Stability provision of electromechanical transducer characteristics in conditions of flight in the upper atmosphere

Аuthors

Grachev N. N.

Higher School of Economics, 20, Myasnitskaya str., Moscow, 101000, Russia

e-mail: nngrachev@mail.ru

Abstract

Scientific results obtained in the work are devoted to the issues of measurement reliability and accuracy of small, slowly changing parameters of low-density gas flows effecting an aircraft in the upper atmosphere. The main trend of the research consists in measuring the aerodynamic forces effecting a flying vehicle in a depleted gaseous environment Measured electric signals coming from primary transducers are often of a low level, sometimes reaching the values less than the noise and interference levels by several orders of magnitude. The most acceptable way of such processes measuring while reaching the specified metrological characteristics is electrochemical modulation (interruption) of the incident gas flow by choppers. It allows obtain the required large gain of the AC signal; easily separate the modulated beam signal from the non-modulated background signal, even if the beam density is lower than this of the background, as well as employ the signal accumulation, which increases the signal-to-noise ratio at the transducer output.

To determine the optimum frequency of electromechanical conversion and ensure the specified accuracy and stability of metrological characteristics, the author proposed employing the method of probabilistic investigation of the stability of the transducer output characteristic. The study of the characteristic's stability is based on the method of probabilistic stability research, ensuring the account for the random character of structural and electro-physical parameters deviations under the impact destabilizing factors and in conditions of mass production. The underlying method of moments allows obtaining the required accuracy with a small amount of computation.

To analyze the stability of the membrane-capacitor transducer transfer characteristic and sel ect the optimum frequency of the flow interruption, programs for computing the nominal values of the frequency response (AFC) and phase-frequency characteristics (PFC) of the transducer, the sensitivity of the response frequency and phase response to the specified parameters were developed. The program for computing the mathematical expectations and dispersion of manufacturing tolerances and temperature coefficients was developed based on the analysis of frequency dependencies of the transducer parameters coefficients effect on its transfer characteristic. Besides, the dependencies of the transducer transfer characteristic fr om temperature at the flow chopper operating frequency, as well as from the temperature change of the transducer membrane were computed.

Based on the measuring transducer transfer function representation in the form of polynomials ratio and analysis of its absolute sensitivity functions to the manufacturing tolerance, structural and electro-physical parameters, as well as destabilizing factors computing dependencies of the transducer transfer function for its stability evaluation and selection of optimal electromechanical conversion frequency were obtained.

Keywords:

velocity pressure high-speed head, the electromechanical tramsducer, parameters stability

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