Open channel flow meters are divided into ultrasonic open channel flow meters, Doppler open channel flow meters, and multi-channel open channel flow meters according to different measurement principles. They are all system monitoring devices for measuring fluid flow in open channels or channels. The open channel flowmeter monitoring system is suitable for measuring the flow of rectangular and trapezoidal open channels and culverts in reservoirs, rivers, water conservancy projects, urban water supply, sewage treatment, agricultural irrigation, water management and water resources. In recent years, it has been widely used.
working principle:
Ultrasonic Open Channel Flowmeter
Using open channel technology, based on the velocity water level calculation method, the flow rate is obtained by measuring the fluid level height, combining the geometric dimensions of the standard weir groove, slope coefficient, channel accuracy, hydraulic slope, and vertical plane correction coefficient of the flow velocity. The flow rate is then calculated by the internal microprocessor of the instrument. Due to its non-contact measurement, open channel flow meters can be applied in harsh environments. Under the control of a microcomputer, the open channel flowmeter emits and receives ultrasonic waves, and calculates the distance between the open channel flowmeter and the measured liquid level based on the transmission time, thereby obtaining the liquid level height. As there is a certain proportional relationship between the liquid level and the flow rate, the liquid flow rate Q can be obtained based on the calculation formula.
Doppler open channel flowmeter
Using the contact measurement method, the sensor is placed at the bottom of the channel. Using the velocity area method, the system calculates the water flow velocity based on the Doppler time effect between the two probes, and then calculates the instantaneous flow rate according to the formula based on the cross-sectional area of the area where the sensor is located.
Multi channel open channel flowmeter
Also known as time difference method open channel flowmeter, it belongs to online measurement. Use ultrasonic time difference method to measure water flow velocity. Install ultrasonic time difference flowmeter sensors on both sides of the channel to measure the average flow velocity in the water. Measure the water level height using an ultrasonic water level gauge and calibrate the hydraulic model using a flow meter integrator to calculate the instantaneous flow rate of the open channel.
Purpose:
Open channel flowmeterThe application field includes urban water supply channels, cooling water supply channels for thermal power plants, drainage channels for sewage treatment inflow and discharge, industrial wastewater discharge, as well as channels for water conservancy engineering and agricultural irrigation.
Selection precautions:
1. The accuracy level and function are selected by the user based on measurement requirements and usage scenarios, achieving cost-effectiveness. For example, in situations such as trade settlement, product handover, and energy measurement, Doppler open channel flow meters with high accuracy levels should be selected; For process control applications, choose different accuracy levels according to control requirements; In some cases where only flow detection is needed without precise control and measurement, ultrasonic open channel flow meters with slightly lower accuracy levels can be selected;
2. If you want to measure flow velocity indicators, you need to choose a Doppler open channel flowmeter or a multi-channel open channel flowmeter; If only measuring flow is selected, an ultrasonic open channel flowmeter can be used;
3. Fluid characteristics mainly refer to the pressure, temperature, density, viscosity, compressibility, etc. of gas. As the volume of gas varies with temperature and pressure, compensation and correction should be considered.
4. Instrument performance refers to the accuracy, repeatability, linearity, range ratio, pressure loss, initial flow rate, output signal, and response time of the instrument. When selecting a flowmeter, careful analysis and comparison of the above indicators should be carried out to select an instrument that can meet the flow requirements of the measuring medium.
5. The installation conditions refer to the flow direction of gas, the direction of the pipeline, the length and diameter of the upstream and downstream straight pipes, the spatial position, and the fittings, all of which will affect the accurate operation, maintenance, and service life of the gas flow meter.
6. Economic factors refer to purchase costs, installation costs, maintenance costs, calibration costs, and spare parts, which are also affected by the performance, reliability, and lifespan of gas flow meters.
characteristic:
Large measurement range, flow measurement is not affected by the backflow of tributaries.
During measurement, the flow sensor is not affected by floating sediment, bubbles, and significant changes in water level. It has a simple structure, small volume, and easy installation, which can cause resistance to water flow.
Standard channels do not require modification and can be installed directly, with low installation and construction costs.
The instrument display output function is complete, which can display measurement data such as water level, flow rate, flow rate, and cumulative flow rate, and has RS-485 communication interface.
◆ It has the function of water level, mud level, and flow rate exceeding the limit alarm.
◆ It has data saving function, which can save the set parameters and flow values in case of long-term power outage.
Technical advantages:
Open channel flow meters are different from other closed full pipe flow meters in that they are flow meters with free surface flow in non full pipe conditions or open channels. The open channel flowmeter based on the open channel principle is widely used in open channel flow measurement due to its low cost and simple operation.