Patent GB-607753-A (GB)
Title: Improvements in magnetic analysis of a magnetic body
IPC: G01R33/12
Filed: 1946-02-11
Abstract: 607,753. Magnetic tests and measurements. MAGNETIC ANALYSIS CORPORATION. Feb. 11, 1946, No. 4240. Convention date, June 9, 1945. [Class 37] Apparatus for the inspection and analysis of magnetic material by investigating the instantaneous wave forms resulting from the effect of magnetic properties of the material upon the shape of sinusoidal currents includes a phase selective circuit by means of which the wave form to be investigated may be shifted so that it appears at the peak of the basic sinusoidal wave. As shown in Fig. 1, an energizing coil 1 is supplied from an A.C. source 2 and may be tuned by a condenser 3, resonance being indicated by an ammeter 4. Secondary coils 6, 7 are arranged in magnetic relation to the coil 1 and to the specimen 5 under inspection, which may be moved at a uniform rate with respect to the coils 1, 6, 7. The coils 6, 7 are connected in series aiding in a phase-shifting network, including a condenser 8 and variable resistor 9. Adjustment of the resistor 9 shifts the phase of the sinusoidal wave appearing at the terminals a, b, of a peak voltmeter, which comprises a potentiometer 10, rectifier 12, pulse amplifier 14, and indicating meter 15. Owing to the magnetic properties of the specimen 5 the sinusoidal wave is distorted by either cyclic transients or a summation of high-frequency components, the phase of which is not appreciably altered by the variation of the resistor 9 required to shift the phase of the low-frequency component, which may thus be shifted with respect to tune, whereas the wave distortions appear stationary when viewed on an oscilloscope 13. In this manner the distortion wave may be made to appear at any desired point or phase of the sinusoidal wave, e.g. at its maximum amplitude. In a modification, Fig. 2, the secondary coils 16, 17 are connected in opposition in a series circuit including the primary winding 19 of a transformer. The secondary winding 20 of this transformer is connected to a phase-shifting circuit including a condenser 22 and variable resistor 21 in series with the secondary winding 23 of a coupling transformer 43. The primary winding 24 of this transformer is connected through a variable reactance 26 to an auxiliary A.C. source 25, which generates a low-frequency sinusoidal wave-form. Any difference in the voltages induced in the coils 16, 17 is due to non-uniformity of the specimen 5 and is too small for satisfactory rectification. By adding the auxiliary potential from the source 25 the resultant may be readily rectified. Fig. 3 shows the circuit connections of the rectifier 12 and pulse amplifier 14. The input terminals a, b are connected to a diode 27 and resistor 30, so that the slider of the potentiometer 10, Figs. 1 and 2, is connected through the phase-shifting network to the cathode of the diode 27, the anode of which is connected to the grid of an amplifying valve 31. A terminal c is directly connected to the output of the diode 27 so that the oscillograph 13 is connected across the resistor 30 when the switch 28 contacts with the terminal c. Across the load resistor 35 of the valve 31 is a second diode 36 shunted by resistor 37 in series with a condenser 38, the common connection of these being connected to the left-hand grid of a double triode amplifying valve 39. The righthand grid is connected to the slider of a potentiometer 40 in the cathode circuit. The plates 44, 45 are connected through similar load resistors 41, 42 to the high-tension terminal B+ and also to the meter 15. The positive peaks of the A.C. current impressed on terminals a, b are rectified by the diode 27, producing unidirectional pulses which are amplified by the triode 31. The A.C. component introduced by this is rectified in the rectifier 36 and the resulting unidirectional output is impressed on the D.C. amplifier 39. The current through the resistor 42 is of steady value depending on the setting of the potentiometer 40, whereas the current through the resistor 41 fluctuates proportionally to the potential applied to the terminals a, h. By adjustment of the potentiometer 40 the meter 15 may be balanced to zero in the absence of voltage fluctuations. By adjusting the potentiometer 10 most of the sinusoidal voltage is balanced out so that the reproduced wave-form is limited to the actual peak values on which are superimposed the wave-form distortion to be observed. The amplitude and shape of these peaks vary with the physical or chemical composition or the physical condition of the material under investigation. Specification 520,328 is referred to.