Method for determining a materials characteristic value of magnetizable metal bodies by means of a micromagnetic sensor assembly, and corresponding sensor assembly
A method is provided for determining at least one material characteristic of a magnetizable metal body by means of a micromagnetic sensor arrangement, which comprises at least one excitation coil having a magnetic core for signal excitation and at least one receiver. The body is magnetized by the sensor arrangement via current or voltage excitation of the sensor arrangement, which comprises at least one sign change between a positive part of a half-wave and a negative part of a half-wave. At least one signal is measured in the receiver, and the signal is Fourier transformed. The material characteristic are determined from at least one Fourier component. The excitation is turned off, and the post-oscillation of the signal is measured in the receiver. At least the part of the signal resulting from the post-oscillation in the Fourier transformation is used.
1. A method for determining at least one material characteristic of a magnetizable metal body by a micromagnetic sensor arrangement, the sensor arrangement comprising at least one excitation coil having a magnetic core for signal excitation and at least one receiver, the method comprising the following steps:
magnetizing the body with a current or a voltage excitation via the sensor arrangement, the excitation comprising at least one sign change between a positive part of a half-wave and a negative part of a half-wave, wherein a frequency of the excitation is at least 500 Hz,
measuring at least one signal in the receiver during the excitation,
Fourier transforming the at least one signal,
determining the material characteristic from at least one Fourier component,
turning off the excitation,
after turning off the excitation, measuring a post-oscillation of the at least one signal in the receiver, and
using at least a part of the at least one signal resulting from the post-oscillation in Fourier transforming the at least one signal.
2. The method as claimed in claim 1 , wherein pulsed excitation is carried out.
3. The method as claimed in claim 2 , wherein the excitation is carried out by precisely one oscillation comprising a positive and a negative half-wave, which follow one another directly.
4. The method as claimed in claim 2 further comprising the following steps in the order mentioned:
magnetizing the body by a first excitation pulse,
turning off the excitation during a first dead time,
exciting the body by a second excitation pulse in a measurement sequence,
turning off the excitation during a second dead time,
a measurement of the induction signal being carried out in the measurement sequence and in the second dead time.
5. The method as claimed in claim 1 , wherein the excitation is carried out with a magnetization frequency of between 500 and 5000 Hz.
6. The method as claimed in claim 1 , wherein the measurement of the signal is carried out by a reception coil having a magnetic core as the receiver.
7. The method as claimed in claim 1 , wherein the measurement of the signal is carried out by a magnetic field sensor as the receiver.
8. The method as claimed in claim 1 , wherein a correlation of the at least one material characteristic with at least one Fourier component is carried out with the aid of test bodies, the Fourier components of which have been measured by a method of claim 1 and wherein the material characteristics of which are known and/or have been determined by other measurement methods before or after determining the Fourier components.
9. The method as claimed in claim 8 , wherein the determination of the correlation is carried out by a machine learning method.
10. The method as claimed in claim 9 , wherein the determination of the correlation is carried out according to a random forest method or by means of a support vector machine (SVM).
11. The method as claimed in claim 1 , wherein a mechanical-technological material characteristic is determined.
12. A micromagnetic sensor arrangement for carrying out the method of claim 1 , the sensor arrangement comprising an excitation coil having a magnetic core for signal excitation and at least one receiver, wherein the magnetic core is made from a nanocrystalline material having a high magnetic permeability.
13. The sensor arrangement as claimed in claim 12 , wherein the receiver is formed by a reception coil having a magnetic core.
14. The sensor arrangement as claimed in claim 12 , wherein the receiver is formed by a magnetic field sensor.
15. The sensor arrangement as claimed in claim 12 , further including a temperature sensor.
16. The sensor arrangement as claimed in claim 12 , wherein the sensor arrangement has a length of between 5 and 10 cm.
17. An inspection pig for an in-line inspection of pipelines, the inspection pig comprising the sensor arrangement as claimed in claim 12 .
18. The inspection pig as claimed in claim 17 , further including 4 to 8 sensor arrangements distributed over a circumference of the inspection pig.
19. The method as claimed in claim 1 , wherein magnetizing the body with the excitation causes a reversal of magnetization in the body.