Principle characteristics of submersible electromagnetic flowmeter

Submersible electromagnetic flowmeter is a kind of flowmeter used for open channel flow measurement by combining the measurement principle of electromagnetic flowmeter with the working principle of throttling device. In the section of the channel, set a gate with a hole, install the submersible electromagnetic flow sensor in the hole of the gate, let the water flow through the sensor, and measure the flow through the electromagnetic flow sensor based on the principle of flow continuity. Drain submersible electromagnetic flowmeter is a kind of flowmeter used for open channel flow measurement by combining the measurement principle of electromagnetic flowmeter with the working principle of throttling device. In the section of the channel, set a gate with a hole, install the submersible electromagnetic flow sensor in the hole of the gate, let the water flow through the sensor, and measure the flow through the electromagnetic flow sensor based on the principle of flow continuity. Channel flow.　　 Similar to the throttling device, when the water flows naturally, the average flow velocity of the channel is relatively low, and the perforated gate will cause the water level difference between the upstream and downstream. According to the rules of energy conversion, the water level difference converts the low flow velocity in the open channel into a higher average flow velocity in the measuring tube. Assuming that the water level difference between the upstream and downstream is h, the acceleration of gravity g, the local resistance coefficient F, and the average flow velocity in the measuring pipe hole is, then 　　 This means that the flow of the channel can be measured by measuring the flow of the diving electromagnetic flow sensor. In order to reduce the local resistance and make the water entering the sensor measuring tube meet the precondition of symmetrical flow velocity distribution in the central axis, the sensor measuring tube must be equipped with nozzle-shaped diversion tubes (diversion nozzles, commonly known as bell mouths) before and after the sensor measuring tube. Figure 2.28 shows the working principle of a submersible electromagnetic flowmeter.　　According to the analysis, the flow velocity through the duct is only related to the upstream and downstream head loss h, and the approaching velocity and the far velocity upstream and downstream of the channel have little effect on it. Therefore, a dummy sensor (simulated sensor) with the same geometric size as the sensor can be installed on the gate. At this time, the average flow velocity flowing through the pipe of the simulated sensor is the same as the flow velocity measured by the sensor. In this way, multiplying the flow measured by the diving electromagnetic flowmeter by the total number of simulated sensors and diving sensors, the flow of the open channel can be obtained. Figure 2.29 shows an example of a submersible electromagnetic flowmeter plus a simulated sensor.　　 Submersible electromagnetic flowmeter is a flowmeter with high measurement accuracy among open channel flowmeters. It not only has all the characteristics of electromagnetic flowmeter, but also is not affected by tidal sand and river rise downstream of the channel. However, it should be noted that when the flow rate is small, the water cannot fill the measuring tube. At this time, a weir plate needs to be installed downstream of the sensor to raise the water level; when the flow rate is too large, the water level difference will raise the upstream water level too high, causing the upstream to overflow. Simulated sensors should be added to increase the circulation area to reduce the water level.