Instrumental Error Sources Research Articles

INVESTIGATION OF THE TEMPERATURE ERROR OF COORDINATE MEASURING MACHINES

Coordinate measuring machines are widely used for technological control of geometric parameters of the surface of various parts in many branches of industrial production. For coordinate measurements of high-precision surfaces, instrumental sources of error can be minimized if the axes of the controlled object are located on the same axis of the reference scale of the comparator or parallel to it. However, in all schemes of construction of coordinate measuring machines, the Abbe principle is violated, which leads to the appearance of a measurement error, which, moreover, increases with the increase in the overall dimensions of the coordinate machine. It is determined that the total error can be determined taking into account two factors: the maximum allowable error calculated without taking into account the temperature variations of the measured object itself; the temperature change of the measured object. It is shown that the resulting error of coordinate measuring machines can be investigated on the basis of the optimization problem of calculating the optimal form of the function of the temperature dependence of the object on time. It is shown that the resulting error integrated in time will reach a minimum value if the temperature dependence functions of the measured object T(t) and the coefficient of thermal expansion α(t) change synchronously in time. Therefore, in order to minimize the error of coordinate measuring machines from changes in time of such indicators as T and α must occur synchronously, i.e. their change in time must satisfy the corresponding certain condition. To quantify the gain in optimizing measurements, we will conduct a model study. To estimate the gain in reducing the error, two model functions have been compiled, the integrals of which, according to a certain condition, must be equal to the integral of the calculated coupling function. It is shown that according to the calculation, the lowest estimate of the reduction of the measurement error with the proposed optimization will be 4.5 %.

Тhe error of a standard air flow velocity measurement procedure in wind tunnels of low subsonic speeds

The standard air flow velocity measurement procedure has been developed in order to unify and standardize the measuring instruments used and data processing algorithms, reduce the development time and certify such standard methods. Sources of error in indirect measurements of air flow velocity in the range 3–105 m/s are investigated. The sources of instrumental error of indirect measurements are analyzed – pressure sensors with digital and analog output signals, pitot tube, temperature and relative air humidity sensors, atmospheric pressure sensors. It is shown that the greatest contribution to the instrumental error is made by measuring the pressure difference and atmospheric pressure. The errors of method, which depends on the measurement model, is considered. A new mathematical model of measurements is proposed, which includes optimal expressions for determining the density of moist air and corrections for compressibility and allows to reduce the methodological error, and requirements for the metrological characteristics of the measuring instruments used are developed, ensuring that the total error of indirect measurements of the flow velocity complies with the allowable limits of ±0,2 m/s. Recommendations are given on the use of measuring instruments and algorithms for processing measurement results, which make it possible to reduce the measurement error by 39 % and develop a standard air flow velocity measurement procedure. The standard procedure is relevant for aviation industry enterprises, where the air flow rate is measured by the pneumometric method.

Digitization of imaging plates from Guinier powder X-ray diffraction cameras.

A Guinier camera equipped with an imaging plate is used to investigate and eliminate the sources of instrumental errors affecting the quality of the obtained scanned Guinier data. A program with a graphical user interface is presented which converts the data of the scanned images into different standard file formats for powder X-ray patterns containing intensities, their standard deviations and the diffraction angles. The program also allows for manual and automatic correction of the 2θ scale against a known reference material. It is shown using LaB6 that the exported X-ray diffraction patterns provide a 2θ scale reproducible enough to allow for averaging diffractograms obtained from different exposures of the imaging plate for the same sample. As shown on a mixture of NaCl and sodalite, the quality of the produced data is sufficient for Rietveld refinement. The software including source code is made available under a free software license.

Generalized error-dependent prediction uncertainty in multivariate calibration

Most of the current expressions used to calculate figures of merit in multivariate calibration have been derived assuming independent and identically distributed (iid) measurement errors. However, it is well known that this condition is not always valid for real data sets, where the existence of many external factors can lead to correlated and/or heteroscedastic noise structures. In this report, the influence of the deviations from the classical iid paradigm is analyzed in the context of error propagation theory. New expressions have been derived to calculate sample dependent prediction standard errors under different scenarios. These expressions allow for a quantitative study of the influence of the different sources of instrumental error affecting the system under analysis. Significant differences are observed when the prediction error is estimated in each of the studied scenarios using the most popular first-order multivariate algorithms, under both simulated and experimental conditions.

The Thirty Gigahertz Instrument Receiver for the QUIJOTE Experiment: Preliminary Polarization Measurements and Systematic-Error Analysis.

This paper presents preliminary polarization measurements and systematic-error characterization of the Thirty Gigahertz Instrument receiver developed for the QUIJOTE experiment. The instrument has been designed to measure the polarization of Cosmic Microwave Background radiation from the sky, obtaining the Q, U, and I Stokes parameters of the incoming signal simultaneously. Two kinds of linearly polarized input signals have been used as excitations in the polarimeter measurement tests in the laboratory; these show consistent results in terms of the Stokes parameters obtained. A measurement-based systematic-error characterization technique has been used in order to determine the possible sources of instrumental errors and to assist in the polarimeter calibration process.

Correcting Systematic Polarization Effects in Keck LRISp Spectropolarimetry to < 0.05%

Spectropolarimetric measurements at moderate spectral resolutions are effective tracers of stellar magnetic fields and circumstellar environments when signal-to-noise ratios (S/Ns) above 2000 can be achieved. The LRISp spectropolarimeter is capable of achieving these S/Ns on faint targets with the 10 m aperture of the Keck telescope, provided several instrumental artifacts can be suppressed. We describe here several methods to overcome instrumental error sources that are required to achieve these high S/Ns on LRISp. We explore high S/N techniques such as defocusing and slit-stepping during integration with high spectral and spatial oversampling. We find that the instrument flexure and interference fringes introduced by the achromatic retarders create artificial signals at 0.5% levels in the red channel which mimic real stellar signals and limit the sensitivity and calibration stability of LRISp. Careful spectral extraction and data filtering algorithms can remove these error sources. For faint targets and long exposures, cosmic ray hits are frequent and present a major limitation to the upgraded deep depletion red-channel CCD. These must be corrected to the same high S/N levels, requiring careful spectral extraction using iterative filtering algorithms. We demonstrate here characterization of these sources of instrumental polarization artifacts and present several methods used to successfully overcome these limitations. We have measured the linear to circular cross-talk and find it to be roughly 5%, consistent with the known instrument limitations. We show spectropolarimetric signals on brown dwarfs are clearly detectable at 0.2% amplitudes with sensitivities better than 0.05% at full spectral sampling in atomic and molecular bands. Future LRISp users can perform high-sensitivity observations with high-quality calibration when following the described algorithms.

Calibration with specified accuracy of triaxial block of navigation accelerometers on the uniaxial rotary stand.

The paper is devoted to solving the problem of calibration with specified precision of triaxial block of navigation accelerometers on the uniaxial rotary stand.In paper introduced all the characteristics, for calibration of triaxial block of navigation accelerometers on the uniaxial rotary stand, instrumental error sources upon which was obtained mathematical errors model of calibration. This model allows to calculate the error which the coefficients of metrology model of triaxial accelerometer unit was identified, if we have the numerical values of precision equipment errors.Using the mathematical errors model of calibration, and the quality criterion of calibration of triaxial block of navigation accelerometers unit, were obtained inequality that used to determine requirements for accuracy characteristics bench equipment, on which the calibration is performed. These requirements ensure the calibration of triaxial block of navigation accelerometers on the uniaxial rotary stand with preset accuracy.Experimental verification was conducted on comparable accuracy errors existing equipment and the requirements to this equipment , confirm the adequacy of the obtained inequalities.As the result of research were identified the most influential sources of instrumental errors, and provided recommendations to reduce their impacts.

Temperature-dependent air broadening of water in the 1250–1750 cm−1 range

A Bruker IFS 120 HR Fourier-transform spectrometer has been used to investigate air broadening of water vapor at a spectral resolution of 3×10−3cm−1 in the wavenumber range 1250–1750cm−1. A new method for generating water vapor/air mixtures employing a 800l stainless steel mixing vessel and a steady flow through the absorption cell has been developed. A total of 46 measurements have been recorded, 33 (26 water+air, 7 pure water) of which have been used in the final analysis. The measurements covered the temperature range 205–315K, total air pressure range 50–1000mb, water partial pressure range 0.001–5mb, absorption path range 16–8500cm and provided sufficient redundancy. Transmittance spectra corrected for various instrumental error sources were used in an automated single spectrum fit line parameter retrieval based on the Voigt profile. Average gas temperatures were fitted from retrieved water line strengths. From the retrieved Lorentzian line widths of each individual transition the air and self-broadening parameters and temperature exponents, γair, γself, nair, nself, or a subset thereof were fitted in an automated procedure. Various methods for validation of data product accuracy and data reduction model as well as comprehensive error analysis were applied. In total 593 γair, 459 nair and 469 γself values are reported, uncertainties for γair are given for reference temperatures 296 and 220K. Only data are reported where the γair uncertainty is <2% or the γair,220K uncertainty is <5%. The average uncertainties for γair, γair,220K, nair, and γself are 0.7%, 2.2%, 0.07, and 3%, respectively. Comparisons with recent experimental work and HITRAN 2004 and HITRAN 2008 are presented.

Mathematical modeling of the accuracy characteristics in problems of precision quantum tomography of biphoton states

A model that approximately takes into account instrumental errors in problems of precision reconstruction of quantum states is considered. The model is based on the notion of coherence volume, which characterizes the quality of the experimental and technological realization of the measurement protocol of a quantum state. Various sources of instrumental errors that affect the reconstruction accuracy of quantum states are mathematically modeled. It is shown that, for precision tomography of quantum states, one should take into account random coincidences that occur because the operating time of the photon detection system is finite. Among other possible sources of instrumental errors of the measurement protocol, one should take into account errors of the rotation angles and optical thicknesses of polarization plates, a possible drift in the parameters of the pump laser, and so on.

Immunoassay as an Analytical Tool in Agricultural Biotechnology

Immunoassays for biotechnology engineered proteins are used by AgBiotech companies at numerous points in product development and by feed and food suppliers for compliance and contractual purposes. Although AgBiotech companies use the technology during product development and seed production, other stakeholders from the food and feed supply chains, such as commodity, food, and feed companies, as well as third-party diagnostic testing companies, also rely on immunoassays for a number of purposes. The primary use of immunoassays is to verify the presence or absence of genetically modified (GM) material in a product or to quantify the amount of GM material present in a product. This article describes the fundamental elements of GM analysis using immunoassays and especially its application to the testing of grains. The 2 most commonly used formats are lateral flow devices (LFD) and plate-based enzyme-linked immunosorbent assays (ELISA). The main applications of both formats are discussed in general, and the benefits and drawbacks are discussed in detail. The document highlights the many areas to which attention must be paid in order to produce reliable test results. These include sample preparation, method validation, choice of appropriate reference materials, and biological and instrumental sources of error. The article also discusses issues related to the analysis of different matrixes and the effects they may have on the accuracy of the immunoassays.

How to Improve Quality Assurance in Fluorometry: Fluorescence-Inherent Sources of Error and Suited Fluorescence Standards

The scope of this paper is to illustrate the need for an improved quality assurance in fluorometry. For this purpose, instrumental sources of error and their influences on the reliability and comparability of fluorescence data are highlighted for frequently used photoluminescence techniques ranging from conventional macro- and microfluorometry over fluorescence microscopy and flow cytometry to microarray technology as well as in vivo fluorescence imaging. Particularly, the need for and requirements on fluorescence standards for the characterization and performance validation of fluorescence instruments, to enhance the comparability of fluorescence data, and to enable quantitative fluorescence analysis are discussed. Special emphasis is dedicated to spectral fluorescence standards and fluorescence intensity standards.

Retrieving sea surface salinity with multiangular L‐band brightness temperatures: Improvement by spatiotemporal averaging

The Soil Moisture and Ocean Salinity (SMOS) mission was selected in May 1999 by the European Space Agency to provide global and frequent soil moisture and sea surface salinity maps. SMOS' single payload is Microwave Imaging Radiometer by Aperture Synthesis (MIRAS), an L band two‐dimensional aperture synthesis interferometric radiometer with multiangular observation capabilities. Most geophysical parameter retrieval errors studies have assumed the independence of measurements both in time and space so that the standard deviation of the retrieval errors decreases with the inverse of square root of the number of measurements being averaged. This assumption is especially critical in the case of sea surface salinity (SSS), where spatiotemporal averaging is required to achieve the ultimate goal of 0.1 psu error. This work presents a detailed study of the SSS error reduction by spatiotemporal averaging, using the SMOS end‐to‐end performance simulator (SEPS), including thermal noise, all instrumental error sources, current error correction and image reconstruction algorithms, and correction of atmospheric and sky noises. The most important error sources are the biases that appear in the brightness temperature images. Three different sources of biases have been identified: errors in the noise injection radiometers, Sun contributions to the antenna temperature, and imaging under aliasing conditions. A calibration technique has been devised to correct these biases prior to the SSS retrieval at each satellite overpass. Simulation results show a retrieved salinity error of 0.2 psu in warm open ocean, and up to 0.7 psu at high latitudes and near the coast, where the external calibration method presents more difficulties.

Polymerase Chain Reaction Technology as Analytical Tool in Agricultural Biotechnology

The agricultural biotechnology industry applies polymerase chain reaction (PCR) technology at numerous points in product development. Commodity and food companies as well as third-party diagnostic testing companies also rely on PCR technology for a number of purposes. The primary use of the technology is to verify the presence or absence of genetically modified (GM) material in a product or to quantify the amount of GM material present in a product. This article describes the fundamental elements of PCR analysis and its application to the testing of grains. The document highlights the many areas to which attention must be paid in order to produce reliable test results. These include sample preparation, method validation, choice of appropriate reference materials, and biological and instrumental sources of error. The article also discusses issues related to the analysis of different matrixes and the effect they may have on the accuracy of the PCR analytical results.

Validation of multi-element isotope dilution ICPMS for the analysis of basalts.

In this study we have validated a newly developed multi-element isotope dilution (ID) ICPMS method for the simultaneous analysis of up to 12 trace elements in geological samples. By evaluating the analytical uncertainty of individual components using certified reference materials we have quantified the overall analytical uncertainty of the multi-element ID ICPMS method at 1-2%. Individual components include sampling/weighing, purity of reagents, purity of spike solutions, calibration of spikes, determination of isotopic ratios, instrumental sources of error, correction of mass discrimination effect, values of constants, and operator bias. We have used the ID-determined trace elements for internal standardization to improve indirectly the analysis of 14 other (mainly mono-isotopic trace elements) by external calibration. The overall analytical uncertainty for those data is about 2-3%. In addition, we have analyzed USGS and MPI-DING geological reference materials (BHVO-1, BHVO-2, KL2-G, ML3B-G) to quantify the overall bias of the measurement procedure. Trace element analysis of geological reference materials yielded results that agree mostly within about 2-3% relative to the reference values. Since these results match the conclusions obtained by the investigation of the overall analytical uncertainty, we take this as a measure for the validity of multi-element ID ICPMS.

Multilateration with the wide-angle laser ranging system: ranging performance and first ground-based validation experiment

A wide-angle laser ranging system has been developed for high-precision multilateration. A laser transmits short pulses in a widely diverging beam toward a network of cube-corner retroreflectors (CCRs). Returned echoes are detected, amplified, digitized, and timed. Impact of instrumental error sources, atmospheric refraction, and scintillation are discussed. The precision of the correlation method for the estimation of times of arrival and a least-squares adjustment method for the estimation of relative CCR coordinates is studied. Data from several ground-based experiments are analyzed. The positioning precision achieved is of 1-2.3 mm in relative radial coordinates and 1.8-3.8 cm in relative transverse coordinates. Results are consistent with a covariance analysis, demonstrating that, as follows: 1) systematic instrumental errors are well corrected; 2) outliers arising from coincident echoes are properly detected; 3) models for forward and inverse problems and estimation techniques are correct. A numerical simulation program based on these models and techniques can be used for optimizing instrumental aspects, providing extensive simulations in various conditions and processing data from future airborne experiments to which the system is devoted.

Simulations of liquid chromatography-diode array detector data including instrumental artefacts for the evaluation of mixture analysis techniques

The application of mixture analysis techniques to liquid chromatography-diode array detector (LC-DAD) data can be hampered by instrumental artefacts. If not properly accounted for, these artefacts may create major problems in the interpretation of the results by introducing additional factors in the analysis that can be difficult to distinguish from minor chemical components. In this paper, we show how the main sources of instrumental errors can be identified and how their effect can be mimicked by a specifically designed simulation procedure. Such realistic simulations are then successfully used to anticipate the expected response for an homogeneous peak even under non-ideal conditions, and hence to facilitate unequivocal interpretation of results.

Real and virtual unipolar regions

Difficulties in relating magnetograph measurements to the actual solar magnetic field are discussed. After a brief review both of problems inherent in the nature of the measurements and of sources of instrumental error, we show that field measurements taken within the photosphere can map out large-scale regions of a single magnetic polarity even though these regions contain no footpoints of large-scale magnetic structures, but instead only aggregates of small, unresolved bipoles. This may occur wherever the density of unresolved bipoles has a preferred orientation and a spatial variation along the direction of that orientation. We call these regionsvirtual unipolar regions, as they are not connected to regions of opposite polarity by field loops or lines passing through the corona. Investigation of these regions shows that they can arise at widely separated locations, and that they may evolve into real unipolar magnetic regions which are connected to the chromospheric and coronal fields. These results can explain a number of puzzling aspects of magnetograph observations of the solar background magnetic field.

Some instrumental effects in the determination of stable carbon isotope ratios by gas chromatography-isotope ratio mass spectrometry

Some sources of instrumental errors in the determination of13C/12C in organic compounds by gas chromatography-isotope ratio mass spectrometry (GC-IRMS) have been investigated. For mass 44 ion beam intensities in the range 1·10−10 to 1·10−8 A, mass-spectrometric pressure effects do not significantly affect data accuracy, thus obviating the necessity of matching sample and reference ion beam intensities for each compound in a complex sample. Data quality is influenced by: (a) the quality of the furnace-tube packing; and (b) the performance of the cryogenic trap. On analysis of large (70 ng) samples, precisions (1σ) of⩽ ± 0.23‰ were obtained using 0.35–0.5-mm-grade CuO. However, there was a marked deterioration in precision (1σ⪯ ± 0.62) when coarse CuO (0.35–1 mm grade) was tested. Use of fine CuO also permits analysis of smaller samples. Inefficient trapping, and release of water during overnight defrosting leads to erroneously lowδ13C-values, accuracies of −1.1 to −0.25‰ resulting from analysis of 70-ng samples. Accuracy error increases to⩽1.86‰ on analysis of 10-ng samples. Efficient water trapping combined with the improvements in furnace performance results in precisions generally much better than±0.4‰ and accuracies better than±0.65‰ for high-molecular-weight compounds (268–338 amu), and very accurate and precise results (better than±0.2‰) for lower-molecular-weight compounds (142–173 amu).

Field measurement of reflectance: some major considerations

Success in determining when, whether, and in what conditions to acquire remote sensing data for describing a given target (e.g., vegetation) is contingent on understanding the reflectance properties of the target and its surroundings. Unfortunately, relatively little information on the reflectance properties of the earth's surface exists in the literature. Field measurements of a target's reflectance are usually made with single-beam instruments by sequentially viewing the target and a white standard reflector, which is assumed to be Lam-bertian. Because variations in atmospheric transmission can occur between the times of measuring the target and reflector, substantial errors in reflectance calculated from these measurements may result. To avoid these errors the irradiance on and radiance from the target must be measured simultaneously. Measurements of the spectral hemispherical-conical reflectance of vegetative canopies were made by simultaneously measuring irradiance and radiance with pairs of portable spectroradiometers. The procedures for calibrating the instruments and for collecting and analyzing spectral reflectance data are described. Major instrumental sources of error and their magnitude are discussed as are problems involved in making such measurements.

Flow cytometric measurement of the polarization of fluorescence from intracellular fluorescein in mammalian cells

Based on the description of a laboratory-built flow cytometer, the necessary modifications of this instrument for the measurement of fluorescence polarization are described. At a maximum rate exceeding 1,000 cells/s, the instrument is capable of measuring simultaneously the horizontally and vertically polarized component of the fluorescence emitted from stained cells excited with vertically polarized light. By mathematical analysis of the accumulated data, the distribution of polarization values in the population is obtained. Various sources of instrumental error have been investigated. The large aperture of the detector optics leads to systematic underestimation of the polarization values. Other errors are negligible, and the instrument is shown to give results consistent with the theory of fluorescence polarization. Application of the instrument is illustrated by experiments with mammalian cells exposed to the fluorogenic substrate fluorescein diacetate (FDA). The polarization of the fluorescence from intracellular fluorescein produced by hydrolysis of FDA is measured, giving information on the cytoplasmic microviscosity. It appears that this microviscosity is constant over the cell cycle. On the other hand, it is significantly affected by the osmolarity of the medium.