RU2654934C1 - Method of calibration of nozzle and device for calibration of nozzle - Google Patents

Abstract

FIELD: measuring equipment.

SUBSTANCE: invention relates to the field of flow measuring technology and is intended for transferring a unit of gas volume flow from the reference nozzle to a calibrated with minimal influence of the transfer function of the comparator on the final transmitted unit of flow. In the method for critical nozzle calibrating, through which gas is passed through the calibrated reference nozzles and the calibrated nozzle in a critical mode and the gas flow rate is measured, according to the invention, two gas flow rates are formed from at least two sets of parallel and previously calibrated reference nozzles, greater and smaller than the estimated flow rate of the calibrated nozzle, alternately connect to a flow indicator – a comparator – a calibrated nozzle and each set of calibrated reference nozzles, the gas is passed in a critical mode and accordingly the pressure drop across the comparator is measured when each set of calibrated reference nozzles is connected and the pressure drop across the comparator is connected when the calibrated nozzle is connected, and the flow rate of the calibrated nozzle is determined from the expression:

where Q1, Q2 – expenses of reference nozzles (less and more than verified), ΔP1, ΔP2 – pressure drops on the comparator when working reference nozzles, ΔP is the pressure drop across the comparator when the calibrated nozzle is being operated, and the pressure difference at the comparator is measured at a portion of the developed laminar flow.

EFFECT: increase in the accuracy of transmission of the unit of flow, stability of the readings in time and independence of mechanical resistance, as well as reducing the influence of the comparator on the accuracy of the result.

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Description

The invention relates to the field of flow measuring equipment and is intended to transfer a unit of volumetric gas flow from a critical critical nozzle to a calibrated one with minimal influence of the transfer function of the comparator on the final transferred flow rate unit.

A known method for determining the critical flow rate in the nozzle (US patent 6,601,460 B1, IPC G01F 1/40, published 05.08.2003. "Flowmeter based on pressure drop across parallel geometry using Boundary layer flow including Reynolds numbers above the Laminar range"), in which the gas flow passing through the thin longitudinal plates causes local resistance. This resistance is recorded by the pressure sensor and converted into an electrical impulse proportional to the volumetric flow rate.

A known method for determining the critical flow rate in the nozzle using temperature converters. These sensors are installed in a critical section and at a certain distance downstream (patent US 4,753,114, IPC G01F 1/36, G01F 1/42, publ. 06/28/1988. "Critical flow detection").

A known method for calibrating critical nozzles by measuring and comparing the pressure at the inlet and outlet of the nozzles (patent JPH08247827 (A) IPC B05B 1/00, B05B 9/01, publ. 30.01.1996. "Convenient calibration device for critical nozzle and method this") .

The principle of operation of the gas volume comparator is described, described in the work “Double piston prover usable as Flowrate comparator for various gases”. XVIII IMEKO WORLD CONGRESS Metrology for a Sustainable Development, September, 17-22, 2006, Rio de Janeiro, Brazil.

A known installation for checking and calibrating meters, flow meters and flow meters, gas meters (patent for utility model No. 135705, IPC G01F D 25/00, publ. 12/20/2013), containing reference flow meters - critical nozzles, each of which is equipped with a shut-off valve , a pump, a receiver (prechamber), a monitoring and control system comprising a shut-off valve control unit, an additional block for generating a set of critical nozzles for a given value of the calibration medium flow rate, made in the form of a program Many modules.

A known method for calibrating critical nozzles and a device for its implementation, which is closest to the claimed one and adopted as a prototype (application No. 2001121223/28, IPC G01F 25/00, publ. 06/20/2003), by which gas is passed through the nozzle in critical mode and measured gas flow rate, from a set of parallel-connected and previously calibrated nozzles form a gas flow rate close to the calculated flow rate of the calibrated nozzle, and using the substitution method, connect the calibrated nozzle and the selected set of failures alternately to the flow indicator brovannyh nozzles, the flow rate is determined from the mathematical expression. A device for calibrating critical nozzles (application No. 2001121223/28, IPC G01F 25/00, published on 06/20/2003), the closest in technical essence to the claimed one and taken as a prototype of the device contains measuring instruments, a vacuum source and a section for installing a calibrated nozzle connected between the vacuum source and the flow indicator, parallel to the site for installing the calibrated nozzle, a set of previously calibrated nozzles is connected, the outputs of which are connected to the vacuum source through their shutoff valves, and the inputs through the flow indicator to the atmosphere yep. However, the known method and device do not provide sufficient accuracy of the transmission of the unit flow rate, stability of readings over time. The relationship of the output signal of real flow indicators with the flow rate always differs from directly proportional, on which the calibration method in the prototype is based. For this reason, the known method and device can be used only at very close costs of the reference and verified nozzles, which requires an unusually large set of reference nozzles.

The technical problem to be solved by the claimed invention is directed is the creation of an effective system for transferring a flow rate unit from an initial reference installation of volumetric and mass flow rate units of gas to its working elements (installations EU-2, EU-3, EU-4).

The technical result, the achievement of which the present invention is directed, is to increase the accuracy of transmission of a flow unit, the stability of readings over time and independence from mechanical resistance, as well as reducing the influence of the comparator on the accuracy of the result.

The technical result is achieved by the fact that in the method for calibrating critical nozzles, according to which a gas is passed through the calibrated nozzle with the calculated flow rate in the critical mode and the gas flow rate is measured, it is new that two gas flow rates are formed - smaller and larger relative to the calculated flow rate of the calibrated nozzles, respectively, in two parallel-connected sections with previously calibrated reference nozzles, are alternately connected to a flow indicator - a comparator - a section with a calibrated nozzle and each portion with the reference calibrated nozzles, the gas is passed in a critical mode, and respectively measure the pressure drop across the comparator by connecting each section with reference calibrated nozzles and the pressure drop across the comparator connecting portion with calibrated nozzle, a value calibrated nozzle flow is determined from the expression:

where Q1, Q2 are the costs of the reference nozzles (respectively, less and more than the calculated flow rate of the calibrated nozzle); ΔP1, ΔP2 - pressure drops on the comparator when connecting the reference nozzles; ΔР is the pressure drop across the comparator when connecting a calibrated nozzle.

Each of the two parallel-connected sections with previously calibrated reference nozzles includes at least one or more nozzles with a total flow rate correspondingly lower and higher than the flow rate of the calibrated nozzle.

The flow indicator is the pressure drop across the comparator, which is measured in the developed laminar flow area at a distance determined from the relationship: l _beg / d = 0.029Re, where l _beg is the initial channel section before the developed laminar flow begins; d is the diameter of the channel; Re is the Reynolds number.

The technical result is achieved in that in a device for calibrating critical nozzles containing a comparator, the input of which is connected to the atmosphere, a pressure sensor, a section for installing a calibrated nozzle with its valves, the output of which is connected to a vacuum pump, and the input with a comparator, is new so that parallel to the site for installing the calibrated nozzle, two sections are connected between the comparator and the vacuum pump, each of them has at least one previously calibrated reference nozzle with a flow rate of ka house portion respectively smaller and larger flow calibrated nozzle portions inputs through its shut-off valve connected to the comparator, and their outputs are connected to a vacuum pump, a comparator formed from a set of laminar flow channels.

The set of laminar channels of the comparator is formed by flat parallel plates located at equal distances between each other and the common side walls.

The pressure sensor is connected to the comparator at a distance l _beg = d × 0,029Re, where l _beg is the initial section of the channel before the developed laminar flow; d is the diameter of the channel; Re is the Reynolds number.

The drawing shows a General view of the installation for calibration of critical nozzles, where

1 - comparator;

2 - pressure sensor;

3 - crane in the area with a calibrated reference nozzle of lower consumption;

4 - reference calibrated nozzle with a lower flow rate;

5 - crane in the area with a calibrated reference nozzle of greater flow rate;

6 - reference calibrated nozzle higher flow rate;

7 - faucet-nozzle block reference calibrated nozzles;

8 - crane in the area with calibrated critical nozzle;

9 - calibrated critical nozzle;

10 - faucet-nozzle block calibrated critical nozzle;

11 - a vacuum pump;

12 - laminar channels of the comparator.

The essence of the method is as follows.

или параболическую зависимость Q(ΔP), что многократно расширяет диапазон допустимых отличий между расходами поверяемого и эталонных сопел. Допустимые отличия между расходами поверяемого и эталонных сопел зависят от степени нелинейности зависимости расхода с выходным сигналом компаратора. Теоретически строго прямо пропорциональной является связь перепада давления с расходом несжимаемой жидкости на участке развитого ламинарного течения в канале. Для газов из-за изменения плотности газа в зависимости от давления эта прямая пропорциональность нарушается, появляется квадратичный член в зависимости между расходом и перепадом давления, однако этот член пропорционален отношению перепада давления на участке канала к абсолютному давлению. При ΔР/Р<0,01 нелинейность зависимости невелика. Именно поэтому использование перепада давления на участке развитого ламинарного течения в ламинарных каналах в качестве индикатора расхода позволяет существенно увеличить допустимые отличия между расходами поверяемого сопла и эталонных сопел.The proposed method allows a linear change

or the parabolic dependence Q (ΔP), which greatly expands the range of permissible differences between the flow rates of the calibrated and the reference nozzles. Permissible differences between the flow rates of the calibrated and the reference nozzles depend on the degree of non-linearity of the flow dependence with the output signal of the comparator. Theoretically strictly directly proportional is the relationship between the pressure drop and the flow rate of an incompressible fluid in the developed laminar flow section in the channel. For gases, due to a change in gas density depending on pressure, this direct proportionality is violated, a quadratic term appears between the flow rate and the pressure drop, however this term is proportional to the ratio of the pressure drop in the channel section to the absolute pressure. At ΔР / Р <0.01, the nonlinearity of the dependence is small. That is why the use of a pressure drop in the developed laminar flow section in the laminar channels as an indicator of flow rate can significantly increase the allowable differences between the flow rates of the calibrated nozzle and the reference nozzle.

A device for calibrating critical nozzles contains a comparator 1, the input of which is connected to the atmosphere, a pressure sensor 2, a section for installing a calibrated nozzle 9 with its shut-off valve - valve 8, with the formation of a crane-nozzle block 10, the output of which is connected to a vacuum pump 11, and inlet with comparator 1. Parallel to the section for installing the calibrated nozzle 9, two sections are connected between the comparator 1 and the vacuum pump 11, with previously calibrated reference nozzles 4 and 6, respectively, with a flow rate in each section, respectively smaller and larger flow rates of the calibrated nozzle 9. The inputs of the sections with calibrated reference nozzles 4 and 6 through their shutoff valves - taps 3 and 5 - are connected to the comparator 1, and the outputs with a vacuum pump 11. The sections with nozzles 4 and 6 with taps 3 and 5 form a crane-nozzle block 7. In each section there is one or a set of previously calibrated reference nozzles 4 and 6 with a total flow rate correspondingly lower and higher than the flow rate of the calibrated nozzle 9.

The comparator 1 is made of a set of laminar channels 12, while the pressure drop across the comparator is an indicator of flow. Comparator 1 is a device that is sensitive to the transmitted value with a known form of the transfer function. Due to the fact that the problem of transferring the flow rate unit is solved, the requirements for the accuracy of determining the shape of the transfer function are the highest. For comparator 1, it is the form of the transfer function that is important, and not its actual calibration values. Therefore, it is advisable to ensure accuracy requirements that satisfy the transfer of a flow rate unit using a well-known, theoretically and experimentally sound physical principle. The set of laminar channels 12 of the comparator 1 is formed by flat parallel plates located at equal distances between themselves and the common side walls.

The pressure sensor 2 is connected to the comparator 1 at a distance l _beg = d × 0,029Re, where l _beg is the initial section of the channel before the developed laminar flow; d is the diameter of the channel; Re is the Reynolds number. In the initial section of the flow l _beginning from the beginning of the pipe, a parabolic velocity profile is formed (stabilized). Outside of this section, we have a stabilized laminar flow, the parabolic velocity profile remains unchanged, regardless of the length of the pipe, provided that it is straightforward and the cross section is constant. The pressure drop on the comparator 1 is measured in the developed laminar flow area. To determine the length of the initial section, you can use the approximate Schiller formula expressing this length, referred to the diameter of the pipe, as a function of the number Re.

A method for calibrating critical nozzles is as follows.

The air flow is organized by a suction compressor station. The working medium (gas) passes sequentially through the comparator 1 and the critical nozzles 4, 6 and the calibrated nozzle 9.

The comparison procedure using comparator 1 is as follows.

At the first stage, the vacuum pump 11 provides a gas flow sequentially passing through the comparator 1 and through the sections with the reference critical nozzles 4 and 6. The parameters for maintaining the critical flow regime in the nozzles 4 and 6 are sequentially controlled and the output signals of the comparator 1 are recorded by the pressure sensor 2. Then a gas flow is created, passing through the comparator 1 and the calibrated nozzle 9. Again, the parameters for maintaining the critical flow mode are monitored and the output signals of the comparator 1 are recorded by the pressure sensor 2. Using the known form of the transfer function of the comparator 1, the flow coefficient of the unknown calibrated nozzle is determined. The pressure drop across the comparator is measured in the developed laminar flow area.

The flow rate of the calibrated nozzle is determined from the expression:

where Q1, Q2 are the costs of the reference nozzles (less and more than the calibrated), ΔP1, ΔP2 are the pressure drops across the comparator during the operation of the reference nozzles, ΔP is the pressure drops across the comparator during the operation of the calibrated nozzle.

Thus, the use of a pressure drop in a developed laminar flow section in laminar channels as a flow indicator can significantly increase the allowable differences between the flow rates of a verified nozzle and reference nozzles, which leads to an increase in the accuracy of transmission of a flow unit, stability of readings over time and independence from mechanical resistance, as well as reducing the influence of the comparator on the accuracy of the result.

Claims (8)

1. A method for calibrating critical nozzles, according to which gas is passed through a calibrated nozzle with a calculated flow rate in a critical mode and a gas flow rate is measured, characterized in that two gas flow rates are formed - smaller and larger relative to the calculated flow rate of the calibrated nozzle, respectively, on two parallel connected sections with previously calibrated reference nozzles, are alternately connected to a flow indicator - comparator - a section with a calibrated nozzle and each section with a calibrated reference nozzles, let gas pass in critical mode and, accordingly, measure the pressure drop across the comparator when connecting each section with calibrated reference nozzles and the pressure drop across the comparator when connecting the section with the calibrated nozzle, and the flow rate of the calibrated nozzle is determined from the expression:

where Q1, Q2 are the costs of the reference nozzles (respectively, less and more than the calculated flow rate of the calibrated nozzle); ΔP1, ΔP2 - pressure drops on the comparator when connecting the reference nozzles; ΔР is the pressure drop across the comparator when connecting a calibrated nozzle. 2. The method according to p. 1, characterized in that each of two parallel-connected sections with previously calibrated reference nozzles includes at least one or more nozzles with a total flow rate, respectively, lower and higher than the flow rate of the calibrated nozzle. 3. The method according to p. 1, characterized in that the flow indicator is the pressure drop across the comparator, which is measured in the developed laminar flow area at a distance determined from the relation: l _beg / d = 0,029Re, where l _beg is the initial section of the channel to the beginning of a developed laminar flow; d is the diameter of the channel; Re is the Reynolds number. 4. A device for calibrating critical nozzles, comprising a comparator whose inlet is connected to the atmosphere, a pressure sensor, a section for installing a calibrated nozzle with its valves, the outlet of which is connected to a vacuum pump, and an input with a comparator, characterized in that it is parallel to the installation section two sections are connected between the comparator and the vacuum pump, each of them has at least one previously calibrated reference nozzle with a flow rate in each section, respectively, smaller and larger the flow rate of the calibrated nozzle, the inputs of the sections through their valves are connected to the comparator, and their outputs are connected to a vacuum pump, the comparator is made of a set of laminar channels. 5. The device according to claim 4, characterized in that the set of laminar channels of the comparator is formed by flat parallel plates located at equal distances between themselves and the common side walls. 6. The device according to p. 4, or 5, characterized in that the pressure sensor on the comparator is connected at a distance l _beg = d × 0,029Re, where l _beg is the initial section of the channel before the developed laminar flow; d is the diameter of the channel; Re is the Reynolds number.

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