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Pojic M.,Institute for Food Technology | Mastilovic J.,Institute for Food Technology | Majcen N.,Metrology Institute of the Republic of Slovenia
Food Chemistry | Year: 2012

The robustness assessment is a part of a method validation protocol, during which several characteristics of an analytical method are also evaluated (e.g. accuracy, repeatability, reproducibility, linearity, intermediate precision, measurement uncertainty) in order to assess its fitness for purpose. The purpose of robustness assessment of the near infrared spectroscopy method (NIRS) is to indicate which factor significantly influence the obtained results, as well as to point to the potential problems that might occur in the routine application of the method. The assessment of robustness of the NIRS method included variation of certain operational and environmental factors at three level (-1, 0, 1) by applying univariate (one-variable-at-a-time, OVAT) and multivariate (multivariate-at-a-time, MVAT) approach to the experimental design. Operational and environmental factors that were varied included the number of subsamples to be measured in the NIRS measurement (1), environmental temperature (2), sample temperature (3), environmental air humidity (4), instrument voltage (5) and lamp aging (6). Regardless the applied experimental design, external factors with significant influence on obtained NIRS results were indicated, as well as pointed the potential problems that might occur in the routine application of the method. In order to avoid them, every effort should be made to stabilize instrument and sample temperature and to standardize the homogeneity and number of subsamples to be measured in NIRS measurement. Moreover, the obtained results highlighted the necessity that the NIRS instruments should work through a voltage regulator. © 2012 Elsevier Ltd. All rights reserved.


Grgic G.,Metrology Institute of the Republic of Slovenia | Pusnik I.,University of Ljubljana
International Journal of Thermophysics | Year: 2011

A thermal imager with a microbolometer focal plane array (FPA) detector which does not require cooling is a relatively new type of instrument. With increasing use of thermal imagers for absolute temperature measurements, there is also an increasing need for their calibration. Five thermal imagers from three manufacturers were evaluated to identify parameters which affect their performance for accurate temperature measurements. Evaluation methods and measurements of parameters such as accuracy, temperature resolution, drift between internal calibration, non-uniformity, size-of-source effect, and distance effect are discussed. Based on the results, it is indicated which parameters should be evaluated in the calibration procedure as well as the uncertainty budget. The suitability of a blackbody for calibration was also addressed, especially in terms of dimensions related to the field of view of a thermal imager at the minimum focal distance. © 2011 Springer Science+Business Media, LLC.


PubMed | Institute for Food Technology and Metrology Institute of the Republic of Slovenia
Type: Journal Article | Journal: Food chemistry | Year: 2014

The robustness assessment is a part of a method validation protocol, during which several characteristics of an analytical method are also evaluated (e.g. accuracy, repeatability, reproducibility, linearity, intermediate precision, measurement uncertainty) in order to assess its fitness for purpose. The purpose of robustness assessment of the near infrared spectroscopy method (NIRS) is to indicate which factor significantly influence the obtained results, as well as to point to the potential problems that might occur in the routine application of the method. The assessment of robustness of the NIRS method included variation of certain operational and environmental factors at three level (-1,0,1) by applying univariate (one-variable-at-a-time, OVAT) and multivariate (multivariate-at-a-time, MVAT) approach to the experimental design. Operational and environmental factors that were varied included the number of subsamples to be measured in the NIRS measurement (1), environmental temperature (2), sample temperature (3), environmental air humidity (4), instrument voltage (5) and lamp aging (6). Regardless the applied experimental design, external factors with significant influence on obtained NIRS results were indicated, as well as pointed the potential problems that might occur in the routine application of the method. In order to avoid them, every effort should be made to stabilize instrument and sample temperature and to standardize the homogeneity and number of subsamples to be measured in NIRS measurement. Moreover, the obtained results highlighted the necessity that the NIRS instruments should work through a voltage regulator.


Lapuh R.,Metrology Institute of the Republic of Slovenia | Sira M.,Czech Metrology Institute | Lindic M.,Slovenian Institute of Quality and Metrology | Voljc B.,Slovenian Institute of Quality and Metrology
CPEM 2016 - Conference on Precision Electromagnetic Measurements, Conference Digest | Year: 2016

This paper presents the evaluation of uncertainty components attributed to the algorithm used to estimate sampled signal parameters. The white noise in the signal will influence the standard deviation of the estimates while signal imperfections like harmonic distortions, interharmonics and even non-white noise would produce bias, leading to non-statistical uncertainties. An a-priori knowledge of sampled signal is required to account for proper evaluation of these uncertainties. © 2016 IEEE.


Voljc B.,Slovenian Institute of Quality and Metrology | Lindic M.,Slovenian Institute of Quality and Metrology | Pinter B.,Slovenian Institute of Quality and Metrology | Kokalj M.,Slovenian Institute of Quality and Metrology | And 3 more authors.
IEEE Transactions on Instrumentation and Measurement | Year: 2013

This paper describes development and evaluation of a new coaxial current shunt for the nominal current of 100 A. The current shunt has been developed for both ac-dc transfer difference measurement and direct measurement of ac current. The direct ac measurement method was proposed by the Slovenian Institute of Quality and Metrology in 2002 and has now been expanded up to 100 A with the shunt described here. The forced air cooling system was implemented and evaluated to improve the shunt characteristics while keeping the current shunt resistors well within the safe operating range. © 2013 IEEE.


Lapuh R.,Metrology Institute of the Republic of Slovenia | Lapuh R.,Slovenian Institute of Quality and Metrology
IEEE Transactions on Instrumentation and Measurement | Year: 2015

This paper describes an algorithm for estimating the frequency, amplitude, and phase of the fundamental component in harmonically distorted waveforms. The algorithm minimizes the phase difference between the sine model and the sampled waveform by effectively minimizing the influence of the harmonic components. It uses a three-parameter sine-fitting algorithm for all phase calculations. The resulting estimates show up to two orders of magnitude smaller sensitivity to harmonic distortions than the results of the four-parameter sine fitting algorithm. © 1963-2012 IEEE.


Lapuh R.,Metrology Institute of the Republic of Slovenia | Lapuh R.,Slovenian Institute of Quality and Metrology | Voljc B.,Metrology Institute of the Republic of Slovenia | Lindic M.,Metrology Institute of the Republic of Slovenia
CPEM 2016 - Conference on Precision Electromagnetic Measurements, Conference Digest | Year: 2016

This paper describes evaluation of Keysight 3458A noise performance. When 3458A is used for sampling, different sources of noise are added to the sampled signal. Some of them (quantization noise, input front-end noise and IADC noise) are covered in this paper. © 2016 IEEE.


Lapuh R.,Metrology Institute of the Republic of Slovenia | Lapuh R.,Slovenian Institute of Quality and Metrology | Voljc B.,Metrology Institute of the Republic of Slovenia | Kokalj M.,Metrology Institute of the Republic of Slovenia | And 2 more authors.
CPEM 2016 - Conference on Precision Electromagnetic Measurements, Conference Digest | Year: 2016

This paper describes the procedure to reduce an estimation bias of interpolated DFT and single-model sine-fit algorithms. Estimation bias reduction of more than an order of magnitude is attainable. The procedure does not modify the estimation algorithm itself and additional knowledge of the measurement system or additional sampled points are not required. © 2016 IEEE.


Lapuh R.,Slovenian Institute of Quality and Metrology | Voljc B.,Metrology Institute of the Republic of Slovenia | Lindic M.,Metrology Institute of the Republic of Slovenia
CPEM 2016 - Conference on Precision Electromagnetic Measurements, Conference Digest | Year: 2016

This paper describes an accurate method to estimate active power of repetitive non-coherently sampled arbitrary signal. For that purpose the window technique was used on not pure sine wave signals where coherent sampling was not possible but the spectral components in the signal were well separated, at least for a few FFT bins. The actual performance of the method can be tuned by the selection of the appropriate time window (Hanning, Blackmann-Harris (BH92),..). © 2016 IEEE.


Lapuh R.,Metrology Institute of the Republic of Slovenia | Lapuh R.,Slovenian Institute of Quality and Metrology | Clarkson P.,Slovenian Institute of Quality and Metrology | Pogliano U.,INRIM - Istituto Nazionale di Ricerca Metrologica | And 2 more authors.
IEEE Transactions on Instrumentation and Measurement | Year: 2011

The measurement of many signal parameters using digital sampling relies on synchronization between the sampling clock and the signal under analysis. Deviations in the frequency of the measured signal from that expected can lead to significant measurement errors. Many techniques for overcoming these problems have been developed. Appraisals of the performance of these algorithms usually involve relatively benign steady-state signals, and the treatment is often heavily mathematical. This paper describes the testing of several algorithms for accurately recovering frequency and harmonic amplitude and phase information from mains-borne waveforms. This paper focuses on their practical use while avoiding abstract mathematical concepts. © 2006 IEEE.

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