首先读取csv文件（来自示波器或其他来源），csv是字符格式的文本文件。然后，对采样波形进行谐波分析，将输入信号分解成：A0直流分量，A1基频分量，A22次谐波，A33次谐波……N噪声。采用的是加hanning窗的FFT算法。最后，求取 总谐波失真率THD（%）(First read the CSV file, and CSV is a character format text file. Then, the input signal is decomposed into A0 DC component, A1 fundamental frequency component, A22 harmonic, A33 harmonic. N noise. The FFT algorithm with Hanning window is adopted. Finally, the total harmonic loss rate THD (%) is obtained.)