Precision digital pressure sensor

UDK: 53.087.92

Key words: sensor error model, pressure, depth, transducer, polynomial

Authors: Yu.G. Svinolupov (National Research Tomsk Polytechnic University, RF, Tomsk), L.A. Naumov (Institute of Marine Technology Problems, Far Eastern Branch of RAS, RF, Vladivostok)

High-precision digital pressure sensors have a very broad scope of application: from pressure measurement in pipelines and wells as part of oilfield instrumentation systems to machines and robots, e.g. in depth gauges of underwater robots designed for different diving operations, including geological ones. This paper presents the results of the research project aimed at designing and analyzing metrological characteristics of a pressure sensor which can be used as a depth gauge of submersibles. The task to develop a depth gauge of a submersible is limited in terms of accuracy (average error should not exceed 0.08%) throughout the measuring range (up to 10,000 meters), as well as in terms of weight and dimensions, which are to be minimized to the greatest extent possible. Another important factor is the requirement of using a Russian pressure sensor as the essential condition of the development project. A choice of a silicon-on-sapphire (SOS) sensor is explained by a number of reasons: first, there are domestic manufacturers of this device; secondly, it has high initial metrological characteristics; thirdly, the developers have necessary calibration and experimental facilities, especially pressure calibrators of 0.02% class, for testing and releasing the device to production. The design was studied and developed on the basis of simulated stresses and strains of the sensor body, as well as optimized geometry, weight and dimensions. Displacement in the area of jointed parts to the maximum extent of 0.1 µm was taken as the criterion of permissible bulk deformation of the body. The further reduction of dimensions requires excluding a cable connection between the sensor and the board. In this case, there is no need to use high-pressure sealed contacts – important elements of cable transmission. Metrological characteristics were developed by using the established approach for modeling a measurement process, especially the pressure transmitter based on a SOS sensor (in the form of a third-degree polynomial), and then ranking models by error value. Polynomial coefficients were determined by solving the regression problem in the calibration phase of the depth gauge (sensor). Conventional methods of the modern error theory, estimates of systematic and random components were used for estimating the total measurement error. High accuracy of the developed measurement error correction method was confirmed at the beginning of the measurement range, e.g. for small depth values. The temporal drift of the sensor which would allow for long-term operation without automatic correction of the temporary drift was investigated. The results are presented in the paper. In order to exclude influence of atmospheric pressure and sea water density on measurement accuracy, it is proposed to collect these data through a digital data channel. Methods for increasing sensitivity and long-term stability are proposed. The developed sensor can be used both for measuring depth of an underwater robot and in digital measuring systems in a variety of industries.
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