A precise automatic a.c. potentiometer for low temperature resistance thermometry

Abstract

An instrument is described which measures resistance without lead errors. Low frequency a.c. is used to avoid thermal errors and reduce current noise. Useful resolution is possible with less than 10⁻¹⁴ W dissipation in the sensor. The indication is direct reading in resistance, has six-decade resolution, is fully automatic in balance, has a digital output signal and follows changes in resistance with a minimum of delay even at very low detector bandwidths.