Reference Instrument Research Articles

Comparison of radon exhalation rate measurements on reference device in open and closed loop by AlphaGUARD in flow-through mode.

Radon-222 (Rn-222) exhalation rate is vital for estimating radiation risk from many kinds of materials. AlphaGUARD measures the radon concentration based on the ionization chamber principle, which is currently recognized as a reference instrument to measure radon. In China, measurements of radon exhalation rate are performed by AlphaGUARD operated in flow-through mode on a reference device to verify measurement accuracy. These measurements are performed in both open and closed loop. AlphaGUARD can fast rapidly the variation of the radon concentration in the chamber, which is tightly pressed against the surface of the medium to accumulate the exhaled radon. When the model is used to obtain the radon exhalation rate, the radon exhalation rates obtained by nonlinear data fitting on the measured radon concentrations are similar to the reference value of the device. The difference of radon exhalation rate values of six measurements is small.

Instrumentation to Measure On-Road Cyclist Noise Exposure: Considerations for Study Design with Smartphones and Sound Level Meters

Cyclist noise exposure has implications for health, comfort, and safety. Methods used for in situ measurement of on-road noise levels for cyclists vary, and the effects of key study design factors have not been investigated. To enable reliable research into cyclist noise exposure, this study aims to determine the accuracy of smartphone noise measurements in comparison with a sound level meter (SLM) reference instrument, and how noise levels are affected by travel speed, air speed, sensor placement, and use of a windscreen. Field data were collected with paired instruments in a typical urban cycling scenario, and comparisons made varying one design factor at a time (smartphone versus SLM, with versus without windscreen, handlebar versus shoulder placement, etc.). Results show that smartphones can generate reliable measurements (compared with SLM) of high-resolution (1-s) cyclist exposure for C-weighted noise, but not A-weighted noise. Sensor placement and windscreen have small effects on noise readings, but air speed and travel speed greatly affect measured noise levels. Future studies measuring on-road noise must consider the effects of wind- and bicycle-generated noise to ensure internal validity. Studies should also consider both study objectives and instrumentation when selecting a noise measure (frequency weighting). Research is needed into bicycle noise generation and perception of traffic noise by cyclists to enhance the reliability of future studies.

Seasonal Field Calibration of Low-Cost PM2.5 Sensors in Different Locations with Different Sources in Thailand

Low-cost sensors (LCS) have been increasingly deployed to monitor PM2.5 concentrations. More than 1500 LCS have been installed in Thailand to increase public awareness of air quality. However, performance of these sensors has not been systematically investigated. In this study, PM2.5 LCS were co-located next to a PM2.5 federal equivalent method (FEM) reference instrument at three Thai locations—in the north, center and northeast. We evaluated the performance of a PM2.5 LCS (PMS7003, Plantower) to understand the key factors affecting performance, including emission sources, relative humidity, temperature and PM2.5 concentration. Low PM concentration and high humidity levels had a significant impact on performance. Sensors in a high traffic emission area showed low correlation. The unadjusted PM2.5 LCS performance varied with locations. Errors were mainly observed at low concentrations. They significantly underestimated concentrations in congested urban environments. After calibration, accuracy was improved with multiple regression models. The performance of sensors only at Chiang Mai (CM) during the dry season and Ubon Ratchathani (URT) during the dry and wet seasons were acceptable with coefficient of variation: 5.8 ± 4.7–6.8 ± 5.0%, slope: 0.829–0.945, intercept: 1.12–5.49 µg/m3, R2: 0.880–0.934 and RMSE: 4.3–5.1 µg/m3. In the congested area in Bangkok (BKK), they underestimated concentrations of small particles.

Genetic Validation of Psoriasis Phenotyping in UK Biobank Supports the Utility of Self-Reported Data and Composite Definitions for Large Genetic and Epidemiological Studies

Genetic Validation of Psoriasis Phenotyping in UK Biobank Supports the Utility of Self-Reported Data and Composite Definitions for Large Genetic and Epidemiological Studies

Evaluation and characterization of imaging polarimetry through metasurface polarization gratings.

Metasurfaces are a new class of diffractive optical elements with subwavelength elements whose behavior can be lithographically tailored. By leveraging form birefringence, metasurfaces can serve as multifunctional freespace polarization optics. Metasurface gratings are novel, to the best of our knowledge, polarimetric components that integrate multiple polarization analyzers into a single optical element enabling the realization of compact imaging polarimeters. The promise of metasurfaces as a new polarization building block is contingent on the calibration of metagrating-based optical systems. A prototype metasurface full Stokes imaging polarimeter is compared to a benchtop reference instrument using an established linear Stokes test for 670, 532, and 460 nm gratings. We propose a complementary full Stokes accuracy test and demonstrate it using the 532 nm grating. This work presents methods and practical considerations involved in producing accurate polarization data from a metasurface-based Stokes imaging polarimeter and informs their use in polarimetric systems more generally.

Field Calibration of a Low-Cost Air Quality Monitoring Device in an Urban Background Site Using Machine Learning Models

Field calibration of low-cost air quality (AQ) monitoring sensors is essential for their successful operation. Low-cost sensors often exhibit non-linear responses to air pollutants and their signals may be affected by the presence of multiple compounds making their calibration challenging. We investigate different approaches for the field calibration of an AQ monitoring device named ENSENSIA, developed in the Institute of Chemical Engineering Sciences in Greece. The present study focuses on the measurements of two of the most important pollutants measured by ENSENSIA: NO2 and O3. The measurement site is located in the center of Patras, the third biggest city in Greece. Reference instrumentation used for regulatory purposes by the Region of Western Greece was used as the evaluation standard. The sensors were installed for two years at the same locations. Measurements from the first year (2021) from seven ENSENSIA sensors (NO2, NO, O3, CO, PM2.5, temperature and relative humidity) were used to train several Machine Learning (ML) and Deep Learning (DL) algorithms. The resulting calibration algorithms were assessed using data from the second year (2022). The Random Forest algorithm exhibited the best performance in correcting O3 and NO2. For NO2 the mean error was reduced from 9.4 ppb to 3 ppb, whilst R2 improved from 0.22 to 0.86. Similar results were obtained for O3, wherein the mean error was reduced from 13 to 4.3 ppb and R2 increased from 0.52 to 0.69. The Long-Short Term Memory Network (LSTM) also showed good performance in correcting the measurements of the two pollutants.

ON THE USE OF SOUND SPEED FOR EVALUATION OF THE PERFORMANCE OF LIQUID ULTRASONIC FLOW METER IN ZERO FLOW CONDITIONS

At present, ultrasonic flow meters have become well known in custody transfer applications in the petroleum industry. Since facilities for calibration of these meters are costly and limited, methods for performance verification in zero flow conditions have been developed. However, for liquid measurement, a method of zero flow verification is not available yet. In this context, this study presents a new method for zero flow test in liquid ultrasonic flow meters, using a highly accurate instrument as a reference for sound speed. The aim is to evaluate the performance, of a multipath liquid ultrasonic flow meter under different pressures and temperatures, by comparing the calculated sound speed with the result from the reference instrument. Additionally, transit time measurement is also verified in order to account for systematic errors. The experiments were conducted with two test fluids: water and mineral oil, with a maximum deviation of 0.25% during comparison. On the other hand, performing a transit time analysis indicates the presence of systematic errors, meaning that transit times can be adjusted in order to improve the performance of the flow meter. Furthermore, a factorial design is performed to investigate the effect of pressure and temperature, indicating a minimal pressure effect on sound speed when compared to the temperature effect.

State of the art of open-air rock art as World Heritage site: past, present and future

Since the 1970’s to the present day, our notions of world heritage and archaeological heritage have changed greatly, a fact that is reflected in the different conventions and charters of ICOMOS and UNESCO. In this research we explore what these changes have been, the state of the art of rock art worldwide, and what are the trends towards the future of heritage declarations, delving into the specific case of outdoor rock art, since its fragile and accessible nature requires specific management plans appropriate to its needs and characteristics, and how the growing trend of naming cultural landscapes as world heritage can be a powerful tool for the conservation, protection and dissemination of these heritage assets and their environments. The main objective of our research lies on the identification of the main features of open-air rock art on the UNESCO World Heritage List, establishing their current situation as to their preservation and social awareness and the policies developed in each particular case. This will be done through research and bibliographical approximation of various research sources, as well as official resources already mentioned: World Conventions, recommendations and ICOMOS charters as reference instruments in the declarations and management strategies of archaeological heritage and rock art.

Book Excerpt: The Inner Beauty of Basic Electronics: A new book shows the surprising complexity inside passive components

THIS HIGH-STABILITY film resistor, about 4 millimeters in diameter, is made in much the same way as its inexpensive carbon-film cousin, but with exacting precision. A ceramic rod is coated with a fine layer of resistive film (thin metal, metal oxide, or carbon) and then a perfectly uniform helical groove is machined into the film. • Instead of coating the resistor with an epoxy, it's hermetically sealed in a lustrous little glass envelope. This makes the resistor more robust, ideal for specialized cases such as precision reference instrumentation, where long-term stability of the resistor is critical. The glass envelope provides better isolation against moisture and other environmental changes than standard coatings like epoxy.

Electrochemical sensors on board a Zeppelin NT: in-flight evaluation of low-cost trace gas measurements

Abstract. In this work, we used a Zeppelin NT equipped with six sensor setups, each composed of four different low-cost electrochemical sensors (ECSs) to measure nitrogen oxides (NO and NO2), carbon monoxide, and Ox (NO2+O3) in Germany. Additionally, a MIRO MGA laser absorption spectrometer was installed as a reference device for in-flight evaluation of the ECSs. We report not only the influence of temperature on the NO and NO2 sensor outputs but also find a shorter timescale (1 s) dependence of the sensors on the relative humidity gradient. To account for these dependencies, we developed a correction method that is independent of the reference instrument. After applying this correction to all individual sensors, we compare the sensor setups with each other and to the reference device. For the intercomparison of all six setups, we find good agreements with R2≥0.8 but different precisions for each sensor in the range from 1.45 to 6.32 ppb (parts per billion). The comparison to the reference device results in an R2 of 0.88 and a slope of 0.92 for NOx (NO+NO2). Furthermore, the average noise (1σ) of the NO and NO2 sensors reduces significantly from 6.25 and 7.1 to 1.95 and 3.32 ppb, respectively. Finally, we highlight the potential use of ECSs in airborne applications by identifying different pollution sources related to industrial and traffic emissions during multiple commercial and targeted Zeppelin flights in spring 2020. These results are a first milestone towards the quality-assured use of low-cost sensors in airborne settings without a reference device, e.g., on unmanned aerial vehicles (UAVs).

Identifying optimal co-location calibration periods for low-cost sensors.

Low-cost sensors are often co-located with reference instruments to assess their performance and establish calibration equations, but limited discussion has focused on whether the duration of this calibration period can be optimized. We placed a multipollutant monitor that contained sensors that measure particulate matter smaller than 2.5 μm (PM2.5), carbon monoxide (CO), nitrogen dioxide (NO2), ozone (O3), and nitric oxide (NO) at a reference field site for one year. We developed calibration equations using randomly selected co-location subsets spanning 1 to 180 consecutive days out of the 1-year period and compared the potential root mean square errors (RMSE) and Pearson correlation coefficients (r). The co-located calibration period required to obtain consistent results varied by sensor type, and several factors increased the co-location duration required for accurate calibration, including the response of a sensor to environmental factors, such as temperature or relative humidity (RH), or cross-sensitivities to other pollutants. Using measurements from Baltimore, MD, where a broad range of environmental conditions may be observed over a given year, we found diminishing improvements in the median RMSE for calibration periods longer than about six weeks for all the sensors. The best performing calibration periods were the ones that contained a range of environmental conditions similar to those encountered during the evaluation period (i.e., all other days of the year not used in the calibration). With optimal, varying conditions it was possible to obtain an accurate calibration in as little as one week for all sensors, suggesting that co-location can be minimized if the period is strategically selected and monitored so that the calibration period is representative of the desired measurement setting.

Aerosol Measurement Degradation in Low-Cost Particle Sensors Using Laboratory Calibration and Field Validation.

Increasing concern over air pollution has led to the development of low-cost sensors suitable for wide-scale deployment and use by citizen scientists. This project investigated the AirU low-cost particle sensor using two methods: (1) a comparison of pre- and post-deployment calibration equations for 24 devices following use in a field study, and (2) an in-home comparison between 3 AirUs and a reference instrument, the GRIMM 1.109. While differences (and therefore some sensor degradation) were found in the pre- and post-calibration equation comparison, absolute value changes were small and unlikely to affect the quality of results. Comparison tests found that while the AirU did tend to underestimate minimum and overestimate maximum concentrations of particulate matter, ~88% of results fell within ±1 μg/m3 of the GRIMM. While these tests confirm that low-cost sensors such as the AirU do experience some sensor degradation over multiple months of use, they remain a valuable tool for exposure assessment studies. Further work is needed to examine AirU performance in different environments for a comprehensive survey of capability, as well as to determine the source of sensor degradation.

Optimizing the configuration of plasma radiation detectors in the presence of uncertain instrument response and inadequate physics

We present a general method for optimizing the configuration of an experimental diagnostic to minimize uncertainty and bias in inferred quantities from experimental data. The method relies on Bayesian inference to sample the posterior using a physical model of the experiment and instrument. The mean squared error (MSE) of posterior samples relative to true values obtained from a high fidelity model (HFM) across multiple configurations is used as the optimization metric. The method is demonstrated on a common problem in dense plasma research, the use of radiation detectors to estimate physical properties of the plasma. We optimize a set of filtered photoconducting diamond detectors to minimize the MSE in the inferred X-ray spectrum, from which we can derive quantities like the electron temperature. In the optimization we self-consistently account for uncertainties in the instrument response with appropriate prior probabilities. We also develop a penalty term, acting as a soft constraint on the optimization, to produce results that avoid negative instrumental effects. We show results of the optimization and compare with two other reference instrument configurations to demonstrate the improvement. The MSE with respect to the total inferred X-ray spectrum is reduced by more than an order of magnitude using our optimized configuration compared with the two reference cases. We also extract multiple other quantities from the inference and compare with the HFM, showing an overall improvement in multiple inferred quantities like the electron temperature, the peak in the X-ray spectrum and the total radiated energy.

Waveguide based passively demodulated photothermal interferometer for light absorption measurements of trace substances.

In this contribution, we present the development of a passively demodulated interferometer based on 3×3 waveguide couplers to measure light absorption of trace gases and aerosol particles via the photothermal effect. In contrast to a "classical" interferometer with two outputs, active quadrature control is not required to ensure a high sensitivity of the system. An algorithm for the evaluation of the photothermal interferometry signal from the outputs of asymmetric 3×3 couplers is detailed. The performance of the algorithm is demonstrated with NO2 calibration experiments using couplers with different working principles (i.e., fused-fiber and planar-waveguide based). The results of a laboratory measurement campaign using aerosolized nigrosin are discussed, and the measured aerosol absorption is compared to a reference instrument. A noise analysis shows interferometer phase noise to be the primary noise component. Improvements to the setup are recommended, which should improve the current instrumental detection limit in terms of absorption coefficient to below the current value of 100Mm-1 (1σ, 60 s). This corresponds to mass concentrations of about 10µg/m3 for submicrometer-size black carbon particles.

Three-Dimensional Method Combining Linearly Structured Light Sensing and Rotary Scanning for Measuring Aviation Bearings

The geometric parameters of aviation bearings need to be accurately measured to ensure that the bearings are correctly assembled for reliable operation and quality purposes. This study aimed to solve the problems presented by the low accuracy and low efficiency of the existing method while avoiding the error introduced by the deviation of the measurement beam from the center of the aviation bearings during measurement. This method determines the spatial posture of the axis of the rotary table using linear structured light sensing, and extracts the spatial point-cloud data of the aviation bearings based on rotary scanning. We propose algorithms for spatial property determination and point-cloud segmentation. To avoid the error caused by the deviation of the measurement beam from the center of the aviation bearings, the point-cloud data are transformed to a new coordinate system prior to extracting the features of the datum plane and raceway. An aviation bearing is measured to verify the validity of the proposed method. The radius and eccentricity of the raceway are 4.900 mm and 0.010 mm with experimental standard deviations of 0.002 mm and 0.001 mm, respectively. For comparison purposes, experiments with a coordinate measuring machine and contourgraph were also performed. The expanded measurement uncertainty considering the repeatability, reference instruments, and temperature drift is 1.6 μ m. The proposed method can be extended to precision noncontact measurements of workpieces with rotary structures.

Laboratory and field evaluation of a low-cost methane sensor and key environmental factors for sensor calibration.

Low-cost sensors enable finer-scale spatiotemporal measurements within the existing methane (CH4) monitoring infrastructure and could help cities mitigate CH4 emissions to meet their climate goals. While initial studies of low-cost CH4 sensors have shown potential for effective CH4 measurement at ambient concentrations, sensor deployment remains limited due to questions about interferences and calibration across environments and seasons. This study evaluates sensor performance across seasons with specific attention paid to the sensor's understudied carbon monoxide (CO) interferences and environmental dependencies through long-term ambient co-location in an urban environment. The sensor was first evaluated in a laboratory using chamber calibration and co-location experiments, and then in the field through two 8 week co-locations with a reference CH4 instrument. In the laboratory, the sensor was sensitive to CH4 concentrations below ambient background concentrations. Different sensor units responded similarly to changing CH4, CO, temperature, and humidity conditions but required individual calibrations to account for differences in sensor response factors. When deployed in-field, co-located with a reference instrument near Baltimore, MD, the sensor captured diurnal trends in hourly CH4 concentration after corrections for temperature, absolute humidity, CO concentration, and hour of day. Variable performance was observed across seasons with the sensor performing well (R 2 = 0.65; percent bias 3.12%; RMSE 0.10 ppm) in the winter validation period and less accurately (R 2 = 0.12; percent bias 3.01%; RMSE 0.08 ppm) in the summer validation period where there was less dynamic range in CH4 concentrations. The results highlight the utility of sensor deployment in more variable ambient CH4 conditions and demonstrate the importance of accounting for temperature and humidity dependencies as well as co-located CO concentrations with low-cost CH4 measurements. We show this can be addressed via Multiple Linear Regression (MLR) models accounting for key covariates to enable urban measurements in areas with CH4 enhancement. Together with individualized calibration prior to deployment, the sensor shows promise for use in low-cost sensor networks and represents a valuable supplement to existing monitoring strategies to identify CH4 hotspots.

Fiber Bragg Gratings for Temperature Measurements Under Thermal Gradients: Comparison Between Two Different Lengths

In recent decades, fiber Bragg grating (FBG) sensors found widespread acceptance in several biomedical applications thanks to their indisputable advantages. Thermal ablation treatments (TATs) account for one of the fields where FBGs have gained large applicability for temperature measurements. The sensing element length can affect the accuracy of the FBG measurement in this application. A longer length provides a more prominent peak in the FBG reflected spectrum, resulting in a higher signal-to-noise ratio (SNR). A shorter FBG length implies a lower SNR but offers the benefits of better spatial resolution. Therefore, the choice of an adequate length can be crucial to minimize measurement errors, but the literature lacks exhaustive investigations on this parameter. The aim of our study is to supply additional knowledge about the effect of two different FBG lengths on temperature estimation in the presence of linear thermal gradients and with gradients mimicking the condition caused by TATs. In both cases, we compared the output of a 10-mm FBG with those of four FBGs 1 mm long, using a thermal camera as a reference instrument. Results suggest the better suitability of shorter sensors to retrieve thermal gradient information along their position instead of the longer FBG, which could lead to unacceptable measurement errors during TATs.

Evaluating the Performance of Low-cost PM Sensors over Multiple COALESCE Network Sites

Air quality is a global concern, with particulate matter receiving considerable attention due to its impact on human health and climate change. Recent advances in low-cost sensors allow their deployment in large number to measure spatio-temporal and real-time air quality data. Low-cost sensors need careful evaluation with both regulatory approved methods and other data sets to understand their efficacy. In this work, PM concentrations measured by deploying low-cost sensors at four regional sites are evaluated through comparison with satellite-based model MERRA-2 and the SASS reference instrument. Daily PM2.5 mass concentration variation was analyzed at four regional sites of India from January 2020 to July 2020, including pre-lockdown and six different lockdown periods. Higher PM2.5 concentration was observed at Rohtak (119 µg/m3) compared to Mahabaleshwar (33 µg/m3), Bhopal (45 µg/m3) and Kashmir sites during the pre-lock down period. During the lockdown period, the PM2.5 mass concentration was reduced significantly compared to the pre-lockdown period at every location, although the PM2.5 concentration was different at each location. The air quality trend was quite similar in both the measurements, however, MERRA-2 reconstructed PM2.5 was significantly lower in the pre-lockdown period compared to the lockdown periods. Significant differences were observed between low-cost sensor measurements and MERRA-2 reanalysis data. These are attributed to the MERRA-2 modelling analysis that measures less PM2.5 concentration as compared to ground-based measurements, whereas low-cost sensor are ground-based measurements but needs corrections as it is subject to the calibration dependencies and biases.

Systematic Comprehensive Evaluation of the Mindray CX-9000 Coagulation Analyzer Performance.

The aim of the study was to conduct a comprehensive performance evaluation of the Mindray CX-9000 fully automated coagulation analyzer for the detection of the seven coagulation items. The performance of activated partial thromboplastin time (APTT), prothrombin time (PT), fibrinogen (FIB), thrombin time (TT), D-dimer (D-D), fibrinogen degradation product (FDP), and antithrombin Ⅲ (AT) was validated for precision, linear range, carryover contamination rate, reference interval validation, inter-method agreement, and anti-interference ability. The intra- and inter-precision (coefficient of variation, CV%) of all seven items was less than the target CV%; the carryover contamination rates for different concentrations and between items were < 10%. The slope of the linear regression equation for the theoretical and measured values of the linear range was within 1 ± 0.05 and R ≥ 0.975. The reference interval quoted from the manufacturer's reference interval passed ≥ 95%. The CX-9000 was compared with the results of the reference instrument STAGO R MAX (STA-R MAX) and the p-values for all items ranged from 0.822 to 0.987. Within the concentration range claimed by the manufacturer, the interference errors produced by all items met the manufacturer's claimed criteria, except for triglycerides which produced interference errors > 10% for the FIB, D-D, FDP, and bilirubin which produced interference errors for the FIB and D-D assays. The CX-9000 automatic coagulation analyzer has good stability and repeatability, a wide linear range of detection, low carryover contamination rate, and high resistance to interference, making it suitable for the testing of clinical specimens.

Calibration of Indian Dobson Spectrophotometer Nos. D112 and D036 during WMO Dobson Intercomparison Campaigns

The present study summarizes the results of calibration of Indian Dobson Spectrophotometer No. D112 and D036 during Dobson inter-comparison campaigns, held at Irene, South Africa from 07 – 18 October, 2019 and at Hohenpeissenberg, Germany from 15.07.2020 to 30.07.2020 respectively. In both the international inter-comparison campaigns, European Regional Standard Dobson Spectrophotometer No. D064 had been used as the reference instrument. According to the results of the inter-comparison of Dobson spectrophotometer instrument no. D112 and no. D036 with Regional Standard Dobson Instrument (D064), these instruments are reliable and their measurements are accurate and appropriate for further analysis as their deviations have been found within the acceptable limits i.e. less than - 0.3% for D112 and less than 0.01 for D036 respectively after final calibration.