Flow meter is an instrument used to measure the flow of fluids in pipelines or open channels. It measures various media, including gas, liquid, slurry, and steam. In the field of automation, flowmeters play an important role as front-end instruments. Each product of flow meter not only has its specific applicability, but also has its limitations. According to the measurement object, there are two categories of closed pipes and open channels; according to the purpose of measurement, it can be divided into total measurement and flow measurement. The instrument are called total meter and flow meter respectively.