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technical article
There is a corresponding relationship between the flow rate of the metal tube float flowmeter in the cone tube
2012-3-14 11:22:45

Metal tube float flowmeter
Suitable for small-caliber and low-velocity medium flow measurement; reliable work, low maintenance and long life; low requirements for straight pipe sections; wide flow ratio of 10: 1; dual-line large LCD display, optional on-site instantaneous / cumulative flow Display, single-axis sensitive indication with backlight; non-contact magnetic coupling transmission; all-metal structure, suitable for high temperature, high pressure and strong corrosive media; can be used in flammable and explosive hazardous situations; optional two-wire system, battery, AC power supply Mode; multi-parameter calibration function; with data recovery, data backup and power-down protection functions.
Technical parameters of metal tube float flowmeter Measurement range: water (20 ° C) 1-200000 l / h air (20 ° C, 0.113MPa) 0.03-4000m3 / h See flow meter, special flow rate can be customized range ratio: standard Type 10: 1 Special type 20: 1
Accuracy: Standard type 1.5 Special type 1.0 Pressure level: Standard type: DN15-DN50 4.0MPa DN80-DN200 1.6MPa
Special type: DN15-DN50 25MPa? DN80-DN200 16MPa
Jacket pressure rating is 1.6MPa
Special models should be negotiated with the factory before selecting and ordering pressure loss: 7kPa-70kPa
Medium temperature: standard type: -80 ℃-+ 200 ℃: PTFE: 0 ℃ -85 ℃
High temperature type: up to 400 ℃
Medium viscosity: DN15: <5mPa.sF15.1-F15.3
<30mPa.sF15.4-F15.8
DN25: <250mPFa.s
DN50-DN150: <300mPa.s
Ambient temperature: LCD type -30 ℃ - + 85 ℃
Pointer -40 ℃ - + 120 ℃
Connection form: standard type: DIN2501 standard flange special type: any standard flange or threaded cable interface specified by the user: M20 * 1.5
Power supply: standard 24VDC two-wire system 4-20mA (10.8VDC-36VDC)
AC type: 85-265VAC? 50HZ

Select the process parameters required for the metal tube float flowmeter 1. The diameter of the process pipeline 2. The name, nature, density, viscosity of the measured process medium 3, the working temperature of the measured medium 4, the working pressure of the measured medium (pressure (The size determines the quality of the float)
5.Flow of measured medium
6. Principle of on-site industrial and mining condition detection The detection part of the metal tube float flowmeter is composed of a vertical conical tube that expands from the bottom up and a float that can move freely up and down along the axis of the conical tube. When the measured fluid passes from the bottom to the ring gap formed by the cone tube and the float, a differential pressure is generated at the upper and lower ends of the float to form a rising force of the float. When the rising force of the float is greater than the weight of the float immersed in the fluid, the float rises. The gap area increases accordingly, the fluid flow velocity at the annulus decreases immediately, the differential pressure at the upper and lower ends of the float decreases, and the lifting force acting on the float also decreases. A height. The height of the float in the cone has a corresponding relationship with the flow rate.
The basic equation of volume flow Q is:
The flow coefficient of the α meter in the formula varies with the shape of the float;
ε The gas expansion coefficient when the measured fluid is a gas, which is usually ignored due to the small correction amount of this coefficient, and it has been included in the flow coefficient through verification. If it is a liquid, ε = 1
△ F circulation ring area, m2;
g local gravity acceleration, m / s2;
Vf float volume, if extended body should also be included, m3;
ρf Float material density, kg / m3;
ρ Density of the measured fluid, if it is the density of the gas on the upstream cross section of the float, kg / m3;
Ff cross section at the working diameter (maximum diameter) of the float, m2;
Gf float weight, kg.
The relationship between the circulation ring area and the height of the float is shown in formula (3). When the structural design has been determined, d and β are constant.
There is a quadratic term of h in the formula. Generally, this nonlinear relationship cannot be ignored. Only when the cone angle is very small can it be regarded as approximately linear.
Where d float maximum diameter (ie working diameter), m;
h The height of the float from the inner diameter of the cone tube is equal to the height from the maximum diameter of the float, m;
β cone angle of cone tube;
a and b are constants. From the formulas (1), (2), and (3), it can be known that under certain conditions, the height of the float in the cone tube and the volume flow have a certain proportional relationship. After reading the height of the float, you can know the corresponding volume flow rate, and then convert the height of the float to the corresponding volume flow rate through the converter. This is the detection principle of the metal tube float flowmeter.
The conversion indicator converter is actually a scale that converts the height of the float in the cone into the corresponding volume flow. Dividing from output signals: local display and remote signal output:
Local display type: The following magnetic steel in the local indicator is coupled with the magnetic steel in the float to rotate. At the same time, the electric pointer indicates the flow intelligent remote transmission type through the dial at the same time. The following magnetic steel is coupled with the magnetic steel in the float, and rotates. At the same time, the magnetic steel and pointer are driven. The magnetic field is converted into an electrical signal by a magnetic sensor, which is subjected to A / D conversion, digital filtering, and microprocessor processing. D / A output, LCD display to show the instantaneous flow and accumulated flow.
的浮子形状而异; The flow coefficient of the α meter in the formula varies with the shape of the float of the metal tube float flowmeter ;
ε The gas expansion coefficient when the measured fluid is a gas, which is usually ignored due to the small correction amount of this coefficient, and it has been included in the flow coefficient through verification. If it is a liquid, ε = 1
△ F circulation ring area, m2;
g local gravity acceleration, m / s2;
Vf float volume, if extended body should also be included, m3;
ρf Float material density, kg / m3;
ρ Density of the measured fluid, if it is the density of the gas on the upstream cross section of the float, kg / m3;
Ff cross section at the working diameter (maximum diameter) of the float, m2;
Gf float weight, kg.
The relationship between the circulation ring area and the height of the float. When the structural design has been determined, d and β are constant.
There is a quadratic term of h in the formula. Generally, this nonlinear relationship cannot be ignored. Only when the cone angle is very small can it be regarded as approximately linear.
Where d float maximum diameter (ie working diameter), m;
h The height of the float from the inner diameter of the cone tube is equal to the height from the maximum diameter of the float, m;
β cone angle of cone tube;
a and b are constants. From the formulas (1), (2), and (3), it can be known that under certain conditions, the height of the float in the cone tube and the volume flow have a certain proportional relationship. After reading the height of the float, you can know the corresponding volume flow rate, and then convert the height of the float to the corresponding volume flow rate through the converter. This is the detection principle of the metal tube float flowmeter.
The conversion indicator converter is actually a scale that converts the height of the float in the cone into the corresponding volume flow. Dividing from output signals: local display and remote signal output:
Local display type: The following magnetic steel in the local indicator is coupled with the magnetic steel in the float to rotate. At the same time, the electric pointer indicates the flow intelligent remote transmission type through the dial at the same time. The following magnetic steel is coupled with the magnetic steel in the float, and rotates. At the same time, the magnetic steel and pointer are driven. The magnetic field is converted into an electrical signal by a magnetic sensor, which is subjected to A / D conversion, digital filtering, and microprocessor processing. D / A output, LCD display to show the instantaneous flow and accumulated flow.
Calculation of caliber, float number and scale
1.Metal tube float flowmeter calculation method (1) According to the data given by the user, select the appropriate formula to calculate the flow rate Qs of the corresponding calibration medium:
Among them: Qs- standard calibration medium (water or air) flow under standard conditions (20 ° C, 0.1013Mpa) Q- user medium flow K-correction coefficient (2) According to the calculated Qs value, check the flow table to determine the selection Float number and the diameter of the measuring tube (the values in the flow meter are the flow values of water or air under standard conditions)
(3) After determining the diameter of the measuring tube and the float number, it is recommended to use the following formula to determine the upper limit value Q of the flow rate scale of the measured medium:
Among them: the maximum flow of water or air corresponding to a certain float number is selected in the Qi flow table.
(4) Because the viscosity correction is not considered in the calculation, there may be a difference from the result calculated by the factory.
2. Determination of the correction coefficient K of the metal tube float flowmeter (1) For liquid medium a, if Q is the liquid volume flow rate, calculate K using the following formula:
b. If Q is the liquid mass flow rate, calculate K using the following formula:
Of which: ρf: selected float density (g / cm3)
Stainless steel float density is 7.8
Polytetrafluoroethylene float (PTFE) density of 3.4
Nickel-based alloy (Hastelloy) density is 8.3
ρ: Density of the measured medium (2) For gaseous medium a, if Q is the volume flow rate of the gas in the standard state (20 ° C, 0.1013Mpa), then use the following formula to calculate K:
b. If Q is the volume flow of the gas in the operating state, calculate K using the following formula:
c. If Q is the mass flow rate of the gas, calculate K using the following formula:
In the above formulas:
ρ: Density of the measured medium: Density of the measured gas medium at 20 ° C, 0.1013MPa (kg / m3)
P: absolute pressure of the measured gas medium (MPa)
T: absolute temperature of the measured gas medium (K)
ρ0: Density of air at 20 ℃, 0.1013MPa (1.205kg / m3)
P 0: absolute pressure of calibration medium (0.1013MPa)
T 0: absolute temperature of calibration medium (293.15K)
d. Auxiliary density conversion formula Among them: ρst: density of the measured gas medium under standard conditions (Kg / m3)
ρt: density of the measured gas medium under operating conditions (Kg / m3)
Tt: Absolute temperature of the measured gas medium in operation (K)
Pt: absolute pressure of the measured gas medium in operating state (MPa)
p0: absolute pressure of the measured gas medium under standard conditions (MPa)
T0: absolute temperature of the measured gas medium in operating state (K)
Metal tube float flowmeter structure
1.High temperature type structure (G type)
The high temperature structure type (G type) is used for medium flow measurement when the temperature of the medium is too high or too low, and the measuring tube needs to be insulated. The high-temperature structure increases the distance between the measuring tube and the indicator to increase heat dissipation and increase the thickness of the thermal insulation material to ensure that the indicator works within the allowed ambient temperature range. Selection is "G" type.
The G-type metal tube float flow meter can measure the flow of medium with a temperature of -80 ℃-+ 300 ℃.
2.Structure with damper device (Z type)
The damper structure is used to measure the medium flow when the inlet flow (pressure) of the flowmeter is unstable, especially for gas measurement. Its structure is shown in the figure.
3.Jacketed structure (T type)
The jacket type structure is used to measure the flow of the medium that needs heat tracing or cooling (such as high viscosity and easy to crystallize). By heating or cooling the medium in the jacket, the low boiling point and low freezing point fluids are not vaporized and crystallized.
HG20594-97 DN15 PN1.6 flange is used for the lead-in and lead-out connection of the heat tracing medium.Other flange specifications can be marked with the manufacturer.The pressure level of the jacket is 1.6MPa.
For the structure of the jacket type flowmeter, please refer to FA standard flowmeter flange and outline dimension drawing.
4.High-pressure type structure (Y type)
The high-pressure structure is used for flow measurement where the pressure of the measured medium is higher than the standard pressure level. The high-pressure type structure is shown in the figure below. At present, the maximum pressure of FFM64 series can reach 32MPa. In addition, the high-pressure type flowmeter can provide a built-in magnetic filter type, and the installation height is 350mm. The maximum pressure of FA, FB and FC models is 10MPa.
Dimensions and weight of high pressure type Note: 1, G is the weight of the instrument (kg)
Installation Precautions of Metal Tube Float Flowmeter In order to make metal tube float flowmeter work normally and achieve certain measurement accuracy, pay attention to the following points when installing the flowmeter:
· The metal tube float flowmeter must be installed vertically on the vibration-free pipe. The fluid flows through the flowmeter from bottom to top, and the verticality is better than 2 °, and the horizontal angle is better than 2 ° when installed horizontally;
· In order to facilitate the maintenance and replacement of flow meters and cleaning of measuring pipes, metal pipe float meters installed on process pipelines should be equipped with bypass pipes and bypass valves;
入口处应有5倍管径以上长度的直管段,出口应有250mm直管段; · At the entrance of the metal tube float flow meter, there should be a straight pipe section with a length of 5 times the pipe diameter and the outlet should have a straight pipe section of 250mm;
If the medium contains ferromagnetic substances, a magnetic filter should be installed; if the medium contains solid impurities, a filter should be considered between the valve and the straight pipe section;
· When used for gas measurement, the pressure of the pipeline should be no less than 5 times the pressure loss of the flow meter to make the float work stably;
· In order to avoid deformation of the flowmeter caused by the pipeline, the flange of the process pipeline must be coaxial with and parallel to the flange of the flowmeter. The pipeline is supported to avoid pipeline vibration and reduce the axial load of the flowmeter. The control valve in the measurement system Should be installed downstream of the flow meter:
· When measuring gas, if the gas is directly discharged into the atmosphere at the outlet of the flowmeter, a valve should be installed at the outlet of the instrument, otherwise the pressure drop at the float will cause data distortion.
· When installing PTFE-lined instruments, do not tighten the flange nuts randomly and asymmetrically, so as not to cause deformation of the PTEF lining;
· Instruments with liquid crystal display, try to avoid direct sunlight to avoid reducing the service life of the LCD; For instruments with lithium battery, try to avoid direct sunlight and high temperature environment (≥65 ℃) to avoid reducing the capacity and life of lithium batteries. .
For small diameter and low flow medium flow measurement; reliable work, low maintenance and long life; low requirements for straight pipe sections; wide flow ratio of 10: 1; dual-line large LCD display, optional on-site instantaneous / cumulative flow Display, backlit uniaxial sensitive indication; non-contact magnetic coupling drive.