1. Mechanics principle: The instruments that belong to this kind of principle include differential pressure type and rotor type using Bernoulli's theorem; impulse type and movable tube type using momentum theorem; direct mass type using Newton's second law.
The target type using the principle of fluid momentum; the turbine type using the angular momentum theorem; the vortex type and vortex type using the principle of fluid oscillation; the pitot tube type using the total static pressure difference, the volume type, weir, and trough type, etc.
2. Electric principle: The instruments used for this kind of principle include electromagnetic type, differential capacitive type, inductive type, strain resistance type, etc.
3. Acoustic principle: Ultrasonic type is used for flow measurement using acoustic principle. Acoustic type (shock wave type) and so on.
4. Thermal principle: There are calorimetric, direct calorimetry, indirect calorimetry, etc. that use thermal principles to measure flow.
5. Optical principle: laser type, photoelectric type, etc. are instruments belonging to this type of principle.
6. Originated from physical principles: Nuclear magnetic resonance, nuclear radiation, etc. are instruments belonging to this type of principle.
7. Other principles: there are marking principles (tracing principles, nuclear magnetic resonance principles), related principles, etc.
Each product has its specific applicability and its limitations. According to the principle of measurement, there are mechanical principles, thermal principles, acoustic principles, electrical principles, optical principles, and atomic physics principles.
Classified according to the structure principle of the flowmeter. There are positive displacement flowmeters, differential pressure flowmeters, float flowmeters, turbine flowmeters, electromagnetic flowmeters, vortex flowmeters, mass flowmeters and plug-in flowmeters among fluid oscillating flowmeters.
According to the measurement object, there are two categories: closed pipeline and open channel; according to the purpose of measurement, it can be divided into total measurement and flow measurement. The meters are called total meters and flow meters.
The total meter measures the flow through the pipeline in a period of time, expressed by the quotient of the total flow in a short period of time divided by the time. In fact, the flow meter is usually equipped with a cumulative flow device for use as a total meter. The total meter is also equipped with a flow signalling device. Therefore, it is no longer practical to divide flow meters and total meters in a strict sense.
