Doppler flowmeter for drainage networks: a method for measuring flow in small-diameter drainage pipelines.

　　At this stage, overseas there have also been instances of… Doppler flowmeter for drainage networks (24V) is tightly integrated with the expansion bladder and bent pipe; the bladder is inserted into the pipeline and expanded under pressure, causing the pipeline to be fully purged. An electromagnetic flowmeter is then used to measure flow in small-diameter drainage networks.

　　The advantage of this method is that it achieves very high measurement accuracy even at high flow velocities, such as 2 m/s.

　　The shortcomings of this method are quite apparent:

　　In small-diameter drainage networks, particularly for measuring inflow and infiltration, flow velocities are generally very low, whereas electromagnetic flowmeters are only suitable for flow rates exceeding 0.5 m/s.

　　In domestic drainage networks, the presence of debris often leads to sediment buildup in Doppler flow meters, reducing the effective cross-sectional area for flow and adversely affecting the performance of electromagnetic flow meters.

　　Different pipe diameters require correspondingly matched electromagnetic flowmeters; electromagnetic flowmeters of different sizes are not interchangeable. Therefore, the electromagnetic flowmeter should be replaced according to the specific pipe diameter.

　　The commonly used pipe diameters are DN100, DN150, and DN250; however, the electromagnetic flowmeters for DN150 and DN250 are too heavy for a single person to assemble inside a sewage inspection chamber.

　　In practical applications, there may be situations where the pipe is fully filled; under such circumstances, Doppler flowmeter for drainage networks In the soaking wastewater, equipment lifespan is compromised.

　　Electromagnetic flowmeters require a straight‑run length of at least 5 diameters upstream and 3 diameters downstream; accordingly, the custom‑made downstream straight section is insufficient in length.

　　Due to the aforementioned challenges, this measurement method exhibits limited applicability in small-diameter drainage networks.

　　The method used by cross-correlation flowmeters to measure flow velocity is based on the principle of ultrasonic reflection.

　　During operation, the flowmeter sensor emits a single ultrasonic pulse at a fixed angle. When this pulse encounters reflective surfaces in the rainwater or wastewater—such as fine particulates, mineral deposits, or gas bubbles—the resulting radar echoes are recorded either as images or as radar echo waveforms. After an interval of several seconds, a second scan is performed, and the corresponding radar echo images or waveforms are again stored. Since these reflective surfaces move synchronously with the flow of rainwater or wastewater, by comparing the intrinsic relationships between the two successive images or waveforms, the locations of the reflective surfaces can be identified, enabling the measurement and calculation of flow velocity.