Measuring instruments
The mixture of argon and mercury vapor with temperature-dependent composition is used as the background gas in different types of gas discharge illuminating lamps. The aim of this work was to develop a model of the low-current discharge in an argon-mercury mixture at presence of a thin insulating film on the cathode and to investigate the influence of film on the discharge ignition voltage at low ambient temperatures. When discharge modeling, we used the obtained earlier expression which describes dependence of the mixture ionization coefficient on temperature. When there was a thin insulating film on the cathode the model took into account that positive charges are accumulated on its surface during the discharge. They generate an electric field in the film sufficient for the field emission of electrons from the metal substrate of the electrode into the insulator and some of them can overcome the potential barrier at the film outer boundary and go out in the discharge volume improving emission characteristics of the cathode.
Calculations showed that at a temperature decrease the electric field strengthes in the discharge gap and the voltage in it are increased due to reduction of the saturated mercury vapor density in the mixture followed by the decrease of its ionization coefficient. Existence of a thin insulating film on the cathode surface results in an increase of the cathode effective secondary electron emission yield which compensates the reduction of the mixture ionization coefficient value.
The results of discharge characteristics modeling demonstrate that in case of the cathode with an insulating film the discharge ignition becomes possible at a lower inter-electrode voltage. This ensures outdoor mercury lamp turning on at a reduced supply voltage and increases its reliability under low ambient temperatures.
The search for new crystalline host materials for the usage in lasers emitting in the eye-safe spectral range of 1.5–1.6 µm is an important task. The aim of this work was to study the growth technique, spectroscopic properties and laser characteristics of new active media – crystals Er3+,Yb3+:Ca2RE2(BO3)4
(RE=Y, Gd).
Calcium-yttrium Er3+,Yb3+:Ca3Y2 (BO3)4 (CYB) and calcium-gadolinium Er3+,Yb3+: Ca2 Gd 2(BO3)4 (CGB) oxoborate crystals co-doped with erbium and ytterbium ions were investigated. Polarized absorption and emission cross-section spectra were determined. The lifetimes of 4I11/2 and 4I13/2 energy levels of Er3+ ions were measured and ytterbium-erbium energy transfer efficiencies were estimated. The calculation of the gain cross-section spectra was performed. By using of Er3+,Yb3+: Ca2 RE 2(BO3)4 (RE=Y, Gd) crystals the laser performance was realized, for the first time to the best of our knowledge. The laser characteristics were studied in a quasi-CW (QCW) laser operation.
The wide band with a peak at the wavelength of 976 nm is observed in the absorption spectra of both crystals. This peak coincides with the emission wavelength of the pump laser diodes for Yb-doped active media. The maximum value of absorption cross-section was 1.7 × 10–20 cm2 for polarization E // b for both crystals. The lifetimes of the upper laser level 4I13/2 of Er3+ ions were 580 ± 30 μs and 550 ± 30 μs for Er,Yb:CYB and Er,Yb:CGB crystals, respectively. The energy transfer efficiencies from ytterbium to erbium ions for an Er,Yb:CYB and Er,Yb:CGB crystals were 94 % and 96 %, respectively. According to gain spectrum of the Er,Yb:CYB crystal the gain band peak is centered at the wavelength of 1530 nm. The maximum QCW output power was 0.5 W with slope efficiency of 13 % regarding to absorbed pump power for an Er,Yb: CYB crystal. The laser beam parameter M2 did not exceed < 1.5.
Based on the obtained results, it can be concluded that these crystals are promising active media for lasers emitting in the spectral range of 1.5–1.6 μm for the usage in laser rangefinder and laser-induced breakdown spectroscopy systems, and LIDARs.
The widespread use of cryogenic fuels in the aerospace industry necessitates additional thermal insulation of aircraft fuel tanks. At the same time a static charge may occur on the heat insulating layer during operation which can lead to an explosion if fuel leaks. To avoid such situations an antistatic conductive coating is applied to the insulation. The aim of the study is to develop a device for remote control of conductive coatings of aircraft fuel tanks which allows to quick find and mark damaged areas.
The developed method consists in changing the electrical capacitance between the conductive coating of the controlled object and the scanning electrode allowing to identify hazardous in terms of sparking closed shape defects. The basic technical requirements for the device were formed and the required minimum size of the monitored defect were indicated. The design features necessary for the implementation of the device were considered. A block diagram were developed on the basis of which an experimental bench for capacitive control were created which were is based on the bridge measurement method.
The article presents the results of the finite-difference calculation of the electric field in the structure of a capacitive sensor in the presence of a defect, the dependence of the capacitance of the sensor on its displacement over the defective area was also obtained. As the result of experimental studies the experimental data obtained confirmed the theoretical calculations and the correctness of the mathematical model with an accuracy of no worse than 5 %, the absolute error of fixing the defect ± 2 mm at a scanning speed of 0,02 m/s. Was shown that the total error of fixing the coordinates of the defect at different positions of the air gap sensor, temperature and scanning speed lies in the range of 1,5–6,5 mm. The materials presented in the article make it possible to increase flight safety by reducing the likelihood of sparking.
Recently in the world practice of aerospace monitoring of the Earth there has been an increasingly active using of methods and devices of hyperspectral imaging. Thus creation of systems designed for recording hyperspectral data and methods for their processing is an actual task for remote sensing of the Earth. The aim of the article was to develop and create a small-sized satellite modular hyperspectrometer in visible and near infrared range, designed to receive information on remote sensing of the Earth in order to constantly update data about state of natural environment and infrastructure objects using videospectral methods with the possibility of comprehensive study of both spectral and spatial characteristics of the observed objects.
A small-scale satellite modular hyperspectrometer has been developed. The distinctive features of the equipment include high spectral resolution and small dimensions. A hyperspectrometer includes two main modules: an optical module and an electronics one. The design feature of the optical module is the use of a concave holographic diffraction grating in a polychromator. The electronics module is based on a single board computer. Their description and design features, a scheme for the formation of a hypercube and software for its further processing are presented in the paper. The developed hardware (test equipment, a space experiment simulator and a spatial scanning system) for efficiency testing is presented also, as well as test measurements ware conducted.
It is worth noting the extremely small dimensions for this class of devices in comparison with analogues as well as the vibration resistance of the equipment.
One of the main conditions of safe operation of gas pipelines is the use of non-destructive diagnostic methods. Particularly important problem is the earlier operational diagnosis of pipes’ material of main gas pipelines based on the evaluation of the stress-strain state, elastic moduli and properties anisotropy by acoustic methods. The aim of the work is to develop methods for acoustic assessment of the stress-strain state, the elastic moduli and the properties anisotropy of pipeline material and to study these characteristics in different sections of main pipelines using a device based on contactless EMA transducers.
Methods are implemented using specialized equipment (the structurescope SEMA) and non-contact electromagnetic acoustic transducers. As an object of research, we used fragments – the cuttings of gas pipelines with circumferential welds both after fabrication and removed from service with stress corrosion cracking, including ones with corrosion damage and without visible damage.
The method of determining the plane stress-strain state of pipeline elements is based on the phenomenon of acoustoelasticity – the dependence of the propagation velocity of ultrasonic waves on mechanical stresses. The method for determining the elastic characteristics of materials and the anisotropy of their properties is based on the relationship between the velocities of ultrasonic waves and the elastic properties of the medium. Both techniques are implemented by sounding the sample in one section using a longitudinal wave and two shear waves with mutually perpendicular polarization planes coinciding with the main stresses, and measuring their propagation times.
It is shown that the stress state distribution both in the circumferential direction and along the generatrix is uneven which is caused by the peculiarities of samples (presence of a welded joint, stress corrosion cracking, long-term operation). The smallest acoustic anisotropy is observed for the Young's modulus. The anisotropy of the properties of most samples is in the range of 12–14 % for shear modulus, 9–10 % for Young’s modulus, 13–15 % for Poisson’s ratio. For samples with stress corrosion cracking a sharp decrease in the anisotropy coefficient is observed which makes it possible to use the indicated characteristics as informative parameters in detecting stress corrosion cracking.
A feature of the proposed methods is high accuracy, due to the absence of necessity to determine the material density and precision measurement of its thickness, the measurement error of which is significant by known methods.
Keywords: main gas pipeline, elastic moduli, acoustic anisotropy of properties, the biaxial stress-strain state, longitudinal and transversal waves.
Methods of measurements, monitoring, diagnostics
Provding a high level of durability of heat exchange equipment of water-cooled reactors under local stochastic temperature pulsations is an important scientific and technical problem for the nuclear power industry. Temperature pulsations produced by mixing non-isothermal coolant flows with high temperature gradient are most dangerous. This work is an experimental study of temperature and stress-strain state of a tube sample under local stochastic temperature pulsations caused by mixing of coolant flows.
To solve the problems posed, a Y-junction with «counter injection» was built, which was included in the thermal-hydraulic research facility. The design of the Y-junction allows study of the thermal-hydraulic characteristics and durability of tube samples made of austenitic steel of 60 × 5 мм. Some tube samples had developed for measuring the temperature, stress-strain state of tube material and temperature field of coolant flow in mixing zone of single-phase coolants with different temperatures. Measuring tube samples were equipped with micro thermocouples and strain gauges.
The experimental data of temperature pulsations, time-averaged temperature field in the coolant flow and on the outer surface of the sample were obtained, and statistical and spectral correlation characteristics of temperature pulsations were analyzed. According to results of measuring the relative strain, values of stresses were calculated.
Devices and research techniques are developed. The combination of coolant flows parameters that provide thermal load of the metal surface at the highest level of stress intensity amplitude was obtained. The study results are used to verify the method for evaluating fatigue of reactor installations materials under stochastic temperature pulsations.
Graphene-based nanostructures are the promising materials for applications as electron emitters.
The aim of the work is to study the field electron emission from the edge of a single graphene plane.
In the semi-classical approximation, a model of field electron emission from the edge of a rectangular graphene sheet has been developed.
The current density of field electron emission into vacuum from the edge of a flat graphene sheet was calculated depending on the magnitude of the pulling electric field strength.
The analysis and comparison of limiting emission currents from graphene and from bulk systems have been carried out.
The results of the work can be used in the development of graphene-based field effect cathodes.
The propagation of a pulsed signal of a surface wave over an object with a non-uniform surface layer, obtained, for example, as a result of surface hardening, with structural damage, is accompanied by the dispersion of the velocity of the wave carrying important information about the parameters of such a layer. The aim of the work is to study the relationship between the acoustic parameters of a pulsed acoustic signal of a surface and subsurface waves and the surface layer of steel specimens hardened by high-frequency hardening, and gray iron-chill. Features of the surface and subsurface waves application for ultrasonic evaluation of physicomechanical properties of solids. Strenghtned inhomogeneous surface layer.
A brief analysis of the known works on determining the depth of hardened surface layers by various methods, including high-frequency hardening, cementation, etc., is carried out. Based on the Oulder integral expression. The dependence connecting the wave velocity, its frequency, the depth of the hardened layer and the spatial distribution of hardness represented as a step with a changing slope of its side surface simulating the transition zone of the hardened layer are calculated.
Using the pulse method and low-aperture transducers with a frequency of 1−3.8 MHz, the dependences of the surface wave velocity on the cutting height of a layer hardened by HDTV hardening are obtained. A comparison of experimental data and calculations of the theoretical model showed a good qualitative correspondence between them, demonstrate a high «sensitivity» of the method in relation to the nature of the change in hardness over the depth of the hardened layer. It is shown that the proposed approach is promising for solving the inverse problem of restoring the spatial distribution of hardness based on experimental data.
The goniometric method was approbated to determine the dependence between amplitude-angle characteristics and depth of the surface steel layers hardened by high-frequency hardening and depth of hardened gray iron specimens layer – with chill. It is shown that the optimal angle corresponding maximum of excited surface wave amplitude in steel specimens is decreasing up to 24–26' vs. hardened depth layer. But when the tested specimens from cast iron this angle decreasing is nearly of 6°. Recommendations on the use of research results in practice are given.
When measuring low-power optical signals, the receiving modules of systems should ensure a sufficiently high accuracy of the received data. In this regard, it is advisable to use photon counters. They are highly sensitive, but are characterized by data recording errors. The aim of this work was to determine the effect of the average pulse count rate of photons at the output of the counter on the reliability of the received information with the dead time photon counter.
An expression for estimating the reliability of the received binary data when they were registered in the fiber-optic communication channel was obtained. This expression takes into account the statistical distributions of the number of pulses at the output of the photon counter.
Studies have shown that with increasing ns0, the reliability of the data obtained at the beginning is practically does not change and is close to unity, and then decreases. Moreover, all other parameters being equal, with an increase in the average duration of the dead time of the prolonging type τd , this dependence decreases with large values of ns0: with ns0 ≥ 66,6·103 s-1 for τd = 0; with ns0 ≥ 74,1·103 s-1 for τd = 5 μs; with ns0 ≥ 83,5·103 s-1 for τd = 10 μs; with ns0 ≥ 95,6·103 s-1 for τd = 15 μs.
Magnetic testing of steels' mechanical properties is based on their correlation with steels' magnetic parameters. The purpose of this work was to establish dependence of the attainable correlation coefficient Rmax between measurement results and the parameter values a on the reduced error of its measurement. The article proposes a model of the correlation field between the parameter true values and the results of its measurement with a given reduced error δ. The merits and legitimacy of using the model for estimation of the achievable correlation coefficient Rmax are substantiated. Analysis of influence of δ parameter measurement in different ranges d of its change on Rmax is carried out. Results are compared with the previous analysis for the relative measurement error. It has been established in this work that the coefficient Rmax calculated for the reduced measurement error is always smaller than Rmax one calculated for the relative measurement error. However in the practically important range of variation of d with δ ≤ 0.05 the difference between the Rmax values calculated for the reduced and relative measurement errors is not large. This allows us to use the developed formula for the dependence Rmax = Rmax (δ, d) at Rmax ≥ 0.8 for both relative and reduced measurement errors δ. The obtained result allows us using the reduced measurement error of a metrologically certified measuring instrument to obtain the maximum attainable correlation coefficient between the true values and the results of measuring a parameter in a given range of its change without measurements. As an example, we define the conditions for the non-destructive testing of steels under which one can use measuring of magnetic parameters with the installation certified based on the reduced measurement error.
Methods of quality estimation of products and processes
The paper identifies the problem of ensuring the reliability of measurement results of quality characteristics as subjective values and their correct application in logical and mathematical models of making decisions. The purpose of this study is to increase the reliability of expert evaluation of individual characteristics of the quality of processes, products, systems.
The article describes basic methodological approaches to subjective measurements represented by the classical, operational and representational theories of measurement. The most acceptable for the purposes of ensuring the reliability of the expert evaluation of the single quality characteristics a representative theory, suggesting that the subjective value can be measured only in nominal or ordinal scales was determined. The contradiction is established: the possibility of measuring of single quality characteristics in the ordinal scale does not meet the needs of specialists in the field of quality, whouse subjective measurements to solve problems of analysis and decision-making, requiring the use of logical and mathematical models; in that way estimates should be expressed at least in the interval scale. The article substantiates the best solution of this problem by use of the rating scale which has properties of both ordinal and interval scales.
Within the framework of the expert methods of quality measurements development two fundamental elements of the methodology of subjective measurements of subjective values from the standpoint of representative theory are formulated: 1) the rating scale as a modified scale of ranks, 2) the method of organization of the measurement process as a method of alternative assessment of expert preferences.
Much attention is given to axiomatic of the rating scale having properties of both ordinal and interval scales. The algorithm of implementation of alternative assessment's of expert preferences method which is based on a special two-stage plan of alternative expert survey and statistical criterion of preferences' stability was suggested. In conjunction, the methodologies of subjective measurements of subjective values ensure the correctness of the rating scale's formation and conversion of the values of quality characteristics in the form of ratings in the corresponding values expressed at least in the scale of intervals.
ISSN 2414-0473 (Online)
