US2067604A - Electric regulation - Google Patents

Description

2 Sheets-Sheet l Filed Jan. 2l, 1935 INVENTOR Hey/wr Mff/,fi

ATTORNEYS of the periods when the winding is :ie-energized, and other factors.

If therefore the winding is intended to control, through its induced magnetic flux, any related apparatus, mechanisms, circuits, or the like, the production of a critical value of flux must be dependent upon achievement of a fixed or critical value of current through the coil, but due to the variability of the resistance of the winding as above pointed out, the voltage necessary to achieve this given value of current from the winding will necessarily vary with the variations in the resistance.

Let it be assumed, for example, that the winding is to achieve, with related means, constancy of voltage in an electrical circuit; if the winding and its related parts are so constructed as to regulate for constancy of current (to produce the above mentioned flux), the voltage neces sary to maintain this constancy of current through the winding varies with the change in resistance of the conductor of the winding, assuming that the winding ls bridged directly across the circuit the voltage of which is to bei maintained constant. I'he result is that very substantial departures from the desired value! of voltage are caused by the change in the resistance of the winding.

It has heretofore been proposed to counteract these effects by placing in series with the winding a relatively large external resistance of zero temperature coeiiicient of resistance and such an arrangement has become wide practice; the theory of such practice is that, by thus greatly increasing the total resistance of the winding circuit, the change in resistance that takes place within the winding itself becomes a small enough yfactor relative to the total circuit resistance to tolerate the nevertheless inescapable fact of change in voltage of regulation. However, such an arrangement does not remedy the difficulty and is moreover of limited scope of application, not to mention its wastefulness of material and electrical energy or low elllciency. Where the energy requirements of the winding or controlling coil are relatively large, the applicability of this prior practice fails unless many disadvantages can still be tolerated.

For example, let it be assumed that the control winding has to be constructed so large that its energy requirement is 100 watts; if the change in resistance of such a winding causes a 15% voltage variation and if it is desired to reduce that variation to a maximum of 5%, it is necessary to have connected in series with the winding an external resistance which is twice that of the winding, the external resistance requiring therefore that an additional200 watts must be dissipated therein. If the range of change of temperature of the control winding is still greater, with corresponding change in' resistance. then ever larger values of external reistance must be used to reduce the ultimate voltage variation. These instances illustrate some of the distinct disadvantages of such prior practice which, in no case, it will be seen, achieve an entire absence of voltage variation. If the winding therefore is employed for regulation of voltage, constancy of voltage cannot be and is not achieved.

One of the dominant aims of this invention is to do away with such disadvantages as have yjust been noted above and to provide a system achieved, and maintained throughout the widely varying conditions of practical use.

Referring now to Fig. l of the drawings, I have there diagrammatically shown an electromagnetic Winding IU of the general character above mentioned; by way of illustration and to clarify a ready understanding of my invention, I have shown the winding I as the control or regulating winding in a system or apparatus for achieving constancy of voltage across the circuit I|-I2, winding I0 being connected, as more clearly hereinafter described, to be responsive to that function (voltage, in this instance) of the electrical energy in the circuit I I-I2 which it is desired to maintain constant.

In so far as certain features of my invention are concerned, the winding ID may control, affect, or actuate or coact with any desired or suitable parts or apparatus which are, by the Winding I0, made to effect a correction of departures from the selected value of the function of the electrical energy that it is desired to maintain constant. For example, the winding ID may be in the form of a relay for controlling a resistance which in turn is made to affect the voltage across the circuit II--I2; thus, for example, a generator I3 (either alternating current or direct current) may be the source o! supply of electrical energy to the circuit II--I2 and the resistance, illustratively in the form of a carbon pile I4, may, under the control oi.' the winding ID, affect the excitation of the ileld Winding l5 of the generator I3, thus to control the voltage of the output of the electrical source I3.

By Way of further illustration, the winding I0 may form part of a solenoid having a fixed core I 6 and a coacting movable core I'l, these two parts being suitably shaped, as by tapering them as is indicated in Fig. 1, so that, with respect' to thevmechanical resistance opposing movement of the movable core Il, the winding I0, at a given or intended energization, will hold the core I1 in whatever position it is moved throughout its range of movement. Movable core Il may be connected to a bell crank lever I8 pivoted at I9, and having its one arm I8a operating upon the free or unanchored end of the carbon pile I4. A spring 20 opposes the pulling effort of the solenoid.

Disregarding resistance changes in the winding Ill, increase in voltage across the circuit II--IZ increases the energization of the winding ID beyond the value corresponding to the voltage desired to be maintained constant across the circuit II-I2, whereupon the pressure on the carbon pile I 4 is lessened, its resistance increased, and the resultant decrease in the excitation of the generator I3 restores the voltage to normal. Should the voltage decrease, a reverse action takes place in that the corresponding decreased energization of the winding IU disturbs the mechanical equilibrium theretofore existing and permits the spring 2|) to swing the lever I8 in clockwise direction, thus increasing the pressure on the carbon pile I4 and correspondingly increasing the excitation of the generator I3 to restore its voltage to normal.

As above pointed out, where the winding I0 is to respond to changes in voltage, it is bridged across the circuit the voltage of which is to be affected. Accordingly one terminal of winding I0 is connected by conductor 2| to one side, con ductor II, of the circuit II-I2; the other terminal of winding ID is connected by conductors 22 and 23 to the other side, conductor l2, of this circuit, but through a temperature-change compensating device generally indicated at R.

The device R includes a member 24 having a negative temperature coeicient of resistance and has thermally related to it means giving the part 24 a thermal capacity which is high compared to the thermal capacity of the part 24 itself. 'Ihe winding I0 may be constructed in any suitable manner; whatever its physical construction, it embodies necessarily the mass of conductor (usually copper) of which it is wound together with such possible related parts as an iron core, parts either of solid dielectric material or of metal between which or upon which the conductor is wound, and like parts, giving the winding an ultimatemasshaving a certain area of exposed surfaceor surfaces which can and do function as heat-radiating or heat-dissipating surfaces. Depending upon such factors as these, varying as they do with the design, purpose, power, or physical dimensions of the winding, the winding is found to have a thermal capacity which is, relatively speaking, large, and it is found that the winding has a corresponding characteristic of rate of rise of temperature beginning with the flow therethrough of its rated energizing current and hence also a corresponding characteristic of rate of decrease of temperature when the energizing current is cut off. The relatively large ratio of thermal capacity ofthe coil to cooling surface area ofthe coil makes this rate of change of temperature relatively low. The device R (Fig. 1) embodying a relatively small part 24 (inherently of small thermal capacity) has thermally related to it one or more members, illustratively two in number as shown at 25 and 26 in Fig. 1, of a material like cast iron, steel, brass, or other suitable metal or material, in sufficient volume or mass to give the device R, with respect to the latters heat-radiating surfaces, a high thermal capacity, and moreover a ratio of thermal capacity to heat-radiating surface of device R that is equal to or commensurate with the ratio of the thermal capacity of the winding Ill to the heat-radiating surface of the winding l0. f

By way of illustration the part 24, having a negative temperature coefiicient of resistance and made of any suitable material having such a coeicient, such as carbon', carbon compositions, psilomelane, galena, silicon, carbide, zincite, graphite, certain alloys (such as bronze made up of 88% of copper and 12% of tin with a small quantity of phosphorus), may be in the form of a disk interposed between the ends of the parts 25 and 26 which are made up in the form of preferably cylinders made, for example, of cast iron.

The members 25-26 may or may not be included in the circuit of the winding l though it is more convenient to include them in that they may thus also serve-as the contactors with the disk-like resistance element 24; the crosssection of metal in the members 25-26 is suiilciently large virtually in any case so as-notmaterially to aiect the resistance of the circuit or to be materially affected by 13R losses therein. In any event the resistor 24, of negative temperature coeflicient and of small mass and hence of small thermal capacity, is in the circuit of the Winding' i0 and has its thermal capacity greatly increased by being thermally related to arelatively large mass such as the metal members 25-26. As the resistor 24 heats up, due to the ow of current therethrough, heat flows from the resistor 24 to the mass 25-26, the total mass of the device R being given such an external or other exposed heat-dissipating surface that the rate at which the temperature of the entire mass of the device R changes with flow of current through the resistor 24 substantially matches1 or equals the rate of change of temperature of the winding l0. Depending upon the relative temperature coeiicients of resistance and upon the relative ohmic resistances of the winding I0 and the resistor 24, the mass of the part or parts 25--26 and the heat-dissipating surfaces thereof may be changed or determined to control the. rise or fall of temperature of the resistor 24 with continued flow of current or cessation thereof respectively so thatthe increment of change of resistance in winding I0 in one direction is exactly counterbalanced by an equal increment of change in resistance in the resistor 24 in the opposite direction.

With this arrangement exact or precise -regulation at the intended voltage may be accom# plished. The action achieved by the above described interrelation of the thermal capacities of the winding and resistor unit may be better understood if reference is now made to Fig.y 'I of the drawings.

In Fig. '7 the curve A represents the voltage of the circuit being regulated over a period of time beginning with the closure of the-regulating circuit (with the parts starting at room temperature) `and terminating at the end of three hours or so when, under the there existing conditions, steady conditions of ultimate temperature had been achieved. CurveA is substantially a straight line with detectible variations therein of only a small .fraction of one per cent. departures from the intended value of voltage to be kept constant. Curve B represents, for the saine period of time, the percentage variations of voltage across the coil I0 of Fig. 1, and shows a progressive increase in voltage from substantially zero to about 5%, representing the steady increase in voltage across the coil I0 necessary to maintain the current therein constant against the steadily increasing resistance accompanying the rise in temperature of the winding I0. Curve C represents the percentage decrease in voltage across the resisor 24 of Fig. 1 and it will be seen that curve C is geometrically similar to curve B, both curves clearly showing that for each increment of increase in resistance in the winding i0 there was a corresponding decrement in the resistance of the resistor 24 and since the same current flows through both winding and resistor, the resultant voltage drops always tota-l the same, namely, the voltage of the circuit Il-l2. Where one voltage drop (that across the winding l0) increased, the other voltage drop (across the resistor 24) decreased in exactly the same extent.

Should the circuit of coil l0 be interrupted at rany time, the rates of heat loss from the thermal masses represented by the winding l0 and by the resistance device R will substantially follow the characteristics of Fig. 'i' so that, should the circuit of the Winding l0 be restored before it is completely cooled olf, as might be the case where winding I0 operates intermittently, the temperatures of the winding l0 and the resistor 24 will have been maintained in their proper relations so that a subsequent closure of the` circuit finds the then existing temperatureresistance condition of the winding I0 exactly compensated for by the then existing temperature-resistance condition of the resistor 24.

The regulation thus achieved will be seen to be virtually perfect inasmuch as curve A is virtually a straight line parallel to the horizontal axis and is devoid of variations or tluctuations beyond a virtually imperceptible or immaterial small fraction of one per cent., even though the temperature of operation varies throughout relatively wide limits. Fig. 8 shows by way of comparison the performance of my system and apparatus as compared with a regulating system and apparatus devoid of the compensating features of construction and action above described; curve D is virtually a reproduction of curve A of Fig. 7 and again shows the high precision at which constancy of voltage is achieved while curve E shows the rate of change and magnitude of change of voltage of regulation., during the period that the regulating coil warms up to operating temperature, even though the control or regulating winding (of curve E) is in series with a resistance having a zero temperature coeilicient of the type earlier above described; Within practical limits of energy consumption and of magnitude of external resistance, curve E demonstrates how the best performance thus achievable is inherently characterized by a change in standard of voltage regulation that is great as contrasted with a small fraction of one per cent. (curve D) achievable with my system and apparatus.

In Fig. 3 I have illustrated a possible modified form or physical embodiment of the resistance device R, simply to illustrate that the device R may be given other forms than that shown in Fig. 1 and more specifically described later herein in connection with Fig. 6. In Fig. 3 the resistance element (corresponding to the resistor 24 of Fig. 1) may take the form of a rod 21, made of any suitable material as above mentioned in connection with the resistor 24; the rod 21 has associated with it one or more masses of a material preferably metal in order to increase its thermal capacity and by way of illustration I have shown the rod 21 of Fig. 3 surrounded by three annular-like (see also Fig. 4) members 28, 29 and 30, preferably of metal, and strung on to the rod 21 but in close thermal contact therewith. The members 28--29--30 are proportioned as to axial length and radial thickness to give the desired heat-absorbing mass and the desired heat-radiating exposed surfaces, all of course appropriately proportioned with respect to the thermal capacity and exposed heat-dissipating surfaces of`the winding |0, as was described in connection with the device R of Fig. 1.

Or, under certain circumstances, the resistor of the device R may take the form of an electrolyte having a suitable temperature coefficient of resistance, preferably negative. The electrolyte might comprise a 5% solution of nitric acid havlng'a temperature coetllcient of 0.015, or it might be a 5% solution of copper sulphate whose temperature coeiliclent is -0.021; these electrolytes are mentioned purely by way of example. In Fig. 5 the electrolyte 3| is contained in any suitable vessel or receptacle 32 and immersed therein are suitable electrodes 33--34 to which the conductors 22 and 23 (see Fig. 1) may be connected in order to relate the resistance device to the winding IIJ. The material of which the receptacle 32 is made is preferably a material of good heat conductivity and, With the body of the electrolyte itself and its own thermal capacity, the receptacle is proportioned so that the resultant heat-radiating surface and thermal capacity are appropriate to cause its rate of rise or fall in temperature to 5 match the rate of rise or fall in temperature 0i the winding I0. If desired or if necessary the thermal capacity may be increased by increasing the mass or volume of the material of which the receptacle 32 is made or by relating to the receptacle 32 one or more members or parts (broadly similar to the parts 25-26 of Fig. l or to the parts 28--29-30 oi' Fig. 3) of metal or other suitable material, such as the part 35 of Fig. 5. For example, if the receptacle 32 is of a circular horizontal cross-section, the part 35 may be in the form of a collar or ring extending about the receptacle 32 and brought into intimate thermal contact with the latter and hence also with the electrolyte 3|.

I have above made brie! reference to Fig. 6 in which is shown in vertical cross-section, on an enlarged scale, the resistance device R 0I Figs. 1 and 2, with its details. Turning, therefore, to Fig. 6, the disk or ring-shaped resistor 24 is shown interposed between the ends of the metal cylinders 25-26, while the parts 25 and 26 respectively are suitably bored out (as is also the resistor 24, as at 24e) to permit the passage through these three parts of a clamping bolt 36 to hold the three parts 25-24--26 in secure assembled relation.

Preferably washers or gaskets 31.-36 of a suitable relatively soft metal, such as lead for example, are interposed between the contacting faces of the three parts in order to insure uniform distribution of the clamping pressure throughout the affected portions of the resistor 24; this feature is of particular advantage where the resistor 24 is made up of a carbon or graphite composition or of a composition described in detail hereinafter. Also the lead washers 31-38 insure a good electrical surface contact with the resistor 24 in that they yield and adjust themselves to unintentional or unavoidable irregularities or variations in the surface of the resistor 24 itself; and further, the washers 31--38 provide good thermal contact between the resistor 24 and the parts 25--2S.

The clamping bolt 36 is threaded at one end or at its two ends to receive the clamping heads or nuts 39--40 in order that the appropriate clamping pressure may be applied and maintained. But the clamping bolt 36 also and conveniently serves to mechanically hold and thus electrically connect to the device R two supporting brackets 4|42 of metal, being suitably apertured to let the clamping rod 36 pass therethrough. The parts are so related and shaped that the clamping rod 36 is insulated from the metal parts 25--26 and also from the connecting and supporting brackets 4 I-42; for this purpose a tube-like insulating bushing 44, provided with insulating washers or flanges 45--46, extends about the bolt 36 and through the apertures in the bracket 4| and cylinder 25 on the one hand and the apertures through the bracket 42 and the cylinder 26 on the other hand. Metallic washers 41 and 48 rest against the insulating parts 45-46 and underneath the nuts 39-40 and thus the parts 42, 26, 38, 24, 31, 25 and 4| are dependably held together mechanically and reliably held in electrical interconnection to form a circuit therethrough which may be traced in the order in which these parts have 75 just been identified. Also a good thermal contact is assured between adjacent or engaging parts. By means of the brackets 4I-42, the device R may be mounted on a suitable base 49 of insulating material (Fig. 6) as by screws or bolts 5|-52 which may be and conveniently are utilized also to bind or clamp the conductors 22 and 23 (see Figs. 1 and 6) of the circuit in which the device R is to be included.

I have above mentioned, by way of illustration, certain specific' examples of materials which may be employed in my system and apparatus and which have a suitable negative temperature coelcient of resistance. Now in accordance with certain other features of my invention, I may employ for the material of the resistance ,medium, such as the resistor 24 or 21 of Figs. 1 and 3 respectively,'material having the characteristic of changing its ohmic resistance with change in voltage applied to the resistance material itself.

Such materials which substantially depart from Ohms law in that the current flowing in the circuit is not necessarily proportional to the voltage impressed are known as ynon-linear impedances, and may take the form of inductances with iron cores, thermionic vacuum tube conductors, gaseous discharge devices such as neon lamps or helium glow lamps, certain electrolytic conductors, and many other devices. Some devices are' pure resistance devices and follow Uhm's law for direct current, such as an iron-1 cored inductance, while on alternating current, the impedance of the device or its resistance to current flow, is dependent upon the impressed voltage and other factors, such as the frequency of alternating voltage. Other materials have a practically instantaneous response to voltage variations, so that the characteristics do not depend upon its immediately previous history, and therefore at any given instant the amount ci current flowing through the material de= pende only upon the voltage impressed at that instant and not upon the current iiowing the previous instant.

.a material may he selected so that as the voltage impressed on the material increases, the current may increase at a greater Yrate than would 'he the case it current were always proportional to the voltage impressed. lllhus, in a pure resistance with alinear impedance characteristic, the current will be proportional to the impressed voltage as shown hy the lcurve F in Figure 9.

With a ncn-linear impedance material used lor the resistance unit, the current may not he proportional to the voltage, as shown in curve G ci Figure 9. lin the latter, the current ci curve Gi increases much more rapidly with velt`= age than does the current oi curve F. Thus, ii in a regulating system a denite current change meist he made in the current ci energization of winding i@ (Figure l) in order to overcome achieve a desired change, the change involtage for a pure' linear impedance as exemplified iny curve F* will reduire the same percent variation in regulated voltage to achieve the required current change as is the magnitude oi the current change in percent of total current owing in winding it.` However, if a nonlinear impedance material is used as the resistance element in the coil circuitni Winding lil, then it is readily apparent that a small voltage variation will result in a relatively large change in current in winding in winding I0, the change in regulated voltage will be much less if a material of a non-linear impedance characteristic such as shown in curve G is used rather than a linear impedance as in curve F.

In alternating current circuits, such an effect is obtainable very readily by placing an ironcored inductance in series with the winding i0, so proportioning the core in the inductance coils that the iron is near or. beyond its saturation value at the voltage at which the system is to regulate.

In both alternating and direct current circuits, materials which have a practically instantaneous response to voltage variations are of advantage due to their independence of the frequency of the system voltage, whether alternating or direct current.

One such material is commercially known as Thyrite, and is described in U. S, Patent No. 1,822,742 issued on September 8, 1931. This material, described in the General Electric Review of February, 1930, has mechanical characteristics ysomewhat similar to those of dry-process porceoi -the current :flowing before the voltage was doubled. Thus, the resistor 24 of Figures l and 6, for example, may be in the form ci a disk or Thyrite, illustratively a disk or annulus oi about three inches in diameter and about oneeighth of an inch in thickness. This material, moreover, also has a negative temperature coefcient or resistance in that its resistance decreases with increase in temperature.

ln addition tcthe advantages resulting from the use of a resistor with a negative temperature cceiricient oi resistance, a resistor made up of this material such as Thyrite, achieves many marked advantages. Illustratively let it be assumed that the winding it) has the rollowing characteristics, namely, a resistance on the order or 100 ohms, an operating voltage on the order ci 50 volts, and an operating current or a critical current or energization ci 0.5 ampere; iet it be assumed, also, that, in accordance with the past practice as hereinabove across the resistance is 100 volts. i variation mechaineal friction and magnetic hysteresis to l oi 3% in the current ci energization due perhaps to any condition of electromechanical unbalance in a regulating or relay system would result in a variation of 1.5 volts across the winding and of 3.0 volts across the resistance making a total voltage variation to which the system and apparatus is subjected of 4.5 volts.

lf, however, instead of using such a resistance in accordance with prior practice, I use a resistor ci 'I'hyrite in" circuit with the above-assumed winding such that the above-mentioned 3% voltage variation (increase in voltage drop across the winding il) due to the increase in current of energization) is effective, due to the alccvedescribed characteristic of the material, to produce a voltage drop across the resistance of only 0.25 volt, then the total voltage variation of the system, instead of being 4.5 volts, becomes the sum of 1.5 volts and 0.25 volt and hence 1.75 volts, resulting in a total voltage variation of only about 1.2% of the total voltage of 150 volts of the circuits I |-|2. Thus the performance of the system and apparatus is vastly improved with respect to the voltage sensitivity of the system including winding I0 and resistor R, a relatively small voltage variation resulting in a large change in current of energization.

The resistance material, having the abovementioned novel characteristics I may employ in various ways; for example, I may embody it in the formin which the resistors of Figs. 1, 3 and 6 are embodied, relating it to appropriate masses of appropriate thermal capacities and heat-radiating surfaces or I may let these resistances of Figs. 1, 3 and 6 take the form or forms above described, including the form in Fig. 5, relying upon the negative resistance coeillcients of temperature and include in the circuit of the corresponding resistor device R and winding I0 an additional resistor made up of a nonlinear impedance characteristic; in Fig. l I have diagrammatically indicated at 55 how the resistor of this material may be thus included in the system and apparatus. In such case I am enabled to reduce the size and thermal capacity of the resistor R due to the coacting eiect of the resistor 55. In such case also I may dispense in the resistor device R with a resistor having a negative temperature coeilicient of resistance and use a resistance of zero temperature coeflicient, retaining yonly the non-linear impedance characteristics of resistance, although commonly a resistance material of non-linear impedance characteristic has also a negative temperature coemcient of resistance.

'I'he ratio of thermal capacity to heat-radiating surface of the device R, to meet any particular or desirable condition of operation, may, moreover, be achieved, or varied as may be desited, in any suitable or desirable way; for example, and again considering illustratively the embodiment shown in Figure l and more in detail in Figure 6, if it is desired to obtain a more rapid rise in temperature in the device R and to obtain a higher ultimate rise in temperature, the parts 25 and 26, illustratively cylindrical as above noted, may be given correspondingly smaller dimensions, as by reducing the axial length, correspondingly to achieve a change in thermal capacity and in cooling surface. For example, and purely by way of illustration, let it be assumed, in Figure 1 or 6, that the disklike resistance element 24 is made of the abovementioned Thyrite material and is approximately one-eighth of an inch thick and three inches in diameter; let it further be assumed that the characteristics of coil I0 are such that there is about a 40 C. rise in temperature with an increase of about 15% in resistance of the copper coil. By giving the solid cylindrical members 25 and 26, illustratively made of iron or steel, a diameter of 3" and an axial dimension of 3" each, the ratio ofthermal capacity of the device R to its heat-radiating surface becomes such that the resistance element 24 is subjected to a. rise in temperature of about C., just about appropriate to achieve the earlier abovedescribed compensation for the temperature rises or changes in the regulator coil 0 and its associated parts.

To illustrate further, let it be assumed, however, that the regulator coil I0 and its associatedl parts have such a ratio of thermal capacity to heat-radiating surface that the rise in temperature thereof is on the order of 55 C. to 60 C. with a resultant increase in resistance, due to this temperature rise, that may be 20% or more. To achieve the desired compensation in the device R, a greater rise in temperature therein is now necessary and hence a different ratio of thermal capacity to heat-radiating surface. Appropriate compensation is achieved by decreasing the axial length of the parts 25 and 26 and it so happens that if they are now made about 2" in axial length instead of 3" as above assumed, an appropriate ratio results to give exactly the compensation fdesired, as earlier above described in detail; inl such case, the rise in temperature of the disk-like resistance element 24 is approximately C. to 120 C.

These two illustrations will suffice to illustrate in detail such changes, based upon two illustrative but diiferent practical requirements, that may be made to obtain a ratio of thermal capacity to heat-radiating surface of the device R that substantially matches the ratio of thermal capacity to heat-radiating surface of the coil and its associated parts.

However, other means may be employed to obtain the desired ratio. For example, and referring now to Figure l0, and'assurning that the coil I0 and its related parts require, in the device R, a lower ratio of thermal capacity to heatradiating surface, I may provide the parts 25 and 26, or either of them, with, for example, heat-radiating fins 60. Or the parts 25 and 26 may be hollowed out or counterbored, as at 25* and 26X. Or, as will now be clear, I may select any appropriate material of which to make the parts 25 and 26, selecting the material in accordance with itself, and appropriately dimensioning the part or parts of such material; for example, iron has a specific heat of 0.1138, aluminum 0.2143, lead 0.0314, and so on.

I may achieve the desired ratio of thermal capacity to heat-radiating surface of the illustrative parts 25 and 26, or either of them, by dimensioning the parts to have the desired thermal capacity and then diminish the existingheat-radiating surface thereof as by covering an appropriate portion of the otherwise available heat-radiating surface with a good non-conductor of heat, such as asbestos in appropriate thickness. In Figure 11 I have shown the parts 25 and 26 provided with a wrapping, of appropriate axial extent, made of such heat-resisting or insulating material, as is indicated at 6i.

And, as will now be clear, the desired ratio may be achieved, changed, or altered, with respect to the device R of Figures 3 and 5, in manners and by means such as those illustratively just described.

Thus, it will be seen that there has been provided in this invention an apparatus in which the objects above-mentioned, together with many thoroughly practical advantages, are successfully achieved. It will be seen that the nvention is of a thoroughly practical character, and is in action dependably precise, and is, moreover, well adapted to meet the varying conditions met with in practice.

as many possible embodiments may be made o1' the above invention and as many changes might be made in the embodiment above set forth, it is to be understood that all matter hereinbefore set forth, or shown in the accompanying drawings, is to be interpreted as illustrative and not in a limiting sense.

I claim:

1. In a system of electric regulation, in combination, a circuit having therein electromagnetic means for controlling a regulating means, y,said electromagnetic means having a certain ratio of thermal capacity to heat-radiating surface thereof and having a positive temperature coefficient of resistance, and means in circuit with said electromagnetic means and having a negative temperature coeiiicient of resistance and substantially the same ratio of thermal capacity to heat-radiating surface as said electromagnetic means.

2. In a system of electric regulation, in combination, a circuit having therein a regulating coil of given ratio of thermal capacity to heatradiating surface and having the characteristic of change in resistance with change in temperature thereof due to 12R loss therein, and means for maintaining the current through said coil substantially constant in spite of change in resistance thereof comprising a resistance element having the characteristic of .changing its resistance as its temperature increases due to 12R loss therein in a direction opposite to the direction in which the resistance of said coil changes, and means thermally related to said resistance element to give it a thermal capacity and heatradiating surface such that the ratio therebetween is'substantially the same as said firstmentioned ratio.

3. In a system of electric regulation, in combination, a circuit having therein a regulating coil Whose impedance changes with change in operating temperature and having serially related thereto a. compensating impedance means, the ratio of thermal capacity to heat-radiating surface of said coil and of said impedance means being substantially the same.

4. In a system of electric regulation, in combination, a circuit having therein a translating device in which is included conductive means whose impedance' changes with change in operating temperature, and means for maintaining the current in said circuit substantially constant as against the change in impedance of said conductive means comprising conductive means connected serially with said rst-mentioned conductive means and having the characteristic of changing its impedance wi@ change in operating temperature but in a direction opposite to the direction in which the impedance of said first-mentioned conductive means changes, and means thermally related to said second-mentioned conductive means to give it a thermal capacity and heat-radiating surface such that the ratio therebetween is substantially the same as the ratio being the thermal capacity and heat-radiating surface of said translating device.

5. In a system of electric regulation, in combination, a circuit having therein a translating device in which is included conductive means whose impedance changes with change in operating temperature, and means for maintaining the current in said circuit substantially constant as against the changelin impedance of said conductive means comprising conductive means cong nected serially with said iirst-mentioned conductive means and having the characteristic of changing its impedance with change in operating in impedance from materially affecting thestandard of voltage regulated by said regulating means comprising compensating impedance means electrically related to said regulating means, the ratio of thermal capacity to heatradiating surface of said regulating means and of said compensating impedance means being substantially the same.

7. In a system of electrical regulation, in combination, a circuit having therein a translating device which has a certain thermal capacity and a certain heat-radiating surface and having the characteristic of changing its impedance with changes in operating temperature, and compensating impedance means electrically related thereto and comprising an impedancev device having the characteristic of changing its impedance in the opposite direction with change in operating temperature but physically having a ratio of thermal capacity to heat-radiating surface different from the ratio of the thermal capacity to heat-radiating surface of said translating device and means physically related to said impedance device to give it an effective ratio of thermal capacity to heat-radiating surface substantially equal tothe ratio of thermal capacity to heat-radiating surface of said translating device.

8. A system as claimed in claim 7 in which the impedance device is in the form of a disklike member and in which the means physically related to the impedance device comprises a metallic means of appropriate mass and heatradiating surface.

9. A system as claimed in claim 7 in which the impedance device is in the form of a disk-like member and in which the means physically related to the impedance device comprises two metallic means, each adjacent to a face of said disk-like member and being together of the desired mass and heat-radiating surface.

10. A system as claimed in claim 7 in which the impedance device is in the form of a disklike member and vin which the means physically. related to the impedance device comprises two metallic means and means for holding them and said disk-like member together with the latter between them.

11. A system as claimed in claim 7 in which the impedance device is in the form of a disklike member and ln which the means physically related to the impedance device comprises two metallic members between which said disk-like member is positioned, and means extending through all three and insulated therefrom for holding them in cooperative physical and thermal relation.

l2. A system as claimed in claim 7 in which the means thermally related to the impedance device comprises a hollow member.

13. A system as claimed in claim 7 in which the means thermally related to the impedance thermal capacity and having means for reducing its heat-radiating surface to the desired eX- tent comprising means of suitable resistance to conducting heat covering a desired portion of the heat-radiating surface.

14. A system as claimed in claim 'l in which the impedance device comprises a material having also the characteristic of changing its resistance at a greater rate than but inversely to the rate of change of voltage impressed thereacross.

15. A system as claimed in claim 7 in which the impedance device is in the form of a disklike member and in which the means physically related to the impedance device comprises two metallic means, each adjacent to a face of said disk-like member and being together of the de-` sired mass and heat-radiating surface, and in which there is interposed between each of the two metallic means and the disk-like member means of good thermal conductivity for insuring good thermal interrelation between the member and said two metallic means.

16. In a system of electric regulation having a work circuit that has an auxiliary regulating circuit connected thereto with electro-responsiveV regulating means in said regulating circuit, the latter having the characteristic of changing its impedance with changes in operating temperature, the combination therewith of an impedance device in series with said electro-responsive means and having the characteristic of changing its impedance so that the current iiow therethrough is substantially a logarithmic function of the voltage, the ratio of thermal capacity to heat-radiating surface of said regulating means and of said impedance device being substantially the same.

1'7. In a system of electric regulation, in combination, a circuit having therein an electrical unit whose impedance changes with change in operating. temperature and having serially related thereto compensating impedance means, the ratio of thermal capacity to heat-radiating surface of said unit and of said impedance means being substantially the same.

18. In an electric circuit, in combination, an electrical unit whose impedance changes with changes in operating temperature, and a compensating impedance means, the ratio of the thermal capacity to the ability to dissipate heat to the surrounding medium of said unit and of said impedance means being substantially the same.

19. An electrical circuit which includes a plurality oi electrical units one of which is a compensating impedance means whose impedance changes with a change in operating temperature and Whose heat-retaining, heat-absorbing and heat-dissipating characteristics are such that with a given variable voltage impressed upon the circuit the temperature of said impedance means will at all times be the same as the temperature of another unit in the circuit.

20. In an electric circuit, an electrical unit having impedance which changes as the operating temperature changes and including portions having heat-generating, heat-accumulating and heat-dissipating characteristics, and a compensating impedance unit having impedance which changes as the operating temperature changes including portions having heat-generating, heataccumulating and heat-dissipating characteristics, said characteristics of said units being substantially similar.

2l. A circuit as claimed in claim 20 in which the compensating impedance unit has -two substantially cylindrical metallic blocks in spaced alignment and a substantially disc-shaped resistance element between the adjacent ends of said blocks.

22. A circuit as claimed in claim 20 in which the compensating impedance unit includes a rodlike resistance element and Washer-like metallic members fitted upon said rod.

23. A circuit as claimed in claim 20 wherein the compensating impedance unit includes a substantially cylindrical portion and washer-like metallic elements mounted upon said substantially cylindrical portion.

24. A circuit as claimed in claim 20 wherein the compensating impedance unit includes a heat-insulating covering which may be adjusted so as to control the heat-dissipating characteristics of the unit.

25. A circuit as claimed in claim 20 in which the compensating impedance unit includes two bracket members adapted to act as mountings for the units and for Wire terminals, two substantially cylindrical metallic elements mounted between said brackets in substantial alignment, a substantially cylindrical resistance element mounted between the adjacent ends of said substantially cylindrical metallic elements, bolt and nut structure holding said elements and said rod elements in place.

FRANK W. GODSEY, JR.

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