The working principle of Jiuxin Shengxin propeller flowmeter
Working principle of propeller flow meter
The working principle of the propeller-type flow meter is: when the water flow acts on the instrument's sensing element-the blade, the blade generates a rotary motion, the faster the water flow, the faster the blade rotates, and there is a certain between the speed and the flow The functional relationship is V = f (n). Therefore, to determine the flow rate of water, in fact, as long as the rotation speed of the instrument blade and the corresponding time are accurately measured. Assuming that the critical speed of the instrument is Vk, the experiment shows that between Vk and the starting speed V0, the function is in the form of a curve, and above Vk is a linear relationship.
The verification results of each instrument are accompanied by a graph and the following verification formula:
V = bn + a
In the formula: V——flow velocity (m / s);
n—— blade rotation rate (rotation speed), equal to the total blade rotation number “Nâ€
Compared with the corresponding speed measurement duration "T", that is n = N / T;
b——hydraulic pitch (corresponding to the original standard K), the unit is m;
a——Instrument constant (corresponding to the original standard C), m / s alone;
The b value and a value are related to the pitch of the blade and the friction resistance of the support system. Therefore, the parts of this part must be used carefully and maintained carefully, otherwise it will affect the accuracy of the flow rate test.
The measurement of water flow speed is actually to measure the number of revolutions generated when the blade of the flow meter is impelled by the water flow within a predetermined time. The rotation number of the paddle is calculated by using the contact mechanism of the instrument to convert it into an electrical pulse signal, which is transmitted to the counting instrument on the water surface part through the wire. Every 20 revolutions of the blade, the contact mechanism contacts once, the counting instrument sends a signal once, the measurer counts this signal number, and multiplies it by 20 times to obtain the actual rotation number of the flow meter blade. Use the stop watch to record the speed measurement duration "T" corresponding to the revolution, and divide the revolution "N" by the duration "T" to obtain the slewing rate "n" of the propeller. Finally, multiply this slewing rate "n" by the hydraulic pitch "b" and add the instrument constant "a" to obtain the measured flow rate.
If the flow rate is less than the critical flow rate Vk, the flow rate can be directly found on the enlarged graph according to the propeller speed "n".
In order to avoid the impact of velocity fluctuations on the speed measurement results, the speed measurement duration should generally not be less than 100 seconds, preferably based on the characteristics of each river, through analysis, analysis and determination.
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