RU2521285C1 - Method to measure mass flow rate of medium - Google Patents

Abstract

FIELD: measurement equipment.

SUBSTANCE: method for the measurement of mass flow rate of a medium involves measurement of volume flow rate by the rotation speed of a meter at zero pressure drop and then the data transfer to a computing unit. The value of drive torque obtained by the computing unit is divided by the rotation speed of the meter.

EFFECT: simplified mass flow rate measurement method at limited instrument composition of the metering device, decreased amount of metering and calculation operations required to be simultaneous for more exact measurement of the medium mass flow rate, simultaneous measurement of two parameters in one instrumentation point.

3 cl, 1 dwg

Description

The invention relates to measuring technique and can be used to measure the flow rate of various environments, in particular in commercial calculations.

Known methods for measuring mass flow rate, for example (P.P. Kremlevsky. Flowmeters and counters of the amount of substance. St. Petersburg Polytechnic. 2002. Book 1 and 2), including flow measurement according to the differential pressure gauge and density using narrowing devices.

The disadvantages of the known solutions is the large error in the measurement of flow, as well as the large dimensions of the device.

A known method of measuring mass flow (Multivariable mass flowmeter Multivariable model 3095 MV. Fischer prospectus - Rosemount 00813-0100-4716 Rev DA 11/98), including measuring the flow rate using a differential pressure meter. Its disadvantage is the need to maintain a certain flow regime (Re number), which limits the measurement range, the use of additional techniques to compensate for flow measurement errors, for example, the requirement for installing certain lengths of sections before and after the device.

In addition, the disadvantage of this method is the relatively small range of flow measurement, less than 10, providing a measurement error of 1%. In addition, the magnitude of the error is not calculated to the current value, but the maximum scale value is taken.

An analogue is the well-known compensation method (PLU 103 A flowmeter manufactured by Pierburg Luftfahrtgerate Union GmbH. Bataverstr. 80 / Postfach 100 261 D-4040 Neuss West-Germany.tel. (02101) 523-1, information leaflet).

The known method of measuring the flow rate, including measuring the volumetric flow rate of the medium at zero pressure drop across the motor by the number of revolutions, has the following disadvantages: mass flow rate can only be obtained with a known density of the measured medium; - differential pressure indicator in the form of an optical pair requires a stabilized power supply; a complex differential pressure sensor - a ground pair of "spool-cylinder", which should not allow unaccounted for leaks; the sensor of deviations of the spool from the equilibrium position is fixed by an optical pair through the transparent glass of the cylinder, which limits the working pressure of the measured flow rate.

To the proposed method, the closest adopted for the prototype is a method of measuring the mass flow of gaseous and liquid media (RU 2279640 C1, 07/10/2006).

According to the known method, there are two measuring sections: the first is a volumetric flow meter with a meter speed sensor and the second is a differential pressure sensor on the constriction device.

The disadvantages of the known method in the implemented device is the relative position of the flow meter volumetric flow and further constricting device, which introduces an additional measurement error due to the possible expansion of the gaseous medium after the constricting device, contributes to an increase in its volume and distortion of the differential pressure sensor readings; additional sections of the pipeline are required before and after the constriction device to obtain reliable results of measuring the differential pressure; the narrowing device is used only to obtain a parameter of the density of the medium, since the total flow rate of the medium is measured by a volumetric flow meter; additional equipment in the form of a narrowing device requires additional calibration of the calibration interval, especially in the range up to Q _min , due to possible paraffin deposits, the presence of additional computational operations in determining the mass flow rate.

The technical result of the invention is to simplify the method of measuring mass flow with a limited instrumentation of the measuring device, i.e. reduction of measurement and computational operations requiring simultaneity for a more reliable measurement of the mass flow rate of the medium, as well as the simultaneous measurement of two parameters in one instrument place.

The technical result is achieved by the fact that a method for measuring the mass flow rate of the medium is proposed, including measuring the volumetric flow rate by the meter’s rotational speed at zero pressure drop and transmitting data to the calculator, characterized in that the magnitude of the meter’s drive torque generated by the calculator is divided by the meter’s rotational speed.

The technical result is achieved in that the magnitude of the torque is determined by the current of the electric drive.

The technical result is achieved in that the magnitude of the torque is determined by the pressure of the hydraulic actuator.

A method for measuring the mass flow rate is proposed, in which the volume flow rate Q is measured at zero pressure drop, and for this mode the calculator maintains the required torque on the meter drive and the calculator determines the mass flow rate by the ratio of this moment on the drive to the meter speed.

To implement the method, a measuring section is organized, where volumetric flow measurements are carried out using a closed control loop for zero pressure drop across the measuring section (rotating meter) using a drive made in electromechanical or pneumohydraulic versions.

Figure 1 presents a diagram of a device that implements the proposed method, where the rotary meter 1 of the volumetric flow meter is driven by a drive 2, the rotational speed of which is measured by the sensor 3. The medium Q enters the input of the measuring section 4 and passes through the rotary meter 1 to the output of the medium 5. The speed n of the meter 1 is supported by the control circuit at ΔР≈0, consisting of a differential pressure sensor 6, a calculator 7 and a drive 2. The measuring section 4 consists of a meter 1 and a differential sensor 6.

The method is implemented as follows.

When the sensor 3 measures the frequency n of the shaft rotation, for example from the electric drive 2, which is proportional to the volume flow Q _about , the pressure drop ΔР≈0 is set on meter 1, which is compensated by the moment M on the shaft of the meter 1 in the entire range of flow rates Q _about or revolutions n . In this equilibrium state ΔР≈0 in the calculator 7 data are generated - on the frequency n of rotation of the actuator 2 from the sensor 3 and on the value of the corresponding torque M.

To reduce the pressure drop to zero ΔР≈0, it is necessary to apply a certain moment M to meter 1, which is determined by the current pressure losses on meter 1.

The moment M can be represented as $$M={\mathrm{to}}_{\mathrm{one}}\Delta R\text{(one)}$$

where k ₁ is the coefficient of proportionality, taking into account the structural (geometric) parameters of the flow meter.

,The pressure drop across the meter is expressed as $$\text{ΔР}={\text{to}}_{\text{2}}\text{ρ}{\text{Q}}_{\text{about}}{}^{\text{2}}\text{(2)}$$

,

where ρ is the density of the measured medium; Q _about - volumetric flow rate; to ₂ is the coefficient of proportionality. We substitute (2) in (1), we obtain $$\text{M}={\text{to}}_{\text{one}}\text{to ρ}{\text{Q}}_{\text{about}}{}^{\text{2}}\text{(3)}$$

For volumetric flow meters, Q _о can be expressed in terms of the meter rotation speed n Q _о = к ₃ n (4), where к ₃ is the proportionality coefficient taking into account the dimension. Substituting (4) into (3), we have M = k ₁ to ₂ ρ Q _rev to ₃ n, whence, taking into account Q _max = ρ Q _rev , we get Q _mas = to ₄ M / n, where $${\text{to}}_{\text{four}}=\mathrm{one}/{\mathrm{to}}_{\mathrm{one}}{\text{to}}_{\text{2}}{\text{to}}_{\text{3}}\text{. (5)}$$

In the case of using an electric drive, we have a current value I proportional to the moment M of the meter, if the pneumatic-hydraulic drive - pressure P.

Thus, the magnitude of the moment M (or current I) of the drive 2, divided by the rotational speed n of the meter 1, taking into account the constant dimensional coefficient k _4, is the mass flow rate of the medium Q _mas in the measuring section 4.

The calculator 7 indicates the output at the same time mass Q _max and volume Q _{about the} flow rate of the medium.

The mass flow measurement of the proposed method has the following advantages:

- the absence of a quadratic dependence "flow - differential pressure",

- a significant expansion of the measuring range while maintaining the error both at the beginning of the scale and related to the end of the range,

- the absence of leaks at zero differential allows you to measure flow with maximum accuracy,

- the medium is not subjected to compression and expansion, passing through the measuring section when measuring volumetric and mass flow,

- minimizing the effects of density and viscosity of the medium,

- in fact, the measurement range depends on the technical capabilities of the meter and the drive (electric motor) with a large range of changes in speed,

- there is no need to introduce a correction of the flow rate signal to obtain corrections for the parameters of the medium and the environment - pressure, temperature, density and viscosity,

- the error is calculated in the entire range from the current value,

- the accuracy of the flowmeter is increased due to the absence of unaccounted for leaks, the influence of viscosity, density, temperature of the medium and the environment is reduced, the accuracy and reliability of the flowmeter when measuring flows with high pressure levels, pressure pulsations over a wide range of temperature changes of the measured medium are increased,

- simplification of the method of measuring mass flow with a limited instrumentation of the measuring device, i.e. reduction of measuring and computational operations requiring simultaneity for a more reliable measurement of the mass flow rate of the medium,

- simultaneous measurement of two parameters in one instrument location to calculate the third - mass flow.

Claims (3)

1. The method of measuring the mass flow rate of the medium, including measuring the volumetric flow rate of the meter at zero pressure drop and transmitting data to the calculator, characterized in that the magnitude of the drive torque is divided by the speed of the meter. 2. The method according to claim 1, the magnitude of the torque is determined by the current of the electric drive. 3. The method according to claim 1, the magnitude of the torque is determined by the pressure drop of the hydraulic actuator.