Working priciple of turbine flow meter: 

When liquid flows through the casing of sensor, the impulse of fluid will provide the blade with a rotation moment as there is an angle between the blade of impeller and the flow direction.

The blade will rotate as the friction moment and the fluid resistance are overcome and it will reach a stable speed when the moments are at balance. Under certain conditions, the rotation speed of blade will be in direct proportion to the flow velocity. Due to the magnetic conductivity of blade, when located in the magnetic field generated by signal detector (made of permanent magnet steel and coils), the rotating blade will cut the magnetic lines and periodically change the flux through the coil

Viscosity has the following effects on the turbine flowmeter:

1.As the viscosity increases, the starting displacement of the turbine flowmeter will decrease, and the response speed will also decrease.

2.Before entering the linear section of the turbine response, the K value continues to rise, and has an exponential growth relationship with the Reynolds number at the inlet of the flowmeter.

3.As the viscosity increases, the K value of the turbine flowmeter will decrease, and the linearity will also deteriorate.