A device for audio-frequency power measurement

A device for the measurement of audio-frequency power, voltage and current is discussed. The full range of power factors are accommodated (cos φ=0 to 1). Voltage and current measuring ranges are 15-600 V and 0.1-10 A, respectively. When cos φ=1, the permissible error of the power measurement is from 50 to 150 p.p.m. over the frequency range of 40 Hz to 10 kHz (including the line power frequency)     

Measurements of wattless power and the power factor with a nonsinusoidal current and voltage

Conclusions The above method can be used both for a direct measurement of wattless power and the power factor in single phase commercial and audio-frequency circuits (Fig. 1) and for checking and calibrating (Fig. 2) single phase VAR meters and phasemeters, including those designed for sinusoidal variables.The differential wattmeter is being used successfully in compensation method calibration and checking of three-phase phasemeters with two voltage coils [5 and 6] and phasemeters with two current coils.     

High-Precision Thermal EMF Comparator for Automatic AC-DC Transfer Measurements

A high-sensitivity EMF comparator, suitable for automatic comparison of standard voltage or current thermal converters is described. One of the two compared EMF's and their difference are simultaneously balanced to null with two potentiometric voltages produced on low-value resistors by controlled currents. Any direct switching or resistance adjustment in the circuit involving the EMF's is avoided. Also the sensitivity control of the two light-beam-coupled nanovolt preamplifiers, utilized as null detectors, is performed only by feedback on the potentiometric voltages. Tracking between these voltages and one of the EMF's reduces the balance instability due to random source variations and drifts. Additional amplitude stabilization is obtained directly on the ac and dc sources by deriving a feedback signal from the comparator. A first implementation of the system allows to obtain balances below the nanovolt level and exhibits a proportional standard deviation of 5 × 10-8 in a series of ten successive intercomparison measures of two thermal voltage converters with output EMF's in the 10-mV range.     

The Application of the Direct Current Comparator to a Seven-Decade Potentiometer

The design and construction of a self-balancing direct current comparator for use in a seven-decade potentiometer is described. The comparator generates an output current whose value, as a proportion of a constant input current, is determined to a very high accuracy by the ratio of the numbers of turns of two windings on a magnetic core. A linear, adjustable voltage scale is obtained by passing this output current through a resistor whose value does not vary with current. Since the voltage adjustment is made by varying turns on a magnetic core and not by means of a resistive divider, the usual problems of contact resistance and thermal electromotive forces associated with this adjustment in conventional potentiometers are avoided. The main sources of error in the comparator and the design techniques used to keep the errors less than the smallest step of the output current are discussed. A self-checking feature whereby the linearity of each step of the output current can be checked quickly and easily is described. The performance of the prototype model is given. The normal range of the potentiometer is from zero to 2 volts in steps of 0.1?V.     

AC/DC Thermal Converters of the ETL

In order to establish alternating current and voltage standards, various types of thermal current and voltage converters have been constructed. From their detailed analysis, the specifications and characteristics have been determined. These converters have been used in a circular international comparison. A precise comparator of 0.1-ppm resolution has been also constructed. The estimated accuracy of current converters is better than 10 ppm up to 100 kHz and that of voltage converters is better than 25 ppm up to 50 kHz and 30 ppm at 100 kHz.     

An intercomparison of AC voltage using a digitally synthesizedsource

An AC voltage intercomparison was conducted by the National Institute of Standards and Technology (NIST) to determine the consistency of AC voltage measurements made at various standards laboratories. The transport standard used for this purpose was an NIST-developed, digitally synthesized sinusoidal voltage source whose RMS (root mean square) value was calculated by measuring the DC level of each of the steps used to synthesize the sine wave. The uncertainty of the calculated voltage at approximately 7 V RMS is typically within ±10 parts per million (p.p.m.) from 15 Hz to 7.8 kHz. This approach incorporates a technique of determining AC voltage with reference to a measured standard DC voltage, which is independent of the traditional thermal voltage converter approach. Preliminary measurements made at each of the participating laboratories agree with the calculated value to within ±20 p.p.m. These results indicate that at 7 V, in the low audio-frequency range, the AC voltage measurement techniques implemented at these laboratories are near the state of the art     

Capacitive Error in Current Comparators

The equations for the capacitive error of various constructions of audio-frequency current comparators are derived and discussed. The experimental procedure for trimming a comparator using an excitation winding is presented. The interrelationship between sensitivity and accuracy is indicated. An approximate diagram showing the size and error as a function of rated current for a matched sensitivity-error design is given.     

An Automatic RMS/DC Comparator

The design of an instrument for the automatic comparison of an ac voltage with a stable dc source is described. A differential multijunction thermal converter is used as an rms/dc converter with an FET-switched input amplifier for ac/dc substitution. The output voltages of the rms/dc converter with ac and dc input voltages are sampled and stored, and the difference amplified and displayed on a panel meter or chart recorder. Accuracy is ±20 ppm of input ranges of 10-200 V at frequencies of 50 Hz-1 kHz, and maximum full scale deflection sensitivity is 0.01 percent of input range. The instrument may be used either as an rms comparator with a linear voltage scale or as a mean-square comparator with a linear power scale.     

The Precise Measurement of Current Ratios

The development of the current comparator, a three-winding current ratio transformer, is reviewed and its characteristics as an alternating current ratio standard are analyzed. Particular attention is given to the use of magnetic shielding and its effect on the accuracy and usefulness of the device. Some error characteristics of three types of audio-frequency current comparators are given and possible applications discussed. These include the calibration of current transformers and impedance comparisons. The adaptation of this device to dc operation is made possible by modulation techniques. A 20 000-ampere self-balancing direct current comparator, designed specifically for the calibration in situ of transductors or direct current transformers, is described. The application of this comparator to the calibration of shunts at high currents also is discussed and some results presented.     

A Two-Dimension Time-Domain Comparator for Low Power SAR ADCs

This paper presents a two-dimension time-domain comparator suitable for low power successive-approximation register (SAR) analog-to-digital converters (ADCs). The proposed two-dimension time-domain comparator consists of a ring oscillator collapsebased comparator and a counter. The propagation delay of a voltage controlled ring oscillator depends on the input. Thus, the comparator can automatically change the comparison time according to its input difference, which can adjust the power consumption of the comparator dynamically without any control logic. And a counter is utilized to count the cycle needed to finish a comparison when the input difference is small. Thus, the proposed comparator can not only provide the polarity of the input, but also the amount information of the input, which helps to skip most of the SAR cycles when the initial input is small. Thus, most energy can be saved when the initial input is small. The proposed timedomain comparator is designed in 0.18 μm CMOS technology. Simulation results demonstrate that the comparator can not only save power consumption, but also give the design flexibility, and the current is only nA level when the supply voltage is 0.6 V.     

A Method for Compensation of Thermal Drift of Ferromagnetic Current Comparator

The current comparator using a ferromagnetic core has several merits especially for application to current A-D converters. Because the comparator utilizes the coercive force of the core to give the threshold value to the performance, drift errors cannot be neglected if the ambient temperature changes. An electronic compensation method for drift and experimental results are described. The temperature drift in the performance of the comparator is decreased from 120 mA to 1 mA over the temperature range of 10°C to 55°C. The thermal drift of the compensated comparator is less than that of the comparator at constant temperature. Using the compensation method, accuracy of the current A-D converter with the comparator is maintained to an order of 0.1 percent of the maximum value of the input over wide temperature range.     

A Time-Domain Sub-Micro Watt Temperature Sensor With Digital Set-Point Programming

To realize the on-chip temperature monitoring of VLSI circuits, an accurate time-domain low-power CMOS thermostat based on delay lines is proposed. Contrary to the voltage-domain predecessors, the proposed circuit can benefit from the performance enhancement due to the scaling down of fabrication processes. By replacing R-string voltage division and voltage comparator with delay line time division and time comparator, only little static power is consumed. The power consumption and chip size can be reduced substantially. Without any bipolar transistor, the temperature sensor composed of a delay line is utilized to generate the delay time proportional to the measured temperature. Instead of a conventional voltage/current DAC or an external resistor, a succeeding multiplexer (MUX) along with a reference delay line is used to program the set-point. The test chips with mixed-mode design were fabricated in a TSMC CMOS 0.35-mum 2P4M digital process. The chip area is merely 0.4 mm². The effective resolution is around 0.5degC with a 256-to-1 multiplexer and -40degC ~ 80degC nominal temperature range. The achieved measurement error is within plusmn0.8degC for a total of 20 packaged chips over the temperature operation range of commercial ICs. The power consumption is 0.45 muW per conversion and a measurement rate as high as 1 MHz is feasible when necessary.     

A Technique for Calibrating Power Frequency Wattmeters at Very Low Power Factors

The application of a current comparator capacitance bridge to the measurement of the error of power frequency wattmeters at zero and very low power factors is described. The desired voltage, current, and power factor, leading or lagging, are established with a capacitive-type artificial load. The power factor is adjusted with reference to a loss-free gas-dielectric capacitor to within 1 × 10-5 or to an accuracy of 1 percent, whichever is greater, and voltage and current to an accuracy of better than 1 percent. Results of the measurements on representative commercially available electrodynamic and electronic wattmeters are given.     

An accurate RMS-DC voltage comparator

An accurate RMS-DC voltage comparator based on an inexpensive solid-state dual-heater-type converter has been developed. The instrument is designed to operate as a null meter with a range of ±1000 p.p.m. of nominal test voltages used in high-accuracy AC calibrations. Test results show that the comparator can determine the RMS value of AC voltages for its 5- and 7-V inputs with an accuracy of better than ±50 p.p.m. for frequencies of 50 Hz to 200 kHz. Voltage inputs of 100 and 120 V can be measured with an accuracy of better than ±30 p.p.m. for frequencies of 50 Hz to 100 kHz     

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.      

The Application of Current Comparators to the Calibration of Current Transformers at Ratios up to 36000/5 Amperes

The design and construction of a multiratio, 36 000-ampex e compensated current comparator and the technique by which it may be cascaded with a second multiratio comparator to calibrate, with a single balance, power frequency current transformers at ratios up to 7200/1 are described. The first comparator has a distributed, single-turn primary winding and a sectionalized 1200-turn secondary winding that may be series-paralleled to obtain eight ratios from 120/1 to 1200/1. A 300-kVA 1100-volt transformer is included in the single primary turn to provide the power required for the calibrations. In size the device is 40 inches in diameter and 20 inches in height, and its weight is 2700 lb. The two comparators are cascaded at nominal currents up to 30 amperes by connecting the secondary winding of the first comparator to the primary winding of the second and by making corresponding interconnections between the two compensation windings. At balance, the actual current ratio of the standard composed of the two comparators in cascade, or the first comparator alone, differs from the corresponding turns ratio by no more than a part per million (ppm).     

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.     

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. Key words: alternating current standard, single junction thermal converters, heat conduction     

Torque ripple reduction in direct torque controlled five-phase induction motor using modified five-level torque comparator

The five-phase induction motor inherently has the minimal torque ripple. However, when it is controlled by direct torque control (DTC) technique, the torque ripple increases due to the presence of a hysteresis torque comparator. The classical five-level torque comparator is presented in the previous literatures to control the torque ripple. However, this comparator has the drawback of wrong selection of zero voltage vectors inside the inner band on the positive side of the comparator, which enables the torque ripple to increase and dc-link utilization to decrease. In this paper, in order to reduce the torque ripple and to increase the dc-link utilization, a modified five-level torque comparator is proposed, which selects either medium or small voltage vectors instead of zero voltage vectors inside the inner band on the positive side of the comparator. In addition to torque ripple reduction and improvement in dc-link utilization, the proposed comparator significantly improves the quality of phase current. All the available 32 voltage vectors are selected through the proposed five-level torque comparator based on the location of x–y stator flux in order to eliminate the x–y stator flux so as to obtain reduced distortion in the phase current. By employing all the available voltage vectors, the freedom of utilization of all voltage vectors in the five-phase induction motor DTC drive is availed. The proposed five-level torque comparator is compared to its classical five-level counterpart through simulation and experimental results in order to validate the proposed DTC strategy.