Experiment name: Application of power amplifier in multi-frequency AC magnetic flux leakage test of steel plate surface defect and its deflection angle.

Research direction: Electromagnetic nondestructive testing.

Experimental content: compare the sensitivity of the AC magnetic flux leakage probe to the steel plate surface defect and its deflection angle under single-frequency and multi-frequency excitation.

The excitation waveform is generated by a function generator, which is converted into a voltage signal and amplified by a constant voltage SLA-100-720 power amplifier to enhance the excitation magnetic field. The receiving coil is mounted in the center of the probe below the exciting coil. The lift-off of the receive coil is about 1mm. The received signal is processed by a multi-function filter to adjust noise reduction, and then digitally displayed by a mixed-signal oscilloscope. In the multi-frequency excitation experiment, the mixed-frequency excitation signal consists of 400Hz and 500Hz. This multifunctional filter can realize signal filtering with cutoff frequency and gain, which can be configured as required. In the experiment, the cutoff frequency is set to 1 kHz and the gain is set to 20 dB.

Test purpose: To verify the superiority of the multi-frequency AC magnetic flux leakage method in the identification of defect deflection angle and size quantification.

Test equipment: Oscilloscope, signal generator, SLA-100-720 power amplifier, etc.

Experimental process: Screen the sensitive frequencies of multiple measurement targets, use multi-frequency technology, mix multiple optimal excitation signals into a composite excitation signal, amplify through the power amplifier, and load it on the detection probe; pick up the vicinity of the defect through the magnetic sensitive element The leakage magnetic field is used to characterize defects.

Test Results:
The experimental results under single-frequency excitation and multi-frequency excitation are compared, and the advantages of the multi-frequency AC flux leakage method in identifying the defect direction are verified, because this method has better signal sensitivity; Depth detection sensitivity is similar but multi-frequency signals are more suitable for quantifying defect depth due to their greater signal strength.

Single frequency stimulus test results

Multi-frequency stimulus test results

The performance of the SLA-100-720 power amplifier in this experiment: Realize the power amplification of 0-60 times of the excitation signal, improve the anti-interference ability of the system, and improve the signal-to-noise ratio.