Related Measurement Uncertainty Research Articles

Uncertainty evaluation of small wear measurements on complex technological surfaces by machine vision-aided topographical methods

Wear assessment is an essential feature within the Industry 4.0 framework to optimise machining and control durability of components made of innovative materials. Complex topographies often make wear measurement a challenging task. Literature tackles it by comparing the final topography with the unworn state, either by empirical methods or by registration via machine vision algorithms. This paper develops a framework to evaluate the related measurement uncertainty, so far lacking, by exploiting instruments metrological characteristics and statistical modelling. This framework is applied to an industrially relevant case study to compare the performances of accredited methods for wear measurement available in literature.

Performance evaluation of a portable 3D imaging system

Portable 3D imaging systems are important tools used by industry for metrology, inspection, and reverse engineering. The Creaform HandySCAN 300 is a portable 3D imaging system that utilizes photogrammetry to orientate a handheld scanner relative to the part under test. The system does not have a well-defined coordinate system or a fixed measurement range and there currently exists a lack of normative standards suitable for evaluating the performance of such a system. We use the determination of sphere-to-sphere distances and the related measurement uncertainty as a proxy for evaluating the systems performance. The error sources of the imaging system were quantified and an improved measurement process that minimized errors was developed. A comparison between measurements by the HandySCAN 300 and a coordinate measuring machine showed good agreement with normalized errors of less than one.

Influence of the frequency response of the photodetector on the heterodyne interferometer-based sound pressure standards in water

The heterodyne interferometer has been used to realize the sound pressure unit directly and absolutely for underwater acoustics and ultrasound, which is considered as the primary standard of the hydrophone calibration instead of the reciprocity method. The widely used demodulation methods are the zero-crossing method and the arctangent method. Recent studies show that the frequency response of the utilized photodetector (PD) in the heterodyne interferometer also significantly influences the results of the sound pressure realization using the two demodulation methods, especially for the high-intensity focused ultrasound application, which is investigated in this paper. Simulations are performed to obtain general conclusions using different types of low-pass filters to simulate the nonideal frequency responses of the PD. Also, experimental results of the frequency response of the utilized PD are then used to analyze the induced relative error of the demodulated acoustic particle velocity so as to evaluate the related measurement uncertainty of the sound pressure realization. The simulation method is useful to choose the required PDs and evaluate the related measurement uncertainty induced by their frequency responses for the optical sound pressure standards and other optical measurement applications.

Quantitative traceable temperature measurement using novel thermal imaging camera.

Conventional thermal imaging cameras, based on focal-plane array (FPA) sensors, exhibit inherent problems: such as stray radiation, cross-talk and the calibration uncertainty of ensuring each pixel behaves as if it were an identical temperature sensor. Radiation thermometers can largely overcome these issues, comprising of only a single detector element that can be optimised and calibrated. Although the latter approach can provide excellent accuracy for single-point temperature measurement, it does not provide a temperature image of the target object. In this work, we present a micromechanical systems (MEMS) mirror and silicon (Si) avalanche photodiode (APD) based single-pixel camera, capable of producing quantitative thermal images at an operating wavelength of 1 µm. This work utilises a custom designed f-theta wide-angle lens and MEMS mirror, to scan +/- 30° in both x- and y-dimensions, without signal loss due to vignetting at any point in the field of view (FOV). Our single-pixel camera is shown to perform well, with 3 °C size-of-source effect (SSE) related temperature error and can measure below 700 °C whilst achieving ± 0.5 °C noise related measurement uncertainty. Our measurements were calibrated and traceable to the International Temperature Scale of 1990 (ITS-90). The combination of low SSE and absence of vignetting enables quantitative temperature measurements over a spatial field with measurement uncertainty at levels lower than would be possible with FPA based thermal imaging cameras.

Quantitative thermal imaging using single-pixel Si APD and MEMS mirror.

Accurate quantitative temperature measurements are difficult to achieve using focal-plane array sensors. This is due to reflections inside the instrument and the difficulty of calibrating a matrix of pixels as identical radiation thermometers. Size-of-source effect (SSE), which is the dependence of an infrared temperature measurement on the area surrounding the target area, is a major contributor to this problem and cannot be reduced using glare stops. Measurements are affected by power received from outside the field-of-view (FOV), leading to increased measurement uncertainty. In this work, we present a micromechanical systems (MEMS) mirror based scanning thermal imaging camera with reduced measurement uncertainty compared to focal-plane array based systems. We demonstrate our flexible imaging approach using a Si avalanche photodiode (APD), which utilises high internal gain to enable the measurement of lower target temperatures with an effective wavelength of 1 µm and compare results with a Si photodiode. We compare measurements from our APD thermal imaging instrument against a commercial bolometer based focal-plane array camera. Our scanning approach results in a reduction in SSE related temperature error by 66 °C for the measurement of a spatially uniform 800 °C target when the target aperture diameter is increased from 10 to 20 mm. We also find that our APD instrument is capable of measuring target temperatures below 700 °C, over these near infrared wavelengths, with D* related measurement uncertainty of ± 0.5 °C.

Assessing measurement uncertainty in meteorology in urban environments

Measurement uncertainty in meteorology has been addressed in a number of recent projects. In urban environments, uncertainty is also affected by local effects which are more difficult to deal with than for synoptic stations. In Italy, beginning in 2010, an urban meteorological network (Climate Network®) was designed, set up and managed at national level according to high metrological standards and homogeneity criteria to support energy applications. The availability of such a high-quality operative automatic weather station network represents an opportunity to investigate the effects of station siting and sensor exposure and to estimate the related measurement uncertainty. An extended metadata set was established for the stations in Milan, including siting and exposure details. Statistical analysis on an almost 3-year-long operational period assessed network homogeneity, quality and reliability. Deviations from reference mean values were then evaluated in selected low-gradient local weather situations in order to investigate siting and exposure effects. In this paper the methodology is depicted and preliminary results of its application to air temperature discussed; this allowed the setting of an upper limit of 1 °C for the added measurement uncertainty at the top of the urban canopy layer.

The statistical uncertainty of the Heydemann correction: a practical limit of optical quadrature homodyne interferometry

Although the Heydemann correction is widely used to demodulate the phase of quadrature homodyne interferometer and encoder signals, the related measurement uncertainty is considered only in a few publications. The statistical uncertainty of the phase, which is the contribution of the high-frequency noise in the input signals, due to the use of a simplified fitting approach in the Heydemann correction, cannot be determined exactly. Therefore, neglecting the correlation between the input signals and the fit parameters, an approximation is provided and verified using Monte Carlo simulations and an iterative fitting method that allows exact determination of the statistical uncertainty of the phase. For the high-quality signals encountered in dimensional metrology applications, only minor differences of a few percent in the uncertainty estimates are observed. Furthermore, for cases in which a number of points used in the fit is sufficiently large, a new, simple, analytic expression for the statistical uncertainty of the phase is derived. It represents a practical limit of optical quadrature displacement interferometry, which already has been reached experimentally. To achieve an expanded measurement uncertainty of 10 pm a signal-to-noise greater than 104 has to be realized experimentally.

The Multiple-Incremental Hole Drilling Method

Abstract Up to now the measurement uncertainties of residual stress determinations using the incremental hole-drilling-method had to be assessed by repeating the measurement at equivalent measurement spots or specimens. Often, the requirements for those repetitions are not given or the effort is spared. The determination of the stress state plus the related measurement uncertainty by only one course of measurement is the main feature of the Multiple-Incremental Hole Drilling Method developed by the Fraunhofer Institute for Mechanics of Materials IWM. The method is based on the generation and processing of multiple strain recordings for each depth increment through a stepwise enlargement of the hole in lateral direction. The results show that the new method allows revealing and quantifying measurement uncertainties of the determined stress-depth profile.