Turbine flow sensor structure (Figure 1), when the measured fluid flows through the sensor, under the action of the fluid, the impeller is rotated by force, and its speed is proportional to the average flow velocity of the pipeline. The rotation of the impeller periodically changes the magnetic field of the magnetoelectric converter. Resistance value, the magnetic flux in the detection coil changes periodically to produce an induced potential with the same rotating frequency, that is, an electric pulse signal, which is amplified by an amplifier and sent to the display instrument for display.

　　 The flow equation of the turbine flowmeter is:

　　Qv = f / K (1)

　　Qm = qvρ (2)

　　 where qv, qm ……respectively volume flow, m3/s, mass flow, kg/s;

f ……The frequency of the output signal of the flowmeter, Hz;

K ……The meter coefficient of the flowmeter, P/m3.

　　The relationship curve between the coefficient of the flowmeter and the flow rate (or pipeline Reynolds number) (Figure 2). The meter coefficient can be divided into two sections, namely the linear section and the non-linear section. The linear section is about two-thirds of its working section, and its characteristics are related to the sensor structure size and fluid viscosity. In the non-linear section, the characteristics are greatly affected by bearing friction and fluid viscous resistance. When the flow rate is lower than the lower limit of the sensor flow rate, the meter coefficient changes rapidly with the flow rate, and the pressure loss and the flow rate are approximately squared. When the flow exceeds the upper limit of the flow, attention should be paid to prevent cavitation. The shape of the TUF characteristic curve with similar structure is similar, and it differs only in the level of systematic error.

Figure 1 Schematic diagram of turbine flow sensor structure

Figure 2 Turbine flowmeter characteristic curve

1. Good repeatability, short-term repeatability can reach 0.05%~0.2%. Because of its good repeatability, such as frequent calibration or online calibration, extremely high accuracy can be obtained, and it is the preferred flowmeter in trade settlement;

2. High precision, generally up to ±1%R, ±0.5%R, high-precision type up to ±0.2%R;

3. Output pulse frequency signal, no zero drift, strong anti-interference ability;

4. High frequency signals (3~4kHz) can be obtained, and the signal resolution is strong;

5. Wide range, medium and large diameters can reach 1:20, and small diameters are 1:10;

6. Compact and lightweight structure, convenient installation and maintenance, and large circulation capacity;

7. It is suitable for high-pressure measurement, and there is no need to open holes on the meter body, and it is easy to make a high-pressure meter;

8. It can be made into a plug-in type, suitable for large-caliber measurement, with low pressure loss, low price, continuous flow removal, easy installation and maintenance.