Derivative controlled magnetic amplifiers

THE CIRCUIT shown in Fig. 1 is of a low-level fast-response magnetic amplifier, as developed for such low-level signals as are provided by thermocouples, strain gauges, etc. Rectifiers are not included in the input circuit, thus eliminating the restriction which they impose on the minimum signal voltage. Low drift, fast response, and high gain are obtained by the use of a combination of delayed positive voltage-current and negative current-voltage feedback. The delayed negative feedback current-voltage from a resistive load is added to the signal voltage in the control circuit of the first stage so that it amplifies the average increments of signal voltage per half cycle of power supply voltage. The positive voltage-current feedback is adjusted to just compensate for rectifier leakage and eddy current losses in the second stage. The function of the second stage is to amplify and sum the output voltage of the first stage.