The rotational speed of the turbine flowmeter is detected by a sensor coil installed outside the housing. When the blade of the turbine flowmeter cuts the magnetic field lines generated by the permanent magnet steel in the casing, the magnetic flux in the sensor coil will change. The sensor coil sends the detected magnetic flux periodic change signal to the preamplifier, and after amplification and shaping, it generates a pulse signal proportional to the flow, which is sent 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.