A signal conversion system wherein variable amplitude, direct current or voltage signals from instrument sensors, which represent the magnitude of measured physical variables by amplitude modulated direct current or voltage signals, are converted to variable amplitude alternating current voltage signals at a frequency determined by the reference signal frequency of the said signal conversion system (usually 60 cycles) (FIG. 1) and a second signal conversion system wherein variable amplitude alternating current signals from instrument sensors, which represent the magnitude of measured physical variables or control signals by amplitude modulated alternating current voltage signals, are converted to variable amplitude direct current or voltage signals (FIG. 2). In both types of conversion, the input signal is filtered for normal mode noise and filtered by a feedback portion of the system for common mode noise. The conversion process also includes mangitude scaling of the variable amplitude input signal, including but not limited to, square root extraction and linear amplitude adjustment.
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