Flow measurement is the science of studying the change of matter, and the law of mass mutual change is the basic law of the development of the relationship between things. Therefore, the measurement object is not limited to the pipeline liquid in the traditional sense. Wherever it is necessary to master the quantitative change, there is a problem of flow measurement. Flow rate, pressure and temperature are listed as the three major detection parameters. For a certain fluid, as long as these three parameters are known, the energy it has can be calculated, and these three parameters must be detected in the measurement of energy conversion. Energy conversion is the basis of all production processes and scientific experiments, so flow and pressure and temperature instruments are the most widely used.