RU2723159C1 - Additive method and device for external excitation of mechanical oscillatory system of vibro-viscometer - Google Patents

Abstract

FIELD: physics.

SUBSTANCE: invention relates to investigation of fluid properties using vibro-viscosimeters. Essence: oscillatory system is brought into mode of oscillations by means of excitation device, frequency of oscillations of excitation device is continuously changed to achieve natural frequency ω₀, which is determined after achieving a preset at each frequency in the operating frequency range of the phase shift between oscillations of the excitation device and oscillations of the output amplified and frequency-filtered position sensor signal and stored in the microcontroller memory, periodically varying the active rigidity of the oscillating system by a known value by adding to the exciting excitation device signal a known portion of the output signal of the probe position sensor, and new values of intrinsic frequency of oscillation system ω_0m are determined, and by values of frequencies ω₀ and ω_0m by calculation method current operating values of oscillating mass m_L and stiffness coefficient k_L of oscillatory system are determined by formulas. Device comprises device vibration excitation vibrating vibro-viscometer, recording and control device based on microcontroller, in memory of which is recorded control program for excitation device and frequency-phase characteristic of frequency-filtering circuit, sensor of probe position, which output is connected to input of electronic amplifier, which output is connected to input of frequency-filtering circuit, two-input adder with switch on second input, first input of adder is connected to output of excitation device, output of electronic amplifier is also connected to second input of adder through switch, control input of which is connected to one of control outputs of device for registration and control of vibro-viscometer.

EFFECT: high accuracy of determining the parameters of the analysed liquid, measured by the vibro-viscometer, by additional determination with allowance for the elastic properties of the liquid, dynamic parameters of the mechanical vibration system of the vibro-viscometer.

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Description

The invention relates to the field of studying the properties of liquids using vibro-viscometers. It can be successfully used to study the dynamic processes of thermostimulated structural adjustment of multicomponent liquids: oil products, vegetable oils, etc.

A known method of external resonant excitation of a mechanical oscillatory system of a vibro viscometer [RF patent No. 2607048 IPC G01N 25/00], in which the probe of a viscometer equipped with a sensor of the geometric position of the probe, with a given driving force is brought into mechanical vibrations by means of an excitation device that generates a harmonic signal of a constant predetermined amplitude and given frequency. The output signal of the probe position sensor is converted by amplification and frequency filtering. Further, preserving the amplitude, the frequency of harmonic oscillations of the pathogen is continuously changed until the natural frequency of the mechanical oscillatory system is reached, which is determined by reaching the phase shift frequency ϕ _s specified at each frequency in the operating frequency range between the pathogen oscillations and the oscillations of the output amplified and frequency-filtered signal of the position sensor, determined according to the equation ϕ _s (ω) = ϕ _f (ω) + π / 2, where ϕ _f (ω) is the value at the frequency ω of the phase shift of the frequency-filtering circuits of the signal of the probe position sensor of the vibro-viscometer.

This method of excitation provides high accuracy in determining the current value of the natural frequency of a mechanical oscillatory system, which is necessary for measuring the viscosity parameters of a liquid, and is quite simply automated by modern means.

A device [ibid] is known for external resonant excitation of a mechanical oscillatory system of a vibro viscometer, including an exciter of oscillations of a mechanical oscillatory system of a vibro viscometer, a probe position sensor and a device for recording and controlling a vibro viscometer based on a microcontroller. The output of the probe position sensor is connected to the input of the electronic amplifier, the output of which is connected to the input of the frequency filter circuit, the output of which is connected to the microcontroller, the output of the microcontroller is connected to the control input of the probe oscillator. In addition, the control program for the pathogen of the oscillatory system and the frequency-phase characteristic of the frequency filtering circuit are recorded in the permanent memory of the programmable microcontroller. The specified method and device are the closest to the invention.

The disadvantage of this method is the inability to separately determine the current values of the oscillating mass and rigidity (elasticity) of the oscillatory system when placing the measuring probe in a liquid with a changing temperature. Their determination in some cases is very desirable, since when the measuring probe of the vibro-viscometer is lowered into the liquid, not only the oscillating mass changes due to the added mass of the liquid, but in some cases the effective stiffness (elasticity) of the vibrational system due to the internal structural elasticity of the liquid when it passes into gel-like state. Failure to take into account changes in the rigidity of the oscillatory system when the probe is in the liquid leads to errors in determining both the attached mass and the viscosity of the liquid. In addition, the determination of the current value of the internal structural elasticity of a liquid is of independent scientific and practical interest for specialists in the field of colloid chemistry and petrochemistry.

The technical task of the invention is to improve the accuracy of determining the measured fluid parameters by a vibro-viscometer by further determining, taking into account the elastic properties of the fluid, the dynamic parameters of the mechanical oscillatory system of the vibro-viscometer.

To solve this problem, it is proposed:

An additive method of external excitation of a mechanical oscillatory system of a vibro-viscometer, in which the mechanical oscillatory system of a vibro-viscometer equipped with a probe position sensor is brought into mechanical vibrations with a given driving force by means of an excitation device, the output signal of the probe position sensor is converted by amplification and frequency filtering, the oscillation frequency is continuously changed the excitation device until the natural frequency ω ₀ is reached, which is determined by reaching the phase shift φ _З specified at each frequency in the operating frequency range between the oscillations of the excitation device and the oscillations of the output amplified and frequency-filtered signal of the position sensor according to the formula φ _з (ω) = φ _ф (ω) + π / 2, where φ _f (ω) is the phase shift of the frequency filtering circuits of the sensor signal, characterized in that the current natural frequency ω _{0 of the} mechanical oscillatory system of the vibro-viscometer is stored in the memory of the microcontroller, during eigenfrequencies ω ₀ periodically change the operating stiffness of the oscillatory system by a known value Δk _m , determined during the initial calibration of the vibro-viscometer by adding to the excitation signal of the excitation device a known fraction of the output signal of the probe position sensor converted by the amplifier, and determining a new value of the eigenfrequency of the oscillatory system ω _0m , and from the obtained values of the frequencies ω ₀ and ω _0m , the current effective values of the oscillating mass m _L and the stiffness coefficient k _{L of the} oscillatory system are calculated using the formulas:

и

and

where ω ₀ is the natural frequency of the oscillations of the unloaded probe; ω _L is the natural frequency of the oscillations of the probe in the liquid, ω _Lm is the natural frequency of the oscillations of the probe in the liquid with an additional change in the exciting force; Δk _m - change in stiffness coefficient under the influence of changes in the exciting force.

According to the claimed method, in the process of studying the liquid, a fraction of the voltage from the output of the position sensor is periodically added to the exciting harmonic signal from the excitation device for a short measuring time interval. The proportion of added voltage, the measuring interval in the mode of additional voltage and the frequency of the change of modes can be set by the operator during the measurement, or by software. The proportion of added voltage is determined by the sensitivity of the probe to the changed voltage of the excitation device. The measuring interval should be sufficient to carry out measurements and determine the parameters of the test fluid.

A device is disclosed that implements an additive method of exciting an oscillatory system of a vibro-viscometer.

An external excitation device for a mechanical oscillatory system of a vibro-viscometer, including a device for exciting oscillations of a mechanical oscillatory system of a vibro-viscometer probe, a device for recording and controlling a vibro-viscometer based on a microcontroller, in the permanent memory of which a control program for the excitation device and frequency-phase characteristic φ (ω) are recorded filter circuit, a probe position sensor, the output of which is connected to the input of an electronic amplifier, the output of which is connected to the input of the frequency filter circuit, characterized in that

the device additionally contains a two-input adder with a switch at the second input, and the first input of the adder is connected to the output of the excitation device, the output of the electronic amplifier is also connected to the second input of the adder through a switch, the control input of which is connected to one of the control outputs of the recording and control device of the vibro-viscometer.

In FIG. 1 is a structural diagram explaining the claimed method and device.

The device includes a series-connected electric controlled vibration exciter 1 of the mechanical oscillatory system of the viscometer, a mechanical oscillatory system of the viscometer (probe) 2, a position sensor 3 of the measuring probe of the viscometer, a linear electronic amplifier 4 signal of the position sensor, 5 - frequency filter circuit containing linear frequency filters in the range of lower and upper working frequencies of a mechanical oscillatory system (probe). The frequency-phase characteristic ϕ (ω) of the filter circuit must be known in advance or experimentally measured. 6 - a programmable microcontroller, in the permanent memory of which is written the control program for the switch, oscillator and the frequency-phase characteristic ϕ (ω) of the filter circuit. The device also includes a controlled two-input adder 7 with a switch 8, while the output of the oscillator 1 is connected to the first input of the adder 7, the output of the electronic amplifier 4 is connected to the second input of the adder via a switch 8, the control input of which is connected to one of the outputs of the microcontroller 6 as a device registration and control of a vibration viscometer.

The claimed invention is as follows.

At the first stage -

The microcontroller 6 opens the switch 8 at the second input of the adder 7 and under the influence of the output signals of the microcontroller, the exciter 1 of the mechanical vibrations of the probe 2 generates a periodic driving force F _v (t) of constant amplitude with the current frequency ω and the initial phase ϕ ₀ . Under the influence of this force, a harmonic signal is generated at the output of the probe position sensor 3, which is shifted in phase by the value ϕ _d (ω) relative to the phase ϕ ₀ . This signal is proportionally amplified by amplifier 4, filtered by frequency by means of a filtering circuit 5, and fed to the input of microcontroller 6 with the resulting phase ϕ _res (ω). The microcontroller 6, in the memory of which the frequency-phase characteristic ϕ _f (ω) of the frequency filter circuit is recorded, determines the phase difference ϕ _res (ω) and ϕ ₀ in accordance with the control program stored in it. If this difference is equal to ϕ _s (ω) = ϕ _f (ω) + π / 2, then the frequency of the output signal of the microcontroller 6 supplied to the input of the exciter 1 corresponds to the natural frequency ω _{0 of the} oscillation system and ω _{0 is} stored in the memory of the microcontroller 6.

If the difference is less than ϕ _s (ω), then the microcontroller 6 incrementally increases the frequency of its output signals while simultaneously controlling the difference of these phases at each step. If the phase difference ϕ _res (ω) and ϕ _{0 is} greater than ϕ _s (ω), then the microcontroller 6 stepwise reduces the frequency of its output signals, while simultaneously controlling the difference of these phases at each step. That is, at the first stage, the operation of the viscometer at the natural frequency ω _{0 of the} mechanical oscillatory system of the viscometer is constantly ensured.

In the second stage -

After a specified time interval, the microcontroller 6 closes the switch 8 at the second input of the adder 7 and the output signal of the amplifier 4 is added to the exciting signal, proportional to the signal of the probe 3 position sensor, then, similarly to the first stage, a new value of the natural frequency ω _{0m of the} oscillatory system is determined in this mode, ω _0m stored in the memory of the microcontroller; then the microcontroller 6 again opens the switch 8, that is, proceeds to the first stage. The interval can be set either by a program or by an operator, repeated consecutive conduction of the first and second stages is required when continuously changing the parameters of the liquid, for example, when changing its temperature, the frequency is determined by the speed of measuring the parameters of the liquid. Using the values of the natural frequencies ω ₀ and ω _0m , the current effective values of the oscillating mass _{0 of the} probe and the stiffness coefficient k _{0 of the} oscillatory system and the damping coefficient (or mechanical resistance of the fluid) are determined by calculation (which is described in sufficient detail below). These calculated values are necessary for accurate determination of the fluid characteristics using a vibro-viscometer.

The mathematical and physical principles underlying the proposed method are described below, which are also given in the description of the patent of the Russian Federation No. 2663305 for the case of using a ball immersed in a liquid and sufficiently distant from the walls of the cell as a viscometer probe.

The sensitive element of the vibro-viscometer is a miniature probe immersed in the test fluid. The probe is rigidly connected to the oscillatory system, which is a second-order mechanical oscillatory link. In an unloaded state, the oscillation parameters of a given link are completely determined by three intrinsic physical parameters: the oscillating mass m ₀ , damping coefficient h ₀ and stiffness coefficient k ₀ . Mechanical vibrations in this system are created at the command of the microcontroller by an electromechanical excitation device 1, which converts the electric voltage U _v (t) into an exciting force F _v (t):

where t is time, α is the conversion coefficient, (Н⋅В ^-1 ).

The response of the mechanical oscillatory system of the vibro-viscometer 2 to the exciting force is evaluated using a position sensor 3 by the voltage U _D (t) at its output, proportional to the geometric deviation x (t) of the oscillating mass m ₀ from the equilibrium position:

where β is the conversion coefficient, (V⋅m ^-1 ).

In the general case, the values of the parameters of the unloaded oscillatory system are functions of the current temperature T: m ₀ (T), h ₀ (T) and k ₀ (T). These functional dependences of the parameters of the oscillatory system on temperature can be theoretically or experimentally obtained at the stage of its design and manufacture.

The response x (t) of the oscillatory system to the exciting force F _v (t) is found by solving the following linear differential equation (see RF patent 2663305):

For F _v (t) = F ₀ sin (ωt), the response x (t) has the form:

x (t) = x _max (ω) sin (ωt + ϕ _v (ω)).

where F ₀ is the amplitude of the exciting force, ω is the circular frequency of the harmonic exciting force, ϕ _v (ω) is the phase shift between the exciting force and the response.

For the second-order vibrational link, which is the mechanical vibrational system of the vibro-viscometer, the following relations are valid (see RF patent 2663305), while the phase shift between the exciting force and the response at the natural frequency of the vibrational system is always π / 2:

Here, ω ₀ is the natural frequency of the unloaded oscillatory system, Q ₀ is its quality factor.

With full or partial immersion of the vibrating mass of the vibro-viscometer in the liquid, the parameters of the oscillatory system change and acquire new values:

where m _L , h _L , k _L are the mass, damping coefficient, and stiffness coefficient of the vibrational system interacting with the test fluid, respectively. A change in the mass and stiffness coefficient of the oscillatory systems also leads to a change in the natural frequency, which takes on the value ω _L.

The values Δm, Δh, Δk are changes in the parameters of the oscillatory system caused by the fluid under study. Δm is the so-called attached mass, i.e. mass of fluid surrounding the probe involved in the oscillations. Friction against a liquid causes a change in the damping coefficient Δh. The value Δk is a change in the stiffness coefficient (it is natural to call it the attached stiffness), associated with the elastic properties of the liquid in contact with the probe. The values Δm and Δh are widely used to determine the properties of the studied fluid, and their accurate and operational determination is the main task of vibro-viscometry. At the same time, the influence of the liquid on the stiffness coefficient of the oscillatory system is usually not taken into account in the calculations, in particular, there is no definition of Δm and Δh in the prototype.

Let us explain the insufficiency of previously used techniques. So, the value of the attached mass Δm, which is used in known methods to determine the bulk density of the liquid ρ _L and the shear (dynamic) viscosity η _L , is determined from equation (4) by the value of the natural frequency ω _{L of the} oscillatory system when the measuring probe is immersed in the test fluid:

Considering by the methodology of the prototype that the change in frequency is associated only with a change in mass, taking into account (6) for the attached mass, Δm = m _L -m _{0 is} obtained. That is, it was not previously taken into account that the stiffness coefficient k _{0 of the} vibrational system interacting with the liquid can change.

Using the calculated value of the mass m _{L of the} oscillatory system, from the expression (5) determine the damping coefficient in the liquid:

where Q _L is the quality factor of the oscillatory system interacting with the liquid. To determine the damping coefficient caused by the influence of the liquid, taking into account (6), Δh = h _L -h _{0 is} obtained.

From the above examples, it is obvious that ignoring the elastic properties of the fluid surrounding the probe can lead to significant errors in the analysis of experimental data. This problem is connected with the fact that for low-frequency vibro viscometers there are no generally accepted methods and means for experimental determination of the stiffness coefficient of an oscillating system interacting with a liquid.

In the inventive additive method of exciting an oscillatory system of a vibro-viscometer, it is proposed to change the exciting force so that such a change is equivalent to a change in the stiffness coefficient of the oscillatory link.

According to the claimed method, in the process of studying the liquid, a voltage from the output of the position sensor converted by amplifier 4, which is proportional to the displacement x (t) of the oscillating mass m, is periodically added to the exciting harmonic signal U _v (t) for a short measuring time interval sufficient to take measurements from the equilibrium position:

where γ is a dimensionless weight coefficient showing how much of the voltage from the output of the position sensor is added to the excitation signal.

In accordance with expression (1), the exciting force will also change:

Substituting the obtained value of the exciting force in equation (3) we obtain:

An analysis of the expression shows that the proposed change in the exciting force is equivalent to a change in the stiffness coefficient of the vibrational link from the value k ₀ to the value k _m = (k ₀ -α⋅γ⋅β) = k ₀ -Δk _m . A change in the stiffness coefficient Δk _m will lead, in accordance with (4), to a change in the natural frequency of the vibrational link from the value ω ₀ to the value ω _0m in the mode of changing the exciting force by adding voltage from the output of the position sensor (the second measurement step is described above).

The value Δk _m can be determined by calculation based on the measurement results: k ₀ (Т) - when calibrating an unloaded oscillatory system of a vibro-viscometer (this is enough to be done once) according to the known passport dependence, as well as from the measured values of the natural frequencies ω ₀ and ω _0m :

Note that the value Δk _m is determined by the value of the weight coefficient γ in equation (9) during the initial calibration of the vibro-viscometer. During the subsequent operation of the vibro-viscometer, the parameter Δk _m remains constant regardless of the temperature and properties of the investigated fluid, as well as the amplitude of the exciting voltage.

The opportunity to control the stiffness coefficient of the oscillatory system allows us to determine in the process of testing the liquid which part in the change in the current value of the natural frequency is caused by a change in the attached mass, and which is related to the influence of the liquid on the system stiffness coefficient. For this, it is necessary to repeat operations similar to those performed during the initial calibration of an unloaded oscillatory system. Measurements of the natural frequency ω _L before the change in the excitation force and the frequency ω _Lm after the change in the excitation force are carried out for the oscillatory system interacting with the investigated fluid. The expression for the magnitude of the change in the stiffness coefficient of this oscillatory system will be similar to (12):

Given that the change in the stiffness coefficient Δk _m under the influence of changes in the exciting force does not depend on the current value of the stiffness coefficient, we can equate the right-hand sides of expressions (12) and (13) and obtain the expression for the stiffness coefficient of the oscillatory system under the action of a liquid:

The stiffness coefficient k _L (T) calculated from (14) allows, using (7), to determine the value of the oscillating mass:

The obtained value of the oscillating mass m _L allows, using (8), to calculate the change in the attenuation coefficient caused by the liquid:

Thus, the inventive additive method allows to separately experimentally and if necessary continuously determine the current effective values of the oscillating mass and stiffness coefficient of the oscillatory system of the vibro-viscometer, taking into account the influence of the test fluid, which improves the accuracy of determination of the test fluid parameters such as Δm and Δh, measured by the vibro-viscometer, and also expand list of defined parameters.

The inventive method and device can be implemented and automated by known means.

Claims (4)

1. An additive method of external excitation of a mechanical oscillatory system of a vibro-viscometer, in which the mechanical oscillatory system of a vibro-viscometer equipped with a probe position sensor is brought into mechanical vibrations by a driving device with a given driving force, the output signal of the probe position sensor is converted by amplification and frequency filtering, continuously changed the oscillation frequency of the excitation device until the natural frequency ω ₀ is reached, which is determined by reaching the phase shift φ _З specified at each frequency in the operating frequency range between the oscillations of the excitation device and the oscillations of the output amplified and frequency-filtered signal of the position sensor according to the formula φ _з (ω) = φ _f (ω) + π / 2, where φ _f (ω) is the phase shift of the frequency-filtering circuits of the sensor signal, characterized in that the current natural frequency ω _{0 of the} mechanical oscillatory system of the vibro-viscometer is stored in the memory of the microcontroller; in the process of registering the natural frequency ω ₀ , the effective rigidity of the oscillatory system is periodically changed by a known value Δk _m determined during the initial calibration of the vibro-viscometer by adding to the exciting signal of the excitation device a known fraction of the output signal of the probe position sensor transformed by the amplifier, and determining a new value the natural frequency of the oscillatory system is ω _0m , and from the obtained frequencies ω ₀ and ω _0m , the current effective values of the oscillating mass m _L and the stiffness coefficient k _{L of the} oscillatory system are determined by calculation:

and

where ω ₀ is the natural frequency of the oscillations of the unloaded probe; ω _L is the natural frequency of the oscillations of the probe in the liquid, ω _Lm is the natural frequency of the oscillations of the probe in the liquid with an additional change in the exciting force; Δk _m - change in stiffness coefficient under the influence of changes in the exciting force; T is the current temperature of the test fluid. 2. An external excitation device for the mechanical vibrational system of the vibro-viscometer, including a device for vibrational excitation of the mechanical vibrational system of the vibro-viscometer probe, a vibro-viscometer recording and control device based on a microcontroller, in the permanent memory of which a control program for the excitation device and frequency-phase characteristic φ (ω) are recorded frequency-filter circuit, a probe position sensor, the output of which is connected to the input of an electronic amplifier, the output of which is connected to the input of the frequency-filter circuit, characterized in that the device further comprises a two-input adder with a switch on the second input, and the first input of the adder is connected to the output of the device excitation, the output of the electronic amplifier is also connected to the second input of the adder through a switch, the control input of which is connected to one of the control outputs of the recording and control device of the vibro-viscometer.

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