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Oct. 25, 1938. " 2,134,539 W. THAL ALTERNATING CURRENT APPARATUS FOR TESTING MAGNETIZABLE MATERIALS Filed April 4, 1955 IVVE ‘14/11. l-(EL ATTOR/VE K5, ‘ Patented ‘Oct. 25,‘ 1938 " UNITED STATESIPATENT OFFICE ALTERNATING CURRENT APPARATUS FOR TESTING MAGNETIZABLE MATERIALS Wilhelm Thal, Berlin- Siemensstadt, Germany, as signor to Siemens & Halske, Aktiengesellsclhaft, Siemensstadt, near-Berlin, Germany, a corpo ration of Germany ' Application April‘ 4, 1935, ‘Serial No. 14,633 Germany April "I, 1934 - va Claims. (01. 175-183)’ Mvinvention relates to alternating current apparatus for testing magnetizable materials. of iron test, that is to say the current-Voltage measurement. An alternating-current source The majority of methods for testing iron are (not shown) is connected to the terminals K1 based on a direct-current measurement. Since, and K2, the test piece P being energized by the 5 however, ‘such a measurement does not take into source through the Winding Wl- The measuring 5 consideration the eddy current losses extremely instrument (ammeter) J is inserted in the cir important for all alternating-current instruments with The Secondary Winding W2 is connected and since, furthermore, the results obtained by to the voltmeter E- Recti?ers R and R’ are in the direct-current ‘measurement do not hold good dicated in series with the ammeter J and the volt for the alternating-current magnetization the meter E respectively- A condenser C is con Epstein apparatus has been contrived which nected across the connections K1 and K2 of the permits of measuring, ‘in the case of altemsh, primary windings and in parallel withthe alter ing-current, the losses and the alternating-cur- nating current source. If i designates the mag rent magnetization ‘within the zone of high sat15 urations, but has the disadvantage that test pieces of great weight must be employed. Besides, various bridge methods have been at ‘the same time contrived for which test pieces of small weight inay be employed. However, these methods re- netizing current, 1111 the number of the turns of the primary Winding, wz that Of the Secondary winding, 6 the induced Secondary E- M- F" qr the cross-section of the test piece in m2 and 1m the mean path of the lines of force in cm the fol lowing results are then Obtained! 20 quire a. very complicated ‘test equipment without “ meeting the exacting conditions of an alternate ing-current apparatus for testing iron. The 20 £Z=LiQ '8" greatest disadvantage of the bridge methods‘lies above all in the fact that with. bridge methods Bmx= 25 hitherto known the measurement is not effected e ' 10 Gauss 222 - qr - WI _B,,,,, with sinusoidal voltage but with sinusoidal cur- 25 ‘In rent, so that a squeezed or‘ pointed ?ux curve . unavoidably results. The wrong test readings owing to are, the eddy consequently, current 30 component of- the higher harmonics in the ?ux. - i . A The ex ressmn Hw=0-4' - T' p ._ 30 J5 cm corresponds in meaning to the otherwise usual expression"‘ampere windings per centimeter of The invention has for its object to provide an apparatus which eliminates the above-mentioned drawbacks of the alternating-current apparatus heretofore known for testing iron, 'i. e., such an 35 apparatus which ful?lls all conditions of a cyclic core lengt .” The expression Binax indicates the maximum induction. The expression a desig magnetization without presenting the drawbacks or restrictions of the aforesaid apparatus. An apparatus of the above-indicated character may be manufactured without considerable ex nates the permeability, Heft the. magnetization actually present. In the last formula the index i. “e?” is suitably added,' not to cm, but to ‘A, as only the value A is variable. 40 40 penditure, if means are provided to ensure in- v dependently of the size of, the test pieces the natural magnetization up to the saturation, i. e., The manner in which the measurement is ef fected must, consequently, ful?ll the condition of a natural magnetization, i. e., the magnetiz tain in‘ the test piece the sinusoidal voltage ing current must be table toassume that curve 45 throughout the entire measuring range. which produces a sinusoidal ?ux in con 45 In the accompanying drawing, Fig. 1 is a dia ‘shape gram illustrating the principle of my invention; nection with the hysteresis character of the Fig. 2 is a diagram showing the relation between In order to meet the above requirement it is. current, magnetic ?ux, and induced voltage, and Fig. 3 is a diagram of an apparatus embodying essential that apart from the test piece, there if conditions are made to cause the flux to main- - material. to my invention. - . For a better understanding of the individual measures required for carrying out the inventive idea Fig. 1 of the accompanying drawing shows diagrammatically in principle the simplest form , ' _ be practically no other linear or non-linear re 50 sistances in the primary circuit. The internal . losses of the 'ammeter must be, therefore, very small as compared to the'magnetization e?’ect of the. test piece. ‘This condition may be ful?lled if a highly sensitive direct-current measuring 65 2,184,589 2 instrument with series recti?er is employed for “succession is, consequently, re?ected by the same in two planes perpendicular to each other and measuring the current. Furthermore, the gen erator supplying the magnetizing current and may indicate on a surface scale the relationship insulating at the same time the instrument from between both values which in?uence the position of the mirrors. The measuring loops of such an the supply circuit must have a small total im indicating or recording apparatus are connected nitude may be connected in parallel relation to according to the invention to the primary cir the generator. Furthermore, the internal losses cuit or to the secondary circuit of a piece of the of the voltmeter connected to the secondary side magnetizable material under test in such a man 10 10 must also be small, in order that the secondary ner that ‘the one mirror deflects in accordance winding may not react on the primary circuit, and with the instantaneous intensity of the exciting in order that the secondary voltage measurement current and the other mirror de?ects in accord may approach. as far as possible the pure E. M. F. - ance with the instantaneous density of the ?ux. measurement. This may be accomplished also Since the ?ux cannot-be directly measured the induced voltage is instead thereof measured ac 15 15 by the use ‘of a highly sensitive direct-current cording to the invention. Since, however, the measuring instrument with series-connected rec ti?er. Finally, it is essential that the greatest ?ux and the secondary voltage are 90° out of possible cross-section of the conductors be chosen phase, the values of the induced secondary volt pedance. , To this end, a capacity of suitable mag so as to maintain the ohmic resistances of both 20 circuits at a very low value. . Brie?y stated the following result is obtained: The impedance may be practically fully com pensated for by a parallel condenser. A highly sensitive direct-current measuring instrument 25 has internal losses of about 0.1 . 10“8 watt. If an e?fect of 10 . 10-‘6 watt, 1. e. hundred times age leading 90° are measured as such values which correspond to the instantaneous values of 20 current. This substitution of the instantaneous values of the induced voltage for‘those of the flux may be easily effected in the case of a sinu soidal behavior of the voltage, since in this case 25 also the?ux varies sinusoidally. To measure the instantaneous values of the the amount of an instrument, is substituted for current or of the induced voltage any of the ar both instruments inclusive of the series and shunt rangements hitherto known such as, for instance, ' resistances thereof and if the condition is made Joubert discs or instead thereof vibrating contact ' synchronous switches with separate excitation, 30 30 to cause this effect to amount only to 1% of the for instance as described in Patent No. 1,931,267 magnetization effect of the test piece in order .to attain a natural magnetization, a magnetization to H. Pfannenmuller, may be employed. For in stance, also independently controlled dry recti effect in iron of l mva. results. ‘ A simple calculation shows that this amount ?ers may be employed. In order to plot predetermined points of the 35 85 may be attained for a magnetic flux density hysteresis loop the measurement must be based B=vl0 in the case of normal sheet irons having within a full period on a series of instantaneous as test pieces only a weight of 10 g. It is, con values of the current curve. To this end, an sequently, possible to carry out accurate alter nating current measurements with test pieces ordinary phase shifter having a range of 360° is 40 having a very small weight, if the above-men tioned rule is adhered to. In practice, however, the conditions are still far more favorable, since the above-indicated ?gures refer to the complete de?ection of the instrument and since the mag netization is besides effected within the zone of the initial permeability with sinusoidal current and voltage curves so that the extreme ratio of the instrument effect to the magnetization effect need not be maintained. In those zones of the magnetizing curve in which this ratio is impor '50 tant, i. e. from about 15 to 20% of the induction in the zone of saturation, the magnetization effect is higher by 102 to 103 so that the natural magnetization is at all events ensured. In prac tice the measurement of a test piece of 10 g. in-. employed by means of which a synchronous mo tor is fed when using Joubert discs. By the use of independently controlled oscil lating or static recti?ers the exciting voltage of ' these recti?ers is supplied by the phase shifter, i. e., two voltages which are 90° out of phase are 45 tapped off in such a connection that for any ro tation of the phase shifter the relative phase position of ' both exciting voltages supplied by the phase shifter remains una1tered._ The measurement of the induced secondary 50 voltage is only permissible, if the magnetization is sinusoidal. However, in the case of the above A particularly convenient realization of the described arrangement oscillating recti?ers are employed at the secondary side which cause the measuring instrument connected behind the same 55 to indicate a de?ection depending upon the arith metical mean. Since according to the known relation the arithmetical mean of the voltage cor 55 dependently of the quality of the material is, therefore, possible. ~ above-described inventive idea results from the ' responds to the maximum value of the ?ux, the 60 consideration that all magnetical values of a arrangement may be also employed, if the mag 60 material are based ‘on the hysteresis loop, and that, therefore, the utilization of the inventive idea for the design of an apparatus which enables the recording of any points whatever of the hys teresis loop represents a considerable advance as to the testing of magnetizable materials, pro vided that the apparatus is simple to manipulate. netization is not sinusoidal. To this end, a coordinate indicator or recording rent and the dot-and-dash wave train illustrates apparatus is employed according to the inven 70 tion, 1. e., an apparatus which indicates the re lationship between two values on a surface scale. Such an apparatus consists, for instance, of two mirror galvanometers, whose axes of rotation of the mirrors are perpendicular to one another. A ray of light falling on the two mirrors in ‘ To explain the above, Fig. 2 shows the rela tionship between the altemating-current mag netic. flux and the ‘induced voltage._ The solid curve represents the exciting current. The 65 dotted wave train represents the ?ux in the test piece which is in phase with the energizing cur the induced secondary voltage lagging the flux by 90". Since the wave trains of the flux and 70 voltage are similar to each other in the case of the sine shape, the ?ux may be replaced by the voltage which'is capable of being measured di rectly. The peak value of the current,‘ conse quently, corresponds to the peak value of the 75 I I induced voltage. 2,184,589 the current is determined at the point designated by A‘ at which the voltage and, therefore, valso the flux pass the zero value, the instantaneous value of the current corresponds to the coercive force, where as at point B where the current has decreased to zero, the voltage value measured cor responds to the remanence. _ ~ 10 in intersection of the hysteresis curve with the axes'of ordinates and abscissae. Consequently, if, for instance, only these values areto be de termined the phase shifter may only be so ad-' justed that in the case of the remanence meas- ' 15 ureme'nt the instantaneous value of the induced voltage andin the case of the coercive force measurement the instantaneous value of the cur rent become zero. The other ordinates indicate thén the corresponding value of the coercive force and of the remanence respectively. Fig, 3 illustrates the diagram of connections of an arrangement according to the invention. The condenser C is connected across the leadswhich connect the system to the alternating current source. I denotes the recording surface. 2 and 3 are the loops and mirrors of both galvanom eters. 4 is the luminous source from which a sharply limited ray of light falls on the recording 35 surface i by the way of both-_mirrors 2 and 3. 5 is the iron test piece‘. 6 is the primary and ‘i the secondary winding of this test piece. The primary winding 6 is connected to the secondary winding of a transformer 8 whose secondary ‘voltage may be adjusted at will. 9 denotes the primary and ID the secondary winding system of an induction regulator or phase-shifter. mirror, a second revolvable mirror ‘ and means connected in the secondary circuit for de?ecting said second mirror, the axes of revolution of said mirrors being perpendicular to each other, a light source and a surface scale being arranged with - respect to said mirrors so that a light beam com The same values may be obtained by the points '30 3 If the instantaneous value of _ nected in the primary circuit for de?ecting said Two phases 90° out of phase are tapped from the sec ondary winding and serve to energize two sepa rately controlled switching arrangements H and 40 I2. The synchronous switching arrangement ll controls the connection’ between the primary circuit 6 and the measuring loop 3 in such‘ a manner that the same instantaneous values are ing from said light source is re?ected successive ly by said two mirrors onto said surface scale, a separately excited synchronous switch arranged 10 in said primary circuit for periodically interrupt ‘ing said circuit, a second separately excited syn chronous switch arranged in said secondary cir cuit for periodically interrupting said secondary circuit, and means for exciting said two‘switching 15 devices, said means being electrically coupled with said current source and designed for exciting said two switches with 90° phase displacement against each other and with a certain phase position with respect to the current of said current source, 20 whereby the instantaneous value of the primary current acts on said means for de?ecting said ?rst-mentioned mirror and the instantaneous value of the voltage induced in said secondary windings acts on said means for de?ecting said 25 second mirror. 2. In an alternating current device for meas uring magnetic properties of a test piece, in com bination, a closed magnetic circuit, at least part of which is the test piece, primary and secondary 30 windings on said magnetic circuit, an alternating ' current source connected in a‘ primary circuit with said primary winding, impedance balancing means connected in said primary circuit for com-1 pensating the impedance of said current source, a 35 revolvable mirror and means connected in the primary circuit for'de?ecting said mirror, a sec ond revolvable mirror and means connected in the secondary circuit for de?ecting said second mirror, the axes of revolution of said mirrors be ing .perpendicular to each other,‘ a light source and a recording surface being arranged with re taken from each phase. ‘The synchronous switch spect to said mirrors so that a beam coming from _ ‘the secondary circuit ‘I of the test piece 5, how ever, with the 'di?erence that the instantaneous values obtained and the instantaneous value of rately excited synchronous switch arranged in said primary circuit for periodically interrupting ing arrangement I! controls in the same manner ' said light source is re?ected successively by said the current are 90° out of phase. The galvanom 50 ' eters 2 and 3 constitute a. voltmeter and an em meter respectively, and each of them is connected in series with the recti?er forming part of the two mirrors onto said recording surface, a sepa said circuit, a second separately excited syn chronous switch arranged in said secondary cir cuit for periodically interrupting said secondary 50 circuit, and means for exciting said two switch switching arrangement I! and II respectively.’ ing devices, said means being electrically coupled 'The zero point of the coordinate system on the surface I’ is given byv the luminous point 4 which is projected by the deenergized galvanom eter systems 2 and 3 ‘on'the recording surface. ‘ Insteadof this recording surface a screen may be used which is designed preferably as an 60 opaque disc. The regulating transformer 8 serves to adjust the desired sensitiveness or the desired induction. The range of measurement of the arrangement may be adjusted at will by the number of turns 6 and ‘I wound on the test 65 piece 5. ' ' I claim as my invention: 1. In an alternating current device for meas uring magnetic properties of a test piece, in com bination, ‘a closed magnetic circuit, at least part of which is’ the test piece, primary and secondary ‘is with said current source and including a phase shifter for producing a phase displacement of 90° between the action of said two switches and a phase position of this action with respect to said current source at which the instantaneous value of the primary current acts on said means for de?ecting said ?rst-mentioned mirror and the instantaneous valueof the voltage inducedin said 60 secondary windings acts on said means for de ?ecting said second mirror. 3. In an alternating current device for meas uring magnetic properties of atest piece, in com bination, a closed magnetic circuit, at least‘ part of which is the test piece, primary and secondary windings on said magnetic cincuit, an alternating current source of negligible total impedance with respect to the impedance of said primary winding, said source being connected with said primary 70 windings on said magnetic circuit, an alternating current source of negligible total impedance with res act to the impedance of said primary winding, sai source being connected-with said primary said primary winding and having a rotatable mir winding. a revolvable mirror and means con ror as actuated member. a second highly sensitive winding, a highly sensitive direct current meas- ' uring device connected in the electric circuit of a 2,184,589 direct current measuring device connected in the circuit of said secondary winding and having also a rotatable mirror forming its actuated member, a light source and a screen having a support com 6 mon with said two measuring devices, said devices, said light source and said screen being arranged on said common support so that the rotation axes of said devices are perpendicular with respect to each other and a beam coming from said light source is reflected successively by said two mir rors onto said screen, a separately‘ excited syn chronous switch arranged in said primary cir cuit for periodically interrupting said circuit, 2. second separately excited synchronous switch ar ranged in‘ said secondary circuit for periodically. interrupting said secondary circuit, and means for exciting said two switching devices, said means including a phase shifter electrically cou pled with said current source and designed for supplying two exciting voltages of 90° phase dif ference to said switches, whereby‘ said two switches and said measuring devices connected with said switches are actuated in accordance with the current of said primary winding and the voltage of said secondary winding respectively. WILHEIM THAL.