Title :
An automated cryogenic current comparator resistance ratio bridge
Author :
Williams, J.M. ; Hartland, A.
Author_Institution :
NPL, Teddington, UK
Abstract :
The method of measurement of two-terminal cryogenic and four-terminal room-temperature resistors using a DC cryogenic current comparator bridge is well established. A bridge which is based on this technique and is fully automated with a computer controlling both the measurement current and the readings of the bridge imbalance current is described. The bridge is designed to measure integer ratios of 1:1 to 1:25 of four-terminal room-temperature resistors in the range 1 Omega to 10 k Omega . An overall accuracy of 1 part in 10/sup 9/ for differences in the ratio from nominal of up to 100 p.p.m. is desired. Some initial determinations of the resolution have been made for a measurement of 10 Omega :100 Omega . These determinations were carried out without the balance servo, and the output from the null detector was measured with a digital voltmeter connected to the computer. An analysis of a set of 11 reversals gave a standard deviation for a single reversal of 1 part in 10/sup 8/ and therefore a standard error of the mean of 3 parts in 10/sup 9/.<>
Keywords :
bridge instruments; comparators (circuits); computerised instrumentation; electric current measurement; electric resistance measurement; low-temperature techniques; measurement standards; resistors; 1 ohm to 10 kohm; DC cryogenic current comparator bridge; automated bridge; computer control; digital voltmeter; four-terminal room-temperature resistors; integer ratios; null detector; resistance ratio bridge; standard error; two terminal cryogenic resistor; Automatic control; Bridge circuits; Computer errors; Cryogenics; Current measurement; Detectors; Electrical resistance measurement; Resistors; Servomechanisms; Voltmeters;
Conference_Titel :
Precision Electromagnetic Measurements, 1990. CPEM '90 Digest., Conference on
Conference_Location :
Ottawa, Ontario, Canada
DOI :
10.1109/CPEM.1990.110054
