Patent GB-336987-A (GB)
Title: New or improved means for testing magnetisable bodies
IPC: G01N27/80
Filed: 1929-06-19
Abstract: 336,987. Potter, E., (Kinsley, C.). June 19, 1929. Magnetic tests and measurements.-In order to obtain information as to the physical characteristics of a magnetizable body, it is magnetized by a coil fed from an alternating source, preferably through a filter which causes the wave of magnetizing current to be sinusoidal. Associated with the sample is a derived circuit, in which an electromotive force wave is induced by the flux produced in the sample. Selected time or frequency components are applied to detecting-apparatus which is selectively rendered responsive to one or more of these components. Electromotive forces of predetermined frequency are introduced into the circuit in order to annul one or more of these components. In this manner information is obtained with regard to different physical characteristics which are associated with particular variations in particular components. Fig. 1 shows apparatus for testing an iron or steel rod &c. 1 which is passed through magnetizing coils 2, 2<1> and a secondary coil 3. The magnetizing coils 2, 2<1> are fed from an alternator 4 through a resonant filter circuit ccntaining an inductance 5 and capacity 6, which causes the magnetizing current to be sinusoidal. The coil 3 is connected to an instrument 10 through a filter 8, 9 resonant to a particular harmonic component of the electromotive-force wave to be examined. A similar circuit containing a filter 8<1>, 9<1> resonant to a second chosen harmonic may be connected to a second instrument 10'. The instruments 10, 10<1> may be indicating instruments or relays and are responsive to changes in the strength of the particular harmonic. In Fig. 2 is shown apparatus for indicating change of phase of a selected harmonic. Rigidly coupled to the exciting alternator 4 is an auxiliary alternator 11 producing current of the desired frequency, which feeds the primary windings 13, 13<1> of a phase-shifting transformer through a condenser 14 and inductance 14'. The secondary winding 15 of the phase-shifting transformer is connected to one winding 10<c> of an instrument or relay of the dynamometer type, for instance that described in Specification 205,843, [Class 35, Dynamo-electric generators &c.]. The other coil 10<b> of this instrument is connected through the resor.ant filter 8, 9, to the secondary coil 3 on the sample 1. The secondary coil 15 of the phase-changer is then adjusted until the currents in the coils 10<b>, 10<c> are in quadrature, as indicated by the absence of a deflecting force. Any change in the phase of the selected harmonic component is indicated by a deflection of the instrument. By connecting the secondary winding 15 of the phase-shifter to a potentiometer wire, a tapped-off portion of which is included in circuit with the coil 3 and a current meter or relay, the instrument is rendered sensitive to changes both in magnitude and phase of the selected harmonic, the winding 15 and the slider of the potentiometer being adjusted until zero deflection is obtained on the instrument. Fig. 4 shows an arrangement by which changes in the derived electromotive force at a particular point on the wave may be observed. The secondary coil 3 is in series with a part of a potentiometer wire 8 and with brushes 14, 14<1> bearing on a disc 11 having a conducting segment 13 and driven synchronously with the alternator 4. Fig. 5 shows an arrangement by which a deep-seated flaw in a massive sample 1 may be detected. The magnetizing coil 2 and secondary coil 3 are wound on a core 4<a>. An auxiliary coil 6a wound on a core 5<a> is supplied with continuous current producing a continuous flux, variation of which due to the flaw is detected in the circuit of the coil 3. The coil 6<a> may alternatively be arranged on the core 4a. Fig. 6 shows a completa apparatus for routine testing. The magnetizing coil 2 surrounding the sample 1 is fed from an alternator 12<b> through a variable resistance 6<b>, ammeter 7b, and filter 8b. On the shaft 17<b> of the alternator 12<b>, which is driven by a motor 18b, are mounted auxiliary alternators 13b - - 16b, which generate currents having frequencies conesponding to the fundamental and harmonics of the primary current wave. The generators 13<b> - - 16b are provided with phase adjusters 21 - - 24, filters 50 - - 53, and adjustable resistances 54 - - 57 connected in series in the circuit of the primary winding of a transformer 60, the secondary winding of which is in series with the secondary coil 3 surrounding the sample 1. In series with this circuit may be connected by a switch 36 either one of a series of voltmeters 26 - - 29 or a signal relay 44 or oscillograph 65. Each of the volt meters 26 - - 29 is responsive only to the frequency of the corresponding generator 13<b> - - 16b, and is provided with a filter 100 - - 103 resonant to that frequency. One coil of each voltmeter is connected through the corresponding filter and jack to the output circuit of the generator 12<b>, the other winding being connected to a pushbutton switch 30 - - 33. One coil 45 of the relay 44 is connected to a plug 43 which may be inserted in any one of the jacks 91, 100, 101, 102, or 103. The second coil 46 is connected to the lower contacts of a switch 39 and is in series with the secondary coil 3 when the switches 36, 39 are both in the lower position. When the switch 39 is in its upper position, the element 66 of the oscillograph 65 is connected in place of the coil 46. With a representative sample in the coils 2, 3 and the switch 36 in its upper position, each generator 13<b> - - 16b in turn is adjusted as to strength and phase of its current until its associated voltmeter gives zero deflection, indicating that that particular harmonic of the voltage wave induced in the coil 3 is neutralized. When this has been effected for all the harmonics, the sample 1 is replaced by sample to be tested, whereupon deviations in the derived voltage wave are observed in the oscillograph 65 or operate the alarm relay 44, the switch 36 being in the lower position. The harmonic components for balancing may alternatively be derived from the alternator 12<b> through filter circuits, phase adjusters, and regulating resistances, instead of from the auxiliary alternators 13b - - 16<b>. The sensitivity of the instrument may be increased by the employment of amplifiers. The derived circuit, instead of being taken from the secondary coil 3, may be taken from the terminals of the magnetizing coil 2, the magnetizing current being rendered sinusoidal by a filter, or may be taken across a resistance or inductance in series with the magnetizing coil, the applied electromotive force being rendered sinusoidal by means of a filter shunted across the mains. Fig. 10 shows an arrangement by which a part of the balancing is performed automatically by the employment of a standard test piece P<1> as well as the sample P under examination. The magnetizing coils 1f, 2f are connected in series with one another and with a filter 6f across the supply mains 5f. The coils 1f, 2f, or fractions thereof, are connected as two arms of a Wheatstone bridge, of which the other two arms are formed by impedances 10f, 11f. The bridge wire is connected to the primary winding of a transformer having a secondary winding 15f connected to the switch 32f and also two secondary windings 13f, 14f connected to harmonic selectors comprising circuits 18f, 16f tuned to the fundamental and harmonic frequencies, and phase adjusters 17<g>, 15<g>. By means of the switch 32f, the secondary winding 15f may be connected either to voltmeters 20f, 25f or to alarm relays 23f, 26g or an oscillograph 65. If the test piece P and standard P<1> are identical, exact balance can be obtained by adjusting the impedances 10<f>, 11<f>. If, however, the samples differ, the residual harmonics are separately balanced out by the phase adjusters 17<g>, 15<g> and resistances 30<f>, 29<f>. Alternatively secondary coils surrounding the samples P, P<1> may be connected to form the arms of the bridge.