RU2762946C1 - Ball-type flow meter for electrically conductive liquid - Google Patents

Abstract

FIELD: measuring equipment.

SUBSTANCE: area of application: invention relates to measuring equipment and can be used in flow measurement of any electrically conductive liquids, in the chemical, food, pharmaceutical industries, electrical and heat power engineering, in housing and communal services and the social sphere as part of automatic systems for recording the consumption of cold and hot water, heat energy. The ball-type flow meter of an electrically conductive liquid consists of a cylindrical body, a screw-shaped guiding apparatus with a hub, installed coaxially therein, an annular channel between the hub and the inner surface of the body, a ball rotatable in the annular channel and made of a dielectric material with zero buoyancy in a liquid, electrodes placed flush in the annular channel on the inner surface of the body, and an electronic circuit. Installed in the annular channel are four electrodes at the vertices of the square, wherein two of said squares, located along the direction of movement of the liquid with the ball, are connected with the common bus of the circuit, and the other two electrodes are connected to the non-inverting and inverting inputs of the single-threshold comparator.

EFFECT: increase in the dynamic range of liquid flow measurement regardless of the type and parameters of the liquid, complete suppression of the impact of the liquid flow rate on the selected mode of operation of the electronic part of the flow meter and reduction in the error of converting the liquid flow into the output pulse frequency (especially at high flow rates), use of a single power source and reduction of the power consumption therefrom nearly by half, use of a single-threshold comparator in the electronic circuit, use of a three-wire communication line of the flow meter with a secondary electronic converter.

1 cl, 5 dwg

Description

The invention relates to measuring equipment and can be used in flow metering of any electrically conductive liquids, for example, water, acids, alkalis and their aqueous solutions, salt solutions in water in the chemical, pharmaceutical, food industries, in electrical and heat power engineering, as part of heat meters, in housing and communal services for accounting of consumption of cold and hot water.

All known design options for ball flow meters are united, firstly, by the use of a tangential or screw flow-guiding apparatus and a ball made of a ferromagnetic material or dielectric capable of rotating in an annular channel, and secondly, the use of one or another method of converting the angular velocity of rotation of the ball into the frequency of the output pulse voltage.

Technical and operational characteristics of ball flowmeters must comply with the "General technical conditions" [Tachometric ball flowmeters GSP, GOST 14012-76, publishing house of standards, 1984].

There are numerous design options for ball primary transducers of the flow rate of liquids, in which a magnetic induction sensor of the rotational speed of a ball made of ferromagnetic material is used [Kremlin P.P. Flow meters and quantity counters. Directory. 4th ed. L. Mechanical engineering, 1989 - 297 p.].

Known ball flow transducer [patent RU 2253843 C1, class. G01F 1/06, publ. June 10, 2005], consisting of a body of non-magnetic material, a restricting sleeve, an open annular cavity with a ball and a signal pickup unit. The disclosed annular cavity is formed by the inner surface of the housing and the outer surface of the restricting sleeve. From the side of the opening of the cavity with the ball placed in it, the housing of the transducer has an annular recess that stabilizes the rotation of the vortex flow.

Known ball flow meter [and.with. SU 1591618 A1, class G01F 1/06, G01F 1/10, publ. 05/27/1988], consisting of a body with inlet and outlet nozzles. A displacer rod and a limiting annular element are coaxially located inside the body, which forms a non-flowing cavity in the body with a ball placed in it. The latter is communicated with the flowing part by an annular slot. In the area where the ball is located on the body, there is a signal pickup unit. To drive the ball into rotation, a jet-guiding device is used, made in the form of tangential channels located in an annular protrusion located at the end of the restrictive annular element from the side of the flowing part of the body.

In the known designs of ball transducers of liquid flow rate into a pulsed electrical output signal, there are disadvantages due to the use of a ferromagnetic ball and a magnetic induction sensor:

1. When the ferromagnetic ball passes near the magnetic circuit of the magnetic induction sensor, it becomes magnetized (attracted) and at a low flow rate of liquid - its adhesion, which causes nonlinearity of the static characteristics and a significant threshold of sensitivity in the region of low flow rates.

2. With the horizontal position of the transducer, since the ferromagnetic ball is heavy relative to the weight of the displaced liquid, that is, it has negative buoyancy, there is an inconsistency in the rotation speed of the ball within one revolution, which increases with decreasing rotation speed, which ultimately distorts the static characteristics of the primary transducer.

The use of a heavy ferromagnetic ball and the use of a magnetic induction method for generating an output pulse signal make it impossible to operate the transducer in a horizontal position and sharply reduce the dynamic range of measurement of the liquid flow rate Q _MAX / Q _MIN and increase the measurement error of the liquid flow rate Q [m ³ / h]. In particular, serially produced ball primary converters "Shtorm-8A" and "Shtorm-32M", used in nuclear power and entered in the State Register of Measuring Instruments under No. 5706-08, have a narrow operating range (4 ÷ 6) and a very large error measurements (1.5-2.5%), according to TU 4213-865-00225555-2007.

Known electro-optical ball primary transducer of liquid flow [patent RU 2548055 C1, class. G01F 1/06, publ. 04/10/2015] in two design options, consisting of a housing with an annular channel, in which the ball can freely rotate, a jet-guide apparatus and a unit for generating an output electrical signal, characterized in that to generate an output electrical (frequency or pulse-number) signal a light emitter and a photodetector are used, which are interconnected by direct optical and reverse positive electronic couplings. But this type of ball-type liquid flow sensor is suitable for measuring the flow rate of transparent liquids only.

Known ball primary transducer of the flow rate of an electrically conductive liquid [patent RU No. 2471154 C1, IPC G01F 1/05, 27.12.2012], consisting of a cylindrical body with an annular channel in which the ball can freely rotate, a stationary jet-guide apparatus and an electrical signal pickup unit , characterized in that the ball is made of a dielectric material with zero buoyancy in the liquid, and in the area of the annular channel, perpendicular to the rolling trajectory of the ball, two electrodes are located through the bushings and flush with the channel surface, due to which the transducer is operable at low liquid flow rates and in the horizontal position of the case.

The closest in design and the achieved technical result to the declared ball flowmeter of an electrically conductive liquid (hereinafter referred to as SHREZH) is an electroball primary transducer of the flow rate of an electrically conductive liquid [patent RU 2566428 C1, cl. G01F 1/06, publ. 10/27/2015], consisting of a body made of a dielectric material, a jet-guiding apparatus, a ball made of a dielectric with zero buoyancy in a liquid, which can rotate in an annular channel, and three electrodes installed in an annular channel in the rolling plane of the ball and flush with its inner surface, of which the middle electrode is connected to the output of the operational amplifier, and the other two electrodes are connected to the inverting and non-inverting inputs of the same operational amplifier, so that the electrical resistances of the liquid between the middle and two other electrodes together with two auxiliary resistors form negative and positive feedbacks spanning the operational amplifier and controlled by a rotating ball. This design of the transducer ensures the independence of the amplitude and steepness of the edges of the output rectangular pulses from the type and physical parameters of the conductive liquid, the position of the primary transducer in space. But this primary transducer of the flow rate of an electrically conductive liquid, considered as a prototype of the claimed SHREZH, has a drawback that manifests itself at high liquid flow rates and reduces the maximum possible measurable liquid flow rate.

If you exclude the "rollover" of the output pulses and, then, their "sticking", then you can increase the dynamic range of the conversion function D = Q _MAX / Q _MIN. To do this, it is necessary to eliminate the disadvantage of the prototype - a universal electro-ball primary transducer of the flow rate of an electrically conductive liquid.

This disadvantage can be explained with the help of the drawing of FIG. 1, on which Ea, Eb and Es are electrodes; + U ₁ and + U ₂ potentials on the electrodes Ea and Eb relative to the electrode ES (common bus of the electronic part of the flow meter) when the voltage at the input of the operational amplifier is positive.

- вектор линейной скорости движения жидкости относительно неподвижных электродов Эа, Эb и Эс, которая задается только струенаправляющим аппаратом и зависит от величины расхода жидкости.In this figure

is the vector of the linear velocity of the liquid relative to the fixed electrodes Ea, Eb and Es, which is set only by the jet-directing device and depends on the value of the liquid flow rate.

From the drawing FIG. 1 it follows that the liquid moving relative to the fixed electrodes Ea, Eb and Es affects the average drift speed of positive and negative ions: between the electrodes Ea and Es, the speed of movement of positive ions increases by the value of the speed of movement of the liquid V, the speed of movement of negative ions also decreases; Between the electrodes Eb and ES, a moving liquid with a speed V increases the speed of movement of negative ions and also decreases the speed of movement of positive ions.

The dependence of the electrical potentials U ₁ and U ₂ not only on the position of the ball relative to the electrodes Ea, Eb and Es and, therefore, the differential voltage U ₁ - U ₂ at the input of the operational amplifier, but also on the ball rotation frequency (fluid flow rate) indicates that that the thresholds of operation of the two-threshold comparator on an operational amplifier with positive and negative feedback set after assembly of the flowmeter will change with a change in the liquid flow rate, and at a sufficiently high flow rate both thresholds of the comparator operation become unipolar. In this case, the pulsed output voltage disappears at the flow meter output, it becomes constant positive or negative, that is, the liquid flow transducer ceases to function.

и

где q⁺ и q^- - электрические заряды положительных и отрицательных ионов жидкости;

и

- концентрации положительных и отрицательных ионов в жидкости; V⁺ и V^- - средние скорости упорядоченного движения (дрейфа) положительных и отрицательных ионов.Let us consider this disadvantage using the theory of electrical conductivity of a liquid. From the theory of electrical conductivity of liquids [Yavorskiy B.M. and Detlar A.A. Physics Handbook. - M. Nauka, 1985-512 p., §III.9.3. Electrical conductivity of liquids, page 195] it is known that the current density i in an arbitrary cross section of an electrically conductive liquid is equal to the sum of the current densities of positive and negative ions i = i ⁺ + i ^- , moreover,

and

where q ⁺ and q ^- are the electric charges of positive and negative ions of the liquid;

and

- concentration of positive and negative ions in the liquid; V ⁺ and V ^- are the average velocities of the ordered movement (drift) of positive and negative ions.

Taking into account the above in relation to the theory of electrical conductivity of liquids, we obtain

If the area of the liquid between the electrodes S, through which the electric current flows, is unchanged, then the current between the electrodes

In a universal electro-ball primary transducer of the flow rate of an electrically conductive liquid, a ball made of a dielectric material rotating with an angular velocity ω in an annular channel modulates the real area of the liquid between the electrodes at the frequency of its rotation, therefore, the current

where S ₁ (ω) and S ₂ (ω) are nonlinear functions characterizing the change in the areas of the liquid between the electrodes, through which electric currents flow, when the dielectric ball rotates in the annular channel of the flow meter.

A change in the magnitude of the electric current between the electrodes causes a change in the potential differences between the electrodes with a frequency *, which in the known design of the flow meter, called the prototype, are converted by an operational amplifier into output rectangular pulses.

The disadvantage of the prototype noted above, which reduces the maximum possible measurable liquid flow rate and, therefore, reduces the dynamic range of flow measurement, follows from the last expression for the current between the electrodes: the current between the electrodes and, therefore, the potential difference between them depends not only on the position of the ball in the annular channel relative to the electrodes Ea, Eb and Es, but also on the velocities of the ions V ⁺ and V ^- between the electrodes, which also depend on the speed of rotation of the ball and liquid.

This disadvantage of flowmeters of an electrically conductive liquid with three electrodes in an annular channel was confirmed during natural tests of four prototypes of flow meters (Du-15, Du-25, Du-32 and Du-40) at the certified stand UPSZHM-150 (serial number 084) in the regional Center standardization and metrology, first in the form of overturning the duty cycle of the output pulses from low values (0 <S << 0.5) to high (0.5 << S <1), then their disappearance (S> 1).

The second disadvantage of a universal electrically-ball primary transducer of an electrically conductive liquid, which is a prototype of the claimed flow meter, is that, firstly, for the power supply of the electronic part, two stabilized voltage sources (U _P1 and U _P2 ) are required, connected in series and with a midpoint. Secondly, the middle electrode is connected to the output of the operational amplifier and during the operation of the flow meter, the voltage on it changes impulsively with a swing almost reaching double the supply voltage (2U _P ).

Since the integrated operational amplifier has a voltage gain of at least many tens of thousands, the voltage at the middle electrode can be much less, which reduces the likelihood of undesirable and destructive electrochemical processes on it, especially if the flow meter operates with a well-conductive and corrosive liquid.

The third drawback is the use of a two-threshold regenerative comparator, implemented on an operational amplifier with positive and negative feedback. This means that after assembling the flowmeter in real production, before the pre-sale check at the Center for Certification and Metrology, it is necessary to carefully set the values of the two comparator response thresholds, taking into account their dependence on the power supply voltages (U _P1 and U _P2 ). All this increases the requirements for the power supply and, in general, reduces the profitability of mass production of flow meters, leads to an increase in the cost of the product and reduces its competitiveness in the market of liquid flow meters.

The objective of the invention is to expand the areas of use of a ball flowmeter of an electrically conductive liquid due to the possibility of measuring the flow rate of a liquid in a very wide range and with the smallest possible measurement error (especially at high flow rates), reducing the power consumption from the power supply, so that an autonomous power supply of the flowmeter from chemical elements can be used , simplification of the circuit of the electronic part of the flow meter and the procedure for adjusting it to the required operating mode, which makes it possible to reduce the cost of the ball flow meter in the conditions of its serial production, and finally, the possibility of using a three-wire communication line of the flow meter with a secondary electronic converter.

The technical result is a significant increase in the dynamic range of measuring the liquid flow rate regardless of the type and parameters of the liquid, complete suppression of the influence of the liquid flow rate on the selected operating mode of the electronic part of the flow meter and reducing the error in converting the liquid flow rate into the output pulse repetition rate (especially at high flow rates), the use of one power supply, and almost half the power consumption from it, the use of a one-threshold comparator in the electronic circuit, the use of a three-wire communication line of the flow meter with a secondary electronic converter.

The problem is solved and the technical result is achieved by a ball flowmeter of an electrically conductive liquid, consisting of a cylindrical body, coaxially inserted into it a helical jet guide apparatus with a hub, an annular channel between the hub and the inner surface of the body, a ball that can rotate in an annular channel and is made of dielectric material, having zero buoyancy in a liquid, electrodes placed flush in an annular channel on the inner surface of the body, in which, unlike the prototype, four electrodes are installed at the tops of a square, two of which, located along the direction of movement of the liquid with a ball, are connected to a common power bus, two others are connected to the inputs of a single threshold comparator on the operational amplifier.

The essence of the invention is illustrated by drawings Fig. 2, Fig. 3 and FIG. 4.

FIG. 2 shows the design of the hydromechanical part of the SHREZh.

FIG. 3 shows an electrical diagram of the unit for picking up a signal from electrodes E1, E2, E3 and E4 and normalizing the output pulse voltage.

FIG. 4 shows the diagrams of voltages U ₁ (ϕ) and U ₂ (ϕ) at the non-inverting and inverting inputs of the operational amplifier DA1 and at the electrodes A1 and A2, respectively.

The hydromechanical part of the SHREZh, as shown in Fig. 2, consists of a cylindrical body 1 made of a dielectric material (glass, plastic or composite material), a jet-guiding apparatus 2 with a hub 3 inserted into it, a ball 4 made of a dielectric and having zero buoyancy in a liquid, which can freely rotate in an annular channel arising between the inner surface of the housing 1 and the outer surface of the hub 3, and four electrodes E1, E2, E3 and E4, placed flush with the inner surface of the body 1 symmetrically with respect to the rolling trajectory of the ball 4.

The stationary stream-directing apparatus 2, which consists of several blades, configured so that the transformation of the inlet linear flow of the liquid into a rotating flow is carried out without stalling and eddies.

The distance between the electrodes E1 and E2, E3 and E4, E1 and E4, E2 and E3 must be the same, and they must be located on the body 1 so that the rolling trajectory of the ball 4 divides the distances between the electrodes E2 and E3, E1 and E4 into two equal parts.

As shown in FIG. 2, the ball 4 rotates clockwise with respect to the flowmeter inlet, passing first under the electrodes E2 and E3, then under the electrodes E1 and E4.

The electrical part of the SHREZH, as shown in FIG. 3, consists of four electrodes E1, E2, E3 and E4, three resistors R1, R2 and R3, a stable supply voltage U _P , an integrated operational amplifier (OA) DA1, operating in the mode of a one-threshold comparator.

Resistances of an electrically conductive liquid R _B1 and R _B2 between electrodes E1 and E4, E1 and E3, E2 and E3, E2 and E4 with resistors R1, R2 and R3 are included in the bridge circuit. The bridge is powered by a stabilized voltage U _P. The output differential voltage of resistor bridge between the electrodes E1 and E2 with the purpose of normalization of the output voltage U _OUT SHREZH connected respectively to the noninverting and inverting inputs of op amp DA1.

The operational amplifier DA1 is connected to a unipolar supply voltage U _P , therefore, with an input differential voltage U _IN . _DIFF = U ₁ -U _2> U _n / k _Y k where _Y - voltage gain of an integral type used op amp output voltage U _OUT flowmeter will be the maximum possible _{VYH.MAKS U.} Since k _U of commercially available integrated op-amp is very high (many tens or hundreds of thousands), the signal taken between the electrodes E1 and E2, may have millivolt level. Typically, the maximum possible output voltage of an integral op-amp of positive polarity is U _OUT.MAX. = U _P -0/6 V. If the input voltage of the op-amp DA1 U _IN.MAX. = U ₁ -U ₂ <0, then the output voltage of the flow meter with a unipolar power supply U _OUT. <0.6 V, that is, very low.

The variable resistor R3 is necessary to adjust the circuit to its initial state, when the ball 4 is stationary in the zone of the annular channel opposite the electrodes, taking into account the real inequality of the industrially produced resistances of the resistors R1 and R2 and the zero shift of the output voltage of the op-amp (at U ₁ - U ₂ , U _OUT ≠ 0).

The resistances of the resistors R1 = R2 are calculated based on the desired value of the current I ₀ , the voltages U ₁ = U ₂ and the known resistance of the liquid R _B1 and R _B2 between the electrodes E1 or E2 relative to the common bus of the circuit (-U _P ), when it is in the initial condition.

After assembly of SHREZh and before its pre-sale verification and sealing, it is necessary to set the required operating mode of the electronic circuit. To this end, using the adjusted resistor R3, it is necessary to ensure such an imbalance in the bridge circuit (operating mode) so that the output voltage of the op-amp DA1 has the required value. For example, if, according to the approved technical specifications for this liquid flow meter, it is required to ensure the state of U _OUT - low voltage relative to the common bus (for an integrated op-amp with unipolar power supply it is not more than 0.6 V), then using the resistor R1 it is necessary to set the overvoltage U ₂ at the inverting input of the op-amp DA1 over the voltage U ₁ in several (2..5) millivolts.

In real operating conditions of SHREZh, in the absence of liquid flow, ball 4 can stop between electrodes E1 and E4, then the liquid resistance between them will be large, the voltage U ₁ at the non-inverting input of the op-amp DA1 will exceed the voltage U ₂ , the differential positive voltage at the input of the op-amp will provide a high constant voltage at the output of the circuit U _Bb1X = U _P - 0.6 V.

Thus, in a static state SHREZH U output voltage _OUT can be high or low, but not pulsed.

When the ball rotates in the annular channel, the fluid resistances are modulated between the electrodes E1 and E4, E1 and E3, E2 and E3, E2 and E4 with the ball rotation frequency, which means that the differential voltage U ₁ - U _{2 is} modulated, and the output voltage will be pulsed with a very short edges due to the very high voltage gain of the integrated operational amplifiers. The process of generating the output pulse voltage U _OUT depending on the voltages U ₁ and U ₂ at the non-inverting and inverting inputs of the OA DA1 and the angular position ϕ of the ball relative to the four electrodes A1, A2, E3 and E4 is shown in FIG. 4.

Let us consider the effect of suppressing the influence of a liquid rotating in an annular channel on the operating mode of the electronic part of SHREZh set by a variable resistance resistor R3 FIG. 5, which shows the vectors of currents of positive and negative ions of the liquid flowing between the electrodes E1 and E4, E1 and E3, E1 and E2, E2 and E3, E2 and E4.

The directions of positive and negative ions flowing in the liquid between contacts A1 and A2 are not shown, because with the frequency of the ball passing under the electrodes, they change their direction depending on the polarity of the differential voltage U ₁ - U ₂ .

If the ball at a given time is in the area of electrodes E1 and E4, then the differential voltage

where R _B is the resistance of the liquid between the electrodes when the ball is far from them, that is, it does not interfere with the movement of positive and negative ions between these contacts; ΔR _B - the absolute increase in the resistance of the liquid between the electrodes when the ball prevents the free movement of ions in the liquid; R1, R2 are the resistances of the sides of the bridge without taking into account some slight displacement of the movable contact of the resistive potentiometer R3 relative to its middle, which is necessary to fix the required initial state of the circuit.

To assess the polarity of the differential voltage U ₁ - U _2, it is quite acceptable to consider R1 ≈ R2 = R, and the differential voltage

and output SHREZH U output voltage _{V OUT} = k (U ₁ - U _2), where k _U - voltage gain op amp DA1, is almost equal to the supply voltage U _P.

If the ball at a given time will be above the electrodes E2 and E3, then the voltage

and the output voltage U _OUT will be extremely low.

It is very important that the differential voltage at the input of the op-amp has a millivolt level, and the current between electrodes A1 and A2 at a real resistance of the liquid will have microampere values. At such low voltages and currents between the electrodes, electrochemical processes do not occur, and the effect of a moving liquid on the mobility of positive and negative ions can be neglected.

Since the moving liquid deflects all the trajectories of the drift of positive and negative ions in phase in the same direction, increasing the length of the corresponding sections of the electrically conductive liquid and, therefore, their electrical resistances, the in-phase voltages U ₁ and U ₂ on electrodes A1 and A2 increase, but the differential voltage U ₁ - U ₂ at the input of OA DA1 remains always unchanged.

So, in the presented SHREZh the technical result is achieved:

- a significant increase in the dynamic range of measuring the flow rate of an electrically conductive liquid due to an increase in the maximum allowable flow rate achieved by suppressing the effect of the fluid velocity in the annular channel on the selected operating mode of the electronic circuit;

- using one power source and reducing the power consumption of the electronic circuit by almost two times;

- the use of a one-threshold comparator on an operational amplifier;

- use of a three-wire communication line with a secondary electronic converter.

Claims (1)

A ball flowmeter of an electrically conductive liquid, consisting of a cylindrical body, coaxially installed in it a helical jet-directing apparatus with a hub, an annular channel between the hub and the inner surface of the body, a ball that can rotate in an annular channel made of a dielectric material having zero buoyancy in the liquid, electrodes , located flush in the annular channel on the inner surface of the housing, and the electronic circuit for generating the output signal, characterized in that four electrodes are installed in the annular channel at the vertices of the square, two of which, located along the direction of fluid movement with the ball, are connected to a common circuit bus, the other two electrodes are connected to the non-inverting and inverting inputs of a one-threshold comparator on an operational amplifier.

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