Briefly describe the principle of a turbine flowmeter?

A turbine flowmeter consists of a turbine, bearings, a pre-amplifier, and a display instrument. Principle of the turbine flowmeter: A turbine is placed at the center of the pipe, with its ends supported by bearings. When fluid flows through the pipe, it strikes the turbine blades, generating a driving torque that causes the turbine to rotate despite the frictional torque and fluid resistance. Within a certain range of flow rates, and for a given viscosity of the fluid, the rotational speed of the turbine is proportional to the fluid velocity. Thus, the fluid velocity can be determined from the rotational speed of the turbine, and the flow rate of the fluid passing through the pipe can be calculated accordingly. The rotational speed of the turbine is detected using sensor coils mounted outside the housing. When the turbine blades cut through the magnetic field lines generated by permanent magnets inside the housing, it causes changes in the magnetic flux in the sensor coils. These sensed changes in magnetic flux are sent to a pre-amplifier, where the signal is amplified and shaped to produce pulse signals proportional to the flow velocity. These pulse signals are then fed into circuits for unit conversion and flow accumulation, which calculate and display the cumulative flow value ； At the same time, the pulse signal is sent to a frequency-to-current conversion circuit, where it is converted into an analog current value that indicates the instantaneous flow rate. The fluid being measured impacts the turbine blades, causing the turbine to rotate; the speed of the turbine changes depending on the flow rate – higher flow rates result in a higher rotational speed of the turbine. The rotational speed of the turbine is then converted into electrical pulses of corresponding frequency by a magnetoelectric conversion device. After being amplified by a pre-amplifier, these pulses are sent to a display instrument for counting and showing. The instantaneous and cumulative flow rates can be determined based on the number of pulses per unit time and the total number of pulses accumulated. The working principle of a turbine transmitter is that as the fluid flows along the axis of the pipe and strikes the turbine blades, a force proportional to the product of the flow rate qv, flow velocity V, and fluid density ρ acts on the blades, causing the turbine to rotate. As the turbine rotates, the blades periodically cut through the magnetic field lines generated by the electromagnet, changing the magnetic flux of the coil. According to the principle of electromagnetic induction, a pulsating potential signal is induced within the coil. The frequency of this pulsating signal is proportional to the flow rate of the fluid being measured. That is: where qv represents the total volume of fluid, and N represents the total number of pulses generated by the transmitter ； ξ is the flow coefficient. ξ is an important characteristic parameter of turbine transmitters; different instruments have different values of ξ, and this value changes over time due to wear and tear resulting from long-term use of the instrument ； It refers to the number of pulses output by the transmitter per unit volume flow rate as it passes through the transmitter. The pulse signal generated by the turbine transmitter is amplified by a pre-amplifier and then sent to the display instrument, thereby enabling the measurement of flow rate.

Just like a windmill, water pushes the blades, cutting through the magnetic field lines

Simply put, the medium drives the impeller to rotate, and the flow rate is measured based on the speed of rotation of the turbine.