RU2683139C1 - Float liquid level gauge - Google Patents

Abstract

FIELD: measuring equipment.SUBSTANCE: invention can be used to determine the height of the level of various liquids in large tanks. Float gauge contains a sensitive element with a length above the maximum allowable liquid level and fixed in a vertical position in the tank a float moving relative to the sensitive element, a power unit, the unit for determining the level and transmission of information associated with the radio channel with the unit for visual information display, the load attached to the bottom of the sensing element. Sensing element is designed in the form of a rigid non-magnetic tube, inside which is a sealed measuring line, made in the form of a bifilar twist of insulated wire with a constant pitch and powered by a constant or alternating voltage from the power supply, on the float vertically one below the other there are two magnetic field sensors, each of which is connected to the pulse shaper, and the outputs of the pulse shaper are connected by means of: spring-loaded conductors, respectively, to the summing and subtracting inputs of the reversing pulse counter, the output of which is connected to the input of the level determination and transmission unit.EFFECT: object is to simplify the electrical circuit and the design of the liquid level meter.1 cl, 2 dwg

Description

The present invention relates to instrumentation and can be used to determine the height of various liquids in large tanks.

Numerous float meters of liquid levels are known [1, 2, 3], which are based on hermetic contacts (reed switches) installed with an appropriate step along the entire length of a non-magnetic vertical tube, and a torus-shaped float that encloses this tube and on which a permanent magnet is mounted . When filling a container (tank) with liquid or when draining it, the float moves along the tube, respectively, up / down. At the same time, reed switches, under the influence of a constant magnetic field, close or open their contacts, which is recorded and analyzed by appropriate electronic equipment. These level meters are simple in technical solution and manufacture, however, they have a low accuracy of measuring the liquid level, since the accuracy depends on the distance between the reed switches, and it can be significant in large tanks.

Known optical level meters, in particular [4]. This meter contains a vertical transparent tube communicating with the controlled reservoir, a float with a laser beam source, flat optical fibers along the entire length of the tube with a two-layer coating (translucent and non-conductive), raster code gratings, photodiodes, decoders, amplifiers-shapers, and an RF generator. The advantage of the meter is the non-contact measurement of the liquid level, as well as the fact that the level gauge is presented immediately in digital form. The disadvantage of the meter is its significant complexity and high cost.

A device is known according to the method for measuring the level of liquid media [5], in which the sensitive element is a ruler vertical along the entire height of the tank with differentially connected thermocouples installed on it with a certain step. If the temperatures of both junctions of the thermo-EMF are equal, no thermocouple will be formed at the output of the thermocouple. In contact with one of the junctions (regardless of whether the liquid level rises or falls), its temperature will change, as a result of which a thermo-emf will appear at the output of the thermocouple, which is then recorded and converted into an information signal accordingly. This is the principle of operation of such meters. The disadvantages of the meter are as follows. Firstly, the value of the thermo-EMF value is directly proportional to the temperature difference of the two junctions. This means that for reliable registration of thermo-EMF and reliable operation of the meter, it is necessary to achieve a large temperature difference of junctions, which, in turn, is not easy to obtain. Secondly, in this meter, the accuracy of the measurement depends on the step of placing thermocouples between each other: the smaller the step, the higher the accuracy. However, the cost of the entire meter will increase significantly.

A known method of determining the liquid level and the liquid level indicator for its implementation [6]. Here in the tank is a vertical gauge with the markings applied to it. The image of this ruler is transmitted by means of a television camera mounted on a float, which moves freely in the vertical direction along the measuring ruler when the liquid level changes. The advantage of the detector is the high accuracy of measuring the liquid level. However, the optics of a television camera will require frequent mandatory maintenance, since aggressive liquid and its vapors have a negative effect on optical elements, which will negatively affect the operational efficiency of this detector.

The closest in technical implementation is a method of measuring the liquid level by a magnetostrictive level gauge and a magnetostrictive level gauge [7]. The level gauge contains: a sensitive element with a sound conductor made of magnetostrictive material placed in a dielectric tube with a piezoelectric element fixed to its upper end and a winding wound along the entire length of this tube placed in an insulating sheath; float with a magnetic block of N permanent magnets; electric pulse generator; oscillation amplifier with a piezoelectric element; pulse shaper; unit for determining time intervals; liquid level determination unit; sound speed adjuster in the sound duct; cargo.

The principle of operation of the level gauge is as follows: the formation of an electrical impulse of a given duration; the conversion of this pulse into 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 excitation coil; the conversion of ultrasonic vibrations into electrical vibrations by deformation of a piezoelectric receiver ferroelectric crystal under the influence of ultrasonic vibrations; measuring the time interval for the passage of ultrasonic vibrations; determination by the known speed of sound in the sound pipe and the measured time interval, the liquid level. The time interval between the passage of ultrasonic vibrations is taken to be the time interval between the instant of supply of the generated pulse of a given duration to the coil of the excitation coil and the instant of formation of electrical oscillations on the piezoelectric receiver.

The advantages of the prototype include high measurement accuracy, low power consumption and operational safety, the ability to measure at remote distances. The disadvantage of the prototype is the significant complexity of the technical solution and manufacture.

The aim of the invention is to simplify the electrical circuit and the design of the float level meter.

This goal is achieved by the fact that in the float meter measuring liquid level, containing a sensor element longer than the maximum allowable liquid level and fixed in a vertical position in the tank, a float moving relative to the sensor element, a power supply, a unit for determining the level and transmission of information associated with the radio channel with a unit for visual display of information, the load secured in the lower part of the sensitive element for its stabilization in the vertical position, sensitive the element is made in the form of a rigid non-magnetic tube, inside of which there is a sealed measuring ruler made in the form of a bifilar twist from an insulated wire with a constant pitch λ ₀ and powered by a constant or alternating voltage from the power supply, two magnetic field sensors are located vertically one under the other, distance between which is equal to L (2n + 1) ⋅λ _0/2 (n -. the integer 1, 2, 3, ...), each of which is connected to the pulse generator and outputs the pulse shapers by biased conductors are connected respectively to the summing and subtracting inputs of a reversible pulse counter, the output of which is connected to the input of the level determination and information transfer unit, moreover, the pulse counter, power supply units and level detection and information transmission units are located above the maximum liquid level, and the float, sensors and former pulses constitute a single measuring unit.

The principle of operation of the float meter is illustrated in FIG. 1, which shows the design of the meter and its functional electrical circuit, and FIG. 2, which explains the physical principle of the meter.

The proposed float meter for liquid level is located inside the tank 1, having a filler and drain line and a valve connecting the internal cavity of the tank with the atmosphere. This valve opens when draining the liquid to equalize the pressure in order to eliminate mechanical deformation of the tank. The float meter contains a sensitive element 2, which is a vertical rigid non-magnetic tube having a length slightly exceeding the maximum permissible liquid level N _MAX in the tank, inside which there is a measuring ruler 3 made in the form of a bifilar twist from an insulated wire with a constant pitch (period) λ ₀ . The line is powered by voltage U _P from the power supply unit (PSU) 4. A float 5 slides on the tube 2 when filling or draining the liquid up and down, on which two magnetic field sensors D1 and D2 6, 7 and pulse shapers FI1 are connected rigidly and FI2 8, 9. The float, sensors and pulse shapers form a single measuring unit (IB) 10.

The outputs of the formers FI1 and FI2 are connected to the corresponding inputs of the reversible pulse counter 11, the output of which is connected to the input of the level determination and information transfer unit (BOUPI) 12. The power supply, pulse counter, and level determination and information transmission unit are located in the instrument compartment (ON) 13 at the top of the tank above the maximum liquid level. Airtight placement of the instrument compartment outside the tank is allowed.

Information on the current liquid level in the tank by block 12 is transmitted via radio channel to the visual information display unit (BWOI) 14 (for example, a display, monitor, etc.), which can be located at a considerable distance from the tank and with which the operator interacts.

To ensure the vertical position of the sensitive element and prevent its oscillations inside the tank when filling or draining the liquid in the upper part, it is attached to the wall of the tank using the appropriate stop (bracket) 15, and in the lower part the corresponding load 16 is attached to it.

Sensors D1 and D2 are mounted on the float so that their sensitivity axes are parallel to each other and oriented perpendicular to the measuring line. The vertical distance between the sensors L is

where λ ₀ is the twisting period;

n is an integer 1, 2, 3, ....

The choice of such a distance between the sensors, in particular, the choice of the number "n", is justified by the fact that in the practical design of the float level meter it is necessary to take into account the real geometric dimensions of the sensors 6 and 7, as well as the length of the period λ ₀ . The number "n" is the number of twisting periods λ ₀ that must be stacked between the sensors so that they produce a signal with the required phase shift (for the operation of a reversible pulse counter). The principle of operation of the meter "n" is not affected.

Rotational movements of the measuring unit 10 relative to the sensing element 2 are excluded, for example, by making a guide corresponding to the entire length of the tube, which enters the groove in the material of the float 5.

In order to eliminate the effects of aggressive liquids, the measuring line 3 is properly sealed in the tube 2.

The tube 2 should be made of a material with low adhesive ability, resistant to aggressive liquids, capable of operating in a wide temperature range. It can be either dielectric or non-magnetic metal (for example, stainless steel). The float 5 should have a gap relative to the tube 2, which ensures its sliding along the tube without mashing. To improve the sliding conditions of the float, the outer surface of the tube and the inner part of the float can be coated with a special film made of a material with a low coefficient of sliding friction, for example, a fluoroplastic film. The guaranteed gap should be large enough so that the inevitable various deposits and contaminants concentrated on the outer surface of the tube and the inner side of the float do not interfere with its movement along the tube for a specified inter-time interval.

On the other hand, the guaranteed clearance should be small enough so that the float is centered on the dielectric tube and the error in measuring the liquid level in the tank due to the skew position of the float relative to the vertical would be minimized.

In connection with this circumstance, some restrictions may be introduced on the characteristics of liquids whose level is measured: their viscosity should be low enough not to interfere with the movement of the float along the sensitive element.

The communication line between the pulse shapers 8, 9 and the reversible pulse counter 11 is made of spring-loaded conductors. The length of these conductors should allow the float (or measuring unit) to move along the tube from minimum to maximum marks. Spring-loaded conductors can be placed in special tubes to protect them from unwanted twisting (not shown in the figure).

Power supply 4 can be either constant or alternating voltage. In accordance with the requirements for electrical safety, it is forbidden to supply external voltage of 220 V 50 Hz to tanks with flammable oil products. From this it follows that in this case, the source of constant voltage should be only a high-capacity battery, which can be, for example, a lithium battery with a full discharge time of several milliamps up to 5 years, after which it is replaced with a new one. To obtain alternating voltage, an alternating voltage generator (usually 2-6 kHz), also powered by a battery, can be used.

If non-flammable liquids are stored in the tank, then it is allowed to supply an external voltage of 220 V 50 Hz to it. In such cases, any stabilized voltage rectifier can be used as a constant voltage source.

The load for BP 4 is a measuring ruler, which is the aforementioned twist of insulated conductors having a low electrical resistance. Therefore, in all these cases, the electrical resistance of the measuring line 3 and the output of the power supply 4 should be comparable, i.e. low resistance.

If the measuring line is powered by a constant voltage, then any galvanomagnetic device can be used as magnetic field sensors: Hall sensor, magnetodiode, magnetoresistor, etc.

If the measuring line is powered by alternating voltage, then small induction sensors (inductors) are best used as magnetic field sensors.

The physical principle of operation of the float meter is considered on the example of supplying the measuring line with alternating voltage using induction sensors (inductors) and is illustrated in FIG. 2.

посередине между проводами (на рисунке не показана) найдется по принципу суперпозиции:

It is known that a bifilar line is called a line consisting of two closely spaced twisted insulated wires along which the same currents flow (I ₁ = 1 ₂ ) in opposite directions. Thanks to this design, the bifilar line practically does not create a magnetic field around itself. However, in the immediate vicinity of the wires, this is not so. In FIG. 2a) presents the case when the wires of the bifilar are in a plane parallel to the plane of the sensor coil, i.e. the axis of the sensor is parallel to the magnetic field vector between the conductors. The resulting magnetic field induction

in the middle between the wires (not shown in the figure) there is a superposition principle:

- индукция магнитного поля, создаваемая первым проводником скрутки в месте расположения датчика 6 (или 7);Where

- magnetic field induction created by the first twist conductor at the location of the sensor 6 (or 7);

- индукция магнитного поля, создаваемая вторым проводником скрутки в месте расположения датчика 6 (или 7);

- magnetic field induction created by the second twist conductor at the location of the sensor 6 (or 7);

I = I ₁ = I ₂ - the amplitude of the current flowing along the measuring line (twisting of two insulated conductors);

r is the distance from the conductive core to the point at which the magnetic field is analyzed (the point of contact of the insulation of the wires).

In FIG. 2, the following letter designations are used: d is the diameter of the conductive core, D is the outer diameter of the insulation, F is the flux of magnetic induction through the cross section of the sensor coil.

From FIG. 2 shows that

Given this, we get:

создает в точке нахождения катушки датчика магнитный поток Ф, вызывающий появление выходного сигнала датчика вследствие электромагнитной индукции.Resulting magnetic field

creates a magnetic flux Φ at the location of the sensor coil, causing the output of the sensor due to electromagnetic induction.

вне проводников направлены в противоположные стороны и взаимно уничтожаются. Между проводниками магнитные поля отдельных проводников складываются. Вектор результирующего магнитного поля направлен перпендикулярно оси катушки, магнитный поток Ф в точке ее нахождения создаваться не будет. Следовательно, при таком взаимном расположении бифилярной скрутки и катушки датчика выходной сигнал будет отсутствовать. Перемещение поплавка 5 с датчиками 6 и 7 по вертикали вдоль витого бифиляра может рассматриваться как вращение бифиляра относительно неподвижного поплавка. В предлагаемой конструкции поплавкового измерителя уровня жидкости принудительный поворот бифиляра относительно катушки датчика обеспечивается скруткой провода и однозначно связан с перемещением поплавка 5 с датчиками 6 и 7. Перемещение поплавка 5 на один период скрутки λ₀ сопровождается появлением на выходе датчика одного импульса. Эти импульсы в формирователях 8 и 9 преобразуются в прямоугольные, достаточные для их регистрации счетчиком импульсов 11.When the bifilar wire rotates 90 ° relative to the sensor coil (Fig. 2b)), there will be no magnetic flux through the sensor coil, since the magnetic fields of individual bifilar wires

outside the conductors are directed in opposite directions and mutually destroyed. Between the conductors, the magnetic fields of the individual conductors add up. The vector of the resulting magnetic field is directed perpendicular to the axis of the coil, magnetic flux Φ at the point of its location will not be created. Therefore, with such a mutual arrangement of the bifilar twist and the sensor coil, the output signal will be absent. The movement of the float 5 with sensors 6 and 7 vertically along the twisted bifilar can be considered as the rotation of the bifilar relative to the stationary float. In the proposed design of the float liquid level meter, the forced rotation of the bifilar relative to the sensor coil is provided by twisting the wire and is uniquely associated with the movement of the float 5 with sensors 6 and 7. The movement of the float 5 by one twisting period λ _{0 is} accompanied by the appearance of one pulse at the output of the sensor. These pulses in the shapers 8 and 9 are converted into rectangular, sufficient for their registration by the pulse counter 11.

The use of two sensors arranged so that one corresponds to the position of FIG. 2a), and the other to the position of FIG. 2b), it is necessary to ensure the operation of the reverse counter 11, which determines the direction of movement of the float and counts the number of periods λ ₀ . If the float with sensors moves along the measuring ruler in one direction, then the pulses are calculated by the summing input. If the float moves in the opposite direction, then the pulses are counted at the subtracting input. The unit for determining the level and transmitting information 12 translates the number of pulses into the liquid level value and transmits information via a radio channel to the unit for visual display of information 14 in a form convenient for the operator. Information can be supplied to BWOIs at the request of the operator or at certain intervals of time, or by another algorithm.

Since the output information parameter in the proposed meter is the number of twisting periods λ ₀ , the requirements for the stability of power supplies are low. In addition, in this case, the presence of external ferromagnetic objects near the measuring line will not affect the accuracy of the measurements.

Float level meter works as follows.

In the meter, two sensors are needed so that one of them switches the counter from the summing mode to the subtraction mode, and the second vice versa. For example, if the float moves up, then a signal is generated at the output of sensor D1, and then at the output of sensor D2. The first pulse from the sensor D1 sets the counter in the summation mode. When the float moves down, a signal is first generated at the output of the D2 sensor, the first pulse of which puts the counter into subtraction mode.

Suppose that at the initial moment the tank is empty and the float is in its lowest position. When pouring liquid, the float 5 begins to move vertically upwards, the sensors 6 and 7 cross the twist of the measuring line. At the output of the first sensor D1, pulses appear, which are formed into rectangular in FI1 and then fed to the summing input of the counter 11. The value of the liquid level H ^{1 is} proportional to the number of pulses N ₊₁ calculated by the pulse counter:

H ¹ = K⋅N ₊₁ ,

where K is the coefficient of proportionality.

The counter works so that, as mentioned above, the first pulse from the output of the sensor D1 puts the counter in the mode of only the summation of pulses. In this case, the pulses from the output of the D2 sensor, although they will be supplied to the subtracting input of the counter, will not be able to exert any influence on the counting of pulses by the summing input.

The determination of the liquid level in the accepted length measurement units takes place in BOUPI 12. The same unit transmits information to the operator via a radio channel.

When draining the liquid, the float moves vertically downward, pulses appear at the output of the second sensor D2. The first pulse from the output of this sensor puts the counter into subtraction mode. In this case, the pulses from the output of the D1 sensor are similar, although they will go to the summing input of the counter, but they will not be able to exert any influence on the counting of pulses at the subtracting input.

Thus, the countdown of pulses from N ₊₁ begins.

Suppose that at some point in time, N _-2 pulses were received at the subtracting input. Then at this moment the height of the liquid level N ² in the tank will be as follows:

The determination of the liquid level in the accepted length measurement units also takes place in BOUPI 12. The same unit likewise transmits information to the operator via radio channel.

If there will again be a liquid inlet, then the pulse counter 11 will sum the pulses only from the output of the sensor D1 with those pulses that were stored in memory at that time.

If further draining of the liquid begins, then the counter 11 will count on the subtracting input, i.e. will subtract the pulses coming only from the output of the sensor D2, from the sum of the pulses, which was stored in memory at that time. Further, the meter works similarly.

Moving the float by an amount equal to the twist period λ ₀ leads to a change in the output signal by one period and corresponds to one unit of the counting device. Therefore, we can assume that the value of λ ₀ is equal to the absolute error of the level measurement.

In turn, the value of this error will affect the accuracy of determining the volume V or mass M of the liquid itself:

where S is the cross-sectional area of the tank;

N _ISM - the measured value of the level.

Hence, the absolute error in determining the volume ΔV of the liquid will be equal to:

Similarly, the absolute error in determining the mass ΔM:

where ρ is the fluid density.

From the principle of operation of the meter it follows that the accuracy of the measurement can be obtained quite high, making the twist step as small as possible. Simple calculations and reasoning show that the step λ ₀ can be brought to several millimeters, which depends on the diameter of the insulation of the wire from which the measuring ruler is made, and the specified accuracy. The larger the diameter (cross-sectional area) of the tank, the higher the measurement accuracy.

The advantages of this float meter are:

1. A fairly simple technical solution, which will make it possible to produce level meters of the most diverse accuracy classes.

2. Universality, which consists in the fact that the measuring ruler can be powered by both alternating and constant voltage.

3. Possibility of use in tanks with flammable oil products.

Information sources

1. Device for measuring the level of fluid in the well and the interface between two fluids with different densities. RF patent for the invention No. 2232268, 2004.

2. Level gauge for liquid. RF patent for the invention No. 2371682, 2009.

3. Liquid level indicator. RF patent for utility model No. 96956, 2010.

4. Light float-free non-contact liquid level meter with a digital output of the results. RF patent for the invention No. 2359237, 2009.

5. A method of measuring the level of liquid media. RF patent for the invention No. 2575472, 2015.

6. A method for determining the liquid level and a liquid level indicator for its implementation. RF patent for the invention No. 2292015, 2007.

7. A method of measuring a liquid level with a magnetostrictive level gauge and a magnetostrictive level gauge. RF patent for the invention No. 2222786, 2004. (Prototype)

Claims (1)

A liquid level meter containing a sensitive element longer than the maximum permissible liquid level and mounted vertically in the tank, a float moving relative to the sensitive element, a power supply, a level determination and information transmission unit connected by a radio channel to a visual information display unit, cargo, fixed at the bottom of the sensor to stabilize it in a vertical position, characterized in that the sensor is made in in the form of a rigid non-magnetic tube, inside of which there is a sealed measuring ruler made in the form of a bifilar twist from an insulated wire with a constant step λ ₀ and powered by a constant or alternating voltage from the power supply unit, two magnetic field sensors are located vertically one below the other, the distance between which L is equal to (2n + 1) ⋅λ _0/2 (n -. the integer 1, 2, 3, ...), each of which is connected to the pulse generator and outputs the pulse shapers by spring-loaded conductors Comm they are respectively connected with the summing and subtracting inputs of a reversible pulse counter, the output of which is connected to the input of the level determination and information transfer unit, moreover, the pulse counter, power supply units and level determination and information transmission units are located above the maximum liquid level, and the float, sensors and pulse shapers form a single measuring unit.

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