Ac-dc Transfer Research Articles

Direct calibration of a true-rms ac voltmeter against a He-free pulsed Josephson standard

Starting from 2019 a new central role is played by quantum standards, owing to the redefined SI, where electrical units are directly linked to the fundamental constants e (elementary charge) and h (Planck constant). Thus, metrologists are nowadays trying to extend the astonishing accuracy attainable in dc measurements to ac and beyond, moving towards calibrations aiming quantum ac voltage generation. Programmable Josephson Voltage Standards are nowadays capable of fulfilling primary metrology requirements only for stepwise-approximated voltage signals up to few hundreds Hz. Pulsed Josephson standards are instead capable of generating arbitrary waveforms at higher frequencies, so are generally called Josephson Arbitrary Waveform Standards (JAWS). Despite of the lower attainable voltage, JAWS are very promising and are the subject of intense research activity. In particular, the capability of generating high spectral purity signals allows high accuracy measurements especially at the low voltage levels (<100mV rms), which are challenging to be performed by the traditional ac-dc transfer difference using thermal converters. We report in the following about our setup for quantum-based calibrations of a true-rms ac voltmeter with low uncertainty, first results obtained and unsolved issues.

Frequency-dependent component of AC-DC transfer difference of a redesigned calorimetric thermal converter

This article presents an analysis of the frequency-dependent component of the AC-DC transfer difference of a calorimetric thermal voltage converter (CTVC) with substantially reduced DC reversal error. It contains an analysis of the effect of this reduction on the AC-DC transfer difference. The analysis was based on the mathematical model of a CTVC waveguide, which was extended by estimation of the residual parameters of the CTVC heater (microwave rod resistor) using the finite element method (FEM). The results of the analysis were validated by laboratory measurements. The article also contains the uncertainty budget of the AC-DC transfer difference of the new CTVC. Despite its high thermal time constant, the CTVC is currently one of the most accurate AC voltage standards in the frequency range from 1 to 100 MHz.

Dual-Using AC-DC Transfer Standard for Characterization of Precision Shunt

Dual-Using AC-DC Transfer Standard for Characterization of Precision Shunt

AC–DC Transfer and Verification of Ultra-Low Frequency Voltage From 0.1 to 10 Hz

A system for ac-dc voltage transfer at ultra-low frequencies is established with dual-heater thermal voltage converter (DHTVC) in this paper. The system is based on the premise that the thermoelectric potential of TVC is square related with the input voltages. The output thermoelectric potential is constant when two orthogonal and equal-amplitude sinusoidal signals are input to the DHTVC. How to evaluate and compensate the key parameters that affect the stability of output thermoelectric potential is discussed in detail. In this paper a verification method is also proposed to prove the accuracy of the ac-dc transfer results at low frequencies based on quantum voltage technology. The high-precision digitizer PXI-5922 is introduced as the transfer standard. The ac-dc difference of sampling error is calibrated using ac-dc voltage transfer with DHTVC as the reference standard at low frequencies down to 0.1 Hz. The dc and ultra-low frequency errors are also calibrated by programmable Josephson voltage standard (PJVS). The uncertainties of calibration results from two different methods are evaluated respectively. The calibration results from ac-dc voltage transfer with DHTVC and PJVS show good agreement and inconsistency is less than 5 μV/V at frequency ranges from 10 Hz down to 0.1 Hz.

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.

ESD Stress Analysis and Suppression in a Single-Junction Thermal Converter

This article presents an outline of Electric Transient Disturbances (ETDs), represented by the ElectroStatic Discharge (ESD) in accordance with the Human-Body Model (HBM), on the AC-DC transfer measurement standard, represented by the Single-Junction Thermal Converter (SJTC) Thermal Element (TE). Mitigation technique against the power dissipation build-up, higher than the operational margins recommended by a manufacturer, on the TE were proposed and modelled using Laplace Transform (LT) analysis. A mathematical model and an optimization algorithm were developed to determine the equivalent circuit model parameters of a Transient Overload Protection Module (TOPM) that would offer adequate protection against destructive power dissipation levels build-up on the TE. The mathematical model was developed using an 8 kV ESD, which was expected to deliver short-circuit current with a peak value of approximately 5.33 A through a load impedance of approximately 1 m\varOmega. The ESD stress signal was injected into the TOPM connected in parallel with the TE. The active power dissipated by the SJTC TE per period of transient response was calculated from the current and voltage obtained from the mathematical analysis, and the results indicate a power dissipation of 10 mW by the TE. From the algorithm, the model parameter that noticeably influences the power dissipation capabilities of the TOPM is the inductance and it must be smaller than 1.2 nH. A CAD based simulation model was developed and analysed. The simulation results agreed with the mathematical model.

Mathematical Modeling and Measurement of Low Frequency Characteristics of Single-Junction Thermal Converters

We derive the analytic solution of the heat flow equation of a single-junction thermal converter (SJTC). The heat is generated by the flow of an electric current through the heater wire, while the thermocouple attached via a ceramic bead to the middle of the heater wire acts as a heat sink. We consider the nonlinearities caused by the Thomson and radiation effects, as well as the temperature dependence of the physical properties of the heater material. The results are used to obtain the expression for the ac–dc transfer difference as a function of the device geometry and material parameters. We report on the very good agreement between the analytical, numerical, and experimental results of the ac–dc difference of the SJTC in the frequency range from 10 Hz to 1 kHz. The results will be useful for the design of thermal converts and their further use in the ac voltage and current metrology.

Trilateral South American project: a reference system for measuring electric power up to 100 kHz – progress report III

Three countries in South America are jointly developing a reference system for measuring electric power up to 100 kHz. The objective is the construction of three similar measuring systems, one for each institute. This project will contribute to provide calibration services in measuring ranges still not covered by the three institutes both in ac-dc transfer and in electric power. The status of its development by the end of 2019 is described here.

Design of a current switching system for high accuracy current sources in AC-DC Transfer applications

A current switching system for AC-DC transfer applications using Single Junction Thermal Converters (SJTC) was designed and tested at Instituto Nacional de Metrología (INM). This switch design can directly commute between a DC reference current source and an unknown AC current source generated by high accuracy calibrators such as Fluke 5720A and Fluke 5730A. Two vacuum latch relays with an estimated switching speed of less than 10 ms were used. A control unit developed over a MSP430 Microcontroller allowed the switching control and serial communication with instruments through LabVIEW. It was found that, it takes between 2 s and 3 s for high accuracy calibrators to switch between an operating DC current and an AC current, or vice versa; therefore, the current commutation time is limited by the calibrator. By using two calibrators and the implemented current switching system it was possible to reduce the commutation time to about 300 ms, which is less than the reported SJTC thermal time constant. The switching system must be fast enough to avoid the calibrators to go to a standby state. The research work showed that the switching system could be used to improve thermal converters operation for the calibration of high accuracy AC current sources and multimeters.

Construction and evaluation of a low-cost AC-DC current shunt

The process of construction and evaluation of a shunt prototype for AC-DC transfer produced by Inmetro, built with low-cost materials and using commercially available thin film chip resistors will be presented. The main objective of this work is fully achieved, obtaining an equipment with characteristics that allow its use as standard in the calibration of AC current sources of high accuracy, in a wide frequency range.

A precision coaxial current shunt for current AC-DC transfer

The paper describes the design and mathematical model of a 50 mA coaxial current shunt developed at Silesian University of Technology (SUT) in Gliwice, Poland. The AC-DC transfer difference of the shunt transimpedance and its phase displacement were calculated based on the mathematical model of the shunt. The results of AC-DC transfer difference calculation were validated by calibration of the shunt at Swedish National Metrology Institute RiSE.

A Review of AC-DC Transfer Standard and Development into Thermoelectric Measurement

A Review of AC-DC Transfer Standard and Development into Thermoelectric Measurement

Interlaboratory Comparison of Thermal AC Voltage Standards

Abstract The article presents results of comparison of the thermal converter of nominal input voltages equal to 10 V from the set of Polish National AC voltage standards, maintained at the Central Office of Measures in Warsaw, with the primary AC voltage 5 V standard, developed and maintained at the AC-DC Transfer Laboratory of the Department of Measurement Science, Electronics and Control at the Faculty of Electrical Engineering of the Silesian University of Technology in Gliwice.

Modeling the AC–DC Transfer Difference of Wideband Cage-Type Current Shunts

A cage-type, current-shunt construction design was adopted in this article as prospectively having a wide bandwidth. A lumped equivalent circuit model for current shunts assembled according to this design is described here. The ac–dc transfer differences of shunts with the nominal currents from 0.5 to 20 A are computed using standard two-port network theory. Cage-type current shunts were constructed and tested to validate the model. The measured ac–dc current transfer differences agree with the predicted values within the standard uncertainties in the whole frequency range of interest (10 Hz–100 kHz).

Planar Multijunction Thermal Converters With Increased Sensitivity Operated in Hermetically Sealed Housings Filled With Noble Gas

The sensitivity of planar multijunction thermal converters was significantly increased by filling the housing with noble gasses, preferably xenon or krypton. The performance was observed for almost two years, and no degradation of the sensitivity was found. Also, the frequency response of the ac–dc transfer difference remains unchanged at high frequencies and even improves below 40 Hz. Using the lowest at present manufacturable heater resistance of 90 $\Omega $ with the noble gas filling, ac–dc transfer at voltages down to almost 70 mV compared to about 100 mV in air becomes possible.

Establishment of High-Voltage AC–DC Voltage Transfer Standards in 1–100-kHz Range at NMIJ

New thin-film range resistors have been developed at the National Metrology Institute of Japan, to re-establish ac–dc voltage transfer standards in the 100–1000-V range at frequencies of 1–100 kHz. In earlier studies, the voltage dependence of the ac–dc transfer difference was observed during step-up procedures above 300 V. One of the possible reasons for this voltage dependence is the temperature rise due to the Joule heating, which may cause changes in the resistance of the resistor, as well as the temperature dependence of the dielectric losses in the resistor coating. In this paper, to reduce the voltage dependence, new thin-film heaters were directly fabricated on an aluminum nitride substrate to prevent heat from accumulating in the range resistor. The voltage dependence was evaluated by measuring the differences in impedance among various range resistors. Negligible voltage dependence in the step-up procedures from 100 to 1000 V was achieved.

Determination of AC–DC Transfer Difference of Calculable Thermal Voltage Converters in 1–30-MHz Frequency Range

This paper presents the results of determination of the ac-dc voltage transfer difference of two calculable thermal ac voltage standards, developed at the Silesian University of Technology, Gliwice, Poland, in 1-30 MHz frequency range. Two experimental methods confirmed with high accuracy the results obtained from the mathematical model.

Determination of Frequency-Independent Component of AC–DC Transfer Difference of SUT Calculable AC Voltage Standards

This paper describes the determination of value of frequency-independent component of ac–dc voltage transfer difference of two calculable thermal ac voltage standards developed and maintained at the Silesian University of Technology Gliwice, Poland. According to our research, the value of this parameter determined with ac–dc transfer measurements is $0.0~\mu \text{V}$ /V with combined standard uncertainty ( $k = 1$ ) equal to $0.3~\mu \text{V}$ /V. The obtained results were validated with fast-reversed direct current method and will be used to supplement the uncertainty budgets of these standards. The presented method does not require expensive quantum ac voltage standards.

A Novel Film Thermal Converter Based on an Electrothermally Excited/Piezoresistively Detected Microbridge Resonator

This paper presents the design, fabrication, and preliminary results of a resonant thermal converter consisting of an electrothermally excited/piezoresistively detected SiO2/Si3N4/Si x N y microbridge resonator and a Ni24.9Cr72.5Si2.6 heating resistor placed on another beam parallel to the microbridge. The noncontact temperature sensing technique reduces the diversion of thermal energy from the temperature sensors, as well as the ac–dc transfer differences due to the capacitive coupling between the heater and the temperature sensor. The semidigital output of the resonant thin-film thermal converter eliminates problems such as intensity fluctuations associated with analog signals. The temperature coefficient of resistance of the Ni24.9Cr72.5Si2.6 film with a thickness of 89 nm is only $-0.86 \times 10^{-6}$ /K. The responsivity of the resonant thermal converter is $9.21~\text {kHz}\cdot \text {W}^{-1}$ in air. The thermoelectric transfer difference measured by the fast-reversed dc method at 1 kHz is $2.8 \times 10^{-6}$ . It indicates that the resonant thermal converter is a promising thermal converter.

Effect of modified multipliers resistors on measurement of AC voltages above 50 V

The effect of the modified multiplier resistor on the measurement accuracy of ac voltages higher than 50 V is studied and evaluated in this paper. Modification in construction is made in the multiplier design which used for higher voltages. Ten resistors are radially connected in series and mounted on a high insulation PCB board instead of using one resistor which has higher power rating and thickness. The introduced multipliers values which are established at the National Institute of Standards (NIS), Egypt are 10 kΩ, 20 kΩ and 40 kΩ for voltages 50 V, 100 V, and 200 V respectively. The high voltage modified multipliers are joined with single junction thermo-elements to produce the modified thermal voltage converters (TVCs). The modified TVCs are calibrated against other standard TVCs at different frequencies 20 Hz, 55 Hz, 1 kHz, 10 kHz, and 100 kHz. The ac-dc transfer differences of the modified TVCs are compared with the traditional TVCs to evaluate its performance. They introduce lower ac-dc differences than the traditional ones specifically at higher voltages and frequencies. The modified TVCs performance is also evaluated by comparing their measurement accuracy and precision at range 100 V with the traditional TVCs.