RU2257566C2 - Viscosity detector - Google Patents

Abstract

FIELD: inspection of technological fluids.

SUBSTANCE: detector has tuning fork. Axial rod of tuning fork passes through base of the tuning fork. Piezoelectric converters and counterweights are mounted at each foot of tuning fork at parting line. Tuning fork is disposed vertically and is suspended at string stretchers by axial rod. Counterweights are shifted relatively parting lines at opposite directions in such a way that at reciprocal oscillations of feet of tuning fork the periodic torque generates relatively vertical axis and sample body disposed at the end of axial rod makes torsional vibrations.

EFFECT: improved precision of measurement.

3 dwg

Description

The invention relates to a technique for measuring viscosity, and more particularly to a device for submersible tuning-fork type sensors intended for use in research laboratories, in medicine, for monitoring process liquids.

Known tuning fork viscometers, for example A. A. Stepichev viscometer, containing two legs and a housing, one of the sides of which is made in the form of a plate into which the legs-rods are welded. The base of the legs located inside the housing is equipped with rigid T-shaped brackets with piezoelectric elements sandwiched between the brackets [A.A. Stepichev, A.S. 329445, published November 11, 1972, Bull. No. 7]. In this design, the nodal point of the tuning fork is located in the plane carrying the rods of the plate, and the piezoelectric elements that are sandwiched between the brackets inside the housing (behind the plate) create an additional strong mechanical connection between the legs, offset from the nodal point, which limits the highest possible quality factor of the structure and, accordingly , maximum sensitivity possible.

The disadvantage is the relatively complex shape of closely spaced streamlined surfaces, which can lead to clogging of the two-component probe with coagulum (in the case of coagulating liquids).

Closest to the proposed invention in technical essence is a tuning fork sensor with an adjacent probe. [A.V. Bogoslovsky, M.A. Poluektov // Physical and chemical properties of disperse systems and their application. - Tomsk, 1988. - p. 34-38]. The sensor is a tuning fork of a "classical" shape, fixed to a nodal point between the legs in the support. Two piezoelectric elements are glued to the legs and two identical probes are installed - a measuring one on one leg, and a counterweight on the other. The measuring probe points down to the test fluid. The counterweight is directed in the opposite direction. During measurements, the fluid loads only one of the legs. The possibility of increasing the sensitivity of such a device by increasing the size of the test body is limited, since the attached mass of the liquid increases and, accordingly, the asymmetry of the load of the legs, the position of the nodal point changes (where the vibration amplitude is zero and the tuning fork is attached to the support), the outflow of energy increases fasteners. At high loads (liquids with a high viscosity, gels, jellies), the imbalance in load symmetry becomes noticeable and limits the dynamic range of measurements.

The disadvantage is the progressive nature of the motion of the test body, this leads to the appearance of frontal resistance and the created deformation of the investigated part does not have a purely shear character, which can affect the measurement results of viscoelastic objects.

The objective of the invention is to eliminate the asymmetry of the mechanical load and the exclusion of the "frontal" component of mechanical resistance.

The technical result is achieved by the fact that the viscosity sensor contains a vertical tuning fork, on each leg of which a piezoelectric transducer is located. Two identical counterweights are attached to or attached to the ends of the legs in such a way that their centers of gravity are displaced in opposite directions relative to the axis of the tuning fork and the midline of each leg, and the probe — a test body in the form of a body of revolution — is fixed at the end of the vertical axis. Axis - an axial rod passes through the base of the tuning fork, which is suspended on a string tensile for two points on it.

Figure 1 shows a traditional sensor. Piezoelectric transducers 4, a counterweight 8 and a test body 1 with the help of fixing screws 6 and glue are installed on each of the legs of the tuning fork in the midline of the latter. The test body and the counterweight are on the same vertical axis, along which the reciprocating oscillation of the test body occurs. The axial rod 2 is connected to the base of the tuning fork and is used to mount it in a support (not shown).

Figure 2 shows the proposed sensor. Piezoelectric transducers 4 and counterweights 8 with mounting screws 6, angles 5 and glue are installed on each of the legs of the tuning fork 3. Piezoelectric transducers are installed on the middle lines of the latter. The counterweights are located on opposite sides of the respective midlines, they are offset in opposite directions by the angles 5. The axial rod 2 is connected to the base of the tuning fork and passes through it. On the rod, on different sides of the base, there are suspension points 7, for which it is held by opposite extensions 9 inside the cylindrical shell 10.

Since the balances are taken out of the plane in which the reciprocating motion of the centers of gravity of the tuning fork legs occurs, a periodic torque is created during their oscillations. A test body in the form of a body of revolution is located at the end of the axial rod and performs torsional vibrations.

For measurements, the sensor can be included in the feedback circuit of the oscillator, providing operation at a frequency of mechanical resonance. In this case, an exciting voltage U _F is applied to one of the piezoelectric elements, and the voltage Uξ, which is proportional to the oscillation amplitude, is reduced from the other. When an oscillating probe is immersed in a liquid, the friction between them and the liquid will cause additional energy dissipation compared to losses when moving in air. To achieve the same torsional vibration amplitude, a larger U _{F is} needed.

For Newtonian fluids, the friction between a body oscillating in harmonic law and the environment is described by the formula

where Z _W - mechanical resistance of the liquid;

F is the force causing the movement;

ξ is the amplitude of the oscillations;

ξ ′ is the amplitude of the oscillation velocity;

ρ is the fluid density;

η is the viscosity of the liquid;

A, B, C, K - proportionality coefficients.

- сопротивление, обусловленное внутренним трением измерительной установки, и общее наблюдаемое сопротивлениеIn reality, in addition to fluid resistance, there is also

- resistance due to internal friction of the measuring unit and the total observed resistance

where U _F0 is the exciting voltage during oscillations of the test body in air;

Uξ is the voltage proportional to the amplitude during oscillations of the test body in air.

With stabilized Uξ

Определяют коэффициент по формулеThe measurements are carried out as follows. Find U _F0 when the probe oscillates in air. Find U _FK when the probe oscillates in a calibration fluid with known values

The coefficient is determined by the formula

по формулеFurther, at constant U is determined Uξ _Fzh of oscillation of the probe in the sample liquid. Find the desired value

according to the formula

An example of a specific implementation.

укреплен в обечайке 10. Концы его ножек имеют противовесы из латуни на уголках, привинченные винтами М6. Масса противовеса с уголком и винтами крепления 30 г. Ширина ножек камертона 20 мм. Диаметр оси 5 мм.Brass tuning fork 3 with resonance frequency

mounted in a shell 10. The ends of its legs have brass counterweights at the corners screwed with M6 screws. The mass of the counterweight with a corner and screws 30 g. The width of the legs of a tuning fork 20 mm The diameter of the axis is 5 mm.

When testing the sensor, the piezoelectric elements were included in the feedback circuit of the oscillator. The value of Uξ was maintained constant at 1B. U _{F was} measured using a digital voltmeter. The test body immersed in the liquid was a hollow cylinder with pointed ends with a diameter of 2 cm and a length of 4 cm.

, которая получена с помощью предлагаемого датчика.Figure 3 shows the relationship between ΔU _F = U _F -U _F0 and

, which is obtained using the proposed sensor.

ΔU _{F was} measured in air (point 0), in octane (1), decane (2), diethyl phthalate (3), and cyclohexane (4).

The graphically determined sensor sensitivity is

Claims (1)

A viscosity sensor containing a tuning fork, the axial rod of which passes right through its base, piezoelectric transducers and a counterweight are installed on each fork of the tuning fork on the midline, characterized in that the counterweight is additionally installed, the tuning fork is located vertically and suspended by string braces from the axial rod, the balances are offset relative to the midlines in different directions in such a way that during the reciprocating oscillations of the legs creates a periodic torque relative to the vertical of the vertical axis so that the test body located at the end of the axial rod performs torsional vibrations.

Images