What are the main classifications of flow meters? What are the measurement principles?

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How to choose a flow meter?

2. What are the main classifications of flow meters? What are the measurement principles? Generally, there are four types of commonly used flow meters: ① mechanical flow meter, ② electromagnetic flow meter, ③ vortex flow meter, ④ ultrasonic flow meter. ① Mechanical flow meter: commonly known as water meter in daily life, the water meter has a rotating structure inside, and the flowing liquid will cause the structure of the internal fan to rotate. The flow rate and fan speed have a certain proportional relationship, and the faster the rotation speed, the greater the flow through the pipeline. At the same time, some mechanical flow meters can also generate pulse signals to represent flow signals and transmit them to PLC. Mechanical flow meters have mechanical moving parts inside, which are not suitable for sewage or liquids containing impurities such as solids and particles. Excessive impurities can block the fan blades and cause damage to the mechanical flow meter. ② Electromagnetic flowmeter: commonly used in the industrial field, the measured liquid must be water or a conductive liquid. Electromagnetic flowmeters have no moving parts, and their working principle is the same as that of the broad characters. It relies on the law of electromagnetic induction, which is Faradays formula: E=B × L × V (dynamic electromotive force). The flowmeter has two excitation coils on the top and bottom to generate a constant magnetic field B. In this way, the positive and negative charged particles in the fluid will receive the force of the magnetic field "Lorentz magnetic force" and separate. At the same time, the electrodes on both sides of the flowmeter will detect the induced electromotive force (E=B × L × V). The electromagnetic flowmeter calculates the flow rate of the liquid based on the measured electromotive force and the distance L between the electrodes, and finally converts it into flow information for display. ③ Vortex flowmeter, also known as Karman vortex or Karman vortex, is a physics theory proposed by Hungarian American aerodynamicist Feng Karman and a doctoral supervisor of Qian Xuesen in China. Vortex street refers to the phenomenon of unstable boundary layer separation that occurs in a fluid containing a blocking fluid under specific conditions. Two asymmetrically arranged vortices are generated on both sides downstream of the blocking fluid, with one vortex rotating clockwise and the other vortex rotating counterclockwise. The two rows of vortices are arranged in a staggered manner, similar to street lamps, hence the name vortex street. In daily life, when the river flows over obstacles, the Carmen Vortex Street is used. At the inlet of the flowmeter, a blocking fluid will be installed to generate vortex streets. The vortex will impact the pendulum sensor behind the blocking fluid to record the frequency of the vortex. The higher the flow velocity, the higher the vortex street frequency. There is a specific relationship between fluid velocity and frequency, and flow meters obtain flow information through internal chip calculations. ④ Ultrasonic Wheel Wave Flow Meter: Ultrasonic waves are a type of sound wave whose frequency can exceed the frequency perceived by the human ear (the human ear can perceive 16-20000 Hz, while ultrasonic waves are greater than 20000 Hz), hence the name. The characteristics of sound wave propagation in fluids are: fast propagation speed when flowing downstream, slo

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