SU864106A1 - Method of magnetic noise structuroscopy of articles from ferromagnetic materials - Google Patents

Description

The invention relates to the nondestructive control of ferromagnetic materials and can be used in the instrument-making, engineering and aviation industries. The known method of magnetic noise restructurography, consisting in TC 4, that the controlled product is re-magnetized along the limiting hysteresis loop, Barkhausen jumps are recorded, and the shape of the spectrum of magnetic noise normalized relative to one of its components is judged by the value of the controlled parameter w. However, the known method is characterized by low control accuracy, due to the strong influence of thermal and instrumental noise, as well as external industrial noise on the measurement results. The closest in technical essence to the invention is the method of magnetic-noise structuroscopy of products made of ferromagnetic materials, which consists in that the product is re-magnetized by a low-frequency field, the spectra of magnetic noise are extracted and their C23 envelopes are detected simultaneously. The low control accuracy of the multilayer ferromagnetic materials of this device is due to the fact that the output signal contains integral information about the structure of the entire magnetization reversal volume. The purpose of the invention is to improve the accuracy of control. This goal is achieved by assigning the difference in the magnetic noise spectra of the monitored and reference parts of the product in each half-period of de-magnetising and determining the monitored parameters from the detected signal versus frequency, and the depth of the layer with detected heterogeneity is determined by the frequency at which the difference in spectra change sign. FIG. 1 shows a block diagram of a device implementing the proposed method; in fig. 2 is a timing diagram of the signal passing through the measuring channel. The device contains installed on the product with a controlled and reference sections 1 and 2, system 3 peremagnevnymi connected to the output

low-frequency generator 4, indicator coils 5 and 6 connected to a series-connected switch 7, broadband amplifier 8, spectrum analyzer 9, synchronous detector 10 and indicator 11 of the parameter being monitored, phase shifter 12, whose input is connected to the output of the generator and the output to the switch inputs and a synchronous detector, and in series connected a derivative meter 13 and a layer depth indicator 14, connected between the output of the synchronous detector and the input of the spectrum analyzer,

The method is implemented as follows.

The winding of the magnetization reversal system transmits the current from the generator 4. The magnetic flux created by this toxin closes across the core of the reversal system 3 and the controlled product, causing the necessary magnetization reversal processes in the latter, which are recorded using indicator coils 5 and b. The law of variation of the magnetic field strength is shown in FIG. 2a The signal from the indicator coil 5 (Fig. 26} goes to one of the signal inputs of the switch 7. The signal from the indicator b (Fig. 2c) goes to the other signal input of the switch 7. The control input of the switch 7 receives a signal from the generator 4, shifted along the phase at a predetermined angle by the phase shifter 12 (Fig. 2d). With a positive control voltage half-wave (Fig. 2g), the switch 7 passes a signal of the indicator coil 5 (Fig. 25) to the input of the broadband amplifier 8, and at a negative half-wave - signal in;} ikatornoy coil b (Fig. 2c).

From the output of the wideband amplifier 8, a signal (Fig. 2A) is fed to a spectrum analyzer 9, from the output of which the current magnetic noise spectrum is supplied (Fig. 2e) to the signal input of the synchronous detector 10. The reference input of the synchronous detector 10 is fed to the phase rotator 12 (Fig . 2d.

If the monitored and model areas have the same properties, then as a result of synchronous detection of the current spectrum (Fig. 2e) at the output of the synchronous detector 10, the signal is zero. If the properties of the monitored section at a certain depth differ from those of the reference region, then a signal appears at the output of the synchronous detector 10. It arrives at the input of the indicator 11 of the parameter being monitored. With an increase in the analysis frequency using the spectrum analyzer 9, at a certain frequency corresponding to

 in the case of a layer with different properties, the magnitude of the signal from the output of the synchronous detector 10 changes dramatically. At the same time, at the output of the derivative meter 13, a signal appears that arrives at the control input of the depth indicator 14. The signal input of the depth indicator 14 receives a signal from the spectrum analyzer 9 proportional to the analysis frequency, the magnitude of which at the time the signal arrives from the measured 13 derivative determines the depth of the layer with different properties.

The proposed method is most effective in the control of two-layer ferromagnetic media.

Claims (2)

1. Author's certificate of the USSR 461346, cl. G 01 N27 / 86, 1972. 2. The author's certificate of the USSR 1 532803, cl. G 01 N 27/86, 1975 (prototype). P