Measurement Techniques

Abstract The important aspects of increasing hydrodynamic efficiency, improving performance and technical characteristics of various heat and mass transfer equipment, as well as ensuring the required regime and flow conditions of fluids with different viscosities have been analyzed. Such heat transfer equipment includes radiators that contain tubes for circulating heat transfer medium. When solving related issues, in addition to studying the flow characteristics of various fluids in circular horizontal tubes (capillaries), it is necessary to determine the conditions, under which the flow of fluid inside capillaries and circular tubes of small diameter is laminar, so it can be described by the Poiseuille equation. The experimental data on determining water flow rates in horizontal circular tubes of various diameters are presented. The dependence of the volumetric flow rate on the pressure drop has been determined. It was shown that the basic parameters that determine the flow characteristics of fluids in horizontal tubes are the tube radius and fluid dynamic viscosity. A flow of distilled water in tubes with diameters of 0.95, 1.6 and 2.0 mm was analyzed at a gauge pressure ranging from 0.266 to 4.000 kPa. It was found that when using a 0.95 mm diameter tube, the dependence of the volumetric flow rate on the gauge pressure remains linear in the entire analyzed range of pressures. An increase in the tube radius increases the likelihood of flow velocity fluctuations and the appearance of a radial velocity component (i.e., the occurrence of the elements of a turbulent fluid flow structure). The water flow regime in tubes with diameters of 1.6 and 2.0 mm deviates from the laminar at pressures exceeding 1.3 and 1.0 kPa, respectively. The dependence of the volumetric flow rate on pressure for a 40% aqueous solution of calcium chloride, as well as transformer, transmission, and engine oils with dynamic viscosities ranging from 0.002 to 0.182 Pa · s remains linear up to the tube diameters of 5–6 mm. The results of studying fluids with different viscosities are presented in the form of a nomogram illustrating the ratio of the tube radius raised to the fourth power to the fluid viscosity as a function of the tube radius. By analyzing this relationship, it becomes possible to predict the flow characteristics of the studied fluid at given tube radius and dynamic viscosity values. The obtained results can be used when designing and operating various heat transfer devices, such as radiators with tubes for circulating a heat transfer medium.

Abstract The article addresses the ambiguity and diversity of requirements provided in regulatory documents and imposed on measurement and unit dissemination procedures comprising the chain of metrological traceability. A unified approach to the study of these procedures based on their classification is justified. Different types of procedures are analyzed: primary reference measurement procedures, reference measurement procedures, calibration procedures, verification procedures, end-user measurement procedures, and measurement procedures. Requirements for the development, study, and approval of the described procedures are considered. The article proposes a classification of procedures according to their place in the chain of metrological traceability, the type of metrological characteristics to be determined, and their application in the sphere of state control. The performed analysis of regulatory documents is summarized in a table describing the main requirements for the development and approval of measurement and unit dissemination procedures. The author considers requirements established for such conformity assessment of measurement and unit dissemination procedures as method certification, validation, and verification. The definitions and scope of application of conformity assessment procedures for measurement and unit dissemination procedures are presented. An analysis of requirements for the conformity assessment of procedures yielded a block diagram that can be used by laboratories to unambiguously select a conformity assessment procedure for approval of the required measurement or unit dissemination procedure, specifically when preparing for accreditation for compliance with ISO/IEC 17025-2017 General Requirements for the Competence of Testing and Calibration Laboratories. The proposed diagram for selecting a conformity assessment procedure for a particular procedure eliminates the ambiguity of requirements specified in regulatory documents.

Abstract Specifics of practical use of the methods for measuring the dielectric properties of materials at different (factory and metrological) laboratories, and impact of such specifics on the measurements results have been considered. The measurements were performed at the factory radio physics lab of the Obninsk Research and Production Enterprise “Technologiya” named after A.G. Romashin, and at the metrology lab of the East-Siberian branch of the Federal State Unitary Enterprise “All-Russian Scientific Research Institute for Physical-Engineering and Radio Engineering Metrology.” The results of measuring the relative permittivity and dielectric loss tangent of solid material samples in the microwave range of electromagnetic radiation were analyzed. Based on the study results, the specifics of practical use of the standard methods for measuring the dielectric properties of materials have been established that were not described in the literature before. To perform measurements, circular waveguide resonators and standardized measurement procedures were used. The following two cavity resonator-based measurement techniques were applied: at a fixed resonance frequency (resonance tuning performed by moving a plunger), and at a fixed resonance length (resonance tuning performed by varying resonance frequency). These techniques were utilized at the factory and metrology labs, respectively. The results of measuring the dielectric properties of the samples showed good reproducibility and were consistent with the requirements for measurement methods. Lower reproducibility of the results was observed when measuring the dielectric properties of the samples of hygroscopic materials, materials demonstrating volumetric non-uniformity of properties, as well as in cases, when the diameter of the measured samples did not meet the measurement technique requirements. The obtained data can be used to improve the reproducibility of the results of measuring the dielectric properties of materials during practical application of the considered measurement methods.

Abstract We consider the problem of analysis of the voice source of speech within the range of short-term observations. The problem of insufficient speed of the available methods for the analysis of voice source is described, regardless of the method of data preparation: either synchronous with the main tone of speech sounds or asynchronous. We propose a method for the analysis of voice sources based on the two-level autoregressive model of the speech signal. We describe a software realization of the developed method based on the Berg-Levinson high-speed procedure of numerical calculations. It is shown that this procedure is characterized by a relatively low level of computation costs and its application does not require synchronization of the sequence of observations with the main tone of speech signal. With the help of software implementation of the proposed method, we designed and performed full-scale experiment aimed at analyzing the vowel sounds in the speech of a reference speaker. The results of this experiment confirmed the elevated speed of the proposed method and enabled us to formulate the requirements to the duration of speech signal for the real-time voice analysis. Thus, the optimal duration of the speech signal should vary within the range 32–128  msec. The obtained results can be used for the development and investigation of digital speech communication systems, systems of voice control, biometrics, biomedicine and other speech systems in which specific voice features of speaker’s speech are of primary importance.