Magnetic amplifiers of the self-balancing potentiometer type

This paper describes a new type of magnetic amplifier having inherent self-balancing potentiometer characteristics. By means of a special compound feedback circuit, extreme stability and the fulfillment of balance conditions in the control circuit are obtained. Positive external feedback or self-feedback produces an effectively infinite gain that is highly degenerated by negative feedback resistance-coupled into the control circuit loop. Thus, in the case of voltage, as well as current input, the balanced control circuit demands practically no energy from the input source. The effective input resistance of a self-balancing magnetic amplifier for voltage measurements is about 100 to 1,000 times higher than the actual input circuit loop resistance; the effective input resistance of a self-balancing magnetic amplifier for current measurements is about 100 to 1,000 times smaller than the actual resistance of the control windings.