Simple real-time Fourier analyzer and its application to analysis of magnetic torque curves

A method for the simple construction of the discrete Fourier analyzer operating in real time is described. The simplicity is realized by using two basic analog elements, i.e., magnetic analog memory elements and Fourier coefficient calculators using operational amplifiers. Practically, the real-time Fourier analyzer for the calculation of the Fourier coefficients with a scheme of 12 ordinates is constructed. The zero drift of this analyzer is ± 0.1 percent/hour for the full scale. The minimum amplitude of analyzable input signal is about 0.02 in ratio to the maximum amplitude. The maximum sampling frequency is approximately 3 kHz and the minimum sampling frequency has no practical limitation. As an example for its application, the magnetic torque curves are analyzed in on-line real time. The analyzed results almost agree with the results calculated by a general-purpose computer in off-line. This real-time Fourier analyzer is simple and suitable especially for the analysis of the signals changing slowly.