CN100342218C - Momentum flowmeter and measuring method thereof - Google Patents

Abstract

The present invention discloses a momentum flowmeter and a measuring method thereof. The momentum flowmeter comprises a water barrier, pressure sensors and a secondary meter, wherein a group of water barrier grids are arranged on the water barrier which can be arranged in a channel; the pressure sensors are respectively arranged at the upper part and the lower part of the water barrier, and can both be connected with the secondary meter which is used for receiving, processing, storing and outputting data. When the present invention is used for measuring, the momentum flowmeter is vertically put into the channel to be fixed, the pressure sensors are firmly connected with the secondary meter, and finally, information is obtained from the secondary meter. The momentum flowmeter of the present invention has the advantages of simple structure, low manufacturing cost, wide adaptability, convenient measurement and high measuring precision. The present invention has wide application prospect for measuring water of channels for middle and small farmlands, and has great economic value and use value.

Description

Momentum flowmeter and measuring method thereof

One, the technical field

The invention relates to water measuring equipment and a method used in farmland irrigation, in particular to a momentum flowmeter and a measuring method thereof.

Second, background Art

Water measurement has been accompanied by the development of hydraulics for over 100 years, and classical water measurement devices such as Venturi tubes and Parshall water tanks are still the main water measurement means in laboratories to date. With the need for irrigation water, not only are these laboratory water-gauging facilities used to channel water, but new methods of water gauging have been developed. In general terms, irrigation area water facilities can be divided into three categories: water for hydraulic buildings, water for special water measuring equipment and non-contact water measuring.

The flow and the water space of the building are calculated by observing the upstream and downstream water levels and the opening degree of a gate of the building according to the overflowing rule of the hydraulic building. With the development of liquid level sensing technology and electronic technology, computers are adopted to automatically detect the upstream and downstream of a sluice and the opening degree of the sluice in the early 80 s and accumulate water quantity. In principle, the flow measuring method requires that the outflow of the building has strong regularity, and the general large and medium-sized buildings can meet the requirement. However, the flow measuring device has large investment and is not suitable for small and medium-sized channels.

The water metering is a classic method using a special water metering device having a triangular weir, a trapezoidal weir, an orifice plate, a water metering jet, a venturi tube, a marshall water tank, and a throat-free water tank. Its advantages are high water-measuring precision. Like hydraulic structures, it is necessary to observe and record the upstream and downstream water levels to calculate the flow rate. The method needs to arrange special water measuring equipment, the manufacturing cost is high, the cost is higher when the channel is larger, and the use of the method in large channels is limited.

The non-contact type water measuring device has various forms according to different principles, and the mature and common water measuring device mainly comprises an electromagnetic flow meter and an ultrasonic flow meter. The electromagnetic flowmeter is mainly suitable for measuring the water quantity of a pipeline, has been developed into a product integrated with a microcomputer, and has higher measurement precision. The market price of the electromagnetic flowmeter with the diameter of one meter is about 10 ten thousand yuan, and the electromagnetic flowmeter is not economically affordable for a wide and large farmland channel. The ultrasonic flowmeter is produced in the seventies, and with the change of computer technology, the ultrasonic flowmeter is driven to develop rapidly, particularly the Doppler ultrasonic flowmeter is successfully researched, and the measuring range of the ultrasonic flowmeter is greatly expanded. The ultrasonic flowmeter is suitable for the flow measurement of large channels. Due to the influence of temperature drift, the accuracy of the ultrasonic flowmeter is unstable, and temperature drift correction is needed. The currently used ultrasonic flowmeter is mainly imported and has higher price. The core component of the domestic ultrasonic flowmeter is mainly imported, but the reliability is poor.

In summary, the disadvantages of the existing water measuring device are: the equipment is a high-grade instrument and meter, the price is high, and the common medium and small agricultural irrigation channels cannot bear the price.

Third, the invention

The momentum flowmeter has the advantages of simple structure, low manufacturing cost, wide adaptability, convenient measurement and high measurement precision.

The purpose of the invention is realized by the following technical scheme:

a momentum flow meter, characterized by: the water-retaining fence comprises a water-retaining fence serving as a special water measuring device (flow measuring device), a pressure sensor and a secondary instrument, wherein a group of water-retaining fence bars are arranged on the water-retaining fence which can be arranged in a channel; the pressure sensors are respectively arranged at the upper part and the lower part of the water blocking fence and are connected with a secondary instrument which can receive, process, store and output data. By the formula

$\left\{\begin{array}{cc}2F_1\·H-\frac{{\mathrm{\α}}_1\·\mathrm{\ρ}\·n\·B_1\·Q^2}{{2B}^2}-\frac{n\·\mathrm{\γ}\·B_1\·h^3}{6}=0& \left(3\right)\\ {2F}_1+{2F}_2-{\mathrm{\ρ\α}}_1\frac{{\mathrm{nB}}_1\·Q^2}{B^{2}h}-\frac{1}{2}{\mathrm{nB}}_1\·\mathrm{\γ}\·h^2=0& \left(4\right)\end{array}\right.$

Obtaining the flow Q in the channel and the water depth value h; wherein H is the height of the water retaining grid, B is the width of the water retaining grid, rho is the density of water, n is the number of the grid bars, B is₁For each grid width, α₁1, the supporting force of both sides of the upper end of the water blocking grid is F₁Both ends of the lower end have supporting force F₂，F₁、F₂Measured by a pressure sensor.

The shape of the water retaining fence can be rectangular or trapezoidal. Uniformly arranging the grids on the barrierN strips, each grid strip is B in width₁The water blocking grid can generate pressure on the pressure sensor under the action of water flow, and the number of the grid bars and the width of each grid bar can be determined according to the specific condition of the water flow. The invention utilizes the impact force generated by the flowing water flow impacting the water retaining grid bars to the water retaining grid, measures the impact force through the pressure sensor, and calculates the water depth, the flow velocity and the flow in the channel according to the momentum principle and the force balance principle.

In the invention, the material of the barrier can be metal, concrete, wood, plastic or glass fiber reinforced plastic and the like.

In the invention, the pressure sensors can be respectively arranged at the top and the bottom of the water blocking fence; the pressure sensor is provided with a remote transmission interface, can receive and transmit the pressure generated by the water-blocking grid under the action of water flow, and the arrangement position of the pressure sensor can also be arranged at the upper part and the lower part of the water-blocking grid, and the derivation formula of the principle part is adjusted correspondingly according to the difference of the arrangement position.

The measuring method of the momentum flowmeter is characterized by comprising the following steps:

A) vertically placing the momentum flowmeter into a channel and fixing, wherein water flows through the water blocking grids;

B) determining that pressure sensors in the momentum flowmeter are all firmly connected with a secondary instrument;

C) and reading the channel water depth and flow from the secondary meter.

The secondary instrument is a data receiving, processing, storing and outputting device, which receives the information of the pressure sensor, calculates the water flow speed and depth in the channel according to the information, calculates the flow in the channel according to a flow formula, calculates the water consumption in each time period according to the flow and the time, calculates the water fee according to the water quantity and the water price, stores the information and the calculation processing result, and outputs or remotely transmits the information and the processing result according to the requirement. The secondary meter can be connected with a printing output device to print required data, and can also be connected with other communication devices through wireless or wire.

The working principle of the invention is as follows:

according to the momentum conservation principle and the force balance principle, the flow and the water depth of water in the channel are reversely deduced by measuring the supporting forces at the upper end and the lower end of the water blocking grid, so that the flow of the channel is measured.

$F_d=\mathrm{\ρQ}\frac{A_0}{A}({\mathrm{\α}}_1{V}_2-{\mathrm{\α}}_2{V}_2)$

In the formula, F_dIs hydrodynamic pressure, rho is water density, Q is channel flow, V₁Is the water flow velocity in the channel, V₂For the velocity of the water after impact on the water-retaining grating, A₁Is the cross-sectional area of the canal, A₀The area of the bars of the barrier submerged in water is A, and the total area of the barrier submerged in water is A.

Wherein, $V_1=\frac{Q}{A_1}=\frac{Q}{B\·h};$

V₂＝0；

A₀＝nB₁h。

A＝B·h

thus is provided with $F_d=\mathrm{\ρ}\frac{{\mathrm{\α}}_{1}n{B}_1\·Q^2}{B^{2}h}$

It has been determined that the supporting forces on both sides of the upper end of the water-blocking grid are F₁Both ends of the lower end have supporting force F₂According to the depth h of water, the hydrostatic pressure can be obtained

$F_j=\frac{1}{2}n{B}_1\·\mathrm{\γ}\·h^2$

According to the principle of force balance, there are

$\left\{\begin{array}{cc}{2F}_1\·H-\frac{h}{2}\·F_d-\frac{h}{3}\·F_j=0& \left(1\right)\\ {2F}_1+{2F}_2-F_d-F_j=0& \left(2\right)\end{array}\right.$

Wherein H is the height of the water retaining grid.

F is to be_d、F_jSubstituting into the above equation system to obtain

$\left\{\begin{array}{cc}{2F}_1\·H-\frac{{\mathrm{\α}}_1\·\mathrm{\ρ}\·n\·B_1\·Q^2}{{2B}^2}-\frac{n\·\mathrm{\γ}\·B_1\·h^3}{6}=0& \left(3\right)\\ {2F}_1+{2F}_2-{\mathrm{\ρ\α}}_1\frac{{\mathrm{nB}}_1\·Q^2}{B^{2}h}-\frac{1}{2}{\mathrm{nB}}_1\·\mathrm{\γ}\·h^2=0& \left(4\right)\end{array}\right.$

In the above two formulae, H, rho, gamma, n, B₁、B、α₁Is a known amount, F₁、F₂Can be measured by a pressure sensor, the unknowns are Q and h, and the simultaneous equation system is solved, namelyThe flow rate and the water depth in the trench can be obtained.

The water measuring device provided by the invention takes the water retaining barrier as a flow measuring device, measures the fixed supporting force of the water retaining barrier through a pressure sensor, and reversely deduces the water flow and the water depth in the channel according to the law of momentum conservation and the external force balance principle in hydraulics. Compared with the prior art, the invention has the advantages that: the device has simple structure, low cost and wide adaptability; the momentum flowmeter has convenient measurement and high measurement precision, and can completely meet the water demand of medium and small channels.

Description of the drawings

FIG. 1 is a schematic structural view of the present invention;

fig. 2 is a schematic structural view of the water fence of the present invention.

Fifth, detailed description of the invention

The momentum flowmeter comprises a water blocking grid 1, a pressure sensor 2 and a secondary meter 3. The water-blocking fence 1 is rectangular in shape, has a height H and a width B, a group of 4 water-blocking fence bars 4 are arranged on the water-blocking fence 1, and the width of each fence bar is B₁(ii) a The water blocking fence 1 is made of metal, and the water blocking fence 1 is fixed in the channel. The two pressure sensors 2 are respectively arranged at the top end and the bottom end of the water blocking grid bar 4, and four pressure sensors 2 can be respectively arranged at four corners of the water blocking grid 1; the pressure sensor 2 is a general pressure sensor with a remote transmission interface and is connected with the secondary instrument 3. The secondary instrument 3 is a receiving, processing, storing and outputting device, which receives the information of the pressure sensor 2, calculates the water flow speed and depth in the channel according to the information, calculates the flow in the channel according to the flow formula, calculates the water consumption in each time period according to the flow and the time, calculates the water charge according to the water quantity and the water price, stores the information and the calculation processing result, and according to the requirementThe above information and processing results are output or transmitted remotely.

The measuring method adopting the momentum flowmeter comprises the following steps:

A) firstly, vertically placing a momentum flowmeter into a channel and fixing, wherein water flows through water blocking grids;

B) determining that pressure sensors in the momentum flowmeter are all firmly connected with a secondary instrument;

C) the secondary instrument receives the information of the pressure sensor, calculates the water flow speed and depth in the channel according to the information, calculates the flow in the channel according to a flow formula, calculates the water consumption in each time period according to the flow and the time, and reads the water depth, the flow speed and the water quantity of the channel from the secondary instrument.

In the invention, the supporting forces of the two sides of the upper end of the fence, which are measured by the pressure sensor, are F₁Both ends of the lower end have supporting force F₂，F₁And F₂Respectively 90 newton and 240 newton, and it is known that the width B of the water bar is 0.8m, and there are 4 water bars each having a width B₁0.05m, 1m high water-retaining grid, 1 x 10 density rho³kg/m³，α₁And (1) calculating the water depth and water quantity of the channel by using a calculation formula.

Substituting known conditions into the following equation:

$\left\{\begin{array}{cc}{2F}_1\·H-\frac{{\mathrm{\α}}_1\·\mathrm{\ρ}\·n\·B_1\·Q^2}{{2B}^2}-\frac{n\·\mathrm{\γ}\·B_1\·h^3}{6}=0& \left(3\right)\\ {2F}_1+{2F}_2-{\mathrm{\ρ\α}}_1\frac{{\mathrm{nB}}_1\·Q^2}{B^{2}h}-\frac{1}{2}{\mathrm{nB}}_1\·\mathrm{\γ}\·h^2=0& \left(4\right)\end{array}\right.$

the obtained water depth h is 0.8m, and the flow Q is 0.32m²/s。

According to the obtained flow and time, the water consumption of each time interval can be calculated, the water fee is calculated according to the water quantity and the water price, the information and the calculation processing result are stored, and the information and the processing result are output or transmitted remotely according to the requirement. The secondary instrument can be connected with a printing output device to print out the required data.

Claims (7)

1. A momentum flow meter, characterized by: the water-blocking device comprises a water-blocking grid (1) serving as a special water measuring device, a pressure sensor (2) and a secondary instrument (3), wherein a group of water-blocking grid bars (4) are arranged on the water-blocking grid (1) which can be arranged in a channel; the pressure sensors (2) are respectively arranged at the top and the bottom of the water blocking fence (1), and the pressure sensors (2) are connected with a secondary instrument (3) capable of receiving, processing, storing and outputting data; by the formula

$\left\{\begin{array}{c}2F_1\·H-\frac{{\mathrm{\α}}_1\·\mathrm{\ρ}\·n\·B_1\·Q^2}{2B^2}-\frac{n\·\mathrm{\γ}\·B_1\·h^3}{6}=0...\left(3\right)\\ 2F_1+2F_2-\mathrm{\ρ}{\mathrm{\α}}_1\frac{n{B}_1\·Q^2}{B^{2}h}-\frac{1}{2}n{B}_1\·\mathrm{\γ}\·h^2=0...\left(4\right)\end{array}\right.$

Obtaining the flow Q in the channel and the water depth value h; wherein H is the height of the water retaining grid, B is the width of the water retaining grid, rho is the density of water, n is the number of the grid bars, B is₁For each grid width, α₁1, the supporting force of both sides of the upper end of the water blocking grid is F₁Both ends of the lower end have supporting force F₂，F₁、F₂Measured by a pressure sensor.

2. The momentum flowmeter of claim 1, wherein: the water blocking fence (1) is provided with a group of water blocking fence strips (4), and the water blocking fence strips (4) generate pressure to the pressure sensor (2) when flowing water flow impacts the water blocking fence (1).

3. The momentum flowmeter of claim 1, wherein: the pressure sensors (2) are respectively arranged at the top and the bottom of the water blocking fence (1).

4. The momentum flowmeter of claim 1, wherein: the shape of the water blocking fence (1) is rectangular or trapezoidal.

5. The momentum flowmeter of claim 1, wherein: the water-blocking fence (1) is made of metal or concrete or wood or plastic or glass fiber reinforced plastic.

6. A method of measurement using the momentum flowmeter of claim 1, comprising the steps of:

A) vertically placing the momentum flowmeter into a channel and fixing, wherein water flows through the water blocking grid bars (4);

B) determining that pressure sensors (2) in the momentum flowmeter are all firmly connected with a secondary instrument (3);

C) and reading the channel water depth and flow from the secondary meter (3).

7. The measurement method using the momentum flow meter according to claim 6, wherein: the secondary instrument (3) is connected with the printing output equipment.

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