Standard Calibration Procedure Research Articles

Partial Discharge Monitoring of Power Transformers by Calibrated UHF Measurements

Partial discharge (PD) measurement is an established technique to detect local defects in the oil/paper insulation. They can be measured by electrical PD measurements according to IEC 60270 or by electromagnetic measurements in the ultra-high frequency range (UHF: 300 MHz – 3 GHz). The electromagnetic emissions of PD are recorded using an UHF sensor which is inserted into the transformer tank. The importance of PD measurements is reflected in the standard for charge-based electrical measurements (IEC 60270). Because of the standard, apparent charge, QIEC, became an essential factor for determining insulation quality in transformers. To be an accepted factor for both, quality testing in factory acceptance tests (FAT) or site acceptance tests (SAT) and continuous PD monitoring, the UHF technology must be as reliable and reproducible as the electrical method. To achieve this, a standardized calibration procedure is needed: It makes UHF measurement results from different systems comparable. Because this calibration procedure was lacking in the past, the UHF technology does not provide comparability between measurement systems and different sensors, yet. However, it shows advantages for on-site acceptance tests like SAT, continuous monitoring, and diagnostic purposes. E.g., regarding signal to noise ratios, the possibility for localization of PD sources and also for practical reasons like preparation times and accessibility on-site. This contribution presents a PD monitoring system which can be calibrated according to the calibration process described recently in Cigré TB 861 and two different types of UHF PD sensors for power transformers. One sensor type is for new transformers using dielectric windows and the other is for retrofitting transformers using their DN50/80 drain valves. A recommendation or strategy on where to place window-type UHF sensors at the tank of new power transformers is also provided in accordance with TB 861. Additionally, this contribution provides a description of the calibration process for UHF PD measurement systems consisting of two steps: 1) Calibration of the measurement instrument analogous to the calibration of the electrical PD measurement circuit using a defined reference signal. 2) Calibration of a UHF sensor using its characteristic antenna factor (AF). Furthermore, it shows three case studies from different power transformers equipped with UHF sensors and UHF PD monitoring systems.

Determination of 145 pharmaceuticals and personal care products in eleven categories in water by ultra-high performance liquid chromatography-triple quadrupole mass spectrometry

Pharmaceuticals and personal care products (PPCPs) are emerging contaminants frequently detected in aquatic environments at trace levels. These chemicals have diverse structures and physicochemical properties and includes pharmaceuticals like antibiotics, antihypertensive drugs, antiviral drugs, and psychotropic drugs that are widely used in large quantities worldwide. Considering the large number of pharmaceuticals currently in usage, it is crucial to establish a priority list of PPCPs that should be monitored and/or treated first. An accurate understanding of the occurrence and levels of PPCPs in aquatic environments is essential for providing objective materials for monitoring these emerging contaminants. Therefore, accurate, efficient, sensitive, and high-throughput screening techniques need to be established for determining and quantifying PPCPs. This study developed a method for the determination of 145 PPCPs (grouped into eleven categories: antibiotics, antihypertensive drugs, antidiabetic drugs, antiviral drugs, β-receptor agonists, nitroimidazoles, H2 receptor antagonists, psychotropic drugs, hypolipidemic drugs, non-steroidal anti-inflammatory drugs, and others) in water. The method was based on large volume direct injection without sample enrichment and cleanup and used ultra-high performance liquid chromatography-triple quadrupole mass spectrometry (UHPLC-MS/MS). Water samples were collected and filtered through a 0.22-μm regenerated cellulose (RC) filter membrane. Subsequently, Na2EDTA was added to the samples to adjust their pH to 6.0-8.0. Internal standards were mixed with the solutions, and because of the addition of Na2EDTA, the interference of metal ions could be eliminated in the determination of compounds, especially for tetracycline and quinolone antibiotics. Among the six filter membranes tested in this study (PES, PFTE-Q, PFTE, MCE, GHP, and RC), RC filter membranes were screened for water sample filtration. The UHPLC-MS/MS parameters were optimized by comparing the results of various mobile phases, as well as by establishing the best instrumental conditions. The 145 PPCPs were separated using an Phenomenex Kinetex C18 column (50 mm×3 mm, 2.6 μm) via gradient elution. The mobile phases were 0.1% (v/v) formic acid aqueous solution containing 5 mmol/L ammonium formate and acetonitrile for positive ion modes, 5 mmol/L aqueous solutions of ammonium formate and acetonitrile for negative ion modes. The samples were quantified using the scheduled multiple reaction monitoring (scheduled-MRM) mode with electrospray ionization in positive and negative ion modes. A standard internal calibration procedure was used to calculate contents of sample. The established method was systematically verified, and it demonstrated a good linear relationship. The average recoveries of the 145 PPCPs at the three spiked levels were in the range of 80.4%-128% with relative standard deviations (RSDs, n=6) of 0.6%-15.6%. The method detection limits (MDLs) ranged from 0.015 to 5.515 ng/L. Finally, the optimization method was applied to analyze the 145 PPCPs in 11 surface water samples and 6 drinking water samples. Overall, 93 (64%) out of the 145 analytes were detected. The total contents of the PPCPs in surface water samples ranged from 276.9 to 2705.7 ng/L. The detection frequencies of antidiabetic, antiviral, and psychotropic drugs were 100%. The total contents of the PPCPs in drinking water samples ranged from 140.5 to 211.5 ng/L, and antibiotics, antidiabetic drugs, and antiviral drugs comprised the largest proportion of analytes (by mass concentration) in drinking water samples. Our method exhibited high analytical speed and high sensitivity. It is thus suitable for the trace analysis and determination of the 145 PPCPs in environmental water and showed improved detection efficiency for PPCPs in water, indicating that it has a high potential for practical applications. This study can extend technical support for further pollution-level analysis of PPCPs in water and provide an objective basis for environmental management.

Author's Reply to Comment by Greaves et al. on “Phosphine in the Venusian Atmosphere: A Strict Upper Limit From SOFIA GREAT Observations”

AbstractIn an attempt to understand the findings presented in the Comment by Greaves et al. (2023, https://doi.org/10.1029/2023GL103539), we followed their data analysis methodology, omitting the hot and cold‐load calibrations that are an important part of the standard SOFIA GREAT instrument calibration procedure. This process requires scaling of the Venus off‐source spectra by an arbitrary factor, which in turn introduces residuals of the intrinsic receiver bandpass shape as spurious components in the resulting line/continuum spectra. Although these additional artifacts can be reduced via Fourier‐domain spectral filtering, their removal depends on an ill‐constrained interpolation of the Venus continuum across the PH3 spectral line positions, resulting in an unreliable final spectrum. We therefore conclude that the PH3 lines claimed to be detected in the Comment by Greaves et al. (2023, https://doi.org/10.1029/2023GL103539) originate from data/analysis artifacts, and confirm our original result that there is no evidence for phosphine in the SOFIA Venus data.

Simplified Characterization of Anisotropic Yield Criteria for an Injection-Molded Polymer Material.

Injection-molded polyethylene plates exhibit highly anisotropic mechanical behavior due to, e.g., the uneven orientation of the polymer chains during the molding process and the differential cooling, especially in the thickness direction. Elastoplastic finite element modeling of these plates in particular is used with isotropic yield criteria like von Mises, trading off accuracy in favor of simpler constitutive characterization and faster solution. This article studies three different anisotropic yield criteria, namely, Hill 1948, Barlat Yld91, and Barlat Yld2004-18P, for the finite element modeling of low-density polyethylene (LDPE) at large uniaxial tensile deformation and compares the accuracy and computation time with von Mises. A simplified calibration technique is investigated to identify the constitutive parameters of the studied Barlat group yield criteria. The calibration process is simplified in the sense that only uniaxial tensile tests with digital image correlation measurements are used for the calibration of all the yield criteria studied in this article, although a standard calibration procedure for the Barlat group yield criteria requires additional material testing using more demanding test setups. It is concluded that both Barlat Yld91 and Barlat Yld2004-18P yield criteria can be calibrated with only a few tensile tests and still capture anisotropy in deformation-stress-strain at different levels of accuracy.

Bioavailability Assessment of Heavy Metals and Organic Pollutants in Water and Soil Using DGT: A Review

In recent years, the diffusive gradients in the thin films (DGT) technique has also been increasingly applied to assess the bioavailability of heavy metals and organic pollutants in the soil. The combination of binding and diffusion phases made from different materials allows for the targeted determination of different target substances. This review briefly introduces the compositions and development of the DGT technique and analyzes the composition structure of DGT and the impact of environmental factors, such as pH, ion strength (IS), and dissolved organic matter (DOM), on the bioavailability evaluation of heavy metals and organic pollutants in soil. Finally, the application potential and broad application prospects of the DGT technique were expected. In addition, standardized DGT technique methods and calibration procedures are conducive to the establishment of a more stable and reliable measurement system to enhance the robustness of the DGT technique application in the soil.

Topologies of ^{76}Ge double-beta decay events and calibration procedure biases

The analysis of the time profile of electrical signals produced by energy depositions in germanium detectors allows discrimination of events with different topologies. This is especially relevant for experiments searching for the neutrinoless double beta decay of ^{76}Ge to distinguish the sought-after signal from other background sources. The standard calibration procedures used to tune the selection criteria for double-beta decay events use a ^{228}Th source, because it provides samples of signal-like events. These samples exhibit energy spatial distributions with subtle different topologies compared to neutrinoless double-beta decay events. In this work, we will characterize these topological differences and, with the support of a ^{56}Co source, evaluate biases and precision of calibration techniques which use such event samples. Our results will be particularly relevant for future experiments in which a solid estimation of the efficiency is required.

Comparison of internal standard and standard additions calibration procedures for the determination of selected heavy metals in treated municipal effluent by MP-AES

We compared the internal standard calibration and standard additions calibration methods in the determination of Cd, Cr, Fe, Mn, Pb and Zn in municipal effluent using microwave-induced plasma atomic emission spectrometer. Comparison was based on validation parameters such as linearities, linear ranges, limits of detection (LOD), precisions and recoveries obtained using both calibration methods. Both methods gave good linearities applicable to a simple linear regression data fitting. Severe loss of linearity was observed at levels beyond 3 mg/L particularly for Zn. Considering this, the compromise linear range for all target analytes was established at LOD–3 mg/L. While the LODs for the target analytes were sufficiently low for both methods, the internal standard method was found to be more sensitive compared to standard additions method. Thus, the optimal linear ranges were accurately established at 0.24–0.96 mg/L for the internal standard and 1.10–1.96 mg/L for the standard additions method. Analyte recoveries including for the certified reference material averaged ∼ 100%. Therefore, all target analytes with the exception of Cd, which was possibly below the method detection limit were confidently detected and accurately quantified in municipal effluent samples. Overall, the excellent quantitative data obtained in this study inferred a high level of confidence in the developed methods in that they differed by less than 10%. Indisputably, the performance of the MP-AES operated in internal standard- and standard additions modes have proved to be a sufficiently sensitive technique especially for heavy metals occurring at sub-ppm levels.

The preliminary exploration on change mechanism of Seebeck coefficient for NiCr/NiSi thin film thermocouple with different thickness

By controlling the thickness of NiCr and NiSi films, a series of NiCr/NiSi thin film thermocouples (TFTCs) were prepared by the sputtering technique. With the standard static calibration procedure for wire thermocouple, the temperature difference mainly happened between NiCr/NiSi compensation wires, but not between pad and hot junction of NiCr/NiSi TFTCs. The incorrect temperature difference resulted in the distorted Seebeck coefficient of NiCr/NiSi TFTCs, which was close to the standard NiCr/NiSi wire thermocouple. Only considering the temperature difference between pad and hot junction of NiCr/NiSi TFTCs, Seebeck coefficient of NiCr/NiSi TFTCs were accurately obtained. Seebeck coefficient of NiCr/NiSi TFTCs was about ∼10 μV/°C, which was obviously lower than that of standard K type NiCr/NiSi wire thermocouple (∼40μV/°C). Besides, Seebeck coefficient of NiCr/NiSi TFTCs gradually increased from 7.32 to 13.36 μV/°C with the increase of NiCr/NiSi film thickness from 400 to 2000 nm. NiCr and NiSi films with different thickness displayed the similar crystal structure, grain size, metal bonds structure, Ni/Cr and Ni/Si atom ratio, as well as similar surface morphology and roughness, which have little influence on Seebeck coefficient of NiCr/NiSi TFTCs. With the increase of NiCr and NiSi film thickness, the sheet concentration of free electron increased gradually, which resulted in the increase of Seebeck coefficient of NiCr/NiSi TFTCs. Because of the limited thickness of NiCr and NiSi film, all Seebeck coefficient values of NiCr/NiSi TFTCs were lower than that of standard K type thermocouple. NiCr/NiSi TFTCs with small thickness NiSi film and large thickness NiCr film could display the relative higher Seebeck coefficient value. And, NiCr/NiSi TFTCs with 800 nm NiSi and 2000 nm NiCr films displayed Seebeck coefficient value of 21.30 ± 0.69 μV/°C. o

A re-calibration procedure for interoperable lipid collision cross section values measured by traveling wave ion mobility spectrometry

Collision cross sections (CCS) have been described as relevant molecular descriptors in metabolomics and lipidomics analyses for ascertaining compound identity. Ion mobility spectrometry (IMS) allows to determine CCS with different techniques, such as drift tube ion mobility spectrometry (DTIMS), traveling wave ion mobility spectrometry (TWIMS) or trapped ion mobility spectrometry (TIMS). In contrast with DTIMS where CCS can be obtained directly with measured drift times and mathematical relationship, TWIMS and TIMS techniques require an additional step of calibration to obtain CCS values. However, literature reports significantly disparate CCS values depending on the calibrant used (often more than 10%), as no consensus has been reached to define a universal CCS reference standard or harmonized calibration procedure. Therefore, publicly available CCS databases cannot be regarded as readily interoperable and exchangeable.Here, we performed a comprehensive evaluation of 11 distinct CCS calibrants in a traveling wave ion mobility spectrometry-mass spectrometry (TWIMS-MS) instrument. We showed that, using lipids from plasma as model compounds, CCS determination drastically fluctuates from one calibrant to the other with up to 25% differences, which precludes direct CCS comparison. Using the large panel of calibration curves generated, we showed that any CCS value can be efficiently re-calibrated relatively to the calibration curve made with the widely used Tune Mix solution whatever the calibration procedure originally used. The re-calibrated CCS values for each calibrant constitute a database which allows to correct any deviation on lipid CCS values whatever the calibrant originally used. Resulting corrected CCS values from plasma lipids were thus efficiently matched to those previously reported in the literature (with deviations<2%). Therefore, this work shows that unique and comparable CCS values can be obtained upon re-calibration relatively to Tune Mix CCS values, while also paving the way for the establishment of a universal CCS database of various metabolite or lipid classes.

CALIBRATION OF PHOTOGRAMMETRIC SYSTEM FOR 3D MEASUREMENTS IN INACCESSIBLE MULTIMEDIA WORKING SPACE

Abstract. Hydrodynamic tunnel has proved to be an effective mean for studying aerodynamic processes using scaled models of real aircrafts. The specificity of study in a hydrodynamic tunnel requires to apply non-contact measuring techniques, such as photogrammetry, for retrieving information on geometrical characteristics of the flow. So reliable calibration of photogrammetric system is a key element for trustworthy analysis of flow behaviour. For 3D measurements in a hydrodynamic tunnel calibration technique must account for refraction effects at optical media interfaces. But often the design of a hydrodynamic tunnel does not allow to perform standard calibration procedure based on image acquisition of a special test field, placed in the working space of the measuring system. The presented study addresses this problem – developing the technique for accurate photogrammetric calibration, for the case of the working space being inaccessible for placing there a test field. The developed calibration technique estimates parameters of interior orientation of the photogrammetric system and parameters of multimedia optical environment by special preliminary procedure, that allows to obtain accurate 3D measurements during experiments in hydrodynamic tunnel. Experimental evaluation of the developed technique demonstrated high accuracy of photogrammetric 3D measurements.

Very low frequency IEPE accelerometer calibration and application to a wind energy structure

Abstract. In this work, we present an experimental setup for very low frequency calibration measurements of low-noise integrated electronics piezoelectric (IEPE) accelerometers and a customised signal conditioner design for using IEPE sensors down to 0.05 Hz. AC-response IEPE accelerometers and signal conditioners have amplitude and phase deviations at low frequencies. As the standard calibration procedure in the low-frequency range is technically challenging, IEPE accelerometers with standard signal conditioners are usually used in frequency ranges above 1 Hz. Vibrations on structures with low eigenfrequencies like wind turbines are thus often monitored using DC-coupled micro-electro-mechanical system (MEMS) capacitive accelerometers. This sensor type suffers from higher noise levels compared to IEPE sensors. To apply IEPE sensors instead of MEMS sensors, in this work the calibration of the entire measurement chain of three different IEPE sensors with the customised signal conditioner is performed with a low-frequency centrifuge. The IEPE sensors are modelled using infinite impulse response (IIR) filters to apply the calibration to time-domain measurement data of a wind turbine support structure. This procedure enables an amplitude and phase-accurate vibration analysis with IEPE sensors in the low-frequency range down to 0.05 Hz.

Robust Filter-Based Visual Navigation Solution with Miscalibrated Bi-Monocular or Stereo Cameras

This work addressed the problem of miscalibration or decalibration of mobile stereo/bi-monocular camera setups. We especially focused on the context of autonomous vehicles. In real-world conditions, any optical system is subject to various mechanical stresses, caused by vibration, rough handling, collisions, or even thermal expansion. Such mechanical stresses change the stereo pair geometry, and as a consequence, the pre-calculated epipolar geometry or any geometric-based approach is no longer valid. The standard method, which consists of estimating the calibration online, fails in such harsh conditions. The proposed method was based on a robust linearly constrained state estimation technique able to mitigate the model mismatch without estimating the model parameters. Therefore, our solution was able to mitigate the errors with negligible use of additional computing resources. We propose to use a linearly constrained extended Kalman filter for a stereo-based visual odometry or simultaneous localization and mapping approach. Simulations confirmed that the method kept the system (and objects of the map) localized in real-time even with huge miscalibration errors and parameter variations. The results confirmed that the method was robust to a miscalibration of all the extrinsic calibration parameters even when the standard online calibration procedure failed.

Calibration of Stereo Pairs Using Speckle Metrology.

The accuracy of 3D reconstruction for metrology applications using active stereo pairs depends on the quality of the calibration of the system. Active stereo pairs are generally composed of cameras mounted on tilt/pan mechanisms separated by a constant or variable baseline. This paper presents a calibration approach based on speckle metrology that allows the separation of translation and rotation in the estimation of extrinsic parameters. To achieve speckle-based calibration, a device called an Almost Punctual Speckle Source (APSS) is introduced. Using the APSS, a thorough method for the calibration of extrinsic parameters of stereo pairs is described. Experimental results obtained with a stereo system called the Agile Stereo Pair (ASP) demonstrate that speckle-based calibration achieves better reconstruction performance than methods using standard calibration procedures. Although the experiments were performed with a specific stereo pair, such as the ASP, which is described in the paper, the speckle-based calibration approach using the APSS can be transposed to other stereo setups.

Reflection Efficiency and Spectra Resolutions Ray-Tracing Simulations for the VOXES HAPG Crystal Based Von Hamos Spectrometer

The VOXES collaboration at INFN National Laboratories of Frascati developed a prototype of a high resolution Von Hamos X-ray spectrometer using HAPG (Highly Annealed Pyrolytic Graphite) mosaic crystals. This technology allows the employment of extended isotropic sources and could find application in several physics fields. The capability of the spectrometer to reach energy precision and resolution below 1 and 10 eV, respectively, when used with wide sources, has been already demonstrated. Recently, the response of this device, for a ρ = 206.7 mm cylindrically bent HAPG crystal using CuKα1,2 and FeKα1,2 XRF lines, has been investigated in terms of reflection efficiency by a dedicated ray-tracing simulation. Details of the simulation procedure and the comparison with the experimental results are presented. This study is crucial in order to retrieve information on the spectrometer signal collection efficiency, especially in the energy range in which the standard calibration procedures cannot be applied.

An integrated parameter calibration method and sensitivity analysis of microparameters on mechanical behavior of transversely isotropic rocks

The calibration of dual-models in particle flow code (PFC) is an open research challenge because of the complexity and dependence of microparameters in each model. Aiming at addressing this challenge, an integrated parameter calibration method based on linear parallel bonding model (LPBM) and smooth joint model (SJM) (CM-LPBM&SJM) was developed in the present work and applied to transversely isotropic rocks. A calibration parameter index system was first proposed. Numerical simulations were conducted to obtain the relationship between macroparameters and microparameters. Subsequently, an LPBM and SJM parameter calibration priority was established by linking microparameters of each model. A macro–micro parameter functional representation system was then developed. In addition, iteration corrections were conducted to improve calibration accuracy. Finally, a set of standardized microparameter calibration procedures for transversely isotropic rocks was proposed. CM-LPBM&SJM solved the challenge of the complexity and dependence of microparameters by establishing microparameter calibration priority. To further verify the feasibility of the proposed method, a case study was conducted, and the error was found to be less than 4%. Hence, CM-LPBM&SJM introduces a new perspective for dual-model parameter calibration.

Reducing Calibration Time in PET Systems Based on Monolithic Crystals.

In the past years, the gamma-ray detector designs based on the monolithic crystals have demonstrated to be excellent candidates for the design of high-performance PET systems. The monolithic crystals allow to achieve the intrinsic detector resolutions well below state-of-the-art; to increase packing fraction thus, increasing the system sensitivity; and to improve lesion detectability at the edges of the scanner field of view (FOV) because of their intrinsic depth of interaction (DOI) capabilities. The bottleneck to translate to the clinical PET systems based on a large number of monolithic detectors is eventually the requirement of mechanically complex and time-consuming calibration processes. To mitigate this drawback, several methods have been already proposed, such as using non-physically collimated radioactive sources or implementing the neuronal networks (NN) algorithms trained with simulated data. In this work, we aimed to simplify and fasten a calibration process of the monolithic based systems. The Normal procedure consists of individually acquiring a 11 × 11 22Na source array for all the detectors composing the PET system and obtaining the calibration map for each module using a method based on the Voronoi diagrams. Two reducing time methodologies are presented: (i) TEST1, where the calibration map of one detector is estimated and shared among all others, and (ii) TEST2, where the calibration map is slightly modified for each module as a function of their detector uniformity map. The experimental data from a dedicated prostate PET system was used to compare the standard calibration procedure with both the proposed methods. A greater similarity was exhibited between the TEST2 methodology and the Normal procedure; obtaining spatial resolution variances within 0.1 mm error bars and count rate deviations as small as 0.2%. Moreover, the negligible reconstructed image differences (13% deviation at most in the contrast-to-noise ratio) and almost identical contrast values were reported. Therefore, this proposed method allows us to calibrate the PET systems based on the monolithic crystals reducing the calibration time by approximately 80% compared with the Normal procedure.

A combined volume correction and standard addition step to simplify environmental chemical analysis

A simple standard addition calibration procedure is described theoretically to allow both quantification of the unknown component of interest in an environmental sample and, simultaneously, measurement of the volume of that sample. The method relies on the addition to the standard solution of an internal standard containing an analyte that is not expected in the sample itself or at such a low concentration as to make no difference. The underpinning mathematics of the technique is described, including the complex correction for variable volume standard addition techniques. The method would be most suitable for the measurement of environmental samples requiring a digestion or extraction step (leading to variable sample volumes) prior to the analysis. Theoretical consideration of this new approach is made with reference to the measurement of metals in ambient particulate matter, where it would dramatically reduce analysis time and the requirement for analyst intervention.

Calibration of hydrological models considering process interdependence: A case study of SWAT model

Calibration is an essential step that is involved in the application of process based distributed hydrological models. The calibration process focuses on improving the performance index values rather than improving the process dynamics. The poor process dynamics in the model reduces its predictive power. The current study proposes a modified calibration approach (MCA) for the Soil and Water Assessment Tool (SWAT) model, which helps to improve the process dynamics in model through constraining the parameters. The modified calibration method uses the association between physically interpretable SWAT model parameters as soft data for calibration. The proposed calibration approach is validated in the Little River Experimental Watershed, USA. The results indicate that the proposed calibration method improves the process representation and spatial prediction in the calibrated model compared to the standard calibration procedure based on streamflow data.

Application of 3-omega method for thin-film heat flux gauge calibration

Double-sided thin-film resistance temperature detector (RTD) heat flux gauges (HFGs) are commonly used to characterize heat transfer rates in high-heat flux environments with complex flow features. These gauges comprise two thin-film RTDs on opposing sides of a dielectric. To deduce accurate heat flux, the RTDs must be properly calibrated and the material properties of the dielectric must be characterized. This study presents a complete gauge characterization method for sensors of this type by applying standard calibration procedures with specially-designed RTDs capable of utilizing the 3-omega method. The 3-omega method quantifies the thermal conductivity and thermal product of a material by measuring the response of a specially designed heater/thermometer deposited on the substrate. This study shows the 3-omega method enables RTD calibrations and thermal property determination over a range of temperatures for individual gauges, reducing the uncertainty in calculated heat flux. Although the method is quite general, this study utilized platinum RTDs with a polyimide dielectric, which is common in turbomachinery applications. The thermal properties obtained through this method agree with previous characterization efforts; however, discrete characterization of seven gauges shows that gauge-to-gauge variation in the dielectric could influence measured heat flux by as much as 30%. This study also builds the framework to characterize the thermal conductivity of the adhesive layer beneath the gauge which is necessary to mount the sensors to the test article. Although often uncharacterized, the adhesive thermal conductivity has a significant impact on matching experimental measurements to simulations. Additionally, this study found that if the thermal conductivity of the dielectric is constant (an assumption that holds for the present study), an in-situ RTD calibration can be performed. In-situ RTD calibration and traditional method RTD calibration agreed to within 0.1%. Overall, this work has practical implications in obtaining high quality measurements from HFGs of this type.

HDR Reconstruction Based on the Polarization Camera

The recent development of the on-chip micro-polarizer technology has made it possible to acquire – with the same ease of operation as a conventional camera – spatially aligned and temporally synchronized polarization images simultaneously in four orientations. This development has created new opportunities for interesting applications including those in robotics. In this letter, we investigate the use of this sensor technology in high-dynamic-range (HDR) imaging. Specifically, observing that natural light can be attenuated differently by varying the direction of the polarization filter, we treat the multiple images captured by the polarization camera as a set captured at different exposure times, useful to the reconstruction of an HDR image. In our approach, we first study the radiometric model of the polarization camera, and relate the polarizer direction, degree and angle of polarization of light to the exposure time of a pixel in the polarization images. Subsequently, by applying the standard radiometric calibration procedure of a camera, we recover the camera response function. With multiple polarization images at known pixel-specific exposure times, we can then proceed to estimate the irradiance maps from the images and generate an HDR image. Two datasets are created to evaluate our approach, and experimental results show the dynamic range by our approach can be increased by an amount dependent on light polarization. We also use two robotics experiments on feature matching and visual odometry to demonstrate the potential benefit of this increased dynamic range.