Application Cases

Experiment Name: Application of Power Amplifier in Multi-Frequency AC Magnetic Flux Leakage Testing of Steel Plate Surface Defects and Their Orientation Angles

Research Direction: Electromagnetic Nondestructive Testing

Experiment Objective: To verify the superiority of the multi-frequency AC magnetic flux leakage (AC-MFL) method in identifying defect orientation angles and quantifying defect dimensions.

Experimental Content:
A comparison was conducted between single-frequency and multi-frequency excitation to evaluate the sensitivity of an AC-MFL probe to surface defects and their orientation angles on steel plates.

The excitation waveform was generated by a function generator, converted into a voltage signal, and amplified by a constant-voltage ATA-3080 power amplifier to enhance the excitation magnetic field. The receiving coil was positioned at the center of the probe beneath the excitation coil, with a lift-off distance of approximately 1 mm. The received signal was conditioned and noise-filtered by a multi-function filter before being digitized and displayed by a mixed-signal oscilloscope. In the multi-frequency excitation experiment, the mixed excitation signal consisted of frequencies of 400 Hz and 500 Hz. The multi-function filter allowed configurable signal filtering with adjustable cutoff frequency and gain. During the experiment, the cutoff frequency was set to 1 kHz, and the gain was set to 20 dB.

Figure: Experimental System Diagram

Experimental Procedure:
The sensitive frequencies for multiple measurement targets were selected, and a multi-frequency technique was employed to superimpose several optimal excitation signals into a composite excitation signal. This composite signal was amplified by the power amplifier and applied to the detection probe. A magnetic sensor was used to capture the leakage magnetic field near defects for characterization.

Figure: Test Data

Experimental Results:
A comparison of the experimental results under single-frequency and multi-frequency excitation demonstrated the advantages of the multi-frequency AC-MFL method in identifying defect orientation, as it provided better signal sensitivity. While both single-frequency and multi-frequency signals exhibited similar sensitivity to the depth of steel plate defects, the multi-frequency signal was more suitable for quantifying defect depth due to its higher signal intensity.

Figure: Single-Frequency Excitation Test Results

Figure: Multi-Frequency Excitation Test Results

Figure: ATA-3080C Power Amplifier Specifications and Parameters