A new microcalorimeter for measurements in 3.5-mm coaxial line

A new microcalorimeter has been realized for implementing the national power standard up to 26.5 GHz in a 3.5-mm coaxial line at the Istituto Elettrotecnico Nazionale (IEN) Galileo Ferraris, Turin, Italy. The system is based on a dry thermostatic cell controlled by Peltier elements. The thermal load consists of a twin sensor system that is alternately supplied with high frequency test power and low frequency or direct current (DC) reference power through adiabatic coaxial lines. This microcalorimeter was originally designed for calibrating bolometric mounts. Recently, it has been modified for thermocouple power sensors, which can operate from DC to 26.5 GHz in a 3.5-mm coaxial line.     

Traceability of photocurrent measurements to electrical standards

In detector output-signal measurements, where the measurement uncertainty critically impacts the total uncertainty of a detector-based radiometric scale realization, traceability of the photocurrent measurement to SI traceable electrical standards is needed. A reference photocurrent-to-voltage conversion scale has been developed and described here. The new standard has internal reference resistors for all signal-gain selections to decrease noise pickup of traditionally used external reference resistors. The internal resistors were calibrated by the NIST Quantum Electrical Metrology Division against standard resistors. Using the substitution method, the reference photocurrent-to-voltage conversion scale was transferred from the converter standard to other converters up to a maximum signal-gain of 10¹⁰ V/A with an expanded uncertainty of 0.013% (k=2). The DC conversion scale was extended to AC mode signal-gain calibrations where the photocurrent measurement uncertainty is 0.05% (k-2).     

Comparison of the NIST and PTB Air-Kerma Standards for Low-Energy X-Rays

A comparison has been made of the air-kerma standards for low-energy x rays at the National Institute of Standards and Technology (NIST) and the Physikalisch-Technische Bundesanstalt (PTB). The comparison involved a series of measurements at the PTB and the NIST using the air-kerma standards and two NIST reference-class transfer ionization chamber standards. Results are presented for the reference radiation beam qualities in the range from 25 kV to 50 kV for low energy x rays, including the techniques used for mammography dose traceability. The tungsten generated reference radiation qualities, between 25 kV and 50 kV used for this comparison, are new to NIST; therefore this comparison will serve as the preliminary comparison for NIST and a verification of the primary standard correction factors. The mammography comparison will repeat two previously unpublished comparisons between PTB and NIST. The results show the standards to be in reasonable agreement within the standard uncertainty of the comparison of about 0.4 %.     

中能X射线空气比释动能基准不确定度分析

根据空气比释动能复现公式建立数学模型,介绍了中能X射线100-250 kV空气比释动能基准测量不确定度的评定方法,分析了空气比释动不确定度的来源.依次对物理常数、有效测量体积、距离定位、电离电流、温度气压以及修正因子不确定度进行了分析.最终得到测量中能X射线空气比释动能的相对合成标准不确定度为0.22％,其中不确定度来源中最大的2个量分别为电离功和修正因子.     

Direct comparison between the NIST 10 V Conventional Josephson Voltage Standard and 2.5 V Programmable Josephson Voltage Standard

In the present paper, the intercomparison results of the NIST 10 V Conventional Josephson Voltage Standard (NIST10) and 2.5 V Programmable Josephson Voltage Standard (PJVS) Systems have been discussed. The two systems were directly intercompared at 1.018 V and 2.511 V from September 2006 to February 2007. The differences between the two systems (i.e. NIST10 — PJVS) at 1.018 V and 2.511 V were 0.21 nV and −0.95 nV respectively. The intercomparison results reveal that the noise of digital voltmeter (DVM) affects the measurement results significantly. Even with DVM of the same model, their noise rejection capability may be different when accuracy of a few nanovolt (nV) is required, although for Zener reference standard measurement, it is sufficient because the measurement uncertainty is dominated by the noise and non-linear drift of Zener reference standard.     

Uncertainty Analysis for Angle Calibrations Using Circle Closure

We analyze two types of full-circle angle calibrations: a simple closure in which a single set of unknown angular segments is sequentially compared with an unknown reference angle, and a dual closure in which two divided circles are simultaneously calibrated by intercomparison. In each case, the constraint of circle closure provides auxiliary information that (1) enables a complete calibration process without reference to separately calibrated reference artifacts, and (2) serves to reduce measurement uncertainty. We derive closed-form expressions for the combined standard uncertainties of angle calibrations, following guidelines published by the International Organization for Standardization (ISO) and NIST. The analysis includes methods for the quantitative evaluation of the standard uncertainty of small angle measurement using electronic autocollimators, including the effects of calibration uncertainty and air turbulence.     

WR19（40~60 GHz）矩形波导微量热计设计

介绍了一种基于热敏电阻功率座的对称双线结构的WR19（40~60 GHz）矩形波导微量热计的设计和修正因子计算方法。该微量热计将作为中国计量科学研究院40~60 GHz微波功率基准,它能够测量比原微量热计频段更宽的传递标准的有效效率,同时给出了测量修正因子的方法。     

Hysteresis and Related Error Mechanisms in the NIST Watt Balance Experiment

The NIST watt balance experiment is being completely rebuilt after its 1998 determination of the Planck constant. That measurement yielded a result with an approximately 1×10⁻⁷ relative standard uncertainty. Because the goal of the new incarnation of the experiment is a ten-fold decrease in uncertainty, it has been necessary to reexamine many sources of systematic error. Hysteresis effects account for a substantial portion of the projected uncertainty budget. They arise from mechanical, magnetic, and thermal sources. The new experiment incorporates several improvements in the apparatus to address these issues, including stiffer components for transferring the mass standard on and off the balance, better servo control of the balance, better pivot materials, and the incorporation of erasing techniques into the mass transfer servo system. We have carried out a series of tests of hysteresis sources on a separate system, and apply their results to the watt apparatus. The studies presented here suggest that our improvements can be expected to reduce hysteresis signals by at least a factor of 10—perhaps as much as a factor of 50—over the 1998 experiment.     

基于反向共轴的大口径平面光学元件面形测量

提出了一种基于反向共轴的大口径平面光学元件面形测量方法。将双位移传感器反向共轴线扫描测量模式和多角度旋转三面互检技术结合,借助直线长导轨有效扩大平面光学元件测量口径,同时测量过程中不需要使用标准平晶,避免引入标准平晶参考面不确定度分量,测量结果直接溯源到激光波长基准。利用该测量方法对3块400mm口径光学平晶进行面形测量,验证了该测量方法的可行性。     

基于温度修正的新微量热计的设计与评定方法研究

提出了一种“温度修正”的有效效率获得方法,并就基于该方法的微量热计设计进行了说明。该方法采用“隔热段测温修正”的方法对热敏电阻座有效效率定标中隔热段的影响进行修正,避开了用散射参数修正的传统方法。由于散射参数测量引入的不确定度是功率基准不确定度的主要来源之一,这种方法从原理上消除了该不确定度引入。最后给出了隔热段温度变化曲线,实验证明方法可行。     

高精密自动绝热量热计

介绍了中国计量科学研究院用新近开发的高精密自动绝热量热计的测量控制系统对美国国家标准技术研究院（NIST）的标准物质α-Al2O3进行的比热测量,并对测量结果和不确定度作了分析。该自动绝热量热计是中国计量科学研究院原有的绝热量热计的发展,它继承了原有量热计的本体,又开发了高精度量热和温度自动测量控制系统。进行了与NIST的数据和其它数据对比以及不确定度分析。测量结果与NIST的数据相比,其相对均方根偏差为0．447％,一致性为0．167％。合成相对标准不确定度为0．333％。结果表明,该自动绝热量热计具有高精密量热和比热测量的能力。     

Precise and traceable (13)C/(12)C isotope amount ratios by multicollector ICPMS

A new method for the measurement of SI traceable carbon isotope amount ratios using a multicollector inductively coupled mass spectrometer (MC-ICPMS) is reported for the first time. Carbon (13)C/(12)C isotope amount ratios have been measured for four reference materials with carbon isotope amount ratios ranging from 0.010659 (delta(13)C(VPDB) = -46.6 per thousand) to 0.011601 (delta(13)C(VPDB) = +37 per thousand). Internal normalization by measuring boron (11)B/(10)B isotope amount ratios has been used to correct for the effects of instrumental mass bias. Absolute (13)C/(12)C ratios have been measured and corrected for instrumental mass bias and full uncertainty budgets have been calculated using the Kragten approach. Corrected (13)C/(12)C ratios for NIST RM8545 (Lithium Carbonate LSVEC), NIST RM8573 (L-Glutamic Acid USGS40), NIST RM8542 (IAEA-CH6 Sucrose) and NIST RM8574 (L-Glutamic Acid USGS41) differed from reference values by 0.06-0.20%. Excellent linear correlation (R = 0.9997) was obtained between corrected carbon isotope amount ratios and expected carbon isotope amount ratios of the four chosen NIST RMs. The method has proved to be linear within this range (from (13)C/(12)C = 0.010659 to (13)C/(12)C =0.011601), and therefore, it is suitable for the measurement of carbon isotope amount ratios within the natural range of variation of organic carbon compounds, carbonates, elemental carbon, carbon monoxide, and carbon dioxide. In addition, a CO2 gas sample previously characterized in-house by conventional dual inlet isotope ratio mass spectrometry has been analyzed and excellent agreement has been found between the carbon isotope amount ratio value measured by MC-ICPMS and the IRMS measurements. Absolute values for carbon isotope amount ratios traceable to the SI are given for each NIST RM, and the combined uncertainty budget (including instrumental error and each parameter contributing to Russell expression for mass bias correction) has been found to be < 0.1% for the four materials. The advantage of the method versus conventional gas source isotope ratio mass spectrometry measurements is that carbon isotope amount ratios are measured as C(+) instead of CO2(+), and therefore, an oxygen (17)O correction due to the presence of (12)C(17)O(16)O(+) is not required. Organic compounds in solution can be measured without previous derivatization, combustion steps, or both, thus making the process simple. The novel methodology opens new avenues for the measurement of absolute carbon isotope amount ratios in a wide range of samples.     

Validation of RF power standard in the frequency range of 100 MHz to 18 GHz by an inter laboratory data comparison

Radio frequency (RF) power is one of the most important quantities in RF metrology. An inter laboratory data comparison of RF power for the validation of a coaxial microcalorimeter has been carried out between Physikalisch-Technische Bundesanstalt (PTB-Germany) and National Physical Laboratory India (NPLI). A coaxial thermistor mount equipped with type N connector is used for this intercomparison. The results show good agreement in measuring the effective efficiency of the coaxial thermistor mount between the two laboratories within their claimed expanded uncertainty. It confirms the equivalence of national standards for RF power in the frequency range of 100 MHz to 18 GHz.     

Calibration and Use of a Reference Standard Directional Coupler for Measurement of Large Coupling Factors

Fixed frequency, point-by-point calibration is outlined for a reference standard directional coupler to be used in steppedfrequency measurement of 40-dB, or greater, coupling factors of directional couplers. If a reference directional coupler has a 40-dB coupling factor, a main-line waveguide output, and a sexless coaxial side-arm output, the best accuracy obtainable in measurement of its coupling factor is estimated to be ±0.03 dB.     

Details of the 1998 Watt Balance Experiment Determining the Planck Constant

The National Institute of Standards and Technology (NIST) watt balance experiment completed a determination of Planck constant in 1998 with a relative standard uncertainty of 87 × 10⁻⁹ (k = 1), concurrently with an upper limit on the drift rate of the SI kilogram mass standard. A number of other fundamental physical constants with uncertainties dominated by this result are also calculated. This paper focuses on the details of the balance apparatus, the measurement and control procedures, and the reference calibrations. The alignment procedures are also described, as is a novel mutual inductance measurement procedure. The analysis summary discusses the data noise sources and estimates for the Type B uncertainty contributions to the uncertainty budget. Much of this detail, some historical progression, and a few recent findings have not been included in previous papers reporting the results of this experiment.     

Assessment of Uncertainties for the NIST 1016 mm Guarded-Hot-Plate Apparatus: Extended Analysis for Low-Density Fibrous-Glass Thermal Insulation

An assessment of uncertainties for the National Institute of Standards and Technology (NIST) 1016 mm Guarded-Hot-Plate apparatus is presented. The uncertainties are reported in a format consistent with current NIST policy on the expression of measurement uncertainty. The report describes a procedure for determination of component uncertainties for thermal conductivity and thermal resistance for the apparatus under operation in either the double-sided or single-sided mode of operation. An extensive example for computation of uncertainties for the single-sided mode of operation is provided for a low-density fibrous-glass blanket thermal insulation. For this material, the relative expanded uncertainty for thermal resistance increases from 1 % for a thickness of 25.4 mm to 3 % for a thickness of 228.6 mm. Although these uncertainties have been developed for a particular insulation material, the procedure and, to a lesser extent, the results are applicable to other insulation materials measured at a mean temperature close to 297 K (23.9 °C, 75 °F). The analysis identifies dominant components of uncertainty and, thus, potential areas for future improvement in the measurement process. For the NIST 1016 mm Guarded-Hot-Plate apparatus, considerable improvement, especially at higher values of thermal resistance, may be realized by developing better control strategies for guarding that include better measurement techniques for the guard gap thermopile voltage and the temperature sensors.     

Permittivity and permeability measurements using striplineresonator cavities-a comparison

The permittivity and permeability of five materials were measured during a comparison of the stripline resonator cavity technique. The National Institute of Standards and Technology (NIST) organized this intercomparison in which a total of seven organizations participated. Each participant measured two dielectric materials and three magnetic materials. Results for this comparison suggest that when the stripline resonator is used, dielectric property measurements are not as accurate as magnetic property measurements, provided that a correction for demagnetization is made. The results are compared to 7 mm coaxial transmission line measurements which have an uncertainty of less than 10% for the relative permittivity, ϵ_r'<15     

Use of the Electrostatic Classification Method to Size 0.1 μm SRM Particles—A Feasibility Study

The use of the electrostatic classification method for sizing monodisperse 0.1 μm polystyrene latex (PSL) spheres has been investigated experimentally. The objective was to determine the feasibility of using electrostatic classification as a standard method of particle sizing in the development of a 0.1 μm particle diameter Standard Reference Material (SRM). The mean particle diameter was calculated from a measurement of the mean electrical mobility of the PSL spheres as an aerosol using an electrostatic classifier. The performance of the classifier was investigated by measuring its transfer function, conducting a sensitivity analysis to verify the governing theoretical relationships, measuring the repeatability of particle sizing, and sizing NIST SRM 1691, 0.269 μm and NIST SRM 1690, 0.895 μm particles. Investigations of the aerosol generator’s performance focused on the effect of impurities in the particle-suspending liquid on the resulting particle diameter.The uncertainty in particle diameter determined by electrical mobility measurements is found to be −3.3% to +3.0%. The major sources of uncertainty include the flow measurement, the slip correction, and a dependence of particle size on the aerosol flow rate. It was found that the classifier could be calibrated to indicate the correct size to within 0.1% for both SRM particle sizes if the defined classification length is decreased by 1.9%.     

An automated guarded bridge system for the comparison of 10kΩ standard resistors

An automated guarded resistance bridge has been specifically developed at the National Institute of Standards and Technology (NIST) for the calibration of high-quality 10 kΩ standard resistors. The system is designed to compare up to 30 nominally equal, four-terminal resistors with a resolution and combined relative standard uncertainty of 0.01×10^-6 and 0.02×10^-6, respectively. It features a self-balancing detector circuit, and a programmable coaxial connector switch for selecting resistors. With a few minor modifications, the system is capable of comparing other nominally equal resistors in the range 100 Ω to 1 MΩ