Precision resistance measurement using very low-frequency alternating current

The use of v.l.f. alternating current as an alternative to direct current for precision resistance measurement is discussed. It is shown that this method of measurement usually enables greater bridge-circuit resolution to be obtained because of increased detector sensitivity and a reduction in the effect of thermal e.m.f.s. For typical standard resistors, the changes in resistance from the d.c. values are found to be small at the frequencies considered. The factors which determine the optimum frequency of measurement and the limits of accuracy attainable are discussed, and suggestions are made regarding possible applications of the techniques described.