1. Force signal alignment in dynamic testing machine calibration applicationsMiha Hiti, 2026, original scientific article Abstract: Calibration of force in measuring systems where the force is time dependent i.e. dynamically changing, introduces additional complexities versus quasi-static calibration conditions. Time variable force signals necessitate accurate time alignment between concurrent signals – measurement series from unit under test and the measurement series from the reference standard need to be synchronised. Different unsynchronised measuring systems are typically used for acquisition of each calibration signal and they need to be time aligned in post- processing to eliminate as much as possible the influence of the sample misalignment from the resulting testing machine indication error. The paper focuses on the time synchronization of measurement series by using cross-correlation to determine the necessary time correction when calibrating testing machines with dynamic cyclic force excitation. Measurements are presented for calibration signals in the examples of 20 kN testing machine compression calibration for 5 kN ± 1 kN cycling force with 1 Hz, 5 Hz, and 10 Hz cycling frequencies, and 1000 kN testing machine tensile calibration for 500 kN ± 100 kN cycling force with 1 Hz cycling frequency. The standard deviation of the error distribution after time correction and clock rate compensation was below 0.2 % for both, 20 kN testing machine calibration, and 1000 kN testing machine calibration.
Keywords: calibration, dynamic testing systems, time-synchronization, cross-correlation
Published in DiRROS: 11.02.2026; Views: 359; Downloads: 71
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2. Can low-cost sensors (LCS) enhance air quality monitoring for personal pollution exposure assessment?Anja Ilenič, Alenka Mauko Pranjić, Janez Ščančar, Radmila Milačič Ščančar, Kumar Prashant, 2025, original scientific article Abstract: Laboratory and field assessments of low-cost sensors (LCS) are essential for ensuring the accuracy of PM2.5 measurements collected by citizens in air quality campaigns. Evaluation of Sensirion SPS30 (LCS SPS30) in controlled laboratory setting showed a coefficient of determination (R2) ranging from 0.81–0.99 and a root mean square error (RMSE) from 0.81–61.72 μg m−3, at average concentration of 21.5 μg m−3. In contrast, co-location assessment at an average concentration of 9 μg m−3 resulted in R2 of 0.5 and a RMSE of 6.82 μg m−3. The results demonstrated that the sensor met micro-environmental monitoring standards (accuracy < 25%) and United States Environmental Protection Agency's performance criteria (RMSE ≤ 7 μg m−3, R2 > 0.7) only at relative humidity (RH) levels below 60%, emphasising its strong sensitivity to RH and the need for RH-dependent data corrections. The observed underestimation or overestimation of PM2.5 readings was primarily attributed to variations in particle composition and concentration. Despite accuracy variations, LCSs can effectively capture spatiotemporal urban air quality patterns and identify pollution hotspots in community monitoring, particularly in low-pollution environments. In a citizen-led PM2.5 monitoring campaign in Maribor, Slovenia, the lowest concentrations were recorded at 15:00 (2.9 μg m−3), while the highest occurred during the morning rush-hour (4.8 μg m−3), likely attributed to the planetary boundary layer’s impact on atmospheric particulate dispersion. Spatial analysis revealed that hotspots clustered near intersections, where vehicle waiting time is the longest.
Keywords: particulate matter, low-cost sensor, Sensirion SPS30, citizen science, calibration
Published in DiRROS: 18.09.2025; Views: 615; Downloads: 272
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3. Improving uncertainty of strain gauge bridge standardsMiha Hiti, 2018, published scientific conference contribution Abstract: The article proposes a procedure for calibration of strain gauge bridge standards with improved relative calibration uncertainty. In contrast to a typical calibration with voltage ratio standards or comparison calibration with other bridge standards, the proposed procedure uses a calibrated reference bridge amplifier, additionally evaluated using combinatorial calibration technique to improve its calibration uncertainty. The resulting uncertainty of ratio steps referenced to zero ratio step is lower than the traditional uncertainty achieved through direct independent traceability to mVV−1 ratio values. The proposed procedure enables direct application of the calibrated bridge standard values with low relative uncertainty for calibration of bridge amplifiers, without the need for additional combinatorial evaluation of each individual bridge amplifier.
Keywords: voltage ratio, linearity check, bridge standard, calibration
Published in DiRROS: 05.04.2024; Views: 972; Downloads: 551
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4. Analysis of loading profile effect on testing machine calibration resultsMiha Hiti, 2021, original scientific article Abstract: The paper presents an evaluation of the loading profile effect on the testing machine calibration. First, a 20 kN force transducer was calibrated in a force calibration machine. This transducer was then used for a number of calibration runs in a 600 kN material testing machine where the time step interval of the same loading profile was varied from 120 s to 0 s. Results show good agreement for most of the range but highlight an increasing error due to synchronization and filtering issues in measured signals when approaching very short step intervals and continuous loading.
Keywords: force calibration, loading profile, measurement uncertainty, continuous loading
Published in DiRROS: 20.12.2023; Views: 1023; Downloads: 612
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5. Compensation of synchronization error effect in testing machine calibrationMiha Hiti, 2021, original scientific article Abstract: The paper presents an evaluation of synchronization issues when performing material testing machine calibration using continuous loading. A procedure for the compensation of a rangewide error in calibrated force values is proposed based on a correction factor determined from static and transient errors difference at a chosen force step. The procedure was applied for a calibration of a testing machine with a 20 kN force transducer and 200 N/s to 2000 N/s loading rates. The results show good performance of the compensation technique, reducing calibration errors to below 1% in non-synchronized signals even under unknown filter and delay setting.
Keywords: force calibration, loading profile, measurement uncertainty, continuous loading
Published in DiRROS: 20.12.2023; Views: 1132; Downloads: 603
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6. Validation of combinatorial evaluation of strain-gauge amplifier linearityMiha Hiti, 2020, original scientific article Abstract: This paper describes a validation of a combinatorial calibration technique based calibration procedure for strain-gauge amplifier calibration. The deviation between two strain-gauge amplifiers at calibration using the combinatorial technique is compared to the deviation between the same two amplifiers at calibration on a force calibration machine as a transducer-amplifier chain under unchanged conditions, serving as an amplifier linearity comparator. This enables the validation to be confirmed with a suitable expanded measurement uncertainty of 3 nV/V.
Keywords: strain-gauge amplifier, calibration, combinatorial technique, validation
Published in DiRROS: 21.08.2023; Views: 1321; Downloads: 528
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7. Model updating concept using bridge Weigh-in-Motion dataDoron Hekič, Andrej Anžlin, Maja Kreslin, Aleš Žnidarič, Peter Češarek, 2023, original scientific article Abstract: Finite element (FE) model updating of bridges is based on the measured modal parameters and less frequently on the measured structural response under a known load. Until recently, the FE model updating did not consider strain measurements from sensors installed for weighing vehicles with bridge weigh-in-motion (B-WIM) systems. A 50-year-old multi-span concrete highway viaduct, renovated between 2017 and 2019, was equipped with continuous monitoring system with over 200 sensors, and a B-WIM system. In the most heavily instrumented span, the maximum measured longitudinal strains induced by the full-speed calibration vehicle passages were compared with the modelled strains. Based on the sensitivity study results, three variables that affected its overall stiffness were updated: Young’s modulus adjustment factor of all structural elements, and two anchorage reduction factors that considered the interaction between the superstructure and non-structural elements. The analysis confirmed the importance of the initial manual FE model updating to correctly reflect the non-structural elements during the automatic nonlinear optimisation. It also demonstrated a successful use of pseudo-static B-WIM loading data during the model updating process and the potential to extend the proposed approach to using random B-WIM-weighed vehicles for FE model updating and long-term monitoring of structural parameters and load-dependent phenomena.
Keywords: monitoring, bridge, viaduct, bridge weigh-in-motion (B-WIM), structural health monitoring (SHM), finite element (FE), calibration, model updating
Published in DiRROS: 29.05.2023; Views: 1548; Downloads: 869
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