This paper describes the implementation of a system for the generation and measurement of DC power and energy for voltages with magnitudes up to 800 V DC and currents up to 400 A DC. Power generation is based on the "phantom" power approach, where the voltage and current of the applied power are generated by separate voltage and transconductance amplifiers. Power and energy measurements are performed using a portable, DC transfer reference meter (TRM), consisting of commercially available instrumentation and transducers. Details of the system design, measurement techniques, and significant sources of error are presented.

Four terminal-pair air capacitors are important transfer standards to calibrate LCR meters up to a frequency of 10 MHz. We report a simple and new method to obtain the frequency dependence of the four terminal-pair capacitance of these standards using a four-channel vector network analyzer (VNA). The frequency dependence of the capacitance of an air capacitor and its uncertainty can be obtained from a single set of measurements without changing connections between the standard and the VNA, as has been the case in previously published work. The calculation of the frequency dependency is straightforward and model-independent. Nevertheless, an elementary model is provided to explain the observed frequency dependence. This article allows every laboratory with a four-channel VNA to measure the frequency dependence of these capacitors. Hence, a significant shortening of the traceability chain is achieved.

We tested a digital impedance bridge in a hybrid structure for comparison of a capacitor with a resistor where the impedance ratio was measured in two separate parts. The modulus of the impedance ratio was matched arbitrarily close to the input-to-output ratio, in magnitude, of a two-stage inductive voltage divider by adjusting the operating frequency of the bridge; the residual deviation between the two together with the phase factor of the impedance ratio was measured using a custom detection system based on a four-channel 24-bit digitizer. The ratio of the inductive voltage divider was calibrated, in situ, using a conventional four-arm bridge with two known capacitors. Fluctuations of the source voltages were largely removed through postprocessing of the digitized data, and the measurement results were limited by the digitizer error. We have achieved an overall bridge resolution and stability of $0.02~{\mu }\text{F}$ /F in 2 h for measuring a 100-pF capacitor relative to a 12 906- $\Omega $ resistor at 1233 Hz. The relative combined standard uncertainty ( $k $ = 1) is $0.13~{\mu }\text{F}$ /F, dominated by the digitizer error.

We tested a simple digital impedance bridge using two nominally equal resistors to form a 1:1 ratio. We focused on resolution and stability of the detectors. Fluctuations of the source voltages were largely removed through postprocessing of the digitized data, and the measurement results were limited by the detector noise. This detector-limited operating condition was first demonstrated using three modified Keysight 3458A multimeters for measurements of the voltage ratios, achieving 0.01 μV/V type A uncertainty in less than 15 min at 1 kHz. In an effort to extend the applicable frequency range and develop a system with off-the-shelf components, we tested a system using three lock-in detectors for measuring small deviations from the perfect AC ratio of unity magnitude, achieving stabilities and resolutions of 0.1 μV/V in a few hours for each point from 1 kHz to 5 kHz.

The results of a comparison on active power meter calibrations at the National Institute of Standards and Technology (NIST) using a source of AC power referenced to either a programmable Josephson voltage standard (PJVS) or a Josephson arbitrary waveform synthesizer (JAWS) is presented. The measurements were made at 60 V RMS, 5 A RMS, and 50 Hz at a power factor of 1.0. The estimated uncertainty of the active power applied to a meter under test (MUT) of the two system configurations is within 2 μW/VA (k=1), and the comparison results demonstrate that the two system configurations agree to within 1 part in 10 6 for applied voltage, current, and phase. A discussion of the measurement techniques and major sources of error are given.

This paper reports our effort to improve a sampling impedance bridge. Custom-modified ac multimeters together with optimized waveform digitizing software enable us to achieve a stability and resolution better than 1 part in 108 for nominal 1:1 voltage ratios around 1 kHz. We wish to leverage this new sampling capability to build a digital impedance bridge, aiming to derive the capacitance unit from the ac quantized Hall resistance.

NOTE: The first page of text has been automatically extracted and included below in lieu of an abstract Bridge Measurement Analysis Svetlana Avramov-Zamurovic1, Bryan Waltrip2 and Andrew Koffman2 1 United States Naval Academy, Weapons and Systems Engineering Department Annapolis, MD 21402, Telephone: 410 293 6124 Email: avramov@usna.edu 2 National Institute of Standards and Technology†, Electricity Division Gaithersburg, MD 21899. Telephone: 301 975 2438, Email: bryan.waltrip@nist.gov Introduction At the United States Academy there are several engineering majors, including Systems Engineering. This program offers excellent systems integration education. In particular the major concentrates on control of electrical, computer and mechanical systems. In addition to several tracks, students have the opportunity to independently research a field of interest. This is a great opportunity for teachers and students to pursue more in-depth analyses. This paper will describe one such experiment in the field of metrology. Very often engineering laboratories at undergraduate schools are well equipped with power supplies, signal generators, oscilloscopes and general-purpose multimeters. This set allows teachers and students to set up test-beds for most of the basic electronics circuits studied in different engineering tracks. Modern instrumentation is in general user-friendly and students like using the equipment. However, students are often not aware that there are two pieces of information necessary to establish a measurement result: the numerical value of the measured quantity and the uncertainty with which that measurement was performed. In order to achieve high measurement accuracy, more complex measurement systems must be developed. This paper will describe the process of analyzing a bridge measurement using MATLAB‡. Measurement Bridge One of the basic circuits that demonstrate the concept of a current/voltage divider is a Wheatstone bridge (given in Figure 1.) A source voltage is applied to a parallel connection of impedances. The source current is divided into a branch with impedances Z1 and Z 2 and a branch with impedances Z3 and Z4. The current flows through the detector when the bridge is not balanced. In order for the student to understand the relationship between the current through the detector and the other elements in the bridge, it is beneficial to calculate the current through the detector. Electrical circuit analysis may be performed using symbolic functions in MATLAB. † Electricity Division, Electronics and Electrical Engineering Laboratory, Technology Administration, U.S. Department of Commerce. Official contribution of the National Institute of Standards and Technology; not subject to copyright in the United States. ‡ In order to describe the procedures discussed in this paper, commercial products are identified. In no case does such identification imply recommendation or endorsement by the National Institute of Standards and Technology or that the materials or equipment specified are necessarily the best available for the purpose.

This paper describes the implementation of a sampling wattmeter for the measurement of sinusoidal active and reactive power over the 50 Hz to 6 kHz frequency range, 20 V to 600 V voltage range, and 0.05 A to 80 A current range. The wattmeter is capable of measuring sinusoidal and distorted voltage and current signals with up to 100 harmonics of the fundamental frequency component. Details of the system design, measurement techniques, and significant sources of error are presented.

This paper describes a programmable capacitor intended for use as the reference impedance in an inductance measurement system. The capacitor is programmable from 1 pF to 39 μF with a resolution of 1 pF and consists of a parallel combination of commercially available capacitors with values that follow the Fibonacci series progression. This paper presents a novel calibration procedure for the programmable capacitor that uses an LCR meter performing only difference measurements and requires only 3 reference capacitance standards within the device's programmable range. Design details and major sources of error for the use of the capacitor in an inductance measurement system are also discussed.

We have recently demonstrated new 2 V PJVS devices configured with two voltage outputs and two sets of least significant bits in order to simultaneously generate two independent stepwise output waveforms. This development improves upon our previous alternating dual waveform method in that the two voltage waveforms can now be measured simultaneously, and the sampler overload condition that existed in the previous configuration has been eliminated. Applications such as the NIST Quantum Watt for ac power calibrations will benefit from these developments through reduced measurement uncertainties and improved flexibility.

A voltage amplifier composed of three cascaded -10:1 gain sections has been developed to extend the voltage range of primary electric power calibrations from 120 to 600 V over the 50-400-Hz frequency range. The gain and phase errors of each amplifier section are continuously measured and corrected in situ using a permuting impedance measurement technique. The amplifier design approach, measurement principles, and initial performance results are presented.

This paper presents the results of a comparison of active/reactive power meter calibrations between the National Institute of Standards and Technology and National Research Council. The comparison was implemented using a transfer standard consisting of a highly stable commercial sampling-type power/energy meter. Active and reactive power measurements were made at 120 V, 5 A, 50 Hz, and 60 Hz. For active power, the measurements were made at applied current phase angles of 0°, +60°, and -60°. For reactive power, the measurements were made at applied current phase angles of +60°, +90°, -60°, and -90° . The results of the comparison indicate agreement to within the stated uncertainties of the participants.

We are integrating an AC waveform source into our Programmable Josephson Voltage Standard system (PJVS). The objective is to provide a convenient, highly automated quantum-referenced source for AC voltage metrology that does not require the use of a thermal voltage converter. The stability of the AC waveform is inferred from the DC voltage reference. The accuracy of the AC waveform is measured utilizing the differential sampling method with a PJVS step-wise synthesized waveform as a reference. Preliminary results show that the AC waveform source is about ten-times more stable than commercial calibrators.

Researchers within the Quantum Electrical Metrology Division at the National Institute of Standards and Technology (NIST) have implemented a calibration procedure for four-terminal-pair capacitance standards from 0.01 μF to 100 μF [1], [2]. This method depends on the accurate characterization of a 1 nF capacitor and an Inductive Voltage Divider (IVD) 1:10 ratio from 100 Hz to 100 kHz. This paper discusses a procedure that evaluates the IVD ratio and offers an enhancement over the current method. Also the evaluation of the 10 nF capacitor is presented and a measurement procedure modification is suggested that significantly improves the result.

AC bridge techniques commonly used for precision impedance measurements have been adapted to develop an eddy current sensor for rail defect detection. By using two detection coils instead of just one as in a conventional sensor, we can balance out the large baseline signals corresponding to a normal rail. We have significantly enhanced the detection sensitivity of the eddy current method by detecting and demodulating the differential signal of the two coils induced by rail defects, using a digital lock-in amplifier algorithm. We have also explored compensating for the lift-off effect of the eddy current sensor due to vibrations by using the summing signal of the detection coils to measure the lift-off distance. The dominant component of the summing signal is a constant resulting from direct coupling from the excitation coil, which can be experimentally determined. The remainder of the summing signal, which decreases as the lift-off distance increases, is induced by the secondary eddy current. This dependence on the lift-off distance is used to calibrate the differential signal, allowing for a more accurate characterization of the defects. Simulated experiments on a sample rail have been performed using a computer controlled X-Y moving table with the X-axis mimicking the train’s motion and the Y-axis mimicking the train’s vibrational bumping. Experimental results demonstrate the effectiveness of the new detection method.

A number of international comparisons of active power meter calibrations were conducted in the past. This paper addresses the international comparison of reactive power meter calibrations at 120 V, 5 A, 50/60 Hz, and power factors 0.5 lead/lag, and zero lead/lag, between 5 NMIs; 3 from the SIM metrology region (NRC, NIST, CENAM) and 2 from the APMP metrology region (NIM and KRISS).

We report the results of the international comparison of low-frequency ac voltage ratio: CCEM-K7. The participants made measurements of a unique travelling standard: an inductive voltage divider which provided the 20 ac voltage ratios chosen for the comparison. The nominal ratios chosen were: 0.1 to 0.9, 0.01 and 1/11 to 10/11. Each of the 17 participants measured the in-phase and quadrature components of all 20 ratios at a frequency of 1 kHz, and 7 laboratories made additional, optional, measurements at a frequency of 55 Hz. The report consists of two separate parts: the first part describes the comparison and provides detailed uncertainty budgets for each participant; the second part describes the method used to analyse the results, gives the results of the comparison and tabulates the raw data provided by each participant.

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.