Andrew D. Koffman

The sensitivity of a method to predict a capacitor's frequency characteristic

Several groups have worked on the characterization of four terminal-pair (4TP) capacitance standards at high frequencies. This paper describes a variation of the technique to predict a capacitors frequency characteristic. The method is sensitive to regression parameter selection and the paper gives a detailed analysis of the techniques used to calculate reasonable values for these parameters. The results of the analysis of the capacitor frequency characteristic prediction methods sensitivity to exponent parameter variation have shown that this sensitivity is a major uncertainty component in the uncertainty analysis of NISTs capacitance standard measurement system.

Uncertainty analysis for four terminal-pair capacitance and dissipation factor characterization at 1 MHz and 10 MHz

The Electricity Division at the National Institute of Standards and Technology (NIST, formerly NBS) has implemented a system to characterize capacitance and dissipation factor for four terminal-pair (4TP) air dielectric capacitors at frequencies from 1 kHz to 10 MHz. This paper describes an extensive uncertainty analysis of the measurement system. The analysis has been divided into three areas: 1 kHz capacitance measurements; network analyzer impedance measurements (covering frequencies from 40 MHz to 200 MHz); and a mathematical extrapolation algorithm that regresses the high-frequency characterization down to frequencies of 10 MHz and below. This algorithm is referred to as the capacitor frequency characteristic prediction (CFCP) method.

Binary versus decade inductive voltage divider comparison and error decomposition

An automatic inductive voltage divider (IVD) characterization method that can measure linearity by comparing IVDs with different structures is suggested. Structural models are employed to decompose an error vector into components that represent each divider. Initial tests at 400 Hz show that it is possible to assign independent errors due to the binary and decade structures with a 2/spl sigma/ uncertainty of 0.05 parts per million (ppm) at the measured ratio values. >

Josephson-based full digital bridge for high-accuracy impedance comparisons*

This paper describes a Josephson-based full digital impedance bridge capable of comparing any two impedances, regardless of type (R-C, R-L, or L-C), over a large frequency range (from 1 kHz to 20 kHz). At the heart of the bridge are two Josephson arbitrary waveform synthesizer systems that offer unprecedented flexibility in high-precision impedance calibration, that is, it can compare impedances with arbitrary ratios and phase angles. Thus this single bridge can fully cover the entire complex plane. In the near future, this type of instrument will considerably simplify the realization and maintenance of the various impedance scales in many National Metrology Institutes around the world.

Digital lock-in amplifier for precision audio frequency bridge

This paper introduces a custom digital lock-in amplifier for detecting the imbalance signal of a precision audio frequency bridge. The lock-in amplifier is designed with a PXI measurement system which is equipped with a signal generator and simultaneous data acquisition adapters. The advantage of this design is that the demodulation algorithm can be flexibly reconfigured when the imbalance signal changes in the AC bridge system. The resolution and linearity of the lock-in amplifier can also be improved by using higher resolution A/D adapters. Simulations and experiments have verified the basic concept of the designed lock-in amplifier.

Evaluation of a Capacitance Scaling System

An improved error analysis of an existing capacitance scaling system for supporting measurements of higher valued (10 nF to 100 ) ceramic-dielectric four-terminal-pair (4TP) capacitance standards over the 100-Hz to 100-kHz frequency range is described. The capacitance scaling system uses a commercial impedance (inductance-capacitance-resistance) meter and a single-decade inductive voltage divider as an impedance comparator. Four-terminal-pair capacitors in decade (10 : 1) steps from 10 nF to 100 F are measured. The systems 10 : 1 scaling error is determined using 100-pF and 1-nF air-dielectric 4TP capacitance standards with known capacitance and loss characteristics over frequency. This paper discusses the significant reductions in measurement uncertainty that were attained through the use of improved calibration standards and measurement method refinements. Details of the uncertainty analysis for a 10-nF capacitor (in the 100-Hz to 10-kHz frequency range) and verification data are presented.

Inductance Measurement Using an LCR Meter and a Current Transformer Interface

This paper describes a new inductance measurement system based on a commercially available LCR meter, a commercially available audio frequency capacitance bridge, 4 terminal-pair (4TP) capacitance and resistance standards, and a multi-stage, programmable-ratio, current transformer. The described measurement system synthesizes equivalent inductance values using the current transformer to combine the applied currents through programmable resistance and capacitance standards. The system takes advantage of the inherent measurement linearity of the LCR meter, and achieves acceptable inductance measurement uncertainty over the 50 Hz to 20 kHz frequency range

The design and self-calibration of inductive voltage dividers for an automated impedance scaling bridge

The design and construction of inductive voltage dividers (IVDs) for use in impedance bridge applications in the 50 Hz to 1 MHz frequency range is described. Two dividers are described; one designed to operate from 50 Hz to 2 kHz and the other designed to operate from 2 kHz to 1 MHz. Preliminary comparison results of the new IVDs over the 100 Hz to 50 kHz frequency range are given. A new bridge to self-calibrate the IVDs is also described. The bridge is based on the straddling method and has been designed to characterize IVDs over the 50 Hz to 100 kHz frequency range.

Milligram mass metrology using an electrostatic force balance

Although mass is typically defined within the International System of Units (SI) at the kilogram level, the pending SI redefinition provides an opportunity to realize mass at any scale using electrical metrology. We propose the use of an electromechanical balance to realize mass at the milligram level using SI electrical units. An integrated concentric-cylinder vacuum gap capacitor allows us to leverage the highly precise references available for capacitance, voltage and length to generate an electrostatic reference force. Weighing experiments performed on 1 mg and 20 mg artifacts show the same or lower uncertainty than similar experiments performed by subdividing the kilogram. The measurement is currently limited by the stability of the materials that compose the mass artifacts and the changes in adsorbed layers on the artifact surfaces as they are transferred from vacuum to air.

Alignment and testing of the NIST calculable capacitor

This paper reports progress on the NIST effort to develop a new calculable capacitor, focusing on improvement of the guard electrode motion control as well as issues associated with the overall electrode alignment. Design of a multi-wavelength Fabry-Perot interferometer which may facilitate testing the calculable capacitor in air is also discussed.