US1763881A - Variable inductance - Google Patents

Description

June 17, 1930. P. P. CIOFFI VARIABLE INDUCTANCE Filed July 8, 1924 CURVE A 65 "/0 NI 55 /o FE AT ZERO TLNSIGN CURVE. B 65% NI 5570 FE. AT 5000 LBS./5Q.IN. CURVE C PURE FE AT ZERO TENlON CURVE. D PURE. FE AT 5000 LBS./5Q.IN.-

+z 3 amnion a I Maqnd'izinq force Patented June 17, 1930 UNITED STATES PATENT OFFICE,

PAUL CIOFFI, OI BBOOEYN, mew YORK, ASSIGNOR TO WESTERN ELECTRIC OOH- PA'NY, OF NEW YORK, N. Y A CORPORATION OF YORK VARIABLE INDUGIANCE Application fled July 8,

This invention relates to a variable inductance and its object is to make possible a continuous variation in inductance over a wide range and without change in resistance. Such a variable inductance is of particular interest in balancing networks employed where it is desired to operate duplex systems over loaded telegraph wires. It is also useful in the shaping networks used at the terminals of long loaded cables.

In accordance with a feature of the invention, the core of an inductance coil is composed of a material, the permeability of which is highly sensitive to mechanical strain or to change in the magnetizing force, or to both, and means are provided for varying the strain exerted upon the core member or the strength of the magnetizing field, or both. The fact that iron and also nickel change their magnetic properties with a change in pressure or tension is well known and is commonly referred to as the magneto-stricture characteristic of the material. However, in these materials, this change is too small to be of any commercial advantage. In the case of certain nickel-iron alloys, when properly heat treated, the magneto-stricture characteristic is very pronounced and in a co nding application of Oliver E. Buckley, rial No. 610,015, filed December 30, 1922, which has issued as Patent No. 1,666,680, on April 17, 1928, this property is taken advantage of in the construction of a dynamometer. As a result of an exhaustive study of the magneto-stricture characteristic of various nickeliron alloys, it has been determined that the change in permeability due to change in tension is not only greatly variable as regards the composition of the alloy but is also dependent to a large degree upon the heat treatment to which the composition is subjected. Thus, with a given composition, it is posible by varying the heat treatment to obtain widely difierent magneto-stricture characteristics. Furthermore, in the case of nickebiron alloys subjected to mechanical strain, the rate of change in permeability with change in magnetizing force, depends not only upon the proportion of nickel and iron' m in the composition, but also upon the heat alloy as compared with iron when subjected 1924. Serial No. 724,768.

tieatment to which the composition is subjecte The various features of the invention may be clearly understood by reference to the accompanying drawing in which:

Fi 1 shows a variable inductance coil embodying the features of the invention, and

Fig. 2 shows curves illustrating the change in permeability of the preferred nickel-iron to varying mechanical strains and to varying magnetizing forces.

Referring to the drawing, the core member 5 preferably consists of a tape of nickel-iron alloy containing nickel and 35% iron, wound around the saddle blocks 6, 6, the ends being secured by some such means as the rivet 7. The lower saddle block 6 is secured by means of a ring member 8 to a support 9 secured in the base 10 of the housing 11. The upper saddle block is secured by means of ring 12 to a support member 13 which is pivotally secured to the hinged member 14 which in turn is pivoted at 15. The thumb screw 16, threaded into the free end of member 14, is adapted to bear against the cover member 17 and thus permit placing the core member 5 under tension. About the core member 5 is placed a winding 18, the ends of which are preferably brought out and connected to a signaling line over a pair of w1res such as shown at 25 and 26 by terminals not, shown.

In order further to provide for change in the inductance of the winding, a source of (11- rect current 19 connected in series with the variable resistance 20 and impedance coils 21, 22 is connected in shunt with the winding 18, condensers 23, 24 being connected as shown to prevent direct current from the source '19 from flowing out on the line over conductors 25 and 26. The function of the impedance coils is to prevent the direct current clrcuit from affecting the alternating current circuit.

The ma etic tape used for the core maybe prepared y fusing together iron and n ckel in the proportion of 65% nickel and 35% 1 ron. The molten composition is then poured in a mould and is rolled or otherwise ormed 1nto a tape of the desired dimensions. A preferred 1 00 method of preparing this material is to mix together pure iron and nickel powders in the proportions stated, compressing the mixture to form a solid mass and then subjecting the composition to the temperature at which nickel fuses, the fusin step being conducted under vacuum to preclude any possibility of contamination. To develop the utmost permeability in this tape, it is heated to a temperature of 960 C. and maintained at this temperature for a period of approximately ten minutes. It is then cooled rapidly at the rate of approximately 30 C. per minute for a peof ten minutes and then cooled more slowly so that it attains room temperature in approximately minutes.

Although the most satisfactory results are obtained when using an alloy containing 65% nickel and 35% iron, very good results may also be obtained with other nickel-iron alloys in which the nickel component predominates and, under some conditions, with alloys in which the nickel content is as low as 45%. Obviously, for different alloys it is necessary to determine experimentally the heat treatment required .to develop the maximum permeability of the material and the magnetizing forces at which the maximum rate of change in permeability takes place. With the preferred composition ,containing 65% nickel, the permeability with zero tension is relatively low and the total change in permeability is great. Therefore, with this material, the efiect of eddy currents is less than would be the case if the range over which the permeability varies was higher.

In Fig. 2, curve A shows the change in permeability of the nickel-iron alloy containmg 65% nickel and 35% iron for various magnetizing forces when subjected to zero tension and curve B shows the corresponding change in permeability when this material is I subjected to a tension of 5000 pounds per square inch. In a similar manner, curve C shows the change in permeability for various magnetizing forces of a very pure grade of iron when subjected to zero tension and curve D shows the changes in permeability under similar conditions when this material is subjected to a tension of 5000 pounds per square inch. It will be noted that with the nickel- 1ron alloy when employing a magnetizing force of approximately .17 gauss, an increase in tension from zeroto 5000 pounds per square ,inch produces an increase in permeability of from approximately 3000 to 51,000, that is, an increase in inductance of approximately sixteen times is produced by applying a tension equivalent to 5000 pounds per square inch. It will also be noted from curve B that with the nickel-iron composition subjected to a tension of 5000 pounds per square inch, a change in the magnetizing force of from zero to .17 gauss produces a change in permeability of from approximately 6500 to In the arrangement disclosed in F1g. 1, a strip .006 of an inch thick and .25 of an mch wide, composed of a nickel-iron alloy containimatcly eight inches. When provided with a proper winding to secure the desired magnetizing force of .17 gauss, the inductance for zero tension was equal to a proximately 1 henry and when the core mem r was sub ected to a tension of 7 pounds, the inductance was increased to approximately 17 henr s. By means of the leverage of the hinge 14,t 1s change in inductance necessitated a pressure of only 3% pounds in line -with the thumb screw 16.

The shape of curve B of Fi 2 may varied by introducing air ga s o desired w dth at the top or bottom or bot of the nlckel-lron alloy strip 5. In general, this will lower the permeability and make the device less sensitive to small variations of current from battery 19.

- What is claimed is:

1. In a variable inductance arrangement, a core of an iron-nickel alloy having a permeability which may be varied over a wide range under mechanical strain, meohamcal means for applying strain to said core to increase its permeability range, a fixed winding about said core, a series path including saidwinding and also including a pair of wires having terminals adapted for connection to a circuit, an adjustable dlrect current source connected to said path for producing abiasing current in said winding tqmalntain a high average permeability of said core, a stopping condenser in said path separate said source from said pair of wires and a choke coil connected between said source and said pair of wires.

2. In an inductance control arrangement, a core and a winding thereon, said winding having an inductance which is controllable by variation of mechanical strain apphed to said core to compensate for variations in .of permeability variation is obtained in response to variations within said limits of the strain, inductive means included in such direct current circuit for choking alternating currents therein, and an alternating current circuit for superimposing an alternating flux on the biasing flux resulting from said magnetomotive force of a magnitude determined by the adjustment of said mechanical means, said alternating current circuit including a capacitance for obstructing the flow of direct current therein.

3. In an electric circuit including an inductive device having a core with a permeability which is highly sensitive to mechanical strain, the method of varying the inductance of said circuit which comprises producing a unidirectional biasing flux by applying a magnetizing force to said core to secure high sensitivity of its permeability at said flux to variations in strain and applying a mechanical strain to said core to secure a desired permeability and adjusting said strain to fiect a diflerent ermeabi ity of said flux.

4. A method 0 operating a variable inductance having a core of magnetic material the permeability of which, at a given magnetizing force, varies over a wide range in accordance with variations in mechanical strain applied to said material which comprises. applying a unidirectional magnetizing force to said core to secure said wide range of permeabilities and varying the mechanical strain in said material to produce any permeability, due to said magnetizin force, within sald range, and applying an a tuna]:- ing magnetizin force to said core to pr0- duce an alternating flux of a magnitude varyin with the mechanical strain.

witness where0f,I hereunto subscribe my name this 7th day of July, A. D. 1924. PAUL P. GIOFFI.

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