The rotating resistance of the rotating cup flow meter is very small, and the v~n linear performance is very good at low and medium speeds.
But the high speed performance is not as good as the propeller flow meter. The rotating cup's axis of rotation is perpendicular to the water flow, hence it is also known as a vertical axis flow meter.
The top and bottom brackets and signal-generating parts of the rotating cup flowmeter must also be watertight, sandtight and lubricable. Since its axis of rotation is vertical, parts such as the eccentric cylinder at its upper part appear to resemble a diving bell, and its water and sand resistance is better.
However, the thimble-like socket support system in the lower part does not have effective measures to protect against water and sand, and cannot even guarantee the presence of lubricating oil. Hence the rotary cup flow meterr not suitable for sandy water currents, but for rivers with fewer floating objects and low flow speed.
This instrument has high sensitivity and is suitable for measuring low flow velocities in general rivers, lakes and reservoirs, especially for measuring low flow velocities in deep water.
Principle of operation
When the water flow acts on the sensing element of the instrument - the rotary cup, because the left and right cups have different concavities and convex shapes, so the pressure is unequal and the difference in pressure creates torque and causes the bell to rotate.
The faster the water flow, the higher the rotating speed of the rotating cup. There is a certain functional relationship between them and this relationship is determined by testing the water tank. The results of each instrument verificationadd a verification formula that looks like this:
where V – flow rate (m /s);
n - Rotation rate of the rotating cup, which is the ratio of the total number of rotating cups N to the corresponding velocity measurement duration T, so n=T(N)( 1/S)
K — hydraulic pitch (m);
C — instrument constant (m/s).
K and C are the coefficients that characterize the performance of the instrument and are related to the size and shape of the rotary cup, the axial play of the rotary shaft, the arc and the smoothness of the thimble and the bearing stone and other factors. Therefore, the coordination relationship of this part must be checked strictly according to the technical requirements.