Scale changing and spectral analysis of analog chart records

Abstract

Data which are contained only in the form of a trace on a strip chart record or on film often may not be fully utilized because of the time and difficulty required for conversion to other forms for analysis. A device is described herein for manually trace following chart records to produce an electrical analog signal. The output signal may be recorded on a strip chart to produce desired amplitude or time scale changes. Time variations of spectral content may be measured by recording the output on a slow speed tape recorder—then speeding up the playback for sonograph analysis. These techniques have been found useful for rapid and inexpensive analysis of analog chart records such as magnetograms.