Features of Ultrasonic Open Channel Flow Meters and Installation Considerations
Ultrasonic Open Channel Flow Meter Features:
1. When the liquid level is below the lowest acoustic path, it can function as a weir flume flow meter (based on the functional relationship between liquid level and flow velocity).
2. There are no restrictions on the cross-section of the measured channel (pipe, culvert), and channel widths up to hundreds of meters can be measured.
3. Since flow rate is calculated based on actual measured flow velocity and liquid level (cross-sectional area), it offers higher measurement accuracy than weir, flume, or channel-type flow meters that only measure liquid level.
4. Multi-path measurement is achievable, with measurement accuracy improving as the number of acoustic paths actually participating in the measurement increases.
Installation Considerations for Ultrasonic Open Channel Flow Meters:
1. When the straight pipe section on site is insufficient, acoustic paths should be arranged in a crossed configuration within the measurement section to compensate for the impact of skewed flow on velocity measurement accuracy.
2. Actual velocity measurement is based on the premise of relatively uniform flow conditions in the channel, which requires the straight section length of the channel (pipe) to meet specified requirements.
3. If facilities such as weirs or gates before and after the on-site measurement section cause vertical flow turbulence, a multi-path measurement method should be adopted to achieve accurate measurement of the average cross-sectional flow velocity.
The determination of the number and height of acoustic paths should be based on measurement accuracy requirements, while also considering the minimum water level, maximum water level, and working water level.
4. For channel-type flow meters, while accurate measurement of flow velocity and water level is certainly important, the most significant factor affecting flow measurement is often the error in the channel cross-sectional area
(such as errors caused by sediment deposition at the channel bottom, uneven channel walls, inconsistent channel width, etc.). Therefore, it is particularly emphasized here that controlling channel cross-sectional area errors requires precise construction of the channel civil works according to design specifications.