Micro-flow verification method of Coriolis principle mass flow meter

Abstract

The invention relates to the field of Coriolis principle mass flow meters, in particular to a micro flow verification method of a Coriolis principle mass flow meter, which comprises the following steps of: changing a standard detected medium from water into high-purity nitrogen, and firstly measuring the mass flow of gaseous nitrogen in a standard state; measuring the temperature and the pressure of the nitrogen in the verification state, and obtaining the nitrogen density in the verification state and the nitrogen density in the standard state through table look-up; according to an ideal gas state equation, a nitrogen mass flow value in a verification state is obtained, and the flow value serves as a standard flow parameter and is compared with a flow value of the micro mass flow meter. According to the utility model, the volatilization influence during water medium verification is completely avoided, the wall-hanging delay phenomenon of water is also avoided, the flow verification time is greatly shortened, and the verification efficiency is improved.

Description

Technical Field

[0001] The present invention relates to the field of Coriolis principle mass flowmeters, and specifically to a method for calibrating the minute flow rate of a Coriolis principle mass flowmeter. Background Art

[0002] Due to the rise of emerging industries such as photovoltaic energy and electric vehicle batteries, mass flowmeters with a flow rate < 0.5 kg / h are widely used in the production process. At the same time, the demand in fields such as precision experiments and production in fine chemical engineering and pharmaceutical formulation is increasing continuously, which puts forward higher requirements for the calibration method of minute mass flowmeters to achieve the purpose of product quality control.

[0003] Currently, the flow calibration method of domestic Coriolis principle mass flowmeters usually adopts the static mass method for water flow calibration, with the medium to be calibrated being water. This calibration method is only applicable to the calibration and verification of mass flowmeters with a caliber of more than 2 mm and a minimum flow rate of 5 kg / h. During the calibration process of minute-caliber mass flowmeters with a caliber of less than 2 mm, due to factors such as the surface tension of water, volatilization caused by environmental temperature, and the accuracy of the electronic balance used for standard mass measurement, this flow calibration method cannot guarantee the required calibration accuracy, and the calibration process takes a long time and has low efficiency. Summary of the Invention

[0004] To solve the above technical problems, the present invention provides a method for calibrating the minute flow rate of a Coriolis principle mass flowmeter, including the following steps:

[0005] Step 1: Replace the standard medium to be detected from water with high-purity nitrogen. First, measure the mass flow rate of gaseous nitrogen under standard conditions (101.325 kPa, 0 °C).

[0006] Step 2: Measure the temperature and pressure of nitrogen under the calibration state, and obtain the density of nitrogen under the calibration state and the density of nitrogen under the standard state by looking up the table.

[0007] Step 3: According to the ideal gas state equation, obtain the mass flow rate value of nitrogen under the calibration state, and use this flow rate value as the standard flow parameter to compare with the flow rate value of the minute mass flowmeter to achieve the purpose of flow calibration.

[0008] Preferably: The high-precision gas mass flowmeter obtains the mass flow rate value V2 of nitrogen under the standard state (actually the standard-state volume flow rate), the temperature sensor obtains the gas temperature T1 under the calibration state, the pressure sensor obtains the gas pressure P1 under the calibration state, looks up the table to obtain the density ρ1 of nitrogen under the calibration state and the density ρ2 of nitrogen under the calibration state.

[0009] Secondly, according to the ideal gas state equation, for a certain amount of gas

[0010] (P1V1) / (T1 + 273.15) = (P2V2) / (T2 + 273.15)

[0011] P1 and P2 are the pressures under the verification state and the standard state respectively

[0012] V1 and V2 are the volumes under the verification state and the standard state respectively

[0013] T1 and T2 are the temperatures under the verification state and the standard state respectively

[0014] V1 = [(P2V2)(T1 + 273.15)] / [P1(T2 + 273.15)]

[0015] Since m = ρV

[0016] m is the mass

[0017] The mass flow rate value of the gas under the verification state is obtained

[0018] q1 = [(P2V2ρ1)(T1 + 273.15)] / [P1(T2 + 273.15)]

[0019] By controlling the photoelectric switch connected to the output pulse signal of the micro mass flowmeter, the set time T and the number of pulses N corresponding to the time are obtained

[0020]

[0021] N is the number of pulses output by the flowmeter under verification within the verification time

[0022] K is the meter coefficient of the flowmeter under verification, kg-1

[0023] The mass flow rate value of the flowmeter under verification (the true mass flow rate value under the verification state)

[0024]

[0025] By comparing the q1 and qm values at each flow verification point, the accuracy error of the corresponding flow detection point can be obtained

[0026] Preferably: The working principle of the Coriolis mass flowmeter is that when the fluid flows in the vibrating tube of the flowmeter, the vibrating tube exerts a force on the fluid, and there is a certain relationship between the magnitude of this force and the fluid flow rate. The mass flow rate of the fluid is obtained by measuring this force directly or indirectly

[0027] Preferably: The measurement methods of the Coriolis mass flowmeter are divided into two types: direct measurement method and indirect measurement method

[0028] Preferably: The steps of the direct measurement method are as follows

[0029] A particle with mass m flows in a vibrating tube at a velocity v. The vibrating tube rotates at an angular velocity ω at a distance r from a fixed point P. The particle m obtains an acceleration, which can be divided into (a) a radial acceleration a with a direction pointing to P and a magnitude equal to rω 2 (centripetal acceleration) and (b) a transverse acceleration a perpendicular to a r and with a magnitude equal to 2vω (Coriolis acceleration). The Coriolis acceleration is obtained by the vibrating tube exerting a force on the particle, and the resulting reaction force F r of the particle. This reaction force F t is the Coriolis force. There is a certain relationship between the mass flow rate and the Coriolis force. Therefore, as long as the Coriolis force is measured, the mass flow rate can be obtained. c c

[0030] Preferably, the steps of the indirect measurement method are as follows:

[0031] When there is no fluid flowing through the vibrating tube, the vibrations at the inlet and outlet of the vibrating tube are in phase; when there is fluid flowing through the vibrating tube, there is a certain delay time Δt between the vibrations at the inlet and outlet of the vibrating tube. The mass flow rate is proportional to this delay time. Therefore, as long as this delay time is measured, the mass flow rate can be obtained.

[0032] Technical effects and advantages of the present invention:

[0033] The present invention is a method for on-line calibration of small flow rates of a Coriolis principle mass flowmeter in a closed form, which completely avoids the evaporation influence during water medium calibration and also avoids the wall adhesion and delay phenomenon of water, greatly shortens the flow rate calibration time, improves the calibration efficiency, and can provide a wider flow rate calibration range by adjusting the nitrogen flow rate, and there is theoretically no lower limit restriction on the flow rate. Description of the Drawings

[0034] Figure 1 is a working principle diagram of the method for calibrating small flow rates of a Coriolis principle mass flowmeter provided by the present invention;

[0035] Figure 2 is a schematic diagram of the Coriolis force principle inside the vibrating tube of the method for calibrating small flow rates of a Coriolis principle mass flowmeter provided by the present invention;

[0036] Figure 3 is a schematic diagram of the vibration conditions of the fluid at the inlet and outlet of the vibrating tube of the method for calibrating small flow rates of a Coriolis principle mass flowmeter provided by the present invention; Detailed Embodiments

[0037] ​​The present invention will be further described in detail below in conjunction with the accompanying drawings and specific embodiments. The invention of the present invention is given for the purpose of illustration and description, and is not exhaustive or limited to the disclosed form. Many modifications and variations will be obvious to those of ordinary skill in the art. The invention is selected and described to better illustrate the principles of the present invention and its practical applications, and to enable those of ordinary skill in the art to understand the present invention and thus design various inventions suitable for specific purposes with various modifications.

[0038] Please refer to Figures 1 to 3 , in the present invention, a method for calibrating the micro flow rate of a Coriolis principle mass flowmeter is provided, including the following steps:

[0039] Step 1: Replace the standard medium to be detected from water with high-purity nitrogen. First, measure the mass flow rate of gaseous nitrogen under standard conditions (101.325 kPa, 0 °C).

[0040] Step 2: Measure the temperature and pressure of nitrogen under the calibration state, and obtain the density of nitrogen under the calibration state and the density of nitrogen under the standard state by looking up the table.

[0041] Step 3: According to the ideal gas state equation, obtain the mass flow rate value of nitrogen under the calibration state, and use this flow rate value as the standard flow parameter to compare with the flow rate value of the micro mass flowmeter to achieve the purpose of flow calibration.

[0042] The high-precision gas mass flowmeter obtains the mass flow rate value V2 of nitrogen under the standard state (actually the standard-state volume flow rate), the temperature sensor obtains the gas temperature T1 under the calibration state, the pressure sensor obtains the gas pressure P1 under the calibration state, looks up the table to obtain the density ρ1 of nitrogen under the calibration state and the density ρ2 of nitrogen under the calibration state.

[0043] Secondly, according to the ideal gas state equation, for a certain amount of gas

[0044] (P1V1) / (T1 + 273.15) = (P2V2) / (T2 + 273.15)

[0045] P1 and P2 are the pressures under the calibration state and the standard state respectively.

[0046] V1 and V2 are the volumes under the calibration state and the standard state respectively.

[0047] T1 and T2 are the temperatures under the calibration state and the standard state respectively.

[0048] V1 = [(P2V2)(T1 + 273.15)] / [P1(T2 + 273.15)]

[0049] Since m = ρV

[0050] Mass m

[0051] Obtain the mass flow rate value of the gas under the verification state

[0052] q1 = [(P2V2ρ1)(T1 + 273.15)] / [P1(T2 + 273.15)]

[0053] By controlling the photoelectric switch connected to the output pulse signal of the micro mass flowmeter, obtain the set time T and the number of pulses N corresponding to the time

[0054]

[0055] N Number of pulses output by the flowmeter under verification within the verification time

[0056] K Meter coefficient of the flowmeter under verification, kg-1

[0057] Mass flow rate value of the flowmeter under verification (true mass flow rate value under the verification state)

[0058]

[0059] By comparing the q1 and qm values at each flow verification point, the accuracy error of the corresponding flow detection point can be obtained

[0060] The working principle of the Coriolis mass flowmeter is that when the fluid flows in the vibrating tube of the flowmeter, the vibrating tube exerts a force on the fluid, and there is a certain relationship between the magnitude of this force and the fluid flow rate. Measure this force directly or indirectly to obtain the mass flow rate of the fluid

[0061] The measurement methods of the Coriolis mass flowmeter are divided into two types: direct measurement method and indirect measurement method

[0062] The steps of the direct measurement method are as follows

[0063] A mass point with mass m flows in the vibrating tube at a velocity v. The vibrating tube rotates at an angular velocity ω at a distance r from the fixed point P. The mass point m obtains an acceleration, which can be divided into (a) a radial acceleration a with a direction pointing to P and a magnitude equal to rω 2 Radial acceleration a r (Centripetal acceleration) and (b) a transverse acceleration a perpendicular to a r With a magnitude equal to 2vω t (Coriolis acceleration). The Coriolis acceleration is obtained by the vibrating tube exerting a force on the mass point, and the resulting reaction force F c Obtained, and this reaction force F c Is the Coriolis force. There is a certain relationship between the mass flow rate and the Coriolis force. Therefore, as long as the Coriolis force is measured, the mass flow rate can be obtained

[0064] The steps of the indirect measurement method are as follows:

[0065] When no fluid flows through the vibrating tube, the vibrations at the inlet and outlet of the vibrating tube are in phase; when fluid flows through the vibrating tube, there is a certain delay time Δt between the vibrations at the inlet and outlet of the vibrating tube, and the mass flow rate is proportional to this delay time. Therefore, as long as this delay time is measured, the mass flow rate can be obtained.

[0066] Obviously, the described invention is only a part of the present invention, rather than the whole of the invention. All other inventions obtained by those of ordinary skill in the art and related fields based on the inventions in the present invention without creative efforts shall fall within the scope of protection of the present invention. Structures, devices, and operation methods not specifically described and explained in the present invention shall be implemented by conventional means in the art unless otherwise specified and limited.

Claims

1. The micro flow calibration method of the Coriolis principle mass flowmeter includes the following steps: Step 1: Replace the standard test medium from water to high-purity nitrogen, and first measure the mass flow rate of gaseous nitrogen under standard conditions (101.325 kPa, 0°C); Step 2: Measure the nitrogen temperature and pressure under the calibration state, and obtain the nitrogen density under the calibration state and the nitrogen density under the standard state by looking up the table. Step 3: According to the ideal gas state equation, the nitrogen mass flow value under the calibration state is obtained, and this flow value is used as the standard flow parameter to compare with the flow value of the micro mass flow meter to achieve the purpose of flow calibration.

2. The micro flow calibration method of the Coriolis principle mass flowmeter according to claim 1, characterized in that The high-precision gas mass flowmeter obtains the nitrogen mass flow value V2 under the standard state (actually the standard volume flow), the temperature sensor obtains the gas temperature T1 under the calibration state, the pressure sensor obtains the gas pressure P1 under the calibration state, and the table is looked up to obtain the density of nitrogen under the calibration state ρ1 and the density of nitrogen under the calibration state ρ2 Secondly, according to the ideal gas state equation, for a certain amount of gas (P1V1) / (T1+273.15)=(P2V2) / (T2+273.15) P1 and P2 are the pressures in the calibration state and the standard state respectively. V1 and V2 are the volumes in the calibration state and the standard state respectively. T1 and T2 are the temperatures in the calibration state and the standard state respectively. V1=[(P2V2)(T1+273.15)] / [P1(T2+273.15)] Since m=ρV m-mass Obtain the mass flow value of the gas under the test state q1=[(P2V2ρ1)(T1+273.15)] / [P1(T2+273.15)] By controlling the photoelectric switch connected to the output pulse signal of the micro mass flow meter, the set time T and the number of pulses N corresponding to the time are obtained. N is the number of pulses output by the flowmeter being tested during the testing time. K is the instrument coefficient of the flow meter being tested, kg-1 The mass flow value of the flow meter being calibrated (the actual mass flow value under calibration) By comparing the q1 and qm values ​​of each flow calibration point, the accuracy error of the corresponding flow detection point can be obtained.

3. The micro flow calibration method of the Coriolis principle mass flowmeter according to claim 1, characterized in that: The working principle of the Coriolis mass flowmeter is that when the fluid flows in the vibrating tube of the flowmeter, the vibrating tube exerts a force on the fluid. There is a certain relationship between the magnitude of this force and the fluid flow rate. This force is measured directly or indirectly to obtain the mass flow rate of the fluid.

4. The micro flow calibration method of the Coriolis principle mass flowmeter according to claim 3, characterized in that: The measurement method of the Coriolis mass flowmeter is divided into two types: direct measurement method and indirect measurement method.

5. The micro flow calibration method of the Coriolis principle mass flowmeter according to claim 4, characterized in that: The direct measurement method steps are as follows: A particle with a mass of m flows in a vibrating tube at a speed of v. The vibrating tube rotates at an angular velocity ω at a certain distance r from a fixed point P. The particle m gets an acceleration. This acceleration can be divided into (a) direction pointing to P, and the magnitude is equal to rω 2 The radial acceleration a r (centripetal acceleration) and (b) with a r vertical, lateral acceleration a equal to 2vω t (Coriolis acceleration). Coriolis acceleration is the reaction force F generated by the vibrating tube exerting force on the particle. c The reaction force F is obtained. c There is a certain relationship between mass flow and Coriolis force, so as long as the Coriolis force is measured, the mass flow can be obtained.

6. The micro flow calibration method of the Coriolis principle mass flowmeter according to claim 1, characterized in that: The indirect measurement method steps are as follows: When no fluid flows through the vibrating tube, the vibrations at the inlet and outlet of the vibrating tube are in phase; when fluid flows through the vibrating tube, there is a certain delay time Δt in the vibrations at the inlet and outlet of the vibrating tube, and the mass flow rate is proportional to the delay time. Therefore, the mass flow rate can be obtained by measuring the delay time.

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