LS25-1 flow meter, ls25-1 flow rate and flow measurement instrument, Ls full series flow meter

>The LS25-1 rotary propeller flowmeter is a river hydrological measurement instrument mainly used to determine the average velocity of water flow at predetermined measurement points in general rivers, channels, reservoirs, lakes and other water flow sections, in order to determine the flow rate of the section.

2、 Main technical indicators

1. Speed measurement range: V=0.06~7.0m/s

2. Working water depth: generally not greater than 24m;

3. Working water temperature: 0~40 ℃;

4. Working water quality: Fresh water (containing moderate amounts)

Mineral or containing sediment

Muddy waters;

5. Accumulated time of continuous work: 8h;

6. Starting speed of the instrument: V0 ≤ 0.05m/s

7. Mean square deviation of verification formula: m ≤ 1.5%

8. Blade pitch: 250mm;

9. The number of revolutions of the blade between each second signal: 20 revolutions

3、 Working principle and calculation method

The working principle of the LS25-1 rotary propeller flowmeter is that when the water flow acts on the sensing element of the instrument - the blade, the blade undergoes rotational motion. The faster the water flow, the faster the blade rotates. There is a certain functional relationship between the rotational speed and the flow velocity, that is, V=f (n). So, to determine the flow rate of water, it is only necessary to accurately measure the number of revolutions of the instrument blades and the corresponding time. Assuming the critical speed of the instrument is Vk, experiments have shown that the function is in the form of a curve between below Vk and the starting speed V0, while above Vk there is a linear relationship.

Each instrument calibration result is accompanied by a curve chart and the following calibration formula:

V=bn+a

In the formula: V - flow velocity (m/s);

N - blade rotation rate (speed), equal to the total number of blade revolutions "N"

The ratio of the corresponding speed measurement duration 'T', i.e. n=N/T;

B - Hydraulic pitch (corresponding to the original standard K), in meters;

A - Instrument constant (corresponding to the original standard C), only m/s;

The values of b and a are related to factors such as the pitch of the blade and the frictional resistance of the support system. Therefore, it is necessary to use and maintain these parts carefully, otherwise it will affect the accuracy of the flow velocity test.

The determination of water flow velocity is actually the measurement of the number of revolutions generated by the blade of the flowmeter when it is stimulated by water flow within a predetermined time. The number of revolutions of the propeller blade 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 through a wire. For every 20 revolutions of the blade, the contact mechanism makes contact once, and the counting instrument sends a signal. The measurer counts this signal and multiplies it by a factor of 20 to obtain the actual number of revolutions of the flow meter blade. Record the corresponding speed measurement duration "T" with a stopwatch, and divide the duration "T" by the speed "N" to obtain the rotation rate "n" of the propeller. ***Afterwards, multiply the rotation rate "n" by the hydraulic pitch "b" and add the instrument constant "a" to obtain the measured flow velocity.

If the flow velocity is less than the critical flow velocity Vk, the flow velocity can be directly calculated based on the propeller speed "n" on the enlarged curve graph.

In order to avoid the influence of flow velocity fluctuations on the speed measurement results, the speed measurement duration should generally not be less than 100 seconds. It is best to determine it based on the characteristics of each river through experiments and analysis.