AC-DC Difference Measurements Research Articles

Ac-Dc Characterization of Coaxial Current Shunts and Application of the Shunt in the Digital Sampling Wattmeter

The purpose of this paper is to give a review of ac-dc characterization of the current shunts and application of the current shunt (nominal current 1A) within the digital sampling wattmeter. It is described the ac-dc transfer difference measurement of six cage type ac shunts from 10 mA up to 10 A using step-up measurement procedure. Furthermore, the substantial part of the measurement setup is fast switching system which is also described in detail. For the purpose of measurement procedure, the application is developed in LabVIEW and whole process is fully automatized. Obtained results are analyzed and shown on graphs. This paper is extended version of two papers: [1] and [2] which are presented on 1st International Colloquium on Smart Grid Metrology. Thus, paper is extended with presented application of the shunt 1 A in the digital sampling wattmeter.

Extending voltage range to 10 V rms in AC–DC difference measurements with AC programmable Josephson voltage standard

The larger-scale programmable Josephson voltage standard (PJVS) chip composed of 524 288 niobium nitride-based overdamped Josephson junctions enables us to generate stepwise-approximated AC waveforms with a root-mean-square (rms) amplitude of up to 10 V. In this study, we have extended the voltage range of the differential sampling system based on the AC-PJVS to an rms value of 10 V with the larger-scale PJVS chip. The sampling digital voltmeter (DVM) that is employed to measure differential voltages is modified to use a 10 MHz reference clock instead of an internal clock. This modification substantially improves the uncertainty of AC–DC difference measurements at low frequencies, which is caused by the internal clock error of the sampling DVM, by preventing the incoherent sampling of the differential voltages. The expanded uncertainties (k = 2) of the AC–DC difference measurements are reduced from 7.0 μV/V to 1.8 μV/V for a frequency of 62.5 Hz and from 8.0 μV/V to 4.4 μV/V for a frequency of 1 Hz. The improvements in the uncertainty are more significant compared with a conventional method at low frequencies, where the accuracy of a thermal voltage converter is reduced.

Uncertainty analysis for ac–dc difference measurements with the AC Josephson voltage standard

A detailed analysis of the uncertainties obtained in ac–dc difference measurements with an AC Josephson voltage standard (ACJVS) is presented. For audio frequencies and for voltages less than 200 mV, ac–dc transfers with the ACJVS may reduce the combined uncertainty by factors of 2–10, compared with conventional methods based on thermal converters. Type A uncertainties are predominantly limited by the thermal transfer standard (TTS), or the digital voltmeter used to acquire the output voltage from the TTS. In agreement with earlier work, the transmission line is the primary contributor to Type B errors for frequencies above 10 kHz. A Monte Carlo sensitivity analysis is used to demonstrate how the uncertainties of transmission line impedance and on-chip inductance impact the accuracy of the rms amplitude conveyed to the TTS.

New Technologies to Improve AC-DC Difference Measurements at NIST

New Technologies to Improve AC-DC Difference Measurements at NIST

Thermal-Transfer Standard Validation of the Josephson-Voltage-Standard-Locked Sine-Wave Synthesizer

This paper describes a Josephson-voltage-standard-locked synthesizer where a calibrator is used as a sine-wave generator, output whose is controlled by the calculable fundamental of the stepwise sinusoidal wave generated by a programmable Josephson junction array. Such a system combines the versatility of a calibrator with the stability and the accuracy of the Josephson voltage standard. The validity of this method was confirmed with the ac-dc difference measurements of a calibrated thermal-transfer standard. The synthesizer uncertainty inferred is below 1.2 μV/V for waveform frequencies up to 1 kHz and root-mean-square amplitudes ranging from 100 mV to 1 V.

Systematic Error Analysis of Stepwise-Approximated AC Waveforms Generated by Programmable Josephson Voltage Standards

We have measured stepwise-approximated sine waves generated by a programmable Josephson voltage standard (PJVS) with several different output configurations. These data are analyzed to characterize the dominant error mechanisms for RMS applications, such as AC-DC difference measurements of thermal voltage converters (TVCs). We present detailed explanations of the fundamental causes and consequences of systematic errors that arise from transitions and consider the overall uncertainties for PJVS ac metrology using this synthesis method. We show that timing-related errors are sufficient to make this waveform synthesis approach impractical for RMS audio-frequency applications. The implications of providing the load current required by devices of low input impedance, such as TVCs, are also discussed.

Improvements in the NIST Calibration Service for Thermal Transfer Standards

We report on multiple improvements made in the calibration services offered for thermal converters and thermal transfer standards in the ac-dc Difference Standards and Measurement Techniques Project at NIST during the past year. The major improvement in this calibration is the increased efficiency made possible by the consolidation of three disparate calibration services - low voltage thermal transfer standards, low- frequency thermal converters, and RF-dc difference calibrations - into a single service. This consolidation has the immediate benefit of offering NIST calibration customers one source for ac-dc calibrations from 2 mV to 1000 V and from 10 Hz to 1 GHz. Additional benefits include lower calibration prices and reduced uncertainties at many points.

High voltage AC–DC difference measurements under humidity step changes

Preliminary results of AC–DC difference measurements using a thermal voltage converter with range resistor under humidity change conditions are reported. The AC–DC difference measurement results, from a Holt-11 thermal converter at 100 and 200 V and frequency range from 40 Hz to 100 kHz, have shown that a first-order differential equation can be used to model this phenomenon. The humidity coefficients for the model are found to be frequency dependent and the time constants are related to the changes of humidity.

Automated comparator for accurate AC-DC difference measurements at the BNM-LCIE

This paper describes the new automated comparator system developed at the BNM-LCIE for the calibration of voltage thermal converters used as national AC-DC transfer standards. The system achieves Type A standard uncertainties of a few parts in 10/sup 7/ in the frequency range from 10 Hz to 1 MHz (100 kHz for voltages above 100 V). Type B standard uncertainties, depending on the type of converters to be compared and on the measurement voltage level, are between a few parts in 10/sup 7/ and a few parts in 10/sup 6/.

AC-DC difference measurements on thermal voltage converters at NRC

Two measurement systems are used at the National Research Council (NRC) of Canada to compare the ac-dc transfer differences δ of thermal voltage converters (TVC's). One comparator operates from 25 Hz to 1 MHz, and the other from 50 kHz to 100 MHz. The standards for measurement of δ are groups of multijunction TVC's at low frequency and a calorimetrie TVC at high frequency.

A Dual-Channel Automated Comparator for AC-DC Difference Measurements

An automated ac-dc difference calibration system is described. The system incorporates a new electronic comparator which determines ac-dc differences of thermal voltage converters (TVC's) by simultaneously measuring the difference between nearly equal ac and dc voltages with both the test and standard instruments. The comparator consists essentially of two practically identical channels each containing a digital-to-analog converter balancing circuit, an operational amplifier to amplify voltage imbalance, and an integrator circuit in which a capacitor is charged during an accurately controlled 10-s period. The difference between the ac and dc voltages applied to the test and standard TVC's is computed from differences in capacitor voltages, and the ac-dc difference is derived from the variation between the test and standard channel indications of this voltage difference. Measurements are made in about half the time required for our manual procedures.