NIST is developing advanced metrology standards for electrical impedance measurements to ensure accurate and consistent measurements across industries and international laboratories. The project focuses on realizing the SI unit of capacitance through NIST’s calculable capacitor, which measures capacitance by measuring length with high precision. This work is crucial for maintaining and improving the precision of impedance measurements and ensuring the consistency of measurement services across different laboratories and industries.
NIST has successfully invested in two key quantum representations of electrical quantities – the Quantum Hall Resistance and Josephson Voltage standards – achieving measurement uncertainties approaching parts in 10^9. However, these standards represent only a few points in a multi-dimensional world of electrical measurements. To address this, NIST is developing a four-terminal-pair digital bridge employing a double-loop technique to compare a 100 pF fused-silica capacitor with a portable 12906 Ω resistor. This method focuses on resolution and stability of the detectors, with fluctuations of source voltages largely removed using noise cancellation techniques in post-processing of the digitized data.
The project also involves characterizing commercial four-terminal-pair capacitance standards from 1 pF to 1 nF over the frequency range from 1 kHz to 10 MHz using a bootstrapping technique with an LCR meter and an inductive voltage divider. NIST measurements of the Calculable Capacitor using Andeen-Hagerling bridges have allowed them to observe and test accuracy, principally non-linearity performance, on a scale that would otherwise be impossible.
Source: https://www.nist.gov/programs-projects/farad-and-impedance-metrology
Keywords: accuracy, metrology, capacitance, impedance, measurement
