US2951984A - Continuous core loss tester, particularly for transformer and dynamosheet steels - Google Patents

Description

Filed June 13, 1955 Sept. 6, 1960 IJZOLTAN CONTINUOUS CORE LOSS TESTER, PARTICULARLY FOR TRANSFORMER AND DYNAMOSHEET STEELS l1 Sheets-Sheet l- This/chess I FEE/kin L IL Gauge Gaugv Current Source Fig. 1a

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I I l I I I I I I Sept. 6, 1960 ZOLTAN 2,951,984

VONTINUOUS CORE LOSS TESTER, PARTICULARLY FOR F l d TRANSFORMERAND DYNAMOSHEET STEELS 1 e June 13, 1955 l1 Sheets-Sheet 10 r In" I III nun/11111117111 INVENTORT ISTVRN ZOLTRN as RTTOR-ESS Sept. 6, 1960 1. zoLTAN 2,951,984

CONTINUOUS CORE LOSS TESTER. PARTICULARLY FOR TRANSFORMER AND DYNAMOSHEET STEELS Filed June 13, 1955 ll Sheets-Sheet. 11

nnoRNesS' I Hungary,

ations of the cross-sectional .magnetizing current 2,951,984 CONTINUOUS CORE L058 TESTER, PARTICULAR- LY FOR TRANSFGRMER AND DYNAMOSHEET STEELS Istvan Zoltan, Budapest, Hungary, assignor to Villamosipari Kozponti Kutato Laboratorium, Budapest,

a Hungarian research institute Filed June 13, 1955, Ser. No. 515,147

v 7 Claims priority, application Hungary June 11, 1954 13 Claims. (Cl. M i-34) This invention relates to a non-destructive electromagnetic apparatus for testing at least one characteristic of ferromagnetic materials, particularly of sheets or 1aminae, and preferably in continuous operation.

Non-destructive tests have hitherto been carried out by placing suitable measuring devices upon the material to be tested. The measuring results, however, were rendered unreliable because of defective magnetic con tact caused by eventual unevenness or oxidation of the material surface. Such devices were not suitable for carrying out the measurements continuously either since they required direct contact with the material to be tested. Moreover, measuring errors arising from variareas of the tested materials and, in case of sheets or laminae, of the thickness thereof, could be corrected and compensated, respectively, only by means of computation.

These disadvantages of previous apparatus are obviated by the present invention which is based on the perception that continuous tests as well as automatic compensation of the measuring errors arising from crosssectionalvariations are possible provided that the relation between/ he tested characteristics of the material and its cross-sectional variations is duly considered.

As regards the two most important magnetic characteristics of ferromagnetic materials, i.e. the permeability and the specific core loss thereof, it is to be stated that: The permeability which is the quotient of the associated maximum values of the induction (B) and the field strength (H) is, in itself, independent of crosssection-al variations of the material. If, therefore, a constant maximum value of induction is warranted in the material while the maximum value of the field strength is derived from the maximum value of the in a manner known per se and indicated, a value will be obtained which is just inversely proportional to the wanted permeability. The maximum one,

value of induction can be rendered constant by deriving an electric signal from and proportional to the cross-sectional variations of the tested material and utilizing it so as to suitably regulate a current source of constant frequency. As a result, he voltage induced in a coil means linking with the flux energized in the inspected material varies proportionally to cross-sectional variations thereof.

It is known that the specific core loss is the loss related to an alternating magnetic field of constant frequency, to the maximum value of a sinusoidal induction and to the unit mass or weight of the material. Consequently, the indicated loss has, even in case of alternating magnetic fields of the above mentioned definition, to be corrected inversely to the deviations from the nominal cross-sectional area. That is, if the cross-sectional area of the inspected material is greater than the nominal value, the weig t of the material is greater as well and a relatively higher value than the specific coreloss would be indicated since the measured core loss is proportional to the weight.

' Alternatively, it is possible to keep the induced voltage,

on the cross-sectional area of the 'second measuring unit for setting up a homogeneous Patented Sept. 6, 1960 of the effects of the var ations of the cross-sectional area and the induction, respectively, which are as regards the core loss mutually opposite,

hat of the latter, is prevalent. As a result, with measuring on basis of the induced voltage of constant average value the specific core loss of materials of relatively larger cross-sectional areas would turn out to be of a value lower than the correct i.e. the thicker material would appear to be of a quality superior to the real value. Consequently, in order to obtain correct measuring results, the indicated .value has to be corrected in function of the cross-sectional deviationsaccording to the 0.7 power.

Thus, the indicated value has to be corrected by the signal derived, from the cross-sectional variations, notwithstanding whether the maximum value of the induction or that of the flux induced in the inspected material is kept constant. In the aforesaid cases, anyhow, this necessitates an indicator means of special construction.

The above measuring methods, however, may be combined so that the signal to be indicated is already of the correct value in which case wat-tmeters of usual construction may be used. Viz,jcontrolling the induced voltage so that the mutuallyopposite effects of the varirespectively, on the value of the core loss are exactly ations of the induction and the crosssectional variations, respectively, on the value of the core loss are exactly compensated, the indicated value will be the specific core loss proper.

Thus, the new non-destructive electromagnetic app-aratus for testing atleast one characteristic of ferromagnetic'materials comprises in combination a first measuring unit for deriving a first electric signal dependent inspected material, a

alternating magnetic field and deriving a second electric signal dependent on the wanted characteristic of the material, path means for guiding the inspected material through said first and said second measuring units, at least one correction member for compensating variations of said second electric signal caused by cross-sectional variations of the material by means of said first electric signal, at least one current source for energizing said first and said second measuring unit, and at least one indicator means adapted to be influenced by said correction member so as to indicate said second electric signal as corrected by said first electric signal. Thus, the working principle of the testing apparatus according to the invention is based on applying an alternating magnetic field of constant frequency within the scope of which the maximum value of the induction is either kept constant or is modified in dependence on the crosssectional variations of the tested material, a nearly sinusoidal form of the induction and the induced voltage, respectively, being warranted, if necessary.

Details of the invention will be illustrated with reference to the accompanying drawings which show, byway of example, embodiments of the invention. In the drawmgs:

Figure 1 is the block diagram of an apparatus ing the general features of the invention and shows a modification.

Figures 2 to 4 illustrate several embodiments of the general arrangement shown in Figure 1.

embody- Fig. 1a

Figure 5 represents the block diagram of the embodiment shown in Figure 2.

Figure 6 is a sectional view of an embodiment of the second measuring unit taken along the line VI-VI of Figure 7.

Figure 7 shows a sectional view VII-VII of Figure 6.

Figure 8 illustratesthe circuit diagram of the measuring unit represented in Figures 6 and 7 when testing the permeability of the material.

Figure 9 is a like circuit diagram in case of testing the specific core loss.

Figures 10 and 11 are circuit diagrams of two further embodiments, respectively, of the indicator means.

Figure 12-shows the circuit diagram of the amplifier of the embodiment represented in Figure 5.

Figure 13 illustrates the circuit diagram of the correction member of the embodiment shown in Figure 5.

Figure 14 is the circuit diagram of the rectifier means and filter means of the embodiment represented in Figure 5.

Figure 15 is the block diagram of the embodiment shown in Figure 3.

Figure 16 illustrates a longitudinal sectional view of an indicator means built integral with the correction member taken along the line XVIXVI of Figure 17.

Figure 17 represents a cross-sectional view taken along the line XVII-XVII of Figure 16.

Figure 18 is the circuit diagram of the indicator means shown in Figures 16 and 17.

Figure 19 illustrates the circuit diagram of a further embodiment of the indicator means shown in Figures 16 to 18.

Figure 20 represents a longitudinal sectional view of a taken along the line practical embodiment of the invent-ion taken along the line- XX-XX of Figure 21.

Figure 21 is a plain view to Figure 20. Finally:

Figure 22 shows a cross-sectional view taken along the line XXIIXXII of Figures 20 and 21.

The same reference numerals refer to like details throughout the drawings. In view of the apparatus described in our co-pending patent application Ser. 490,876, filed February 28, 1955, now Patent No. 2,842,737, being particularly adapted to carry out the cross-sectional measurements as required by the present invention, the details common to both descriptions are referred to by same reference numerals. Unlike details, however, are designated so as to enhance the simultaneous study of both subject matters and insofar as analogy is present, this should be obvious from the system of reference signs. Therefore, the reference numerals begin with 80. Likewise, details of like character but in mirror-image arrangement bear primed reference numerals. Details of like character and similar arrangement are distinguished by a subscript. Electromagnetically analogous yet with respect to their connections elements of compensating action are distinguished by an a affixed to the reference numeral proper. With modified details the original reference numeral is complemented by a 0. Thus, the system of designations is quite identic with that applied in the description of our above mentioned co-pending patent application.

In Figure 1, reference numeral 40 designates a measuring system or unit for deriving a first electric signal dependent on the cross-sectional area of the inspected material, reference numeral 80 refers to a second measuring system or unit for setting up a homogeneous alternating magnetic field and deriving a second electric signal varying with the 'wanted characteristic of the inspected material, reference numerals 41 and 81 indicate path means for passing the inspected material 45 through the measuring units 40 and 80, respectively, reference numeral 84 denotes a correction member for utilizing the aforesaid first .electric signal to compensate the variations of the said second electric signal caused by crosssectional variations of the inspected material, reference numeral 83 designates a current source for energizing the measuring units 40 and 80, respectively, and reference numeral 82 refers to an indicator means adapted to be influenced by the correction member 84.

The measuring unit 40 is an electromagnetic apparatus for gauging the cross-sectional areas of ferromagnetic materials, particularly bars and sheets. The gauging is effected by means of A.C. magnetic fluxes energized in open magnetic circuits which become closed by the passing test materials. In consequence hereof the A.C. magnetic fluxes traverse the test material as well and permit to derive an electric signal, more particularly a voltage signal directly from the alternating magnetic fluxes. If the A.C. magnetic fields are homogeneous in the open portions of the magnetic circuits and the latter are sufiiciently energized to produce a substantially saturating flux in the test material, the electric signal derived from the A.C. magnetic fluxes in the material will be characteristic of its cross-sectional areas. Thus, with variations of the crosssectional areas, also the fluxes energized in the test material will vary correspondingly so that the electric signal derived therefrom will be characteristic of such changes.

The homogeneity of the A.C. magnetic field in the region where the test material links with the A.C. magnetic fluxes is obtained by applying a measuring unit which comprises at least one pair of open magnetic circuits symmetrically arranged with respect to a common reference plane which faces their open portions, and by producing in these open magnetic circuits mutually opposed alternating magnetic fluxes. Thus, the mutually opposite poles of the open magnetic circuits will be of the same polarity so that the flux lines are caused to pass along the open portions of the magnetic circuits unidirectionally. These unidirectional alternating magnetic fields which prevail in the open portions of the magnetic circuits will go through the test material if it .is passed along the common reference plane and will change in number according to the cross-sectional area of the former. Obviously, by the test material proper and by the variations of its cross-sectional areas also the reluctance of the open magnetic circuits will vary correspondingly so that a measuringcoil arranged along the latter will permit to derive the desired electric signal. By the symmetrical arrangement of the open mag netic circuits transverse displacements of the test material with respect to the magnetic circuits are prevented from influencing the measuring results since the alteration of the magnetic reluctance of one of the magnetic circuits is associated with an opposite variation of the magnetic reluctance of the other magnetic circuit. Such a unit for measuring the cross-sectional variations of ferromagnetic materials has been described in closer details in our above mentioned copending patent application.

The current source 83 differs from the current source disclosed in our above mentioned co-pending patent application in that it comprises also a distributor means which is in general a stabilized A.C. power supply known per se enabling the first measuring unit 40 to be fed through circuit 90 and the corrector member 84 to be fed through circuit 91. This corrector member receives a signal dependent on the cross-sectional variations of the inspected material 45 through a circuit 92 from the thickness gauge 40 and feeds the indicator means and the second measuring unit as shown in Fig. l. The indicator means 82 may also receive a signal from the second measuring unit 80 through a circuit 94 as will be described in connection with Fig. 1a. The electric signal derived in the first measuring unit 40 from the crosssectional variations of the inspected material serves, generally, for controlling, through a circuit 92, the corrector member 84.

However, according to the applied measuring principle, the distributor means 430 may be connected to the l 82 so as to compensate variation in the weight of the inspected material. an embodiment is represented as to its general features second measuring unit 80 so as to by-pass th'e corrector but hereinafter more fully described manner in direct reciprocal action with the corrector member 84. The indicator means 82 has the voltage induced in the measuring unit 86 impressed thereupon through a circuit M which is the output circuit of the measuring unit 80.

The circuits concerning the latter alternative are represented in Fig. 1a. In this case, the corrector member 84 is inserted in the indicator means 82 so as to enable a current source supplying an induced voltage of constant average value to be applied. Then, the corrector member M is mechanically coupled to a power meter 820. The correction of the indication of the second electric signal is obtained through a reciprocal action in the specially built indicator means 82.

The embodiments shown in Figs. Z-and 3, respectively, are distinguished from those of Figs. 1 and 1a in that the corrector member 84 is inserted in the current source 83 so that correction takes place in the current source 83 proper. In this case, the feeding voltage fed through circuit 93 to the indicator means 82 and to the second measuring unit 80 is adjusted by the corrector-member 84 so that indicator means 82 indicates a corrected signal. As a result, the indicator means 82 may be of the usual measuring instrument type which, according to its structure, is suitable to measure either the permeability (Fig. 2) or the specific core loss (Fig. 3).

If simultaneous measuring of the permeability and the specific core loss is aimed at, for measuring the permeability a corrector member shall be insertedin the current source 83 so as to warrant the constant maximum value of the induction energized in the inspected material 45 and, for measuring the specific core loss; a corrector member shall be inserted in the indicator means the loss fluctuations caused by Such in Fig. 4 which shows that the corrector member is subdivided. One portion 84 thereof is inserted in the current source 83 for adjusting the feed-ing voltage whereas its other portion 84 forms one part of the subdivided indicator means 82 82 The separately arranged portion 82 of the indicator means serves for indicating the permeability while its portion 82 indicates the specific core loss. Obviously, this embodiment corresponds to a combination of the embodiments shown in Figs; 1a and 2, respectively.

The embodiment according to Fig. 5 shows several complementary features with respect to the embodiment illustrated in Fig. 2. In particular, the distributor means 430 is combined with an oscillator means 95 which serves for supplying a voltage of constant frequency and amplitude to the circuit 91 independently of the fluctuations of the mains frequency and voltage. The original function of the distributor means 430 is then accomplished by an auxiliary distributor means 430 The voltage supplied by the complemented distributor means 430 to the circuit 91 and corrected by the corrector member 84 is impressed through a circuit 91 upon an amplifier means 96 the output circuit of which is connected to the circuit 93. With the represented embodiment the current source 83 of the apparatus is formed jointly by the distributor means 43%, the corrector member 84 and the amplifier means 96. Within the current source 83 the oscillator means 95, the corrector member 84 and the amplifier means 96 are supplied with power by means of the auxiliary distributor means 430 through the circuit 90 Furthermore, the measuring unit 40 has a counter-measuring unit 40a connected to it in bucking relation whereby magnetic fluxes which are independent of the test material become compensated as has been described in connection with Fig. 25 of ou'rabove in our above mentioned co -pending mentioned co-pending patent application, the countermeasuring unit 40a being connected to the current source 83 by means of a circuit a. The output'signals of the measuring units it) and 40a are impressed upon a rectifier means 97 through circuits 92 and 92a, respectively. The difference signal characteristic of the cross-sectional area of the inspected material 45 is impressed by the rectifier means 97 through a circuit 92 upon a filter means 98 of delayed action wherefrom the delayed and filtered resulting signal is lead through a circuit 92 into the Corrector member 84 inserted in the current source 83. The measuring unit 80 is fed by the current source 83 through the indicator means 82. I

If the apparatus is to be used to measure the specific core loss it is preferable to induce a nearly sinusoidal voltage in the output circuit 94- of the measuring'unit 8t). This may be accomplished by providing the measuring unit 89 with an input circuit of possibly low impedance. For this purpose, the unit comprising the oscillator means and the amplifier means 96 may be substituted by a synchronous generator known per se. The corrector member 84 is then formed e.g. by the energizing circuit of the synchronous generator regulated by electronic means known per se. It is, however, more preferable to warrant the low impedance of the input circuit 93 by providing the current source 83 with an organ supplying a sinusoidal voltage, e.g. a known per se oscillator means 95 supplying a sinusoidal voltage of constant frequency and amplitude, and with an amplifier 96 which has negative feed back 940 from the voltage induced inthe output circuit 94 of the second measuring unit 88 as is represented-in Fig. 5. Embodiments of the measuring unit 86 are represented in Figs; 6 and. 7. In this case the inspected material 45 is surrounded by a measuring coil means 870 and an energizing coil means 86 as was the case with the measuring coil means 47th and the energizing coil means 46 patent application. In order to warrant the homogeneity of the magnetic field in the second measuring unit 80 and to delimit the measured portion of the inspected material, it is preferable to arrange at least one yoke means'along the path of the material for conducting the magnetic flux, as has been fully described in connection with the measuring unit 40 inour above mentioned co-pending patent application. With the represented embodiment, two such yoke means 88 and 83 have been applied the leg portions 39' and 89", respectively, of which ensure, on the one hand, the confinement of the inspected portion of the material 45 to the desired spacial extension as is necessary when measuring the core loss and, on the other hand, a low reluctance value of the magnetic circuit. V If only the permeability is to be measured, he measuring unit' 80 may be formed without yoke means as well provided that the evenness of the alternating magnetic field is warranted along the inspected portion of the tested material. However, in case of applying yoke means care has to be taken that the yoke means and the air gaps constitute possibly low magnetic reluctance and the core loss of the yoke means is of low value. The possibility of completely compensating, the eifects connected therewith and adapted to decrease the accuracy of the measuring results will hereinafter be more fully described." Otherwise, the measuring unit 80 is, as regards its structure and details, similar to the measuring unit 40 described in our above mentioned co-pending patent application the embodiments of which may serve as models when. constructing the measuring unit 80.

Fig. 8 is the circuit diagram of the embodiment of the measuring unit 8% shown in Figs. 6 and 7. Otherwise,

Fig. 8 represents a detail of an apparatus suitable for 93 in a manner known per" se, eg by means of a coil system 99 having a mutual inductance of a known value to above.

I "7 and inserted in the indicator means 82. The primary of the coil system 99 is connected to the circuit 93. The voltage induced in the secondary and rectified by a rectifiermeans 100 is indicated by an instrument 101 which is of the DArsonval moving coil type and is provided with a reciprocal scale, referred to in the preamble of the specification. The voltage of the current source 83 fed through circuit 91 to the power amplifier is controlled by the corrector member 84 in direct proportion to the thickness of the inspected material so as to have the maximum value of the induction energized in the inspected material 45 rendered constant. In order to obtain a constant value of induction in the inspected material 45, the amplifier 96' has to operate as a power source of very low and possibly negative internal impedance so as to swallow up the varying voltage drops across the impedances in circuit 93 due to current variations caused by the variations of the permeability of the inspected material. For this purpose, on the one hand, the secondary coil of the output transformer of the amplifier 96, the magnetizing coil 86 of the main gauge 80 and the primary coil of the mutual inductance 99 are of possibly low resistance and, on the other hand, a degenerating voltage is taken from the secondary coil 870 of the main gauge surrounding the inspected material 45, thus forming with the magnetizing coil 86 and with the inspected material a transformer, the degenerating voltage being fed back through the circuit 940 to the input of the amplifier 86. The power amplifier 96 is energized by a rectified and filtered DC. voltage via circuit 90 which is an output circuit of a conventional rectifier power source known per se and inserted in the current source 83.

If, in contradistinction, measuring the specific core loss by means of a simple wattmeter is aimed at, the voltage of thecurrent source 83 is by means of the correction member 8-4- controlled in such a manner that the efiects of the weight variations due to deviations from the nominal thickness of the inspected material 45 and the alterations of the induction opposite to and greater than the former on the specific core loss compensate one another, as has been likewise referred to in the preamble of the specification. Such an embodiment is represented in Fig. 9 where the indicator means 82 has a simple wattmeter 102 inserted therein. In this case the amplifier means 96 is fed through circuit 91 from the corrector means 84 by an adjusted voltage as referred The connections and the operation of the amplifier are the same as in the embodiment shown in Fig. 8 with the difference that the indicator means 82 is, apart from being inserted in circuit 93, inserted also in circuit 94 since in this case the indicator means 82 comprises a power meter 102 for an indicating instrument.

The effect of the energization independent of the inspected material 45 on the indicated value may be compensated by a suitable empirical calibration of the indicator means 82.

If the excess energization constitutes a considerable portion of the whole energization, the effect of the former will preferably be eliminated from the indication by means of compensation. This may be necessary e.g. when measuring the permeability or the specific core loss of materials of higher quality. For this purpose, the second measuring unit 80 has a counter-measuring unit 80a oppositely connected to it which requires an energization equal to that of the excess value.

When measuring the permeability, e.g. the apparatus shown in Fig. 10 may be applied. With this embodiment, the coil system 99 has a counter-coil system 99a connected to it through a circuit 93a. Both these circuits are energized by the amplifier 96, the connections of which being the same as described in connection with the embodiments shown in Figs. 8 and 9, respectively. As is obvious from the drawing, the primary of the coil system 99 carries only the current of the energizing coil means 86 of the measuring unit whereas in the primary of the counter-coil system 99a flows only the current of the energizing coil means 86a of the counter-measuring unit 80a, the effect of this current being equivalent to that of the excess energization. The secondaries of the coil system 99 and the counter-coil system 99a are connected against each other. As a result, the indication is not influenced by the current of the excess energization.

With core loss measurements the losses arising from the excess energization in the yoke means may be compensated e.g. by applying the embodiment shown in Fig. 111. In this case, the voltage coil of the wattmeter 103 forming the indicator means 82 is acted upon by two current coils 104 and 104a which are inserted in the circuits 93 and 93a, respectively, in such a manner that their effect should'be opposite as regards the coil 193. Since the loss in the counter-measuring unit 80a is equal to the loss in the yoke means, this additional loss is compensated in the indication by means of the oppositely connected current coils 104 and 104a.

The compensation may be extended to the power consumption of the indicator means 82 proper which arises essentially in a series resistance 105. For this purpose, a counter-coil 86a of the counter-measuring unit 30a may be shunted by a resistance 195a as shown in Fig. lla.

The counter-measuring unit 80a may wholly be substituted by the suitably sized resistance 105a if testing is carried out in the hereinafter described manner so that the voltage induced in the measuring coil of the measuring unit 80 and in the output circuit 94 thereof, respectively, is kept constant or else if the cross-sectional variations of the inspected material 45 are small and, consequently, the controlled voltage supplied into the input circuit 93 is varied within close limits.

If the permeability and the specific core loss are to be measured simultaneously, the compensations illustrated in Figs. 10 and 11, respectively, may obviously be combined. Full compensation may be obtained if the counter-measuring unit 80a is energized so that the flux of the yoke means is closed in itself. With e.g. a countermeasuring unit 80a formed in correspondence with the measuring unit 80 of the Figs. 6 and 7 such an energization means that with no measuring coil means 870 and inspected material 45 halves of the energizing coil means are arranged each on a yoke means and one of the latter is reversed under an angle of 180 so that their fluxes should be'closed in each other.

Hereinafter the amplifier means 95, the corrector member 84, the rectifier means 97 and the filter means 93 will more fully be described.

Amplifier Fig. 12 represents an embodiment of the amplifier means 96 of the apparatus shown in Fig. 5. The amplifier means is formed essentially by a phase inverter and input amplifier tube 106 and by two push-pull power amplifier tubes 107 and 107 with matching on the former by an R.C. coupling. With the represented embodiment, the input amplifier tube 1% and the power amplifier tubes 107' and 107" have been represented as a twin triode and triodes, respectively. The RC. coupling is formed by condensers 193' and 103" and resistors 109' and 109". The resistances 110, 11. and 112 of the phase inverter tube 106 are selected so that the A.C. components of its amplified output signals after the condensers 108' and 168" should be equal yet of opposite sign. A suitable biasing voltage of the power amplifier tubes 107' and 197" is adjusted by means of a grid bias or cathode resistance 113. The anode circuit 114 of the tubes 107' and 197" comprises an output transformer 115 by which the amplifier 96 is connected to the circuit 93 with suitable matching thereon. The

amplifier means 96 has the input signal from the circuit .9 91 through a grid resistance 116 impressed thereupon whereas the aforesaid negative or degenerative feed back is supplied thereto through a feed back resistance 117 inserted in a voltage circuit 940. The degree of the feed back varies with the resistance 116 and 117 in a manner known per se. Otherwise, the degenerative feed back may be increased by inserting a further amplifier stage before the phase inverter stage. In such cases care has to be taken that the degenerative character of the voltage feed back should be maintained.

Corrector member Details of the corrector member 84 are illustrated in Fig. 13. 'Its principal feature is a control pentode 118 which has its supply voltage from the circuit 90 the input signal from the circuit 91 and the control signal from the circuit 92 impressed thereupon. An A.C. component of the output signal of the pentode 11-8 appears in the circuit M The AC. input signal appears on a resistance 119 inserted in the circuit 91. With the represented embodiment, the resistance 119 forms the grid resistance of the third grid of the pentode 118 performing the function of a control grid. The needed bias voltage is supplied by a battery 120. The output signal appears on a load resistance 121 inserted in the anode circuit the AC. component of which is separated and forwarded into the circuit 91 by a condenser 122. The control signal voltage appears on a resistance 123 in the circuit 92 With the represented embodiment, the resistance 123 forms the grid resistance of the gain regulating grid of the pentode 118. The needed biasing voltage of the regulating grid is likewise supplied by the battery 120. (The constant biasing voltages of the regulating grid and the control grid may obviously be of different values.) The biasing voltage of the regulating grid and thus the gain of the pentode 118 is controlled or regulated by a voltage signal coming through the circuit 92 and appearing on the grid resistance 123. The screen grid potential of the pentode 118 is adjusted by a load resistance 124 in the anode circuit and filtered by means of a condenser 125. With the represented embodiment, the amplitude and the home or neutral position of the input signal voltage of the corrector member 84 comprising the regulating tube 118 is, selected so that the distortion of the output signal should be possibly small. On the other hand, the regulating signal voltage has to be selected so that the regulation of the gain of the pentode 118 should be of linear nature. With higher requirements as to accuracy, it is preferable to apply a pentagrid converter rather than the regulating pentode 118.

Rectifier Details of the rectifier means 97 and the filter means 98 are illustrated in Fig. 14. The rectifier means 97 serves to produce a difference signal arising from crosssectional variations of the material and appearing on the load resistance 53 and 53a. A signal voltage proportional to the mean value of the difference signal voltage appears in the output circuit 92 of the rectifier means 97 on a condenser 129 through a voltage divider composed of resistances 127 and 128. Therefore, the load resistances 53 and 53a as well as the voltage divider resistances 127 and 128 are selected so that the conductance of a node 130 looking from the condenser 129 should be possibly equal in the charging and discharging periods of the latter. a

Filter The signal voltage produced in the rectifier means 97 in the above described manner and proportional to the average value of the difference signal voltage is supplied through the circuit 92 into the filter means 98. The latter serves first of all-to eliminate those A.C. cornponents from the regulating signal voltage which might cause distortions in the output signal should they reach the grid of the regulating tube 118. It might be used, however, also to delay the regulating signal voltage supplied through the circuit $2 into the corrector member 84. The delay may preferably be selected so that the indication should be corrected in dependence on the cross-sectional diversities of the material when the indication in the measuring unit 8% is actuated by a crosssectional area associated with the correcting signal. For this purpose, a per se known R.C. filter chain consisting of resistances 131 and 132 and of condensers 133 and 134 is inserted between the input circuit 92 and the out put circuit 92 of the filter means 98.v The time constant of such filter chains may be selected in consideration of the aforesaid viewpoints as regards the delay.

in operation, the apparatus according to Fig. 5 is put in circuit whereafter a sample of the material 45 having a nominal cross-sectional area is introduced as a reference piece into the measuring units 40 and 80. Likewise, a reference piece 45a of the nominal cross-sectional area is accommodated in the counter-measuring unit 40a. The frequency of the oscillator is adjusetd to the nominal value and its potential controlled so that the mean value of the voltage induced in the circuit 94 is equal to the maximum value of the induction selected for the measurement. Thereafter, the reference piece 45 of a nominal cross-sectional area is substituted by reference pieces 45 of known cross-sectional areas larger and smaller, respectively, than the nominal value according to the upper and lower limits of the accepted range of tolerance.

When measuring the permeability, the regulationof the corrector member 84 is e.g. by means of varying the resistances 127 and 128 of the rectifier means 7 adjusted so that in the circuit 94 a voltage is induced which, in both cases, corresponds to the nominal value of induction and thus is proportional to the cross-sectional areas. After removing the reference piece 45 the apparatus is ready for service within the ranges delimited by such preliminary measurements.

The material 45 to be tested is then passed through the first measuring unit 41 and afterwards through the second measuring unit 80. If its cross-sectional areas deviate from the nominal value, a difference signal of the proper sign appears in the rectifier 97 and after going r through the filter means 93 regulates the correction member 84 according to a suitable delay. The inspected crosssectional area of the material 45 arrives therewhile in the measuring unit 80 and the permeability value associated therewith is readable on the scale of the indicator means 82 according to its actual value independently of eventual cross-sectional variations.

If the core loss is to be tested, the regulation is, e.g. likewise by means of the resistances 127 and 128, adjusted by using reference pieces of known specific core loss but of a cross-sectional area which is larger or smaller than the nominal value. The adjustment is correct if the indicator means 82, which with core loss measurings is formed as a wattmeter and, therefore, connected also to the output circuit 94, indicates the actual value of the specific core losses of the reference pieces 45. In contradistinction to measuring the permeability, the induction is not constant now and the rate of variation of the signal voltage appearing in the output circuit 94 of the measuring unit so is smaller than that of the cross-sectional areas as has been referred to in the preamble of the specification. Obviously, the calibration of the wattmeter can be valid but for one nominal cross-sectional area. Thus, with measuring materials of other cross-sectional areas the series resistance of the wattmeter has to be matched on a Weight associated with the new nominal cross-sectional area.

The abovedetailed description refers to the embodiment shown in Figs. 2. and 5. Hereinafter the apparatus illustrated in Figs. 3 and 15 will be described which is devised for measuring the specific core loss. It is distinguished from the embodiment shown in Fig. 5 in that the corrector member 84 is inserted in the indicator means 82 rather than in the current source 83. As a result, the current source 83 works without regulation and warrants a voltage of constant amplitude induced in the output circuit 94 of the measuring unit 80.

Details of the indicator means 82 are represented in Figs. 16 to 18. It comprises an electrodynamic wattmeter 820. The corrector member 84 is formed by a coil means or corrector coil 136 energized by the first electric signal, i.e. by that derived in the first measuring unit 4-0 and adapted to rotate together with the moving or voltage .coil 163 of the wattmeter 820 in a separate homogeneous magnetic field 135 which is independent of the field of force of the Wattmeter 820. The plane of turns of the .coil means 136 is in the zero position of the wattmeter 825B perpendicular to the direction of the homogeneous magnetic field 135. The voltage coil 103 of the wattmeter 8201s fixed to the upper portion 137 of a twopart shaft and is connected by means of current leads of low restoring torque 138 and 138 to the circuit M. The other portion 1.37 of the two-part shaft is connected to the shaft portion 137 by means of a sleeve 139 made of electrically insulating material. The corrector coil means 136 is fixed to the shaft 137 137 and its current leads are electrically connected each to a shaft portion 137 and 137 respectively. The shaft 137 137 is inserted between taut suspending strips 140 and 146 whereby it is electrically connected to the circuit 92. The indicator means 82 is formed as a light beam instrument the mirror 141 of which is fixed to the shaft portion 137 between the voltage coil 103 and the corrector coil 136. The homogeneous magnetic field 135 is set up by a permanent magnet 142 and delimited by inserts 144 and 144" made of soft magnetic material, eg of ductile or soft iron, arranged between the poles 143 and 143 thereof. The inserts 144 and 144" are fixed to an insert 145 made of non-magnetic maetrial and serve, on the one hand, to warrant the homogeneity of the magnetic field 135 as regards the coil means 136 and, on the other hand, to enable a damping frame 146 to be efiectively arranged between the poles 143' and 1143". In the circuit diagram shown in Fig. 18 the joint rotation of the voltage and corrector coil means 103 and 136 is refered to by a double arrow 147.

In operation of the combined corrector and indicator means shown in Figs. 16 to 18 no signal appears in the circuit 92 if'the material passing through the apparatus has a cross-sectional area of the nominal value. Then, the wattmeter 820 indicates the power consumption of the measuring unit 80 sensed by means of the circuits 93 n and 94. The best part thereof is formed by the core loss arising in the inspected material 45. Viz, when the voltage coil means 103 becomes deflected from its zero position against the torque of the taut strips 138 and 138", it takes the corrector coil means 136 of the corrector member 84 along by means of the shaft 137 137 The corrector coil means 136, however, carries no current now and thus no reciprocal action is originated 'by its displacement with respect to the homogeneous magnetic field 135, i.e. the indication of the wattmeter 82% is not influenced by the corrector member 34. As a result,

the sensed power is indicated by the wattmeter 820 by means of the mirror 141 and of not represented projection means known per se without correction on a scale which has been calibrated in consideration of the extrinsic losses as regards the inspected material .45. If the crosssectional area of the inspected material 45 is different from the nominal valuealsothe circuit 92 supplies a signal so that with rotation of the corrector coil means -136caused by the voltage coil 193 of the wattmeter 820 .a reciprocal action is taking place between the former .andathe homogeneous magnetic :field .135 which-is propor- -measuring unit 80 is compensated as well.

tional' to the aforesaid signal and the angle of rotation. Thus, the deflection of the wattmeter 820 is increased or decreased by this reciprocal action according to the polarity and magnitude of the signal coming through the circuit 92 and thereby the indication of the indicator means 82 is corrected corresponding to the cross-sectional variations. It is noted that such a correction must not be considered as perfectly accurate but within the range of relatively minute deflections where the sine of the deflection angle may be substituted by the deflection angle itself. This requirement can be met with by suitably increasing the length of the light beam, e.g. by means of additional mirrors in a manner known per se.

Obviously, the indicator means 82-shown in Figs. 16 to 18 may be complemented by the compensation means described in connection with Fig. 11. The circuit diagram of such an embodiment of the indicator means 82 is represented in Fig. 19. This embodiment differs from that shown in Fig. 11 in that the countermeasuring uni-t 80a is formed by the suitably selected resistance 105a by which in addition to the own power consumption of the wattmeter 824) the power consumption of the On the other hand, apart from the compensating elements 104a and 105a, the represented embodiment differs from that according to Figs. 16 to 18 in that the corrector coil means 136 has a series resistance 148 which serves for regulating the magnitude of the correcting action. The size of the cross-sectional area of the inspected material 45 and its deviations from the nominal value, respec tively, can be read from an instrument 54 connected to the circuit 92 it necessary, as shown in Fig. 19a. In case of minor requirements as to accuracy, the delay member 98 may even be dispensed with.

In operation of the embodiment shown in Fig. 15, the apparatus is started up in a manner described in connection with Fig. 5 when measuring the specific core loss. The only diiference is that with the represented embodiment the induced voltage is constant and the corrector member 82 being inserted in the indicator means 34 the magnitude of the correction is by means of a resistance 148 connected in series with the corrector coil means 136 adjusted so that the indicator means 82 indicates likewise the specific core loss independently of the crosssectional diversities.

In the foregoing the structure and operation of embodiments corresponding to Figs. 2 and 3, respectively, have more fully been described. An embodiment corresponding to that shown in Fig. 4 would consist of a reasonable combination of both previously described apparatus and, therefore, is not represented in drawings. The starting up of such a combined system differs from that of the previously described ones that the corrector member 84 inserted in the current source 83 is adjusted in the same manner as was the case described in connection with Fig. 5 relating to carrying out permeability tests.

The adjustment of the corrector member 84 inserted in the indicator means 82 is, on the other hand, effected like in the case of the embodiment shown in Fig. 15. In

consideration of what has been said in the preamble of the specification it has to be borne in mind that the testing is performed on basis of an induction of constant value as was the case with the embodiment shown in Fig. 5 rather than with a constant value of the induced voltage as would be in compliance with the embodiment illustrated in Fig. 15. This means that in order to obtain the right correction, the polarity has to be reversed as regards that in Fig. 15 andthe magnitude of the correctionhas to be selected in accordance With tests based on constant induction values.

With the embodiment shown in Figs. 20 to 22 the thickness measuring unit 40 is formed by magnetizing .coil .rneans io' and 46" arranged on yoke means 48' and .4 u i har i e te ash be we n .t st a vs s L- shap'ed girder members 58 and 58", respectively, their mutual vertical position being secured by four threaded pillars 59 connected to the girder members 58' and 58 by means of nuts 60' and 60", respectively.

The path means referred to by reference numeral 41 in the previously described embodiments is constructed substantially as follows:

Referring to Fig. 20, the girder members 58' and 58 have skid-shaped guides 62 and 62 attached to them by means of studs 61 and 61", respectively. For sake of clarity, these studs 61 and 61 are not represented in Fig. 20. The guides 62' and 62" are used, on the one hand, to introduce the material to be gauged inbetween the yoke means 48 and 48 and, on the other hand, to prevent a contact between the material to be gauged and the leg portions 49 and 49" of the yoke means 48 and 48", respectively. Therefore, the sizes are selected so that the distance between the guides 62 andGZ is less than the distance between the leg portions 49 and 49" of the yoke means 48' and 48", respectively, as is particularly shown in Fig. 20.

For passing the test material, pairs of rolls 64' and 64 coated with rubber layers 63' and 63", respectively, are arranged for conveyor means in front of and behind the guides 62 and 62". The rubber layers 63 and 63" serve for elastically compensating or taking up crosssectional variations of the test material.

The pairs of rolls 64 and 64" are supported, on the one hand, by means of bearings 65' and 65" and, on the other hand, by double-action worm gears 68 and 68", respectively, the latter being driven by means of a common spindle 67 subdivided by couplings 66. The spindle 6.7 is. connected, by means of the left extreme coupling 66in Fig. 21, to the shaft of a driving motor 69 of the gauging apparatus.

Thedriving motor 69, the worm gears 68' and 68", the bearings 65' and 65" as well as the pillars 59 are all arranged on a common base frame 70. The apparatus has been represented discontinuously so as to indicate that, in case of gauging average thickness values of relatively broader materials, the measuring unit as represented can be associated with further units of like construction. This has been also described in connection with Figs. 31 to 33 of our above said co-pending patent application. The path means of the measuring unit 80 referred to by reference numeral 81 in the previously described figures is of the following construction:

The measuring unit 80 is arranged behind the second pair' of rolls 64' and 64" of the conveyor means arranged on the base plate 70 and more fully described in our above. mentioned co-pending patent application. Its energizing coil means 86 and measuring coil means 870 are accommodated on'a subdivided coil support 149 and 149 made of non-magnetic material. Grooves of the coil supports 14-9 and149" are, in a manner shown in Figs. 20 and 22, engaged with guard plates 150' and 150", respectively, made of electrically insulating mate-,

rial and serve to prevent a direct contact of the material passed through the measuring unit 80 with the measuring coil means 870; The skeletons of the coil means 86' and 870 are formed jointly by the coil supports 149' and 149" as well as by the guardplates 150'and 150",

and isaccommo'dated between the concave surfaces. of two flanged lids 151" and 151", respectively, made of non-magnetic material. The lids 151' and 151" have cast bosses 152' and 152", respectively, in their four corners These bosses are slipped over stud bolts or anchor screws 153 fixed to the base plate 70 of the apparatus and serve to flank the coil system 149, 149", 15,0, 150", 870, 86 which is held down in its position by means of screw nuts 154 tightened on the stud bolts 1'53.

7 The convex sides of the lids 151, and 151 are insulated from and contiguous to the laminated yoke means 88 and 88'', respectively. The contiguity of the yoke means 88" and the lid 151" is obtained by an insert 155 made 14 of insulating material and accommodated between the yoke means 88" and the base plate 70. The stud' bolts or anchor screws 153 are insulated from the bosses 152' and 152" in a manner known per se and, therefore, not represented in the drawing. Thus, the lids 151 and 151, the stud bolts or anchor screws 153 and the base plate 70 cannot form an electric circuit closed in itself and adapted to impair the accuracy of the measurement.

The inspected material is removed from the measur= ing unit by a pair of rolls 64 and 64 which is similar to that used for feeding the material and to transfer it from the measuring unit 40 into the measuring unit 80. Driving is taking place in a like manner as is suggested by the identity of the reference numerals.

In operation, the measuring unit 40 is rendered ready for service in a manner described in our above mentioned co-pending patent application. The starting up of the measuring unit will be carried out according to the nature of the characteristic of material to be tested and the structure of the apparatus in the above described manner. Thereafter, the electric motor 69 is started up and thereby the pairs of rolls 64 and 64" set into rotation by means of the parts 66, 67, 68 and 68". The material to be tested is fed between the first pair of rolls 64' and 64" and passed first through the thickness measuring unit 40 then by means of the second pair of rolls 64 and 64" through the measuring unit 80 for measuring the characteristic of material to be tested. The material already tested withdraws from the apparatus through the. last pair of rolls 64' and 6 in the direction of an arrow 156.

What I claim is:

1. An electromagnetic apparatus for non-destructivel'y testing a characteristic of ferromagnetic materials, comprising in combination a first measuring unit for deriving a first electric signal dependent on the cross-sectional area of the materal to be tested, a second measining unit for setting up a homogeneous alternating magnetic field and deriving a second electric signal in dependence on the wanted characteristic of said material, path means for guiding said material through said first measuring unit and through said second measuring unit, at least one corrector member for compensating variations of said second electric signal caused 'by cross-sectional variations of said material by means of said first electric signal, at least one current source for energizing saidfirst measuring unit and said second measuring unit, and at least one indicator means for indicating said second electric signal as corrected by said first electric signal.

2. An apparatus as claimed in claim 1, wherein said indicator means is adapted to be influenced by said corrector member so as to indicate said second electric signal as corrected by said first electric signal.

3. An electromagnetic apparatus for non-destructively testing a characteristic of ferromagnetic materials, comprising in combination a first measuring unit for deriving a first electric signal dependent on the cross-sectional area of the material to be tested, a second measuring unit for setting up a homogeneous alternating magnetic field and deriving a second electric signal in dependence on the wanted characteristic of said material, path means for guiding said material through said first measuring unit and through said second, measuring unit, at least one current source for energizing said first measuring member is adapted to control the voltage of said current.

15 source so. that the maximum value of the induction energiz'ed in said material is rendered constant. 5. Anapparatus. as claimed in claim 3 for measuring the specific core loss of said material wherein the corrector member is adapted to control the voltage of said current source so as to enable the eilects of deviations from the nominal cross-sectional area of said material and of alterations of the induction opposite to and greater than the former on the specific core loss to be compensated by one another.

6. An electromagnetic apparatus for non-destructively testing a characteristic of ferromagnetic materials, comprising in combination a first measuring unit for deriving a first electric signal dependent on the cross-sectional area of the material to be tested, a second measuring unit for setting up a homogeneous alternating magnetic field and deriving a second electric signal in dependence on the wanted characteristic of said material, path means for guiding said material through said first measuring unit and through said second measuring unit, at least one current source for energizing said' first measuring unit and said second measuring unit, at least one indicator means, and at least one corrector member for com pensating variations of said second electric signal caused by cross-sectional variations of said material by means of said first electric signal, said corrector member being inserted in said indicator means so as to enable a current source supplying an induced voltage of constant average value to be applied.

7. An apparatus as claimed in claim 6 for measuring the specific core loss wherein said indicator means comprises.

an electrodynamic wattmeter having a voltage coil means, and said corrector member is formed by a corrector coil means for being energized by said first electric signal and by electromagnetic means for setting up a proper homogeneous magnetic field for said ccrrector coil means which is arranged therein so as to be adapted to rotate with said voltage coil means, in the zero position of said wattmeter the plane of the turns of saidcorrector coil means being perpendicular'to the direction of said proper homogeneous magnetic field.

8. An electromagnetic apparatus for non-destructively and simultaneously measuring the permeability and the specific core loss of ferromagnetic materials, comprising in combination a first measuring unit for deriving a first electric signal dependent on the cross-sectional area of the material'to be tested, a second measuring unit for setting up a homogeneous alternating magnetic field and deriving a second electric signal in dependence on the permeability and the specific core loss, respectively, of

said: material, path means for guiding said material through said first measuring unit and through said second measuring unit, at least one current source for en ergizing said first measuring unit and said second measuring unit, indicator means for indicating the measured values of the permeability and the specific core loss, respectively, and corrector members inserted in said current source and said indicator means for compensating variations of said second electric signal caused by crosssectional variations of said material by means of said first electric signal so as to Warrant a constant maximum value of the induction energized in and for eliminating loss fluctuations caused by cross-sectional variations of said material, respectively.

9. An electromagnetic apparatus for non-destructively testing a characteristic of ferromagnetic materials, comprising in combination a first measuring unit for deriving a first electric signal dependent on the cross-sectional area of the material to be tested, a second measuring unit for setting up a homogeneous alternating magnetic field and-deriving a second electric signal in dependence on the wanted characteristic of said material, said second measuring unit having an input circuit of possibly low impedance so as to obtain a sinusoidal induced voltage in an, outputcircuit; thereof, pathrneans for guiding said material through said first measuring unit and through said second measuring unit, at least one corrector member for compensating Variations of said second electric signal caused by cross-sectional variations of said material by means of said first electric signal, at least one current source for energizing said first measuring unit and said second measuring unit, and at least one indicator means for indicating said second electric signal as corrected by said first electric signal.

10. An apparatus as claimed in claim 9 wherein said current source comprises a sinusoidal voltage source and an amplifier means having negative feed back from the voltage induced in said output circuit of said second measuring unit so as to warrant an impedance of low value in said output circuit thereof.

ll. An electromagnetic apparatus for non-destructively testing a characteristic of ferromagnetic materials, comprising in combination a first measuring unit for deriving a first electric signal dependent on the cross-sectional area of the material to be tested, a second measuring unit for setting up a homogeneous alternating magnetic field and deriving a second electric signal in dependence on. the wanted characteristic of said material, path means for guiding said material through said first measuring unit and through said second measuring unit, at least one yoke means arranged along said path means for conducting the magnetic flux so as to enable said alternating magnetic field to be rendered homogeneous in said second measuring unit and to delimit a portion of said material for being tested, at least one cor-rector member for compensating variations of said second electric signal caused by cross-sectional variations of said material by means of said first electric signal, at least one current source for energizing said first measuring unit and said second measuring unit, and at least one indicator means for indicating said second electric signal as corrected by said first electric signal.

12. An electromagnetic apparatus for non-destructively testing a characteristic of ferromagnetic materials, comprising in combination a first measuring unit for deriving a first electric signal dependent on the cross-sectional area of the material to be tested, a second measuring unit for setting up a homogeneous alternating magnetic field andderiving a second electric signal in dependence on thewanted characteristic of said material, path means for guiding said material through said first measuring unit and through said second measuring unit, at least one corrector member for compensating variations of said second electric signal caused by cross-sectional variations. of said material by means of said firs-t electric signal, at least one current source for energizing said first measuring unit and said second measuring unit, at least one indicator means for indicating said second electric signal as corrected by said first electric signal, and a countermeasuring unit oppositely connected to said second measuring unit and selected so as to require an energization equal to excess energizations as regardssaid material'and thereby to eliminate the effect of said excess energizations on the indication;

13; 'An apparatus as claimed in claim 1 wherein conveyor means are provided for passing said materialalong said path means through said alternating magnetic field so as to enable the electric signal associated with subsequent cross-sectional areas of said material to be derived and indicated continuously by said indicator means.

References Cited in the file of this patent UNITED STATES PATENTS

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