Classified by measuring principle
(1) Mechanics: The instruments belonging to this type 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; use of fluids Targets of the momentum principle; turbines using angular momentum theorem; vortex-type, vortex-type using fluid oscillation principle; Pitot tube type using total static pressure difference, and positive displacement, enthalpy, trough, etc.
(2) Electrical principle: The instruments used for this kind of principle include electromagnetic type, differential capacitive type, inductive type, strain resistance type and so on.
(3) Acoustic principle: Ultrasonic type is used for flow measurement using acoustical principle. Acoustic type (shock wave type) etc.
(4) Thermal principle: The use of thermal principles to measure the flow of heat, direct calorimetry, indirect calorimetry and so on.
(5) Optical principle: Laser type, photoelectric type, etc. are instruments belonging to this type of principle.
(6) Original in physics principle: nuclear magnetic resonance type, nuclear radiation type etc. are instruments belonging to this kind of principle.
(7) Other principles: Marking principle (tracer principle, nuclear magnetic resonance principle), related principles, etc.