Ultrasonic open channel flow meters are widely used for monitoring water, wastewater, and industrial effluents. They offer non-contact measurement, making them ideal for environments where contamination, corrosion, or clogging is a concern. This guide explains how they work and what factors you must consider before purchasing one.

1. Working Principle

An ultrasonic open channel flow meter operates by using an ultrasonic sensor to measure the liquid level in an open channel. It then combines this level data with the preset geometry of the channel (such as Parshall flumes, V-notch weirs, or rectangular weirs) and hydraulic formulas to calculate instantaneous flow and totalized flow.

Key Advantages:

  • Non-contact measurement – no direct contact with liquid
  • Highly resistant to corrosion
  • Minimal risk of clogging
  • Easy installation and low maintenance

2. Key Factors When Choosing an Ultrasonic Open Channel Flow Meter

A. Fluid Type and Operating Conditions

  • Medium: Is it clean water, wastewater, rainwater, or a chemical liquid?
    • For corrosive liquids, choose sensors with PTFE-coated probes.
  • Surface Conditions: Does the surface have foam, steam, turbulence, or floating debris?
    • Opt for devices with false echo suppression and advanced signal processing.
  • Temperature: For outdoor or extreme environments, check the meter’s operating temperature range.

B. Measurement Range and Accuracy

  • Range: Ensure the device can handle your maximum and minimum flow rates.
  • Accuracy:
    • Standard applications: ±2–3%
    • High-precision cases (e.g., trade billing): ±1% or better

C. Weir/Flume Type and Dimensions

The type and size of the channel structure are crucial. Make sure the flow meter supports your specific weir (V-notch, rectangular) or flume (Parshall, Palmer-Bowlus) and can be calibrated accordingly.

If you haven’t installed the structure yet, choose standardized weirs and flumes for easier integration.

D. Features and Outputs

  • Output Signals: 4–20mA analog output, relay alarms, RS485 Modbus for SCADA systems
  • Remote Monitoring: Wireless options like NB-IoT, 4G, or LoRa for smart water networks
  • Display: Local display with intuitive menus and multi-language support
  • Data Logging: Built-in storage to prevent data loss during outages
  • Power Supply: Options include 220V AC, 24V DC, or solar power for remote locations

E. Installation and Protection

  • Check installation space and avoid mounting above foam or heavy turbulence.
  • Protection Rating:
    • Main unit: IP65 (dustproof & water-resistant)
    • Sensor: IP67/IP68 for submersion resistance

For installation tips, visit Aister Instruments’ guide on ultrasonic open channel flow meters.

Some of the leading ultrasonic open channel flow meter manufacturers include:

  • Aister – Known for cost-effective solutions for industrial applications
  • Q&T Instrument – Advanced ultrasonic technology for open-channel monitoring
  • Pulsar Measurement, Lanry Instruments, and FLO-CORP – Trusted globally for accuracy and durability

Final Thoughts

Choosing the right ultrasonic open channel flow meter depends on your medium, installation environment, accuracy needs, and data requirements. Always verify compatibility with your weir/flume type, consider communication outputs, and check protection ratings for long-term reliability.

When in doubt, consult reputable manufacturers like Aister, Q&T to ensure you get a solution tailored to your application.