RU2463566C1 - Method of determining level of liquid and floating magnetostrictive level gauge for realising said method - Google Patents

Abstract

FIELD: physics. ^ SUBSTANCE: method involves generating and transmitting an electric pulse of given duration, converting the generated electric pulse to ultrasonic oscillations in an acoustic line, converting the ultrasonic oscillations to electric oscillations on an acoustic transducer, measuring the time interval of passage of ultrasonic oscillations, determining the level of the liquid from the known speed of sound in the acoustic line and the measured time interval, wherein alternating magnetic flux is generated locally on the level of the measured liquid. The floating level gauge has an electroconductive acoustic line, a processing unit, a float mounted on the acoustic line and capable of moving along said acoustic line, and a conducting element. The level gauge also has an alternating current generator, an acoustic transducer connected to the top end of the acoustic line, a discriminator-former, an intermediate transformer, and the float has an electric pulse generator, a rectifier, a toroidal transformer and an exciting coil lying concentrically with the opening of the float, said exciting coil being connected to the electric pulse generator. ^ EFFECT: high reliability and accuracy of measurement owing to localisation of magnetic flux energy on the level of the position of the float on the surface of the liquid. ^ 5 cl, 3 dwg

Description

The invention relates to measuring equipment and can be used to measure the liquid level mainly in tanks.

A known method of measuring the liquid level, based on the calculation of the time interval between the moment of excitation of the sound wave in the sound pipe and the appearance of an electric pulse on the measuring winding. The appearance of this electrical impulse occurs in connection with the magnetoelastic effect (AS USSR 3838381, IPC G01F 23/28, 1981).

Known magnetostrictive level gauge (RF patent No. 2083956, IPC G01F 23/28, 1997), containing a sensing element placed in a dielectric tube, which is sealed in the lower part and is resistant to interaction with the liquid, the level of which is measured; a sound pipe made of a wire (rod) made of magnetostrictive material (a material with a significant magnetoelastic effect, for example, low-carbon steel), a measuring coil uniformly wound round to round on a sound pipe, the length of which determines the range of level measurement h, a piezo emitter, a float with a block of n permanent magnets , where n = 1,2 ... i, placed evenly around the sound duct on the insulating shell with the possibility of movement along it, as well as the load attached to the lower end of the sound duct in working condition uu for its tension link connecting a measuring winding unit with a secondary electronic equipment (calculators), and the second communication line connecting terminal ends with a block piezo secondary electronic apparatus with the ultrasonic vibration generator that is part of the block.

Known technical solutions have a disadvantage due to the fact that the need to supply large voltages (above 20 V) to the piezo emitter to ensure stable operation of the device complicates the development of explosion-proof equipment. In addition, increasing accuracy requires the installation of a complex system of magnets in the float, as well as the expensive technology of measuring coil winding over the entire length of the measurement range.

Closest to the proposed is a method of measuring the liquid level with a magnetostrictive level gauge (RF patent No. 2222786, IPC G01F 23/28, publ. 01/27/2004), including the formation and supply of an electric pulse of a given duration, the conversion of the generated electric pulse to ultrasonic vibrations in the sound duct by deforming the sound duct, forming an alternating magnetic flux along the entire length of the winding of the field coil by supplying an generated electrical pulse of a given duration to the winding excitation ears, acting on a constant magnetic field flowing through the winding of the field coil of the field coil and changing the resultant magnetic field, the formation of a constant magnetic field at the level of the measured fluid, the conversion of ultrasonic vibrations into electrical vibrations by deforming the piezoelectric receiver's ferroelectric crystal under the influence of ultrasonic vibrations, measuring the interval transit time of ultrasonic vibrations, determination by known sound velocity in the sound duct and the measured time interval of the liquid level, and for the time interval of the passage of ultrasonic vibrations take the time interval between the time of supply of the generated pulse of a given duration to the coil of the excitation coil and the time of formation of electrical oscillations on the piezoelectric receiver.

The disadvantage of this method is that the energy of the exciting pulse in the winding is distributed over the entire length of the sound guide, which determines the low sensitivity of the method. At the same time, a weak sound signal is subject to distortion in poor acoustic conditions (noise of the infused fluid, industrial noise, etc.). In addition, the winding of the field coil along the entire length of the sound pipe is technologically complex and time-consuming. Improving the accuracy of measurements requires the installation of a complex system of magnets, which also increases the cost of construction.

Closest to the proposed device is an ultrasonic level meter (RF patent No. 2104501, IPC G01F 23/28, publ. 02/10/1998), which contains a sound pulse generator connected to the first end of the waveguide, a float concentrically mounted on the waveguide with the ability to move along it, the first coupling coil and a permanent magnet polarized along the bore of the float, the processing unit, the second and third coupling coils placed in the float, the first coupling coil mounted on the surface of the bore of the float, a constant the rotor is located on the outside of the first coupling coil, the second coupling coil is wound on the inserted first closed magnetic circuit and connected to the leads of the first coupling coil, the first closed magnetic circuit is located in the float, and its hole coincides with the hole of the float, the waveguide is electrically conductive, and its ends are electrically interconnected through a conductive element with the formation of a short-circuited coil, the processing unit includes a pre-amplifier and is connected to the terminals of the third communication coil, wound th to the introduced second closed magnetic circuit, located concentrically on one of the generators of the closed loop.

The disadvantage of this device is the presence of significant losses on the magnetization reversal of the magnetic circuits of the second and third communication coils. In addition, a short-circuited coil connecting the second and third communication coils forms a loop antenna, in which part of the useful signal is spent on radio emission. If the walls of the fluid reservoir are made of a material that does not shield electromagnetic interference, this antenna also receives interference. As a result, the useful signal is attenuated against the background of noise, which leads to a loss of accuracy, and sometimes the impossibility of measurement.

The present invention aims to create such a method for determining the level of a liquid and a float level meter for its implementation, which can improve the reliability and accuracy of measurement by localizing the energy of the magnetic flux at the level of the position of the float on the surface of the liquid.

The problem is solved by a method of determining the liquid level, including the formation and supply of an electric pulse of a given duration, converting the generated electric pulse to ultrasonic vibrations in the sound pipe, converting ultrasonic vibrations to electric vibrations on an acoustic transducer, measuring the time interval for the passage of ultrasonic vibrations, determining from a known speed of sound in sound duct and the measured time interval of the liquid level, in which From the prototype, the conversion of an electric pulse to ultrasonic vibrations in the sound duct is performed by forming an alternating magnetic flux locally at the level of the measured liquid, and to calculate the time interval for the passage of sound vibrations simultaneously with the generated electric pulse of a given duration being supplied to the excitation coil, an electric counting pulse is sent for a time interval the passage of ultrasonic vibrations take the time interval between the moment of receipt of the electron natural momentum of reference and the moment of formation of electrical vibrations on the acoustic transducer.

The problem is also solved by a float level gauge containing an electrically conductive sound duct, a processing unit, a float mounted on the sound duct with the ability to move along it, and a conductive element, which, unlike the prototype, additionally contains an alternating current generator, an acoustic transducer connected to the upper end of the sound duct, a discriminator -shaper, intermediate transformer, and the float contains an electric pulse generator, a rectifier, concentric with with a float, a toroidal transformer and an excitation coil connected to an electric pulse generator, the alternating current generator, an intermediate transformer, a conductive element connected in series with the sound duct, a toroidal transformer and a rectifier form the power supply circuit of the electric pulse generator, which forms a discriminator-shaper connected to it reference pulse transmission channel.

In addition, according to the invention, the conductive element can be made continuous and is adjacent to it along the length of the sound duct so that it passes into the hole of the float without friction.

In addition, according to the invention, the conductive element can be formed by several insulated cores uniformly spaced around the sound duct.

In addition, according to the invention, the field coil can consist of two parts with one winding direction and coaxial arrangement, between which a block of permanent magnets with a polarization transverse with respect to the axis of the coil and an open magnetic circuit surrounding the coil on the outside is inserted.

The specified result is achieved in the invention due to the following.

The formation of an alternating magnetic flux locally at the level of the measured liquid makes it possible to concentrate the energy of the electric pulse, which provides an increase in the power of ultrasonic vibrations and weakening the influence of interference. This makes it easier to process the useful signal and, therefore, increase the reliability and accuracy of the measurement. To do this, the electric pulse generator is located in the float, which is powered by a toroidal transformer with a rectifier. The power circuit of the specified generator also performs the function of transmitting information from the float to the processing unit.

The invention is illustrated by drawings, where Fig. 1 shows a functional diagram of an implementation of a method and a device, Fig. 2 shows a cross section of a sound duct with an additional conductor formed by several cores, and Fig. 3 shows a construction of an excitation coil consisting of two parts.

The level gauge (Fig. 1) contains a sound pipe 1, the upper end of which is connected to the acoustic transducer 2. The acoustic transducer is electrically connected to the input of the amplifier-shaper 3, the output of which is connected to the input of the processing unit 4, the other input of which is connected to the output of the discriminator-shaper 5, connected to the secondary winding II of the intermediate transformer 6, the primary winding I of which is powered by an alternator 7. Conducting element 8 is connected in series with the sound duct. The circuit formed is the load of the secondary winding II of the intermediate transformer 6. On the sound duct 1 there is a float 9 containing a pulse generator 10, a rectifier 11, a toroidal transformer 12 and an excitation coil 13 with an open magnetic circuit 14. The primary winding of the toroidal transformer 12 is a single coil: sound duct 1, conducting element 8. The secondary winding of the toroidal transformer through the rectifier 11 feeds the electric pulse generator 10, the output of which is connected to the excitation coil 13.

If the conductivity of the sound duct is insufficient to power the float, it can be replaced by a conductor of sufficient cross section. For this, the conductive element is extended by the length of the sound duct, mechanically adjoins to it and is pulled together with it. The conductive element can be composed of several insulated cores 15, symmetrically surrounding the core of the sound duct (figure 2).

In the case of the execution of the excitation coil of two parts (figure 3), both parts of the coil and the magnet are placed in the ring 16 of the magnetic circuit and are closed externally with lid washers of the same material. The magnetic system obtained in this way creates multidirectional constant magnetic fluxes in the sections of the sound duct passing through the parts of the coil. The magnetic field pulse of one part of the coil is added with a constant magnetic field, and for the other part of the coil is subtracted, thereby achieving the amplification of the ultrasonic pulse of the magnetostriction effect in the sound pipe.

All elements and nodes of the level gauge can be implemented according to known schemes. The pulse generator 10 is built on logic and delay elements (Ugryumov E. Digital circuitry. - SPb .: BHV - Petersburg, 2004). Amplifier-shaper 3 can be made in the form of an exponential amplifier or comparator with a given switching threshold (Titze U., Schenk K. Semiconductor circuitry: in 2 t.: Transl. From it. - T.1. - T.2: - M. Dodeka-XXI, 2008. - (Series “Circuitry”), discriminator-shaper 5 can be made in the form of a two-threshold comparator (see ibid.), The signal input of which is supplied with voltage from the secondary winding, and two other inputs - from the primary winding of the intermediate transformer 6, but with predetermined constant displacements (positive and negative.) The voltages on the windings of the intermediate transformer differ mainly in the electrical reference pulse, on the basis of which the comparator generates a digital reference pulse for the processing unit.

The processing unit can be implemented in the form of an integrated analog-to-digital circuit of programmable logic (E. Ugryumov. Digital circuitry. - St. Petersburg: BHV - Petersburg, 2004, Ch. 7, Ch. 8.). The task of the processing unit includes determining the time interval between two pulses, dividing this interval by a predetermined speed of sound, as a result of which the path traveled by ultrasound is obtained, subtracting this value from the given height of the acoustic transducer above the bottom of the tank, and outputting the liquid level value thus obtained with a digital code .

The method of measuring the liquid level with a float level meter is as follows.

The alternating current generator 7 feeds the intermediate transformer 6, the secondary winding of which is connected to a closed circuit formed by the conductive element 8 and the sound duct 1. The toroidal transformer 12 located in the float 9 has a single winding from the conductive element 8 and the sound duct 1, so the float 9 can move freely through the sound duct. The secondary winding of the toroidal transformer 12 is loaded with a rectifier 11 supplying a rectified current pulse generator 10, which in turn delivers electric current pulses to the excitation coil 13. The magnetic circuit of the excitation coil 13 is a bracket 14 with ferromagnetic properties and the gap coinciding with the hole of the float through which passes the sound duct 1. The pulses of the magnetic field of the excitation coil 13 initiate a magnetostrictive sound effect in the sound duct. At the same time, the pulse generator 10 supplies an electric pulse to the winding of the toroidal transformer 12, causing a voltage surge in the secondary winding of the intermediate transformer 6, which is detected by the discriminating driver 5. The counting pulse, together with the signal from the driver amplifier 3, determines the ultrasonic transit time from the float to acoustic transducer fixed to the end of the sound guide 2. Both pulses are fed to the inputs of the processing unit 4. Arithmetic-logic device b eye treatment 4, formed in accordance with the set therein in advance a program computes the time interval between pulses. The resulting time interval is divided by the value of the specified speed of sound. The distance thus calculated from the float to the acoustic transducer is then subtracted from the set value of the height of the acoustic transducer above the bottom of the tank. The result of the calculations is the liquid level presented in a digital code or in an analog way.

Thus, the proposed invention improves the reliability and accuracy of determining the liquid level.

Claims (5)

1. The method of determining the liquid level, including the formation and supply of an electrical impulse of a given duration, the conversion of the generated electrical impulse to ultrasonic vibrations in the sound duct, the conversion of ultrasonic vibrations to electrical vibrations on the acoustic transducer, the measurement of the transit time of ultrasonic vibrations, the determination of the known speed of sound in the sound duct and a measured time interval of the liquid level, characterized in that the conversion of electric A pulse into ultrasonic vibrations in a sound duct is produced by forming an alternating magnetic flux locally at the level of the measured fluid, and to calculate the time interval for the passage of sound vibrations, an electric pulse of reference is sent to the excitation coil winding of a given duration and the time interval for the passage of ultrasonic vibrations is taken time interval between the moment of receiving the electrical impulse of reference and the moment of time tim generate electrical oscillations by an acoustic transducer. 2. A float level gauge containing an electrically conductive sound pipe, a processing unit, a float mounted on the sound pipe with the ability to move along it, and a conductive element, characterized in that it further comprises an alternating current generator, an acoustic transducer connected to the upper end of the sound pipe, a discriminator-shaper, an intermediate transformer, and the float contains an electric pulse generator, a rectifier located concentrically with the hole of the float toroidal transformer and to an excitation coil connected to an electric pulse generator, wherein the alternator, an intermediate transformer, a conductive element connected in series with the sound pipe, a toroidal transformer and a rectifier form a power supply circuit of the electric pulse generator, which together with the discriminator-shaper connected to it forms a reference pulse transmission channel . 3. The level gauge according to claim 2, characterized in that the conductive element is continuous and adjacent to it along the length of the sound pipe so that it passes into the hole of the float without friction. 4. The level gauge according to claim 3, characterized in that the conductive element is formed by several insulated cores evenly spaced around the sound duct. 5. The level gauge according to claim 2, characterized in that the excitation coil consists of two parts with one winding direction and coaxial arrangement, between which a block of permanent magnets is inserted with polarization transverse to the axis of the coil and an open magnetic circuit surrounding the coil from the outside .

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