RU2334213C2 - Oscillatory viscometer - Google Patents

Abstract

FIELD: physics; engineering procedures.

SUBSTANCE: oscillatory viscometer contains mechanical vibrator with test body and three electromechanical converters. One of electromechanical converters is motion signal source and through rectifier is connected to one of inputs of comparator on other input of which reference voltage comes. The output of the comparator is connected with driving input of controlled amplifier main input of which is connected to limiting amplifier, and the output - to the second converting generator of mechanical force. The input of the limiting amplifier is connected to the converting motion signal source. To the second input of the comparator through the additional rectifier one more electromechanical converter mounted on vibrator and connected to the limiting amplifier is attached, on signal of which reference voltage is formed.

EFFECT: expansion of measurement possibilities due to elimination of motion amplitude dependent signal invariable component.

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Description

The invention relates to techniques for measuring viscosity, and more specifically to a device for vibrating viscometers intended for use in research laboratories, in medicine, for monitoring technological processes.

The essence of measurements using viscometers of this type is to identify the inhibitory effect of the liquid on the test body oscillating in contact with it. They use devices consisting of a mechanical vibrator connected to a test body - a probe, an electronic control circuit and electromechanical converters.

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 vibrational velocity;

ρ is the fluid density;

η is the viscosity of the liquid;

A, B, C, K - proportionality coefficients.

In reality, in addition to the resistance of the liquid during measurements, it is necessary to take into account Z ₀ , the resistance due to the internal friction of the measuring unit. Moreover, the total observed resistance Z = Z _W + Z ₀ .

In the class of devices under consideration, the motion-inducing force and velocity of the test body are proportional to the corresponding electric signals U _F and U _ξ . Therefore, the relations

Z = BU _F / U _ξ ; Z ₀ = BU _F0 / U _ξ0 ,

where U _F0 and U _ξ0 , due to the presence of Z ₀ , correspond to vibrations of the test body in air.

нелинейным образом. При стабилизации U_ξ=U_ξ0 измеряемый сигнал U=U_F связан с

линейным образом.The experiment is usually carried out or at a constant value of the force - measure the obtained amplitude of the oscillations; or at a constant value of the amplitude (speed) of movement - measure the force required to create a given amplitude. When the effective force U _F = U _{F0 is} stabilized, the measured signal U = U _ξ is associated with

nonlinear way. When stabilizing U _ξ = U _{ξ0, the} measured signal U = U _F is associated with

in a linear fashion.

.

.

U ₀ = U _F0 , depends on the given amplitude of motion.

Known viscometers containing a vibrator with a test body - a probe and two electromechanical transducers connected to it in the feedback circuit of an electronic oscillator are connected. In this case, the oscillator consists of a series-connected input amplifier and an amplifier-limiter [Soloviev AN, Kaplun AB Vibration method for measuring the viscosity of liquids. Novosibirsk .: Nauka, 1970. - 139 p.].

нелинейной функцией.The force exciting the movement is generated from the output voltage of the limiter and has a constant value, while the output analog signal is proportional to the amplitude of movement and is associated with the value

nonlinear function.

Closest to the proposed is a viscometer [Development of a vibration viscometer for general industrial use and experience in its implementation. A.P. Dzyuba, N.P. Zorin, V.N. Krutin, I.A. Pykhteev, L.A. Ushakov. / Vibration viscometry, collection of works, Siberian Branch of the Academy of Sciences of the USSR, Institute of Thermophysics, Novosibirsk, 1976, pp. 78-87]. It consists of a vibrator with two electromechanical converters and a self-oscillator in the form of a feedback loop. The self-oscillator contains a device for comparing the DC, an independent OH voltage reference source and a controlled AGC amplifier. Using a control signal, an AGC control signal is generated, which changes the transmission coefficient of the circuit in such a way as to compensate for a possible change in the amplitude of motion of the probe. The magnitude of the amplitude is set using OH and compared with the motion signal at the input of the CSS.

The structure of such a viscometer is shown in figure 1.

The vibrator 1 is a frequency-setting element and has two electromechanical converters 1.1 and 1.2. The electromechanical converter 1.1 converts the electrical voltage supplied to it into mechanical force and excites the movement. An electromechanical converter 1.2 converts the amplitude of the oscillations into a proportional electrical signal. They are included in the feedback circuit of the oscillator. The oscillator consists of an input amplifier 2, an amplifier-limiter 3 and a controlled amplifier 12. The gain of the controlled amplifier 12 is determined by the control signal, which forms a comparison device 10. At its two inputs, a signal is supplied from the rectifier 6 connected to the input amplifier 2 and from a constant source voltage 14. Using a constant voltage source 14 sets the amplitude of the oscillations. If the signal of the amplitude of movement at the input of the comparator 10 is equal to the reference voltage of the source 14, the voltage at the control input of the controlled amplifier 12 is 0. Otherwise, the difference between the output voltages of the constant voltage source 14 and the rectifier 6, which changes the transfer coefficient controlled amplifier 12 and the magnitude of the exciting force until then, until you reach a signal amplitude of motion equal to the specified value. A rectifier 13 for amplitude control, a comparator 5 for determining the oscillation frequency, an amplifier 7 for providing the required level of the control signal, and a DC amplifier 8 for adjusting the sensitivity can be connected.

The measurement takes place at a constant value of the amplitude of the oscillations. The value of the force exciting the movement is determined when the test body is in the air in a calibration and controlled fluid.

линейной функцией и содержит постоянную составляющую U₀.The output analog signal is generated from the control voltage 10, is proportional to the magnitude of the exciting force, is associated with the value

linear function and contains a constant component U ₀ .

Further, this signal is recorded by the operator or is subjected to the procedure of subtracting the constant component. Its value should be determined earlier in the conditions of calibration in air at a given amplitude of motion. Thus, in order to conduct a measurement with a different oscillation amplitude (for example, to change the sensitivity or with a minimum amplitude - in order to exclude the influence of the measurement on the liquid structure), a change in the subtracted value and recalibration are required. This complicates the work of the operator.

The presence of the initial U ₀ in the exciting electric signal limits the dynamic range of the possible additional voltage associated with the fluid resistance (U _max -U ₀ ), where U _max is the maximum possible voltage across the converter. This is important for measurements with large amplitude when controlling the linearity of the rheological behavior of complex colloidal solutions, for example, drilling fluids. Suppose that the maximum possible voltage is 15 V (corresponds to the output voltage of a standard operational amplifier), and the required amplitude of movement is achieved at U ₀ = 13 B. The remaining dynamic margin of 2 V is very small and limits the possibility of measurement only to low-viscosity liquids.

The objective of the invention is to eliminate the amplitude-dependent motion of the DC component of the signal.

The technical result is achieved by the fact that the viscometer includes a vibrator with three electromechanical converters and an oscillator in the form of two feedback loops, one of which is a reference voltage generator for the second.

A vibrating viscometer containing a mechanical vibrator with a test body and electromechanical transducers, one of which is a source of a motion signal and connected through one rectifier to one of the inputs of the comparison device, the other input of which receives the reference voltage, and the output of the comparison device is connected to the control input of the controlled amplifier, the main input of which is connected to an amplifier-limiter, and the output - with a second electromechanical converter - a generator of mechanical force, while the input the limiter amplifier is connected to the electromechanical converter - the source of the motion signal, another electromechanical converter mounted on the vibrator and connected to the limiter amplifier is connected to the second input of the comparison device through the additional rectifier, from which the signal forms the reference voltage.

The structure of the proposed device is shown in figure 2.

The vibrator 1 is a frequency-setting element and has three electromechanical converters 1.1; 1.2 and 1.3. Electromechanical converters 1.1 and 1.3 convert incoming electrical voltages into mechanical force. An electromechanical converter 1.2 converts the amplitude of the oscillations into an electrical signal.

The feedback loop that sets the frequency and amplitude of movement consists of an input amplifier U (2) and an amplifier-limiter UO (3). Converters 1.1 and 1.2 are connected to the output of the UO and the input of Y.

The amplitude-supporting circuit consists of an input amplifier U (2), an amplifier-limiter UO (3), a preliminary amplifier 11, and a controlled AGC amplifier (12). The gain of the AGC is determined by the control signal, which forms the US comparison device (10) using rectifiers 6 and 9 from the motion signal from the electromechanical converter 1.2 and the force signal from the electromechanical converter 1.1.

The second input of the comparison device receives the reference voltage, which is generated using the associated additional rectifier 9 and the repeater 15 from the signal on the electromechanical converter 1.1, Fig.2, which is additionally mounted on the vibrator and connected to the amplifier-limiter 3.

The transmission coefficient of circuit 2-6 is set so that when the test body 1.4 is out of the liquid, the signal at the output U (2) is equal to the signal at the electromechanical converter 1.1 and thus compensates the internal resistance of the installation Z ₀ .

To control the amplitude of motion, determine the frequency of oscillations, provide the required level of the control signal and regulate the sensitivity, a rectifier 13, a comparator 5, an amplifier 7, and a DC amplifier 8 can also be connected.

The scheme works as follows. The two inputs of the comparison device receive signals from rectifiers 6 and 9. If the signal proportional to the amplitude of movement of the rectifier 6 is equal to the reference voltage of the rectifier 9 supplied through the repeater 15 from the amplifier-limiter of the primary circuit, the voltage at the control input of the controlled amplifier 12 is 0. V Otherwise, a voltage difference arrives at the control input, which changes the transmission coefficient of the controlled amplifier 12 and creates an additional force on the electromechanical converter 1.3 until Electromechanical converter 1.2 does not establish a signal of the amplitude of motion equal to the specified value.

линейным образом и не содержит постоянной составляющей.There is a separation of the exciting electric voltage and the acting force into two components. The fraction of the total force generated by the electromechanical converter 1.1 is proportional to Z ₀ .. The fraction of total force generated by the supporting electromechanical converter 1.3 is proportional to the other component of the mechanical resistance. It turns on during additional braking of the test body due to the surrounding fluid. The output analog signal is formed from the voltage at the electromechanical converter 1.3, is connected with

linearly and does not contain a constant component.

In the exciting electrical signal on the electromechanical converter 1.3 there is no initial U ₀ . Suppose the maximum possible voltage is 15 V (corresponds to the output voltage of a standard operational amplifier), and the required amplitude of movement is achieved at U ₀ = 13 B. A voltage of 13 V is set on the electromechanical converter 1.1. The dynamic margin of 15 V by 1.3 does not decrease.

The measurement is carried out at a given amplitude of oscillations:

1. Find the signal U _k when the probe moves in a calibration fluid with known values of ρ _k η _k .

.2. Determine the coefficient by the formula

.

3. Determine U _W when the probe moves in the test fluid.

по формуле

=KU_ж.4. Find the desired value

according to the formula

_W = KU.

Concrete example

A brass tuning fork 3 with a resonance frequency of f ₀ ≈ 400 Hz is suspended on strings. At the end of one of its legs, a test body is installed in the form of a thin hard pointed rod made of stainless steel (needle). A brass counterweight is mounted on the other leg. The width of the tuning fork legs is 20 mm. Piezoelectric elements with a diameter of 12 mm and a thickness of 0.5 mm made of ceramic PZT - 19 are also installed on the flat legs of the tuning fork. On one of the legs is a converter 1.2 connected to an input amplifier. On the opposite leg are two similar converters 1.1 and 1.3. They are connected to the output stages of the feedback loops of the oscillator assembled on 140 series microcircuits. 1.1 - to the master circuit, 1.3 - to the supporting circuit.

The test body was immersed in controlled fluids to the same depth of 20 mm. The value U _ξ 1 was set; 2 and 3 V. It was measured using a digital voltmeter.

, полученные с помощью предлагаемого вискозиметра. Чувствительность датчика составляет 0.6 при U_ξ = 1 В; 1.2 при U_ξ = 2 В и

при U_ξ = 3 В, при этом отсутствует постоянная составляющая сигнала.The value of the output signal was determined during probe movement in air (point 0), octane (1), decane (2), diethyl phthalate (3), and cyclohexanol (4). Figure 3 shows the relationship between U and

obtained using the proposed viscometer. The sensitivity of the sensor is 0.6 at U _ξ = 1 V; 1.2 at U _ξ = 2 V and

at U _ξ = 3 V, while there is no constant component of the signal.

Claims (1)

A vibrating viscometer containing a mechanical vibrator with a test body and electromechanical transducers, one of which is a source of a motion signal and connected through one rectifier to one of the inputs of the comparison device, the other input of which receives the reference voltage, and the output of the comparison device is connected to the control input of the controlled amplifier, the main input of which is connected to an amplifier-limiter, and the output - with a second electromechanical converter - a generator of mechanical force, while the input the limiter amplifier is connected to an electromechanical converter - a source of a motion signal, characterized in that another electromechanical converter mounted on a vibrator and connected to the limiter amplifier is connected to the second input of the comparison device through a vibrator, from which a reference voltage is generated.

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