NASA CP Basic Principles Book
Indice ROCarneval


Operating and Maintenance Instructions

adaptaed from:

Hard spot inspection trolley • PLAMAT-M • 18201
Operating and Maintenance Instructions • V2.0
Fundamental principles

2.5 Upper harmonics

The generation of the alternating magnetic field in the measuring sample is carried out by a sinusoidal excitation with the yoke. A closer inspection of the time signal of the tangential magnetic field in the sample results in the finding that the curve shape of the measured field signal is not purely sinusoidal. Especially in the range after the zero transition distortions are detectable (see Figure 9). The reason is the non- linear behavior of the ferromagnetic hysteresis. By Fast Fourier Analysis (FFT) of the measured field a fundamental wave and the upper harmonic parts can be numerically determined. The upper harmonic parts give information about the ferromagnetic properties of the tested material.

Harmonic distortion
Figure 9: Harmonic distortion

The following micro-magnetic parameters are considered for the upper harmonics analysis:
Vmag [V] amplitude of magnetization voltage
Imag [A] amplitude of magnetization current
 K [%] Klirr factor of magnetization current
 A3 [%] 3rd harmonics amplitude of magnetization current
  P3 [rad] 3rd harmonics phase of magnetization current

Harmonic distortion
Figure 10: Visualization of harmonic distortion

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