Features of Ultrasonic Open Channel Flowmeter and Installation Precautions
Ultrasonic open channel flowmeter features:
1. When the liquid level is below the lowest acoustic path, it can be used as a weir or flume flowmeter (based on the functional relationship between liquid level and flow velocity).
2. The cross-section of the measured channel (pipe, culvert) is not limited, and the channel width can be up to hundreds of meters.
3. Since the flow rate is calculated based on actual measured velocity and liquid level (cross-sectional area), it offers higher accuracy compared to weir, flume, or channel flowmeters that only measure liquid level.
4. Multi-path measurement is supported, and measurement accuracy improves with the number of acoustic paths actually participating in the measurement.
The following issues should be noted during the installation of an ultrasonic open channel flowmeter:
1. When the straight section of the field is insufficient, the impact of oblique flow on velocity measurement accuracy should be compensated by arranging acoustic paths crosswise in the measurement section.
2. The measured velocity is based on the assumption that the flow regime in the channel is relatively uniform, which requires that the straight section of the channel (or pipe) meets the required length.
3. If there are weirs, gates, or other structures before and after the field measurement section that disturb the vertical flow regime, a multi-path measurement method should be adopted to accurately measure the average flow velocity over the cross-section.
The number of acoustic paths and their heights should be determined based on measurement accuracy requirements, while also considering the minimum water level, maximum water level, and operating water level.
4. For channel-type flowmeters, accurate measurement of velocity and water level is certainly important, but the error in the cross-sectional area of the channel often has the greatest impact on flow measurement
(e.g., errors due to sediment deposition at the bottom, uneven channel walls, inconsistent channel width, etc.). Therefore, it is emphasized here that to control the cross-sectional area error, the civil construction of the channel must be carried out precisely according to the design.