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technical article
Metal tube float flow meter with independent measuring tube indicator
2012-3-21 16:47:04

是工业自动化过程控制中常用的一种变面积流量测量仪表。 Metal tube float flowmeter is a variable area flow measurement instrument commonly used in industrial automation process control. It has the characteristics of small size, large detection range and convenient use. It can be used to measure the flow of liquid, gas and steam, especially suitable for medium flow measurement with low flow rate and small flow. Measurement features:

1. Robust all-metal structure design type float flow meter 2. Indication of measuring tube with independent concept design 3. Optional stainless steel, Hastelloy, titanium, PTFE material measurement system 4. Low pressure loss design 5. Short stroke, Small structure design, total instrument height 2506, magnetic coupling structure to ensure data transmission, more stable signal 7, insulation or heat tracing jacket 8, vertical, horizontal, various installation methods are more suitable for different use occasions 9, suitable for small diameter and low Velocity medium flow measurement 10. Reliable work, low maintenance, long life 11. Low requirements for straight pipe sections 12, wide flow ratio 10: 1 13, dual-line large LCD display, optional on-site instantaneous / cumulative flow display, With backlight 14, single-axis sensitive indicator 15, non-contact magnetic coupling transmission 16, all-metal structure, suitable for high temperature, high pressure and strong corrosive media 17, can be used in flammable and explosive hazardous places 18, select two-wire system, battery 、 AC power supply mode 19 、 Multi-parameter calibration function 20 、 With data recovery, data backup and power failure protection functions

The flow detection element of the metal float flowmeter is composed of a vertically tapered tube that expands from bottom to top and a float group that moves up and down along the axis of the cone tube. When the measured fluid passes from the bottom to the ring gap 3 formed by the cone 1 and the float 2, 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 ring gap area increases, the fluid velocity at the ring gap immediately decreases, the differential pressure at the upper and lower ends of the float decreases, and the lifting force acting on the float also decreases. Until the rising force equals the weight of the float immersed in the fluid, the float is stable. At a certain height. The height of the float in the cone has a corresponding relationship with the flow rate. The basic equation of the volume flow Q is (1) when the float is a non-solid core hollow structure (load adjustment amount), then in the formula (2) α-the flow coefficient of the meter, which varies with the shape of the float; ε-is The gas expansion coefficient when the measured fluid is gas 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 annular area, m2; g——local gravity acceleration, m / s2; Vf——volume of float, if it is extended, it should also include, m3; ρf——density of float material, kg / m3; ρ——density of measured fluid, if Gas is the density on the upstream cross section of the float, kg / m3; Ff-cross-sectional area at the working diameter (maximum diameter) of the float, m2; Gf-mass of the float, kg. The relationship between the circulation ring area and the height of the float is shown in equation (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. m2 (3) where d——the maximum diameter of the float (that is, working diameter), m; h——the height of the float from the cone diameter equal to the maximum diameter of the float, m; β——the cone angle of the cone; a, b --constant. The typical structure of a 15-40mm transparent cone-shaped tube float meter is shown in Figure 2. The most commonly used transparent conical tube 4 is made of borosilicate glass, and it is customarily referred to as a glass tube float flow meter. The flow indexing is directly engraved on the outer wall of the cone tube 4, and an indexing scale is also installed beside the cone tube. The inner cavity of the cone tube has two types: a smooth surface of the cone and a rib (or plane) with a guide. The float moves freely in the cone tube, or moves under the guidance of the ribs of the cone tube, and the instrument with a smooth inner surface of a larger mouth is also guided by a guide rod. Typical structure of metal tube float flow meter with right-angle installation, usually suitable for instruments with a diameter of 15-40mm or more. The cone tube 5 and the float 4 constitute a flow detection element. There is an extension of the guide rod 3 in the sleeve (not shown in Figure 3), and the displacement of the float is transmitted to the conversion part outside the sleeve through magnetic steel coupling and other methods. The conversion part has two types: local indication and remote signal output. In addition to the right-angle installation structure, there is a straight-through structure with the inlet and outlet center lines concentric with the tapered tube, which is usually used for instruments with a diameter of less than 10-15mm.

Metal tube float flowmeter (down-in, right-out) measurement part characteristics 1. Robust all-metal structure design type float flowmeter 2. Measuring tube indicator with independent concept design 3. Stainless steel, Hastelloy, titanium, PTFE material measurement system 4, low pressure loss design 5, short stroke, small structure design, total instrument height 250 6, magnetic coupling structure to ensure data transmission, more stable signals 7, insulation or heat tracing jacket 8, vertical, horizontal, various This installation method is more suitable for different occasions. 9. It is suitable for small-diameter and low-velocity medium flow measurement. It is reliable in operation, small in maintenance and long in life. 11. It does not have high requirements for straight pipe sections. Large two-line LCD display, optional on-site instantaneous / cumulative flow display, with backlight 14, single-axis sensitive indication 15, non-contact magnetic coupling drive 16, all-metal structure, suitable for high temperature, high pressure and strong corrosive media 17, available In flammable and explosive dangerous places 18, choose two-wire system, battery, AC power supply mode 19, multi-parameter calibration function 20, with data recovery, data backup and power failure protection functions

Main parameters of metal tube float flow meter (down-in and right-out) ◇ Measurement range: water (20 ℃) 1-200000 l / h

Air (20 ° C, 0.1013MPa) 0.03-4000m3 / h; see flow meter, special flow can be customized

◇ Range ratio: standard type 10: 1

◇ Accuracy: standard type 1.0; special type 0.5

◇ Pressure level: Standard type: DN15-DN50 4.0MPa DN80-DN200 1.6MPa

Special type: DN15-DN50 25MPa DN80-DN200 16MPa

Jacket pressure level is 1.6MPa; special models should be negotiated with the factory before selection and order

◇ Pressure loss: 7kPa-70kPa

◇ Media temperature: Standard type: -80 ℃-+ 200 ℃: PTFE: 0 ℃ -85 ℃

High temperature type: up to 400 ℃

◇ Viscosity of medium: DN15: η <5mPa.s (F15.1-F15.3)

η <30mPa.s (F15.4-F15.8)

DN25: η <250mPFa.s

DN50-DN150: η <300mPa.s

◇ Ambient temperature: LCD type -30 ℃ - + 85 ℃

Pointer -40 ℃ - + 120 ℃

◇ Connection form: Standard type: DIN2501 standard flange

Special type: any standard flange or thread specified by the user

◇ Cable interface: M20 * 1.5

◇ Power supply: Standard type: 24VDC two-wire system 4-20mA (10.8VDC-36VDC)

AC type: 85-265VAC 50HZ

Battery type: 3.6V@7.5AH lithium battery, can be used continuously for more than three years.

◇ Alarm output: upper or lower limit instantaneous flow alarm

Open collector output (maximum 100mA @ 30VDC internal impedance 100 ohms)

Relay output (contact capacity 1A @ 30VDC or 0.25A@250VAC or 0.5A@125VAC )

◇ Pulse output: cumulative pulse output, minimum interval 50 ms

◇ LCD display: instantaneous flow rate display value range: 0-50000

Accumulated flow display value range: 0-99999999 (with decimal point)

◇ Protection level: IP65

◇ Explosion-proof mark: intrinsically safe iaⅡCT5; flameproof dⅡBT6

Intelligent 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: Measuring range: water (20 ° C) 1-200000 l / h air (20 ° C, 0.113MPa) 0.03-4000m3 / h See flow meter, special flow can be customized

Range ratio: standard type 10: 1 special type 20: 1

Accuracy: standard type 1.5 special type 1.0

Pressure rating: 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 selection and order

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 thread specified by the user

Cable interface: 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, the flow of the measured medium 6, the industrial and mining conditions on site

Detection principle The detection part of the metal tube float flowmeter is composed of a vertically conical tube that expands from bottom to top 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 equation (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, b are constant

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. 的检测原理。 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 .

Conversion indicator

The converter is actually a scale that converts the height of the float in the cone into the corresponding volume flow. Divided from the output signal: there are on-site display type and remote transmission signal output type: on-site display type: the following magnetic steel in the local indicator is coupled with the magnetic steel in the float to rotate, while the electric pointer passes the scale The disk indicates the intelligent remote transmission of the flow at this time. The following magnetic steel in the intelligent indicator is coupled with the magnetic steel in the float to rotate. At the same time, the magnetic steel and pointer are driven, and the magnetic field is transformed by a magnetic sensor. The electric signal is processed by A / D conversion, digital filtering, microprocessor processing, D / A output, LCD liquid crystal display to display the instantaneous flow rate and accumulated flow rate. The converter is actually a scale that converts the height of the float in the cone into the corresponding volume flow. Divided from the output signal: there are on-site display type and remote transmission signal output type: on-site display type: the following magnetic steel in the local indicator is coupled with the magnetic steel in the float to rotate, while the electric pointer passes the scale The disk indicates the flow rate at this time. The intelligent remote transmission type is coupled by the following magnetic steel in the intelligent indicator and the magnetic steel in the float to rotate. At the same time, the sensing magnetic steel and pointer are driven, and the magnetic field is changed by a magnetic sensor. Transformed into electrical signals, A / D conversion, digital filtering, microprocessor processing, D / A output, LCD liquid crystal display to display the instantaneous flow rate and cumulative flow rate.