RU2094771C1 - Vibration pickup - Google Patents

Abstract

FIELD: measurement technology. SUBSTANCE: vibration pickup has turning fork with two legs, piezoelectric transducers mounted at base of legs, and probe connected to turning fork. Piezoelectric transducers are installed in recesses located at base of legs. EFFECT: higher accuracy of measurement. 1 dwg

Description

 The invention relates to a technique for measuring viscosity, and more particularly to a device for vibration sensors intended for use in viscometers, coagulators, etc.

 Known tuning fork sensors [1] This sensor has two piezoelectric transducers glued to the legs of a tuning fork near its base. At the end of one of the legs, a ball is soldered perpendicular to it on the rod, which is a test body, immersed in the liquid during measurements.

 The vibration viscosity sensor [2] contains a tuning fork with two legs, at the base of which one piezoelectric transducer is installed, a hollow spring with an inlet and an outlet is installed between the legs of the tuning fork, during which the test fluid passes and when the tuning fork vibrates, it experiences periodic deformation.

 Such sensors are easy to manufacture. Their common drawback is (with a specific manufacture of tuning fork and test body) the inability to increase the sensitivity of the sensor to the required value.

 The technical result is to increase the sensitivity of the sensor.

 The specified technical result is achieved by the fact that in a vibration sensor containing a tuning fork with two legs, the piezoelectric transducers installed at the base of the legs, the probe attached to the tuning fork, part of the material is removed under the piezoelectric transducers, and the piezoelectric transducers are installed in the recesses to replace the removed material.

 The drawing shows a prototype, the proposed device and diagrams arising in them, mechanical stress. The sensor consists of a tuning fork 1, piezoelectric elements 2, probe 3. The tuning fork is mounted on a support 4. The probe is immersed in a variable fluid 5.

For measurements, the sensor must be included in the feedback circuit of the oscillator, providing operation at the resonance frequency. In this case, an exciting electric voltage U _{F is} supplied to one of the piezoelectric elements, and the electric voltage Yε, proportional to the amplitude of the arising mechanical vibrations, is removed from the other.

 When the tuning fork legs make a movement, elastic forces arise in its body, which prevent the shape from changing: the elastic forces during elastic deformation are proportional to mechanical deformation.

 In the case under consideration, we have the following type of deformation: variable tension-compression, a change in the length of the outer and inner layers of the legs material along their axes with a boundary along the neutral layer.

где r радиус кривизны нейтрального слоя, а величина 1/r представляет собой кривизну нейтрального слоя;
E коэффициент, зависящий от материала и называемый модулем продольной упругости.According to Hooke's law for a uniaxial stress state, normal mechanical stresses vary along the height of the cross section in proportion to the distance y from the neutral layer

where r is the radius of curvature of the neutral layer, and 1 / r is the curvature of the neutral layer;
E is a coefficient depending on the material and is called the modulus of longitudinal elasticity.

где

представляет собой момент S инерции поперечного сечения относительно нейтральной оси X.The curvature of the neutral layer during bending is proportional to the bending moment M _and and inversely proportional to the value EI _x , called stiffness

Where

represents the moment S of inertia of the cross section relative to the neutral axis X.

 The drawing shows the maximum instantaneous value of the mechanical stresses arising during tension of the outer layers of the material. Analysis of the diagrams shows that for the same amount of bending moment, the smaller the cross-sectional area of the outer layer, the greater the mechanical stress and, consequently, the greater bending at a given place, namely under the piezoelectric transducer. Therefore, for the same deformation of the considered structure, various external forces F are required and the smaller, the smaller the cross-sectional area in the zone of the piezoelectric transducers. Consequently, a tuning fork with recesses at the base of the legs is more sensitive.

Under conditions of excitation of oscillations U _{F, the} magnitude of the applied electric voltage is proportional to the deforming force, U _{ξ is the} magnitude of the electric voltage arising on the piezoelectric element, which is proportional to the deformation, it is maintained constant.

Z_ж механическое сопротивление жидкости;
F сила, вызывающая движение;
ξ амплитуда колебаний;
x′ амплитуда скорости колебаний;
ρ плотность жидкости;
h вязкость жидкости;
A, B, C коэффициент пропорциональности.For Newtonian fluids, the friction between the test body and the fluid oscillating in harmonic law is described by the formula

Z _{W the} mechanical resistance of the liquid;
F the force causing the movement;
ξ vibration amplitude;
x ′ amplitude of the oscillation velocity;
ρ fluid density;
h fluid viscosity;
A, B, C proportionality coefficient.

обусловленное внутренним трением измерительной установки (подвеса) и

где Z механическое сопротивление;

возбуждающее напряжение при отсутствии контакта пробного тела с жидкостью;

напряжение, пропорциональное смещению при отсутствии контакта пробного тела с жидкостью.In addition to fluid resistance, there is also resistance

due to internal friction of the measuring unit (suspension) and

where Z is the mechanical resistance;

exciting voltage in the absence of contact of the test body with liquid;

voltage proportional to the displacement in the absence of contact of the test body with the liquid.

K(U_F U_Fo).For stabilized U _ξ, we have

K (U _F U _Fo ).

 The measurements are carried out as follows.

/(U_Fk U_Fo),
где ρ_к, η_к плотность и вязкость калибровочной жидкости.Find the value of U _Fo in the absence of contact of the probe with the liquid (medium from air). Find U _Fk upon contact of the test body with the calibration fluid. The coefficient K is determined by the formula
K

/ (U _Fk U _Fo ),
where ρ _k , η _{k the} density and viscosity of the calibration fluid.

Further, at a constant value of U _ξ , U _{F of the} test fluid is determined.

по формуле

K(U_F U_Fo)
или по калиброванной зависимости, которая может быть построена после определения U_F ряда жидкостей с известными значениями

.Find the desired value

according to the formula

K (U _F U _Fo )
or according to a calibrated dependence, which can be constructed after determining U _{F of a} number of liquids with known values

.

теоретически в диапазоне нескольких порядков.Using the proposed vibration sensor provides an increase in sensitivity

theoretically in the range of several orders.

 The sensor allows you to reduce the size of the probe and, accordingly, the volume of the investigated fluid.

Claims (1)

 A vibration sensor comprising a tuning fork with two legs, piezoelectric transducers mounted at the base of the legs and a probe attached to the tuning fork, characterized in that the piezoelectric transducers are mounted in recesses at the base of the legs.