A tree root is placed in the center of the pipeline and supported by bearings at both ends. When the fluid passes through the pipeline, it impacts the impeller of Roots flowmeter and generates a driving torque for Roots flowmeter, which makes the turbine flowmeter rotate against the friction torque and fluid resistance torque. In a certain flow range, the rotational angular velocity of Roots flowmeter is proportional to the fluid velocity for a fluid medium with a certain viscosity. Therefore, the fluid velocity can be obtained by the rotational angular velocity of Roots flowmeter, and the fluid flow through the pipeline can be calculated. The rotating speed of Roots flowmeter is detected by the induction coil installed outside the casing. When the blade of Roots flowmeter cuts the magnetic field lines generated by permanent magnet steel in the shell, it will cause the change of magnetic flux in the induction coil. The sensing coil sends the detected magnetic flux periodic change signal to the preamplifier, which generates a pulse signal proportional to the flow after amplification and shaping, 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 analog current and then indicates the instantaneous flow value.