Ac-dc Difference Research Articles

Establishment of new automated multi range thermal current converter

<p>A new automated multirange thermal current converter (TCC) has been designed and implemented at the National Institute of Standards (NIS), Egypt. Five single junction thermal current converters (SJTCCs) have been connected in parallel on PCB with an LCD, keypad and a microcontroller to control a five fast switching relays. This TCC has been designed to cover the ac current ranges from 500 mA to 5 A at frequencies from 40 Hz up to 100 kHz. The construction of the new automated TCC has been presented to solve some problems of using shunt resistance at high currents. Furthermore, a new automatic calibration system has been established to calibrate the established TCC against another standard TCC. This software program has been specially designed using MATLAB program to overcome the problems of manual calibration and measurement. The expanded uncertainties are estimated for all ranges at different frequencies and also, the ac-dc differences. The performance of the new automated TCC is also evaluated by comparing its accuracy by measuring ac currents at different frequencies with the performance of a traditional TCC.</p>

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.

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.

Low-Frequency Characteristics of Silicon-Based High-Current Multijunction Thermal Current Converters Fabricated by Wet Chemical Etching

A single-unit thermal converter for precision ac current measurement is desirable because of its relatively small package and low power dissipation. In this article, high-current multijunction thermal converters (HC-MJTCs) on silicon (Si) substrates fabricated by wet chemical etching have been investigated at input rms currents of up to 2 A. The use of wet chemical etching aids the fabrication of a freestanding nitride–oxide membrane, maintaining the Si heat reservoir under the heater of the HC-MJTC intact. Below 10 mPa, the output voltage from the HC-MJTC and the thermal time-constant increase by approximately six times, implying improved efficiency of the thermal current converter. The absolute value of the ac–dc differences of the device was less than $17~\mu \text{A}$ /A over input current levels of up to 2 A at frequencies above 100 Hz. However, input current level-dependent ac–dc differences were observed at frequencies below 400 Hz even under vacuum. This behavior originated primarily from a change in the electrical resistance of the heater in this Si-based device. Therefore, these low-frequency ac–dc differences can be substantially compensated using the measured ac and dc electrical resistances of the heater.

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.

Low-Frequency AC–DC Differences of a Series–Parallel Circuit of Thermal Converters

A series–parallel connected thermal converter (TC) arranged in an $m \times m$ matrix of a heater and an $m^{2}$ -series connected thermocouple are proposed to reduce low-frequency ac–dc differences. The electrical circuit theory on the proposed circuit suggests that the low-frequency ac–dc differences of $m \times m$ series–parallel connected TCs decrease in proportion to 1/ $m^{2}$ , avoiding any degradation in the output voltage and a time-consuming measurement. A significant reduction of the low-frequency ac–dc differences by a factor of 10 for the proposed circuit is experimentally demonstrated with no decrease of the output voltage, which is consistent with the electrical circuit theory.

Characterization of high-precision resistive voltage divider and buffer amplifier for ac voltage metrology

A high-precision voltage buffer and a 10:1 resistive voltage divider have been constructed for use in ac voltage and electrical power metrology. Long-term stability of the buffer's dc response has been demonstrated by two dc sweeps performed 20 days apart, with best-fit linearized gain varying less than 1 μV/V. The absolute ac gain has been measured using a high-precision digital multimeter for 10 Hz and 1 kHz with results consistent with dc within 5 μV/V. This value agrees with the characterization of ac–dc difference using thermal converters from different producers with a variety of resistance for various voltages from 1 V to 5 V. The ac–dc difference was further characterized better than 40 μV/V for the same voltages up to 100 kHz and better than 100 μV/V for 3 V at 1 MHz. Absolute ac gain and ac–dc difference has also been measured for the voltage divider and buffer combination from 10 V to 50 V, with similar agreement up to 1 kHz. The ac–dc difference from 10 Hz to 100 kHz of this combination shows an agreement well within 30 μV/V in this entire voltage span with a total response not exceeding 125 μV/V. This make the voltage divider and buffer combination suitable for sampling electrical powers for a wide range of voltages.

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.

Novel Broadband Calibration Method of Current Shunts Based on VNA

Usually high wideband ac current and harmonics measurements are accurately achieved in industry and laboratories by using high accuracy shunts or standard shunts. For particular applications, such as power and transient measurements, it is mandatory to evaluate the shunt impedance phase and magnitude according to the frequency bandwidth of interest before to measure the current with such sensors. High electrical current shunt beyond 1 A is calibrated in magnitude up to 100 kHz and in phase angle up to 200 kHz only by a few National Metrology Institutes. The existing traceable measurement methods to characterize these sensors are limited in frequency to 100 kHz, with expanded uncertainties of the ac–dc difference (magnitude) and the phase angle of more than $5 \times 10^{-6}$ and $62~\mu $ rad at 100 kHz, respectively. A new traceable calibration method to measure and characterize current shunts at high frequencies is presented in this paper. This measurement method is based on the use of a vector network analyzer. The measurements are presented up to 60 MHz, but theoretically, the presented method does not exhibit a specific frequency limitation. Only the characteristics of the shunt under study can impose limitation in practice. While uncertainties are higher than those provided by the existing methods, the method presented in this paper is the only method able to perform in one step a broadband and simultaneous measurement of the magnitude and phase of current shunts up to few megahertz with acceptable uncertainties.

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.

AC–DC Disk Resistors Made of Surface Mount Components

Disk resistors are widely used in micropotentiometers up to frequencies in the radio frequency range. They offer very small AC–DC differences but the permissible power dissipation is quite small. Also, the resistance value is poorly defined due to the lack of four-terminal connections. This can be overcome by newly designed disk resistors made of surface mount device components [1]. They are also well suited as AC–DC current shunts for currents up to several amperes.

Improved Automated System for AC Voltage Calibrations Using Extending Range Resistors

Some improvements are presented in this paper to the previously introduced automated multi-range multipliers system. These multipliers; range resistors are selected automatically by using electronic relays controlled by a micro-controller that connects the suitable multiplier to the thermal voltage converter to calibrate the required ac voltage. The modifications done on the old system are mainly in used resistors and connectors. The ac–dc transfer differences for the improved and the old multipliers systems combined with the same thermal converter are determined automatically against another standard thermal voltage converter. The obtained ac–dc differences results and their repeatability; Type A for both systems are compared to evaluate the performance of the new one. The new system introduces a better performance, smaller ac–dc differences and Type A, especially in the high voltage and frequency ranges.

New generation of cage-type current shunts developed using model analysis

<p>This paper describes a new generation of cage-type ac/dc current shunts from 30 mA up to 10 A developed using a lumped circuit element model. Comparison of the calculated and measured values shows agreement better than 6 ppm in the ac-dc difference at frequencies up to 100 kHz.</p>

New internal multi-range resistors for ac voltage calibration by using TVC

Accurate calibration of ac voltages up to 1000 V by using thermal converters requires range resistors connected in series with the converter. The combination of a thermal converter and range resistor is known as the thermal voltage converter. In this paper, multi-range internal range resistors are designed and implemented in the National Institute for Standards (NIS), Egypt to cover the ac voltage ranges from 10 V to 750 V. The range resistor values are 2 kΩ, 10 kΩ, 20 kΩ, 40 kΩ, 100 kΩ, and 150 kΩ to cover the voltage ranges 10 V, 50 V, 100 V, 200 V, 500 V, and 750 V, respectively. The six range resistors are mounted in series with a single-junction thermo-element in the same box to provide a new thermal voltage converter. The required range resistor is selected by using a six-pin selector switch. Each resistor is connected to a selector pin. The new thermal voltage converter ranges are automatically calibrated against other standard thermal voltage converters at different frequencies by using a LabVIEW program to determine their ac–dc transfer difference at each range. The expanded uncertainties are estimated according to the GUM for all ranges at different frequencies. The performance of the new thermal voltage converter is also evaluated by comparing its ac–dc differences and its accuracy in measuring the ac voltage at different frequencies with a traditional thermal voltage converter.

Electrical Effect in Silver-Point Realization Due to Cell Structure and Bias Voltage Based on Resistance Measurement Using AC and DC Bridges

Electrical effects related to insulating leakage represent one of the major factors contributing to uncertainties in measurements using high-temperature standard platinum resistance thermometers (HTSPRTs), especially during the realization of the silver freezing point ( $$961.78\,^{\circ }\hbox {C}$$ ). This work is focused on the evaluation of the differences in resistance measurements observed when using AC resistance bridges and DC resistance bridges, hereafter, termed the AC–DC differences, as the result of various electrical effects. The magnitude of the AC–DC difference in several silver-point cells is demonstrated with several HTSPRTs. The effect of the cell structure on the AC–DC difference is evaluated by exchanging some components, part by part, within a silver-point cell. Then, the effect of the bias voltage applied to the heat pipe within the silver-point furnace is evaluated. Through the analysis of the experimental results and comparison with the reports in the literature, the importance of evaluating the AC–DC difference as a means to characterize the underlying electrical effects is discussed, considering that applying a negative bias condition to the furnace with respect to the high-temperature SPRT can minimize the AC–DC difference. Concluding recommendations are proposed on the components used in silver-point cells and the application of a bias voltage to the measurement circuit to minimize the effects of the electrical leakage.

Final report: EURAMET.EM-S39

The AC-DC difference of a set of current shunts produced by the Norwegian Metrology Service (Justervesenet), were measured by PTB and Justervesenet, in a bilateral comparison, where Justervesenet acted as the organizer and pilot laboratory. The nominal values of the current shunts are 30 mA, 100 mA, 300 mA, 1 A, 3 A, 5 A, 10 A and 20 A, which were measured at their nominal values for the frequencies 10 Hz, 20 Hz, 55 Hz, 110 Hz, 400 Hz, 1 kHz, 5 kHz, 10 kHz, 20 kHz, 50 kHz and 100 kHz. All current shunts were measured in combination with Planar Multi-junction Thermal Converters produced by PTB.The results show that there is a degree of equivalence within 0.4 for all measured values, and that for frequencies below 10 kHz, the value is typically below 0.2. Hence, there is a very close agreement between the measurements, which are not correlated by traceability chains, and the properties of the current shunts have been documented by the comparison. 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 CIPM Mutual Recognition Arrangement (CIPM MRA).

AC shunt calibration using a current‐bridge method and its validation

An AC shunt calibration system using a current‐bridge method is developed, and its measurement uncertainties are estimated. A comparison of the calibration results obtained using the current‐bridge method with the results using DC resistance and AC–DC difference methods was performed to verify the system. These comparison results show that the current‐bridge‐based system performs well with small measurement uncertainties for both the AC resistance and phase angle of the AC shunts up to 1 kHz. © 2014 Institute of Electrical Engineers of Japan. Published by John Wiley & Sons, Inc.

On the Current Shunts Modeling

This paper describes mathematical modeling of cage-type ac current shunts. A calculable model was developed using lumped circuit elements. The transimpedance, ac–dc difference, and the phase angle error of a shunt can be derived from the model. An uncertainty analysis of the model was done by means of Monte Carlo methods. Comparison of the calculated and measured values shows an agreement better than 6 $\mu\Omega/\Omega$ in the ac–dc difference and 110 $\mu{\rm rad}$ in the phase angle error at frequencies up to 100 kHz.

Improved Stability of Thin‐Film Multijunction Thermal Converters

SUMMARYWe have demonstrated the long‐term stability and environmental durability of a high‐performance thin‐film multijunction thermal converter (TMJTC) with an improved thin‐film thermopile design. We fabricated a new TMJTC with an improved deposition pattern for a Bi‐Sb‐Cu‐based thin‐film thermopile in order to avoid interface delamination between the Bi and the Cu layers. Our TMJTC exhibited good frequency properties, with an ac–dc difference of less than 5 μV/V in the range from 10 Hz to 100 kHz, at a root‐mean‐square (rms) voltage of 10 V. The long‐term stability of the TMJTC has been significantly increased owing to the performance of the developed thin‐film thermopile, as compared with that of previously fabricated TMJTCs, exhibiting an ac–dc difference of less than 2 μV/V after 18 months at room temperature. We also evaluated the temperature, relative humidity, and pressure characteristics of the TMJTC in accordance with the International Electrotechnical Commission (IEC) standards for electronic devices. The measurement results showed that the dependence of the ac–dc transfer difference on the temperature, humidity, and pressure was less than 1 μV/V, which is comparable to the results of thermal converters, constituting the primary standard.