A New Construction of the Mutual Inductor Used as Quadrature Standard

For the purpose of getting very low impurity, this paper suggests a new construction of toroidal solenoidal mutual inductance. Its secondary winding is formed by carving the silver-plated marble or quartz toroid with a very narrow groove for shaping a completely astatic metal-foil winding. In order to get the lowest impurity, the paper also gives the optimal silver layer thickness at a given magnitude of mutual inductance, the optimal ratio of inside radius to outside radius, and the optimal ratio of height to width of the cross section of the toroidal marble. The theoretical analysis of the mutual inductor is coincident with the experiment. The time constant of the device which is defined by the ratio of loss tangent to angular frequency is at the order of 10-9 to 10-10. It is used as a quadrature standard for calibrating the phase error in the power-measuring circuit and is convenient to isolate the current circuit and the voltage circuit.