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Introduction to several less common types of mass flow meters from ABB: 1. Momentum flow meter: This type of meter was developed in the 1960s and is commonly used to measure the flow rate of oils with high viscosity. Its main component is a disc-shaped target; as the liquid flows, the fluid particles strike the target, causing it to move slightly. The amount of this displacement reflects the flow rate. 2. Variable-area flowmeters: Rotameter sensors were developed quite early on, but their widespread use in industrial applications came in recent decades. It has advantages such as high sensitivity, simple structure, intuitiveness, low pressure loss, wide measurement range, and low cost. It consists of a conical tube and a rotor placed inside the conical tube that can move up and down freely. The sensor is mounted vertically on the measurement pipeline; the fluid to be measured flows from bottom to top, pushing the rotor, and the height at which the rotor remains suspended serves as a measure of the flow rate. 3. Fluid oscillation flow meter: It measures flow rate by utilizing the principle that there is a definite relationship between the frequency of the vortices generated by a vortex generator inserted into the fluid and the flow velocity. Its feature is low fluid pressure loss ； It can be used for measuring liquids and gases, and it is capable of measuring flow velocity as well as mass flow rate ； It requires stable flow conditions, and strict pipeline specifications are needed; there must be straight sections of a certain length before and after the vortex generator, which makes it relatively expensive. 4. Electromagnetic flowmeters: The electromagnetic flow sensor is a new type of flow meter that has been developed with the advancement of electronic technology, and it is now widely used in the measurement of flow rates for various conductive liquids. According to Faraday’s law of electromagnetic induction, when a conductive fluid flows through a measuring instrument, it is equivalent to a conductor moving through a magnetic field while cutting across the magnetic field lines, which in turn generates an electromotive force E. This electromotive force is proportional to the average flow velocity. In principle, electromagnetic flowmeters are not affected by factors such as the temperature, pressure, density, and viscosity of the fluid. Moreover, there are no obstructing or moving components inside the pipe, so the original state of the fluid remains unchanged. It can be used in flow rate ranges from 0 to 102 m/s. Suitable for flammable, explosive, and highly corrosive media. But it also has limitations in certain aspects ； The medium to be tested must be a conductive liquid with a conductivity greater than 10-3 S/m ； It cannot be used to measure the flow rate of ferromagnetic media ； The signal is susceptible to interference from external magnetic fields.