Ac-dc Difference Research Articles

Quartz Planar Multijunction Thermal Converter as a New AC–DC Current Transfer Standard Up to 1 MHz

The new generation of PMJTCs on quartz membranes and on quartz crystal chips developed at the PTB results in new ac-dc current transfer standards for the current of 10 mA and the frequency range from 10 kHz to 1 MHz, accompanied with small uncertainties. For a PMJTC with a heater resistance of 240 Omega the uncertainties for frequencies up to 100 kHz are smaller than 1 muA/A and up to 1 MHz they increase to 5 muA/A (k=1). A model for the PMJTC has been developed which allows calculating the ac-dc current transfer difference as well as the attributed uncertainties. The agreement of the simulation and the measurement were tested for high heater resistances of 700 Omega and 240 Omega, for which quite large ac-dc differences are calculated. The good agreement validates the model

Key comparison CCEM-K6.c of ac–dc voltage transfer standards at selected frequencies between 1 MHz and 100 MHz

From August 1995 to September 1998, the CCEM-K6.c Key Comparison (which started as the CCE 92-05 comparison) of ac–dc voltage transfer standards at selected high frequencies between 1 MHz and 100 MHz was carried out. Subsequently, from December 1998 until mid 2000, some participants carried out additional measurements.Two travelling standards were measured by 15 national standard institutes. The results at all selected frequencies in the range from 1 MHz to 100 MHz show a good agreement between most of participants. The agreement at 1 MHz is within 10 µV/V for most of the participants. The span of the majority of the reported ac–dc differences at 50 MHz is less than 0.6 mV/V, which is similar to a previous comparison but with more participants. Even at 100 MHz, most obtained results are within a span of 3 mV/V, which is considered to be a good agreement.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 Mutual Recognition Arrangement (MRA).

Behavior and frequency dependence of ac-dc high voltage transfer standard under humidity step changes

AC-DC difference from different type of AC-DC transfer standards placed under step humidity change conditions were measured at 200 V, 600 V, and 1 kV in the frequency range from 40 Hz to 100 kHz. The measured results have shown that the humidity affects the AC-DC difference of a high voltage AC-DC transfer standard significantly at high frequencies and that a first order differential equation can be used to model the behavior. The humidity coefficients of the model are found to be frequency dependent and the time constants are related to the change of the humidity. Furthermore, the humidity effect was also found to be device dependent due to the construction of the range resistor. It will imply consequences for the measuring procedures of further international comparisons in the field of AC-DC transfer.

Measurement of thermoelectric effects in a thermal converter using a NbN/TiN/NbN josephson junction array

The AC-DC transfer difference due to thermoelectric effects in a thermal converter was evaluated using a NbN/TiN/NbN Josephson junction array as an ultra-stable fast-reversed DC (FRDC) source. The Josephson junction array was connected in parallel with a conventional semiconductor FRDC current source, as an add-on voltage-stabilizer for the input of the thermal converter. The AC-DC difference due to thermoelectric effects was evaluated with a standard measurement (type-A) uncertainty of the order of 0.01 /spl mu/V/V, four-times better than that with the conventional semiconductor FRDC source.

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.

A new binary inductive divider comparator system for measuring high-voltage thermal converters

National Measurement Institutes have traditionally used bootstrapping or build-up techniques to determine the AC-DC difference of high-voltage thermal converters (HVTCs) in terms of the AC-DC difference of lower-voltage converters. We describe a method of determining the AC-DC difference of HVTCs that is independent of the build-up process. A description of the system and technique is given and preliminary data are presented.

EUROMET Project 432: Frequency performance of 12 906 Ω and 6453 Ω reference resistors for ac quantum Hall effect experiments

The Czech Technical University (CTU), acting as pilot laboratory in an international comparison, has fabricated and provided as transfer standards four terminal-pair thermostatted travelling resistance standards with nominal values of 12906 Ω and 6453 Ω. Vishay S 102 K resistors form the resistive elements of these standards and 100 Ω platinum resistance thermometers make it possible to monitor their inner temperature. The laboratories participating in the comparison (five in Europe and one in Canada) were requested to measure the frequency dependences and time constants of the travelling standards by comparing them with resistors with calculable frequency performance. Calculable resistors of several different designs (monofilar, bifilar, quadrifilar and octofilar) were available. For both travelling standards, the ac-dc differences of the parallel equivalent resistance, as reported by the different laboratories, are within 13 parts in 108 at 500 Hz and 70 parts in 108 at 5000 Hz. The reported time constants differ by less than 3.9 ns and 4.8 ns, respectively.

A planar Bi-Sb multijunction thermal converter with small ac-dc transfer differences

A planar Bi-Sb multijunction thermal converter was fabricated on the LPCVD Si/sub 3/N/sub 4//SiO/sub 2//Si/sub 3/N/sub 4/-diaphragm, prepared by silicon bulk micromachining, which thermally isolated a bifilar Pt- or NiCr-heater and the hot junctions of a Bi-Sb thermopile from the silicon substrate. The voltage responsivity, the ac-dc transfer difference, and the fluctuations of the output thermoelectric voltage and heater resistance were discussed to investigate the design factors of a thermal converter. The respective voltage responsivities in air and in a vacuum of the thermal converter with a built-in NiCr-heater were about 14.0 mV/mW and 54.0 mV/mW. The ac-dc voltage and the current transfer differences in air were about /spl plusmn/0.60 ppm and /spl plusmn/0.11 ppm in the dc reversing frequency range from 10 Hz to 10 kHz. They are sufficiently small to be used as practical ac standards. Compared to the thermal converter with a built-in Pt-heater, the thermal converter with a built-in NiCr-heater demonstrated a higher voltage responsivity and smaller ac-dc transfer differences, while exhibiting slightly larger fluctuations in output thermoelectric voltage and in heater resistance.

Evaluation of AC-DC difference of thermal converters using an SFQ-based D/A converter

Digital-to-analog (D/A) converters based on the Josephson effect are promising for ac voltage standards because they produce voltage steps with ultimate precision and stability. We are currently developing a single-flux-quantum (SFQ)-based D/A converter, designed for synthesizing sinusoidal waveforms for metrological applications. In this paper, we examine feasibility of an ac-dc transfer difference measurement for a thermal converter using the SFQ-based D/A converter.

AC and DC voltages from a Josephson arbitrary waveform synthesizer

We have synthesized and measured ac and dc voltages using a Josephson arbitrary waveform synthesizer. On-chip filtering has enabled the first practical operating margins for ac and arbitrary waveforms. Using a digital voltmeter, we demonstrate the operating margins and linearity of 101 synthesized dc voltages and confirm the flatness of a single voltage step. We present the first ac-dc and ac-ac voltage measurements of the synthesizer at 3.65 mV using an ac-dc thermal transfer standard. This quantum-based standard source can be used to measure the ac-dc difference of thermal transfer standards at small voltages.

Calibration of HF thermal voltage converters using an asymmetrical tee

This paper discusses systematic errors in the AC-DC difference determination resulting from the comparison of thermal voltage converters with different input connectors. Tests of two asymmetrical tees, with GR-874 and type-N arms, as well as the internal tee of the NRC calorimetric thermal voltage converter, are presented.

High-frequency AC-DC differences of NML single-junction thermal voltage converters

Frequency-dependent AC-DC transfer differences of a new set of single-junction thermal converters that serve at NML as primary standards for AC-DC transfer have been determined. The new determination has led to a reduction of the standard measurement uncertainty from 30 /spl mu/V/V to less than 10 /spl mu/V/V at frequencies up to 1 MHz.

The ac-dc difference of single-junction thermal converters

A nonlinear parabolic partial differential equation of heat conduction subject to the Robin boundary conditions is considered. The equation describes energy conservation in the heater wire of a single-junction thermal converter for both ac and dc currents. In the audio-frequency range the temperature distribution along the heater is calculated and the ac-dc difference deduced by means of the Picard iterative technique. The previously neglected effects of radiation and the thermal properties of the heater wire are included. An expression for the ac-dc difference is also derived in the low-frequency regime. The thermal conductance of the thermocouple, which has previously been neglected, is taken into account. The calculated increase in the ac-dc difference is consistent with recent measurements. The solution in this limit is found by both an eigenfunction-expansion method and the Laplace-transform method. Comparison of the solutions obtained by the two methods gives some useful formulae for the summation of numerical series.

Development of a new type of electrometic AC-DC transfer standard

A new type of electrometric AC-DC transfer standard is now under development at IEN. In this paper, the theory of this device and an analysis of the impact of some physical effects on the AC-DC difference, the description of the prototype, and preliminary experimental results are presented. The electrometric AC-DC transfer standard can now operate at the same level as resolution of thermal converters, even without the control of the distance between the electrodes. The measurements performed by the instrument are compatible with those obtained by means of calibrated thermal converters.

CCE 92-05 intercomparison of ac-dc voltage transfer standards at high frequencies (1-50 MHz)

From August 1995 to May 1998, the CCE 92-05 intercomparison of ac-dc voltage transfer standards at high frequencies was carried out. Two travel standards were measured by 15 national standards institutes. The results in the frequency range from 1 to 50 MHz show a good agreement between the majority of participants. The span of the majority of the reported ac-dc differences at 50 MHz is less than 1000 /spl mu/V/V, which is similar to a previous intercomparison but with a greater number of participants.

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/.

Calorimetric thermal voltage converter as a wideband calculable standard of AC-DC difference

Calorimetric thermal voltage converter as a wideband calculable standard of AC-DC difference

Evaluation of low-frequency AC-DC difference of coaxially mounted thermal voltage converter

The paper describes results of measurements of AC-DC transfer difference of a coaxially mounted, thermal voltage converter. Results of experiments, conducted in the 1 kHz to 1 MHz frequency range, are compared with results of simulations, using a simplified model of the converter. AC-DC transfer difference contributions, originating in the input connector and elements of the coaxial enclosure, are presented.

Thermal converter with quartz crystal temperature sensor for ac-dc transfer

The design and features of an experimental thermal ac-dc converter with frequency output are presented. A bulk acoustic wave LC-cut quartz resonator with linear frequency versus temperature characteristic is used as a temperature sensor. The resonator is excited through an inductively-coupled Butler oscillator. The sensitivity of this device is about 1 kHz/spl middot/K/sup -1/. In order to reduce the electromechanical coupling between the heater and the vibrating area, a thin-film Ni-Cr heater was sputtered at a location where the convex surface of the resonator intersects the nodal plane of the vibrations. The overall temperature coefficient of the output frequency is about -0.3%/spl times/K/sup -1/. The responsivity of the device is 300 kHz/spl times/W/sup -1/. The short-term stability of the output frequency permits an ac-dc transfer at the 10/sup -6/ level. The ac-dc voltage transfer difference of the converter is less than 10/spl times/10/sup -6/ at an input voltage of 3 V in the frequency range from (1-5) kHz. Below 1 kHz, the ac-dc transfer difference increases proportionally to the input power and doubles with a decade decrease of the input frequency. No resonances of the quartz plate were detected between 5 kHz and the frequency of the strongest fundamental thickness shear mode (9.5 MHz). Hence the converter can be probably used up to 1 MHz.

Evaluation of the calculable high frequency AC-DC standard

A calculable, high-frequency (HF) ac-dc transfer standard has been developed at NMi Van Swinden Laboratorium (VSL). An improved model which contains a more detailed description of the thermal element with the end disc, connecting leads, and the housing is presented together with the results of the ac-dc transfer measurements. The major result is a calculated shift of about 3400 /spl mu/V/V in the ac-dc difference at 100 MHz of the 4 V HF ac-dc standard. Based on this model, a 2 V standard is under development. The first results of this standard confirm the new modeling.