Kosterov O. Improvement and investigation of the national primary measurement standard for the unit of sound pressure in air

The thesis is devoted to the solution of the actual scientific and technical problem – the refining of metrological characteristics of the State primary standard of Ukraine of the unit of sound pressure in the air by improvement of the standard, to the complex analysis of sources of uncertainty during microphone calibration, to the identification and exploration of the most influential components of uncertainty in order to improve the methods and the measuring instruments that will reduce the uncertainty of reproduction and transference of the unit of sound pressure. The scientific novelty of the obtained results is as follows: According to the results of research aimed at developing and improving the standard unit of sound pressure in the air, the following results were obtained: 1. For the first time, according to the results of analysis and research of mathematical model of microphone calibration process, it is established that the main factors determining metrological characteristics of the state primary standard of sound pressure unit in the air are: estimates of electrical transmission impedance, environmental parameters, microphone parameters and small volume camera size; 2. For the first time, based on the results of research of the mathematical model of the microphone calibration process, an improved structure of the state primary standard of the sound pressure unit in the air was proposed and implemented, which allowed: 10 - for LS1 type microphones: reduce the uncertainty of their calibration by 0.01 dB - 0.04 dB; - for LS2 type microphones: expand the frequency range of measurements from the range (31 Hz - 20 kHz) to the range (2 Hz - 25 kHz), in addition, reduce the uncertainty of their calibration by 0.02 dB - 0.05 dB; 3. For the first time, the frequency dependences of noise influence with normal distribution in measuring channels on the standard deviation of microphone calibration results using Monte Carlo simulation were established and a significant increase in their influence at infra-low frequencies was shown; 4. For the first time, when introducing the thermal conductivity correction, a method for estimating the coupling frequency value is proposed and the use in the frequency band below this value is proposed - the specified low-frequency correction model, and in the high-frequency region - the broadband model to reduce uncertainty in the operating frequency range. The practical significance of the obtained results is as follows: the comparative analysis of the existing methods and means of reproduction of the unit of sound pressure in the air in the world’s leading acoustic laboratories has been performed and the theoretical basis of improvement of the standard has been defined; the structural scheme of the improved national standard of the unit of sound pressure in the air has been defined; an improved standard unit for pressure calibration of laboratory standard microphones in the frequency range from 2 Hz to 25 kHz of the State primary standard of the sound pressure unit in the air has been created and put into operation; the following calibration procedures have been developed and implemented: “Calibration procedure of the standard unit UE-2PU of the State primary standard DETU 10-01-11”, "Procedure for pressure calibration of the measuring microphones against the State primary standard DETU 10-01-11 in the frequency range from 2 Hz to 25 kHz"; 11 international key comparison COOMET.AUV.A-K5 has been conducted and, as a result, 15 lines of measuring and calibration capabilities in the field of acoustics of Ukraine were updated in KCDB BIPM.