A test system for calibrating flickermeters

This paper describes a new calibration system for testing flickermeters. The test system is used to generate and measure all the combinations of amplitude changes and frequencies required for calibrating flickermeters. Two computer-controlled waveform generators are used to produce the test conditions. The percent modulations of the test waveforms are measured with two high accuracy sampling voltmeters. Digital logic and software control ensures that the modulated signals are only measured when either maximum or minimum modulation occurs. Test data indicates that the percent modulation of the waveforms generated by the calibration system for square wave and sinusoidal modulations are within 0.002% and 0.005%, respectively, of the nominal values specified in IEC Standard 61000-3-3.     

利用VM-7衰减校准系统实现微波阻抗参量测试

通过对VM-7衰减校准系统的构成原理及阻抗参量测试方法的分析研究,充分利用其动态范围宽、灵敏度高、频率范围宽等显著优点,提出了利用VM-7衰减校准系统结合驻波比电桥来实现微波阻抗参量测试的方案,对构造原理、实现过程和测量结果的不确定度分析进行了详细介绍。经过实测验证:系统稳定性好、准确度高,可为微波阻抗参量的计量测试提供一套切实可行的解决方案。     

A new automatic system for calibrating the solid state DC voltage reference standards at NIS,Egypt

A new automatic system for calibrating the solid state DC voltage reference standards (Zener Diode reference standards) has been established at National Institute for Standards (NIS), Egypt to disseminate the unit of volt in the country. Besides, this system has been implemented as a coherent structure that, from the national DC voltage reference standards, can disseminate the traceability of all the instruments under calibration. The system consists of a set of programmable instruments and proper software. The software of the system has been built using the Laboratory Virtual Instrument Engineering Workbench (LabVIEW) graphical language. The system hardware is configurable by the operator on the basis of the specific calibration to be performed and it allows large number and different models of Zener diodes to be act either as reference units or as units under calibration. The design and the implementation of the system software have been discussed in details. Furthermore, the system validation has been carried out for the measurement repeatability and the results compatibility in both automatic and manual modes.     

A method for calibrating the line-focus-beam acoustic microscopy system

Absolute accuracy of the line-focus-beam (LFB) acoustic microscopy system is investigated for measurements of the leaky surface acoustic wave (LSAW) velocity and attenuation, and a method of system calibration is proposed. In order to discuss the accuracy, it is necessary to introduce a standard specimen whose bulk acoustic properties, (e.g., the independent elastic constants and density) are measured with high accuracy. Single crystal substrates of gadolinium gallium garnet (GGG) are taken as standard specimens. The LSAW propagation characteristics are measured and compared with the calculated results using the measured bulk acoustic properties. Calibration is demonstrated for the system using two LFB acoustic lens devices with a cylindrical concave surface of 1-mm radius in the frequency range 100 to 300 MHz.     

Method for calibrating system parameters of a multidirectional interferometers system

A multidirectional interferometer system has been proposed and developed to measure the position and orientation of a positioning stage. In this method the system parameters, such as positions of the corner-cube reflectors and directions of the rays in the interferometers, must be determined beforehand. However, it is difficult to find ways to determine the system parameters for each different system with necessary accuracy. This paper proposes a systematic method for calibrating the system parameters when the number of the interferometers is larger than the degrees of freedom of the stage. The method is verified for a two-dimensional stage by both simulation and experiment.     

Homography-based method for calibrating an omnidirectional vision system

We present a homography-based method for calibrating an omnidirectional vision system with a parabolic mirror. Assuming that the intrinsic parameters of the camera are known a priori, we focus on finding the solution for the mirror parameter and its positions. We first estimate the homographic matrix partially using six or more point correspondences. Then the rotation matrix and two components of the translation vector can be estimated. Finally, the remaining parameters are computed. In this method, a closed-form solution for all the variables is obtained using the homographic matrix. Another advantage is the enhanced robustness in implementation via the use of two over-constrained linear systems. Numerical simulations and real data experiments are also performed to validate the proposed algorithm.     

A system of secondary standards for photon dosimetry

Translated from Izmeritel'naya Tekhnika, No. 10, pp. 48–49, October, 1990.     

A hybrid method for calibrating acoustic arrays

A method to calibrate the elements of large arrays devoted to underwater applications is presented. The goal is to measure the sensitivity and directivity of the elements over their full bandwidth. The main constraint comes from the bounded geometry of the experimental setups that limits the duration of the time windows available for analyzing the received signals. Using a short wideband pulse is detrimental to obtaining high signal-to-noise ratios. A classical method for handling this problem is time-delay spectrometry (TDS), which is based on the transmission of a linear frequency- modulated signal combined with a sliding frequency filter. An alternative, hybrid method based on the transmission of a sequence of time-frequency-limited signals is proposed. This hybrid method is shown to provide the same spectral density as TDS in the frequency scanning, but the filtering process is quite different. The transmitted signals are designed to take advantage of the coherent sums of the received signals to track the time of flight of the direct paths between the source and the elements. In addition, a fitting process based on the calibration geometry of data acquisition enables the boundaries of the interference-free time windows to be precisely delineated. An example of the application is described.     

一体化温度变送器自动校准系统研制

针对一体化温度变送器校准工作中使用仪器繁多、连接线路复杂、数据处理工作量大等问题,研制一体化温度变送器自动校准系统。该系统包括标准恒温槽、多路数据采集装置、标准铂电阻温度计和计算机,其中多路数据采集装置将标准铂电阻配套仪表功能和直流电流表功能进行集成化设计,设置一路标准器通道和六路被校准仪器通道,可实现多支一体化温度变送器的同时校准。系统通过计算机控制程序可实现自动温度控制、温场判定、数据采集及处理以及生成校准记录等功能,且控制准确、自动化程度高。