Comparison CCEM-K4.2017 of 10 pF and 100 pF capacitance standards

Abstract

In 2017 the Consultative Committee for Electricity and Magnetism (CCEM) commissioned a key comparison of electrical capacitance standards, the second time this quantity has been compared since the implementation of the Mutual Recognition Agreement by the Comité International des Poids et Mesures (CIPM—MRA) in 1999. This comparison—CCEM-K4.2017—was piloted by the Bureau International des Poids et Mesures (BIPM) and included seven National Metrology Institutes (NMI) belonging to four Regional Metrology Organizations. The measuring scheme adopted for the comparison was that of a star comparison consisting of a set of bilateral comparisons between the participating NMIs and the BIPM, whose capacitance reference base served as a common reference. For each of the bilateral comparisons, the measurands were the capacitance values of 10 pF travelling standard capacitors belonging to the NMIs and, optionally, the values of 100 pF standards. All the participants have been chosen from those able to realize and maintain a representation of the farad at the best known level of accuracy. Four of them, including the BIPM, were taking their traceability from dc or ac quantum Hall effect standards and, the four others, from a calculable capacitor. The comparison results analysis have evidenced an agreement within about ±5 parts in 108 for the mandatory 10 pF measurements and within about ±10 parts in 108 for the optional 100 pF measurements. Also, excepted for one of the participants, a good agreement has been found for the ratio 100 pF:10 pF (within ±5 parts in 108). In addition to the comparison, it has been possible to evaluate the difference between the value of R K (von Klitzing constant) measured by electrical means from calculable capacitors and its last CODATA recommended value (CODATA 2014 adjustment). A difference of (43 ± 23) parts in 109 (k = 1) has been found which is consistent with the difference that can be computed from the experimental data used in the CODATA 2014 adjustment of fundamental constants. This report presents the details of the measurements and analysis having led to these results. Main text To reach the main text of this paper, click on Final Report. Note that this text is that which appears in Appendix B of the BIPM key comparison database kcdb.bipm.org/. The final report has been peer-reviewed and approved for publication by the CCEM, according to the provisions of the CIPM Mutual Recognition Arrangement (CIPM MRA).

Comparison of a 100-pF Capacitor With a 12 906-Ω Resistor Using a Digital Impedance Bridge

“…The digital impedance bridge enables us to measure the capacitance of C in reference to RH with a Type A uncertainty (k = 1) of 0.02 μF/F. Repeated measurements show that the results of C using the digital bridge are consistent, within 0.11 μF/F, with its capacitance measured against the Farad Bank, which is used to maintain the capacitance unit at the National Institute of Standards and Technology (NIST) and is traceable to the calculable capacitor [17]. The difference can be partly attributed to the frequency dependence of C because the digital bridge functions near 1233 Hz to keep the impedance ratio close to 100:1 in magnitude while the capacitance measurement relative to the Farad Bank has been restricted to 1592 Hz.…”

“…In the future, we plan to modify the front analog circuit of the digitizer to reduce its error. The uncertainty for the frequency dependence determination, which has currently been limited by the stability of a reference 1 pF cross capacitor at NIST, can also be significantly reduced [17,18].…”

Dual Josephson impedance bridge: towards a universal bridge for impedance metrology

“…Dedicated quadrature bridges, designed specifically for this task, have been optimized over the last 50 years [ 45 ]–[ 52 ]. Nowadays, 100 pF capacitance standards can be calibrated in terms of R K with a relative uncertainty of only a few parts in 10 8 [ 8 ], [ 11 ]. Although a few versions of transformer-based quadrature bridges have been designed to be operated at multiple frequencies [ 9 ], [ 53 ], [ 54 ], most of them only work at a single frequency: 1233 Hz for comparison of 10 nF to 12.906 kΩ and 1592 Hz for comparison of 10 nF to 10 kΩ.…”

“…Figure 8 shows the results of the calibration of 100 pF capacitance standards performed at 1 233.147 Hz over a 20 day period. Two calibration chains have been used: the METAS classical calibration chain using a quadrature bridge and a 1:10 ratio bridge (described in [8]) and the new calibration chain that only uses the DJIB.…”

“…State-of-the art impedance bridges [5][6][7][8][9][10] depend on ratio transformers or inductive voltage dividers (IVDs) to generate voltages whose ratio is accurate and stable. These bridges have been optimized over many years and are now able to compare impedance standards with an accuracy as small as 4 nΩ/Ω for specific impedance ratios and relative phase angles [11].…”