采用电补偿方案的新一代立式计算电容装置

针对立式计算电容最大不确定度来源的端部效应误差,中国计量科学研究院经过多年改进,研制出的最优中空电补偿电极在计算电容模型装置上,没有采用加装钉子头进行补偿的电补偿方案,并完成了诸如端部效应误差的补偿效果、偏心效应误差等电气性能验证试验,成功应用在新一代立式计算电容装置上。实验结果表明,采用电补偿方案的新一代立式计算电容装置复现1 pF电容单位的相对标准不确定度为1.0×10^-8。     

水量热法加速器光子水吸收剂量绝对测量与国际比对

为实现加速器光子水吸收剂量绝对测量,研制了水量热计系统,在此基础上取得国际互认并建立加速器光子水吸收剂量基准,进一步提高了我国放疗剂量量值传递能力。通过水浴与半导体制冷系统二级控温,将量热计水模体的温度漂移控制在0.5μ℃/s。利用惠斯通交流电桥测量辐射所致的热敏探针阻值变化,逐次校准热敏探针和交流电桥,实现了医用加速器光子水吸收剂量的绝对测量,合成标准不确定度为0.30%。参加了国际计量局加速器光子水吸收剂量关键比对,复现的6MV和10MV光子水吸收剂量值与比对参考值之比分别为0.9917和0.9949,在不确定度允许的范围内一致。     

可动屏蔽型计算电容复现电容单位的方法研究

中国计量科学研究院建立了标准不确定度为2×10-8的可动屏蔽型计算电容装置。该装置复现电容单位量值只与屏蔽电极所移动的轴向长度有关。采用激光干涉仪测量这个长度时,一般无法提供干涉条纹数。经典方法采用替换方法,逐步从已知的小整数扩大到大整数。过程复杂,所需条件多。提出了一种新的复现电容单位的方法。对应复现电容量值的干涉条纹整数由一个准确度等级相对较低的仪器直接确定。其干涉条纹小数则通过电容电桥的两次平衡确定。所需结构及过程简单,操作方便。给出了该方法的详细内容及其优点,报告了检查装置线性的实验及其结果。     

钼靶X射线空气比释动能的国际关键比对

为支撑国内乳腺诊断X射线空气比释动能的量值溯源体系，中国计量科学研究院完成了钼靶X射线空气比释动能率的量值复现，其量值复现不确定度为0.3%,并于2018年与国际计量局完成了BIPM.RI(I)-K7关键比对工作，两机构对相同2个传递电离室的校准因子偏差小于0.04%,比对结果合成不确定度为0.28%,比对结果进入国际计量局关键比对数据库(KCDB),实现了国际互认。     

低能X射线空气比释动能国际关键比对

为促进我国在低能X射线空气比释动能计量领域内的量值统一并达到国际等效,中国计量科学研究院(NIM)于2018年采用平板自由空气基准电离室复现低能X射线空气比释动能,并通过传递电离室Radcal-RC6M在国际计量局(BIPM)低能X射线辐射场中开展了间接比对,其比对结果在合成标准不确定度为0.37%范围内与国际计量局等效一致,该比对结果已纳入国际计量局的关键比对数据库(KCDB)。     

医用加速器光子水吸收剂量量值体系的研究与应用

研制石墨空腔电离室,搭建电离电流测量系统,复现Co-60γ射线水吸收剂量(u=0.37%),参加国际比对取得等效互认,建立了国家基准;研制开放式量热芯,搭建惠斯登交流电桥,通过H_2/N_2饱和水体系和热损定量评估,复现加速器光子水吸收剂量(u=0.35%@10MV),并参加国际比对取得等效互认。建立了我国医用加速器光子水吸收剂量量值体系,并实现了临床放疗剂量的量值溯源。     

我国建成新一代计算电容装置

正由中国计量院承担完成的"十一五"国家科技支撑计划项目课题"精细结构常数测量关键技术及电容基准的研究",日前顺利通过专家组验收。该课题研制的国际新型立式可移动屏蔽电极计算电容装置测量精细结构常数,复现1皮法(pF)电容单位的标准不确定度达到2.0?10-8,接近国际最好水平。据课题负责人、中国计量院首席研究员陆祖良介绍,本课题研究过程通过国际合作,使我国在该领域的研究很快进入国际前沿。     

电容损耗因数的绝对测量及传递装置

本文介绍利用变间隙保护环电容器的损耗特性进行损耗因数的绝对测量(真值测量)和传递。被测对象的电容量范围为100～1000pF,可扩展到10000pF。所用装置的测量总不确定度小于2×10~(-7)(2σ)。该装置能对电容损耗因数用替代法进行直接传递,而无需作变压器比例臂等方面系统误差的修正。     

基于主成分分析的流量装置比对传递标准稳定性研究

设计了一种电磁流量计与涡轮流量计串联的水流量装置比对传递标准,采用主成分分析方法实现了对比对数据中参比装置量值离散度与传递标准量值波动度的分离,介绍了其原理与实施流程。针对主成分方法的适用性进行了研究,并根据不同主成分间的量值关系提出一套传递标准稳定性的评价标准。以一次水流量装置比对的实验数据为例,从传递标准稳定性角度检验了比对结果的有效性,并给出其估计值为0.015%。该方法提高了比对结果评判标准的可靠性,同时还可用于优化比对路线,缩短比对时间。     

扭矩国际比对的技术实现

一、关键比对背景世界上各国国家计量院的扭矩标准装置,采用不同的技术原理和结构复现扭矩值。对一个国家级计量研究院来说,关键比对是验证各国量值一致性的重要方法。2004年3月22日到24日,国际计量局(CIPM)质量和相关量咨询委员会(CCM)力学工作组在南非举行的会议中作出决议,决定进行两个不同扭矩范围1kNm、20kNm的CCM扭矩关键比对,并同意仅     

Towards accurate measurement of the frequency dependence of capacitance and resistance standards up to 10 MHz

Progress toward an understanding of the frequency dependence of capacitance and resistance standards at frequencies up to 10 MHz is presented. A qualitative comparison is also made for capacitance and dissipation factor measurements between the National Physical Laboratory (NPL) high-frequency four terminal-pair (4TP) bridge and a commercial impedance analyzer for the first time. A set of novel high-frequency calculable coaxial resistance standards, of nominal 100 /spl Omega/ and 1 k/spl Omega/ values, have been developed and their calculated frequency dependence up to 1 MHz is given.     

Evaluation of the frequency dependence of the resistance and capacitance standards in the BIPM quadrature bridge

The Bureau International des Poids et Mesures (BIPM) has established a measurement chain allowing calibration of capacitance standards in terms of the quantized Hall resistance (QHR). An important element in the chain is a quadrature bridge linking a pair of ac resistors of values 2R/sub K/ /spl ap/ 51.6 k/spl Omega/ to a pair of capacitance standards. The quadrature bridge can be operated at five different frequencies: 513, 1027, 1541, 3082, and 6164 Hz. For such measurements, we use different ratios (1/1, 4/1 and 1/4) for the main inductive voltage divider in the quadrature bridge and three different pairs of capacitors of values 3000, 2000, and 1000 pF. A calculable coaxial resistance of 1290.6 /spl Omega/ (R/sub K//20) is used as a reference to evaluate the frequency dependence of the 51.6-k/spl Omega/ resistances. This allows the calibration of capacitance standards at the five different frequencies. The measured frequency dependences of 10 and 100 pF capacitance standards are reported.     

Analysis of Nonideal Effects on a Tomography-Based Switched-Capacitor Transducer

This paper presents a nonideal analysis of a fully-integrated switched-capacitor capacitive transducer for electrical capacitance tomography system. The investigation establishes different types of error source models as well as practical mismatch effects in the derivation of second-order analytical expressions. The analyses are conducted on the basis of heavy stray capacitances of 150 pF typically, in the context of a minimum detection capacitance ranging from 1 to 10 fF. The predicted results agree very well with the HSPICE simulation results using Level 49 BSIM3 models of AMS 0.6-mum CMOS process technology with a single 5-V supply. The conservative simulation results have shown that the capacitive transducer differential output displays a baseline dc offset of 0.083 mV at 25 degC, a change in baseline capacitance of 1 fF from 25 to 40 degC and an output temperature coefficient of 0.045 mV/degC from 25 to 100 degC at the measuring capacitance of 1 pF. Both the predicted and simulated results presented here are better than that of the reported works     

Analysis of a Direct Interface Circuit for Capacitive Sensors

We present the theoretical analysis and performance results of a direct microcontroller unit (MCU) interface circuit for capacitive sensors based on the charge-transfer method, when stray capacitances are considered. The interface circuit can implement two alternative two-point calibration techniques that reduce the effects of stray capacitance, temperature, and MCU parameters that depend on the power supply voltage. The best measurement deviation achieved from 0 $^{circ}hbox{C}$ to 50 $^{circ}hbox{C}$ and for power supply voltage from 4.0 to 5 V is below 0.01 full-scale range (FSR) for the two subranges from 10 to 100 pF and from 100 pF to 1 nF and 0.08 FSR for the subrange from 2 to 10 pF.      

薄膜电容真空计电源的研究

介绍了利用交流电桥和相敏检波（PSD）原理设计的薄膜电容真空计电源的电路实施方案、主机电路结构和实测性能，对其中关键的小电容测量方法进行了深入的研究，在8h内测量，电容差值的漂移可小至10－3pF。主机结构采用微机控制和真空计模块化设计，可构成复合真空计或用于组装其他真空计。初步测试结果表明，这种真空计用单规管可以实现从大气至1Pa，覆盖五个数量级的真空度测量。     

硅片表面超薄氧化硅层厚度测量关键比对CCQM-K32

利用X射线光电子能谱技术,建立了硅片表面超薄氧化硅层厚度（小于10 nm）准确测量方法。中国计量科学研究院参加了国际关键比对CCQM-K32,根据公布的国际关键比对结果,中国计量科学研究院的测量结果与参比的各国国家计量研究院的测量结果达到了等效一致,测量结果的不确定度为4.6%～7.0%。     

Compact inductance standard

A portable Maxwell-Wien bridge as a part of the Korea Research Institute of Standards and Science (KRISS) inductance standard has been developed. Two auxiliary resistive-capacitive networks (analogous to a "Wagner ground") provide excellent stability of the bridge balance and impose less strict requirements on the components of the networks. Removable capacitance and ac/dc resistance standards used in the bridge arms make it possible to realize the inductance unit in terms of capacitance and resistance in the frequency range 500 Hz to 3 kHz. Investigations of the standard and results of preliminary (trial) comparison with the Mendeleyev Institute for Metrology demonstrate that the bridge can be used for measurement of 10 and 100 mH inductance standards with an uncertainty within (1-3) /spl mu/H/H at frequencies of 1 and 1.6 kHz. The use of this bridge as a constituent part of a transportable standard gives an opportunity to eliminate any uncertainty arising from instability of the standard inductors.     

New Fused-Silica-Dielectric 10-and 100-pF Capacitors and a System for Their Measurement

New instruments have been designed to bring to standards laboratories the improved accuracy of capacitor calibrations developed by the National Bureau of Standards. The new 10-and 100-pF reference standard capacitors, based upon an NBS design, use a fused-silica dielectric with gold electrodes to provide the time and voltage stability required for calibrations to parts in 107. To maintain the capacitor temperature constant to within 0.01 °C, one model of the capacitors is designed for use in an oil bath, the other model is fitted with a new, stable, thermostatically controlled air bath. The system to measure these capacitors with a precision of parts in 108 consists of a bridge, detector, and oscillator. For these special measurements and for the general calibration of a wide range of capacitors, the new transformer-ratio-arm bridge has 12 capacitance decades and a range of 10 MAF-10-7 pF, and five conductance decades and a range of 103110-10 tmho. The new phasesensitive detector and power oscillator provide high sensitivity to bridge imbalance over the frequency range 10 Hz-100 kHz.