US 1608872 A
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Description (OCR text may contain errors)
Patented Nov. 30, 1926.
UNITED STATES PATENT OFFICE.
CYRIL T. WALLIS, OF ROCHESTER, NEW YORK, .ASSIGNOR TO NORTH EAST ELECTRIC OOMRANY, OF ROCHESTER, NEW YORK, A CORPORATION OF NEW YORK.
TEMPERATURE Application filed Kay 7,
This invention relates to the compensation of electromagnetic instruments for the. effect of temperature-changes.
In an electromagnetic instrument in which vthe effectof a current of electricity, fiowing in or producing a magnetic field, 18 to be measured, or to be utilized directly or indirectly in the measurement of some other quantity, it is-usually necessary or preferable to use a conductor, for such current, of some relatively low-resistance metal, such as copper or aluminum. Such metals have relatively high temperature coeffieients of resistance, and in the use of such instruments inaccuracy may arise from changes in the resistance of the conductor due either to changes in atmospheric temperature or to the direct heating of the conductor by the current flowing in it.
To compensate automatically for such changes in resistance, it. has heretofore been proposed to utilize, in the magnetic circuit of an electromagnetic instrument, a shunt consisting of an alloy having the characteristic that its permeability decreases with rise in temperature. Such a shunt acts to diminish the strength of the field, with diminishing temperature in the instrument, more or less in proportion as the efliciency of the conductor increases with the corresponding diminution of resistance.
The alloys best known, heretofore, for the purpose, are certain alloys of nickel and iron. In these alloys however, the temperature-reluctance curve is not a straight 1ine,;owing to the fact that the reluctance increases more rapidly, with increase in temperature, in thelower range of atmospheric 'temperatures than it does in the higher ran e. The resistance of copper and other meta s follows a substantially straight line, however, throughout the ordinary range of atmospheric temperatures, and accordingly a nickel-iron alloy will not give exact temperature-compensation in an elec- =tromagnetic instrument, but only a roughapproximation to this result.
. The object of the present invention is to provide a magnetic shunt which will give substantially perfect com ensation throughout a substantial range 0 temperatures, and particularly a shunt having a substantially straight temperature-reluctance line. I
I have. discovered that this can be accomplished by the use of a shunt consisting of COMPENSATION.
1923. Serial No. 037.394.
bodies of two different alloys, the alloys be ing so chosen that the characteristic lmeofthe one alloy is carved in the opposite direction from that of the other alloy, within the designated range of temperatures, and the two alloys being used in such proportions that the joint effect is a uniform or straight-line change of reluctance with tem perature. The alloys which I have found most suitable for the purpose in question are a nickeliron alloy having approximately 28.78% of nickel, and the alloy of nickel and copper commonly known as Monel metal. Both of these alloys contain also a small percentage of manganese, which seemsto have anobscure relation to their magnetic qualities, but is in any case important for metallurgical reasons.
In a magnetic field having a density of k 100 lines per square centimeter, the two alloys in question should be used in about the proportions. of 64% nickel-ironand 36% Monel-metal, and as so used their combined permeability follows a line which" .is straight, within the limits of error in measurement, through a range of 0 to 120"v the flux-density in the compensating bodies when subjected to a magnetic field of constant strength, at the several given temperatures. From this diagram it will be apparent that the temperature-permeability of the nickel steel follows an upwardly concave curve. While thccorresponding line of the Monel metal is oppositely curved, and that these opposite curvatures combine in a sum or resultant which is approximately straight ihrough the range from 0 to 120 Fahreneit.
This compensating device may be used in electromagnetic instruments of various r Fig. 2 shows its application to an;
e ect voltmeter or ammeter, provided with a per- .manent Wet 5, which is used to produce a field in w ich a' coil or armature (not shown) may move. When not compensated .for' temperature, such an instrument must w ature, in order that its reading ma --10 -m g b so ll s not sensib y to housed in an atmosphere of definite terli;
accurate, and the current passed throu its 1 6 .thecoilf. Tliese limitations may bereqv'ed, however, by the use of a compensa "3* betweenflthe poles of the .magnet. ll a ing shell 1 of Monel-metal.
set fo'rth in sshunt isshown as comprisinga cylin-, drieal core 6-- ofnickel-steel, and a surroundcup 10, turning on an axis 11, is moved by interposed in a gap in the ring-magnet, the magnet being somagnetized that its extrem- T used in'=parallel--ins tead, as shown in the inductive drag of a ring-shaped permanent magnet 12 which is rotated upon a shaft 13. The compensating alloys 14 andlfi are ities 16 and 17 constitute its poles. In this instance the two alloys are shown as arranged so as to be traversed in series by the magnetic flux, but obviously they ma be le .2" and 3.
It .wm be understood that the several specific instances of the use of this invention whih have been shown and described are "gonly' a few among many possible uses. It
,will also be apparent that while the alloys used'may, and usually will be so selected and proportioned as to secure an approximate I rical measuring instrument such as a straight-line resultant, as in Fig. 1, the invention is not limited to such use. By suitable selection and proportions the dissimilar alloys may be caused to secure a resultant following a curve of almost any desired form, and the novel and valuable nature of mitsthe automatic compensation of an instrument according to a law or laws which are not limited to the idiosyncrasies of any particular metal or alloy.
The lines givenin Fig. 1 were obtained in --a magnetic field having a density of 100 lines per square centimeter. .difierent strength it may be necessar to use In a field of the dissimilar alloys in proportions iil'erent from those shown. This is a matter which may readily be determined by experiment in any given case.' 7 he invention claimed is: 1. Means, for compensating for the effect of temperature changes in an electromagnetic instrument, comprising bodies of dissimilar magnetic alloys located in a magnetic circuit of the instrument, said alloys being such that their temperature-permeability lines are oppositely curved through a substantial range of temperatures.
2. In an electromagnetic instrument, the combination, with a magnet, of a magnetic shunt associated therewith and com rising bodies of two dissimilar alloys suc that their temperature-permeability lines are oppositely curved so as to produce a resultant approximating a straight line.
3. In an electromagnetic instrument, the combination, with a magnet thereof, of a magnetic compensating device comprising two bodies of dissimilar alloys located between the les of said magnet, said alloys having di erent temperature-permeability characteristics so as to compensate the instrument in accordance with a law (liflerent from that of either alloy.
cyan. T. WALLIS.
- the invention resides in the'fact that it per-