Gladyshevskyi M. Method and ultrasonic mean of measurement control for flowing medium flowrate

The thesis paper is concerned with solving an important scientific and practical task of in-creasing the accuracy and probability of flowing medium flow rate measuring control based on the use of ultrasonic amplitude-frequency method. The present state of methods and means of measurement control for flowing medium flowrate is analyzed, their advantages and disadvantages are revealed. Such method is ultrasonic method, which despite disadvantages has many advantages over other methods, such as: zero lag and contactless of measurement; the absence of moving parts in the flow and pressure losses in the pipelines. The mathematical model of the ultrasonic wave propagation in a fluid medium is pro-posed, which describes the behavior of the signal in the near zone due to changes in the frequency and flow velocity. It is established that the density of the flowing medium and its temperature, sig-nificantly influences the magnitude of the output signal and for natural gas the adiabatic index and the compressibility factor of gas. An ultrasonic amplitude-frequency method for measuring the flow velocity is proposed, which consists in determining the resonance frequency of an ultrasonic wave, that is uniquely associated with the velocity of the flowing medium, which corresponds to the last diffractive maximum of the near zone. This approach has allowed to reduce the zone of insensitivity and thereby to increase the accuracy and probability of measurement control of flowing medium and use it as a mean of measurement control for flowing medium flowrate in conduits with small cross-section. The mathematical model of the ultrasonic measuring transducer of the flowing medi-um velocity was developed and the obtained dependency was simulated, from which it is evident that the dependence of the resonance frequency of the ultrasonic wave on the flow velocity does not depend on the flow direction. The dependence of the change in the frequency of the ultrasonic signal from time is obtained, that is results in high response speed. The device for measurement con-trol of natural gas flowrate was developed, which can be applied in gas pipelines with small diame-ter (from 25 mm) and in conditions of sharp change of flowrate. The simulation of this device was carried out, based on the equivalent scheme of the measuring transducer with the bandpass filter. The simulation results showed the adequacy the proposed method. The reaction time of the system on the frequency change of the generator was estimated. The algorithm of measurement control of flowrate is given. The analysis results of experimental studies of the mean of measurement control for flowing medium flowrate has been carried out, which showed the convergence of theoretical and experimental characteristics. Model error does not exceed 10%. The dependences of the general law of the distribution of the measurement error of the flow velocity measurement are given and it is established that the distribution law is normal. The errors of the first α = 0.035 and the second kind β = 0.0028 ÷ 0.0002 were calculated. The probability of acceptance by mean of measurement con-trol of the correct result is 0.96, which is 1% higher than that of known means. The analytical de-pendences of static metrological characteristics were obtained and the influence values on the meas-urement channel of the control instrument were estimated. It has been established that the measure-ment error value does not exceed 1%.