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Pulse output vortex flowmeter
1、 Working principle and flow rate frequency relationship equation 1. Working principle: When a cylindrical object is vertically inserted into the mea
Product details
1、 Working principle and relationship between flow rate and frequency
1. Working principle
When a column is vertically inserted into the measuring tube, the fluid alternately generates regular vortices on both sides of the column (as follows
As shown in the figure, this type of vortex column is called a Karman vortex street. The release frequency of Karman vortex street is related to the flow velocity and the width of the column. It can be expressed as follows:
F=St • v/d...... (Formula 1)
In the formula: F - Release frequency of Karman vortex street
St - coefficient (known as Strouhal number)
V - Flow velocity
D - width of the columnar object
2. Relationship between traffic and frequency
The release frequency f of the Karman vortex street is directly proportional to the flow velocity v, so the instantaneous flow rate can be calculated by measuring the release frequency of the Karman vortex street.
Strouhal number is an important coefficient of vortex flowmeter. In the flat part of the curve where S t ≈ 0.17, the frequency of vortex release is related to the flowThe speed is directly proportional, so the detection frequency f can be used to obtain the flow velocity v, and the volume flow rate can be calculated from v. Namely:
The vortex release frequency of the L U G B series vortex flow sensor is determined by the alternating action of vortices on the detection sensor (probe)Stress is detected through piezoelectric elements inside it.
2、 Main technical performance parameters
Table 1 Main Technical Performance Parameters
|
Measurement medium |
Saturated steam, superheated steam, liquid, gas |
|
accuracy class |
±1.0%,±1.5% |
|
Measurement repeatability |
0.3%， 0.5% |
|
Working pressure |
1.6MPa, 2.5Mpa, 4.0 Mpa (customized) |
|
Fluid temperature |
（-40℃～150℃），（-40℃～250℃），（-40℃～350℃） |
|
output signal |
Three wire voltage pulse or two-wire 4-20mA standard current |
|
Working power supply |
DC12V,DC24V， Lithium battery 3.6V |
|
work environment |
Temperature: (-25 ℃~55 ℃), humidity:< 95% |
|
Installation method |
Horizontal, vertical, inclined, inverted (suitable for high-temperature steam) |
|
Connection method |
Flange card installation |
|
flow rate range |
Liquid 0.5-5m/s, gas (vapor) 5-50m/s |
3、 How to choose the right type
The selection of instruments is a very important task in instrument applications. To obtain accurate measurement results, attention should be paid to the following when selecting instruments: medium temperatureDegree, pressure, flow range, and installation environment, among which the selection of flow range is particularly important. If the flow rate is too small, the instrument cannot detect the signal, and if the flow rate is too high, the instrument cannot detect the signalLarge and prone to generating noise.
1The specifications and models of sensors should be based on the volumetric flow rate, pressure, temperature, density, viscosity, and configuration of the measured liquid medium under working conditionsUse a display instrument to select. The flow range of the selected sensor should cover the volumetric flow rate of the measured medium under working conditions.
2The flow rate measured by the sensor refers to the volumetric flow rate under working conditions. When providing the mass flow rate or standard of the tested medium in working conditionWhen the volumetric flow rate is in a quasi state, it must be converted to the volumetric flow rate in a working state. Similarly, when providing density under standard conditions, it is also necessary toConvert to density in working condition.
3Selection of sensor diameter
★Select according to fluid pipeline
Select sensors with corresponding diameters based on the inner diameter of the pipeline. If the flow range of the measured medium is within the range of4If the flow range is determined, selectThe sensor is suitable.
★Select according to the flow range of the tested medium
Based on the maximum flow rate of the tested medium, select the sensor with the corresponding upper limit of flow rate for the medium in Table 4 and the corresponding diameter, and then proceed according to the4Tiao TiDetermine the minimum flow rate using the provided method. If it meets the flow range of the measured medium, the selected sensor is appropriate.
If the above requirements are not met, sensors of other diameters should be re selected to meet the flow range of the measured medium. When the transmission of two pathsWhen sensors can be selected, sensors with smaller diameters should be chosen.
4Determine the flow range of the tested medium
★The maximum traffic can be based on the traffic upper limit values in Table 4;
★The general method for determining the minimum flow rate is as follows:
1) Based on the density of the tested medium in its working stateρCalculate the minimum flow rate:
In the formula:Q0—The lower limit of flow given in Table 4（m3/h）
ρ0—Reference density, liquidρ0=1000Kg/m3
gasρ0=1.293Kg/m3
ρ—Density of the tested medium in working condition（Kg/m3）
2）According to the kinematic viscosity of the tested medium in its working stateγCalculate minimum flow:
QVγmin = 30Dγ(m3/h) …………………………………Formula（4）
In the formula:D — Inner diameter of sensor（m）；
γ—Kinematic viscosity under working conditions（cst）
3) compareQVρminandQVγminSize, take the larger value as the minimum flow rate.
Table 2Saturated water vapor density table (based on pressure)-Pressure is absolute pressure
|
pressure |
1.0 |
2.0 |
3.0 |
4.0 |
5.0 |
6.0 |
7.0 |
8.0 |
9.0 |
10.0 |
|
Temperature ℃ |
99.1 |
119.6 |
132.9 |
142.9 |
151.1 |
158.1 |
164.2 |
169.6 |
174.5 |
179.0 |
|
density |
0.579 |
1.107 |
1.618 |
2.120 |
2.614 |
3.104 |
3.591 |
4.075 |
4.556 |
5.037 |
|
pressure |
11.0 |
12.0 |
13.0 |
14.0 |
15.0 |
16.0 |
17.0 |
18.0 |
19.0 |
20.0 |
|
Temperature ℃ |
183.2 |
187.1 |
190.7 |
194.1 |
197.4 |
200.4 |
203.4 |
206.2 |
208.8 |
211.4 |
|
density |
5.616 |
5.996 |
6.474 |
6.952 |
7.431 |
7.909 |
8.389 |
8.868 |
9.349 |
9.803 |
Table III Common gas density table
|
Gas name |
0℃ 3 |
20℃ 3 |
Gas name |
0℃ 3 |
20℃ 3 |
|
dry air |
1.2928 |
1.205 |
acetylene |
1.1717 |
1.091 |
|
nitrogen |
1.2506 |
1.165 |
methane |
0.7167 |
0.668 |
|
hydrogen |
0.0898 |
0.084 |
ethane |
1.3567 |
1.263 |
|
oxygen |
1.4298 |
1.331 |
propane |
2.005 |
1.867 |
|
chlorine |
3.214 |
3.00 |
ethylene |
1.2604 |
1.174 |
|
ammonia |
0.771 |
0.719 |
propylene |
1.914 |
1.784 |
|
carbon monoxide |
1.2504 |
1.165 |
carbon dioxide |
1.977 |
1.842 |
Table 4 Reference flow range
four、passfeelimplementof
The sensor installation includes the body, gasket, flange, and double headed bolt. It adopts a flange clamping type and can be installed on horizontal and vertical pipelines.
1Precautions for installation
★The fluid flow direction must be consistent with the flow direction mark on the sensor body;
★When installing sensors, during the welding of flanges or pipelines, the sensors should not be placed on the pipeline to avoid damage caused by high pipeline temperature during welding
Electronic amplification circuit for sensors;
★The flanges on both sides of the sensor must be kept parallel and concentric with the pipeline, otherwise it is easy to leak and affect the measurement accuracy.
2Requirements for pipeline vibration
Firstly, when selecting the installation location for sensors, try to avoid vibration sources as much as possible. If there is strong vibration at the outlet of the air compressor, sensors cannot be installed
The device should be installed after the gas storage tank; Secondly, elastic hoses can be used for connection, which can be considered for small diameters. Thirdly, installing pipeline supports can reduce
Vibration, such as upstream and downstream of sensors2DInstall fastening devices and add shock-absorbing pads at each location. Fourth, use anti vibration amplification plates.
3Installation requirements for the environment
★The sensor can be used in outdoor areas, and its enclosure protection level isIP65.
★There should be ample space around the installation of sensors, preferably with lighting and power sockets, for easy wiring and regular maintenance.
★Electrical installation should avoid strong external magnetic field interference and electrical noise, and wiring should be kept away from high-power transformers, motors, and high-power power sources
For shielded cables, try to protect them with separate metal sleeves and do not arrange them in parallel with power lines.
★For explosion-proof products, their usage environment should be reviewed according to the explosion-proof mark to ensure compliance with explosion-proof requirements, and during use,
Users are not allowed to change the wiring method of the explosion-proof system on their own, nor are they allowed to open the instrument at will.
4Sensors are installed on the side of horizontal pipelines
Regardless of the type of fluid being measured, sensors can be installed on the upper side of horizontal pipelines. Especially for measuring superheated steam, saturated steam, and high-temperature liquids,
If conditions permit, it is best to use side mounting, so that the temperature of the fluid has less impact on the amplifier.
5Inverted sensor in horizontal pipeline
This installation method is generally not recommended. This installation method is not suitable for measuring general gases and can be used for measuring saturated steam
For measuring high-temperature gases and situations that require frequent cleaning of pipelines, tilting can also be used45°perhaps60°Installation.
6Requirements for bypass pipes
When the fluid in the pipeline that needs to be cleaned or the pipeline where the sensor is installed cannot be stopped for maintenance of the sensor, a bypass can be installed
Connect the pipes as shown in the following figure.
7Installation position of sensor with temperature and pressure external compensation
Installation and use steps of pressure transmitter:
1)Open on the user pipelineΦ12Small hole (there is no strict requirement for this size);
2)Welding internal threaded short pipes;
3)Rotate the valve (with ball valve) and condenser tube in sequence;
4)When using for the first time, close the valve, fill the condenser tube with water, and screw on the pressure transmitter;
This can protect the transformer from being damaged by high-temperature media.
5)During operation, open the valve.
8Requirements for upstream and downstream straight pipe sections
In order to ensure the normal and accurate operation of the instrument, there must be a certain straight pipe section upstream and downstream of the sensor installation point to weaken and eliminate adverse vortices
To adjust the flow field, the requirements for the front and rear straight pipe sections are as follows:
★When the concentric contraction fully open gate valve is used, there should be a sensor upstream15DLong straight pipe section
★When expanding the pipe, there should be a sensor upstream25DLong straight pipe section
★one90°There should be bends and sensors upstream20DLong straight pipe section
★On the same plane2individual90°There should be bends and sensors upstream25DLong straight pipe section
★Different planes2individual90°There should be bends and sensors upstream40DLong straight pipe section
★When there is a regulating valve, there should be a sensor upstream50DLong straight pipe section
The above are the requirements for the upstream straight pipe section, as long as there is a sensor downstream5DLong straight pipe section,DFor sensor aperture
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