US2027312A - Magnetic amplifying and control system - Google Patents

Description

MAGNETIC AMPLIFYING AND CONTROL SYSTEM Filed July 23, 1954 I 2 Sheets-Sheet l 4 6 5 7 b 19 CURRENT //v 5 CURRENT //v 5 INVENTOR Ola/v; 83W

Jan. 7, 1936. A. FITZ GERALD 2,027,312

MAGNETIC AMPLIFYING AND CONTROL SYSTEM Filed July 25, 1954 2 Sheets-Sheet 2 INVENTOR Patented Jan. 7, 1936 PATENT OFFICE MAGNETIC AMPLIFYING AND CONTROL SYSTEM Alan S. Fitz Gerald, Wynnewood, Pa. Application July 23, 1934, Serial No. 736,558

27 Claims.

This invention relates to magnetic amplifiers and more particularly to electric relay and control systems which employ saturating reactors, such as, for example, apparatus of the general type I have described in my co-pending application, Serial No. 676,785, filed June 21, 1933.

In general my invention provides improved circuits and methods whereby the sensitivity of such systems is greatly increased, and in which responsive action of greater variety, scope, and selectivity, is achieved.

It is accordingly an object of my invention to provide a greater gain per stage than hitherto possible.

It is a further object of my invention to provide a magnetic amplifying system which is responsive to lower minimum input power level than hitherto.

It is. yet another object of my invention to provide a polarized saturating reactor system, that is, a system selectively responsive in accordance with the polarity of the input energy.

It is a still further object of my invention to provide an electric control and amplifying system having control characteristics analogous to those of a latched-in type of electric relay or circuit-breaker. By this is meant a control system capable of energizing, or substantially deenergizing, a load circuit, selectively, in accordance with a momentarily applied control eifect, the condition of energization or substantial deenergization, respectively, being maintained indefinitely after said control efiect is withdrawn.

It is yet another object of my invention to provide an electric control and amplifying system having "pre-setting control characteristics. By this is meant a control system which, when it is connected to a source of power, '5 capable of energizing, or maintaining in a substantially de-energized condition, a load circuit, selectively, in accordance with a control effect momentarily applied, and withdrawn, at any time prior to the connection of the control system to the source.

It is still another object of my invention to provide a saturating reactor control and amplifying system operating with time delay action.

These and other novel features which I believe to be characteristic of my invention will be set forth with particularity in the appended claims. My invention itself, however, both as to its organization and method of operation, together with further objects and advantages thereof, may best be understood with reference to the following description taken in connection with the accompanying drawings, in which:

Figure 1 is an electric circuit diagram representing an embodiment of my invention;

Figure 2 is a diagrammatic illustration of one type of saturable core device to which my invention pertains;

Figures 3, 4, 5, and 6 are curves to illustrate the operation of my invention;

Figure 7 is an electric circuit diagram of another embodiment of my invention, and;

Figures 8, 9, and 10 are electric circuit diagrams of modifications of the embodiment of my invention illustrated in Figure '7.

Referring now more particularly to Fig. 1 of the drawings, there is illustrated a system utilizing the magnetic amplifier of my invention to control the energization of a load circuit I from an alternating current supply circuit 8. The circuit I may be connected directly to a power consuming device such as a motor II, or to the input of a further stage of amplification as shown in Fig. 7. This apparatus includes a saturable reactor comprising a. magnetic core I having an alternating current or impedance winding 2 and three direct current saturating windings 3, 4 and 5. The structural configuration of the core I and the disposition thereon of the several windings may be in accordance with any of the several well-known types of saturable reactors of the prior art, although I have illustrated in Fig. 2 the general proportions of the core I, together with the arrangement thereon of the windings which I have found to be particularly satisfactory for the practicing of my invention.

As shown in the figures, the alternating or impedance winding 2 comprises two sections connected in parallel and arranged on adjacent limbs of the core I. The parallel-connected sections of winding 2 are energized from the supply circuit 8 through a. disconnecting switch l0 and, if desired, a voltage-ratio determining transformer 9. The saturating winding 3 of the core I is energized with a uni-directional current variable in accordance with the current in the winding 2, as by means of a full wave rectifier 6, the alternating current side of which is connected in series with the winding 2 while the direct current side is connected to the winding 3. The load circuit 1 may be energized in series with the winding 2 or, in case it is to be energized with direct current, in series with the winding 3, as illustrated.

The saturating winding 4 of the core I represents the main direct-current saturating or input winding of the magnetic amplifier and may be energized from any suitable source of control potential, preferably reversible in polarity and adjustable in magnitude. As illustrated, this winding 4 is connected to be energized, through an adjustable resistor I2, from a battery I3 tapped at a midpoint, together with keys I4 and I5, by means of which the winding 4 may be selectively energizedfrom either section of the battery I3 with positive or negative excitation. By positive excitation is meant that which is additive with respect to the magnetomotive force of the winding 3, while, obviously, negative excitation is that of an opposite sense.

The winding 5 is adjustably energized from any convenient source of direct current, preferably, as illustrated, by means of a rectifier I6, supplied from the source 8, through adjustable resistor I1. As indicated in the drawings, the relative polarity of the windings 3 and 5 should be such that the magnetomotive i'orcesdue to these windings are in opposition.

In describing the action of this circuit it will be best first to assume that the current flowing in winding 5 is zero, and to describe the action of the circuit without taking winding 5 into account. The manner in which the current in winding 5, in Figure 1, modifies the action of the circuit, will then later be described.

In order to explain the operation of the circuit it will be necessary to consider the magnetizing action, of the various windings, on the core I, and this effect is best illustrated by a series of curves.

I show therefore in Figure 3 a curve A which represents the basic saturation curve of the alternating current magnetic circuit in the core I, namely, the two short middle limbs. For the purpose of this curve it is assumed that the alternating. voltage of the source 8 may be varied and applied to the winding 2 in series with the rectifier 6, the winding 3 being omitted and the resistance of I being assumed negligible. Figure 3 therefore shows the relation between the direct current output of 6 and the applied alternating voltage. this curve therefore consists of a simple saturation curve of the two middle limbs of I with the magnetizing current as read by an ammeter of the rectifying type. Figure 3, therefore, is a curve of familiar form characteristic of the metal of which the core I is constructed.

The second curve B'in Figure 3 will be referred to later.

Figure 4 shows further curves, again showing the relation between the applied alternating voltage and the current in I; this time with the winding 3 present and connected as shown in the diagram.

It will be seen on referring to Figure 4 that two curves are shown, a curve C and a curve D.

The feature of unusual interest about the circuit shown in Figure 1 is that It can be caused to function in accordance with either of the curves C or D without any change in structure or connection. v

At one time, if the voltage be increased from zero upwards the current in I will be found to increase rapidly in accordance with the curve C. At another time, on applying the alternating voltage and gradually increasing it, only a very small current according to curve D will be found in the circuit I. However, if the alternating voltage be steadily increased a pointVi on the curve will be found. At this point the circuit becomes unstable and the electrical conditions in the cir- It will be immediately apparent that I cuit are suddenly transferred from curve D to curve C.

I have ascertained that this duality of action is not a random effect but can readily be predetermined. Furthermore, it can be pre-determined by an extremely small amount of electrical energy relative to the power level in the circuit I.

I have found that, when the circuit is energized by applying a gradually increasing alternating l0 rent, I1, in accordance with curve C willfiow in 20 the circuit 1. If, on the other hand, the circuit has elected tofollow curve D, a low current of I2 will be found in the circuit I, and each time the voltage V2 is applied a current of value I:

will flow, if no extraneous controlling effects are introduced. I

If, now, the winding 4 be energized by means of one or other of the keys I4, I5, I have found that the following interesting action results. With a voltage V2, if it be assumed by hypothesis that Q the higher value of current Ii. flows in the circuit I, closing the key I4 will produce no significant result but pressing the key l5 will cause the current in I to be reduced from the value I1 to the value I2. However, when the key is released the 35 value I2 persists. If, now, the circuit be de-energized, by withdrawing the voltage V2, and then subsequently the voltage be re-applied any number of times, current of the value I2 will, on each occasion, flow in the circuit. If, while this current is flowing the key I5 bev depressed, no appreciable effect will be observed, but if the key I4 be depressed the current in 1 will suddenly change from curve D to curve C, a current of value I1 being given instead of 12. Again,"no'matter how 45 often the circuit be de-energized by withdrawing the alternating voltage V2, each time V2 is applied, the curve C value of current I1, will flow.

On referring to the diagram it will be observed that, when key I4 is depressed, the winding 4 is 50 excited with direct current of such polarity that the magnetizing effect upon the core I is in the same direction as the effect of winding 3, whereas, when key I5 is depressed winding 4 is energized with the opposite polarity so that its mag- 55 netizing efiect opposes that of the winding 3. Thus, when the circuit is functioning in accordance with curve C, the winding 4 has no efiect when it is energized so as to assist winding 3, but, when it is energized with the opposite polari- 60 ty, so as to oppose winding 3, it causes the circuit to transfer from curve C to curve D. Likewise when the circuit is functioning in accordance with curve D, winding 4 has no effect if it is energized so as to oppose the action of 3, but if it be energized so that the effects of 3 and 4 are additive, the characteristic performance of the circuit is abruptly transferred from curve D to curve C.

It is therefore seen that this circuit has the interesting and important feature that it responds selectively in accordance with the polarity of the saturating current applied to the reactor.

One of the limitations of saturating reactor systems hitherto known and available has been '5 their inabilityto distinguish between positive and negative polarity of. the saturating current.

Furthermore, not only does this circuit respond selectively in accordance with the polarity, but the response thereto is in the first place extremely positive and in the second place unusually sensitive. The change in current value from I1 to I: represents a change of considerable magnitude. Thus the diilference between the power delivered to the circuit I when key I4 is pressed, and the power furnished when key I5 is actuated, is a substantial amount. Nevertheless, the amount of power, applied to winding 4, necessary positively to bring about this change in either direction is extremely small. Substantially less than 1 milliwatt developed in winding 4 will control several watts output.

However, not only will energization of the winding 4, while current is flowing in 1, cause this current to be increased or decreased in accordance with the polarity of the input current; I have found that excitation of the winding 4 may pre-determine the action of the circuit.

Thus if the circuit be disconnected from the source 8 by means of the switch I0 and if the key l4 be depressed momentarily, and the circuit be connected to the source at any time after the key has been released, the high value of current 11 will flow in the circuit. No matter how often the circuit be disconnected and reconnected to the source 8, I1 will fiow each time, if neither of the keys is depressed.

If, however, while the circuit is de-energized, the key i5 be depressed the next time the circuit is energized I: will flow instead of I1. As before, disconnection and reconnection to the source 8 will have no efiect upon the pre-disposition oi the circuit to function in accordance with curve D instead of curve C.

The above remarks, it should be noted, apply to the action of the circuit when the applied voltage V2 does not exceed the critical value V1 at which curve D reverts to curve C. I have studied the conditions which determine the value of this critical voltage V1, and have found that up to a maximum value of V1, above which the curve D cannot persist, the value of the critical voltage depends upon the intensity of the magnetizing efiect of the winding 4. With very weak currents applied to 4, curve D reverts to curve C at substantially lower values than that shown in Figure 4. With all values of energize.- tion of winding 4 above a clearly defined magnitude the critical voltage V1 remains substantially constant.

I have further found that when a controlling excitation is applied to the winding 4 so as to cause the current in the circuit 1 to be decreased from I1 to I2, or vice versa, the period of instability during which the transfer from curve D to curve C, or vice versa, takes place, varies inversely in accordance with the magnitude of the controlling excitation in the winding 4. If the amount of excitation applied to the winding 4 is relatively high the transfer will take place substantially instantaneously. However, if the controlling excitation does not very greatly exceed the threshold value a time delay action is obtained. I have found that time delays up to an appreciable fraction of a minute can be provided in this manner, by adjustment of the resistance In the foregoing discussion of the action of the circuit shown in Figure 1 it has been assumed that the applied alternating voltage has a value V: less than the critical value. I find, in practice, that still more useful and satisfactory performance can be furnished by this circuit if it be operated at a voltage somewhat greater than the critical value. Not only can substantially greater useful output into the load circuit 1 be obtained, but this output may be controlled by the application, to the control winding 4, of considerably less input power.

Considering now the curves C and D, only the windings 3 and 4, as previously, being taken into account, if a voltage Va', exceeding the critical voltage, be applied, it will be seen that irrespective of whether curve C or curve D be considered the value of the current in the circuit 1 will be Is as shown in Figure 4. At this value of voltage the only efiect of the control winding 4 will be, that, during each alternating cycle, as the instantaneous value of the voltage varies between zero and V3 the current in I will, if positive excitation be applied to 4, follow curve C exclusively; or, if 4 be excited negatively, it will follow curve D initially, reverting to C as the voltage increases.

When a. higher voltage is employed the use of a current in the winding 5 introduces useful and remarkable characteristics.

It will be seen, on referring to Figure 1, that the winding 5 carries negative excitation the value of which is adjustable by the resistance I'I. That is, the excitation of the winding 5 is opposed to that of the winding 3. The eiiect of the winding 5, on the current in the circuit 1, will therefore be of the same nature as the effect of a negative current in 4.

Thus, if the circuit is functioning so as to provide a current in I in accordance with curve C sufficient excitation applied to the winding 5 will cause the circuit to transfer to the characteristics of curve D, thus reducing the value of the current in l to a lower value. However, since the current in 5 is not reversible the opposite action is not furnished, when the circuit is being worked at a voltage less than V1.

The action of the current in the winding 5 is shown in the curves in Figure 5, which show the relation between the current in the circuit 1 and the current in the winding 5 under two conditions first, when the applied voltage is V2, less than the critical value V1, and second, when it is V: above the critical value, the two curves being designated, respectively E and F.

Let it be assumed that at voltage V2 the current in winding 5 is initially zero, and that positive excitation is, or has been, applied to the winding 4. In accordance with curve C in Figure 4 the current in the circuit 1 will be I1. The value I1 is shown in Figure 5, curve E, corresponding to zero value of the current in winding 5. Let the current in winding 5 now be steadily increased. It will be found that at first no very marked effect is manifested. A slight reduction in the current in the circuit 1 takes place, the rate of this reduction somewhat increasing as higher values in the current of 5 are reached. However, as the current in 5 reaches a still greater value it will have a more marked effect upon the current in the circuit l, and, at the point shown on the curve corresponding to a current, in the winding 5, of I4, the circuit will become unstable and the current in the circuit I will abruptly change to the value shown in Figure 5, curve E, slightly exceeding the value Is in Figure 4. If, now, the current in the winding 5 be reduced, still further commensurate reduction takes place in the current in the circuit 'las shown in Figure 5. When the current in the winding 5 is again zero the current in the circuit 1 remains at the value 12 of Figure 4.

Following this action the circuit is pre-disposed to function in accordance with curve D, which it will continue to do indefinitely if disconnected from, and reconnected to, the alternating source, until such time as positive control is again applied by pressing the key l4.

Let it now be assumed that the 7 same procedure is carried out at a value of applied alternating voltage Va, exceeding the critical value V1 in Figure 4, and which corresponds to the value of current I3 in the circuit I.

Referring again to Figure 5, this value of current, I3, is shown by curve F at zero value of the current in the winding 5.

On increasing the current in the winding 5, as before, at first little efiect is seen on the value of the current in 1; with higher values of the current in 5 a more perceptible reduction of the current in I will be noted, and, ultimately, when the current in winding 5 reaches the value I5, the current in I suddenly falls to a low value not greatly exceeding the value I2 of curve D in Figure 4. On reducing the current in 5 as before further concurrent reduction is seen in the current in circuit 1 towards the value I2. However, in accordance with curve F, the value I: corresponding to zero current in the winding 5 is not reached, and, at the value It of current in the winding 5, the circuit again becomes unstable and reverts to curve C.

From the above curves it will be apparent that, over a large range of values of current in winding 5, there are two alternative values, of the current in I, which can exist, the curve C values, and the curve D values, of Figure 4.

Hitherto the resistance of the circuit 1 has been neglected. I have found that, when the circuit 1 has an appreciable resistance, and when suitable values of the applied voltage and the ampere turns of the winding 5 are selected, characteristics in accordance with Figure 6 may be obtained. Figure 6 is a curve of exactly the same type as Figure 5, showing the relation between the current in circuit I and the current in the winding 5. By selection of suitable circuit constants and voltages, it will be observed that the shape of the loop embraced by the upward and downward control of the current in the winding 5 has been changed, so as to give a substantial change in value of current in the circuit 1 between curve C operation and curve D operation in Figure 4 and at the same time, the width of this loop, that is to say, the range of values of the current in winding 5 which gives the controlling action, is reduced.

Referring to Figure 6 it will be observed that with a current of I7 the high, or curve C value, of the current in I is given, but with Is, a somewhat higher value of the current in 5, the lower or curve D value, is given. The curve in Figure 6 is substantially proportional to values that can be obtained in practice. I have found that the circuit may be adjusted so that the range between 11 and I8 may be of the order of 30% of I8 Let it now be assumed that the value of the current in winding 5 be adjusted to a value of I9 approximately midway between I7 and I8. For this value of the current in the winding 5, as has already been explained in respect of Figure 5, two alternative values, I10 and In respectively, of the current in the circuit 1, are possible. Thus, if the-value of the current in the winding pressed while the circuit is energized or while it 5 be initially I, but be reduced to I7 and restored to 19, the current in 1 will 'be I10. Alternatively, if the current in 5 be increased from I9 to Is and again reduced to I9, the value of current In in circuit 1 will ensue. 5

It is entirely practical and, in some instances, may be preferable to control the circuit by adjustment of the current in winding 5. in this manner.

However, exactly the same efiect may be pro- 10 vided by the winding 4 in a more convenient manner.

Suppose, for example, the value of the current which flows in the winding 4 when either of the keys I4 or I5 are depressed, be adjusted so that 15 the ampere turns set up by 4 correspond to the ampere turns set up in the winding 5 by a current of the value approximating to Is minus I7 or Ia minus I9. When neither of the keys M or I5 is operated the saturating excitation applied to 20 the core I by the joint action of windings 4 or 5 corresponds of course to 19. If, now, the key l4 be depressed, giving positive excitation to winding 4, that is to say, excitation in oppositionto that of the winding 5, the resultant saturating 25 excitation, applied to the core I, will correspond to a current of I7 in winding 5.

- Alternatively, if the key I 5 be depressed, giving negative excitation in winding 4, this will be added to that of the winding 5, giving a re- 30 sultant saturating efiect corresponding to a current of Is in winding 5.

It will readily be seen, therefore, that with the above arrangement, the current in 5 being permanently adjusted to a value approximating I9, 35 the following action will be furnished by this circuit.

Assume that the circuit is connected to the supply, at voltage Va, and that a value of I10 obtains in the circuit 1. If the key M be depressed 0 nothing will happen but if the key l5 be depressed the current will change from I10 to In. If neither of the keys are further actuated the value 111 will obtain indefinitely no matter how often the alternating current supply to the circuit 45 be interrupted.

If however, the key 14 be actuated the current in I will revert to value I10.

This value will again be maintained indefinitely, if no further controlling action is ex- 50 erted, despite supply interruptions.

Furthermore, the above controlling action will be manifested, in exactly the same manner, irrespective of whether the keys l4, l5 are deis disconnected from the supply circuit.

In order better to illustrate the action of this circuit I give below some typical numerical values taken from a practical embodiment of my invention which I have constructed and tested. It should, however, be clearly understood that my invention may be carried into effect on any desired scale of magnitude and may be modified in any manner conformable with the purpose and application for which it is to be employed. I am therefore in no way to be limited by the following data which is included only for the purpose of facilitating the understanding of my invention.

In the apparatus referred to, the core I con- 0 sisted of approximately 1 inch stacking of silicon steel laminations of the proportions shown in Figure 2 having dimensions approximately 4 x of 180 turns, winding 3 and winding each consisted of 300 turns, and winding 4 had 1800 turns. Good quality rectifiers of the copper oxide type were employed.

With the above circuit constants, V1 varied up to about volts, V2 was about 6 volts, and V3 approximately 12 volts.

The values of the currents in the circuit I referred to in'Figure 4 were as follows. I1 was approximately 0.3 ampere, 12 was of the order of 20 milli-amperes, and I: was about 0.75 ampere.

Referring to Figure 5 the corresponding values of the current in the Winding 5, 14, I5, and 16 were respectively 0.1 amp., 0.3 amp. and 0.13 amp.

With the apparatus specified above, operating at a supply voltage of volts 60 cycles and controlling the current in an external load resistance by means of the keys I 4, I5, and winding 4, the following results were obtained. The winding 4 had 1800 turns and its resistance was approximately 20 ohms.

The characteristic controlling effect of the circuit, as above described, was manifested for all values of external load resistance between zero and 15 ohms. With 5 ohms external resistance, and with the current in winding 5 adjusted to approximately 0.25 ampere, a current of milliamperes, in either direction, applied to the winding 4 was suflicient to cause the current in circuit I, including the 5 ohms resistance, to change from 0.2 ampere to 0.8 ampere, or vice versa, according to the polarity of the current in 4.

It will be noted that this represents a power input to the winding 4 of less than 15 milli-watts and that this causes the power in the circuit I to increase from 0.2 watts to 3.2 watts, a change of 3 watts. The ratio between the input power and the output power-change is seen to be more than 200.

With a. resistance of 15 ohms in the circuit 1, and a current of about 50 milli-amps in winding 5, 3 milli-amps in the winding 4, in either direction, was sufiicient to effect the transition from one value of current to the other in the circuit I; but with this value of resistance the change was of reduced extent, namely, 0.2 ampere to 0.4 ampere,

or vice versa.

However, this operating condition furnishes still greater gain, or efiective ratio between input and output. 3 milli-amperes in 20 ohms represents less than of a milli-watt. A change of 0.2 ampere to 0.4 ampere in 15 ohms represents an increase from 0.6 watt to 2.4 watts, a change of 1.8 watts. This gives an amplification ratio of approximately 10,000.

When the value of the current in the winding 4 was barely suflicient to actuate the circuit, the current in the circuit I changed very slowly from the low value to the high value or vice versa, time delays of more than seconds being noted. However, when the current in 4 appreciably exceeded the minimum operating value the change took place substantially instantaneously.

While space does not permit a full discussion of the physics of the above phenomena, the action which takes place appears to be consistent with the following hypothesis, which, however, it is to be expressly understood in nowise limits or restricts my invention, which may be readily practiced from the foregoing disclosure independently of the underlying principles involved.

It will be seen that the initial portion of the curve D in Figure 4 is substantially the same as the curve A in Figure 3 so that it is apparent that,

when the circuit is functioning in accordance with curve D, the winding 3 does not produce any additional saturating effect. On the other hand, when the circuit is performing in accordance with curve C the winding 3 clearly exerts a considerable saturating eifect which substantially increases the value of the current in the circuit 1.

The value of the current in 1, and therefore the excitation of the winding 3, is substantially controlled by the effective reactance of the winding 2. Because of the rectifier 6, no counter E. M. F. is set up by the winding 3 so that the latter does not contribute directly to the total reactance of the circuit; it does, however, modify the reactance of 2, by increasing the flux-density.

The reactance of the winding 2 is, of course, proportional to the rate-of-change, or slope, of the saturation curve A in Figure 3.

I show in Figure 3 a second curve B representing the differential of curve A. Curve B therefore shows the relation between the reactance of the winding 2 and the current therein, for the condition to which curve A refers, that is to say, in the absence of winding 3. Curve B, of course, corresponds in shape to av permeability curve of the material of which the core I is made.

On referring to the reactance curve B it is seen that with increasing current in the winding 2, the reactance increases rapidly from a low value to a maximum and thereafter is more slowly decreased. It is apparent that the action of the circuit in electing either curve C or curve D is dependent upon the direction of the slope of the reactance curve B, that is to say, whether the reactance becomes, more or less, when the excitation is increased.

Let us first consider the initial portion of the curve B in which the reactance increases rapidly as the magnetization of the core I is increased, it being recalled that curves A and B refer to the characteristics of the saturating reactor without the winding 3. What will be the effect of adding this winding? Obviously, for any given value of current in the circuit I the addition of winding 3 will tend to produce a greater magnetizing effect. This, in accordance with curve B, will cause an increase in the reactance and therefore a decrease in current. In other words, over this portion of the curve the effect of the winding 3 is to decrease the current and not to increase it.

The critical voltage V1 in Figure 4 approximates to the value of voltage in Figure 3 at which the peak of the reactance curve B is reached. If the voltage be increased to the value V3, which is beyond the peak of the reactance curve, conditions are now opposite. Any increase in excitation tends to cause a decrease in impedance and under this condition, the winding 3 exerts a building-up effect tending to boost the current in the circuit I to the higher value shown in curve C.

It will be noted that since the circuit is alternating, the effects described, step by step, in the foregoing, all take place during each alternating cycle, as the voltage increases from zero to the maximum value. This being home in mind it will be appreciated that a relatively small controlling efiect manifested at the instant when the voltage is in the neighborhood of zero can readily predetermine the action of the circuit. The remarkable manner in which the action of this circuit can be predetermined by excitation applied when the circuit is disconnected from the alternating current source may be due to the fact that the portion of the magnetic circuit which is magnetized by the saturating windings 3, 4, or 5, is of considerably greater dimensions than the magnetic circuit, comprising only the two small center limbs, which is associated with the winding 2. Presumably the retentivity of the larger circuit is sufiicient to provide a residual magnetic eifect in the smaller circuit which is sufiicient, in accordance with the polarity thereof, that is to say, according to whether its direction is positive or negative, to prevent the operation of the circuit from passing the critical point; or alternatively, to cause it to do so.

While I have shown in Figure 2 a magnetic circuit having proportions which give satisfactory action, I have found that other shapes and proportions likewise manifest the phenomena described.

I have also found that operation in accordance with my invention is obtained with standard silicon alloy steel of commercial quality such as is widely used in electrical machinery. I have further ascertained that when there is used a nickel alloy of high permeability such as the material known as permalloy which is described in the Elmen Patent No. 1,586,884, June 1, 1926, the same type of operation is obtained with very, much greater sensitivity and efiectiveness and, for best operation of my invention, I prefer to use the said, or similar, material.

The great utility of the above system in practical electrical engineering applications will be immediately apparent.

Suppose, for example, that I includes an industrial load device such as, for example, an electric motor II, an illuminating circuit, or the like, and that I 4, and I5, respectively correspond to electric control start and stop buttons. On pressing I4 the motor will be energized or the light will be illuminated, whichcondition will continue indefinitely until I5 be pressed, upon which the energy in the circuit I will be reduced to a negligible amount, such that the motor will come to rest or the current in the lighting circuit will be reduced to a value greatly less than that which gives visible glow in a filament. I have found that in accordance with Figure 6 the power in watts developed in the circuit 1 after pressing I5 may be reduced to approximately. 5% or less, of the value which obtains after pressing I4.

I wish it to be understood that the arrangement comprising battery I3 and keys I4 and I5 is shown in Figure 1 primarily with the intent of facilitating the description and explanaton of the operation of this circuit and that my nvention contemplates controlling the load I in accordance with any manual or other controlling efiect which is capable of manifesting, directly or indirectly, a change in electrical magnitude or in polarity.

Obviously, the battery I3 and keys I4 and I5 are not necessarily to be located in proximity to the saturable core control circuit and load device II, but may be at any desired distance therefrom, if a remote controlling action is required.

Having described in reference to Figure 1 the essential elements and operating principle of my invention I show in Figure '7 a practical application thereof comprising a multi-stage polarized magnetic amplifying system arranged in accordance with my invention.

' While I have only shown two stages in order to simplify the drawings and explanation I wish it to be understood that any further number of stages as may be desired may be used. It will be appreciated by those skilled in the art that the action between one stage and another will follow the same principles for any number of stages and this action may therefore be clearly disclosed and explained by showing two stages only. 5

In Figure 7 I show a first stage polarized magnetic amplifying circuit substantially in accordance with Figure 1 comprising a saturable core I, having windings 2, 3, 4, and 5, rectifiers 6 and and I6, adjustable resistor I'I, supplied from an 10 alternating current source 8 through a transformer 9, all as described and shown in Figure l.

I show also a second stage circuit similar to that in the first stage having a core I00, alternating current winding 20, direct current windings 30, 40, and 50, rectifiers 60 and I60, and adjustable resistor IIIl, all having functions analogous to the similar elements in Figure 1. The output circuit 1 of the first stage is connected to the input winding 40 of the second stage. The output circuit -'III of the second stage may be connected to the input of a third stage if desired. However, in Figure 7 I show the output of the second stage connected to a load circuit IiIl which maybe, for example, a motor, beacon light, orfother utility device.

In Figure 'Iit will be observed that the'input winding 4 is connected through conductors I8 across the diagonals of a bridge circuit I9 consisting of two resistance elements 2] and 22 and two photo- electric cells 23 and 24. The bridge circuit is energized across the opposite diagonals from a source 25. I show in the diagram a pair of light-sources 26 and 21 for directing light, respectively, on to the photocells 23 and 24. Let it be assumed that an object 28 is caused to move in the direction indicated so as successively to interrupt the light falling upon first 23 and subsequently 24.

With light falling simultaneously upon both 23 and 24 the bridge I9 is adjusted so that there is no E. M. F. across the diagonals and accordingly no energization is applied to the winding 4. The polarity of the source 25 is such that, if the light falling upon 23 is interrupted causing an increase in the resistance of 23, a positive excitation will be applied to 4. That is to say, excitation tending to magnetize the core I in the same direction as the winding 3. Later whenthe light reaching 24 is interrupted by 28 a negative voltage will be applied to 4.

Having regard to the action of the polarized saturating reactor circuit shown in Figure 1 it will be apparent that as the object 28 proceeds in the designated path, in passing 23 the current in the output circuit 1 and in the winding 40 will be increased from a low value to a high value. When the object interrupts the light to the photocell 24 the current in 40 will be again reduced to a low value.

The action of the second stage may now be considered.

The circuit comprising windings 20, 30, 40, and 5|] may be caused to operate in more than one way according to the adjustment of the circuit constants.

In accordance with the relation between the turns in the winding 30 and the turns of winding 20, the second stage may be caused to operate in a substantially similar manner to the first stage or alternatively it may be given the characteristics of a straight magnetic amplifier such as I have described in my copending application Serial No. 676,785, with increased gain and effectiveness.

Let it first be considered that the number of 76 turns in winding 30 lie between 50 per cent and 200 per cent of the turns of winding 20, so as to cause the second stage to have characteristics such as have been described in reference to the curve in Figure 6. For the core structure previously referred'to 75 per cent is a good ratio.

In Figured it will be obvious that a magnetizing effect applied to the core corresponding in magnitude to the effect of a current of 1?, or less, gives a, high value of output current I10. On the other hand, magnetization corresponding to a value of current of Is, or greater, causes a low value of output current I11.

In Figure 1 it will be recalled in order to bring about a change in the value of the output current, the current in 5 was adjusted to the value I9 and the magnetizing effect due to the current was augmented or reduced according to the polarity of the excitation applied to the winding 4.

In the second stage, the method of control through the winding 40 is slightly difierent due to the fact that the current in the output circuit 1 does not reverse. Under one condition there will be a low current in the winding 40 and under another condition there will be a very much higher current but of the same polarity.

Thus, in the second stage the current in 50 is adjusted to such a value that the difierence be-,

Thus, when a negative excitation is applied to 4 and the current in 40 is low, the output of the second stage to the load device H will likewise correspond to the low value In in Figure 6. Again when positive excitation is applied to 4 and the current in 40 increases to the high value the output of the second stage will likewise increase in accordance with I10.

As an alternative the steady value of the current in 50 and the polarity of excitation of 40 may be adjusted so that excitation due to 50 plus the excitation due to 40 with the low value of current in 40 corresponds to I: in Figure 6 and when the current in 40 is increased to the high value the .total magnetizing effect corresponds to Is. This causes the opposite controlling action, but since the winding 4 may obviously be connected so as to receive either polarity it is immaterial which of the above arrangements, in respect of the windings 40 and 50, be employed.

Alternatively, if the number of turns of the winding 30 are given a somewhat lower value,-say,

- 10 to 20 per cent of the turns of 20, the second stage will function in accordance with the action described in my co-pending application Serial No. 676,785, as modified by the regenerative action of the winding 30, instead of as described with reference to Figure 1 of the present application. i

Under these circumstances, apart from the action of the winding 30, the circuit constant and adjustments should be made as specified in my co-pending application, Serial No. 676,785, the elements in the present Figure 7 corresponding to the elements in Figure 1 of my co-pending application in the following manner. Thecore H10 in Figure 7 corresponds to the core 2i in the copending application. Winding 20 corresponds to winding 23, winding 50 corresponds to winding 25, winding 40 corresponds to winding 22, resistance I10 corresponds to resistance 26, in each case the first mentioned numeral referring to the present application.

In accordance with the methods described in my co-pending application, Serial No. 676,785, the current in the winding 50 will be adjusted so that it exactly compensates for and neutralizes the magnetic effect of the current in 40, when this is controlled by the first stage so as to have the low value. In other words, when negative excitation is applied to 4 so that the current in 1 and 40 has the low value, there should be no saturating effect at all applied to the core I00 due to the joint action of 40 and 50.

When a positive excitation is applied to the Winding 4 so that the current in 4. increases to the high value the whole of the difference between the high value and low value of the output of the first stage is applied to saturate the core of the second stage.

Due to the regenerative action of the winding 38 the output to the load I III will be several times as great as would be the case if no winding 30 be used. According to the above explanation therefore it. will be seen that in Figure 7 the current in the load device 0 will. be controlled photo-electrically in the following manner. Suppose, for example, that the load device IIO is a railroad grade crossing alarm signal such as a. circuit including a red flashing light and a warning bell and that the object 28 represents a train. When the train passes the first photocell the alarm will be put into action and the bell will continue to ring and the light to flash until the train passes the sec- 0nd photocell.

The above, of course, is only one out of many similar applications of this nature.

It will be obvious to those skilled in the art that energization of the load circuit may be initiated by momentarily switching off the light source 26 and may be terminated by extinguishing 21. Again if both lights are normally out momentarily flashing 21 will energize the circuit and flashing 26 will de-energize it.

I show in Figure 8 a practical'application of this last principle, only the method of the energization of the winding 4 being illustrated, it being understood that Figure 8 is intended to apply to an amplifying and control circuit of the type shown in Figure 7.

In Figure 8 I show a bridge circuit l9, resistances 2| and 22, photocells 23 and 24 energized from a source 25, all as in Figure 7.

In Figure 8 I show a single light source 29 arranged to throw a beam of light which embraces both of the photocells 23 and 24.

In Figure 8, I employ photocells responsive selectively to difierent light wave-lengths. That is to say, to different portions of the spectrum; in other words, to light of different colors. It is well known to those skilled in the art that photocells responsive to different wave-length may readily be provided in accordance with the material of which the photocell electrodes are constructed and the gases or other elements with which they are associated. Alternatively, filters 3i and 32, as shown in Figure 8, may be employed to the same effect. Suppose, for example, that the photocell 23 and filter 3! respond to red orinfra -red rays and that the photocell 24 and filter 32 are responsive to substantially shorter wavelength such as, for example, green or ultra-violet.

In accordance with the arrangement shown in Figure 8 I cause the light source 29 to emit light of two alternative wave-lengths or color values. This I may do either by the use of suitable alternative gaseous light sources or by the use of a filter 33 having two portions, 34 and 35, respectively, the first of which emits light to which 23 is responsive and 24 is non-responsive and the second of which emits light which actuates 24 but has no effect on 23.

Suppose, for example, that the load devices represent air port landing lights or other aviation utility device and that the light source 29 is mounted upon an aircraft.

If the aircraft be approaching the airport at night and causes a beam of green light to shine upon the photocells, only the photocell 24 will respond. This will apply positive excitation to the winding 4 and will cause the landing lights to be illuminated. On leaving the airport the ground lights may be extinguished in a similar manner by shining a red light upon the photocell 23 when negative excitation will be applied to winding 4 and the landing lights circuit will' be substantially de-energized.

If desired, a similar result may be brought about acoustically or by radio or any other signalling method embodying the emission of sig nals of characteristic frequency.

Such an arrangement I show in Figure 9. In Figure 9, the winding 4 is connected through the conductors l8 to a bridge circuit I9 including resistors 2| and 22 and a pair of rectifiers 36 and 31. The rectifiers 36 and 31 are energized from a transformer 38 having a primary winding 39 and secondary windings 4| and 42. Rectifier 36 is connected to secondary winding 4| through a tuned circuit comprising a capacitor 43 and a reactor 44. In like manner rectifier 31 is connected to secondary winding 42 through a second tuned circuit comprising a capacitor 45 and a reactor 46. The primary Winding 39 of the transformer 38 is energized through a microphone 4'! from a direct current source 48.

The values of the capacitors and reactors 43, 44, 45, and 46, are chosen so that the two circuits resonate at different frequencies.

It will be apparent that the bridge circuit IS in Figure 9 will operate in the following manner. If the rectified current outputs of 36 and 31 are exactly equal, current will circulate through 2| and 22 and 36 and 31, and. the points to which the conductors l8 are connected will be at equal potential. Thus, no voltage will be applied to the winding 4. It will be apparent that this condition will obtain if the microphone 41 receives a tone signal having a frequency midway between the two resonant frequencies. For all frequencies other than the above stated frequency, the outputs of 36 and 31 will be unequal and unbalance voltage will be applied to the winding 4. The polarity of excitation of winding 4 will depend upon whether the output of 36 preponerates over that of 31 or vice versa. Thus winding 4 will be excited with a polarity which will depend upon whether the signal frequency is above or below that frequency at which the bridge is balanced. For example, any tone signal above a given frequency will cause the landing lights to be illuminated whereas any lower frequency will cause the lights to be extinguished.

If desired, instead of utilizing a two frequency system of control similar results may be brought about by utilizing signals of different duration.

I show such an arrangement in Figure 10.

While it is, of course, entirely immaterial so far as my invention is concerned whether the signal is transmitted by light rays, sound waves, carrier current or any other method, I show in Figure 10 an arrangement for selectively con- 5 trolling the arrangement shown in Figure 7 in accordance with radio signals.

In Figure 10, I show the winding 4 excited through the conductors 8 across the diagonals of a bridge circuit 9, which in Figure 10 con- 10 sists of two resistors of fixed value 2| and 22 and two non-linear resistances 5| and 52. The nonlinear resistances 5| and 52 may be devices such as are known as ballast tubes or other similar resistance elements having an appreciable temperature co-eflicient.

Alternatively, non-linear resistance elements made of a material such as is known as thyrite or the like, may be used.

The bridge circuit I9 is energized uni-directionally from the output circuit 53 of a radio receiver 54 energized from a source 55.

The non-linear resistances 5| and 52 being included in opposite arms of the bridge, in the well known manner, it will be apparent that the bridge will be balanced only when the non-linear resistors 5| and 52 have specific resistance value. These values, as is well known, will vary withv energization of the circuit and, if 5| and 52am thermal elements, with time.

When the bridge is balanced there will be no I Y excitation applied to the winding 4. When the bridge is above the balance point positive excit'a tion will be applied to the winding 4, and when the bridge is below the balance point, the winding 4 will receive negative energization.

Suppose, for example, that non-linear resistors 5| and 52 are thermal elements having an appreciable time delay action and let it be assumed a that a signal is received by 54 such as to furnish 40 to the bridge circuit |9 energization suflicient in magnitude to raise the temperature of 5| and 52 to a point well above the balance point of the bridge l9. Previous to the reception of the signal 5| and 52, being at ambient temperature, the bridge will be unbalanced so that negative excitation is applied to winding 4. If a prolonged signal is received by 54, when output energy from 54, resulting from the signal, is first applied to the bridge circuit l9, negative excitation will be applied to 4. As the elements 5| and 52 heat up the 'energization of 4 will decrease until, at the balance point of the bridge, 4 will receive zero excitation. .With increasing temperature rise of 5| and 52 the bridge unbalances in the positive 55 direction so as to excite the winding 4 with a positive current.

It is therefore seen that according to the arrangement shown in Figure 10 a, signal of any duration greater than a predetermined amount will cause the landing lights, or other utility device llll, to be energized. On the other hand,

a short signal will have the opposite effect.

It will also be apparent to those skilled in the art that signals of differing intensity may also have a similar effect. With this arrangement non-linear elements such as thyrite which do not manifest time delay effects may be used.

Although I have chosen a particular embodiment of my invention for the purpose of explanation, many modifications thereof will be apparent to those skilled in the art to which it pertains. My invention therefore is not to be limited except in so far as is necessitated by the prior art and the-spirit of the appended claims.

What I claim as new and desire to secure by Letters Patent of the United States is:

1. An electrical control system comprising, an alternating current supply circuit, a load circuit, a saturable core device having a saturating winding and a reactance winding connected to control the energization of said load circuit from said supply circuit, means for energizing said saturating winding with a current variable in accordance with the magnetization of the core of said device, the ratio of the magnetomotive forces of said windings being such that, for given supply voltage, connections, and circuit constants, the system has a plurality of conditions of stability furnishing a plurality of different current values in said load circuit in accordance with a magnetic condition of the core of said device, and means for predetermining which of said conditions of stability shall obtain so as selectively to control the current in said load circuit.

2. An electrical control system comprising, an alternating current supply circuit, a load circuit, a saturable core device having a saturating winding and a reactance winding connected to control the energization of said load circuit from said supply circuit, means for energizing said saturating winding with a current variable in accordance with the magnetization of the core of said device, the ratio of the magnetomotive forces of said windings being such that, for given supply voltage, connections, and circuit constants, the system has a plurality of conditions of stability furnishing a plurality of difierent values of the current in said load circuit, one of said conditions being characterized in that the reactance of said reactance winding increases with increase of magnetization, and another of said conditions being characterized in that the reactance of said reactance winding decreases with increase of magnetization, and means for pre-determining which of said conditions of stability shall obtain so as selectively to control the current in said load circuit.

3. An electrical control system comprising, an alternating current supply circuit, a load circuit, a saturable core device having a saturating winding and a reactance winding connected to control the energization of said load circuit from said supply circuit, means for energizing said saturating winding with a current variable in accordance with the magnetization of the core of said device, the ratio of the magnetomotive forces of said windings being such that, for given supply voltage, connections, and circuit constants, the system has a plurality of conditions of stability furnishing a plurality of different values of current in said load circuit, one of said conditions being characterized in that the magnetization of the core of said device is caused to vary between the limits of zero and the value of flux density at which maximum permeability occurs and another of said conditions being characterized in that the magnetization of said core is caused to exceed said maximum permeability value, and means for pro-determining which of said conditions of stability shall obtain so as selectively to control the current in said load circuit.

4. An electrical control system comprising, an alternating current supply circuit, a load circuit, a saturable core device having a saturating winding and a reactance winding connected to control of conditions of stability giving different values of current in said load circuit, said means being proportioned so as to cause the current in said reactance winding to vary between zero and the value at which maximum reactance occurs, when one of said conditions of stability exists, and to cause said current to exceed the value at which maximum reactance occurs, when another of said conditions of stability exists, and means for predetermining which of said conditions of stability shall obtain so as selectively to control the current in said load circuit.

5. In combination, an alternating current supply circuit, a load circuit, a saturable core device having a direct current saturating winding and an alternating current winding connected to control the energization of said load circuit from said supply circuit, means for energizing said saturating winding with a direct current variable in accordance with the current in said alternating current winding, the ratio of the magnetomotive forces of said windings being such that, with unchanged energization, under one residual magnetic condition of said core a relatively small current flows in said load circuit and under another residual magnetic condition of said core a substantially greater current flows in said load circuit, and means for controlling said magnetic condition so as selectively to determine the amount of said current.

6. In combination, an alternating current supply circuit, a load circuit, a saturable core device having a direct current saturating winding and an alternating current winding connected to control the energization of said load circuit from said supply circuit, means for energizing said saturating winding with a direct current variable in accordance with the current in said alternating current winding, the ratio of the magnetomotive forces of said windings being such that the magnetomotive force of said direct current winding increases the build-up of current from zero in said alternating current winding under one residual magnetic condition of said core, and reduces the build-up of current from zero dnsaid alternating current winding under another residual magnetic condition of said. core, and means for selectively varying said residual magnetic condition to control the energization of said load circuit.

'7. In combination, an alternating current supply circuit, a load circuit, a saturable core device having a direct current saturating winding and an alternating current winding connected to control the energization of said load circuit from said suppy circuit, means for energizing said saturating winding with a direct current variable in accordance with the current in said alternating current winding, the ratio of the magnetomotive forces of said windings being such that the ma netomotive force of said direct current winding increases the build-up of current from zero in said alternating current winding when the residual magnetic condition of said core has one polarity, and reduces the build-up of current from zero in said alternating current winding when said residual magnetic condition has the opposite polarity, and means for selectively magnetizing said core with either polarity so as to control the energization of said load circuit in accordance with the said polarity.

8. In combination, an alternating current supply circuit, a load circuit, a saturable core device having a direct current saturating winding and an alternating current winding connected to con- Y trol the energization of said load circuit from.

of said load circuit from said supply circuit,

said supply circuit, means for energizing said saturating winding with a direct current variable in accordance with the current in said alternating current winding, the ratio of the magnetomotive forces of said windings being such that the magnetomotive force of said direct current winding increases the build-up of current from zero in said alternating current winding under one magnetic condition of said core and reduces the build-up of current from zero in said alternating current winding under another magnetic condition of said core, means for connecting said alternating current winding to said supply circuit and for disconnecting same therefrom, and means for pre-conditioning said core when said alternating current winding is disconnected from said supply circuit, so as topre-determine the amount of energization of said load circuit when said alternating current winding is subsequently connected to said supply circuit.

9. In combination, an alternating current supply circuit, a load circuit, a saturable core device having a direct current saturating winding and an alternating current winding connected to control the energization of said load circuit from said supply circuit, means for energizing said saturating winding with a direct current variable in accordance with the current in said alternating current winding, the ratio of the magnetomotive forces of said windings being such that under one residual magnetic condition of said core the cfiect of said direct current winding is to cause to flow in said load circuit a current greater than that which would obtain in the absence of said direct current winding, and under another residual magnetic condition of said core theefiect of said direct current winding is to cause a current to flow in said load circuit smaller than that which would obtain in the absence of said direct current winding, and means for controlling said magnetic condition so as selectively to determine the amount of said current.

10. In combination, an alternating current supply circuit, a load circuit, a saturable core device having a direct current saturating winding and an alternating current winding connected to control the energization of said load circuit from said supply circuit, means for energizing said saturating winding with a direct current variable in accordance with the current in said alternating current winding, means for applying a controlling magnetomotive force of reversible polarity to said core and for withdrawing same, the ratio of themagnetomotive forces of said alternating current winding and said direct current winding being such that the value of the current in said load circuit is thereafter determined in accordance with the polarity of said controlling magnetomotive force.

11. An electrical control system comprising, an alternating current supp 1y circuit, a load circuit, a saturable core device having a direct current saturating winding and an alternating current winding connected to control the energization rectifying means energized in accordance with the current in said alternating current winding, said direct current winding being energized with rectified current from said rectifying means, the ratio of the magnetomotive forces of said windings being such that the magnetomotive force of said direct current winding increases the build-up of current from zero in said alternating current winding under one residual magnetic condition of said core and reduces the build-up of current from zero in said alternating current winding under another residual magnetic condition of said core, and means for selectively pre-determining said magneticcondition to control the energization of said load circuit.

12. An electrical control system comprising, an alternating current supply circuit, a load circuit. a saturable core device having a direct current saturating winding and an alternating current winding connected to control the energization of said load circuit from said supply circuit, means for energizing said saturating winding with a direct current variable in accordance with the current in said alternating current winding, the ratio of the magnetomotive forces of said windings being such that a characteristic curve showing the relation between the voltage of said supply circuit and the current flowing in said load circuit has two alternative forms, in accordance with residual magnetic conditions of the core of said device, and means for pre-determining which of said two characteristic curves the performance of the system will follow, so as selectively to control the current in said load circuit.

13. An electrical control system comprising, an alternating current supply circuit, a load circuit, a saturable core device having a direct current saturating winding and an alternating current winding connected to control the energization of said load circuit from said supply circuit, means for energizing said saturating winding with a direct current variable in accordance with the magnetization of the core of said device, the ratio of the magnetomotive forces of said windings being such that, for given supply voltage, connections, and. circuit constants, the system has a plurality of conditions of stability furnishing a plurality of different current values in said load circuit in accordance with a residual magnetic condition of the core of said device, and means for pre-determining which of said conditions of stability shall obtain so as selectively to control the current in said load circuit.

14. An electrical controlsystem comprising, an alternating current supply circuit, a load circuit, a saturable core device having a direct current saturating winding and an alternating current winding connected to control the energization of said load circuit from said supply circuit, means for energizing said saturating winding with a direct current variable in accordance with the current in said alternating current winding, the ratio of the magnetomotive forces of said windings being such that, for given supply voltage, connections, and circuit constants, the system has a plurality of conditions of stability furnishing a plurality of diiferent current values in said load circuit in accordance with a residual magnetic condition of the core of said device, and means for applying to said core a pre-determined magnetomotive force for changing said magnetic condition so as to cause the control system to change from one of said conditions of stability to another, thereby changing the value of said load circuit current.

15. In combination, an alternating current supply circuit, a load circuit, a saturable core device having a direct current saturating winding and an alternating current winding connected to control the energization of said load circuit from said supply circuit, means for energizing said saturating winding with a direct current variable in accordance with the current in said alternat-' anemia motive forces or? said windings being such that,

with unchanged supply voltage, under one re sidual magnetic condition of said core a relatively small current flows in said load circuit, and under another residual magnetic condition of said core a substantially greater current flows in said load circuit, and means, including a resistance of variable value, for controlling said magnetic condition so as selectively to determine the amount of said load circuit current.

16. An electrical control system comprising, an alternating current supply circuit, a load circuit, a saturable core device having a direct current saturating winding and an alternating current Winding connected to control the energization of said load circuit from said supply circuit, means for energizing said saturating winding with a direct current variable in accordance with the current in said alternating current winding, the ratio of the magnetomotive forces of said windings being such that a characteristic curve, showing the relation between the voltage of said supply circuit and the current flowing in said load circuit, has two alternative forms, in accordance with residual magnetic conditions of the core of said device, and means, including a variably conducting circuit element, for pie-determining which of said two characteristic curves the performance of said system will follow, so as selectively to control the current in said load circuit.

17. An electrical control system comprising, an alternating current supply circuit, a load circuit, a saturable core device having a direct current saturating winding and an alternating current winding connected to control the energization of said load circuit from said supply circuit, means for energizing said saturating winding with a direct current variable in accordance with the magnetization of the core of said device, the ratio of the magnetomotive forces of said windings being such that, for given supply voltage and connections, the system has a plurality of conditions of stability I furnishing a plurality of different current values in said load circuit in accordance with residual magnetic conditions of the core of said device, and means, comprising a circuit element subject to electrical variations, for predetermining which of said conditions of stability shall obtain, so as selectively to control the current in said load circuit.

18. An electrical control system comprising, an alternating current supply circuit, a load circuit, a saturable core device having a direct current saturating winding and an alternating current winding connected to control the energization of said load circuit from said supply circuit, means for energizing said saturating winding with a direct current variable in accordance with the magnetization of the core of said device, the ratio of the magnetomotive forces of said windings being such that, for given supply voltage and connections, the system has a plurality of conditions of stability furnishing a plurality of different current values in said load circuit in accordance with a residual magnetic condition of the core of said device, a further direct current saturating winding for modifying said residual magnetic condition so as to cause the control system to change from one of said conditions of stability to another, and means, comprising a variable circuit element connected to control the energization of one of said direct current windings, for causing said load circuit current to change from one value to another in accordance with variations of said circuit element.

19.:An electrical time-delay controi system comprising, an alternating current supply circuit, a load circuit, a saturable core device having a direct current saturating winding and an alternating current winding connected to control the energization of said load circuit from said supply circuit, means for energizing said saturating winding with a direct current variable in accordance with the current in said alternating current winding, the ratio of the magnetomotive forces of said windings being such that, for given supply voltage, connections, and circuit constants, the system has a plurality of conditions of stability furnishing a plurality of different current values in said load circuit in accordance with the polarity of the residual magnetic condition of the core of said device, and means for applying to said core a reversible direct magnetomotive force of pre-determined magnitude, for causing the control system to change from one of said conditions of stability to the other, in accordance with the polarity of said magnetomotive force, so as to cause said load circuit current to change from one value to another, the time of said change varying inversely in accordance with the magnitude of said magnetomotive force.

20. An electrical control system comprising, an alternating current supply circuit, a load circuit, a saturable core device having a direct current saturating winding and an alternating current winding connected to control the energization of said load circuit from said supply circuit, means for energizing said saturating winding with a direct current variable in accordance with the magnetization of the core of said device, the ratio of the magnetomotive forces of said windings being such that, for given supply voltage, connections, and circuit constants, the system has a plurality of conditions of stability furnishing a plurality of different current values in said load circuit in accordance with the polarity of the residual magnetic condition of the core of said device, and means for applying to said core a reversible direct magnetomotive force of pre-de termined magnitude, for causing the control system to change from one of said conditions of stability to another, in accordance with the polarity of said magnetomotive force, so as to cause said load circuit current to change from one value to another.

21. An electrical control system comprising, an alternating current supply circuit, a load circuit, a saturable core device having a direct current saturating winding and an alternating current winding connected to control the energization .of said load circuit from said supply circuit, means for energizing said saturating winding with a direct current variable in accordance with the magnetization of the core of said device, the ratio of the magnetomotive forces of said windings being such that, for given supply voltage, connections, and circuit constants, the system has a plurality of conditions of stability furnishing a plurality of dilTerent current values in said load circuit in accordance with a residual magnetic condition of the core of said device, a further direct current saturating winding for modifying said residual magnetic condition so as to cause the control system to change from one of said conditions of stability to another, and means for energizing said last mentioned direct current saturating winding so as to cause said load circuit current to change from one value to another in accordance with the current in said last mentioned direct current winding.

22. An electrical control system comprising,'an alternating current supply circuit, a load circuit, a. saturable core device having a direct current saturating winding and an alternating current winding connected to control the energization of said load circuit from said supply circuit, means for energizing said saturating winding with a direct current variable in accordance with the magnetization of the core of said device, the ratio of the magnetomotive forces of said windings being such that, for given supply voltage, connections, and circuit constants, the system has a plurality of conditions of stability furnishing a plurality of different current values in said load circuit in accordance with residual magnetic condit-ions of the core of said device, a plurality of.

further direct current saturating windings for modifying said residual magnetic conditions so as to cause the control system to change from one of said conditions of stability toanother, and means for energizing said last mentioned direct current saturating windings so as to cause said load circuit current to change from one value to another in accordance with a relation between the currents in said last mentioned direct current windings.

23. An electrical control system comprising, an alternating current supply circuit, a load circuit, a saturable core device having an alternating current winding connected to control the energization of said load circuit from said supply circuit, a first direct current saturating winding and a second direct current saturating winding, means for energizing said first saturating winding with a direct current variable in accordance -with the current in said alternating current winding, the ratio between the magnetomotive forces set up by said alternating current winding and said first saturating winding being such that the system has two conditions of stability giving, respectively, a low value of current in said load circuit, and a higher value of current therein in accordance with the polarity of the residual magnetic condition of the core of said device, means for generating control signals of different characteristics, means for receiving said signals, and means for deriving therefrom'a direct current of reversible polarity, said polarity being determined in accordance with said signal characteristics, said second saturating winding being connected to receive said reversible current so as to control the residual magnetic condition of said core in accordance with said signal characteristics whereby the current in said load circuit may be caused to change from one of said values to the other of said values by means of said signal.

24. An electrical control system comprising, an alternating current supply circuit, a load circuit, a saturable core device having an alternating current winding connected to control the energization of said load circuit from said supply circuit, a first direct current saturating winding and a second direct current saturating winding, means for energizing said first saturating winding with a direct current variable in accordance with the current in said alternating current winding, the ratio between the magnetomotive forces set up by said alternating current winding and said first saturating winding being such that the system has two conditions of stability giving, respectively a low value of current in said load circuit, and a higher value of current therein in accordance with the polarity of the residual magnetic condition of the core of said device, means for generating control signals of different fre- .quencies, means for receivingsaid signals, and means for deriving therefrom a direct current of reversible polarity, said polarity being determined in accordance with said signal frequencies, said second saturating winding being connected to receive said reversible current so as to control the residual magnetic condition of said core in accordance with said signal frequency whereby the current in said load circuit may be caused to change from one of said values to the other of said values by means of said signal.

25. An electrical control system comprising, an alternating current supply circuit, a load circuit, a saturable core device having an alternating current winding connected to control the energization of said load circuit from said supply circuit, a first direct current saturating winding and a second direct current saturating winding, means for energizing said first saturating windin: with a direct current variable in accordance with the current in said alternating current winding, the ratio between the magnetomotive forces set up by said alternating current winding and said first saturating winding being such that the system has two conditions of stability giving, respectively, a low value of current in said load, circuit, and a higher value of current therein in accordance with the polarity of the residual magnetic condition of the core of said device, photo-electric means, means for directing light to said photo-electric means, means for modifying the light received by said photoelectric means, and means for deriving from said photo-electric means a direct current of reversible polarity, said polarity being determined by said modifying means, said second saturating winding being connected to receive said reversible current so as to control the polarity of said residual magnetic condition in accordance therewith whereby the current in said load circuit may be changed from one of said values to the other of said values by means of said light modifying means.

26. An electrical control system comprising an alternating current supply circuit, an output circuit, a saturable core device having a first direct current saturating winding and an alternating current winding, said alternating current winding being connected to control the energization of said output circuit from said supply circuit, a first rectifying means, energized in accordance with the current in said alternating current winding,

said first direct curren't winding being energized with rectified current from said first rectifying means, a second direct current saturating winding, a second rectifying means energized from said supply circuit, said second direct current winding being energized with rectified current from said second rectifying means so as to oppose the effect of said first direct current saturating winding, means for adjusting the value of the current in said second direct current saturating winding to a pre-determined value, the ratio between the turns of said first direct current saturating winding and said alternating current winding and the value of the current in said second direct current winding being so chosen that for given supply voltage, connections, and circuit constants, the system has two conditions of stability giving two different values of current in said output circuit in accordance with the polarity of residual magnetic conditions of the core of said device, a third direct current saturating winding, means for generating signals of different characteristics, means for receiving said signals, and means for deriving from said signals a direct current of reversible polarity, said polarity being determined in accordance with said characteristics, said third direct current saturating winding being connected to receive said reversible current so as to cause the current in said output circuit to be changed from one of said values to the other of said values, selectively, in accordance with said signal characteristics.

27. An electrical control system comprising an alternating current supply circuit, an output circuit, a saturable core device having a first direct current saturating winding and an alternating current winding, said alternating current winding being connected to control the energization of said output circuit from said supply circuit, a first rectifying means, energized in accordance with the current in said alternating current winding, said first direct current winding being energized with rectified current from said first rectifying means, a second direct current saturating winding, a second rectifying means energized from said supply circuit, said second direct current winding being energized with rectified current from said second rectifying means so as to oppose the effect of said first direct current saturating winding, means for adjusting the value of the current in said second direct current saturating winding to a pre-determined value, the ratio between the turns of said first direct current saturating winding and said alternating current winding and the value of the current in said second direct current winding being so chosen that for given supply voltage, connections, and circuit constants, the system has two conditions of stability giving two different values of current in said output circuit in accordance with the polarity of residual magnetic conditions of the core of said device, a third direct current saturating winding, means for generating signals of different characteristics, means for receiving said sig nals, means for deriving from said signals a direct current of reversible polarity, said polarity being determined in accordance with said characteristics, said third direct current saturating winding being connected to receive said reversible current so as to cause the current in said output circuit to be changed from one of said values to the other of said values, selectively, in accordance with said signal characteristics, to gether with a second saturable core device, controlled from said output circuit, and means for causing said second device to be subjected to a saturating magnetomotive force in accordance 25 with the diiference between the current in said output circuit and the current therein corresponding to one of said stable conditions.

ALAN S. FITZ GERALD.

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