NIST measurement service for DC standard resistors

Abstract

At the National Institute of Standards and Technology (NIST), the U.S. representation of the ohm is based on the quantum Hall effect, and it is maintained and disseminated at various resistance levels by working reference groups of standards. This document describes the measurement systems and procedures used to calibrate standard resistors and current shunts of nominal decade values in the resistance range from 10 −5 Ω to 10 12 Ω. Resistance scaling techniques used to assign values to the working standards are discussed. Also included is an assessment of the calibration uncertainties at each resistance level. * The abbreviation ppm (parts-per-million) is used in place of an equivalent SI ratio such as µΩ/Ω or µV/V when it does not appear in combination with SI terms.* Evanohm is a commercial alloy having a resistivity of about 1.34 µΩ-m with a nominal composition of 75 % Ni, 20 % Cr, 2.5 % Cu, and 2.5 % Al. By suitable annealing and heat treatment, its TCR can be adjusted to nearly zero from (20 to 30) °C.

Advanced Temperature-Control Chamber for Resistance Standards

“…The simulations were performed with Fluid Flow (CFX) from the ANSYS software package. 1 The Fluid Flow software not only accommodated our numerical model for optimizing placement of fans and structural elements, but it also allowed a visual random-particle representation of the expected air flow.…”

“…The expanded uncertainties, describing deviations within 2σ of the mean, of these measurements vary from 0.04 µΩ/Ω to 100 µΩ/Ω across more than twenty decades of resistance. Several factors influence the accuracy and the repeatability of these measurements, and among them, constant temperature control during measurement remains one of the more critical factors required to produce results with the lowest possible uncertainties [1][2][3][4][5][6]. Figure 1 illustrates the behavior of the deviation a 10 GΩ resistor from its nominal value with respect to temperature.…”

Gain Calibration of Current-to-Voltage Converters

“…The resistance of each gain setting is calibrated by comparison to NIST resistance working standards using 2-terminal to 4-terminal adapters at the BNC connectors. The NIST resistance standards are traceable to the quantized Hall resistance (QHR) [6].…”

Standard Platinum Resistance Thermometer Calibrations from the Ar TP to the Ag FP

“…The first part is the maintenance of the ohm. The reference resistors (1 Ω, 10 Ω, and 100 Ω) are calibrated biannually at NIST [50]. The second part is the thermostatic control of those reference resistors.…”