Abstract: A current ratio device for use in constructing a current transformer comprises a first magnetic core, a second magnetic core, a measuring winding electromagnetically coupled with the first core but not with the second core, and a compensating winding electromagnetically coupled with both cores. An externally powered amplifier has its input connected to receive the voltage waveform across the measuring winding. Its output provides a compensating current through the compensating winding equal to a magnetizing current required to magnetize the second core. The amplifier output also provides a measuring current through the measuring winding in the direction opposite that of the compensating current and equal to the compensating current multiplied by the ratio of turns in the compensating and measuring windings.

Abstract: A converter for converting a series of digital input bits to an analog output employs a direct current comparator having a magnetic core and primary and secondary ratio windings coupled with the core. The primary winding is divided into two sections. A first group of the more significant input bits varies the number of turns of the first primary section which is traversed by a first direct current. A second group of less significant input bits varies the number of turns of the second primary section traversed by a second direct current. A direct current is also passed through the secondary winding, this secondary current being varied proportionally with the number of turns of the first primary section traversed by the first primary current. Modulation-detection windings arranged inside the core (which also acts as a magnetic shield) detect any net ampere-turns unbalance of the primary and secondary currents in the ratio windings.

Abstract: The ac current comparator bridge measures the resistance of an unknown resistor at 50-60 Hz with an accuracy in the order of 10 parts per million. The current in the unknown resistor is compared, using a current comparator, to the current in a reference resistor for the in-phase component, and to the current in a reference capacitor for the quadrature component or phase defect. Once an ampere-turn balance is achieved in the comparator by adjusting the winding turns, the unknown resistor's values are a function of the reference resistor, the reference capacitor, the voltage sources driving the currents through the unknown resistor and the references, as well as the turns of the windings.

Abstract: This reference source provides a current which is of relatively high magnitude and which leads the voltage by substantially 90.degree.. It includes a reference capacitor which is highly stable and pure but of low capacitance, and a power capacitor which has a high capacitance. The capacitors are connected together at one end for coupling to a voltage source. A current comparator compares the currents flowing through the reference capacitor and the power capacitor, and provides a difference signal. A circuit generates a current in response to the difference signal and adds the generated current to the current through the power capacitor resulting in a current having a waveform and phase substantially identical to the reference capacitor current which leads the voltage source voltage by substantially 90.degree..