About the choice of water flow measurement instrument
The measurement of water flow is not difficult. Most of the flowmeters of different principles can be used to measure the flow of water, but it is not a matter of just installing one and it will definitely work well. The following is a simple analysis of the pros and cons of the flow meters used to measure various water quality flows. 1. Measurement objects with high sediment content. Water flow measurement objects with high sediment content are common in raw water. For example, the measurement of water flow is not difficult. Most of the flowmeters of different principles can be used to measure the flow of water, but it is not a matter of just installing one and it will definitely work well. The following is a simple analysis of the pros and cons of the flow meters used to measure various water quality flows. 1. Measurement objects with high sediment content. Water flow measurement objects with high sediment content are common in raw water. If a throttling differential pressure flowmeter or an average velocity tube differential pressure flowmeter is selected, the pressure taking valve and the sewage valve are often blocked by the sediment, which affects the use. In contrast, plug-in vortex flowmeters and plug-in electromagnetic flowmeters do not have such a situation. Large-caliber water flowmeters tend to have low flow rates, and sediment in the water is easy to deposit on the inner wall of the measuring tube, which reduces the flow cross-sectional area, resulting in a high flow rate, so it should be cleaned regularly. 2. Measurement objects used for process monitoring and control. Water flow meters for process monitoring and control generally do not require as high measurement accuracy as those used for trade settlement. The main considerations are reliability, price, and the type of output signal. In the old devices of industrial and mining enterprises, the most used is still the throttling differential pressure flowmeter. In new installations, people prefer to use vortex flowmeters. This is because the installation of throttling differential pressure flowmeters is complicated, the maintenance workload is large, and the pressure loss is large. Installation and maintenance are very simple, so the throttling type differential pressure flowmeter is squeezed out of the market in water flow measurement. But the vortex flowmeter can only solve part of the water flow measurement problem, because the vortex flowmeter with a larger caliber is more expensive than the electromagnetic flowmeter with the same caliber, and the vortex flowmeter with the largest caliber can only be DN300~DN400. The smallest diameter vortex flowmeter is now DN15, and its minimum measurable water flow is 0.32/m3h, while the electromagnetic flowmeter’s diameter is from DN2.5 to DN3000, and the measurable flow is from 0.0053 to 305000m3/h, so the coverage Much wider than the vortex flowmeter. In terms of the lowest flow rate that can be measured, the vortex street can only reach about 0.4m/s, while the electromagnetic flowmeter can measure normally at 0.1m/s. The price of large-caliber electromagnetic flowmeters is also very expensive. The economical solution is to choose plug-in flowmeters. Commonly used are averaging tube, plug-in vortex flowmeter and plug-in electromagnetic flowmeter, etc. The plug-in vortex flowmeter can be measured. The lower limit of the flow rate is 0.32m/s, and the electromagnetic flow probe can measure the lower limit of the flow rate is unlimited, but the error is slightly larger, about (±0.2%R+1mm/s) 3. The measurement object is in a gas-liquid equilibrium state. For water in a gas-liquid equilibrium state, such as boiler deaerator water tank outlet water, to measure its flow, the flow meter should be installed after the booster pump. If it is installed before the booster pump, the flow will always flow through the flow meter. There is a certain pressure loss. The water in the gas-liquid equilibrium state will cause part of the liquid to vaporize due to the pressure drop, causing the flowmeter to show a high value. 4. Sewage flow measurement. Sewage is characterized by dirty, and some are corrosive. The sewage conveyed by the pipeline can be measured by electromagnetic flowmeter, and the sewage discharged through the open channel is suitable for measurement by the open channel flowmeter. 5. Flow measurement of deionized water. Deionized water and high-purity distilled water are water with extremely high purity, and their conductivity is about 3 orders of magnitude lower than the conductivity that can be measured by a general-purpose electromagnetic flowmeter, so they cannot be measured with an electromagnetic flowmeter.
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