The turbine flowmeter consists of a turbine, bearings, preamplifier, and display instrument.
The principle of a turbine flowmeter is to place a turbine in the center of the pipeline, supported at both ends by bearings When the fluid passes through the pipeline, it impacts the turbine blades, generating a driving torque on the turbine, causing it to overcome friction torque and fluid resistance torque and rotate Within a certain flow range, for a certain viscosity of the fluid medium, the rotational angular velocity of the turbine is proportional to the fluid flow velocity Thus, the fluid velocity can be obtained by the rotational angular velocity of the turbine, and the fluid flow rate through the pipeline can be calculated
The speed of the turbine is detected by a sensing coil installed outside the casing When the turbine blades cut the magnetic field lines generated by the magnetic steel inside the casing, it will cause changes in the magnetic flux in the sensing coil The sensing 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 rate, 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 also sent to the frequency current conversion circuit, which converts the pulse signal into an analog current quantity and indicates the instantaneous flow rate value
The tested fluid impacts the turbine blades, causing the turbine to rotate. The rotational speed of the turbine changes with the flow rate, that is, as the flow rate increases, the rotational speed of the turbine also increases. The rotational speed of the turbine is then converted into electrical pulses of the corresponding frequency by a magneto electric conversion device, amplified by a preamplifier, and sent to a display instrument for counting and display. The instantaneous and cumulative flow rates can be calculated based on the number of pulses per unit time and the cumulative number of pulses.
The working principle of a turbine transmitter is that when the fluid flows along the axis of the pipeline and impacts 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, driving the turbine to rotate. While the turbine rotates, the blades periodically cut the magnetic field lines generated by the electromagnet, changing the magnetic flux of the coil. According to the principle of electromagnetic induction, a pulsating electric potential signal will be induced in the coil. The frequency of this pulsating signal is proportional to the flow rate of the measured fluid, 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 transmitters, and different instruments have different ξ values, which vary with the wear and tear of the instruments during long-term use; Its meaning is the number of pulses output by the transmitter when a unit volume flow rate passes through the transmitter.
The pulse signal output by the turbine transmitter can be amplified by an amplifier before being sent to the display instrument for flow measurement.