Absolute Measurement Uncertainty Research Articles

Long‐Term Bias Stability of the GOES‐NOP Magnetometers

AbstractWe characterize the long‐term bias stability of the GOES‐NOP series magnetometers (GOES‐13, 14, and 15) using data from 2013 through 2018. Bias stability is inferred using three methods: comparing the inboard and outboard measurements on each spacecraft, comparing the individual measurements to the TS04 magnetic field model, and comparing measurements between different GOES‐NOP spacecraft. Comparisons between the inboard and outboard magnetometers demonstrate that GOES‐14 and GOES‐15 measurements are stable within approximately 1–2 nT. The GOES‐13 inboard magnetometer has known contamination issues that hinder a useful inboard/outboard comparison, but inter‐spacecraft comparisons with GOES‐14 and GOES‐15 indicate that the GOES‐13 outboard magnetometer is also stable to 1–2 nT. Direct comparisons of each measurement to the TS04 magnetic field model support the conclusion that there is little long‐term bias drift over the 6‐year period. Model uncertainty and the variability of the field at geostationary orbit create a noise floor that is similar to the variability of the magnetometer biases. While these relative comparisons do not provide absolute measurement uncertainty, they do constrain the stability of the observations, allowing for future absolute calibration of the DC bias through different methods.

Emissivity measurements on reflective insulation materials

Abstract The development and use of new thermal insulation products in many industrial sectors, ranging from building insulations to power generation or satellite applications, requires the accurate knowledge of the radiative properties of the investigated material, i. e. its emissivity. A major objective of the research project “Improvement of emissivity measurements on reflective insulation materials” within the framework of the European Metrology Programme for Innovation and Research was to improve and validate reference techniques for the measurement of the total hemispherical emissivity of low emissivity foils with an absolute measurement uncertainty below 0.03. The calibration and measurement procedures developed within this project shall lead to a significant benefit for industrial manufacturers of reflective foils as well as for the end-users of the industrial instruments used to characterize them.

Operation of X-ray gas monitors at the European XFEL.

X-ray gas monitors (XGMs) are operated at the European XFEL for non-invasive single-shot pulse energy measurements and average beam position monitoring. They are used for tuning and maintaining the self-amplified spontaneous emission (SASE) operation and for sorting single-shot experimental data according to the pulse-resolved energy monitor data. The XGMs were developed at DESY based on the specific requirements for the European XFEL. In total, six XGM units are continuously in operation. Here, the main principle and experimental setup of an XGM are summarized, and the locations of the six XGMs at the facility are shown. Pulse energy measurements at 0.134 nm wavelength are presented, exceeding 1 mJ obtained with an absolute measurement uncertainty of 7-10%; correlations between different XGMs are shown, from which a SASE1 beamline transmission of 97% is deduced. Additionally, simultaneous position measurements close to the undulator and at the end of the tunnel are shown, along with the correlation of beam position data simultaneously acquired by an XGM and an imager.

Top-down evaluation of matrix effects uncertainty

Many measurements in chemistry are affected by matrix effects responsible for larger deviation between results from the analysis of various matrices than observed from the replicate analysis of the same matrix. The identification of cases where matrix effects are relevant is useful to know if measurement robustness to matrix effects can significantly reduce the measurement uncertainty, e.g. by performing time-consuming standard addition calibrations or additional matrix clean-up. This work presents a methodology to estimate the percentage contribution of matrix effects to the measurement uncertainty by comparing the intermediate precision estimated from the analysis of a sample with the dispersion of analyte recovery observed form the analyses of samples with different matrices. The measurement model was divide in two intervals of the studied quantity: Interval I between the limit of detection and two times the limit of quantification, where the absolute measurement uncertainty is constant, and Interval II above or equal to two times the limit of quantification where the relative measurement uncertainty is constant. The division of measurements scope in these intervals allowed the comparison of information collected at different values of the studied quantity. The developed methodology was successfully applied to the analysis of total Cr, Cu, Li, Mn and Zn using a procedure developed by OSPAR and acid extractable Ni and Pb according to the EPA3051A standard in marine sediments. Matrix effects are responsible for 7.7 to 79% of the global uncertainty. For Interval II, the relative expanded uncertainty ranged from 12% to 25% and is fit for the environmental monitoring of sediments according to the way the performance of laboratories is assessed in QUASIMEME proficiency tests. The developed measurement uncertainty models produced results compatible with reference values of one Certified Reference Material and 65 proficient test samples independent of the ones used to estimate the measurement uncertainty. The used data and performed calculations are presented in a user-friendly MS-Excel spreadsheet, available as Electronic Supplementary Material, that can be used for other determinations.

Precise In-Process Strain Measurements for the Investigation of Surface Modification Mechanisms

The question, how certain surface layer properties (for example, hardness or roughness) can be specifically influenced in different manufacturing processes, is of great economic interest. A prerequisite for the investigation of the formation of surface layer properties is the metrological assessment of the material stresses during processing. Up to now, no commercial in-process measuring system exists, which is able to determine material stresses in the form of mechanical strains in high-dynamic manufacturing processes with sufficient accuracy. A detailed analysis of the resolution limits shows that speckle photography enables deformation measurements with a resolution in the single-digit nanometer range. Thus, speckle photography basically offers the potential to measure material stresses during processing. Using the example of single-tooth milling, the applicability of speckle photography for in-process stress measurements is demonstrated. Even in such highly dynamic manufacturing processes with cutting speeds up to 10 m/s, the absolute measurement uncertainty of the strain is less than 0.05%. This is more than one order of magnitude lower than the occurring maximal strain. Therefore, speckle photography is suitable for characterizing the dynamic stresses and the material deformations in manufacturing processes.

Airborne shape measurement of parabolic trough collector fields

As the optical efficiency of the solar field has a high impact on the overall performance and economics of a solar thermal power plant, qualification methods determining the geometrical accuracy of solar concentrator systems have gained high importance. However, it has not been possible yet to measure the geometrical accuracy of larger fractions of the solar field, resolving the relevant single characteristics like local mirror slope deviations, panel alignment and gravitational deformation. This paper describes the development and assessment of a measurement technique for the qualification of parabolic trough collector modules based on the distant observer method called TARMES (Trough Absorber Reflection Measurement System). Instead of a stationary camera at ground level taking pictures of a turning collector, the new approach called QFly makes use of an airborne camera vehicle which allows a completely automated and fast measurement of large numbers of collectors under relevant operating conditions. The new approach was validated against a stationary TARMES and photogrammetric measurement, supplemented by an extended uncertainty analysis. This analysis includes an assessment of the uncertainties of input parameters and their influence on measured local slope deviations. By applying a Monte Carlo approach, the effects on the RMS values of the local slope deviations of mirror panels and collector modules were investigated. Furthermore it includes an evaluation of the influence of the measurement sample rate. The results suggest an absolute measurement uncertainty for the RMS of slope deviations at module level of about ±0.1milliradians.

Spatio-temporal noise and drift in fiber optic distributed temperature sensing

Distributed temperature sensing (DTS) allows for simultaneous measurement at many remote locations along an optical fiber probe and is a valuable tool in a broad range of applications, such as downhole oil production, dike structural monitoring or fire protection. The specific requirements on spatial, temporal and temperature resolution and on absolute measurement uncertainty vary with the applications. We investigate the spatio-temporal noise and drift properties of two exemplary Raman backscatter DTS systems and discuss the effect of spatial and temporal data averaging. An Allan deviation analysis provides insight into the optimal degree of averaging for a given distance range along the fiber probe. A temperature calibration procedure is employed to retrieve the temperature sensitivity of the DTS system and to compensate for the systematic spatial slope of recorded DTS temperature measurement traces. In response to small temperature steps of a thermally homogeneous and stable water bath environment, we observe a temperature resolution of approximately 0.05 °C at a chosen 1000 m sampling distance along the fiber probe.

Further Generalization of the Low-Frequency True-RMS Instrument

<para xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> This paper shows that the use of random uniform dither in harmonic measurement can significantly shorten both the word of the input A/D converter and the word of the applied base function (sine and/or cosine, prestored in memory), without accuracy loss. This simplifies the hardware for a precise instrument for harmonic measurement. Theoretical considerations demonstrate that the upper limit of the absolute measurement uncertainty is identical for every harmonic coefficient. It is shown theoretically, by simulation, and by experiment that a 6-bit dithered A/D converter word, an 8-bit dithered base function word, and a 6 <formula formulatype="inline"><tex Notation="TeX">$\times$</tex> </formula> 8 (14-bit) multiplier word assure a measurement of 16 harmonics (16 sine and 16 cosine components) with 13-bit accuracy. The measurement of 1 <formula formulatype="inline"><tex Notation="TeX">$\times$</tex></formula> 16 harmonics is realized in a small programmable-logic-device (PLD) chip. </para>

A new high-aperture 193 nm microscope for the traceable dimensional characterization of micro- and nanostructures

A new deep UV transmission microscope for traceable micro- and nanometrology is currently being set up at the Physikalisch-Technische Bundesanstalt (PTB), the National Metrology Institute of Germany. The new microscope is especially designed to enable linewidth measurements of micro- and nanostructures with an unsurpassed absolute measurement uncertainty of down to 10 nm (95% confidence interval). The optical resolution is about 100 nm. The main field of this tool will be critical dimension (CD) metrology of photomasks used in optical lithography. In particular, this system offers the possibility of ‘at-wavelength’ metrology for the currently applied 193 nm lithography technology. The high lateral resolution will be attained by means of 193 nm excimer laser radiation for illumination in conjunction with a high-aperture objective (NA = 0.9). The illumination and imaging system will provide various imaging modalities, ranging from ordinary brightfield to specially structured illumination schemes. Traceability to the SI unit ‘meter’ will be accomplished by means of laser interferometry. The mechanical set-up is characterized by an ultra-stable bridge construction on a granite base and has been designed with special emphasis on realizing a positioning stability in the nanometer range. The instrument is being set up in the Clean Room Centre of the PTB and will be ready for operation in mid 2009. Simulation calculations, based on a rigorous optical modeling of the expected microscope images, are presented. These simulations are made for the important application of measuring Cr structures on quartz photomasks. Based on these simulations and on available data of the uncertainties of various experimental parameters—including instrument and sample parameters—expected uncertainty budgets for the measurement of the width of Cr lines on quartz substrates are estimated.

Solution to the chemical uncertainty principle challenge

This expression summarizes the relationship between both uncertainties relative and absolute (Fig. 1). One must remember that this expression describes the approximate trend, not the exact relationship. Nevertheless, the trend is obvious standard analytical practice cannot provide both low absolute uncertainty and low relative measurement uncertainty. The lower the absolute measurement uncertainty (error), the larger the relative measurement uncertainty and vice versa. Philosophically speaking, the very fact that the exponent in Eq. (1) is less than unity leads to an increase in the relative standard deviation as the amounts of analyte decreases. Mathematically this implies the existence of an “absolute zero” for analytical chemistry, a concentration at which reliable measurement is no longer practically possible. This level is reached at the relative measurement uncertainty of ∼66%. This is evident from the standard definition of the detection limit, γDL=3 s. Remember that u=2 s, therefore uR=2/3 at the classical detection limit (3 s). Combining the expressions uR=2/3 and uR≅0.020γ leads to: lg g ffi 10:1 or g ffi 1 10 10 0:1 ppb ð Þ