Low Measurement Uncertainty Research Articles

Calibration techniques for quantitative NO measurement using Laser-Induced Fluorescence

Laser-Induced Fluorescence (LIF) is an essential optical diagnostic technique for the high-resolution and low-uncertainty measurement of combustion species concentration in a variety of applications and conditions. Two different calibration techniques are explored in this study to obtain quantitative Nitric Oxide (NO) concentration measurements in flames. The first technique, the most employed in the literature, uses the extrapolation of the fluorescence signal from seeded to nascent NO and is only valid under negligible NO reburn conditions. The second technique uses the optical calibration of the experimental setup to relate it to a modelled LIF signal and can be applied regardless of NO reburn. Both of these techniques are explored under two different assumptions: constant and non-constant interfering LIF signal on the NO absorption spectrum. While the former is most often used in the literature, the latter is necessary when the LIF signal from interfering species cannot be distinguished from the NO-LIF signal, especially in high pressure conditions. Hence, a total of four techniques are presented in this work and are found to be in excellent agreement when performed in different flame conditions. The calibration techniques are applied to three lean, atmospheric, laminar, premixed, methane-air flames to explore their field of applicability. Specifically, the study explores the relevance of the techniques in reburn conditions, which occur mostly in high pressure, rich, highly-seeded, or NH3-containing flames. This study aims to offer the reader a portfolio of calibration techniques to use according to the conditions in which they need to be applied. While this study was carried out measuring NO concentration in a stagnation flame burner, the concepts and equations presented can be transposed to the measurement of other species and to other experimental configurations.

Accurate high-temperature profile sensing with dense multipoint arrays of regenerated fiber Bragg gratings

A spectrally and spatially dense sensor array consisting of 15 regenerated fiber Bragg gratings (RFBGs) over a length of 30 mm is presented for precise and fast multipoint temperature sensing up to 700°C. For the first time, it could be shown that with a dense fiber Bragg grating (FBG)-based sensor array the accuracy requirements of Class 1 thermocouples could be achieved and even exceeded. This also represents the highest spatial density of FBG-based high-temperature multipoint sensing reported so far. The mitigation of broadband losses during the regeneration process was studied, revealing the advantages of the low broadband loss characteristics of the RFBGs, especially when larger numbers of measuring points are required. Low measurement uncertainties were achieved by a new, improved calibration methodology and by an analysis of interferences of an FBG with the side lobes of spectrally neighboring FBGs as well as their suppression by a suitable arrangement of the Bragg wavelengths within the array and corresponding data processing. The capabilities of this multipoint sensor technique were demonstrated by resolving the temperature profile within the calibration volume of a calibration furnace and by resolving the temporal and spatial temperature gradients within the flame of a Bunsen burner. The results are of great importance for fiber-optic sensing of high-temperature profiles in real-world applications.

Suitability Study of Optical Coordinate Measuring Machine for Quality Assessment and Wear Phenomena Identification of Blade Edge and Surface of Planer Technical Knives.

This article discusses a comparative analysis of the wear and quality of planer knife blades used in wood planers. The novelty in this work is the use of a simple coordinate measuring machine with a vision system to assess the wear of the cutting edges of planer knives. The primary objective of the research described in this paper was to verify whether the wear of the cutting edge of planer knives can be measured quickly and accurately using an optical coordinate measuring machine with a vision system. To date, contact profilometry methods have been used for this purpose, which require a specialist apparatus and qualified measuring equipment operators and are expensive and time-consuming. The research presented in this work was conducted on twelve planer knives. The condition and wear of the working surfaces of the tested knives were assessed using an optical digital microscope. The wear of the cutting edge of the knives was measured using two methods: the contact profilometry method and an optical coordinate measuring machine equipped with a vision system. The edge profiles and their parameters obtained by the optical method were compared to the results of measurements with a stylus profilometer. Based on the research and analyses conducted, it was found that the optical method used in this research significantly shortens the time of measuring the wear of the cutting edges of planer knives. In addition, this method has a wider measurement range, and the obtained measurement results are characterized by lower measurement uncertainty.

Customized-accuracy simultaneous sensing of temperature, pressure and acoustic impedance based on FBS in optical fiber

In this work, it is proposed a novel customized-accuracy simultaneous sensing of temperature, pressure and acoustic impedance based on forward Brillouin scattering (FBS) in optical fiber. By observing the variations in frequency shift-temperature, frequency shift-pressure and frequency shift-acoustic impedance for different radial acoustic modes in certain types of fibers, we propose a novel method for simultaneously measuring three parameters (temperature, pressure and acoustic impedance) using the changes of frequency shift of three FBS scattering peaks. It is very interesting that we can utilize numerous sensitivity combinations of three measured parameters corresponding to different frequency shifts in optical fibers, allowing for the selection of different combinations of measurement accuracy for temperature, pressure and acoustic impedance sensing, and thus meeting the different requirements for measurement accuracy in specific measurement applications. In a proof-of-concept experiment, a 1060-XP fiber is used as the sensing fiber. By choosing suitable sensitivity combinations of coefficients of frequency shift-temperature, frequency shift-pressure and frequency shift-acoustic impedance of the fiber, we achieve high-accuracy simultaneous measurement of temperature, pressure and acoustic impedance with low measurement uncertainties of 0.13 °C, 0.04 MPa and 0.006 MRayl, respectively. The proposed method not only realize temperature, pressure and acoustic impedance simultaneous sensing for the first time, but also open up a new way of fiber optic sensing with customized multi-parameter sensing accuracy.

An improved algorithm for the estimation of the root mean square value as an optimal solution for commercial measurement equipment

This paper demonstrates that direct changes in the algorithm for the estimation of the root mean square value of a voltage signal of an arbitrary waveform can lead to improved performances and lower measurement uncertainty of commercially available instruments without requiring any upgrade of their existing hardware. The research conducted and presented here is an original contribution to the development of estimation techniques and mathematical models for measurement oriented purposes regardless of the number of samples in the given period relying on mathematical calculation of the equal complexity as in the methods already in use. The theoretical approach examines the problem of numerical integration focusing on modified Simpson's 1/3 rule and modified Simpson's 3/8 rule used for the purpose of the estimation of the root mean square value when a small number of samples per period is available. It highlights the limitations of Simpson's 1/3 rule and Simpson's 3/8 rule, and shows that the newly proposed algorithm is optimal with respect to measurement accuracy and precision even in cases when the ratio of the sampling frequency and the signal's fundamental frequency is low. All theoretical results have been validated experimentally.

Inter-comparison study of wind measurement between the three-lidar-based virtual tower and four lidars using VAD techniques

ABSTRACT The accurate three-dimensional wind field obtained from a Doppler lidar not only helps to comprehend the refined structure of complex airflow but also provides important and valuable solutions for many fields. However, the underlying homogeneity assumption of the typical wind retrieval methods, such as Doppler Beam Swinging (DBS) and Velocity Azimuth Display (VAD) based on a single-lidar, will introduce the measurement uncertainty in complex terrain. In this paper, a new design of a wind measurement campaign involving seven lidars was carried out, which contained the three-lidar-based Virtual Tower (VT) using a time-space synchronization technique and four single-lidars with different elevation angles. This study investigates the performance of VT and VAD measurements under various conditions and evaluates the sensitivity of wind measurement uncertainty of VAD to the horizontal spatial- and probe volume-average effects associated with elevation angles of the laser beam. The inter-comparison results between VT and four VADs show consistent trends with small relative errors under neutral atmospheric conditions with weak wind velocity. Under convective or high Turbulence Intensity (TI) conditions, the relative errors between VT and VAD become larger and more fluctuant. Moreover, it is found that the measurement uncertainty of VAD increases at a given elevation angle with the increasing measurement heights, which is caused by the horizontal homogeneity associated with the conical scanning area. Additionally, the simulated and measured results of four VADs indicate that a larger elevation angle corresponds to a lower measurement uncertainty for a given height.

Resolution enhanced sea ice concentration: a new algorithm applied to AMSR2 microwave radiometry data

Abstract Passive-microwave sea ice concentration (SIC) algorithms employ different frequencies and polarisations in their operational implementations. Commonly, these algorithms utilise combinations such as 19/37 GHz, yielding reduced measurement uncertainties but at a coarse spatial resolution. Alternatively, these algorithms can solely use 89 GHz, producing a higher spatial resolution but with increased measurement uncertainties. This study evaluates the application of a resolution-enhancing SIC algorithm (reSICCI3LF), initially developed for the coarser Special Sensor Microwave Imager / Sounder, on the Advanced Microwave Scanning Radiometer. By applying reSICCI3LF, we aim to produce a 5 km SIC for 2013–2020 in the Fram Strait and the Barents and Kara Sea region that gains the benefits of both types of algorithms, high spatial resolution and low measurement uncertainty. We present the algorithm tuning, spectral analysis of spatial resolutions, and validation against the Round Robin Data Package of 0% and 100% SIC points and SIC derived from Landsat-8. The findings demonstrate that the reSICCI3LF algorithm produces a SIC field with fine details, achieving a balance between high spatial resolution and lower measurement uncertainties compared to a 89 GHz based SIC. Consequently, this resolution-enhanced SIC technique can potentially initialise higher-resolution coupled ocean and sea ice forecasting systems through data assimilation.

High-accuracy high temperature measurement based on forward Brillouin scattering of polyimide-coated optical fiber

In this paper, a novel method for high-accuracy high temperature measurement is proposed, which is based on forward Brillouin scattering (FBS) of double-coated optical fiber with polyimide outer coating. The temperature variation changes the acoustic properties of polyimide-coated fiber that is suitable for high temperature measurement in the range of 120 ∼ 220 ℃. An interesting feature is that different radial acoustic modes have different frequency responses in the polyimide-coated fiber. Another interesting phenomenon is that the temperature linearly depends on the frequency shift of FBS spectrum with high sensitivity from 120 ℃ to 220 ℃. By using one acoustic mode with a high frequency shift-temperature sensitivity, we propose a novel high temperature measurement method based on FBS with high measurement accuracy. The experimental result shows that the low temperature measurement uncertainty of 0.02 ℃ can be achieved. The proposed method is expected to be used for high-accuracy temperature measurement applications within a temperature range of 100 ∼ 200 ℃, such as underground oil layer detection, power plant monitoring and high-power electrical systems monitoring.

Design of a Waveguide Calibration Kit Consisting of Offset Shorts for Low Measurement Uncertainty

Design of a Waveguide Calibration Kit Consisting of Offset Shorts for Low Measurement Uncertainty

Lubrication Film Friction Model for Grooved Annular Seals

Grooved liquid annular seals have a significant influence on the design of turbomachines. Corresponding lubrication film models need to account for the different friction behavior of the grooves compared to plain seals. However, there is a lack of reliable and validated models for this purpose. Thus, the applicability of a friction factor model is explored and a calibration method is presented. A single square groove is investigated by means of 96 steady-state RANS simulations for different operation conditions and groove geometries. The results are used to calibrate the friction model and successfully verify it in terms of the pressure drop over the groove. For validation, two full grooved seals with relatively large square grooves were investigated by experiment. The friction model was incorporated in a lubrication model and compared to the measurement data for the pressure difference and the resulting force for specified leakage and eccentricity. The model predictions for the pressure difference can be considered very good. The force predictions show significant deviation, but can be considered acceptable given the low force magnitudes and measurement uncertainty. The results offer a general validity to our friction model approach, assumptions and the calibration method.

Modernization of the instrumentation requirements to support ISO noise test standards

ISO TC43/SC1/WG28 develops the basic machinery noise test standards for products and equipment. This includes the determination of sound power levels in the ISO 3740 series and the measurement of operator/bystander sound pressure levels in the ISO 11200 series. The instrumentation requirements for these standards have historically been based on a reference the sound level meter standard, IEC 61672, supplemented by another to IEC 61260 for fractional octave filters. Both IEC standards are fundamentally based on the concept of the measurement system being a packaged sound level meter. Many modern implementations of these standards no longer use a sound level meter. Many now use multi-channel, computerized instrumentation systems and custom software. These systems provide measurement equivalence to the IEC sound level measurement standards. However, they don’t fully comply with all of the requirements in these IEC standards. Many acoustic testing programs have chosen to ignore these non-complianceissues, have implemented systems that are more efficient, lower measurement uncertainty and provide measurement equivalence to IEC 61672 and IEC 61260. As industry has already decided to implement these systems, there is a need to develop modernized instrumentation requirements to support the basic sound power and sound pressure level measurement standards using current technology.

Review of optical reporters of radiation effects in vivo: tools to quantify improvements in radiation delivery technique.

Radiation damage studies are used to optimize radiotherapy treatment techniques. Although biological indicators of damage are the best assays of effect, they are highly variable due to biological heterogeneity. The free radical radiochemistry can be assayed with optical reporters, allowing for high precision titration of techniques. We examine the optical reporters of radiochemistry to highlight those with the best potential for translational use in vivo, as surrogates for biological damage assays, to inform on mechanisms. A survey of the radical chemistry effects from reactive oxygen species (ROS) and oxygen itself was completed to link to DNA or biological damage. Optical reporters of ROS include fluorescent, phosphorescent, and bioluminescent molecules that have a variety of activation pathways, and each was reviewed for its in vivo translation potential. There are molecular reporters of ROS having potential to report within living systems, including derivatives of luminol, 2'7'-dichlorofluorescein diacetate, Amplex Red, and fluorescein. None have unique specificity to singular ROS species. Macromolecular engineered reporters unique to specific ROS are emerging. The ability to directly measure oxygen via reporters, such as Oxyphor and protoporphyrin IX, is an opportunity to quantify the consumption of oxygen during ROS generation, and this translates from in vitro to in vivo use. Emerging techniques, such as ion particle beams, spatial fractionation, and ultra-high dose rate FLASH radiotherapy, provide the motivation for these studies. In vivo optical reporters of radiochemistry are quantitatively useful for comparing radiotherapy techniques, although their use comes at the cost of the unknown connection to the mechanisms of radiobiological damage. Still their lower measurement uncertainty, compared with biological response assay, makes them an invaluable tool. Linkage to DNA damage and biological damage is needed, and measures such as oxygen consumption serve as useful surrogate measures that translate to in vivo use.

Optimisation of distillation as an isolation method for the determination of low methylmercury concentrations in urine samples

Methylmercury (MeHg) speciation in urine requires a robust, reproducible and sensitive technique that enables reliable measurements in limited sample volumes. Conventional MeHg extraction by acid digestion allows for processing of only small amounts of urine digest, making accurate MeHg determination in low-concentration samples virtually impossible. Distillation has been proven as an efficient isolation method with very low detection limits for measuring MeHg in water samples; therefore, in this study, it was optimised for urine samples. Combined with aqueous phase ethylation, purging with nitrogen, preconcentration on Tenax trap, isothermal gas chromatography and cold vapour atomic fluorescence detection, distillation achieved high and repeatable urine spike recoveries of 94% ± 7%. Larger measured aliquot volume led to a significantly lower limit of detection (LOD) for distillation compared with acid digestion (1.1 versus 5.5 pg g−1 urine). Thirty-two general population urine samples were analysed using both methods, and the results were compared. Distillation led to better separation of MeHg from inorganic Hg and the matrix. Good correlation was observed between the results obtained by the two methods for samples with MeHg concentrations above 10 pg g−1 urine (slope = 0.9492, R2 = 0.9879). For samples below this MeHg concentration, distillation was superior, enabling the measurement of MeHg in 9 out of 12 urine samples that were below the LOD of acid digestion. Distillation had significantly lower measurement uncertainty, particularly in the low-concentration samples, where the expanded combined standard uncertainty of the acid digestion method reached as high as 43.2% (k = 2), predominantly owing to poor sample repeatability.

Feedback Methods for Vector Measurements Using an All-Optical Atomic Magnetometer.

In this work, we look to compare three methods of feedback for the ultimate purpose of measuring the transverse vector components of a magnetic field using a synchronous light-pulse atomic scalar magnetometer with a few tens of fT/Hz sensitivity in Earth-field-scale magnetic environments. By applying modulation in the magnetic field to orthogonal axes, the respective vector components may, in principle, be separated from the scalar measurement. Success of this technique depends in significant part on the ability to measure and respond to these perturbations with low measurement uncertainty. Using high-speed least-squares fitting, the phase response of the atomic spins relative to the first harmonic of the optical pump pulse repetition rate is monitored and correspondingly adjusted into resonance with the natural Larmor precession frequency. This paper seeks to motivate and compare three distinct methods of feedback for this purpose. As a first step toward the full development of this technique, the present work uses a simplified version with modulation applied only along the bias field. All three methods investigated herein are shown to provide results that match well with the scalar magnetometer measurements and to depend on both the applied modulation amplitude and optimal feedback response to achieve low relative uncertainty.

Thermally enhanced upconversion luminescence of Cr3+ in Er3+-Yb3+-Cr3+ tri-doped garnet phosphors for sensitive optical thermometry

Luminescence thermometry is strongly desired in many fields due to the capability of remote temperature measurement with fast response and high spatial resolution. For developing excellent luminescence thermometer, we systematically investigated the upconversion (UC) emissions from Er3+-Yb3+-Cr3+ tri-doped garnet-structured phosphors under the excitation of 980 nm laser. The influence of Ga3+/Al3+ dopant ratio in Y3Al5-xGaxO12 on the UC luminescence was studied in detail by the X-ray diffraction patterns, Raman spectra, FT-IR spectra and Judd-Ofelt theory. Research revealed that the increase of Ga3+ doping content could reduce the symmetry of rare earth (RE) ions site and simultaneously weaken the nonradiative relaxations, favoring the RE luminescence and the subsequent energy transfer (ET) from RE to Cr3+. More importantly, because of the thermally strengthened ET from Er3+ ions, about 27-fold enhancement in Cr3+ UC luminescence was successfully achieved within Er3+-Yb3+-Cr3+ tri-doped Y3Ga5O12 as temperature ascended from 303 to 873 K, which consequently leaded to the emission color switching in response to temperature change. These advances in the as-prepared garnet phosphors provide potential opportunity for vision-guided temperature sensing with high sensitivity (∼ 4.38% K−1) and low measurement uncertainty (∼ 0.29 K).

Alternative Approach Leading to Reduction in Measurement Instrument Uncertainty of EMI Measurement

Abstract Even in the field of electromagnetic compatibility, low measurement uncertainty means high measurement quality. Although there are standardized procedures for obtaining the uncertainty of such a measurement, which facilitate uncertainty estimation, modern approaches show further reduction possibilities. The paper presents an alternative approach to reducing measurement instrument uncertainty in the case of electromagnetic interference measurement based on many years of our experience and a large number of measurements in this field. In the paper, two different methods of uncertainty reduction are described. The first method is based on a detailed analysis of the sources of uncertainty and the subsequent division of the analyzed frequency band into more subranges. Another method uses the choice of the antenna factor, which also contains information about the test site where the measurement is carried out. In this way, despite a lengthy analysis, it is relatively easy to achieve a measurement instrument uncertainty that is below the maximum measurement uncertainty given by the CISPR standard.

Distributed Impact Wave Detection in Steel I-Beam with a Weak Fiber Bragg Gratings Array.

In this paper, acoustic, dynamic and static strain variations along a steel I-beam generated by an impact load are reconstructed simultaneously within a single measurement. Based on the chirped pulse φ-OTDR system with the single-shot measurement technique, both a higher strain-sensing resolution and a higher measurable vibration frequency are achieved. In addition, a weak fiber Bragg gratings array (WFBGA) with enhanced Rayleigh reflection is employed as a sensor, providing high signal-to-noise ratio Rayleigh traces, resulting in lower measurement uncertainty. In the experiments, the damping constant and fundamental frequency of the damped harmonic oscillator could then be measured based on the recovered strain variation profile for further structural health analysis. Compared with commercial strain gauges, linear potentiometers, and OFDR systems, the proposed sensing system ensures a distributed, quantitative, and high-frequency sensing ability, with an extensive range of potential applications.

Absolute wavelength scanning interferometry for measuring the thickness of optical elements.

A technique for measurement of the thickness of optical elements using absolute wavelength scanning interferometry is presented in this paper. To achieve high-grade optical components and systems, the thickness of both planar and non-planar optical components must be measured with an accuracy of a few micrometers. The proposed technique is based on the Fizeau interferometer and interconnects data from three different tunable laser diodes yielding a long effective wavelength range and thus low measurement uncertainty. The uncertainty of the central thickness measurement ranges from hundreds of nanometers to a few microns. The method allows to measure the thickness of both flat optical elements as well as lenses with curved surfaces. Moreover, the areal information provided by the interferometry and its high angle sensitivity help to quickly and precisely align the measured component and reduce misalignment errors. The results of thickness measurements have been validated and cross-tested with other techniques. In addition to the thickness, the technique provides some additional information (wedge, surface form error) in the case of flat samples and can be easily and quickly modified (mounting of a Fizeau transmission sphere) to measure other essential parameters of optical elements. Thus, this one approach can replace many single-purpose measuring devices while maintaining high accuracy.

Calibration of angle standards

Main textOptical polygons and angle gauge blocks are the primary artifacts for disseminating the unit of angle to industry. The Consulative Committee for Length (CCL) has designated the calibration of such angle artifacts as a key comparison topic area in order to ensure world-wide traceability and equivalence of angle measurements at the lowest measurement uncertainties. This report describes the key comparison in the topic area of angle metrology for the SIM region. An optical polygon and six angle gauge blocks were measured by five national metrology institutes (NMI). The comparison was successful and the results of the participants are reported. One NMI reported values that were initially inconsistent with the key comparison reference value for the optical polygon.To reach the main text of this paper, click on Final Report. Note that this text is that which appears in Appendix B of the BIPM key comparison database https://www.bipm.org/kcdb/.The final report has been peer-reviewed and approved for publication by the CCL, according to the provisions of the CIPM Mutual Recognition Arrangement (CIPM MRA).

Low‐cost outdoor spectral irradiances determination and its application on Concentrator Photovoltaic module power rating and energy yield calculation

AbstractIn this work, a method to calculate the aerosol content in the atmosphere and the prevailing spectral irradiance of the sunlight is introduced. This method does not aim for low measurement uncertainty but for cost effectiveness and does not require sophisticated equipment. The bases of the method are the clear sky direct normal irradiance (DNI) and a look‐up table calculated with the software tool SMARTS2. The ratio of clear sky DNI to the prevailing DNI in combination with the look‐up table allows the determination of aerosol optical depth (AOD), spectral matching ratios (SMR), and spectral irradiances. Besides the prevailing DNI, the following ambient condition parameters are required: Air pressure, relative humidity, and ambient temperature. This means a weather station and a pyrheliometer are sufficient for the determination of the prevailing spectral irradiance. Obviously, this method cannot guarantee the same accuracy as conventional spectral irradiance measurement methods (e.g., using a spectroradiometer). However, in this work, we demonstrate the potential of this new method as a fall‐back strategy for missing spectral irradiance data. This method is worth using when (C)PV module power output data needs to be evaluated in dependence of the composition of the spectral irradiance, but no regular spectral irradiance data are available. In this paper, the AOD and SMR values determined with the introduced method are compared to measurement data with common measurement devices demonstrating a satisfying agreement. The spectral irradiances calculated with this method are successfully tested for using as the basis for energy yield calculations and for the determination of the CPV module power output at Concentrator Standard Conditions according to IEC 62670‐1.