Flowmeters are further divided into rotary flow meters, throttling flow meters, slit flow meters, volumetric flow meters, electromagnetic flow meters, ultrasonic flow meters, and weirs. Classified by medium: liquid flow meters and gas flow meters.

Flow measurement is widely used in various fields such as industrial and agricultural production, national defense construction, scientific research, foreign trade, and people's lives. In the production of the petroleum industry, flow measurement runs through the entire process from oil extraction, transportation, refining and processing to trade sales. Any link cannot be separated from flow measurement, otherwise normal production and trade exchanges of the petroleum industry cannot be guaranteed. In the chemical industry, inaccurate flow measurement can lead to imbalance in the distribution ratio of chemical components, inability to ensure product quality, and even serious production safety accidents. In the production of the power industry, the measurement and regulation of medium flow rates such as liquids, gases, and steam play an important role. The accuracy of flow measurement not only has great economic significance for ensuring the operation of power plants under optimal parameters, but also has become an important link in ensuring the safe operation of power plants with the development of high-temperature, high-pressure, and large capacity units. If the instantaneous feed water flow of a large capacity boiler is interrupted or reduced, it may cause serious dry pot or pipe explosion accidents. This requires the flow measurement device not only to achieve accurate measurement, but also to send out alarm signals in a timely manner. In the production of the steel industry, the flow measurement of circulating water and oxygen (or air) during the steelmaking process is one of the important parameters to ensure product quality. In industries such as light industry, food, and textiles, flow measurement is also indispensable.

The commonly used transducers are external clamp type and plug-in type. The single channel ultrasonic flow meter has a simple structure and is convenient to use, but it has poor adaptability to changes in flow distribution. The rapid development of microelectronics and computer technology has greatly promoted the upgrading of instruments, and new types of flow meters have emerged like mushrooms after rain. So far, it is said that over a hundred types of flow meters have been put into the market, and many thorny problems in on-site use are expected to be solved. The work on modern flow measurement technology in China was relatively late and was set at the upstream end of measurement flow channel 6, relative to holes 11 and 12, to reduce the flow of measured fluid into holes 11 and 12; Measurement control component 19 for measuring the propagation time of ultrasonic waves between ultrasonic transducers 8 and 9; And a calculation component 20 for calculating the flow rate based on the signal of the measurement control component 19.

Flowmeters should avoid ferromagnetic objects and equipment with strong electromagnetic fields (such as large motors, transformers, etc.) as much as possible to avoid the magnetic field affecting the working magnetic field and flow signal of the sensor. The flow signal line and excitation line between the sensor spoon converter. However, based on the analysis of damaged components in lightning faults, most of the induced high voltage and surge current that caused the faults were introduced from the power lines in the control room, while the other two approaches were relatively few. Due to the fact that electromagnetic flow meters have a much higher chance of measuring suspended solids or dirt than other flow instruments, the probability of failure caused by the attachment layer on the inner wall is relatively high. If the conductivity of the adhesive layer is similar to that of the liquid. Common debugging failures are usually caused by improper installation.