共查询到20条相似文献,搜索用时 31 毫秒
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为了准确评估X射线剂量监测用防护仪表的校准因子的不确定度,依据有关技术规范,用标准电离室对参考点位置处的剂量当量率参考值进行测量;采用替代法获得待校仪表的显示值,从而确定校准因子结果的相关影响因素,并分别对影响量的不确定度进行评定;得出仪表校准因子的相对扩展不确定度为5.0%(k=2)。影响校准因子不确定度的主要来源包括校准用辐射场的均匀性、标准电离室本身的刻度因子及能量响应、剂量当量转换因子、待检仪表显示值的统计标准偏差等。在对该类仪表的校准过程中,通过提高标准参考值的不确定度水平可以改善校准因子的不确定度。 相似文献
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J.M. Hidalgo 《Vacuum》2008,82(11):1151-1156
A study of the calibration of leaks by comparison with reference standard leaks calibrated at a National Metrology Laboratory is presented. The simplicity and efficiency of the method make it suitable for calibrations of leaks carried out at the industrial level. A commercial leak tester equipped with a mass spectrometer tuned to helium is used for the comparison. The main origins of uncertainties and their contributions to the expanded uncertainty are presented. In particular, discussion is devoted to the long-term stability, shift, or depletion of the reference standard leaks and the resulting impact on the expanded uncertainty. Results of application of the procedure for calibration of a leak of similar metrological characteristics to the reference standard leaks are also presented. 相似文献
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J. F. Song F. F. Rudder Jr. T. V. Vorburger J. H. Smith 《Journal of research of the National Institute of Standards and Technology》1995,100(5):543-561
National and international comparisons in Rockwell hardness tests show significant differences. Uncertainties in the geometry of the Rockwell diamond indenters are largely responsible for these differences. By using a stylus instrument, with a series of calibration and check standards, and calibration and uncertainty calculation procedures, we have calibrated the microform geometric parameters of Rockwell diamond indenters. These calibrations are traceable to fundamental standards. The expanded uncertainties (95 % level of confidence) are ±0.3 μm for the least-squares radius; ±0.01° for the cone angle; and ±0.025° for the holder axis alignment calibrations. Under ISO and NIST guidelines for expressing measurement uncertainties, the calibration and uncertainty calculation procedure, error sources, and uncertainty components are described, and the expanded uncertainties are calculated. The instrumentation and calibration procedure also allows the measurement of profile deviation from the least-squares radius and cone flank straightness. The surface roughness and the shape of the spherical tip of the diamond indenter can also be explored and quantified. Our calibration approach makes it possible to quantify the uncertainty, uniformity, and reproducibility of Rockwell diamond indenter microform geometry, as well as to unify the Rockwell hardness standards, through fundamental measurements rather than by performance comparisons. 相似文献
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G. P. Eppeldauer 《Mapan》2009,24(3):193-202
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). 相似文献
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本文介绍了基于放大率和分辨率测定校准裂隙灯显微镜的方法,在对总放大率误差、左右放大率相对误差校准的基础上,对影响裂隙灯显微镜成像质量的分辨率和裂隙像尺寸进行校准,建立了可溯源到国家长度基准的裂隙灯显微镜的校准装置,分析了上级定标和自身装置的不确定度来源。该装置的测量结果的相对扩展不确定度为1. 7%,基本满足目前裂隙灯显微镜的校准要求。 相似文献
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在350kHz~30MHz频段内,为了准确得到环天线所处位置的场强,环天线的天线系数需要校准。三天线法是一种校准天线系数的绝对方法,需要3个环天线,两两组对测量,且不需要任何参考标准。介绍了三天线法校准环天线的原理,基于矢量网络分析仪建立校准系统,并评定校准系统的测量结果不确定度。基于K(i,j)的计算公式复杂,很难计算出其引入的不确定度,因此采用数字电磁学代码(NEC)建模评定K(i,j)的不确定度。评定结果表明,在350kHz~30MHz频段内4个典型频点的扩展不确定度小于0.81dB(k=2)。 相似文献
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针对频域信道测量中测量仪器引入的不确定度进行了深入分析。矢量网络分析仪是频域信道测量中最重要的测量仪器,测量前必须进行自校准。深入分析不同校准方法所引入的测量不确定度是合理选择自校方法的量化依据。测量不确定度分析基于蒙特卡洛法。由于在频域信道测量中需要对多个频点进行测量,而各频点间的测量结果存在较强的相关性,因此在应用蒙特卡洛法的基础上引入了基于协方差矩阵的分析方法,从而考虑了相关性的影响,给出了更为准确合理的不确定度分析,最终有效地指导了自校方法的合理选择。实验表明,是否考虑相关性,对信道参数的测量不确定度有较大影响。基于对测量不确定度的定量分析,可以得出直通校准是更适合于信道测量的矢网自校准方法的结论。 相似文献
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防护水平电离室剂量计是辐射防护的主要计量器具,需要在窄谱参考辐射质下进行检定和校准。利用EGSnrc软件模拟了参考辐射质X射线能谱,分析得到的能谱分辨率和平均能量与ISO 4037-1推荐值的最大偏差分别为7.1%和1.04%,均满足规范要求。依托60~250kV X射线空气比释动能国家基准装置,在窄谱系列参考辐射质下完成了距离X光机1m处参考点的空气比释动能量值复现;然后通过替代法对两个传递电离室进行校准并完成量值传递;最后利用传递电离室复现的2.25m处的空气比释动能率对PTW-32002球形电离室进行校准,获得相应的校准因子,校准因子相对扩展不确定度为2.2%(k=2)。 相似文献
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荧光量子效率是发射与吸收的光子数之比,是表征荧光材料发光性能的关键参数。然而,用于绝对法测量荧光量子效率的光路和探测器未经校准溯源或是校准方法不当,会造成测量光谱的不准确,进一步影响荧光量子效率计算结果的不准确。采用汞氩灯对单色仪进行校准,保证了激发波长和发射波长的准确性,利用标准辐射源对光路、发射单元单色仪和探测器进行光谱相对强度校准,保证了激发波段和发射波段光谱相对强度的准确性;最后从测量模型出发,对测量不确定度进行了分析,得到在300~360nm的激发光波段和370~900nm的发射光波段内相对合成标准不确定度为3.58%,相对扩展不确定度为7.16%,k=2。通过对单色仪波长校准以及对光谱相对强度进行校准,为荧光量子效率的准确测量提供了参考。 相似文献
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Jokela K. Hyysalo P. Puranen L. 《IEEE transactions on instrumentation and measurement》1998,47(2):432-438
The radiation safety tests for hand-held mobile phones require precise calibration of the small electric field probes used for the measurement of specific absorption rate (SAR) in phantoms simulating the human body. In this study, a calibration system based on a rectangular waveguide was developed for SAR calibrations at 900 MHz. The cross-sectional dimensions of the waveguide are a=190 mm and b=140 mm. The waveguide is loaded with a rectangular liquid slab where the dielectric parameters of the medium simulate human muscle and brain. The precise SAR reference is derived from the temperature rise during a short-term (10-15 s) microwave heating of the lossy slab by measuring with sensitive thermistor-type probes equipped with highly resistive lines. The thermistor probes are calibrated against a calibrated mercury thermometer. To improve the uniformity of the electric field at the calibration position, the thickness of the tissue equivalent slab was varied to adjust the standing wave pattern. This resulted in an almost threefold reduction in the positioning error of the E-field probe. The absolute uncertainty of the calibration is estimated to be ±5% (2σ) not including the uncertainty of the conductivity. The difference between the thermally measured SAR and a value computed with the FDTD method was well within this limit of uncertainty. This kind of closed waveguide system is more compact and requires less microwave power than open field calibration systems. Moreover, no radio-frequency interference is generated 相似文献
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The uncertainty of comparison calibrations is often limited by temperature gradients and the stability of the isothermal zone.
Traditionally, an equalizing block inserted into a bath or furnace is used to provide an isothermal zone during calibration.
In this paper, the design and performance of a multi-entrance fixed point (MEFP) filled with mercury is described, with the
goal to replace an equalizing block with the phase transition of mercury during melting/freezing. During this investigation,
three thermometers were calibrated against a standard in the same bath at − 39 ˚C, using both the standard equalizing block
and MEFP. The measurement results clearly indicate that use of MEFP decreases the uncertainty contributions from temperature
gradients and the stability of the bath by an order of magnitude compared to the standard equalizing block. 相似文献
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提出了一种太赫兹阵列探测器响应度校准溯源方法。首先,使用阵列探测器的每一像元对太赫兹辐照场中心进行逐一扫描,识别有效像元、死像元和过热像元,并对有效像元响应值进行归一化处理,获得阵列探测器的相对辐照度响应值。其次,使用中心像元对太赫兹辐照场进行扫描测量,扫描总面积大于太赫兹光斑尺寸,保证太赫兹功率被完整测量,获得中心像元与其他有效像元的太赫兹功率响应值。最后,用标准太赫兹功率计标定高莱功率计,扩展太赫兹功率校准量限,实现微瓦级太赫兹辐射功率测量溯源,用高莱功率计测得的太赫兹辐射源总功率对阵列探测器测得的积分响应值进行校准,得到阵列探测器辐照度响应绝对值。对探测器进行测量校准和不确定度分析,测得辐照度响应度的相对扩展不确定度为Urel=20%(k=2),测量结果可溯源至国家太赫兹辐射功率标准。 相似文献
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基于非正交轴系全站仪坐标测量系统的结构特点和测量模型,用数学分析的手段对其进行误差分析和测量不确定度评定。确定系统的主要误差分量是转台旋转角误差和激光跟踪仪测距值误差,并用GUM法评定各分量的不确定度。通过测量模型推导出系统的测量不确定度,并用MATLAB进行仿真,结果表明:当测距值不变时,测量不确定度几乎不受水平角变化的影响,而随着垂直角绝对值的增大而增大,当角度值不变时,测量不确定度随着被测点到视准轴上标定点的距离值增大而增大。实验初步验证了仿真结果的准确性。 相似文献