RU2308019C1 - Device for measuring density of low-density liquids - Google Patents

Abstract

FIELD: measuring technique.

SUBSTANCE: device comprises movement converter made of magnetostrictive wave guide mounted in the housing made of a nonmagnetic material. The housing is provided with toroidal floats with balancing chains arranged at various levels and magnets mounted in the floats. The wave guide is provided with the recording coil connected with the pulse generator. The chains are sectional and made of heavy and light members connected in series. The heavy member is connected with locator secured to the housing of the converter. The light member is connected to the float.

EFFECT: expanded functional capabilities.

1 dwg

Description

The invention relates to devices for measuring the density of liquids, including stratified in height, for example, petroleum products.

There are many devices of the float type for measuring the density of liquids, an overview of which is well presented in the book by S. S. Kivilis "Density meters", ed. "Energy", M., 1980. All these densitometers are classified according to two functional principles - with partial immersion of the float and with full immersion of the float.

Readings of densitometers with partial immersion of the float, i.e. located on the surface, depend on the surface tension of the liquid, which, in turn, is determined by a number of factors (such as pressure, temperature, wettability) and, as a rule, is a variable. This leads to a decrease in measurement accuracy.

To exclude the influence of surface tension allow densitometers with floaters full immersion (float-weight densitometers). Density meters of complete immersion include the so-called chain densitometers, the principle of operation of which is described in the book by S. S. Kivilis “Density meters”. Using chains allows you to balance the float in a wide range of density.

A technical description of a submersible densitometer is presented in GB Patent No. 20133900 A G01N 9/18, publ. 08/15/1979, containing a float with a chain and an electrode system associated with a bridge circuit to assess the electrical conductivity of the liquid and determine the position of the float by measuring the resistance of the zones of the liquid. However, this device is only suitable for measuring the density of electrically conductive liquids, such as electrolytes, and does not allow measuring the density of non-conductive liquids, such as petroleum products.

An interesting technical solution is the device for measuring the level and density according to patent RU 2188400. (G01N 9/10, publ. 08.27.2002). The device comprises a converter unit, including an amplifier driver, a pulse generator, a counter, a memory register, a register with parallel input and sequential shift of information, two start pulse shapers, an address decoder, a ready signal shaper, a lock shaper, two keys, an exchange bus, four multiplexers , encoder address decoder and k level and density sensors. Each of the sensors contains a sound duct installed in a protective casing in the form of a string of magnetostrictive material, a read coil and two floats with magnets located on them. The sensors are installed in two rows and are offset in height relative to each other to ensure overlap of the working areas. In the upper part of all sensors, except the upper one, there are mounted rigidly attached and hermetically closed in the upper part shrouds of non-magnetic material in the form of a bell, inside of which, from the lower side, during the operation, floats of sensors with magnets fixed to them can enter. The device allows you to measure the density at different levels in the tank, but it has several disadvantages:

1. Density measurement is carried out under the hood where the interface between the media (air-liquid) is artificially created. The densitometer floats operate at this interface, and therefore there are additional errors that depend on the surface tension of the liquid, which in turn is determined by a number of factors (wettability of the floats, meniscus presence, pressure, temperature, etc.) and is usually a variable.

2. The presence of a cap with an air cushion limits the pressure at which density can be measured (for example, completely unsuitable for liquefied gas).

3. The displacement transducer measures the relative distance between the floats (level and density), and not the position of one float, which leads to additional errors.

An interesting technical solution is presented in the densitometer described in the USSR copyright certificate No. 397813 G01N 9/10, publ. 09/17/1972 The specified densitometer contains a balanced, vertically moving float immersed in a liquid with a magnet mounted on it, means for balancing the float, for example a chain, a transducer for moving the float into an electric signal, the float being made in the form of a toroid enclosing a nonmagnetic enclosed in a tubular body material, a float displacement transducer made in the form of a ferrite-semiconductor distributor connected to the output of a clock pulse generator.

The above densitometer has a high noise immunity. However, its resolution is determined by the size of one element of the ferrite-semiconductor distributor and the distance between adjacent elements, i.e. its readings are discrete, and an increase in its accuracy and sensitivity requires an increase in the number of ferrite-semiconductor elements and a decrease in their geometric dimensions (for example, for a relative error of 0.1% and a 10 cm float movement, 1000 pieces of ferrite-semiconductor elements are needed, and the size they should be 0.1 mm, in practice now such ferrite-semiconductor distributors are not feasible). In addition, with the help of one densitometer it is impossible to perform simultaneous measurements at different levels, which is a necessary requirement when measuring the density of stratified liquids, for example, petroleum products. Therefore, the solution of the problem of measuring density at different levels requires the installation of several densitometers, and this, when using a ferrite-semiconductor distributor, directly increases the cost of the measuring system, which will consist of several densitometers. Attention is also drawn to the design feature of fastening chains in a known densitometer: with one end they are attached to the float from below, and with the other end they are fixed at the base of the pipe, i.e. at the conditional boundary between the media (air - liquid), while measuring at a great depth is not feasible due to the too long chains. In addition, it should be noted that the disadvantage of this densitometer, as well as other known chain densitometers, is the limited working area determined by the length of the measuring element (in this case, ferrite-semiconductor). This, in turn, imposes certain requirements on chains and floats, which have to be made either large-sized with a large number of chains or chains must be made of heavy metals, for example platinum-iridium alloys, which makes them very expensive. But the most serious drawback of a ferrite-semiconductor converter is the narrow temperature range associated with the loss of magnetic properties of the materials used both at low (below minus 60 °) and at high temperatures (above 100 ° C). This significantly limits the scope of use of these densitometers, for example for measuring the density of liquefied gases and high-temperature melts (in the chemical industry).

The closest in technical essence to the proposed densitometer is the densitometer described in RF patent No. 2273838, publ. 04/10/2006, The indicated densitometer for liquid, contains a balanced vertically moving float immersed in the liquid in the form of a toroid with magnets placed in it, means for balancing the float, for example a chain, a transducer for moving the float into an electric signal, placed in a tubular body made of non-magnetic material, covered by a toroidal float, while the float displacement transformer is made in the form of a magnetostrictive waveguide with a read coil located on it and connected to it by the pulse shaper, the read coil is connected to the input of the amplifier-shaper, the output of which is connected to the input of the signal processing unit, the output of which is connected to the input of the pulse shaper, the balancing chains of the floats are attached at one end to the float, and at the other end to a latch rigidly fixed to the housing displacement transducer, and the number of floats and their mounting elements is n pieces with their location at different heights depending on the required number of density measurement points and liquids.

The indicated densitometer has continuous measurement with a high sensitivity threshold, a wide range of operating temperatures and good temperature stability, the ability to measure density at different levels without being tied to the boundary of the conditional medium separation, without increasing the complexity of the float displacement meter with a sufficiently long densitometer length (several meters).

However, to measure the low density of liquids, for example, liquefied gas, in the indicated densitometer, the use of a float with a chain suspension above the float, in which the float is in the lower working position, i.e. at the lowest measured fluid density, the weight of the chain moves to the suspension. Such a technical solution requires an increased size (diameter) of the tank hatch, which makes it difficult to install densitometers on the existing tank farm, especially the old one. The use of floats with a chain suspension below the float is designed for a higher liquid density, since the weight of a part of the chain is added to the weight of the float even at the lower operating point.

The subject of the invention is a density meter for a liquid with a low density, comprising a balanced vertically moving float immersed in a liquid in the form of a toroid with magnets placed in it, means for balancing the float in the form of chains, a transducer for moving the float into an electrical signal placed in a tubular body made of non-magnetic material, covered by a toroidal float, made in the form of a magnetostrictive waveguide with a read coil located on it and connected to it with a pulse finder, a read coil is connected to the input of the driver-amplifier, the output of which is connected to the input of the signal processing unit, the output of which is connected to the input of the pulse former, the balancing chains of the floats are attached at one end to the float, and at the other end to a latch rigidly fixed to the housing of the displacement transducer and the number of floats and their fastening elements is n pieces with their location at different heights, depending on the required number of points for measuring the density of the liquid, while the chains are made integral and consist of heavy and light parts connected in series, the heavy part being attached to a latch rigidly fixed to the transducer housing, and the light part being attached to the float.

The technical result is the creation of a new density meter for a liquid with a low density, having continuous measurement with a high threshold of sensitivity, a wide range of operating temperatures and good temperature stability, the ability to measure density at different levels without reference to the boundary of the conditional partition of the media, without increasing the complexity of the meter for displacing the float when a sufficiently large length of the densitometer (several meters), the ability to use a variety of materials for balancing chains ek densitometer be mounted in tanks with a small diameter of the hatch, which gives savings in material due to the reduced size and reduction of the hatch mounting flanges densitometer sizes. These technical improvements make it possible to obtain low-cost multichannel densitometers for measuring low density liquids.

The indicated properties are obtained due to the use of composite chains consisting of heavy and light parts connected in series as a counterweight to the floats, the heavy part being attached to a latch rigidly attached to the transducer body and the light part being attached to the float.

The drawing schematically shows a device densitometer.

The numbers in the drawing indicate:

1 - the first float;

2 - the second float;

3 - n-th float;

4 - a permanent magnet inside the float;

5 - magnetostrictive waveguide;

6 - read coil;

7 - case of non-magnetic material;

8 - pulse shaper;

9 - amplifier-driver;

10 - signal processing unit;

11 - the heavy part of the balancing chain;

12 - the easy part of the balancing chain;

13 - clamps for floats.

The first, second, and n-th toroidal floats 1, 2, and 3 with magnets 4 inside them and the light parts of the balancing chains 11 attached to them, the heavy parts of the balancing chains 12 are attached to the latches 13, which are rigidly fixed to the housing of the non-magnetic material 7 of the transducer displacements, floats are located outside the body of non-magnetic material 7, inside of which there is a magnetostrictive waveguide 5 and a read coil 6. The entire structure is placed in the reservoir with the studied fluid. The pulse shaper 8 is configured to generate rectangular ultrasonic pulses with a duration of not more than 10 μs, an amplitude of 12 V, and a frequency of 10 Hz, necessary to create an ultrasonic wave around the waveguide 5. The amplifier-shaper 8 is configured to amplify a signal taken from the read coil 6 and the formation of single rectangular pulses with a duration of not more than 10 μs and an amplitude of 5 V, necessary for subsequent processing of the signal in the signal processing unit 10, configured to lease time intervals between the pulses in the incoming pulse shaper 8 and the pulses arriving from the amplifier-shaper 9, followed by conversion of information received in the digital value sample liquid density.

The operation of the densitometer is as follows.

The density measurement is based on measurements of the propagation time of ultrasound in a magnetostrictive waveguide. The propagation velocity of ultrasound in the waveguide is practically independent of pressure and humidity. The influence of temperature is automatically compensated using a special algorithm for processing time intervals of ultrasound propagation.

At the command of the signal processing unit 10 using the pulse shaper 8, the ultrasonic wave is generated by the principle of magnetostriction directly in the waveguide 5, made of a special steel wire with magnetostrictive properties and located inside the body of non-magnetic material 7.

The interaction of an alternating magnetic field created by a current pulse in a waveguide 5 and a field of permanent magnets 4 causes a deformation of the crystal structure of the waveguide, which creates a mechanical wave propagating with ultrasonic speed. An ultrasonic wave arising at the locations of the magnets 4 propagates along the waveguide 5 in both directions from the place of occurrence. In the upper part of the waveguide, ultrasonic waves are converted by a read coil 6 into electrical pulses due to the inverse magnetostrictive effect and then are damped by a damper. These pulses are fed to an amplifier-shaper 9, where they are converted into a rectangular shape, and then fed to a signal processing unit 10. The time interval between the moment of generation of an ultrasonic wave and its conversion into electrical pulses is proportional to the measured distance, i.e. the position of the float 1, 2 or 3, and, accordingly, the density of the liquid at this level. In the presence of several floats with magnets placed in them, several ultrasonic waves arise, equal to the number of floats. In this case, the moments of conversion of ultrasonic waves into electrical pulses are spaced in time, and analysis of the number of pulses and the corresponding time intervals will determine the position of each float and thus measure the density of the liquid at the appropriate level. It should be noted that due to the use of a magnetostrictive waveguide as a displacement sensor, it is possible to use steel balancing chains, abandoning heavier and more expensive materials, because there are no strict requirements for restricting float movements during density measurement, while the chains are made up and consist of light 11 and heavy 12 parts connected in series, and the heavy part 12 is attached to the latch 13, rigidly mounted on the transducer housing, and the light part 11 is attached to the float, which ensures the distribution of most of the weight of the chain (its heavy part 12) in the lower position of the float on the latch, and this reduces the lower limit of density measurement. With an increase in the density of the liquid in the tank, the float will float, while the weight of the heavy part of the chain will gradually be redistributed between the retainer and the float as the float emerges, which allows to expand the operating range of density measurement in the direction of increase. When the float leaves the working area due to lower liquid levels in the tank, the float rests on the latch 13, which eliminates the tangling of the balancing chains.

It should also be noted that due to the use of low operating voltages and low currents, the described densitometer is easily implemented in explosion-proof design, which allows it to be used when measuring density in explosive atmospheres, for example, when working with oil products or liquefied gases.

At the applicant enterprise, a prototype was made, and then a prototype of the described densitometer was described, and tests were carried out that fully confirmed the correctness of the proposed solution.

Claims (1)

Density meter for a liquid with a low density, containing a balanced vertically moving float immersed in a liquid in the form of a toroid with magnets placed in it, means for balancing the float in the form of chains, a transducer for moving the float into an electrical signal placed in a tubular body made of non-magnetic material, covered by a toroidal float made in the form of a magnetostrictive waveguide with a read coil located on it and a pulse shaper connected to it, a coil with reading is connected to the input of the amplifier-driver, the output of which is connected to the input of the signal processing unit, the output of which is connected to the input of the pulse generator, the balancing chains of the floats are attached at one end to the float, and at the other end to a latch, rigidly fixed to the housing of the transducer, and the number of floats and their fastening elements is n pieces with their location at different heights depending on the required number of points for measuring fluid density, characterized in that the chains are full of components and consist of heavy and light parts connected in series, the heavy part being attached to a latch rigidly fixed to the transducer body, and the light part being attached to the float.