Classification and working principle of open channel flowmeter

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  Classification and working principle of open channel flowmeter

  Open channel flowmeter is different from other closed full pipe flow instruments. It is a flow instrument with free toilet surface and natural flow in non full pipe state or open channel. Open channel flowmeter based on open channel principle is widely used in open channel flow measurement because of its low price and simple use. According to different measurement principles, open channel flowmeter can be divided into ultrasonic open channel flowmeter, Doppler open channel flowmeter and multi-channel open channel flowmeter. They are all system monitoring equipment for measuring fluid flow in open channels or channels. The open channel flowmeter monitoring system is applicable to the flow measurement of rectangular and trapezoidal open channels and culverts such as reservoirs, rivers, water conservancy projects, urban water supply, farmland irrigation, sewage treatment, water administration and water resources, as well as all urban water supply diversion channels, power plant cooling diversion river drainage channels, sewage treatment inflow and discharge channels Wastewater discharge from industrial enterprises and channels for water conservancy projects and agricultural irrigation. According to different installation requirements, it is divided into fixed open channel flowmeter and portable open channel flowmeter. Portable open channel flowmeter is divided into two types: ordinary measurement and comparative measurement.

  working principle:

  1、 Ultrasonic open channel flowmeter:

  Using the open channel technology, based on the velocity water level calculation method, the flow is obtained by measuring the fluid level height, combined with the geometric size of the standard weir groove, slope coefficient, channel accuracy, hydraulic ramp and velocity vertical plane correction coefficient, and then calculated by the microprocessor in the instrument. Due to non-contact measurement, open channel flowmeter can be used in harsh environment. Under the control of microcomputer, the open channel flowmeter transmits and receives ultrasonic waves, and calculates the distance between the open channel flowmeter and the measured liquid level according to the transmission time, so as to obtain the liquid level height. Because there is a certain proportional relationship between the liquid level and flow, the liquid flow Q can be finally obtained according to the calculation formula.

  2、 Doppler open channel flowmeter:

  Using the contact measurement method, the sensor is placed at the bottom of the channel. Through the velocity area method, between the two probes, the system calculates the overflow velocity according to the Doppler time effect, and then calculates the instantaneous flow according to the formula through the cross-sectional area of the area where the sensor is located.

  3、 Multichannel open channel flowmeter

  Also known as TDOA open channel flowmeter, it belongs to on-line measurement. The ultrasonic time difference method is used to measure the water velocity. Install the ultrasonic time difference velocity meter sensor on both sides of the channel to measure the average velocity in the water, measure the water level height through the ultrasonic water level meter, calibrate the hydraulic model through the flowmeter integrator, and calculate the instantaneous flow of the open channel.