Design and calibration of a noise measurement system

The setup principle and calibration method of a noise measurement system for frequencies from dc to 10 kHz are described. This system measures the current noise power spectral density of some device, and consists of a low-noise current preamplifier, a voltage preamplifier, and a dynamic signal analyzer which implements the fast Fourier transform (FFT). The noise aspects of the whole system can be modeled as a serial noise voltage generator and a parallel noise current generator at the input port, plus a system free of noise. The cross correlation of the two noise generators is an imaginary number because the system input stage is composed of some junction field effect transistors (JFET's). Via the thermal noise measurement of several resistors, we derive the magnitudes of the noise generators in addition to the input impedance and the total system gain. The imaginary cross correlation is obtained by the noise measurement of pure capacitance. With a well-calibrated procedure, we can measure the noise power down to 2×10^-27 A²/Hz. Two systems with different input stages were calibrated with the same procedure and the noise measurement results of the various resistance values with the two systems all agree well with theoretical values. One of these with an input stage which has a much smaller noise current generator shows great improvement in the noise measurement of the high-impedance device     

Decentralized linear quadratic power system stabilizers for multi-machine power systems

Linear quadratic stabilizers are well-known for their superior control capabilities when compared to the conventional lead?Clag power system stabilizers. However, they have not seen much of practical importance as the state variables are generally not measurable; especially the generator rotor angle measurement is not available in most of the power plants. Full state feedback controllers require feedback of other machine states in a multi-machine power system and necessitate block diagonal structure constraints for decentralized implementation. This paper investigates the design of Linear Quadratic Power System Stabilizers using a recently proposed modified Heffron?CPhillip??s model. This model is derived by taking the secondary bus voltage of the step-up transformer as reference instead of the infinite bus. The state variables of this model can be obtained by local measurements. This model allows a coordinated linear quadratic control design in multi machine systems. The performance of the proposed controller has been evaluated on two widely used multi-machine power systems, 4 generator 10 bus and 10 generator 39 bus systems. It has been observed that the performance of the proposed controller is superior to that of the conventional Power System Stabilizers (PSS) over a wide range of operating and system conditions.     

Liquid-crystal-display projector-based modulation transfer function measurements of charge-coupled-device video camera systems

We demonstrate the ability to measure the system modulation transfer function (MTF) of both color and monochrome charge-coupled-device (CCD) video camera systems with a liquid-crystal-display (LCD) projector. Test matrices programmed to the LCD projector were chosen primarily to have a flat power spectral density (PSD) when averaged along one dimension. We explored several matrices and present results for a matrix produced with a random-number generator, a matrix of sequency-ordered Walsh functions, a pseudorandom Hadamard matrix, and a pseudorandom uniformly redundant array. All results are in agreement with expected filtering. The Walsh matrix and the Hadamard matrix show excellent agreement with the matrix from the random-number generator. We show that shift-variant effects between the LCD array and the CCD array can be kept small. This projector test method offers convenient measurement of the MTF of a low-cost video system. Such characterization is useful for an increasing number of machine vision applications and metrology applications.     

A Simulation Generator for Flexible Manufacturing Systems Design and Control

Recent developments in simulation languages have enabled the modeling of complex and large systems. Systems modeling using simulation has many advantages. Even though the creation of realistic models using a simulation language is becoming easier, it is not trivial. Simulation languages are not designed to be problem-specific. Furthermore, the art of systems modeling can be quite time consuming.

This paper describes a user-oriented simulation generator for the design and control of flexible manufacturing systems (FMS). The simulation generator serves as a preprocessor to the SIM AN simulation language. The generator converts data into a simulation model and automatically runs the simulation program. Standard output is provided by the simulation program, as well as plots and histograms of performance measures of interest to the analyst.

Model development is significantly simplified by the simulation generator described in this paper. Simulation generators can be developed in a relatively short period of time by using an existing simulation language. Simulation generators represent a very attractive alternative to specialized simulation languages.     

FPGA Implementation of a Digital Sequential Phase-Shift Stroboscope for In-Plane Vibration Measurements With Subpixel Accuracy

This paper describes a sequential phase-shift stroboscope and a subpixel imaging system that is able to measure with high resolution weak in-plane harmonic motions, such as those of microelectromechanical systems (MEMS). The synchronization of both MEMS stimulus and light strobe can be obtained by either using the camera output frame signal or driving the external trigger of the camera, depending on the operation principle of the camera. Experimental results concern a small silicon cantilever resonator excited in its first and second vibration modes and a quartz tuning fork. Two optical configurations have been developed. The first one is based on the use of a macroobjective for large fields of view with micrometer resolution displacement measurement, and the second is based on an optical microscope for weak amplitude vibration measurements with a resolution down to a few nanometers. The whole logic unit of the stroboscopic signal generator is implemented into a low-cost field-programmable gate array, thus offering high flexibility.      

Failure-Processing Scheme Based on Kalman Prediction and Reliability Analysis for IDF-used 25 kVA Generators

A 25 kVA generator is one of the most important components in the power system of an indigenous defensive fighter (IDF). However, the generators have failed frequently since being equipped on IDFs. The poor reliability and long repair time of a 25 kVA generator have seriously impacted the availability of IDFs. This study aims to build a failure-processing mechanism for the 25 kVA generators based on the state-estimation function of the Kalman filter. By way of this mechanism, the left- or right-side load of the fighter can be switched from the supplied generator that is going to fail to the other generator before the abnormal generator actually fails. Therefore, this mechanism not only mitigates the impact resulting from the irregular power on systems of the fighter, but also obtains reaction time to shutdown the generator that is going to fail so as to perform a preventive maintenance or other effective actions on the generator such that the further failures can be avoided. In the simulations of this study, the failure times predicted by the Kalman filter are compared with the results obtained by Monte Carlo simulation for judging the prediction accuracy. In order to simulate more accurately, an exponential attenuator is placed at each end of the outputs of both the generator and the Kalman filter so as to conform to the actual aging model. The prediction errors are acceptable. Besides, reliabilities of the generators in four different configurations are compared to know the effect of redundancy design.     

仪表着陆信号发生器校准研究

仪表着陆信号发生器是仪表着陆系统机载设备的专用检测设备,目前国内还没有公开发布的关于仪表着陆信号发生器的国家或行业范围内的检定/校准技术标准。本文通过对仪表着陆系统原理进行剖析,从仪表着陆信号发生器工作特点入手,对航向信标、下滑信标、指点信标等信号特点进行分析,给出了计量特性,并基于频谱分析仪直接测量法给出了各项计量特性的校准方法,同时对频谱分析仪引入的测量不确定度进行了分析,用GUM法评定了扩展不确定度。结果表明,给出的校准方法可满足仪表着陆信号发生器关键参数的校准需求,使用频谱分析仪校准符合仪表着陆信号发生器各计量特性的量值溯源要求。     

脉冲信号发生器自动检定/校准系统

脉冲信号发生器被广泛应用在电子测量和数据通信领域。利用Visual Basic高级语言，开发基于GPIB接口的脉；中信号发生器自动检定／校准系统。该系统能够完成对脉冲信号发生器的自动检定／校准，测量数据自动保存在数据库，实现检定／校准证书自动生成，利用网络打印检定／校准证书。     

Identification of transfer functions with time delay and itsapplication to cable fault location

A Gaussian frequency-domain maximum likelihood estimator (MLE) to estimate the transfer function of linear continuous-time systems with time delay is presented. The stochastic framework is an errors-in-variables model, which means that the input as well as the output of the system is disturbed with noise. The estimator is applied to a practical measurement problem, namely the estimation of the location of discontinuities, e.g. faults in electrical cables from a reflectogram. Experimental results for coaxial lines show that it is possible to identify simultaneously the location of the discontinuity and a rational approximation of the generator mismatch, the fault impedance, and some of the cable parameters     

A high precision 24-GHz FMCW radar based on a fractional-N ramp-PLL

A 24-GHz FMCW radar system is presented using a fractional-N phase-locked loop ramp generator. This fractional-N ramp generator achieves relative ramp nonlinearities below 10/sup -8/. Among others linear frequency ramps are important tools in high precision FMCW radar systems. Highly linear frequency ramps make post measurement error correction feasible. Other important aspects of the high performance FMCW radar system are the design of the microwave circuit and the digital signal processing of the IF signals. Furthermore, a large RF bandwidth of more than 3 GHz obtained by thorough simulations results in a high range resolution and a good potential measurement accuracy. To maintain this high potential accuracy, a phase slope algorithm is used to calculate the precise range value leading to a significantly better precision with absolute range errors below 0.8 mm, compared to the commonly used spectral center algorithm.     

Simple Time-Delay Circuit with Very High Duty Cycle

A voltage-controlled time-delay arrangement with a duty cycle equal to unity is described. This performance of the circuit is based on the use of a new monostable switch with complementary transistors. The monostable switch, derived from a free-running multivibrator with very small mark/space ratio is employed as the trigger time base generator, the recovery time of which is very short. Such a time base generator is suitable for various applications in the measurement instruments. Connected to the Schmitt trigger, this timing circuit is very useful in the design of wide-range time-delay arrangements. The experimental performance of the presented time-delay arrangement is as follows: the delay-time variation in one range from about one microsecond to several milliseconds; the delay time/control voltage linearity better than ± 0.15 percent for the control voltage greater than 0.5 volt; the temperature stability of about 0.2 percent in the temperature range from 25-100°C.     

Repeatability and Reproducibility Standard Deviations in the Measurement of Trace Moisture Generated Using Permeation Tubes

Permeation-tube moisture generators are used in industry as calibrated sources of water vapor and carrier gas mixtures. Measurements were made using three permeation-tube moisture generators of the type used in the semiconductor industry. This paper describes repeatability and reproducibility standard deviations in measurement of moisture concentration from such generators. Repeatability refers to measurements within a system and reproducibility refers to measurements between systems. Two independent methods were used to measure the realized concentration of water vapor. The first measurement, the calculated value, was determined using calibrated permeation rate of permeation-tube and flow rate of dry carrier gas. This is the industrial method of evaluating moisture concentration. The second measurement, the measured value, was determined using the low frost-point generator at the National Institute of Standards and Technology (NIST) and a quartz-crystal-micro-balance. Four pairs of independent measurements for each generator and for six nominal levels in the range from10 nL/L to 100 nL/L were made. The characteristic used to quantify repeatability and reproducibility standard deviations in industrial measurements is the calculated value minus the measured value. Repeatability standard deviation ranges from 1 nL/L to 2 nL/L, approximately. Reproducibility standard deviation ranges from 2 nL/L to 8 nL/L, approximately. The documentary ASTM standard E691-99 was used for both data validation and quantification of the repeatability and reproducibility standard deviations.     

Standard stochastic pulse signals: Applications, reproduction, certification

We consider notions of application, modelling, and certification for stochastic pulse signals with normalized statistical characteristics as a means for monitoring metrological parameters of information measurement systems. We describe a signal model, present examples of its application, and consider a generalized functional scheme for a generator and principles for algorithmic certification of the model. Translated from Izmeritel'naya Tekhnika, No. 6, pp. 24–33, June, 1997.     

A fast method of finding minimal cutsets in a risk monitor

This paper introduces a new fast method to find minimal cutsets to calculate CDF (core damage frequency) in a risk monitor. The new method, called McFarm (a Missing Cutsets Finding Algorithm for Risk Monitor), is a fast and accurate algorithm to find minimal cutsets to calculate CDF by changing the fault tree to a simpler one. McFarm shows good results especially for non-safety systems out-of-service (OOS) cases and for OOS cases of supporting systems, such as the diesel generator and component cooling water, which are located at many places and lower levels in the fault tree structure. The fast calculation achieved in the OOS cases of supporting systems is due to adopting the ‘Super OOS AND gate’ concept. McFarm can be used for multiple-equipment OOS as well as single-equipment OOS. McFarm was tested by using two risk-monitor models for Korean nuclear power plants (i.e. for YGN 3,4 and for UCN 3,4) with KIRAP. However, McFarm can be used for the risk monitors which use any quantification methods such as CAFTA, IRRAS, etc. Because McFarm just changes the fault tree to a simpler one, thereafter any quantification methods can be applied to the simplified fault tree.     

Wavelength Mismatch Correcting Elements for Volume Holograms Written on a Laser Pattern Generator

Abstract

Holographic optical lenses based on volume gratings commonly suffer from severe aberrations due to wavelength mismatch between recording (blue-sensitive material) and application (often employing diode lasers). Here, methods are described for the precompensation of the aberrations at the recording. Both, aberrations in the phase of the reconstructed wave from the desired wave (‘wave aberration’), as well as aberrations in intensity resulting from deviations from the Bragg condition during reconstruction (‘Bragg aberration’) need to be compensated for. The design method for generating the computer generated holograms is described which are used as precompensating elements in the recording step of the interferometrically produced holographic optical elements. The computer generated holograms are written on a laser pattern generator. Test results of our laser pattern generator are shown to demonstrate its capability for this process. The measurement of the aberrations at the design wavelength in the near infrared is a very important step because it allows to eliminate in a second recording process misadjustment errors which will occur during the first recording step. By modification of at least one of the computer generated holograms the convergence of the procedure can be achieved.     

An instrument for measuring the voltage standing-wave ratio of a generator

Conclusions The comparison results confirm the relatively high accuracy of measurement of the standing-wave ratio by means of the above instrument.The instrument can also be used for matching the generator when its potput is insufficiently decoupled and there is a possibility of the results being distorted by the reaction of the adjustable plunger on the generator. For avoiding this reaction another hole should be made in the body of the plunger, and an absorbing sliding wedge placed in it. The protruding wedge lowers the standing-wave ratio of the instrument and decreases its effect on the generator. When the instrument is used for accurate measurements of the standing-wave ratio the absorber is pushed inside the plunger and produces hardly any effect on the operation of the instrument.     

Measurement problems in technological shaping processes

The problem of building a quality assurance system for computerized integrated manufacturing in machine building is discussed. Fundamental trends in this area require a new statement of the problem as one of information and measurement technology. The concept of observation as applied to the dynamics of complex controlled systems can be used to define the scope of the measurement processes and their interrelations during the shaping of machined pieces.     

Radio frequency controlled synthetic wavelength sweep for absolute distance measurement by optical interferometry

We present a new technique applied to the variable optical synthetic wavelength generation in optical interferometry. It consists of a chain of optical injection locking among three lasers: first a distributed-feedback laser is used as a master to injection lock an intensity-modulated laser that is directly modulated around 15 GHz by a radio frequency generator on a sideband. A second distributed-feedback laser is injection locked on another sideband of the intensity-modulated laser. The variable synthetic wavelength for absolute distance measurement is simply generated by sweeping the radio frequency over a range of several hundred megahertz, which corresponds to the locking range of the two slave lasers. In this condition, the uncertainty of the variable synthetic wavelength is equivalent to the radio frequency uncertainty. This latter has a relative accuracy of 10(-7) or better, resulting in a resolution of +/-25 microm for distances exceeding tens of meters. The radio frequency generator produces a linear frequency sweep of 1 ms duration (i.e., exactly equal to one absolute distance measurement acquisition time), with frequency steps of about 1 MHz. Finally, results of absolute distance measurements for ranges up to 10 m are presented.     

光纤式质量流量计的研究

研究出一种光纤传感器与电磁涡流传感器相结合的新型质量流量计,并给出理论模型和实际系统结构。该流量计对旋涡发生体进行了独特设计,即将光纤嵌入到旋涡发生体内部构成光纤式升力检测器。利用光纤的微弯损耗特性,检测出流体流经旋涡发生体时产生的变动升力大小,结合信号电极测量出的涡流频率,由单片机计算出流体质量流量。与其它质量流量计相比,光纤式质量流量计结构简单,抗干扰能力强。以水为被测对象的实验证明,其测量结果的相对误差在1%以内。     

8098单片机在位移监测系统上的应用

本文介绍了8098单片机在位移监测系统上的应用,较详细地说明了系统的硬件、软件的总体设计,特别是提高系统抗干扰能力的设计。该系统已成功的用于中、小型汽轮机的位移监测,具有较高的精度和可靠性。