RU208494U1 - MAGNETOSTRICTION LEVEL FOR LIQUID LEVEL MEASUREMENT WITH COMPENSATION OF ERRORS CAUSED BY LINEAR EXPANSION OF THE TANK WALLS - Google Patents

Abstract

The utility model relates to measuring technology and can be used to measure the liquid level in tanks, which require compensation for errors caused by linear expansion of the tank walls. a magnetically permeable bellows (flexible metal corrugated hose), which is placed in a fluoroplastic tube, which provides free sliding along it of a magnetic float (one or more) associated with the controlled liquid, as well as protection against sticking. Due to the property of the bellows to stretch or shrink, a constant tension of the measuring element is ensured regardless of the linear expansion of the walls of the tank, while the lower part of the measuring device is rigidly attached to the bottom of the tank by means of a fixation device in such a way that when the bellows is stretched, the fixation device remains stationary relative to the bottom of the tank. The essence of the utility model lies in the combined use in the design of a magnetostrictive level gauge of a bellows that can freely stretch and contract in the presence of a linear expansion of the tank walls, providing a constant tension of the measuring element, as well as a fixation device in the lower part of the level gauge, which is securely fixed at the bottom of the tank, while on a reference magnet is fixed to the fixation device, the position of which is used to correct measurements of the liquid level in the tank, taking into account the linear expansion of the tank walls, and also to use used to determine the speed of sound when measuring the liquid level in tanks in which there is no linear expansion of the tank walls or it is not required to take it into account. a measuring device that ensures its constant tension with a linear expansion of the tank walls, and also allows you to fix the position of the reference magnet at a given distance relative to the bottom of the tank, which provides the formation of a reference point to compensate for additional errors in liquid level measurements.

Description

Technology area

The utility model relates to measuring technology and can be used for measuring the level of a liquid in tanks, in which compensation of errors caused by linear expansion of the tank walls is required.

State of the art

Known analogs for measuring the level of liquid.

There is a known method for measuring the level of a liquid [1], including the formation and supply of an electric pulse of a given duration, the transformation of the generated electric pulse into ultrasonic vibrations in the acoustic conduit by deforming the acoustic conduit, forming an alternating magnetic flux along the entire length of the winding of the excitation coil, and the magnetic flux is formed by supplying the generated electric a pulse of a given duration into the winding of the excitation coil, acting through a variable magnetic flux flowing through the section of the excitation coil winding on a constant magnetic field and changing the resulting magnetic field, converting ultrasonic vibrations into electrical vibrations by deforming the crystal of the ferroelectric of the piezoelectric receiver under the influence of ultrasonic vibrations, measuring the transit time of ultrasonic vibrations , determination from the known speed of sound in the acoustic duct and the measured time interval of the liquid level, and for int The time interval for the passage of ultrasonic vibrations is taken as the time interval between the moment of supply of the generated pulse of a given duration to the winding of the excitation coil and the moment of formation of electrical vibrations on the piezoelectric receiver.

A magnetostrictive level gauge [1], operating on this principle, contains a sensitive element with a sound conductor of magnetostrictive material placed in a dielectric tube, a winding wound on a dielectric tube, at least one float with a magnetic block of n permanent magnets, where n = 1, 2 ... i, placed around the insulating shell with the ability to move along it, an electric pulse generator, a level detection unit, a piezoelectric receiver, a digital pulse shaper from converted electrical oscillations from a piezoelectric receiver, a unit for determining the time interval between the moment of formation of the magnetoelastic effect and the moment of formation of the piezoelectric effect ... These blocks are connected to each other in a corresponding way.

The disadvantage of the method implemented in the device [1] is the low accuracy in the measurement ranges of more than 10 meters. It is not possible to correct level measurements to compensate for errors caused by linear expansion of the tank walls.

There is a method [2] for determining the level and other parameters of a fractionated liquid, including the formation and supply of an electric pulse of a given duration, the transformation of the generated electric pulse into ultrasonic vibrations in the acoustic conduit, produced by the formation of a variable magnetic flux locally at the level of the measured liquid, the transformation of ultrasonic vibrations on the piezoelectric receiver into an electric signal, calculating the time interval for the passage of ultrasonic vibrations, calculating the known speed of sound in the acoustic conduit and the measured time interval of the liquid level, characterized in that the formation of an alternating magnetic flux is carried out by autonomous modules placed in active floats under the control of microprocessors that carry out coding, which makes it possible to transmit additional information about the parameters of the liquid at the location of the floats and to distinguish the electrical impulses received on the piezoelectric receiver by belonging to the specific different floats, while the first, received by the piezoelectric receiver from each float, the electrical impulse is the pulse of the origin until the second appears, which arises from the arrival of an ultrasonic wave propagating downward from the float and reaching the piezoelectric receiver due to reflection from the lower end of the acoustic conduit, and the calculated time interval is obtained by subtracting from this value the time interval formed from the fixed at a known distance to the bottom of the same autonomous module, and adding to this result a previously measured correcting additive, which allows after a calculated time interval equal to the ultrasound propagation time of the double length of the part of the acoustic conduit located below the float , determine the thickness of the liquid layer, not the distance from the float to the acoustic transducer, and compensate for the errors caused by the temperature coefficient of expansion of the acoustic duct.

A magnetostrictive level gauge [2], which implements this method, contains a piezoelectric receiver, a sensing element with a sound conductor of magnetostrictive material placed in a magnetically permeable tube, at least one float with a magnetic block of n permanent magnets (ring magnets with a radially oriented magnetic field), where n = 1, 2 ... i, placed around the tube with the ability to move along it, an electric pulse generator, a unit for determining the time interval between the moment of formation of the magnetoelastic effect and the moment of formation of the piezoelectric effect, a unit for determining the level, characterized in that active autonomous modules with measuring circuits controlled by microprocessors and excitation coils of the acoustic conduit to each of the floats and an additional active autonomous module located at a known distance from the bottom of the tank. The magnetostrictive level gauge [2] additionally contains a "Radomskiy anchor", which is a column with a weighted base, three pointed supports and a sealed volume in the upper part to accommodate an autonomous module.

The disadvantage of analogue [2] is a significant lower unmeasured zone, while the design of the "Radomsky anchor" contains moving parts that are prone to contamination in the presence of deposits on the bottom of the tank, which leads to failure of the anchor mechanism. The overall dimensions of the "Radomskiy anchor" structure are not capable of providing installation of the level gauge on flanges with a diameter of less than 100 mm, which greatly narrows the scope of application. This level gauge uses floats with active batteries, which require constant monitoring and regular replacement, and their presence greatly narrows the operating temperature range. This method does not allow the use of metal floats (only plastic floats are applicable), which limits the use of the level gauge in aggressive environments.

The closest analogue, taken as a prototype, is a magnetostrictive linear displacement transducer [3], which includes a measuring device and an electronic transducer, and the measuring device is made in the form of an excitation coil wound on a dielectric tube along which a magnetic positioner can move freely (one or several), having the ability to connect to the controlled object, inside the dielectric tube is a sound conductor made of material with a pronounced magnetostrictive effect, and a piezoelectric element is fixed at one of the ends of the sound conduit, while the electronic transducer contains a number of units, including an electric pulse generator, an amplifier and a receiving driver. signal, a calculator, characterized in that the driver of the receiving signal is made in the form of an amplitude selector, and the piezoelectric element is made in the form of an electroacoustic transducer, while the electronic transducer also contains a commutator, with united with an electroacoustic transducer, an amplitude regulator, one of the inputs of which is connected to a generator of electrical impulses, and the output is connected to a commutator and an excitation coil, the calculator is connected to an amplitude selector and to the second input of an amplitude regulator. that the amplitude selector is configured to cancel interference when an ultrasonic signal is detected by changing the response threshold according to the algorithm developed by the computer.

The given device allows the prototype to be used for a wide range of level measurements with a sufficiently high accuracy (up to 25 m), while with increased resistance to changes in external factors and the absence of influence from aging of elements.

The disadvantage of the prototype is the design of the measuring element, which does not allow correcting the level measurements, taking into account the compensation of errors caused by the linear expansion of the tank walls.

The proposed utility model provides a solution to the technical problem of increasing the accuracy and stability of level measurements in a wide range, due to the design properties of a flexible measuring element, at the same time, it makes it possible to compensate for errors caused by linear expansion of the tank walls and thermal expansion of the acoustic pipeline due to the possibility of installing a reference magnet at a fixed distance from the bottom of the tank.

Disclosure of the essence of the utility model

The magnetostrictive level gauge contains a calculator and a measuring device made in the form of an excitation coil wound on a dielectric tube placed inside a magnetically permeable bellows (flexible metal corrugated hose), which is placed in a fluoroplastic tube, which provides free sliding along it of a magnetic float (one or more), connected with controlled fluid, and anti-caking.

Due to the ability of the bellows to stretch or contract, a constant tension of the measuring element is ensured regardless of the linear expansion of the tank walls, while the lower part of the measuring device is rigidly attached to the bottom of the tank using a fixing device, so that when the bellows is stretched, the fixing device must remain stationary relative to the bottom of the tank. A magnet is attached to the fixation device, which serves as a reference, the position of which is used to subsequently correct measurements of the liquid level in the tank, taking into account the linear expansion of the tank walls, and also serves as a reference point used to determine the propagation velocity of ultrasound when measuring the liquid level in tanks in which there is no linear expansion of the tank walls or it is not required to take it into account.

Inside the dielectric tube of the measuring element, there is a sound conductor made of a material with a pronounced magnetostrictive effect, which appears during the interaction of fields - the electromagnetic field of the excitation coil and the magnetic field of a movable float (one or more) or a reference magnet. An electroacoustic transducer is fixed at the upper end of the acoustic conduit, which is involved in converting the ultrasonic signal of the magnetostrictive pulse into an electrical signal for further processing in the computer, and also participates in the procedure for calculating the propagation velocity of ultrasound in this acoustic conduit according to the algorithm described in the prototype [3].

The essence of the utility model lies in the combined use of a bellows (flexible metal corrugated hose) in the design of a magnetostrictive level gauge, which can freely stretch and contract in the presence of linear expansion of the tank walls, providing constant tension for the measuring, as well as a fixing device in the lower part of the bellows, which is securely fixed to the bottom reservoir. In this case, a reference magnet is fixed on the fixing device, the position of which is used to correct measurements of the liquid level in the tank taking into account the linear expansion of the tank walls, and also used to determine the speed of sound when measuring the liquid level in tanks in which there is no linear expansion of the walls or it is not taken into account. required.

Description of graphic illustrations

FIG. 1 shows a functional diagram of the implementation of a magnetostrictive level gauge for measuring liquid level, where the positions are indicated:

1 - calculator

2 - measuring device

3 - fixation device

4 - reference magnet

5 - tensioning / fixing device

6 - sound conductor placed in a dielectric tube with a wound excitation coil

7 - flexible corrugated hose (bellows) magnetically permeable

8 - flexible fluoroplastic tube

9 - movable magnetic float

10 - electro-acoustic transducer

FIG. 2 shows some geometric parameters of the device for fixing the magnetostrictive level gauge at the bottom of the tank.

Implementation of the utility model

The utility model contains a calculator 1, a measuring device 2 and a fixing device 3 (Fig. 1).

The measuring device 2 consists of a bellows 7 placed in a fluoroplastic tube 8, inside which there is a sound conductor made of a material with a pronounced magnetostrictive effect, located inside a dielectric tube, with an excitation coil wound over it, while the path of movement of a magnetic float 9 passes along the fluoroplastic tube, associated with a controlled liquid, the level of which is controlled and measured by the described utility model. The tension / fixation device 5 connects the upper part of the bellows and the fluoroplastic tube so that, in the presence of linear expansion of the tank walls, it allows the bellows to expand or contract freely, providing constant tension of the measuring element regardless of the linear expansion of the tank walls, as well as fixing the upper part of the bellows on the tank roof ...

The lower part of the bellows with a fluoroplastic tube is rigidly and hermetically connected to the fixing device 3, to which either a weight or a magnet is fixed (Fig. 2), which rigidly fixes the lower end of the measuring device at the bottom of the tank, so that when the bellows is stretched under the action of a linear expansion of the walls of the tank, the fixing device 3 remains stationary relative to the bottom of the tank. On the upper cut of the fixation device, at a known distance from the bottom, a reference magnet 4 is fixed, the position of which is used to correct measurements of the liquid level in the tank taking into account the linear expansion of the tank walls, and also used to determine the propagation velocity of ultrasound when measuring the liquid level in the tanks, in which there is no linear expansion of the tank walls or it is not required to take it into account. The design feature of the fixation device with a reference magnet 4 allows the level gauge to be securely fixed to the bottom of the tank for the entire period of operation.

At the end of the acoustic pipe, placed in a dielectric tube with a wound excitation coil 6, an electro-acoustic transducer 10 is fixed in the upper part, which is connected to a calculator 1, consisting of components similar to the structure of an electronic transducer in the prototype [3].

The components of the calculator 1 provide excitation of the electromagnetic field in the excitation coil of the measuring device 2, and also generate an electrical pulse for the electro-acoustic transducer 10, which converts it into a probing ultrasonic pulse necessary to determine the propagation velocity of ultrasound in a specific acoustic conduit under specific external conditions.

The magnetostrictive level gauge works as follows.

First, the propagation time of the ultrasonic signal along the sound line from the movable float 9 to the electro-acoustic transducer 10, mechanically connected to the tank roof, is measured. A signal from a calculator 1, which creates a magnetic field in the excitation coil, is supplied to the excitation coil wound on a dielectric tube with a sound conductor 6 located in it. An ultrasonic signal in the sound line arises at the place of interaction of the magnetic fields of the excitation coil and the magnet of the float 9, which is located near the sound line 6 and is mechanically connected to the controlled level. Ultrasound propagates from the location of the float 9 to the ends of the sound line 6, is detected by a stationary electro-acoustic transducer 10, is converted into an electrical signal, which is fed to the calculator 1. With the help of the calculator 1, the time interval from the moment the electric pulse is applied to the excitation coil until the moment of detecting the ultrasonic signal is recorded, which is directly proportional to the distance between the float 9 and the electro-acoustic transducer 10.

Then, in a similar way, the propagation time of the ultrasonic signal along the sound line 6 from the reference magnet 4 to the electro-acoustic transducer 10, mechanically connected to the tank roof, is measured, while the fixed time interval is directly proportional to the distance between the reference magnet 4 and the electro-acoustic transducer 10.

Next, the propagation velocity and amplitude of the ultrasonic signal are measured along the entire length of the acoustic duct 6 by emitting a probing ultrasonic signal provoked by an electrical signal from the calculator 1, which is fed to the electroacoustic transducer 10.

The time interval for which the probing ultrasonic signal passes along the entire length of the acoustic conduit is recorded and, after reflecting from its end, returns to the electro-acoustic transducer 10. The propagation velocity of the ultrasonic signal in this acoustic conduit is calculated from the known length of the acoustic conduit and the time of its passage by ultrasound.

Calculation of the liquid level in the reservoir using the described utility model can be implemented in two ways, differing in the presence of taking into account the linear expansion of the walls of the reservoir or in the absence, if it is not required to be taken into account.

In the first case, in the presence of linear expansion of the tank walls, the calculation of the liquid level in the tank is performed in accordance with the following relationship (see Fig. 1):

,

,

- расстояние от дна резервуара до подвижного поплавка, м;where

- distance from the bottom of the tank to the movable float, m;

- расстояние от электроакустического преобразователя до подвижного поплавка, м, изменение которого, с одной стороны, связано с перемещением подвижного поплавка, а с другой - с линейным расширением стенок резервуара;

- the distance from the electroacoustic transducer to the movable float, m, the change of which, on the one hand, is associated with the movement of the movable float, and on the other, with the linear expansion of the tank walls;

- расстояние от электроакустического преобразователя до реперного магнита, м, изменение которого связано только с линейным расширением стенок резервуара;

- the distance from the electroacoustic transducer to the reference magnet, m, the change in which is associated only with the linear expansion of the tank walls;

- точная длина (паспортное значение) устройства фиксации уровнемера на дне резервуара, совпадающее с расстоянием от дна резервуара до реперного магнита, м;

- the exact length (passport value) of the device for fixing the level gauge at the bottom of the tank, coinciding with the distance from the bottom of the tank to the reference magnet, m;

As a result of measuring the propagation time of the ultrasonic signal along the sound line from the movable float 9 to the electro-acoustic transducer 10, and then from the reference magnet 4 to the electro-acoustic transducer 10, we have the following relations:

и

,

and

,

- время приема полезного сигнала ультразвуковой волны (временной интервал между импульсом возбуждения и импульсом, выделенным электроакустическим преобразователем 10) от подвижного поплавка 9, с;where

- the time of reception of the useful signal of the ultrasonic wave (the time interval between the excitation pulse and the pulse allocated by the electroacoustic transducer 10) from the movable float 9, s;

- время приема полезного сигнала ультразвуковой волны (временной интервал между импульсом возбуждения и импульсом, выделенным электроакустическим преобразователем 10) от реперного магнита 4, с;

- the time of reception of the useful signal of the ultrasonic wave (the time interval between the excitation pulse and the pulse isolated by the electro-acoustic transducer 10) from the reference magnet 4, s;

- скорость распространения ультразвука в звукопроводе, которая зависит от параметров окружающей среды, таких как температура, плотности и т.д. С целью определения скорости распространения ультразвука электрический импульс определенной формы от вычислителя 1 подается не в обмотку катушки возбуждения, а на электроакустический преобразователь 10, при этом ультразвуковая волна распространяется по звукопроводу, отражается от конца и возвращается обратно к электроакустическому преобразователю, а скорость распространения звука в звукопроводе определяется формулой:

- the speed of propagation of ultrasound in a sound line, which depends on environmental parameters, such as temperature, density, etc. In order to determine the speed of propagation of ultrasound, an electric pulse of a certain shape from the calculator 1 is supplied not to the winding of the excitation coil, but to the electro-acoustic transducer 10, while the ultrasonic wave propagates along the sound line, is reflected from the end and returns back to the electro-acoustic converter, and the speed of propagation of sound in the sound line is defined by the formula:

,

,

- известная точная длина (паспортное значение) измерительного элемента уровнемера, совпадающая с расстоянием от электроакустического преобразователя до нижнего конца звукопровода, м;where

- the known exact length (passport value) of the measuring element of the level gauge, which coincides with the distance from the electro-acoustic transducer to the lower end of the acoustic duct, m;

- время приема полезного сигнала ультразвуковой волны (временной интервал между зондирующим импульсом, поданным в электроакустический преобразователь и сигналом импульса упругой деформации, выделенным электроакустическим преобразователем).

- the time of reception of the useful signal of the ultrasonic wave (the time interval between the probing pulse fed to the electroacoustic transducer and the signal of the elastic deformation pulse isolated by the electroacoustic transducer).

As a result of mathematical transformations of the previous relations, the calculation of the liquid level from the bottom of the tank using a utility model, taking into account the compensation of the linear expansion of the tank walls, is carried out according to the following formula:

.

...

In the second case, in the absence of linear expansion of the tank walls or the absence of the need to take it into account, the calculation of the liquid level in the tank is carried out in accordance with a similar ratio:

,

,

- расстояние от дна резервуара до подвижного поплавка, м;where

- distance from the bottom of the tank to the movable float, m;

- расстояние от электроакустического преобразователя до подвижного поплавка, м, изменение которого, с одной стороны, связано только с перемещением подвижного поплавка;

- the distance from the electroacoustic transducer to the movable float, m, the change of which, on the one hand, is associated only with the movement of the movable float;

- известное расстояние от электроакустического преобразователя до реперного магнита, м, точно измеренное в процессе установки измерительного устройства уровнемера;

- the known distance from the electroacoustic transducer to the reference magnet, m, accurately measured during the installation of the measuring device of the level gauge;

- известная точная длина (паспортное значение) устройства фиксации уровнемера на дне резервуара, совпадающее с расстоянием от дна резервуара до реперного магнита, м.

- known exact length (passport value) of the device for fixing the level gauge to the bottom of the tank, coinciding with the distance from the bottom of the tank to the reference magnet, m.

от подвижного поплавка 9 электроакустическим преобразователем 10 рассчитывается расстояние

, прямо пропорциональное времени

и скорости распространения ультразвука

, которая в данном случае определяется по известному расстоянию

и времени приема полезного сигнала

от реперного магнита 4 электроакустическим преобразователем 10.As a result of similar measurements of the reception time of the useful signal

from the movable float 9, the electro-acoustic transducer 10 calculates the distance

, directly proportional to time

and the speed of propagation of ultrasound

, which in this case is determined by the known distance

and the time of reception of the useful signal

from reference magnet 4 by electro-acoustic transducer 10.

As a result of mathematical transformations of the described ratios, the calculation of the liquid level from the bottom of the tank using the utility model, in the absence of linear expansion of the tank walls, is carried out according to the following formula:

.

...

The technical result of the utility model consists in increasing the accuracy and stability of measurements of the liquid level in tanks, due to the use of a bellows in the design of the measuring device, which ensures its constant tension during linear expansion of the tank walls, and also allows fixing the position of the reference magnet at a given distance relative to the bottom of the tank, providing correction for liquid level measurements. At the same time, an increase in the accuracy and stability of measurements is realized through the use of a magnet that acts as a reference, the position of which is used to correct measurements of the liquid level taking into account the linear expansion of the tank walls, as well as used to determine the propagation velocity of ultrasound when measuring the liquid level in tanks, in which there is no linear expansion of the walls or it is not required to take it into account.

The basic elements of the level gauge can be executed, for example, as follows.

The corrugated hose (bellows) 7 is made of steel grade AISI.316 and is placed inside a flexible PTFE tube 8 of the PFA-Ex type, while the bellows 7 is fixed in a stretched state using a tension / fixation device 5 during the installation of the level gauge on the installation pipe of the tank.

Sound duct 6 is made in the form of a rod made of low-carbon steel grade 10, placed in a fluoroplastic tube, on which an excitation coil made of a winding wire of PET-155 brand is wound in a single layer with a turn to the turn.

The movable magnetic float 9 and the reference magnet 4 are made on the basis of an annular permanent magnet with axial or radial magnetization.

The fixing device 3 can be made in the form of a load or a powerful magnet, which ensures reliable fastening to the bottom of the tank.

Calculator 1 is implemented on a set of elements such as a microcontroller, field-effect transistors according to an electronic key circuit, operational amplifiers according to an inverting amplifier circuit, a digital-to-analog converter according to a two-threshold comparator circuit, an amplitude controller according to a voltage-controlled current generator circuit.

Sources of information

1. RF patent No. 2222786, cl. G01F 23/28, 2003.

2. RF patent №2518470, class. G01F 23/28, 2012.

3. RF patent №134631, class. G01B 17/00, 2013 - prototype.

Claims (1)

A magnetostrictive level gauge for measuring the level of a liquid, including a measuring device with a magnetic float, rigidly fixed on one side - on the roof, on the other side - on the bottom of the tank, made of a flexible metal bellows, which ensures its constant tension during linear expansion of the walls of the tank, and also makes it possible to fix the position of the reference magnet at a given distance relative to the bottom of the tank using a fixing device, not allowing it to come off the bottom of the tank due to the ability to freely stretch and contract within certain limits, while the position of the reference magnet is used to correct measurements of the liquid level in the tank taking into account the linear expansion of the tank walls, as well as to determine the propagation velocity of ultrasound when measuring the liquid level in tanks in which there is no linear expansion of the tank walls or it is not required to take it into account.

Images