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July 30, 1946- R. A?. PFUNTNER ET AL 2,405,050 MAGNETIC COMPASS DEVIATION CQMPENSATQR Filed March 2, 1945 ? 2 Sheets-Sh閑t l Figl. Irwventors; Richard ADFUTW?UWGT?, Eleanor D.Wi son, b E? 6: x) ?yTh n" Attorney. _ July 30, 1946. R. A. PFUNTNER ET AL 294959050 MAGNETIC COMPASS DEVIATION CQMPENSATOR Filed March 2, 1945 2 Sheets-Sheet 2 ' 45a A 4/3 2 Inventors: Richard A. PFuntnen Eleanor? D. Wilson, Th iv? Attorney. Patented July 30, 1946 2,405,050 UNITED STATES PATENT OFFICE 2,405,050 MAGNETIC COMPASS DEVIATION COMPEN SATOR Richard A. Pfuntner, Saugus, and Eleanor D. Wilson, Brookline, Mass, assignors to General Electric Company, a corporation of New York Application March 2, 1945, Serial No. ?580,504 9 Claims. (Cl. 33-225) 1 2 The present invention relates generally to mag current, and, in addition, polyphase connections netic compasses, and more particularly to a new which are supplied with second harmonic cur rents from a remotely located compensator trans mitter unit. 'The second harmonic currents flow ing in "the coil and the resulting second har and improved deviation compensator used for compensating for the e?ect of stray magnetic ?elds in the vicinity of the compass. Magnetic compasses of the so-called remote indicating type are now widely used on aircraft, these compasses having the advantage that the magnetic compass and its associated transmitter may be located in a wing or some remote part of monic ?uxes produced in the core cause unidi rectional magnetic flux to flow across the diam eter of the core. The transmitter is provided with ?magnetic means for varying the magnitude and polarity of the second harmonic currents sup plied to the compensator core whereby the mag nitude and direction of the unidirectional ?eld the fuselage of the aircraft where ?the effects of local magnetic ?elds and disturbances are less se vere, the remote receiver indicator being located produced across the diameter of the core may in the control cabin or some other convenient be adjusted to compensate, i. e., cancel out, location. Deviation compensators for compasses, 15 effect of any stray magnetic ?eld in the vicinity including the remote indicating type, frequently of the compass. are located adjacent the direction-sensitive ele For a better and more complete understanding ment of the compass, the compensator usually of the invention reference should now be made to comprising a number of small permanent mag the following detailed description and to the ac nets adjustably mounted so that the compensat companying drawings in which Fig. 1 is a dia ing auxiliary field produced thereby can be made grammatic View, in perspective, of a remote in to be equal and opposite to the ?eld caused by dicating magnetic compass provided with a com the plane?s permanent magnetism or other per pensator and compensator transmitter unit manently magnetized bodies in the vicinity of the forming the subject matter of the present inven compass. Such deviation compensators require 25 tion, Fig, ?2 is a v?schematic vwiring diagram show local adjustment and are subject to the disad ing the manner in which the windings of the vantage that remote compass transmitters are compensator and transmitter units shown in Fig. usually located in a small, cramped space so that frequently adjacent equipment or even part of the airplane structure has to be removed to ren der the deviation adjustment accessible. An object of the present invention is to provide a new and improved deviation compensator for a 1 are electrically interconnected, and Fig. 3 shows a modi?cation in which the compensator carries 30 separate windings for the second harmonic cur rents and the transmitter has two separate cores and associated windings ?for the production of second harmonic currents which are fed to the magnetic compass. compensator. Another object of the invention is to provide a 35 Referring to Fig. 1 of the drawings, the devi deviation compensator that is remotely adjust ation compensator forming the subject matter able so that there is no need for having access of the present invention is shown as being used to the remotely located compass. in connection with a standard, remote-indicat A further object of the invention is to provide ing, magnetic compass used on aircraft compris a remote controlled compass-deviation compensa tor which is relatively simple, inexpensive, and Which can be applied to any compass or device used to detect the direction of the earth's mag netic ?eld. Further objects and advantages of my inven tion will become apparent as the following de 40 ing a compass transmitter unit I and an indi cator receiver 2, the two units being coupled to gether by means of an electric cable 32 which carries the necessary signal ?impulses for repro ducing the?compass indications of the transmit 45 ter I at the remotely located receiver indicator 2. The compass transmitter unit I may comprise scription proceeds. a conventional compass element comprising a pair According to the present invention deviation compensation is accomplished by the provision of permanent magnets 3 which are pendulously supported on a vertical post 4 by means of a jew of an annular core of permeable magnetic ma 50 elled bearing 5 so that the compass magnets :3 terial which is located in magnetic relation with are free to swing in .-a horizontal plane and seek the directional element of the compass. The core the magnetic meridian. Angular position of the has coil means associated therewith having ?a sin compass magnet 3 in the transmitter unit is re gle phase connection adapted to be connected to produced at the receiver indicator unit 2 by a well a source of alternating or periodically varying 55 known ?second harmonic 'telemetering system 2,405,050 4 comprising a transmitter ring 6 located beneath the compass magnet, the ring being electrically uniformly distributed exciting winding 23, the end spondence. Mounted for rotation within the re ceiver ring 1 are a pair of permanent magnets 8 responding polyphase connections of the corn pensator winding l3 and the transmitter winding which are mechanically coupled to a compass 23 are electrically connected. Associated with the core 22 of the transmitter unit are a pair of cylindrically shaped permanent connections of which are brought out at points 21% and 25 to form single phase connections which connected by the cable 32 to a similar ring 1 are connected to the alternating current supply at the receiver indicator. The permanent mag net ?eld. from the compass magnet 3 which is Cl leads l8 and El". The winding 23 is also provided with tapped connections 26 and 2i which are produced across the diameter of the transmitter located so that the connections 25 and 2'! and ring 6 causes a ?ow of second harmonic current the common connection ?2.5 are equally spaced between the transmitter receiver rings 6 and ?I, around the periphery of the winding 23 to form these currents causing a unidirectional magnetic ?eld to flow across the diameter of the receiver 0 symmetrical polyphase connections corresponding to the polyphase connections !5, i8 and i9 of the ring ?I, the angular position of the ?eld extend compensator winding i3. As shown, the cor ing across the rings 6 and 1 remaining in corre card 9. The permanent magnets 8 tend to main tain themselves in alignment with the unidirec magnets 28 and 2d, the magnets being mounted tional magnetic ?eld ?owing across the diameter of ring 1 so that the compass card 9 reproduces the angular position of the compass magnet 3 relative to the aircraft on which the compass sys tem is mounted, the cardinal characters on the compass card 9 being read against the station ary index it]. The remote indicating compass adjacent the core on opposite sides thereof. The magnet 23 is mounted on a rotatable shaft 30 the axis of rotation of which coincides with the axis of the magnet cylinder and extends in the direc tion or" the line Al, A2. The magnet 25} is mounted on a rotatable shaft M, the axis of rotation of system thus far described is entirely convention 25 which coincides with the axis of the magnet cyl inder and extends in the direction of the line al and forms no part of the present invention El, E2. As shown, the axes Al, A2 and BI, B2 as the deviation compensator, which will now be are mutually perpendicular and lie in planes in described, is applicable to all types of magnetic cluding mutually perpendicular diameters of the compasses including both the pivoted magnet core 22. and induction types. The cylindrical magnets 28 and 29 are each The deviation compensator, forming the sub magnetized across a diameter of the cylinder so ject matter of the present invention, comprises that diametrically opposite points on the surface a compensator ring i I which may be mounted, as of the cylinder constitute north and south poles, shown, in the upper portion of the compass trans mitter unit i so that it is in a position to mag 35 as indicated. When the magnets 28 and 29 are netically influence the compass magnets 3. The rotated to the position shown, the magnet 28 will ring H is mounted in a horizontal position so that the axis of the ring coincides with the axis of rotation of the compass magnet 3. cause a unidirectional magnetic ?ux to flow across a diameter of the core 22 in the direction of axis Bi, B2, and the magnet 2:?. will cause a unidirectional magnetic flux �to ?ow across a diameter of the core 22 in the direction of the As- shown in Fig. 2, the compensator ring H comprises a closed core [2 which is preferably, axes A2, Al. The magnetic ?uxes (pi and �produced by the magnets '28 and 29 return to opposite poles of the magnets through the core although not necessarily, annular in shape. The core is also preferably laminated and formed of a highly permeable magnetic material, such as, for example, magnetic material known to the 45 22, as indicated by the flux arrows and in this manner the ?uxes link the winding 23. trade as ?Permalloy? or ?Mumetal.? The core 12 The ampere turns of the windings l3 and 23 on carries a uniformly distributed winding it, the the compensator and transmitter cores i2 and end connections of which are brought at adjacent points on the ring, the end points of the winding 21 are selected such that alternating current sup 50 plied from the supply lines it and ii? causes par being numbered i4 and H5, The coil connections it and 55, which may be termed a single phase connection, are connected to a source of alternating current supply, the supply leads being numbered l6 and H. The winding i3 is provided with tapped con 55 nections i8 and Hi, the taps being spaced so that the connections l8 and i9 and the common con tial saturation of the cores i2 and 22. The par tial saturation in the core 22 causes a periodic variation in the permeability of the core which, in turn, causes an accompanying periodic varia tion in the unidirectional ?uxes M and �which link the winding 23, As the result of the periodic variation or pulsation of the ?uxes pi and Q52, second harmonic currents and voltages are in nection it are located at three equally spaced duced in the winding 23. Due to the symmetry points around the periphery of the coil, i. e., they are 120� apart, these connections being termed 60 of the polyphase interconnection between the windings l3 and 23 of the compensator and trans polyphase connections. Second harmonic cur mitter, corresponding second harmonic currents rents supplied from a remotely located trans and voltages are induced in the winding l3 of the mitter unit, indicated generally at 20, are intro compensator. The second harmonic currents in duced into the winding i3 through the polyphase connections l5, l8 and I9, and the second har 65 duced in the winding E3 of the compensator pro monic currents cause a unidirectional compen duce second harmonic ?uxes which circulate sating magnetic ?eld to flow across the diameter of the core l2, as will be more fully described. around the core l2 and across diameters thereof in the same relative directions as the ?uxes The compensator transmitter unit 2E! comprises (M and �circulate in the transmitter core 22. 70 Second harmonic ?uxes in the core l2 are alter nating in nature, but due to the periodic satura tion of the core 92 due to the flow of exciting current of fundamental frequency in the wind ing it a rectifying action takes place so that the 75 magnetic ?uxes ?owing across the� diameter of a ring 2! which may be similar to the compen sator ring H, the two rings being electrically interconnected by electric connections indicated generally at 39. As shown in Fig. 2, the trans mitter ring 2! comprises an annular core 22 of permeable magnetic material, the core carrying a 2,405,050 5 the core l2 are unidirectional in nature. 6 windings 23 and is. since they are mutually per pendicular. Therefore, it is possible to adjust the magnetic ?ux M and 45!? without in any way Thus the unidirectional ?ux produced across the diameter of core 22 by the magnet 28 produces a corresponding unidirectional ?ux ' ?owing across the diametric axis Bl?, B2? of the com pensator core. Similarly, the unidirectional mag netic flux e2 produced by the permanent magnet 29 and ?owing across the diametric axis A2, Al affecting the mutually perpendicular magnetic CR ?uxes �and e2?, and vice versa. This feature is very desirable since it facilitates the deviation compensation adjustment which will now be de scribed. With the above understanding of: the invention of the transmitter core 23 produces a correspond ing unidirectional flux </>2? flowing across the 10 both as to the structure and. organization of the elements and the manner in which the compen diameter of the compensator core E2 in the di sating component magnetic fields of varying rection of the diametric axes A2?, Al?. The two ?uxes a!? and � produced across the mutually perpendicular diameters combine to produce a resultant unidirectional ?ux (pa. As shown in Fig. 1 of the drawings, suitable deviation adjustment knobs 33 and 34 are provid ed by means of which the permanent magnets 28 and 29 can be rotated about their respective axes Al, A2 and BI, B2, the knobs 33 and 34 being mechanically connected to the shafts 353 and 3! by shafts 35 and 36, and gears 31 and 38. By rotating the permanent magnets 28 andv 29, the components of unidirectional flux pro duced thereby and flowing in the direction of the axes Al, A2 and Bi, B2 may be adjusted with reference to both magnitude and direction. In this manner the magnitude and polarity of the second harmonic currents ?owing from the com strength at right angles to each other may be produced across the diameter of the? compensator core l2, the manner in which the device func tions to compensate for eil?ect of a stray magnetic ?eld upon the reading of the compass will readily be understood. The compensator ring II is ori ented so that the axis Al?, A2? is parallel to the longitudinal axis of the aircraft on which the compass system is installed. In adjusting the compensating device, the aircraft is headed by means of a transit or otherwise so that its fore and aft axis, and the axis Al?, A2?, are exactly parallel to the north-south meridian of, the earth?s magnetic ?eld which is represented by the vector 46 in Fig, 1. The presence of a stray magnetic ?eld, such for example as might. be caused by the engine or some other magnetic pensator transmitter to the compensator, and 30 part of the aircraft becoming magnetized, would exert a turning moment on the compass mag consequently the magnitude and direction of the nets 3 so that the compass card 9 will not give the indication that it would otherwise give in the absence of such a disturbing magnetic ?eld. As as viewed from the top in Fig. 1, so that the .., suming that this disturbing magnetic ?eld is of such magnitude and direction that its horizontal north and south poles are brought into alignment component is represented by the vector B in Fig. with the axis Cl and C2 of the core 22, there 1, this horizontal component of the disturbing will be no component of unidirectional ?ux ?ow ?eld may itself be resolved into two components ing across the diameter of the core in the direc at right angles to each other. These components tion of the axes Bl, B2, and consequently the . are component BS parallel to the direction of the flux ? will be reduced to zero. If rotation of earth?s magnetic ?eld, and also to the fore and the magnet 28 is continued for 90 degrees more, aft axis of the aircraft, and a component Ba at the magnet poles will be reversed from the posi right angles to the direction of the earth?s mag tion shown in Fig. 1 and the ?ux. will ?ow in the direction of the diameter B2, Bl. This will 4:3 netic ?eld and. lying exactly athwartship. Since the fore and aft axis of the aircraft is headed cause a corresponding reversal in the flux ? corresponding unidirectional ?uxes ' and oil? may be adjusted as desired. Thus, for example, if the magnet 28 is rotated 90� counterclockwise, in the compensator core so that its direction will north and south, the component BS exerts no in ?uence, i. e., turning moment, on the compass correspondingly be in the direction of the diame magnets 3, since, as pointed out above, this com ter B2?, Bl?. By rotating the magnet 23 to in termediate angular positions it will be apparent 50 ponent is parallel to the direction of the earth?s magnetic ?eld. The component Ba, however, that the magnitude and direction of the unidi which is at right angles to the direction of the rectional ?ux es] and �l' can be varied as de earth?s ?eld, will cause the compass magnets 3 sired. Similarly, by rotating magnet 29, the mag to be de?ected from the true north-south posi nitude and direction of the unidirectional ?uxes tion which they would otherwise normally occupy �and � can also be adjusted as desired. Thus 55 in the earth?s ?eld so that the indication of the it will be apparent that by correlated adjustment obtained by rotating the adjusting knobs 33 and 34 and the permanent magnets 28 and 29, a re sultant unidirectional ?ux ?owing across the diameter of the compensator core l2 can be ob tained having any desired magnitude and direc tion. . remote compass card 9 is erroneous. This errone ous indication may be corrected by rotating the adjusting knob 33 so as to rotate the permanent magnet 28 until a compensating component of magnetic ?eld exactly equal to and opposite in direction to the component Ba is produced by the compensator ring in the direction of the diameter Bl?, B2?. When this point is reached, the north It is important to note that the only possible interference between the magnetic ?elds produced index line on the compass card 9 will be exactly by the magnets 28 and 29 is in the direction of 65 opposite the stationary reference index II]. the axis Cl, C2 of the core. Interference in this In order to effect the athwartship compensa direction, however, is immaterial, since magnetic tion, the aircraft is headed east and west by ?ux ?owing in this direction does not circulate means of a transit or otherwise. The component around the transmitter core 22 and therefore does B5 of the stray magnetism that was formerly par not result in the generation of second harmonics 70 allel to the direction of the earth?s ?eld will now currents in the winding 23. There is no inter be at right angles thereto, and consequently will ference between the unidirectional magnetic exert an in?uence or turning moment on the ?uxes �l and �which extend in the direction of compass magnets 3 such as to de?ect them from the axes Bl, B2 and Al, A2, and which are effec the positions that they would ordinarily occupy tive in producing second harmonic currents in the 75 in the earth?s ?eld with the result that the com 2,405,050 7 8 pass card 9 will not indicate true east or west, core 22a is provided with a uniformly distributed exciting winding 4511 which is electrically con nected to the alternating current supply lines l6, H, as shown. The core is also provided with two as the case may be. The effect of the compo nent BS may be balanced out, however, by ro tating the adjusting knob 34 and the permanent magnet 29 until an auxiliary component ?eld CR diametrically opposite polyphase windings 4 l a and 42a which are located adjacent the diametric axis exactly equal to and in opposite direction to that Al, A2, the polyphase windings being connected of the component BS is produced by the com in series opposition and also connected to corre pensator ring H in a direction of the axis Al?, AZ?. This adjustment may be made by rotating the knob 34 and observing when the stationary index It] lies in coincidence with the east or west index line on the compass card 9, as the case may be. ' sponding windings 4| and 42 on the compensator core. The cylindrical permanent magnet 28 ex tends across the diameter of the core 22a and is mounted for rotation about the diametric axis Al, A2. In a similar manner, the transmitter core 2% is provided with a uniformly distributed The deviation transmitter unit 20 may be con veniently located adjacent the remote indicat? 15 exciting winding 45b which is connected to the alternating current supply lines [6, l1, as shown. ing compass indicator 2 and the above-described The core 221) is also provided with a set of poly deviation compensation adjustment can be made phase windings 43b and 44b which are located without need for access to the compass transmit adjacent the diametric axis Bl, B2, the windings ter unit I which may be located in a wing tip or at some remote location in the fuselage. 20 being connected in series opposition and also connected to corresponding windings 43 and 44 It is not necessary that the compensator ring on the compensator core. The cylindrical per H be mounted above the compass magnets 3 as manent magnet 29 extends across the diameter shown in Fig. 1 of the drawings, the only require of the core 221) and is mounted for rotation about ment being that the ring l i be mounted in hori zontal position and that the axis of the ring 25 the diametric axis Bl, B2. The permanent magnet 23 produces a uni coincide approximately with the axis of rota directional magnetic ?ux which circulates in tion of the compass magnets. Thus, if it is de the core 22a so as to link the polyphase windings sired to reduce the overall height of the trans ill a and 42a, causing second harmonic currents mitter unit 1, the ring H may be located below the compass magnets and, if the physical dimen 30 to be induced therein, these currents also ?ow ing in the corresponding windings M and 42 of sions of the compass transmitter ring 8 are suf the compensator. This causes a corresponding ?cient, the compensator ring may even be mount unidirectional flux � I ? to ?ow across the diameter ed within the transmitter ring. of the compensator core in a direction of the axis It is to be noted that one of the advantages of this system of deviation compensation over a 35 B l ?, B2?. As in the case of the embodiment shown system where direct current excited electromag in Fig. 2, by rotating the permanent magnet 28 the nets are used is the fact that the strength of the magnitude and polarity of the second harmonic compensating ?eld produced by the compensator current flow can be adjusted to obtain the desired ring H is insensitive to changes in supply volt in the saturated region of the magnetization magnitude and direction of the component 4A? of the compensating ?eld. Similarly, the permanent magnet 2d produces a unidirectional ?ux �which flows through the curve. core 222) so as to link the polyphase windings 43b age over a considerable range. The reason for this is the fact that the cores l2 and 22 operate In Fig. 3 of the drawings, there is shown a modi?ed arrangement in which separate wind ings are provided for carrying the second har monic currents which are effective in producing unidirectional magnetic ?elds across the diam eter of the compensator ring ll. Also in this and 44?], thereby inducing second harmonic cur rents in these windings which also ?ow through corresponding windings 43 and 44 on the com pensator core. This produces a unidirectional magnetic field 452' across the diameter of the compensator core in a direction of the axis A2?, Al '. By rotating the permanent magnet 29, the polarity and magnitude of the second harmonic currents, and consequently the magnitude and di rection of the component � of the unidirectional compensating ?eld can be adjusted as desired. Thus, by a correlated adjustment of the perma nent magnets 28 and 29 the resultant compensat phase windings 4!, 42, 43 and 44. The poly ing unidirectional magnetic ?eld can be made phase windings which carry the second harmonic equal and opposite to the horizontal component currents are shown in heavier lines in the draw of the stray magnetic ?eld whereby the desired ings to distinguish them from the exciting wind ings. The exciting winding 40 is connected to (if) deviation compensation adjustment is obtained in the same manner as previously described in con the alternating current supply lines 56 and l?! as nection with the embodiment of the invention shown. The diametrically opposite polyphase shown in Fig. 2. windings 4| and 42 are connected in series op The arrangement shown in Fig. 3 has the ad position, as are the diametrically opposite poly vantage that the magnets 28 and 29 may be phase windings 43 and 44, in vorder to obtain a physically spaced from each other so as to avoid cancellation of the voltages of fundamental or any possible mutual demagnetizing action of the supply frequency induced therein caused by a magnets due to interaction of their ?elds. Also, circulation of pulsating magnetic flux of supply with this arrangement the magnets may be poled frequency induced by the exciting winding All. at opposite ends of the cylinder rather than across As shown, the polyphase windings 4t, 42, 43 and the diameter, the magnets being mounted to ro 44 are grouped so that they lie adjacent the dia tate about the axis of'the associated core rather metric axes Al?, A2? and Bi?, B2?. than the axis of the cylinder in a manner similar In this modi?cation the transmitter unit 20 to the relation of the compass magnets 3 rela is provided with two separate cores 22a and 22b for-medv of ymagnetically permeable material. The > tive to the transmitter ring 8. Such'a construc modi?cation two separate cores are used in the : transmitter so that the permanent magnets 28 and Y253 can be physically separated if desired. In this modi?cation the compensator core if? is pro vided with a uniformly distributed exciting wind~ ing 40 and. two sets or pairs of grouped poly- .-~ 2,405,050 9 tion is more efficient magnetically in that a 10 cated remote from said compass, said cores hav greater ratio of length of the magnetic material ing similar coil means associated therewith, the along the magnetic axis to area perpendicular to coil means associated with each core having a the axis may be obtained. single phase connection and polyphase connec While we have shown and described particular tions, the corresponding polyphase connections embodiments of our invention, it will occur to of said cores being electrically interconnected, those skilled in the art that various changes means for supplying a periodically varying cur and modi?cations may be made without depart rent to the single phase connections of said cores, ing from our invention, and we therefore aim in means for producing a unidirectional magnetic the appended claims to cover all such changes and 10 ?eld across a ?rst diameter of said second core modi?cations as fall within the true spirit and whereby a unidirectional ?eld is produced across scope of our invention. What we claim as new and desire to secure a corresponding diameter of said ?rst core, means for producing a unidirectional magnetic ?eld by Letters Patent of the United States is: across a second diameter of said second core 1. A compass compensating device comprising a 15 at right angles to said ?rst diameter whereby uni closed core of permeable magnetic material lo directional ?eld is produced across corresponding cated in magnetic relation with said compass, diameter of said ?rst core, and means for vary means for producing a periodically varying mag ing the magnitude and polarity of the unidirec~ netic flux in said core, means for inducing second tional magnetic ?elds in the direction of said ?rst harmonic magnetic ?uxes in said core at spaced and second diameters of said second core whereby points around the periphery thereof, whereby to to vary the magnitude and direction of the result produce a compensating unidirectional magnetic ing unidirectional ?eld produced across the di ?eld across said core, and means for varying the polarity and magnitude of said second harmonic ?uxes whereby to vary the magnitude and direc ameter of said ?rst core. 5. A remote controlled deviation compensator for a magnetic compass comprising a ?rst annu tion of said unidirectional compensating magnetic ?eld. lar core of permeable magnetic material located in magnetic relation with said compass, a second 2. A deviation compensator for a magnetic com annular core of permeable magnetic material lo pass comprising a closed core of permeable mag? cated remote from said compass, said cores hav netic material located in magnetic relation with 30 ing similar coil means associated therewith, the said compass, coil means associated with said core, coil means associated with each core having a said coil means having a single phase connection single phase connection and polyphase connec and polyphase connections, means for supplying tions, the corresponding polyphase connections said single phase connection with a periodically of said cores being electrically interconnected, varying current, means for supplying second har- ? means for supplying a periodically varying cur monic currents to said polyphase connections rent to the single phase connections of said cores, whereby a unidirectional magnetic ?eld ?is pro a ?rst elongated cylindrical permanent magnet duced across said core, and means for varying the associated. with said second core and extending in polarity and magnitude of said second harmonic current whereby to vary the magnitude and di 40 the direction of a ?rst diameter of said second core, a second elongated cylindrical permanent rection of said unidirectional ?eld. magnet also associated with said second core and 3. A compensating device for a magnetic com extending in the direction of a second diameter pass ccmprising an annular core of permeable of said second core at right angles to said ?rst magnetic material located in magnetic relation with said compass, coil means on said core having bl diameter, said cylindrical permanent magnets being magnetized across a diameter of the cylin a single phase connection and polyphase connec der so that mutually perpendicular unidirection tions, a source of periodically varying current al magnetic ?elds are produced across said second connected to said single phase connection to pro core in the direction of said ?rst and second di duce a periodically varying ?ux in said core, transmitter means for supplying second harmonic ameters whereby corresponding unidirectional magnetic ?elds are produced across correspond currents to said polyphase connections to produce a compensating unidirectional magnetic ?eld ing diameters of said ?rst core, and means for across said core, a ?rst adjusting means associ separately rotating said ?rst and second mag ated with said transmitter means for varying nets about their cylinder axes so as to vary the the polarity and magnitude of said second har magnitude and polarity of the unidirectional monic currents supplied to said polyphase con ?elds produced thereby in a direction of said nections so as to vary the magnitude and direc ?rst and second diameters whereby to Vary the tion of the component of said unidirectional ?eld magnitude and direction of the resultant unidi in the direction of the ?rst diameter of said core, rectional ?eld produced across the diameter of a second adjusting means associated with said said ?rst core. transmitter means for varying the polarity and 6. A compensating device for a magnetic com magnitude of said second harmonic current sup pass comprising a circular core of permeable plied to said polyphase connection so as to vary magnetic material located in magnetic relation the magnitude and direction of the component of with said compass, said core having an exciting the unidirectional magnetic ?eld in a direction of winding connected to a source of periodically a second diameter of said core at right angles to varying current and two sets of polyphase wind said ?rst diameter whereby the magnitude and di ings, said polyphase windings being so arranged rection of said compensating unidirectional mag that when one of said sets of polyphase windings netic ?eld may be varied by the correlated adjust is energized with a second harmonic current a ment of said ?rst and second adjusting means. 70 unidirectional magnetic ?ux is produced across 4. A remote controlled deviation compensator a ?rst diameter of said core and when the other for a magnetic compass comprising a ?rst annu set of said polyphase windings is connected to lar core of permeable magnetic material located a source of second harmonic current a unidi in magnetic relation with said compass, a second rectional magnetic flux is produced across a sec annular core of permeable magnetic material lo 75 ond diameter of said core extending at right an 2,405,050 11 12 gles to said ?rst diameter, means for supplying second harmonic currents to said two sets of polyphase windings, and means for separately varying the polarity and magnitude of the sec ond harmonic current supplied to each of said polyphase windings whereby to vary the magni tude and direction of the resultant unidirectional axes passing through each set of polyphase wind ings being mutually perpendicular, a ?rst trans mitter for supplying second harmonic current to one of said sets of polyphase windings, a second transmitter for supplying second harmonic cur rent to the other of said sets of polyphase wind ings, said ?rst and second transmitters each hav ing adjusting means associated therewith for ?ux produced across the diameter of said core. varying the polarity and magnitude of the sec~ '7. A compensating device for a magnetic com pass comprising a circular core of permeable 10 ond harmonic currents supplied to said sets of polyphase windings whereby to vary the magni magnetic material located in magnetic relation tude and direction of the right angle components with said compass, coil means in inductive rela of the resulting unidirectional magnetic ?eld tion with said core, said coil means having a pair produced across the diameter of said ?rst core. of single phase connections and two pairs of poly 9. An electromagnetic device adapted to be phase connections, means for supplying a periodi 15 used as a transmitter of second harmonic cur~ cally varying current to said single phase connec rents comprising a core of permeable magnetic tions, said polyphase connections being arranged material, coil means on said core having a single so that when a source of second harmonic current phase connection and polyphase connections, is connected to one of said pairs of polyphase con nections a unidirectional magnetic ?ux is pro 20 means for connecting said single phase connec tion to a source of alternating current, a ?rst duced across a ?rst diameter of said core and when a source of second harmonic current is con elongated cylindrical permanent magnet asso nected to the other of said pairs of polyphase con nections a unidirectional magnetic flux is pro ciated with said core and extending in a direc tion of a ?rst diameter of said core, a second duced across a second diameter of said core ex tending at right angles to said ?rst diameter, means for supplying second harmonic currents to said pairs of polyphase connections, and means for separately varying the polarity and magni-v tude of the second harmonic currents supplied to each of said pairs of polyphase connections whereby to vary the magnitude and direction of the resultant unidirectional ?ux produced across 25 elongated cylindrical permanent magnet also as sociated with said core and extending in a direc tion of a second diameter of said core at right angles to said ?rst diameter, said cylindrical per manent magnets being magnetized across the diameter of the cylinder so that mutually per pendicular, unidirectional magnetic ?elds are produced across said core in a direction of said ?rst and second diameters, and means for rotat ing said ?rst and second magnets about their 8. A remote controlled deviation compensator 35 cylinder axes so as to vary the magnitude and polarity of the unidirectional ?elds produced for a magnetic compass comprising an annular thereby in the direction of said ?rst and second core of permeable magnetic material located in diameters whereby to vary the magnitude and magnetic relation with said compass, a dis? polarity of the second harmonic voltages devel tributed exciting winding and two sets of poly phase windings on said core, the polyphase wind 40 oped across said polyphase connections. RICHARD A. PFUN'I?NER. ings of each set being diametrically opposite and ELEANOR D. WILSON. connected in series opposition and the diametric the diameter of said core.