Extension of the NIST AC-DC Difference Calibration Service for Current to 100 kHz

The NIST calibration service for ac-dc difference of thermal current converters relies on multijunction thermal converters as the primary standards, and various thermal converters and thermoelements (TEs) as the reference and working standards. Calibrations are performed by comparing the ac-dc difference of a customer’s thermal current converter to the ac-dc difference of a NIST standard current converter. Typical artifacts accepted for calibration include single-junction thermoelements, multijunction thermal converters, and transfer shunts for use with TEs. This paper describes the standards on which the calibration service is based and the results of the study to characterize the NIST standards over the extended frequency range from 50 kHz to 100 kHz at currents from 1 mA to 20 A. The general method for the frequency extension at high frequency involves the use of thermoelements in the 5 mA range, with small frequency dependence, as the starting point for build-up and build-down chains to cover the whole range from 1 mA to 20 A.     

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     

An Automatic System for AC/DC Calibration

An automatic ac/dc difference calibration system using direct measurement of thermoelement EMFs is described. The system operates over a frequency range from 20 Hz to 100 kHz, covering the voltage range from 0.5 V to 1 kV. For all voltages, the total uncertainty (including the uncertainty of the specific reference thermal converters used) is 50 ppm at frequencies from 20 Hz to 20 kHz, inclusive, and 100 ppm at higher frequencies up to 100 kHz. In addition to ac/dc difference testing, the system can be used to measure some important characteristics of thermoelements, as well as to calibrate ac voltage calibrators and precision voltmeters. Results of intercomparisons between the new system and the manual NBS calibration system, using single-range, coaxial-type, thermal voltage converters as transfer standards, are reported. The results indicate that the ac/dc differences measured are accurate to well within the combined total uncertainty limits of the two systems.     

Development and Implementation of Current Tee for AC High Current Calibration

Thermal current converters or thermal transfer standard with AC–DC current shunts act as the reference standards for accurate and precise measurements of low frequency current in the frequency range from 40 Hz to 10 kHz. At present CSIR-NPL, India has the AC–DC current transfer difference (δ _x) calibration facility upto 20 A. To extend our AC current calibration range from 20 A to 100 A, a current Tee for AC high current using LC connectors has been indigenously designed and developed. This paper presents the development of current Tee for AC high current calibration. The calibration results for assigning ‘δ _x’ at 30 A current shunt with respect to 20 A are shown and the same measurement technique has been used to extend the current range up to 100 A.     

A 100 A, 100 kHz transconductance amplifier

A high-current, wide-band transconductance amplifier is described that provides an unprecedented level of output current at high frequencies with exceptional stability. It is capable of converting a signal voltage applied to its input into a ground-referenced output rms current up to 100 A over a frequency range from DC to 100 kHz with a useable frequency extending to 1 MHz. The amplifier has a 1000-W output capability ±10 V of compliance, and can deliver up to 400 A of pulsed peak-to-peak current. The amplifier design is based on the principle of paralleling a number of precision bipolar voltage-to-current converters. The design incorporates a unique ranging system controlled by opto-isolated switches, which permit a full-scale range from 5 A to 100 A. The design considerations for maintaining wide bandwidth, high output impedance, and unconditional stability for all loads are discussed     

Integrated Calibration System for Accurate AC Current Measurements up to 100?kHz

This paper describes the establishment of an integrated calibration system for accurate AC current measurements at National Institute of Standards, Egypt. The measurement system consists of a new assembled thermal current converter (TCC) associated with an appropriate hardware and automation software. The system has been used for a wide range of AC current from 5?mA to 20?A at frequencies from 10?Hz to 100?kHz. The assembled TCC at rated current of 5A was modified and recalibrated in PTB, Germany to enhance the system reliability. The estimated uncertainty budget of this system is presented in this paper.     

Thermally regulated low-noise, wideband, I/V converter, usingPeltier heat pumps

An ultra-low-noise current-to-voltage converter capable of detecting currents of 1 pA or less in a bandwidth from dc to 20 kHz is described. This instrument exhibits the dc performances typical of a picoammeter together with the low noise level and the wide bandwidth of a modern current-to-voltage converter. Thanks to an excellent dc stability over time, continuous monitoring of phenomena involving currents in the picoampere range can be carried out, for hours or even days. Moreover, ultra-low-noise ac measurements of these currents in the kilohertz range can be performed. A new nonheating thermal controller, using the concept of letting the instrument operate 30°C below room temperature, has been designed and built. Two small Peltier heat pumps have been employed to cool the critical parts of the system, thus achieving a long-term stability of a few hundredths of degrees centigrade. With minor modifications in the input stage of this instrument, a high-transimpedance, ultra-low noise prototype has been built, which shows an input equivalent current noise as low as 4 fa/√(Hz) at 100 mHz     

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)     

Universal digital measuring system

A universal measuring instrument is proposed for investigating the quasi-dc and dynamic current-voltage characteristics of two-terminal networks and the transient amplitude-frequency and phase-frequency characteristics of various types of electronic equipment. Signals can be measured in the voltage range 10 mV to 100 V and the current range 1 mA to 1 A. Signals are generated with voltage amplitudes in the range 10 mV to 10 V and current amplitudes in the range 1 mA to 2 A. The sampling frequency range of input and output signals is 1 kHz to 20 MHz in steps of 1 kHz. The errors in measuring instantaneous values of voltage and current are respectively 2.5% and 3% in the frequency range 0–5 MHz. Translated from Izmeritel'naya Tekhnika, No. 6, pp. 52–54, June, 1998.     

Intercomparison of reflectances observed by GOME and SCIAMACHY in the visible wavelength range

We compare the Earth reflectances of the spectrometers Global Ozone Monitoring Experiment (GOME) and Scanning Imaging Absorption Spectrometer for Atmospheric Chartography (SCIAMACHY) over their overlapping wavelength range (240-800 nm). The goal is to investigate the quality of the radiometric calibration of SCIAMACHY using calibrated GOME data as a reference. However, severe degradation of the GOME instrument in the UV since 2001 prevents it from being a reliable reference below 500 nm. Above 500 nm, GOME is reliable and we find substantial disagreement between GOME and SCIAMACHY, of the order of 15%-20%, which we can attribute completely to the current calibration problems of SCIAMACHY. These numbers are supported by a previous study in which SCIAMACHY was compared with the imager Medium Resolution Imaging Spectrometer (MERIS) onboard the Envisat satellite.     

Precision Measuring Equipment for Electrical Power in the Range of Audio Frequencies

The design and construction of an electrodynamic wattmeter for precise measurement in the range of direct current to 20 kHz is discussed. The method of operation, construction, and compensation for effects and errors is described. Calculations, test results, and several test methods are described and show that the instrument is capable of high accuracy and resolution in the power and audio frequency range.     

Measurement of Phase Angle Errors of Precision Current Shunts in the Frequency Range From 40 Hz to 200 kHz

This paper describes the measurement techniques and results of the determination of phase angle errors of a set of National Measurement Institute, Australia, precision current shunts, rated from 100 mA to 20 A, in the frequency range from 40 Hz to 200 kHz. The standard uncertainties of the determination range from 1.3 murad at low frequencies to less than 150 murad at 200 kHz     

Measurement and control of current/voltage waveforms of microwavetransistors using a harmonic load-pull system for the optimum design ofhigh efficiency power amplifiers

One of the most important requirements that RF and microwave power amplifiers designed for radiocommunication systems must meet is an optimum power added efficiency (PAE) or an optimal combination of PAE and linearity. A harmonic active load-pull system which allows the control of the first three harmonic frequencies of the signal coming out of the transistor under test is a very useful tool to aid in designing optimized power amplifiers. In this paper, we present an active load-pull system coupled to a vectorial “nonlinear network” analyzer. For the first time, optimized current/voltage waveforms for maximum PAE of microwave field effect transistors (FET's) have been measured. They confirm the theory on high efficiency microwave power amplifiers. The proposed load-pull setup is based on the use of three separated active loops to synthesize load impedances at harmonics. The measurement of absolute complex power waves is performed with a broadband data acquisition unit. A specific phase calibration of the set-up allows the determination of the phase relationships between harmonic components. Therefore, voltage and current waveforms can be extracted. The measurement results of a 600 gate periphery GaAs FET (Thomson Foundry) exhibiting a PAE of 84% at 1.8 GHz are given. Such results were obtained by optimizing the load impedances at the first three harmonic components of the signal coming out of the transistor. Optimum conditions correspond to a class F operation mode of the FET (i.e., square wave output voltage and pulse shaped output current). A comparison between measured and simulated current/voltage waveforms is also presented     

A Direct-Reading Current-Comparator Bridge for Scaling Four-Terminal Impedances at Audio Frequencies

A direct-reading current-comparator bridge circuit, for scaling four-terminal impedances which do not deviate from nominal by more than a few thousand parts per million, is described. The scaling is performed at constant voltage and the impedances are treated as true four-terminal devices in that, at balance, no current is drawn from the potential terminals. The principal feature of the circuit is the use of a compensation winding to excite the magnetic shield of the current comparator and thus suppress the effect of lead unbalances. Possible applications of the bridge include the scaling of four-terminal resistance standards between 1 milliohm and 100 ohms at frequencies ranging from 50 Hz to 1600 Hz. Construction details and calibration of a current comparator for use in a 10-to-1 ratio bridge are 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.     

Progress in the United States on Electromagnetic Standards and Measurements at 30 kHz to 1 GHz, 1963 through 1965

A digest of highlights is presented on the most significant U. S. contributions to the measurement of attenuation, impedance, phase, field strength, thermal noise, current, and voltage at 30 kHz to 1 GHz. A total of approximately 30 contributions are digested. The following accomplishments are among them: a supersensitive detector for a complex-insertion-ratio measurement system having accuracies of about 0.0005 dB/10 dB at 30 MHz; exact equations for mutual and self-inductance of various combinations of filaments, tapes, and bars; a modified Twin-T-Bridge for measuring resistances of 100 to 10 000 ohms to 15 MHz; a set of Q-factor standards for frequencies to 45 MHz based on data and experience accumulated over five years; a unique adjustable characteristic-impedance coaxial line; measurement of Q's greater than 100 000 of cryogenic circuits at frequencies to 300 MHz; a novel Tee-junction to enable calibrations of voltmeters of any practicable input impedances with VSWR's ranging from 1 to 200, to 1 GHz and higher; a miniaturized dipole-antenna field strength meter, employing a semiconducting plastic transmission line, to measure complex nearzone fields of 0.1 to 1000 volts per meter, from 150 kHz to 30 MHz; and a prototype 3-MHz model of precision thermal noise-power comparators for an equivalent noise-temperature range of 75 to 30 000°K at accuracies of 0.2 to 1 percent.     

A linearization method for commercial Hall-effect currenttransducers

The need for high-current transducers featuring wide-band and high-insulation levels is becoming a more and more impelling need in the electric power network, as the current distortion increases due to the proliferation of nonlinear, time-variant loads. The closed-loop Hall-effect current transducers show a good compromise between cost and metrological performance. On the other hand, they may introduce an unacceptable nonlinearity error when the dynamic range of the input current is a reduced portion of the dynamic range of the transducer and may show a large drift of their gain with temperature. The paper proposes a simple method for reduction of the nonlinearity error when the input signal is an unbiased sinewave and the automatic calibration of the gain. Experimental results are also reported, showing the method effectiveness     

Design and identification of an equivalent circuit for an LCT component: inventory and representation of losses

A new kind of passive component, the LCT [integrated inductor (L), capacitor (C), and transformer (T)] is becoming very fashionable in the switch mode power supply area. Starting from our knowledge in transformer characterization, we recently elaborated an equivalent circuit for this component. This equivalent circuit is fully deducible from impedance measurements. No dismounting of the component is needed, and no information about its internal design is required. This paper aims mainly to present the new equivalent circuit and the method leading to its identification using a commercial impedance analyzer. The LCT intended to a 300-W power supply working at 200 kHz has been built and characterized between 100 Hz and 40 MHz. Analyzing the frequency dependence of the real part of serial and parallel impedances, several kind of losses rarely taken into account have been identified. Among these losses are those related to the capacitor insulator and those due to the dielectric constant of Mn-Zn ferrite core. Equivalent circuits are supplied to represent every type of loss, and their accuracy is checked.     

Measurement of the internal impedance of traction rails at 50 Hz

The electrical behavior of sample steel traction rails is analyzed considering the resistance and the external and internal inductance. Measurements are performed on two rail arrangements at different current levels (up to nearly 2 kA) at 50 Hz and over an extended frequency range (50 Hz to 100 kHz) at low currents, so that skin effect and saturation phenomena are clearly visible. Great accordance with the results obtained using Carson's formulas is found