Measurement Techniques

Abstract We describe the results of currently topical investigations of the method used for the production of activated carbon from the biomass wastes with the help of microwave carbonization. As compared with ordinary carbonization in thermal furnaces, the procedure of microwave carbonization proves to be a more energy-efficient and environmentally friendly method. However, at present, the problem of guaranteeing the required reproducibility and thermal stability of this process remains unsolved. In the course of microwave irradiation, the temperature of the biomass samples continuously varies and, moreover, complex physicochemical processes run inside these samples. Therefore, in order to determine optimal modes of microwave treatment, it is necessary to know the temperature dynamics of biomass samples. It is proposed to determine the required temperature dynamics of biomass samples by the method of spectral pyrometry. The method is based on the separation of the sections of thermal radiation spectra of the samples that coincide with the Planck function with variable temperature. In these sections, the samples exhibit the properties of gray radiators. The method proves to be efficient for an unknown emission coefficient continuously varying as a function of microstructure, chemical composition, and phase state of the sample. The sample irradiated with microwaves is a weighted amount of cotton linter treated by orthophosphoric acid with a weight of 1 g. The source of microwaves is a magnetron-type generator with a maximum output power of 600 W and a working frequency of 2450 MHz. The thermal spectra of irradiated samples were recorded by using small-size spectrometers operating in visible (350–760 nm) and near infrared (650–1050 nm) bands. The time of irradiation of samples with microwaves varied within the range 60–180 sec. The obtained spectra are processed with the help of the Spectral Pyrometry program, which reads and processes the recorded spectrum, constructs the plots on the Planck and Wien coordinates, and computes temperatures. The analysis of the accumulated results reveals different types of spectra of thermal radiation of the irradiated sample, namely, the spectra similar to the spectra of a perfect radiator, spectra with different temperature zones of the sample, and spectra with atomic lines and molecular bands. The accumulated results prove to be useful for the investigation of the influence of microwaves on various objects, for the study of processes running in the course of carbonization of the biomass, and for the development of more efficient modes aimed at getting activated carbons by the microwave method.

Abstract The paper discusses the specifics of measuring and monitoring moisture reserves in the atmosphere using radar methods, involving standard meteorological and satellite-based observation data, as well as methods of microwave sounding and optical spectroscopy. It is noted that among the above-listed methods, the most economically efficient are the optical methods (e.g., spectral LIDAR, active and passive, ground-based), which make it possible to promptly and adequately determine the atmospheric moisture reserves in the known greenhouse gas absorption lines, as well as replace and supplement radar data. The equipment that implements the optical methods includes inexpensive and readily available portable transceiver lenses, as well as compact and lightweight fiber-optic radiation sources and receivers, which are convenient for use when performing satellite-based measurements. A spectral method for measuring the concentration of water vapors in the atmosphere in the presence of solar radiation has been proposed and tested. The location of the measurements is the northeast of the Moscow region. When processing the results of measurements carried out on a single water absorption line, it was found that the experimental data match the results of direct meteorological measurements with an error of about 7.5%. It was established that on the water absorption line (approximately 1653 nm), the interfering factor is the nearby methane absorption line, which introduces a systematic error into the measurement results. It was suggested that the probable reason of the results deviation from the meteorological measurement data has to do with the absorption cross-section of methane molecules being approximately four orders of magnitude larger than that of water vapor molecules. As a result, emitted light is absorbed mostly by methane, thus reducing the fraction of water vapor absorption at a wavelength close to the methane absorption line. Compensatory corrections have been introduced, making it possible to determine the water vapor concentration and moisture reserves in the air column with an error of several percent at this wavelength. The proposed spectral method enables long-term monitoring of the water vapor concentration and moisture reserves in the atmosphere, and allows obtaining live data in real time. The experimental data, on average, agree with the measurement results obtained using radiometers that operate in the microwave range. The obtained results can be used to promptly estimate the moisture reserves and water vapor concentration in the entire surface layer of the atmosphere over large areas, to calibrate radiometers and radars, and to improve the accuracy of measuring the above parameters and forecasting dangerous natural phenomena, such as hurricanes, floods, and landslides.

Abstract The article considers models of miniature elastic scattering lidars with similar optical schemes, analyzing the possibility of their application in determining the microstructure of the atmospheric surface layer. A microlidar model is proposed, whose main feature is a small sensed volume of the atmosphere. It is assumed that on short sensing paths in the limiting case, a small sensed volume may contain no particles. In this case, the minimum backscatter signal corresponds to molecular scattering, while the exceeding of this minimum by the signal is associated with the presence of a particle. The molecular component of the backscatter signal is constant and comparable to the tabulated value of the backscattering coefficient in the optical model of the atmosphere. This allows the average value of the total backscatter signal (from molecules and particles) to be put into correspondence with the overall backscattering coefficient. The authors consider a model of a minilidar whose optical scheme is similar to that of a microlidar but increased in scale. The minilidar can be used to determine the microstructure of the atmospheric surface layer on longer paths as compared to the microlidar. For both schemes, the average values of atmospheric backscatter signals are the same. When using a minilidar, the backscatter signal is formed by a layer measuring from a few meters to several tens of meters. In this case, the sensed volume can be determined using perforated screens and reflecting spheres. It is shown that the minilidar-to-microlidar sensed volume ratio is equal to the similarity coefficient to the fourth power, which enables the comparison of data measured by means of these lidars. These complementary measurement results allow the model of an equivalent atmosphere containing monodisperse aerosol to be put into correspondence with the examined atmosphere. The obtained results provide a means to develop a detailed procedure for determining the concentration of equivalent particles in the surface layer of atmospheric aerosol using micro- and minilidars.

Abstract Reference platinum resistance thermometers are described—currently the most accurate contact sensors for measuring temperature. One of the most important characteristics of the error of a reference platinum thermometer is considered—resistance instability in the interval between verifications. For several years we analyzed the instability of 27 standard platinum thermometers received for verification at the All-Russian Research Institute of Metrology named after. D.I. Mendeleev. It has been established that the instability of resistance in the equivalent temperature of most thermometers at the triple point of water exceeds \(\pm 0.002^{\circ}\mathrm{C}\) , and sometimes reaches several hundredths of a degree. The reasons for the resistance instability, as well as the instability of the relative resistance of thermometers, are analyzed. The error caused by the instability of the thermometer can be reduced from hundredths to thousandths of a degree if the relative resistance of the thermometer is used as the measured parameter. This conclusion was made based on an analysis of changes in the interpolation function of the thermometer in the interval between calibrations and calculation of the thermometer error in the temperature range between calibration points. It is proposed in the regulatory documents on the verification methodology to provide for additional periodic verification of standard thermometers at the triple point of water. Additional verification will improve the accuracy of temperature measurements. The results obtained will be useful to users of reference platinum thermometers and specialists of verification centers.