The Fourier transform is used in many fields as an efficient method for signal analysis. But itss real-time processing has not come into wide use, because the necessary instruments are too expensive and not handy. This paper describes a method for the simple construction of a realtime Fourier analyzer and its application to magnetic torque curves.
The real-time Fourier analyzer is constructed by two basic components, a Fourier coefficient calculator and a memory element. The calculating circuit for the Fourier coefficient can be made easily by a newly developed circuit using a single operational amplifier which allows both positive and negative multiplication and addition. A magnetic element is used as the analogue memory element. The magnetic memory element is easily made from a magnetic core and has semi-permanent memory time. Practically, the real-time Fourier analyzer for the calculation of the Fourier coefficient with a scheme of 12 ordinates is constructed by these components. The characteristics of this analyzer are as follows. The zero drift is ±0.1%/hour on the full scale. The minimum amplitude of the analyzable input signal is about 0.02 in ratio to the maximum amplitude.
As an example for its application, magnetic torque curves are analyzed in real time. The analyzed results are almost identical with the results calculated by a general purpose computer in off-line. This simply constructed real-time analyzer will be suitable for the analysis of signals which do not have a very high frequency component, for example, magnetic torque curves, electrocardiograms, seismic data, etc.