A System for Accurate Direct and Alternating Voltage Measurements

A system for calibrating and using a group of dc and ac standards has been developed at NBS to meet increasing needs for greater accuracy in the measurement of direct and rms alternating voltages at audio frequencies. With a group of saturated cells, a universal ratio set as a potentiometer, a simplified self-calibrating volt box, and a new differential-thermocouple ac-dc comparator, an accuracy of 10 ppm can be obtained for direct voltage measurements and 40 ppm for rms alternating voltage measurements between 20 and 20 000 c/s, in terms of the direct volt and the ac-dc transfer standards maintained at NBS.     

High-Precision Digital Volt Ratiometer by a Method of Measuring Difference of Magnetic Field among Three Windings

The purpose of this work is to establish a highly accurate automatic ratio measuring instrument for dc voltage and resistance. In voltage and resistance ratio measurements, accuracy of 0.1 ppm has now become necessary due to recent developments in quantum metrology. To obtain the accuracy, we have just developed a technique to automatically compensate the measuring error caused by the deviation of electrical components, such as resistances used in the instrument. The instrument described incorporates this technique. With internal reference voltage and resistance, it can be a precision voltohmmeter and also, it can be standardized to an external standard with an accuracy of 0.1 ppm.     

An RMS Digital Voltmeter/Calibrator for Very-Low Frequencies

A portable rms digital voltmeter (DVM) has been developed at NBS to support vibration measurements over the ranges of 0.1 to 50 Hz and 2 mV to 10V. A self-contained calibrator provides for self-calibration and may be used for calibrating other VLF voltmeters. The calibrator basically consists of a Kelvin-Varley divider fed by a reference voltage (either dc or sinewave generated by a ROM-DAC combination) A multijunction thermal converter (MJTC) was selected as the sensing device in the rms/dc converter of the DVM since its low ac/dc difference facilitates calibration of the ac calibrator. Factors affecting accuracy and response time are analyzed. The DVM response time is 40 s for the lowest input frequency. Its accuracy (percent of reading) is 0.1 percent above 0.5 Hz and 5 mV and 0.2 percent below these values. The ac calibrator accuracy is 0.02 percent. Measurement accuracy improves by a factor of about 4 for transfer measurements (comparing input voltages with ac calibrator voltages) Means for extending this accuracy to 0.01 percent are discussed.     

Digital measurement of amplitude-modulated signal parameters by scanning with a calibrated dc voltage

Different methods of measurement of amplitude-modulated signal parameters are proposed and analyzed. The methods are based on scanning the instantaneous signal values with the aid of program-controlled dc voltage levels varying in uniform and nonuniform steps. Block diagrams of modulation meters and their estimated accuracy of amplitude-modulation factor measurements are given. Translated from Izmeritel’naya Tekhnika, No. 8, pp. 58–63, August, 1996.     

The Calibration of DC Resistance Standards by an AC Method

Techniques recently developed at the National Physical Laboratory (NPL) have enabled the zero-frequency (or dc) value of 4-terminal Laboratory Standard Resistors readily to be determined to an accuracy of two parts in 107 from a few measurements made in the frequency band 40 c/s to 600 c/s. A Kelvin double-bridge network is used, the ratio arms consisting of inductively-coupled voltage dividers with an accuracy and discrimination of one part in 107 over the whole frequency range. Experimental results and constructional details of the inductive dividers are given together with the theoretical considerations underlying the principle of the method.     

Thermal Instrument for Measurement of Voltage, Current, Power, and Energy at Power Frequencies

The design of an instrument for precision measurement of ac voltage, current, power, and energy is described. It has been developed as a standard for evaluating the performance of instrumentation used in the power frequency range (45-65 Hz). Its accuracy relies on a continuous ac/dc transfer which is achieved by automatically balancing the alternating current derived from the quantity to be measured against the equivalent direct current, both passing alternately through the heater of a thermal converter. Since the instrument can be calibrated with direct voltage and current, its total systematic error is limited by the ac/dc transfer to ±0.0005 percent of full scale for voltage and current, and ±0.001 percent of full scale for power and energy measurements.     

Precision RF Voltage Standard Using a Thermistor Bridge Covering the HF-UHF Range

This paper describes a thermistor mount designed so that residual inductances of leads in the thermistor are eliminated for use in the UHF range. The output voltage of the thermistor bridge is evaluated by the dc substitution method with an accuracy of 0.3 percent for 0.3-1 V over frequencies up to 1.5 GHz. The output voltage agrees with the voltage derived from power and impedance standards within the accuracy.     

Wideband wattmeter based on RMS voltage measurements

A wideband wattmeter for measuring active power over a frequency range of dc to 500 kHz is described. The wattmeter is based on the three-voltmeter method in which three rms voltage measurements are used to calculate power. The wattmeter active power uncertainty is estimated to be within 0.03% from dc to 20 kHz and within 1.5% to 500 kHz     

Analytical Solutions of the Frequency Shifts of Several Modes in Dynamic Force Microscopy Subjected to AC Electrostatic Force

Kelvin probe force microscopy is currently used to measure contact potential difference and topography of sample on a nanometer scale, based on the behaviors of the first two resonant frequencies. In this study, an analytical method to determine the frequency shifts of several modes in dynamic force microscopy subjected to AC electrostatic force is proposed. The numerical results determined by the proposed method are close to the experimental ones. If the amplitude and the frequency of the AC voltage are suitable, a large frequency shift and a linear relation between the frequency shift and the tip-sample distance will be obtained. In other words, properly controlling the AC voltage will increase the accuracy of measuring the sample's topography. Moreover, it is found that even without an optimized compensation dc voltage, increasing the first frequency shift and decreasing the tip radius and the half open angle of the tip can increase the accuracy of measuring a step height. Finally, it is found that when the oscillation amplitude and the tip-sample distance are constant, increasing the negative dc voltage will increase the accuracy of the measurement of contact potential by using the frequency shift. In addition, an assessment of the conventional perturbation method is presented and the two methods are compared.     

Measurement uncertainties arising from unpowered shipment of dcvoltage references

We have measured the hysteresis in output voltage arising from loss of power for three Fluke 732B dc voltage references. Continuously powering the internal temperature-controlled oven provides the best accuracy with such Zener-diode-based dc voltage references. Batteries are used to provide power continuity when shipping between laboratories. We have shown that for these particular instruments, an apparent hysteresis induced by humidity is likely to dominate any hysteresis arising from loss of battery power when transit between laboratories takes three days or more. Our conclusion is that as much, if not more, care needs to be taken when dealing with humidity than with loss of battery power when shipping between laboratories. When the highest accuracy of dc voltage comparison is required, it becomes necessary to apply voltage corrections using the measured values of humidity coefficients and the relative humidity occurring during transit     

Cryogenic Voltage Comparator System for 2e/h Measurements

The design and operation of a cryogenic voltage comparator system for precision 2e/h measurements is described. Major improvements embodied in the new 2e/h system include the use of 1) a single microstripline-coupled Josephson tunnel junction to obtain usable step voltages up to 10 mV at 10.0 GHz, 2) a cryogenic voltage divider comprised of two resistors whose ratio is calibrated with a low-temperature dc current comparator, 3) a superconducting quantum interference device (SQUID) null detector, and 4) superconducting switching. The accuracy of the present 196:1 divider system is estimated to be about 2 parts in 108 on the basis of preliminary tests and is limited by resistor self-heating during calibration.     

An electrostatic voltage comparator

The principles of the construction of an electrostatic dc and ac voltage comparator using a systems approach for increasing its accuracy are considered.     

Longitudinal combined discharge extinction in low pressure nitrogen

This paper reports the registered extinction curves of the longitudinal combined discharge in nitrogen when rf and dc voltages were applied to the same electrodes. The application of dc voltage is shown first to lead to an increase in the rf discharge extinction voltage; at the same time, the “cathode” sheath thickness increases and the number of charged particles in the plasma volume decreases. The discharge extinction curve first shifts to the range of higher rf voltage and gas pressure values, and the region of multi-valued dependence of the rf extinction voltage on gas pressure vanishes. At larger dc voltage values, when the “cathode” sheath breakdown occurs, the rf discharge extinction voltage decreases and approaches zero at the dc extinction voltage for the dc self-sustained discharge.     

The present state and future prospects for developing the standard base of Russia for measurements of dc voltage

The problems involved in developing the standard base of Russia in the area of measurements of dc voltage in the range up to 1000 V are considered. __________ Translated from Izmeritel’naya Tekhnika, No. 11, pp. 42–44, November, 2007.     

Automated Digital Measurements of CV Curves and Derivatives, and of Capacitance Transients for Semiconductor Evaluation

A system of instruments is presented for automated digital measurements of voltage and/or time dependent capacitances. The system has been designed for the evaluation of semiconductor materials and devices. It is based on a fast capacitance-inverse-to-frequency converter (FCFC), where a direct conversion is obtained with high accuracy, and where the device to be tested can be subject to dc, modulated, and pulsed voltage bias. The output frequency (of the order of 1 MHz) accurately foliows capacitance variations, even if occurring in short times (less than 100 Ms). Biasing circuits, a multichannel scaler, and logic interface circuits complete the system. Stationary and nonstationary CV curves and time variations of capacitances can be accuratety measured. The precision can be improved by averagng over many repetitions of the measurement. Derivatives (first and higher orders) of CV curves can also be directly and accurately measured by using a technique based on voltage modulation and synchronous reversible counting. This feature also makes it possible to obtain accurate measurements of doping profiles in semiconductors. Representative experimental results obtained with the system are shown.     

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     

A Method of Converting an Alternating Voltage into a Direct Voltage by Stabilizing an Alternating Current and Comparing it with a Direct Current

A method of converting an ac voltage into a dc voltage using two electrothermal converters, whose currents are maintained the same and unchanged during operation, is proposed. One possible version of the ac/dc converter is considered.     

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.      

Improving the emf and dc voltage measuring system (discussion paper)

The concept of a new system of emf and dc voltage measurements is and methods of its implementation capable to satisfy the predicted demands of the Russian economy for 2003–2010 are proposed as a matter of discussion. Translated from Izmeritel'naya Tekhnika, No. 10, pp. 34–37, October, 1998.     

The use of a quadrupole electrostatic trap to transfer the dimensions of the volt in the 10 V–10 kV range

The problems involved in using a quadrupole trap for charged particles in order to increase the accuracy of the measurement of dc voltage in the 10 V–10 kV range are considered. __________ Translated from Izmeritel’naya Tekhnika, No. 10, pp. 49–51, October, 2007.