Uncertainty Budget for the NIST Hybrid Humidity Generator

A detailed uncertainty budget for the new hybrid humidity generator (HHG) that has been constructed at the National Institute of Standards and Technology is presented. The HHG generates frost/dew points from ?70?°C to +85?°C using calibration gas flows up to 150 L?·? min^?1. For frost/dew points above ?15?°C, the two-pressure method is employed, and for frost points at or below ?15?°C, the divided-flow method is used (hence, the name ??hybrid??). The total expanded (k?=?2) uncertainty is estimated for HHG generation of the following quantities: frost/dew point, mole fraction, and relative humidity. The total uncertainty is estimated separately for the two-pressure and divided-flow methods.     

A 12-Mc, Nine-Bit Digital Function Generator

This paper describes some developed equipment found very useful in evaluating circuits that require digital inputs. For example, D-A converters are generally tested by using their associated A-D converter as a test-signal source. Since the A-D converter itself introduces errors, the measurement of analog input and output indicates over-all performance but not individual converter performance. The digital function generator allows separate evaluation of D-A converters by synthesizing useful test functions from discrete samples. Comparison of the known input with the output gives an accurate performance check. The present equipment generates up to sixteen different samples, represented by nine-bit words in parallel form, at a word rate of 12 Mc. A discussion of useful test functions for determining D-A converter linearity and transient response will include discussion of digital sine waves, ramps, and step functions. Although D-A converter evaluation is stressed, the equipment is also useful for other tasks.     

Performance and Validation Tests on the NIST Hybrid Humidity Generator

A new humidity generator has been constructed at the National Institute of Standards and Technology. Once fully operational, the NIST hybrid humidity generator (HHG) will generate frost/dew points from −70°C to +85°C using calibration gas-flow rates up to 150 standard liters per minute and is expected to outperform the present humidity generator at NIST in terms of accuracy. The HHG combines the two-pressure and divided-flow humidity-generation techniques (hence, the name “hybrid”). The centerpiece of the HHG is a heat exchanger/saturator that is immersed in a temperature-controlled bath stable to within 1 mK. For dew/frost-point temperatures above −15°C, the two-pressure principle is employed. For frost points at or below −15°C, the water-vapor/air mixture is produced by mixing metered streams of moist air produced by the two-pressure method with purified, dry air. A series of performance and validation tests on the HHG in the two-pressure mode, including measurements of temperature gradients and pressure stability in the generator under various operating conditions, and comparison of the humidity generated by the HHG to that generated by the other NIST humidity-generation standards, are reported.     

函数信号发生器频率偏差校准值的不确定度评定

本文以实例论述函数信号发生器频率校准值的不确定度评定过程。     

脚踏健身传动加热装置

根据国家倡导节能环保的需求,提出了健身和加热为一体的生活理念,设计了新型的脚踏健身传动加热装置,由人蹬踏踏板,通过人力驱动压缩机使汽化体制冷剂在吸收大气能量后被压缩成为高压高能量的气体,然后在冷凝作用下将热量传递给水,从而加热水。因此,健身与加热同步进行的方式,为时下绿色节能提供了新的思路。     

A Pseudo-Random Noise Generator

If the individual outputs of a cascade of bistable multivibrators are combined, we get useful waveshape, spectral, and probability-density function properties. Four modes are examined: equal amplitude, amplitude proportional to square root of frequency, amplitude proportional to frequency, and amplitude inversely proportional to frequency.     

高压脉冲发生器

本文介绍一种高压脉冲发生器,它适用于一些储能设备中高压脉冲放电开关的触发,引爆高压火花隙雷管等场所.文中较为详细地介绍了仪器各个组成部分的电路原理,同时结合研制过程中实测的一些数据,具体分析了引起高压脉冲输出时产生延迟和晃动的原因.     

Harmonic Analyzer/Generator

A method of measuring the phase angle and magnitude of "n" harmonics corresponding to a periodic signal is described. The method includes the generation of sinusoidal bursts to reproduce significant components of distorted and complex signals; burst amplitude, burst initial phase, and burst frequency correspond, respectively, to harmonic amplitude, harmonic phase angle, and harmonic frequency.     

A Hazard-Free Walsh-Function Generator

Outputs of a Gray code counter are used to synthesize digital Walsh functions that are free from hazards. This method, which produces sequency-ordered Walsh functions, also uses a binary code to select the order.     

Pulse Generator and Flip-Flops

A simple pulse generator can be constructed using IC gates. Such a pulse generator is described and its use to construct edge-triggered flip-flops is demonstrated. A flip-flop for use in a phase comparator is described. Desirable and undesirable characteristics for this application are discussed and examples of R-S and J-K flip-flops given.     

An Exponential Current Generator

A current getlerator has been constructed from two operational amplifiers and a thermostated twin transistor. The current is an exponential function (5) of a controlling voltage. At currents greater than 100 ?A, the transistor exhibited a resistive effect, for which it was possible to compensate for internally. The generator was tested over the current range 30 nA-15 mA and was found to perform almost ideally, with a slope of 1.008 of the theoretical and a standard deviation of 0.3 perceht. Some preliminary measurements have shown the generator to be useful down to 10 pA. The use of the generator for electrochemical kinetic measurements is described.     

Microcomputer-Controlled Precision Pneumatic Pressure Generator

An increasing variety of avionics require precision pneumatic pressure stimuli during organization and intermediate maintenance. The accuracy and long-term stability requirements approach the best mercurial standards. Pressure stimuli must be coordinated and varied at precise rates that are beyond the frequency response of mercury columns and many electromechanical sensors. Test systems are frequently required to simultaneously monitor and evaluate unit under test (UUT) response and generate pneumatic stimuli. In addition, the environment is frequently hostile, maintainability is paramount, performance must always be known and warmup time must be nil. Comprehensive trade studies, tests, and analyses were performed. This initial work indicated a new pressure generator should be a "smart" instrument and should use a pressure sensor not a density sensor. Current field and production experience indicates performance objectives have been exceeded and this new type of precision pressure generator can be readily incorporated in a variety of test systems or be used "stand-alone". This paper discusses the design implementation, features, and characteristics of this microcomputer controlled precision pneumatic pressure generator-a new "smart" test instrument.     

A Predictable Subnanosecond Step Generator

Determination of the response of a time domain instrument to a voltage step is preferable to determination in terms of its response to sine waves. Unfortunately the output waveshape of a voltage or current step generator cannot be evaluated as easily as that of a sine wave source. Consequently, investigators rely (or should rely) upon waveform predictability rather than waveform measurement when employing step generators in system characterization. One form of a predictable step generator is discussed that is useful in the subnanosecond to tens of nanoseconds time region after the step edge. A practical realization of this form is given that has predictability to within 1 percent in that time region from 350 picoseconds to 6 nanoseconds after an 80-picosecond rise-time step edge.     

A Precision Digital Phase Generator

The design of a digital phase generator which produces two outputs of frequency f, between which the phase shift can be varied from 0 to 360° in steps of 1°, from an input frequency of 360f, is described. The system design is described in detail. The circuit design and the choice of the circuit elements are discussed. Fast logic elements have been used in the construction of the instrument. A brief analysis of the performance of the system is also given. From the experimental results, which agree with the calculated performance, it is found that the accuracy of the system varies and is as high as 0.05 percent when the phase shift is 359°. The accuracy of the system is limited only by the propagation delays of the logic elements used and therefore can be improved by using faster logic elements.     

Reference Waveform Flat Pulse Generator

The NBS Reference Flat Pulse Generator (RFPG) is used to transfer dc voltage and resistance standards to the nanosecond domain. It provides a step amplitude of 1.000 V (open circuit) from a source impedance of 50.0?. The transition duration is 600 ps, and all perturbations are damped out to less than ±10 mV within 5 ns. It can also be used as a time interval transfer standard.     

产生任意波形信号的系统及其在标准微位移发生装置中的应用研究

描述了能够产生任意波形信号的信号发生系统的构成、工作原理和关键技术,并将能产生任意波形信号的标准信号发生系统应用于标准微位移发生装置中,控制标准微位移发生装置产生任意形状的标准微位移运动轨迹及模拟标准器形状轮廓轨迹,以实现对微米测量范围的位移传感器的动态校准.通过实验验证了该系统及标准微位移发生装置的准确性及实用性.     

汽轮发电机组轴承的可靠性分析

本文提出了汽轮发电机组轴承振动的可靠性分析方法。该方法把轴承的失稳转速、机组运行转速和危急保安器的动作转速处理为随机变量，使用概率设计法在设计或运行阶段确定轴承不失稳的可靠性指标，文中还给出了该方法的应用实例。     

基于DDS技术的信号发生器

分析DDS信号发生器的工作原理基础上,根据系统指标合理地采用了DDS技术,以AD9854芯片为核心,设计了一种结构简单性能优良的信号发生器。详细分析了该信号发生器的系统结构和软硬件设计。