The Calibration of DC Resistance Standards by an AC Method

Techniques recently developed at the National Physical Laboratory (NPL) have enabled the zero-frequency (or dc) value of 4-terminal Laboratory Standard Resistors readily to be determined to an accuracy of two parts in 107 from a few measurements made in the frequency band 40 c/s to 600 c/s. A Kelvin double-bridge network is used, the ratio arms consisting of inductively-coupled voltage dividers with an accuracy and discrimination of one part in 107 over the whole frequency range. Experimental results and constructional details of the inductive dividers are given together with the theoretical considerations underlying the principle of the method.