Strain measurement by optical correlation

The application of optical correlation measurements to evaluating elastic strain and plastic strain in metals is discussed in this paper. A selected area of the metal surface is illuminated by coherent light. The optical correlation intensity is then measured by transmitting light scattered from the surface through a holographic filter, in which information about the topography of the surface at an earlier time is stored. Changes in surface topography arising from rigid-body displacement, elastic strain, or plastic strain, respectively, cause corresponding changes in optical correlation intensity. Correlation changes arising from surface translation or rotation can be compensated for. An analysis of the process of holographic reconstruction from an elastically strained surface gives good agreement with the experimental results. The correlation technique is sensitive to elastic strains of the order of 10^–5 and to monotonic plastic strains of the order of 10^–4; the change in correlation intensity is essentially linear with increasing plastic strain, up to a maximum strain of about 10^–3.     

A new representation of power spectral density and correlation function by means of fractional spectral moments

In this paper, a new perspective for the representation of both the power spectral density and the correlation function by a unique class of function is introduced. We define the moments of order γ$\gamma$ (γ∈C$\gamma \in \mathbb{C}$) of the one sided power spectral density and we call them Fractional Spectral Moments (FSM). These complex quantities remain finite also in the case in which the ordinary spectral moments diverge, and are able to represent the whole Power Spectral Density and the corresponding correlation function.     

有效值法交流共模抑制比测量不确定度评定

为解决影响工业现场的数据采集系统精度的共模干扰问题,以波形分析方式研究了交流共模干扰的表现形式,揭示了其同时含有直流偏移叠加交流波动和本底噪声的典型特征。提出以波形有效值幅度进行干扰强度表征,并进行共模抑制比的定量表述;同时使用有效值叠加模型对系统本底噪声的影响予以剔除,提高了共模抑制比的测量精度。基于该方法与流程讨论了其主要的不确定度来源—信号源误差、数据采集系统增益误差、幅度测量误差、幅度分辨力误差以及测量重复性等。进行了测量不确定度分析和评价,结合实例给出了通道共模抑制比的不确定度评价结果,验证了所述方法的实用性与可行性。     

高精度分光光度计测量光谱透过率

由安光所自行设计的高精度分光光度计目的是高精度测量滤光片透过率。该系统特点是基于双光栅单色仪的全自动单光束测量仪器。在出射光路中引入了积分球,用来消除光束的偏振性和不均匀性,而且在信号接收部分提出了将滤光片和探测器作为整体考虑,优点是接近滤光片的实际使用环境,减少了其实际测量误差。着重叙述了该仪器的设计过程和不确定度分析。测量的不确定度源包括光源的稳定性,双单色仪重复性、再现性,光束的均匀性,内反射,探测器线性、稳定性、偏振性、均匀性,系统杂散光。经本仪器测量的滤光片透过率合成不确定度为5.859×10-3,完全满足测量精度要求。     

Gas detection by correlation spectroscopy employing a multimode diode laser

A gas sensor based on the gas-correlation technique has been developed using a multimode diode laser (MDL) in a dual-beam detection scheme. Measurement of CO(2) mixed with CO as an interfering gas is successfully demonstrated using a 1570 nm tunable MDL. Despite overlapping absorption spectra and occasional mode hops, the interfering signals can be effectively excluded by a statistical procedure including correlation analysis and outlier identification. The gas concentration is retrieved from several pair-correlated signals by a linear-regression scheme, yielding a reliable and accurate measurement. This demonstrates the utility of the unsophisticated MDLs as novel light sources for gas detection applications.     

High-accuracy spectrometer for measurement of regular spectral transmittance

A high-accuracy spectrometer has been developed for measuring regular spectral transmittance. The spectrometer is an automated, single-beam instrument that is based on a grating monochromator, reflecting optics, and an averaging sphere detector unit with a silicon photodiode. The uncertainties related to wavelength calibration, detector nonlinearity, system instability, beam displacement, polarization, stray light, interreflections, and beam uniformity are determined for the visible spectral range from 380 to 780 nm. A total uncertainty of 3 × 10(-4) (1σ) is estimated for transmittance measurements of homogeneous neutral-density filters. The uncertainty of the wavelength scale is 0.06 nm. As a specific application, calibration of V(λ)-correction filters is studied. To verify the accuracy of the transmittance measurements, a comparison of the measured and predicted transmittances of a sample of high-purity fused silica is made, revealing agreement at the 5 × 10(-4) level.     

Interferometric measurement of the modulation transfer function of a spectrometer by using spectral modulations

We present our results on measurement of the modulation transfer function (MTF) of a given spectrometer by using the sinusoidally modulated spectrum from a Michelson interferometer with white light. We studied the MTF by varying the periodicity of the spectral fringes produced by the interferometer. Experimental data are fitted to a theoretical model to derive the spectral slit width from the measured MTF of the spectrometer.     

Group delay dispersion measurement of a dispersive mirror by spectral interferometry: comparison of different signal processing algorithms

We built a dispersive white-light spectral interferometer for precisely measuring the dispersion properties of a multilayer thin-film structure. A novel algorithm with improved robustness to measurement errors is presented by combining a windowed Fourier transformation with wavelet-based differentiation. Compared with previously published algorithms, this method shows substantial resistance to measurement errors. The group delay dispersion properties of bulk materials and a homemade chirped mirror are measured by our apparatus, and the measurement result manifests considerable accuracy and robustness. The technique shows reasonable potential for the characterization of ultrabroadband chirped mirrors.     

Anisotropy of Gum Metal analysed by ultrasonic measurement and digital image correlation

ABSTRACT

The mechanical anisotropy of a multifunctional titanium alloy, Gum Metal, is investigated in this paper. The structural characterisation showed a strong <110> texture for Gum Metal, that is a result of the cold-swaging process applied during its manufacture. Gum Metal was treated as a transversally isotropic solid because of this texture. A significant difference from Young’s moduli of the alloy was detected from the ultrasonic measurement of parallel and perpendicular directions to the alloy swaging direction. Samples of Gum Metal cubes were compressed in two different orientations. During the deformation process, two perpendicular walls of each sample were monitored by two visible range cameras for further two-dimensional digital image correlation analysis, this confirmed a strong plastic anisotropy in Gum Metal.

This paper is part of a Thematic Issue on The Crystallographic Aspects of Metallic Alloys.     

Errors of correlation methods of signal-parameter measurement

Conclusions Periodic errors occur in the absence of noise but can be eliminated by choosing an integration time that is a multiple of half the repetition period. If the signal-to-noise ratio is 0.5, the periodic errors become irremovable, whereas the effects of the noise can be neglected for 2.Translated from Izmeritel'naya Tekhnika, No. 3, pp. 33–35, March, 1979.     

离子色谱仪最小检测浓度测量不确定度评定

以电导检测器为例,分析了离子色谱仪最小检测浓度的测量不确定度,并进行评定。不确定度的主要来源有基线噪声、测量重复性、进样体积和标准溶液浓度。     

X-ray spectral determination of gold in geological samples after its concentration by low-temperature fire assay

The technology of gold extraction to lead from its mixture with the sample powder during lowtemperature alkaline fusion is developed. The optimal ratios of masses for the sample, lead, and alkali, as well as heating conditions, temperature, and fusion duration, are determined for satisfactory gold recovery. A low temperature of fusion makes it possible to lighten the structure of furnaces, to decrease energy consumption, and to shorten the duration of the entire cycle from the beginning of fusion until the next set of crucibles is loaded. Using the modular approach, a furnace can be assembled in a small area for the simultaneous fusion of a great number of samples. The results of determining gold by the X-ray fluorescence method obtained by using the proposed concentration technology satisfy the regulatory requirements with respect to accuracy.     

Simultaneous measurement of foveal spectral reflectance and cone-photoreceptor directionality

An instrument for simultaneous measurement of foveal spectral reflectance and cone-photoreceptor directionality is described. The key element is an imaging spectrograph (spectral range of 420-790 nm) with its entrance slit conjugate to the pupil plane of a human eye. A 1.9-deg spot on the retina is sampled in 1 s. Video observation of the retina and the pupil facilitates proper alignment. Measurements were performed on 21 healthy subjects. Model analysis of the spectra provided densities of photostable ocular absorbers. As an example, macular pigment and melanin are discussed in more detail. Spatial profiles exhibited the optical Stiles-Crawford effect, reflecting cone-photoreceptor directionality.