Improving the Efficiency of Measurements of Combustible Gases Concentration by a Thermocatalytic Sensor

Thermocatalytic sensors are widely used in gas analysis systems and have high reliability and low cost. However, errors in measuring the concentration of combustible gases related to the non-linearity of the conversion characteristic and the influence of ambient temperature fluctuations significantly limit the scope of their application.Purpose of reseach. Development of a method for measuring gas concentration by thermocatalytic sensors, which allows reducing measurement errors by tuning out due to ambient temperature influence and linearization of the conversion characteristic.Problems. They are as follows: to develop a method for temperature stabilization of a thermocatalytic sensor; to make a structural and functional scheme for the sensor activation; to obtain a mathematical description of the method and substantitation for tuning out as a result of temperature influence; to experimentally confirm the possibility of linearization of the sensor conversion function in the thermal stabilization mode.Methods. The mathematical description of the method applies the theory of heat transfer and the theory of electrical circuits with discrete signals. When analyzing existing solutions and synthesizing the device, methods for calculating circuits with nonlinear elements and the theory of measurement systems have been used. The real conversion function has been obtained through an experimental method.Results. A method for measuring gas concentration by a thermocatalytic sensor with the use of a microcontroller and PWM has been developed. It allows reducing errors due to tuning out as a result of ambient temperature influence. A mathematical description of the method has been given. An experiment has been performed. It demonstrates the effectiveness of using temperature stabilization to linearize the conversion characteristic.Conclusion. The paper proposes a method for temperature stabilization of thermocatalytic gas sensors. The method makes it possible to increase the accuracy of measurements by tuning out due to the influence of temperature fluctuations and linearization of the conversion function. The possibility of linearization of the sensor function has been experimentally confirmed. It characterizes the dependence of the output signal on the concentration of combustible gas. Using this method allows you to reduce the cost of the sensor, improve the quality factors of the sensor, such as the reliability and stability of parameters.

Computer modeling of parametric converters with frequency and phase control

Осуществлено математическое моделирование параметрических преобразователей, использующих режим повышенной чувствительности. Названный режим преобразователей позволяет повысить эксплуатационные показатели аппаратуры авиационно-космических систем. Показано, что преобразователи с фазовым управлением обладают линейными характеристиками и являются более перспективны. Применение в них цифровых фильтров ведет к повышению стабильности частоты и точности настройки, а также минимизируется погрешность характеристики преобразования. Mathematical modeling of parametric converters using high-sensitivity mode is carried out. The named mode of converters allows to increase operational parameters of the equipment of aerospace systems. It is shown that phase-controlled converters are more promising because they have linear characteristics and allow the use of digital filters, which leads to an increase in frequency stability and accuracy of adjustment, and also minimizes the error of the conversion characteristic.

Solution of the Interference Models Identification Problem

An approach to constructing the static characteristics of a system from experimental data is considered. It is noted that in many cases the problem is solved by applying the "black box" concept, according to which the data of an experiment containing the values of the measured input and output quantities are used. In practice, the input and output variables in the experiment are determined with certain errors. It is shown that in solving the problem within the framework of the conventional approach, the availability of various sources and generating factors of interference models is often ignored, which leads to a significant distortion of error estimates and to formation of an inadequate conversion characteristic. In view of this circumstance, the types and sources of errors appearing in constructing the static characteristic are determined, and the models of noises emerging during measurements under real field conditions and during a calibration experiment are studied, and it is shown that they have fundamentally different effects on the measurement result.

Application of the Hurst index to evaluate the testing of information gathering system components

The performance of the technical object is determined based on the evaluation of its parameters. Sensors of physical quantities are used to collect data on the values of the parameters of the controlled object. The performance evaluation of an object depends on the accuracy of the parameter measurement. The measurement accuracy is determined by the sensor conversion characteristic. If the sensor calibration tests are performed correctly, the conversion characteristic will accurately reflect the relationship between the measured parameter and the output electrical signal. A method for assessing the quality of the conversion characteristics of the microprocessor sensor, which is based on the use of Hurst index. The sensor of slowly changing physical quantities is considered. Based on the results of several test cycles obtained at a fixed ambient temperature, a series similar to the time series is formed. The initial series is subjected to additional processing before evaluation. The Hurst exponent is determined for the obtained series. The value of the Hurst index determines the quality of the test results. The possibility of using fractality index to assess the quality of tests is also considered.

Reversible Addition-Fragmentation Chain Transfer (RAFT) Polymerization of Poly(ethylmethacrylate) with Pendant Carbazole Groups

Carbazole containing polymers have captured the interest of researchers for use in optoelectronics. For an important material to exhibit its optoelectronic properties intrinsic uniformity in the molecular level is required. Thus, a monomer of ethyl methacrylate with pendant carbazole group was synthesized and polymerized via Reversible Addition-Fragmentation Chain Transfer (RAFT) to produce polymers with controlled molecular weight distribution and narrow polydispersity index (PDI). This method of polymerization was compared with that of free radical polymerization by gel permeation chromatography (GPC). The RAFT’s polymerization kinetics was observed to follow a plot of number average molecular weight (Mn) versus % conversion, characteristic of living polymerization. It was also shown to possess polymer chain extension capability. The structure of the monomer and the polymers were characterized by Fourier-Transform Infrared Spectroscopy (FT-IR) and Nuclear Magnetic Resonance (NMR).