RU192716U1 - Electronic-acoustic device for measuring the level, density and viscosity of liquid media - Google Patents

Abstract

The device relates to measuring technique and can be used to measure the level, density and viscosity of liquid media in tanks, taking into account the possible separation of the liquid during storage. The device comprises a generator 1, forming a probe signal in the frequency range, which is input to the electro-acoustic transducer 2. The received acoustic signal is reflected from the reflector 3, located at an angle of 45 degrees to the surface of the transducer, and then passes by acoustic receivers 4 located at a known distance height, which transmit an electric signal to a multi-channel signal processing device 5. Signals reflected from the boundaries of the media are also recorded by receivers 4 for further th processing. The technical result is to increase the accuracy of measuring the attenuation of the sound wave, which, in turn, allows you to measure the viscosity of the liquid. 1 ill.

Description

The device relates to measuring technique and can be used to measure the level, density and viscosity of liquid media in tanks, taking into account the possible separation of the liquid during storage.

Known electronic-acoustic device for measuring the level of liquids, based on the fixation of the propagation time of the probe and reflected acoustic pulses in the direction of the media boundary (patent for invention RU 1757304 With G01F 23/28 publ. 08/30/1994, utility model RU16313 U1 G01F 23/28 publ . 12.20.2000). An ultrasonic level gauge is also known (utility model RU48629 U1 G01F 23/28, published October 27, 2005), comprising a multi-channel generator, a strobe pulse generator, a processing and indication unit, a measuring channel, a reference channel and a channel for measuring the level of produced water. The acoustic part of the measuring channel is made in the form of a L-shaped pipe, consisting of a vertical, with a longitudinal slit, and a horizontal section with an opening in the lower part to remove deposits. A transducer is placed in a horizontal pipe section, the radiating surface of which is located vertically, and a reflector oriented at an angle of 45 ° to the surface of the transducer.

A common disadvantage of these devices is the inability to measure the density of products.

The prototype of the claimed utility model is an electronic-acoustic device for measuring the level and density of petroleum products (utility model RU150171 U1 G01F 23/28, G01N 29/024 publ. 02/10/2015), containing an excitation pulse generator, an acoustic measuring channel made in the form of a L-shaped pipe, consisting of a vertical and horizontal section with a hole in the lower part to remove deposits, and in the horizontal section of the pipe there is a transducer, the radiating surface of which is located vertically, and the reflector is a reference at an angle of 45 ° to the surface of the transducer, while intermediate acoustic reflectors located at a fixed distance along the vertical pipe are added to the acoustic part of the measuring channel, and the electrical signal processing circuit consists of an excitation pulse generator and a microprocessor-based signal processing unit connected in parallel to the electro-acoustic transducer measuring channel.

The main disadvantage of this device is the inability to measure the viscosity of the liquid due to the low accuracy of measuring acoustic attenuation, due to two reasons. The first reason is a significant difference in density between air and the nearest liquid medium, as a result of which the coefficient of reflection of an acoustic wave from the interface between air / liquid tends to unity and is almost independent of density. The second reason for the decrease in accuracy arises during operation - the walls of the pipe of the measuring channel are covered with a coating that changes the acoustic impedance of the waveguide and, as a result, affect the amplitude and final measurements.

The task is to expand the functionality by adding a measurement of the viscosity of liquid media.

The problem is achieved in that in a device containing an excitation pulse generator, the output of which is connected to an acoustic transducer, the emitting surface of which is located vertically and the reflector oriented at an angle of 45 ° to the surface of the transducer, according to the utility model, acoustic receivers are located vertically above the reflector at fixed distances whose electrical outputs are connected to a multi-channel signal processing device.

The essence of the utility model is illustrated in the drawing, which shows a structural diagram of the proposed device. The circuit includes an excitation pulse generator 1, an acoustic transducer 2, an acoustic signal reflector 3, acoustic receivers 4 located at a fixed distance in height, a multi-channel signal processing device 5. Measurement of the parameters of liquids is carried out in the tank 6.

The device operates as follows. The generator 1 generates a probe signal in the frequency range 50-500 kHz, which is fed to the input of the electro-acoustic transducer 2. The received acoustic signal is reflected from the reflector 3, then passes by the acoustic receivers 4, which transmit the electric signal to the multi-channel signal processing device 5. Reflected from the boundaries media signals are also recorded by receivers 4 for further processing.

The main way to determine the liquid level in acoustic measurements is to measure the propagation time of the signal from the acoustic transducer to the boundary of the media and vice versa. The propagation time is directly affected by the speed of sound in the medium, which depends on many factors, such as chemical composition, density, temperature. To obtain the exact speed of sound in the medium being measured, various methods are used: in the prototype, reference reflectors are used for measurement, which make it possible to measure the real speed of sound at the closest known interval in front of the medium boundary. In the proposed device, instead of reference reflectors, acoustic receivers are used, while the liquid level in the tank N is determined by the formula:

where H _n is the height of the n-th acoustic receiver, while n is the number of the acoustic receiver closest to the bottom of the liquid / air interface;

Δt is the time it takes the acoustic wave to travel back and forth between the media boundary and the nearest acoustic receiver;

c _n is the speed of sound in the interval between the nearest immersed in the liquid and the previous acoustic receiver. It is believed that it is not much different from the speed of sound in the medium between the boundary of the media and the nth acoustic receiver;

t _n is the time taken by the acoustic wave to reach the n-th acoustic receiver.

The density of a liquid can be determined in two ways. In the first case, if the chemical composition of the liquid is known in advance, one can use the known empirical relationships. A number of liquids have a known dependence of density on the speed of sound. For petroleum products, the dependence, with an error of less than 2%, is given below:

In the general case, when a fluid with unknown parameters is measured, a second measurement method can be used. The essence of this method is to measure the acoustic pressure in the medium, as well as the acoustic pressure passed through a material with known parameters - the so-called buffer rod. Thus, each such acoustic receiver consists of two piezoelectric elements, where the first removes the sound wave directly from the liquid, and the second - the sound wave passed through the buffer rod with known properties. The density of the liquid in this case will be calculated by the formula:

where c _n is the speed of sound near the acoustic receiver, measured by the formula (1);

c _m , ρ _m is the speed of sound and density of a known material;

K is the ratio of the amplitude of the signal passing through the buffer rod to the amplitude of the direct signal.

To find the viscosity, the dissipative coefficient b is first determined from the formula:

where Z is the attenuation of sound in amplitude;

x - the segment on which the attenuation is measured;

ρ _n , c _n - density and speed of sound on the segment;

ω is the frequency of the acoustic signal.

The dissipative coefficient b for a liquid is described by two main components:

where η, ζ, are shear and bulk viscosities.

With a known coupling coefficient υ between them, the shear viscosity is equal to:

The use of acoustic receivers instead of reference reflectors provides several advantages. Firstly, each receiver captures a direct signal from a large-amplitude emitter, which increases noise immunity, and as a result, an increase in the accuracy of determining the speed of sound in the intervals between receivers, which leads to an increase in accuracy as a whole. In systems with reference reflectors, the signal reflected from the reference point in amplitude is ten times weaker because there is a significant return path to the acoustic transducer, while the number and reflectivity of the reference points is very limited so as not to cause strong attenuation of the propagating signal. Thus, the use of separate acoustic receivers also virtually removes restrictions on their number and the pitch between them. Secondly, due to the lack of the need to send a weak acoustic signal back along the same path to the acoustic transducer, it becomes possible to abandon the waveguide. In this case, the signal reflected from the boundary of the media is fixed by the nearest acoustic receiver. The rejection of the waveguide simplifies the maintenance of the system - it is enough to monitor the cleanliness of the working surfaces of electro-acoustic devices and reflector.

The third advantage of using acoustic receivers is the ease of determining the boundaries of the stratified liquid in the tank (the boundary between the first and second medium in the drawing). The reflection coefficient from the media boundary is determined by the expression:

where ρ ₁ , ρ ₂ are the density of the first and second medium, respectively;

c ₁ , c ₂ - the speed of sound in the first and second medium, respectively.

With a slight difference between the products ρ ₁ ⋅c ₂ and ρ ₂ ⋅c _2, the reflection coefficient may be insignificant. In the device with reference reflectors described in the prototype, the problem arises of distinguishing signals from reference reflectors with reflection signals from the boundary of the media of the layered liquid, since their amplitudes can be at the same level.

A fourth advantage is that in the absence of a waveguide, fluid can circulate freely in the region of acoustic receivers. When using waveguides, as in the prototype, the same stratification and liquid level inside the waveguide is not provided as outside it. The connection of the volume of the waveguide with the tank occurs at the bottom of the tank and the waveguide will be filled with a denser medium from the bottom of the tank. Partially, the problem is solved by openings in the waveguide, which can also serve as reference reflectors, however, the exchange of liquid from the internal cavity of the pipe with the reservoir is still difficult. The absence of a waveguide in the proposed device guarantees an accurate measurement result of layered media.

When implementing the device for acoustic transducer 2 and acoustic receivers 4, piezoelectric transducers made of TsTS-19 material were used. Acoustic receivers are made in the form of a cylinder with a diameter of 5 mm, with such dimensions, the acoustic shadow does not affect the following receivers. Sensitive surfaces of the receivers were directed down the reservoir, which complicates their pollution, while reflection from the boundary of the media is accepted by the nearest receiver without complications. Mirror 3 was made of stainless steel. For additional focusing of the acoustic beam, it can have a parabolic shape. It should also be noted that, in practice, a correction factor is introduced into formula (4) in view of the difference between the acoustic beam and the resulting scattering for each receiver.

In comparison with analogs, this device, due to the location of acoustic receivers at a known distance in height, provides an increase in the accuracy of measurement of the attenuation of a sound wave, which makes it possible to measure the viscosity of a liquid. In addition, a height distribution profile can be obtained for all measured parameters.

Claims (1)

An electronic-acoustic device for measuring the level, density and viscosity of liquid media, containing an excitation pulse generator, the output of which is connected to an acoustic transducer, the emitting surface of which is located vertically, and a reflector oriented at an angle of 45 ° to the surface of the transducer, characterized in that it is vertically above the reflector Acoustic receivers are located over fixed distances, the electrical outputs of which are connected to a multi-channel signal processing device.

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