An Analog Circuit for Accurate OCVD Measurements

An electronic circuit for making accurate open-circuit voltage decay measurements is presented. The circuit overcomes the main limitations that occur in the standard method when used for carrier lifetime characterization because it realizes the ldquoopen-circuit conditionsrdquo of the device under test with an impedance higher than 100 MOmega and reduces the noise that is inherent in the differential operation of the method.     

Optical Fiber Dual-Reflectometer for Accurate Measurements

In order to measure the reflection coefficients of opt fiber components as accurately as possible, a new "dual-reflectometer" method is proposed. This method is capable of eliminating the major systematic errors in incoherent continuous-wave reflectometers. Experiments have been made using a measurement system with a light-emitting diode (LED) and graded-index multimode fibers. Experimental results show the effectiveness of the method.     

NIST Sampling System for Accurate AC Waveform Parameter Measurements

This paper summarizes efforts at the National Institute of Standards and Technology (NIST) to develop a waveform sampling and digitizing system with accuracy comparable to that of an ac-dc thermal transfer standard for ac voltage measurements over the frequency range of 10 Hz to 1 MHz. In the frequency range from 1 kHz to 1 MHz, the sampler's gain flatness is better than that available from the best commercial digital multimeter. In ac-ac comparisons referenced to 1 kHz, the system agrees with a NIST-calibrated thermal transfer standard to within 17 muV/V from 20 Hz to 100 kHz for measurements made at both 1 and 0.1 V. The sampler's excellent dynamic linearity and flat input impedance are also discussed     

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.     

Millimeter-Scale Piezoresistive Cantilevers for Accurate Force Measurements at the Nano-Newton Level

This paper reports a development of millimeter-scale cantilevers equipped with piezoresistive deflection sensing metrology as a force sensor at the micro- and nano-Newton level. The cantilevers was designed and fabricated to minimize the error during the force transfer or calibration, so that they have full-bridge type piezoresistors, a large length and width and reference marks to facilitate the positioning of probes or tips onto the piezoresistive cantilevers. Their 6 mm-long and 0.4 mm-wide dimensions can reduce the error due to incomplete contact (or loading) position. The reference marks on the cantilever can give you a range of stiffness and force sensitivity with a single piezoresistive cantilever. The stiffness can vary from 25 N m^?1 at the first mark to 0.04 N m^?1 at the last. The full-bridge piezoresistors give an electrical signal proportional to the applied force with superior temperature independency. The fabricated piezoresistive cantilevers were calibrated with the KRISS nano force calibrator (NFC). The results showed that the stiffness and the force sensitivity at the last mark was determined to be 0.0502 N m^?1 and 0.357 (mV/V) μN^?1, respectively. The performances were tested by calibrating stiffness of commercial cantilevers using the cantilever-on-cantilever method with a fabricated cantilever and comparing calibration results with stiffness obtained from calibration using the NFC. Two results match to each other within approximately 10 % discrepancy.     

磁性材料磁热效应的研究

设计组装了一种冰量热计法磁致热效应测量仪,它可用于测量交变场下铁磁样品磁致热的绝对量。从磁热测量的结果,得到了一些单一磁样品和磁－良导体复合样品的磁致热效应实验规律。     

Enhanced Portable LUT Multiplier with Gated Power Optimization for Biomedical Therapeutic Devices

Digital design of a digital signal processor involves accurate and high-speed mathematical computation units. DSP units are one of the most power consuming and memory occupying devices. Multipliers are the common building blocks in most of the DSP units which demands low power and area constraints in the field of portable biomedical devices. This research works attempts multiple power reduction technique to limit the power dissipation of the proposed LUT multiplier unit. A lookup table-based multiplier has the advantage of almost constant area requirement’s irrespective to the increase in bit size of multiplier. Clock gating is usually used to reduce the unnecessary switching activities in idle circlet components. A clock tree structure is employed to enhance the SRAM based lookup table memory architecture. The LUT memory access operation is sequential in nature and instead of address decoder a ring counter is used to scan the memory contents and gated driver tree structure is implemented to control the clock and data switching activities. The proposed algorithm yields 20% of power reduction than existing.     

Accurate Linewidth Measurements in Aperture Limited In-line Fraunhofer Holography

Abstract

Methods for accurate width analysis of line objects in aperture limited in-line Fraunhofer holography are described. One approach involves size correction utilizing the nature of the error commonly introduced. The other technique used involves measuring the width at a certain normalized intensity and not at the apparent edge. The general background is discussed in detail using an opaque object model.     

Accurate Measurements of the Zero-Dispersion Wavelength in Optical Fibers

We have developed a frequency-domain phase shift system for measuring the zero-dispersion wavelength and the dispersion slope of single-mode optical fibers. A differential phase shift method and nonlinear four-wave mixing technique were also investigated. The frequency-domain phase shift method is used to produce Standard Reference Materials that have their zero-dispersion wavelengths characterized with an expanded uncertainty (k = 2) of ± 0.060 nm.     

Accurate Software-Related Average Current Drain Measurements in Embedded Systems

Performing accurate average current drain measurements of digital programmable components (e.g., microcontrollers, digital signal processors, System-on-Chip, or wireless modules) is a critical and error-prone measurement problem for embedded system manufacturers due to the impulsive time-varying behavior of the current waveforms drawn from a battery in real operating conditions. In this paper, the uncertainty contributions affecting the average current measurements when using a simple and inexpensive digital multimeter are analyzed in depth. Also, a criterion to keep the standard measurement uncertainty below a given threshold is provided. The theoretical analysis is validated by means of meaningful experimental results     

用集成功放组成的精密功率放大器

介绍了一种用厚膜集成功放加上稳幅电路组成的精密功率放大器,其稳定度、频率响应和波形失真都达到了很高的指标。     

扩展目标的精确定位研究

本文在分析电视跟踪算法精度的基础上,对扩展目标的精确定位作了初步的讨论。对几种亚象素边缘定位算法和曲线拟合算法作了计算机仿真,并给出了仿真结果。     

Accurate Thermal Conductance and Impedance Measurements of Transition Edge Sensors

Past measurements of the thermal coupling of superconducting transition edge sensor (TES) calorimeters suspended on SiN membranes produced wide-ranging values for the exponent of the thermal coupling through the membranes. We present a measurement technique that is less susceptible to current dependence of the phase transition than the previous measurements. An initial measurement produced the expected exponent for a 2-D phonon gas: thermal conductance is proportional to T ². In doing these measurements, we employ a modification to Lindeman’s equivalent circuit technique for measuring TES complex impedance.      

Relaxation Time Measurements by an Electronic Method

In many experiments, one is faced with the problem of measuring the time constant of decaying signals. The paper describes a simple electronic system that permits the direct measurement of time constants. The system was used in connection with relaxation experiments on hydrogen and rubidium masers and was found to operate well. The use of a computing counter in the systems gives the possibility of making averages on several experiments and obtaining the standard deviation of the results from the mean. The program for the computing counter is given.     

A Precision Stabilized Sine-Wave Source for AC Power Measurements

The design of a stable sine-wave source for error determination of ac-measuring instruments is discussed. The electronic amplitude control circuit has been constructed using standard integrated circuits. The fluctuations of its rms output voltage, observed over the period of 1 h, are 1 · 10-6 peak-to-peak. Since the total harmonic distortion is less than 1 · 10-3, its contribution to the error of the rms value may be neglected.     

Comparison of Electronic Transport Measurements on Organic Molecules

We compile, compare, and discuss experimental results on low‐bias, room‐temperature currents through organic molecules obtained in different electrode–molecule–electrode test‐beds. Currents are normalized to single‐molecule values for comparison and are quoted at 0.2 and 0.5 V junction bias. Emphasis is on currents through saturated alkane chains where many comparable measurements have been reported, but comparison to conjugated molecules is also made. We discuss factors that affect the magnitude of the measured current, such as tunneling attenuation factor, molecular energy gap and conformation, molecule/electrode contacts, and electrode material.     

A Two-Sinker Densimeter for Accurate Measurements of the Density of Natural Gases at Standard Conditions

A special reference densimeter has been developed for accurate measurements of densities of natural gases and multicomponent gas mixtures at standard conditions of temperature and pressure (T _s = 273.15 K and p _s = 0.101325 MPa). The densimeter covers the range from 0.7 kg · m^?3 to 1.3 kg · m^?3; the total measurement uncertainty in density is 0.020 % (95 % level of confidence). The measurement principle used is the two-sinker method, which is based on the Archimedes buoyancy principle. The certified calibration laboratory of E.ON Ruhrgas AG, Germany, uses this densimeter to verify the standard densities of certified calibration gases (binary and multicomponent gas mixtures). Moreover, the densimeter is used to determine the compositions of commercially available binary gas mixtures with a small uncertainty of (0.01–0.03) mol%.