Ultrasonic Open Channel Flowmeter 4-20mA IP65 Non-Contact Measurement

The ultrasonic open channel flowmeter is an instrument that uses ultrasonic principles to measure the liquid level height in open channels (such as drainage channels, rivers, and non-full pipes, etc.), and then combines standardized geometric dimensions and hydraulic models to calculate the fluid flow rate.

• Non-contact measurement: The sensor does not come into contact with sewage or corrosive liquids, is not affected by medium corrosion, foam or suspended solids, and has a long service life.
• Easy installation: It only needs to be installed above the channel, does not affect the water flow, and there is no need to cut off the channel.
• Low maintenance: There are no moving parts, and it is not prone to clogging.
• Powerful functions: It can display instantaneous/cumulative flow, and has multiple signal outputs and communication interfaces.

• Ultrasonic Flowmeter Host (Secondary Instrument)
• • Ultrasonic probe: The core sensor, responsible for transmitting and receiving sound waves.
  • Host/Transmitter: Processes time signals, calculates the liquid level, and converts the liquid level into instantaneous flow and cumulative flow based on the built-in mathematical model (formula). It usually comes with display, data storage, and output functions (4-20mA, RS485, relay, etc.).
• Standard Weir (Primary Component)

  This is the foundation of the entire measurement, its role is to form a stable water level-flow relationship at a specific location. Common types include:

  • Parshall Flume: The most commonly used type, with a constricted throat that can create a backwater effect, strong sediment passing capacity, and low head loss.
    • Features: It has standard sizes such as BS, LH, SH types, etc., and each size corresponds to a fixed empirical formula.
  • Triangular Weir/Rectangular Weir (Weir): Install a baffle with a notch (triangular or rectangular) in the channel.
    • Features: High measurement accuracy, but large head loss and prone to accumulation of debris.
  • Submersible: Suitable for non-full flow conditions where the water flow fills the pipe or culvert.

Key point: The ultrasonic flowmeter itself does not generate the flow formula; it only measures the liquid level and then uses the corresponding weir formula to calculate the flow. Selecting the wrong weir type or inputting incorrect weir dimensions will result in completely incorrect measurement results.

• Determine channel conditions: flow range, channel shape and size, water quality (whether it contains a large amount of floating debris and sediment).
• Select weir type: Choose between Parshall flume, triangular weir, etc. based on flow range, accuracy requirements and allowable head loss.
• Select instrument range: Determine the measurement blind zone and range of the instrument based on channel depth and maximum water level.
• Output and communication: Select 4-20mA, pulse output or RS485/MODBUS and other communication protocols based on requirements.

• Weir Channel Installation:
• Must be installed horizontally. There should be sufficient straight channel sections upstream and downstream (typically 5-10 times the channel width upstream and 3-5 times the channel width downstream) to ensure smooth water flow.
• Flowmeter Installation:
  1. Should be installed directly above the maximum water level of the weir channel.
  2. The probe face should be perpendicular to the water surface.
  3. Avoid the turbulent areas near the inlet and outlet of the weir channel.
  4. Ensure that the distance between the probe and the water surface is greater than the blind zone of the instrument at the highest water level (e.g., 0.3m to 0.5m).
  5. For larger channels, it is recommended to use a fixed bracket to prevent shaking.

Summary: The ultrasonic open channel flowmeter is a system that combines both hardware and software. Its accuracy is half dependent on the quality and installation of the hardware (the meter and standard flume), and the other half on the correctness of the software (the internal parameter settings of the meter). Correct selection, standardized installation and regular maintenance are the keys to ensuring its long-term stable operation.