Use of a Superconducting Modulator in a Voltmeter with 10−12 V Resolution

Publisher Website
Google Scholar
Abstract
Various methods of measuring low dc voltages at cryogenic temperatures have been used for purposes of investigating thermoelectric properties, resistive dependence on various parameters, superconducting phenomena, and other effects. These generally involve resolution on the order of 10−10 V or less and source resistances on the order of 10−6 Ω or less. A voltmeter suitable for this type of work is described. The instrument employs a superconducting parametric amplifier modulator described by Ries and Satterthwaite as a null sensing element in a feedback system. The modulator consists of a tuning fork which creates a time‐varying mutual inductance between 2 sets of superconducting coils. The system equations and experimental data indicate that for low source resistance the accuracy and time constant of the voltmeter are essentially independent of source resistance. The noise is less than 10−12 V and the time constant is about 1.5 sec for source resistances of zero to 3×10−7 Ω. The modulator is well suited for production, and is quite insensitive to operating temperature and vibration. The voltmeter has reliability and repeatability typical of commercial room‐temperature instrumentation.

This publication has 13 references indexed in Scilit: