiometer ll. Then, by Kirschoffs laws, for the parallel resistances (tube 3 and section 2I |8) in series with the section 2|--I6 of the potentiometer, a decreased resistance of the tube 3 will cause an increase of the current flowing between points l6 and 2|, so that the potential at point 2| increases in proportion. Likewise, the potentials of points 20 and 22 increase and the potential difference between points 2| and i8 decreases, in proportion. This redistribution along the potentiometer causes important reactions upon the tubes in the system.

Firstly, the effect of variation in the plate current in tubes I and 2 upon the potential and current distribution along the-potentiometer I! -may be neglected, as in a practical case these variations were of the order of 0.5 milliampere or less, whereas the potentiometer current was 100 milliamperes, and the fluctuations of the power tube 3 was about 50 milliamperes, and hence the re-distribution of currents and voltages is due solely to the variable conductance of the tube 3.

Secondly, the potential of the grid 1 is made slightly more'positive than before. The space current in the tubes l and 3 increases, and in the tube 2 decreases. The increased conductance of the tube 3 causes the re-distribution of potentials indicated above, and the potentials of the points 20, 2|, 22 become more positive. The filament 5 is connected to point 20, and its potential is accordingly increased. The space current in tube 2 therefore decreases because (1) the grid potential becomes more negative, and (2) the filament potential becomes more positive. This constitutes a distinctive feature of the invention and contributes to produce a greater increase by amplification than is the case when the potential of the filament remains constant, and gives the regenerative effect, since the filament potential of the tube 2 depends on the current flowing in the succeeding tube. The opposite effect is obtained in the tube 3, so that when the potential of the grid 9 increases, the potential of the filament 6 also increases, so that the amplification in the tube 3 is slightly decreased. The final effect when three tubes are employed, as shown in Fig. I, is a gain of amplification because the gain in the tube 2 considerably outweighs the loss in the tube 3. The first tube is not in such case affected by the regeneration, as its filament 4 is maintained at the fixed potential of the point Hi. In case more than three tubes be connected in a similar manner, there will always be a gain of amplification, since the regenerative effect in each subsequent tube will be less than that in the preceding tube, and there is always a gain in the second tube where the regenerative effect first appears: and the same gain of amplification is obtained if only two tubes be employed, the second being a power tube, although the result is not then so apparent as with three tubes.

3. The third method of operation is the most important, and constitutes an entirely new method of employing electron discharge tubes with associated circuits. This method is a further development of the second, in which the amount of regeneration is increased above a certain critical value, whereby the performance of the system becomes abrupt and discontinuous; there is a substantially instantaneous passage from a condition at which a certain amount of plate current fiows through the output coil to a condition at which a widely difi'erent amount flows, and this passage is provoked by a very small change of the applied potential. These amounts of current remain fairly constant when the applied potential departs in the respective direction from this critical value. The abrupt efiect greatly resembles that of a contact switch in making or breaking a circuit: and hence is called the contact effect. It usually occurs at substantially the same critical value whether the input potential is increasing or decreasing in value;

This is represented by the graphic diagram of II in which the plate current in tube 3 and the applied grid potential on tube I are plotted as coordinates. If the grid potential on tube I be originally negative, and be steadily increased from a value A to a critical value B, the plate current in the tube 3 changes but very little in passing from the value K to the value N. A discontinuity however occurs at the critical value B, so that a further increase of grid potential in the tube causes the plate current in tube 3 to jump abruptly from the value N to the value M, which generally is that of the saturation current in the tube 3. A further increase of applied grid potential on tube- I to the value C produces substantially no further change of the plate current in passing from the point M to the point Q.

When the applied grid potential on tube l is decreased from an initial value C, an inverse action occurs. As the potential approaches a critical value B which is very close to the critical value B With an increasing grid potential, the plate current abruptly drops from the value M which is substantially equal to the value Q, to a Value N. A further decrease of grid potential from the value B to the value A produces substantially no further change of the current. The points M, M and N, N are very close together, and respectively represent substantially the same current values. In practice, it has been found possible to make the zone B-B very narrow, and its position within the range AC may be varied at will.

In an actual instance; this potential diiference was varied from 5 to 2030 millivolts, and in one particular instance was reduced to 0.1 millivolt; with a plate current variation in the last stage of about -40 milliamperes in each case. The potentiometer I! had a resistance of about 3500 ohms, resistors24, 25 about 200,000 ohms each, and the gid bias potentials were about 1 /2 volts as before. The phenomenon is very erratic when the grid potential lies between B and B: there is no actual grid control and the plate current moves from high to low value upon the occurrence of extremely slight changes.

The slightest increase at B or decrease at B acts as a trigger to release the contact eifect".

, strictly identical point of the grid voltage of the first tube.

This contact eiIect appears to require no spontaneous alternating current self-excitation, though of the same nature as the self excitation of a shunt-wound direct current generator.

When a generating and a receiving circuit exchange energy, theequilibrium may be defined as stable when a small departure of the system from this equilibrium position disappears spontaneously in the course of time if the system is left to itself. The Kaufman criterion (Ann. d. Phys. (4) 2, 158, 1900) may be phrased: The equilibrium of an electric system is stable when the slope of the tangent to the characteristic of the receiver at the point of equilibrium is greater than the corresponding slope for the generator:

and is unstable in the opposite case.

In Fig. III, the curve G is plotted from the plate current Lip and the grid voltage V; of the tube 3 of Fig. I; and the straight line P represents the effect of the reaction to the potentiometer due to the variation of the plate current in the tube 3. This variation appears as explained above as a variation of the filament potential of tube 3, i. e., as an equivalent opposite variation of the grid potential of this tube, and can therefore be represented on the same diagram as the characteristic curve G of this tube. In this case G is the generator curve, and P1 and P: the receiver curves: at N, the slope of G is less than the slope of P1, and the system is stable, and the same is true at M with respect to P2.

The theory shows that for a variation of the grid potential of tube I there. is a displacement of the straight line substantially parallel to itself from P to P Line P intersects the curve G only at the point N, while line P intersects it only at the point M: these points N andM in Fig. III correspond to those in Fig. II. Although generally lines P and P are curved instead of straight, the same remarks hold: and the maximum sharpness occurs when the shapes of the curves P, P are substantially identical with the shape of the curve G, in which case it is suiilcient to give the slightest change at B or B in Fig. II to the grid potential of tube I to release the phenomenon through the whole range from N to M in Fig. 111, or vice versa.

The tubes 2 and 3 therefore have a mutual controlling action upon each other; when one is a maximum, the other is at a minimum and vice versa. In practice, it is preferable to have one or the other at a saturation value at alltirnes. When tube 2 is at saturation, the tube 3, with its opposite characteristic in the circuit system of the present invention, is delivering a constant current of minimum value (l. e., the graph from K to N in Fig. II) and when tube 3 is at saturation, (graph from M to Q in Fig. II) its reaction upon tube 2 reduces the current in this latter tube to a minimum. Hence the values of current output from tube 3 are dependent upon the saturation currents in tubes 2 and 3, and are substan: tially constant at a maximum or a minimum.

The "contact effect therefore occurs where the electron discharge tube is associated with circuits which afford at two widely separated positions stable current equilibrium separated by a zone of instability, and whereby the passage from one position to the other is accomplished by means of a very small variation of applied potential, which displaces the receiver curve from its position P determining current stability at the value N to the position P determining such stability at value M.

It may be stated that oscillograms show that the time for passage from N'or M or from M to N is of the order of one two-thousandth of a second.

The above description of the circuit arrangements of the electron discharge tubes demonstrate the method of obtaining the .contact effect, and hereinafter a number of applications of this contact effect to the regulation and control of mechanisms will be described.

Fig. V represents the application of this contact effect to the voltage regulation of a direct current generator 34. The electron discharge tube system and its circuits have the same reference characters in Fig. I, and theoutput of the last tube 3 passes through the coil 28 which in this instance is the field coil of a direct current exciter 35 which is connected by the conductors 60 with the auxiliary field 36a of the generator 34. It will be understood that the generator 34 may have the customary main fields 36. The control winding 36a has a sufficient value in ampere-turns to counteract the effect of the armature reaction in the generator 34 during the regulation. Connected in parallel across the generator terminals 38, 39 is a source of reference voltage 31 such as a battery whose voltage may be maintained very nearly constant, and the purpose of which is to determine the magnitude of the voltage to be maintained by the generator 34 at all loads. The negative terminal of the source 31 is connected to the negative terminal 38 of the generator 34;

and the positive terminal of the source 31 is connected to the grid 1 of the tube I, while the end terminal l6 of the potentiometer I1 is connected by a conductor 6| with the positive terminal 39 of the generator 34. It is preferred to connect a small regulating battery in shunt of a potentiometer 3| in the circuit between the reference battery 31 and the grid 1 of the tube, so that the exact potential of the batteries 31 and 30 may be closely regulated. The load onthe generator 34 is conventionally represented by the lamps 42. The operation of this voltage regulating system is as follows: 3

Assuming that initia1ly the generator is at a condition of no load and that its terminal voltage is exactly equal to the electromotive force of the source 31. The potentiometer 3| for this particular position must be adjusted so as to impress upon the grid 1 of the tube l a potential slightly more negative than that corresponding to the point B in Fig. II. The voltages of the generator 34 and of the reference source 31- annul each other under this condition of operation. The current fiowingin the coil 28 is therefore either zero or very small, and is represented by the value N in Fig. II. Therefore the exciter 35 under such condition delivers substantially nocurrent through the auxiliary winding 36a, and the voltage of the generator 34 is determined by the main winding 35.

If a load 42 is placed upon the generator, its terminal voltage decreases and no longer 'annuls the effect of the reference battery 31: the grid voltage of the tube I increases accordingly and go s beyond the critical value B in Fig. II. In passing the value B the plate current abruptly jumps from the value N to the value M, releasing the transient: in this way, the plate current of the tube 3 flowing through'the output coil 28 is suddenly increased in value, whereby the exciter 35 will deliver current through the conductor 60 and the auxiliary Winding 36a of the generator 34, with a resultant increase in the voltage from the generator. As this generator voltage increases, it will restore the mains to the initial condition of predetermined constant voltage. On

the other hand, when the voltage of the generator increases in proportion to the reference voltage until they are equal to each other again, which is equivalent to the decrease of the applied grid voltage on tube I from C to beyond B in Fig. II, the reverse phenomenon occurs and the current flowing through coil 28 now drops from the value M to the value N, so that the auxiliary winding 36a no longer receives current from the exciter 35, and the generator again is excited by its main winding 36 alone.

This action resembles that of a Tirril regulator of the well known type employing vibrating switch contacts: oscillation will usually occur in the same manner as with this device. Such oscillation is represented in Fig. IV, in which the upper graph a represents the fluctuation of the current through the coil 28 and the middle graph 2) represents the corresponding fluctuation of the voltage across the generator terminals while the lower graph 0 represents the load on the generator. If at a certain instant S, the generators output increases from In to h, the plate current through the coil 28 will remain at its maximum value for a slightly longer time than at its minimum" value, but the voltage E of the generator will maintain substantially the same value as before, with but a slight minimum fluctuation. If at a time T, the load is increased to a greater value 12, at which the current through the coil 28 continues, this particular value. l2 of generator currents corresponds to the maximum range of the regulator, beyond which it cannot maintain a constant voltage E across thegenerator terminals. If at a certain time U, the load on the generator is further increased to the value la, the regulator cannot deliver a greater excitation than for the current value l2, and a drop of voltage across the generator, begins at this point.

The regulator thus has a well defined range which varies according to the constructional dimensions given the parts, and may be made adequate for any particular purpose.

It is apparent that the connections shown on Fig. V between the positive terminal of the generator 34 and the filament 4 on the one hand, and between the positive terminal of the source of reference voltage 31 and the grid 1 on the other hand may be reversed with regard to each other if the connections of the auxiliary field winding 36a be reversed with regard to the terminals of the exciter 35. In a similar manner, the condition represented on Fig. IV may be modified in various ways, and for example, its performance shown at the left from the point S may be made to correspond to the full load condition, and its performance represented between the points T and U will correspond to the position of no load; in which case the action of the coil 36a must be differential with respect to that of the main field winding 36 of the generator 34.

Many other connections and combinations of the above described elements are of course possible without departing from the general method of regulation shown in Fig. IV. Instead of ob- 20 along the potentiometer.

taining the reference voltage from a separate source as the battery 31, it is possible to obtain it from the potentiometer I! as shown in the diagram of Fig. VI. In this only two tubes are employed representing the second and third tubes in the circuit of Fig. I. The filament 5 of tube 2 is shown in Fig. VI as being connected to a point 20, which is separated from the negative terminal l6 of the potentiometer I! to obtain a potential difference equal to the ohmic drop between these two points. The negative terminal 38 of the generator 34 is connected to the point l6, and the positive terminal 39 to the grid 8 of the tube 2 by a conductor 62. The potential difference between the points I6 and 20, will maintain the grid potential of tube 2 normally while the terminal voltage to the generator 34 supplies the small voltage necessary to counteract this and to produce the potential at which the contact effect is released. In this case, the

potential difference between the points l6 and 20 will act as the reference voltage, and an adjustment thereof may be made by sliding contact The method of operation of the circuit in Fig. VI is therefore as follows:

Assume that initially the generator voltage 3839 is slightly below the critical voltage B at which the contact eifect is released in the system formed by the devices 2 and 3. If the voltage of the generator 34 increases, the potential of the grid 8 of the tube 2 will be increased and the contact effect" will be released, the current jumps to the full saturation value in tube 2, and for reasons previously explained, the current in the tube 3 will drop abruptly to a low value and cut down the field of the exciter 35 as in Fig. V, and thus diminish the excitation of the auxiliary field 36a of the generator 34. As soon as the voltage of the-generator 34 decreases by a very small amount, the effect is produced in the opposite direction. The equilibrium at this point of given voltage will thus be dynamical as in the above case, although an arrangement according to the diagram of Fig. VI will be less sensitive than that of Fig. V, since not only is a lesser number of stages employed but also the potential of the filament of tube 2 (point 20, on the potentiometer l'l) increases at the same time that the plate potential is increasing, and vice versa; it is, however, sufficient for practical industrial purposes.

It is possible to obtain the utmost precision of voltage regulation with the employment of an additional tube l in front of tube 2, according to the general diagram shown in Fig. VI. For this purpose, the arrangement is made specifically the same as in Fig. 1, except that the staggering ofthe potentials between the points l6 and 20 will occur as in Fig. VI.

Fig. VII shows another example for the voltage regulation by an alternator 34 utilizing the same principle of the contact effect. The load 42 is supposed to be balanced between the phases, as is usually the case, so that it is sufficient to regulate the voltage of only one phase. A small potential transformer, with a primary winding 40' connected across one phase of the alternator, has a secondary 40" connected at one terminal to the point N5 of the potentiometer l1, the other end of this transformer secondary being connected to the grid 1 of the vacuum tube l which in this instance operates as a rectifier since suitable negative bias is obtained on the grid of this tube by the potential difference between the points 16 and iii of the potentiometer I1; in order to obtain with the coupling resistor 24, which is connected at each end by the condensers 42, 43 with the terminal l E. The remaining elements are connected exactly as before, and the performance and,.operation may be explained in connection with Fig.

VIII, in which E represents the dynamic curve of tube l corresponding to the given impedance, and the sinusoidal curve K represents the normal electromotive force induced in the secondary 40" of the transformer. The point L from the zero point 0 of the graph represents the potential drop between points 16 and lfi' of the potentiometer it. The wave K produces a rectified wave is which is smoothed out by the filter system so as to obtain a practically steady direct current of amplitude Io which passes to the resistor 24 and the potential of the point 26 differs from that of point 22 by the ohmic drop of this current along the resistor 24. The potential of the point 26 is therefore substantially constant, and varies only with corresponding variations in the potential wave K. If the potential at the generator rises to the new value K on Fig. VIII, a new rectified wave k is produced which in turn is smoothed out by the filter system so as to obtain the direct current of amplitude I through the resistor 24. If the constants of the circuits of the several tubes are properly proportioned, as

set forth above, this rise of potential will release the contact eifect or transient as before: and again a very small change in the amplitude of .the potential wave at the generator will produce a very great change in the current output of the system, and this occurs at a very fixed and constant point of the operation when once established. A steady voltage is therefore maintained across the alternator terminals in spite of any fluctuations of the load.

In Fig. IX, such a system is employed to control the excitation of a three-phase alternator in accordance with the condition of the loads upon all three phases. In this case the voltage regulating transformer has the primary phase windings 40 40 40 associated with the respective secondary phase windings 40, 40 40 which are each coupled to the grid of a respective tube I l I The filaments of these tubes are supplied in multiple with current from the secondary winding i3 of a transformer with its primary 5i connected to a source 50. The middle point of winding I3 is connected as before to a point [6' on the potentiometer H, so that the control potential is determined by the drop along the potentiometer I? from point 16 to point [8. The tubes I l i act as rectifiers, and the current passing through each of them is smoothed out by the choke coils 4 l 41 4 l, and the bypass condensers 70 10 10 for the respective tubes, and the condenser H for the common output. It is preferred to connect this common output through a further choke coil to the grid of the tube 2 in a manner similar to that described heretofore. The neutral point of the secondary windings 40 40, 40 is connected to the negative terminal I6 of the potentiometer. The operation is substantially the same as before, and the potential at the common output point 26 of the tubes I, I P controls the rest of the system. The other connections are the same as before. 1

While the foregoing illustrations have shown the employment of such a system for regulating output potentials in generators, it must be understoodthat many other uses are possible. For example, in Fig. X is shown a system employed for the speed regulation of an electric motor 80. The field coil 8| of this motor is its normal shunt coil, while coil 28 is the output coil of the tube 3 of the system, and is an auxiliary field winding for the motor. A small tachometer generator 82, preferably of the magneto type to assure a constant magnetic field intensity is positively driven from the motor 80 as shown by the mechanical connection 83, the voltage produced 1 by the generator 82 is a function of its speed, and

i. e., the contact effect".

Although specific examples of the arrangement and connection of the various parts, and dimensions thereof, are given by way of examples which have been found operative in practice, yet it will be recognized that the invention is not limited to these illustrations, but may be modified within the scope of the appended claims. What I claim is: 1. In a potential regulator for a generator having a field including an electron discharge tube system including a plurality of such tubes connected in cascade, means for establishing two separated points of equilibrium for said system corresponding to input potential variations thereon, means to apply an input potential upon said system to cause said system to operate at one of said points of equilibrium, means responsive to potential changes at said generator to modify said inputv potential whereby to cause said system to operate at said other point of equilibrium, and means controlled by the currents delivered by said system under said alternative conditions to vary the excitation of the field winding.

2. In a potential regulator for an electric generator having a field winding, an electron discharge system including aplurality of such tubes,

circuit connections between said tubes whereby one of said tubes is saturated at a low current intensity at a predetermined value of the output potential of said generator and another of said tubes is coupled to said first tube to deliver a low output current under such saturation condition in latter connections between said tubes whereby said second tube is saturated and delivers a high current intensity into its output at a diifering output potential of said generator, and means whereby the variation of current intensity in the output of said second tube modifies the field excitation of said generator.

3. In a potential regulator for an electric generator, said generator having a main field winding and an auxiliary field winding, an exciter connected to said auxiliary field winding, an

electron discharge system comprising a plurality generator, circuit connections between said tubes whereby a predetermined difference between said grid potential and said proportional potential shall cause an abrupt increase in the output current of said system, and means whereby said output current will vary the excitation of said exciter.

4. In a potential regulator for an electric generator, an electron discharge system including a plurality of electron discharge tubes connected directly and successively from plate to grid, means to impose a grid potential upon the first tube of said system with respect to its filament, a potentiometer, a source of direct current connected to said potentiometer, a connection between the negative end of said potentiometer to the cathode of said first tube, connections between said tubes and said potentiometer whereby said tubes shall derive their space current and grid bias from said potentiometer, means for heating the individual filaments of said tubes, and output conductors from the plate of such tube to the positive terminal of said potentiometer, and means included in said output conductor to accomplish a variation in the excitation of said generator.

5. In a potential regulator for an electric generator, a potentiometer, a source of direct current connected to said potentiometer, a pluralityof electron discharge tubes connected successively-from plate to grid, means for imposing between the grid of the first tube of said plurality and the negative end of said potentiometer a potential proportional to the output potential of said generator, taps on said potentiometer and conductors leading therefrom to the filaments, grids and plates of the discharge tubes whereby to deliver thereto bias potentials and space currents, and an output conductor connected to the last tube of said plurality and to the positive end of said potentiometer, and means included in said output conductor to vary the field excitation of said generator.

6. In a potential regulator for an electric generator device having a field winding, an electron discharge tube system including a plurality of.

tubes, circuit connections between said tubes whereby one of said tubes is saturated at a low current intensity at a predetermined value of the output potential of said electric generator device andanother of said tubes is coupledto said first tube to deliver a low output current under into its output circuit at a differing output potential of said generator, a direct current exciter connected to said field winding and having a potential regulating coil connected in the output circuit of said second tube.

'7. Means for controlling the output voltage of an electrical device having a field winding comprising in combination, a plurality of electron discharge tubes each having a cathode, grid and plate, means for directly coupling the plate of the first tubeto the grid of the second tube, circuit connections from the output terminals of said device to the cathode and grid respectively of the first tube, a source of alternating current, means for heating the filaments of said tubes with energy from said source, a source of direct current voltage connected to said field windin and means for controlling the voltage generated by said voltage source in response to the plate current of the second of said tubes.

8. In combination with a polyphase alternating current generator having a field winding, a rectifier having input and output circuits, means coupling said rectifier input circuit to the output terminals of said generator, a filter circuit coupled to the output circuit of said rectifier, and means for controlling the current through said field winding in response to variations in the current transmitted through said filter circuit.

9. A voltage regulator adapted to control the voltage applied to an electrical device from a voltage source comprising, an electron discharge tube system including a plurality of electron discharge tubes connected in cascade, said system being provided with an input circuit and an output circuit, means for establishing two separated points of equilibrium for said system corresponding to input potential variations thereon, means to apply an input potential upon the input of said system to cause the system to operate at one of said points of equilibrium, means responsive to potential changes of the voltage source to modify said input potential and thereby causesaid system to operate at the other point of equilibrium and means controlled by the output currents delivered by said system under said alternative conditions to control the voltage applied to the electrical device.

NICOLAI MINORSKY.

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