This paper is devoted to the current model of vibration-amplitude liquid densimeter developed by the authors. Firstly, the necessity to develop vibration-amplitude liquids densimeters with straigt-flow sensing elements (resonators) belonging to the "low costlow accuracy" category is justified. The resonator structure, developed as the result of the search using the heuristic method, is described. The proposed resonator is a tube rigidly fixed at the ends with additional weights attached symmetrically at the vertical axis at the points of the antinodes of the second fundamental oscillation mode in order to improve the resonator quality-factor by suppressing parasitic harmonics. The structure provides the possibility to restore the resonator natural oscillation frequency (decreased with time) to the primary one. It may be achieved by sequence screwing rods with different lengths into additional masses. The choice of the operating frequency of oscillations equal to 100 Hz is proved. It ensures invariance to the presence of solid inclusions in measured liquid and simplifies the electromagnetic excitation system. There are also theoretical relations obtained as a result of solving a differential equation of natural oscillations of a rigidly fixed tube with additional point masses, which are symmetrically located relatively vertical axis. They allow determining the own resonator oscillations frequencies for given parameters. The description of the operating model of the vibration-amplitude liquids densimeter, obtained experimentally and its calibration characteristic, is given.

The article is devoted to the study of the influence of the flow velocity of the measured pity on the readings of the vibration-frequency density meter. For this purpose, the process of free proper transverse vibrations of a resonator made in the form of a homogeneous tube rigidly fixed at the ends, along which the fluid flow is organized, is investigated. A differential equation of the resonator’s own transverse oscillations is compiled, taking into account the elastic forces, inertia forces and friction forces acting on the resonator. At the same time, the Coriolis force is neglected, in view of the rigid fastening of the ends of the tube. Taking into account the fact that the resonator oscillations are supported by the self-oscillation system, the friction force is compensated by an external force and in the differential equation the friction force becomes zero. As a result of solving the differential equation, the dependence of the frequency of self-oscillations of the resonator on the flow velocity of the measured liquid is determined. Possible ways to reduce the influence of the fluid flow velocity are determined. The conclusion is made about the expediency of determining the limit value of the fluid flow rate when determining the operating conditions of the density meter.

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