The mass flowmeter is that the volume of fluid is a function of fluid temperature and pressure, and is a dependent variable. The mass of fluid is a variable that does not change with time, space temperature and pressure. As mentioned above, among the constant flow meters, such as orifice flowmeter, laminar mass flowmeter, turbine flowmeter, vortex flowmeter, electromagnetic flowmeter, rotary flowmeter, ultrasonic flowmeter and elliptical flowmeter, the flow measurement value is the volume flow of fluid. The fluid quantity involved in scientific research, production process control, quality management, economic accounting, trade handover and other activities is generally quality. The volume flow of the fluid measured by the above flowmeter cannot meet the requirements of the flowmeter, and it is usually necessary to obtain the mass flow of the fluid. Previously, the fluid mass could only be obtained indirectly through correction, conversion and compensation after measuring the parameters such as temperature, pressure, density and volume of the fluid.
This measurement method has many intermediate links, and the accuracy of mass flow measurement is difficult to be guaranteed and improved. With the development of modern science and technology, some metering methods and devices for direct measurement of mass flow have emerged, which has promoted the progress of flow measurement technology.
The instruments for measuring fluid flow are collectively called flowmeters or flowmeters. Flowmeters are important instruments in industrial measurement. With the development of industrial production, the requirements for the accuracy and scope of flow measurement are increasing. Flow measurement technology is new. In order to adapt to various ways, various types of flowmeters have been introduced one after another. There are more than 100 kinds of flow meters that have been put into operation before.
Classify according to the structure principle of flowmeter. There are volumetric flowmeter, differential pressure flowmeter, floating flowmeter, turbine flowmeter, electromagnetic flowmeter, vortex flowmeter, mass flowmeter and plug-in flowmeter among fluid oscillation flowmeters.
According to the survey object, there are two categories: closed pipeline and open channel.The total meter measures the flow through the pipeline in a short period of time, which is expressed by dividing the total flow in a short period of time by the quotient of the time. In fact, the flowmeter is usually equipped with a cumulative flow device, which is used as a total meter to make the flow. The total meter is also equipped with a flow transmitter. Therefore, it is of practical significance to divide the flowmeter and the total meter in a strict sense.
Classification according to measurement principle
1. Mechanical principle: differential pressure type and rotary type of Bernoulli theorem for instruments of this kind; Impulse form and movable tube form of Li’s momentum theorem; The direct mass formula of Leighton’s law; The target formula of fluid momentum principle; The turbine formula of Li’s momentum theorem; The vortex type and vortex street type of the fluid oscillation principle; The pipe type, volume type, weir type and trough type with total static pressure difference.
2. Electrical principle: Instruments based on this principle include electromagnetic type, differential capacitance type, inductive type, strain resistance type, etc.
3. Acoustical principle: ultrasonic and acoustic (shock wave) methods are used for flow measurement based on acoustic principle.
4. Optical principle: laser type, photoelectric type and other instruments belong to this principle
Post time: 21-10-22