The principle of turbine flowmeter is to place a turbine in the center of the pipeline, and its two ends are supported by bearings. When the fluid passes through the pipeline, it impacts the turbine blades and generates driving torque for the turbine, which makes the turbine rotate against friction torque and fluid resistance torque. In a certain flow range, the rotational angular velocity of the turbine is directly proportional to the fluid velocity. Therefore, the fluid velocity can be obtained by the rotational angular velocity of the turbine, and the fluid flow through the pipeline can be calculated.

The rotational speed of the turbine is detected by a sensor coil installed outside the casing. When turbine blades cut the magnetic field lines generated by permanent magnet steel in the casing, the magnetic flux in the induction coil will change. The sensor coil sends the detected magnetic flux periodic change signal to the preamplifier, amplifies and shapes the signal, generates a pulse signal proportional to the flow, and sends it to the unit conversion and flow integration circuit to obtain and display the accumulated flow value. At the same time, the pulse signal is sent to the frequency-current conversion circuit, which converts the pulse signal into analog current and then indicates the instantaneous flow value.

The measured fluid impacts the turbine blades, causing the turbine to rotate. The rotating speed of the turbine changes with the flow rate, that is, the rotating speed of the turbine is also high. Then, the rotating speed of the turbine is converted into electric pulses with corresponding frequency by a magnetoelectric conversion device, which are amplified by a preamplifier and sent to a display instrument for counting and displaying. According to the number of pulses and cumulative pulses per unit time, the instantaneous flow and cumulative flow can be obtained.

The working principle of the turbine transmitter is that when the fluid flows along the axial direction of the pipeline and impacts the turbine blades, a force proportional to the product of flow qv, flow velocity V and fluid density ρ acts on the blades to push the turbine to rotate. When the turbine rotates, the blade periodically cuts 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 will be induced in the coil, and the frequency of this pulsating signal is proportional to the flow rate of the measured fluid, that is, where qv is the total volume of the fluid and n is the total number of pulsations generated by the transmitter; ξ is the flow coefficient.

ξ is an important characteristic parameter of turbine transmitter. Different instruments have different ξ, which changes with the long-term wear of instruments. Its meaning is the number of pulses output by the transmitter when the unit volume flow passes through the transmitter.

The pulse signal output by the turbine transmitter is amplified by the preamplifier and sent to the display instrument, thus realizing the flow measurement.

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