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Types of liquid flow meters and principles
sales01@cxflowmeter.com
According to the scene where the flowmeter is used, it can be divided into the flowmeter used in the pipeline and the flowmeter used in the open channel.
According to the scene where the flowmeter is used, it can be divided into the flowmeter used in the pipeline and the flowmeter used in the open channel.
1. Flowmeters used in pipelines
The working principle of the vortex flowmeter is that when a column is vertically inserted into the measuring tube, the fluid passes through both sides of the column to alternately generate regular vortices (as shown in the figure), which is called the Karman vortex street. Therefore, it is called a vortex flowmeter. The release frequency of the Karman vortex street is related to the flow velocity and the column width. A pressure sensor is placed at the vortex at the back end of the column to measure the frequency of pressure change, so that the speed of liquid flow can be calculated, and then the flow rate of the pipe can be calculated according to the cross-sectional area of the pipe.
Advantages of vortex flow meter: vortex flowmeter has no moving parts, the measuring element has a simple structure, reliable performance, long service life and high accuracy;
Disadvantages of vortex flowmeter: poor adaptability to measuring dirty media, high requirements for straight pipe sections, and poor anti-vibration performance.
Turbine flowmeter is a kind of velocity flowmeter, which uses gas to drive the impeller of the flowmeter to rotate, and the speed of the impeller rotation is proportional to the volume flow of the fluid. The flow rate is proportional to the pulse signal, the flow rate of the liquid is obtained after calculation, and then the flow rate of the pipe is calculated according to the cross-sectional area of the pipe.
Advantages of turbine flowmeter: compact and lightweight structure, easy installation and maintenance, and large flow capacity.
Disadvantages of turbine flowmeters: It is impossible to maintain the accuracy for a long time, and the cleanliness of the medium is required to be high, and it is not suitable for places where the flow rate changes rapidly.
According to Faraday's law of electromagnetic induction, when a conductor moves in a magnetic field to cut magnetic lines of force, an induced potential e is generated at both ends of the conductor, and its direction is determined by the right-hand rule, and its magnitude is the same as the magnetic induction intensity B of the magnetic field. The conductor is in the magnetic field. The length L of the conductor is proportional to the moving speed u of the conductor. When the magnetic induction intensity B of the magnetic field and the length L of the conductor in the magnetic field are constant, the flow velocity of the liquid can be calculated according to the electric potential e, and then the pipe can be calculated according to the cross-sectional area of the pipe. traffic.
The advantages of electromagnetic flow meter: the structure of the transmitter is simple, the electromagnetic flowmeter has no mechanical inertia, has a sensitive response, can measure the instantaneous pulsating flow, and has good linearity.
Disadvantages of electromagnetic flowmeters: Electromagnetic flowmeters are susceptible to external electromagnetic interference. At present, electromagnetic flowmeters cannot be used to measure liquid media with very low conductivity. The conductivity of the measured liquid medium cannot be lower than 10-5 (S/ cm), which is equivalent to the conductivity of distilled water, and is powerless to petroleum products or organic solvents.
2. Flow meters used in open channels
There are two kinds of flowmeters used in open channels, one is Doppler ultrasonic flowmeter and the other is radar flowmeter.
Doppler ultrasonic flowmeter:
The Doppler ultrasonic flowmeter uses the Doppler frequency shift physical principle to measure the water flow velocity, and then adds a sensor to measure the water depth, and the water flow can be calculated by inputting information such as the width of the river surface. Due to the low frequency of ultrasonic waves, which can penetrate liquids, they are mostly suitable for measuring fluids containing solid particles or bubbles, but not for measuring pure water. Because the frequency is low, the Doppler frequency difference generated when measuring moving objects is small, so the measurement accuracy is relatively poor, and the ultrasonic flowmeter is installed at the bottom of the river, which is easily buried by sediment and requires frequent maintenance and cleaning. It is very troublesome to use and maintain in the field. In addition, the frequency emitted by the Doppler source is greatly affected by temperature, which causes the measurement result to be greatly affected by temperature.
The radar flowmeter also uses the Doppler frequency shift physical principle to measure the water flow speed, but the radar frequency is very high. According to the same speed according to the Doppler principle, the higher the frequency, the larger the Doppler frequency difference, so that in the processor The accuracy of the measurement can also be very high in the case of limited computing power. The frequency of the radar flowmeter is so high that it cannot penetrate the water, so even the flow rate of clear pure water can be measured. The radar flowmeter is installed above the water surface and does not contact the water surface, so there is no risk of being buried in sand, and almost no maintenance is required in the field. The radar current meter of Beijing Zhongke Blue Electric Technology Co., Ltd. adopts the frequency source of the phase-locked loop circuit. The transmission frequency is not affected by the temperature at all, and the measurement accuracy of the temperature in the range of -40-85 degrees is not affected. The shell is treated with baking varnish, and the corrosion resistance is particularly good. The plastic cover is made of asa plastic, which is resistant to ultraviolet rays for 10 years and has a waterproof level of IP68. It is extremely reliable in field use and requires no maintenance during use. The adjustment of parameters is remotely operated with a 4G IoT module can. The radar water level gauge installed on the radar flow of Beijing Zhongke Blue Electric Technology Co., Ltd. adopts FMCW modulation, which achieves very high measurement accuracy, and is much more sensitive than the current radar level gauge of the pulsed horn. The antenna adopts FMCW modulation. The first is the microwave lens antenna, which is very small in size and has a very small beam, which avoids the problem that the horn antenna is likely to cause spiders to form webs in the wild and affect the measurement.
If you want to know more detailed parameters and quotations of different flow meters, please contact winny: sales01@cxflowmeter.com
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