JPS6375620A - Apparatus for measuring flow rate of open channel - Google Patents

Abstract

PURPOSE:To measure a flow rate in real time with stable accuracy, by generating a magnetic field in an open channel in the direction right-angled to a water flowing direction and measuring a flow speed, the electromotive force generated in the direction right-angled to the magnetic field and a water level to subject the measured values to arithmetic processing. CONSTITUTION:Power is supplied to an exciting coil 2 from an exciting power source 3 to generate a magnetic field in an open channel 1. Electromotive force is measured by an electromotive force measuring device 4 through a pair of the electrodes 4a, 4b arranged to both banks of the open channel 1. The output signals of the power source 3 and the electromotive force measuring device 4 are converted to digital signals by an A/D converter to be inputted to an arithmetic processor 7. The output signals of the sensors 5a, 6a of a water level meter 5 and a conductivity meter 6 are converted to digital signals by an A/D converter to be inputted to the operational processor 7. The arithmetic processor 7 applies arithmetic processing to the input signals to calculate a flow rate which is, in turn, recorded on a recorder 9.

Description

[Detailed description of the invention] (Industrial application field) This invention is applicable to water supply, sewerage, agricultural and industrial waterways, artificial rivers,
In addition, it is necessary to measure the flow rate in all open channels, including general rivers, or in pipe channels where the water level changes sequentially as in open channels, such as full pipe flow or free water surface flow. f1 measuring device C2 is concerned.

(Prior art) Flow rate measurement methods for open channels include the current velocity measurement method, which uses a current meter to measure the flow rate, and the float side method, which measures the flow rate by dropping a float from a bridge, etc. to determine the flow velocity. etc. are known.

(Problems to be Solved by the Invention) However, all of the conventional methods described above not only lack stability in measurement accuracy, but also have problems in terms of time (difficult to perform two consecutive measurements) and The problem was that it required manpower.

An object of the present invention is to provide a flow rate measuring device that can solve the conventional problems as described above.

(Means for Solving the Problems) First, the principle of the flow rate measuring device according to the present invention will be explained.

Generally, when a conductor moves in a magnetic field, an electromotive force is generated that is proportional to the speed of the conductor's movement, according to Faraday's law of electromagnetic induction 1:

Here, in Fig. 1 (an open channel as shown in -), if a magnetic field with magnetic flux density B is generated in a direction perpendicular to the flow velocity V of flowing water, the flow velocity and magnetic field are An electromotive force E is generated in the direction. When the open channel 1 has a rectangular cross section, the magnitude of the electromotive force E is expressed as E=b−vφB (1) where b is the channel width.

On the other hand, since the flow fQ of water in the open channel l is Q=i)@11φV (2), from equations (1) and (2), Q=h fist-
...(3) It can be expressed as follows, and by measuring the water depth and the generated electromotive force E, the flow tQ can be determined.

The flow measuring device of the present invention is based on the above principle, and includes an excitation coil that generates a magnetic field in an open channel at right angles to the flow velocity of the flowing water, and a magnetic field that measures the flow velocity and magnetic field (two directions at right angles to the generated electromotive force). It includes an electromotive force measuring member, a water level measuring member that measures the water level of the water flow, and a calculation member that inputs each output signal of the electromotive force measuring member and the water level measuring member and calculates the flow rate based on these output signals C2. (Embodiment) Fig. 2 shows an embodiment of the present invention, in which the upper ζ
; An excitation coil 2 that is supplied with power from an excitation power supply 3 and generates a magnetic field in the open channel 1 is arranged, and a pair of 'IK poles 4a and 4b of an electromotive force measuring device 4 are arranged on both banks, and the excitation coil 2 is arranged to generate a magnetic field in the open channel 1. ￥i
The output signals of the i source 3 and the electromotive force measuring device 4 are A/D converted and input to the arithmetic processing unit 71. Furthermore, the open channel 1f; each sensor 5a of the water level gauge 5 and the conductivity gauge 6;
fia are arranged, and their output signals are A/D converted and input to the arithmetic processing unit 7.

In addition, in case C2 when the conductivity of the riverbed also changes, the conductivity of the riverbed is separately measured, and the measurement signal is input to the arithmetic processing unit 7 via the A/D converter.

The electromotive force measuring device 4 includes an amplifier circuit, a filter circuit, a phase detection circuit, a smoothing circuit, etc., and uses a phase detection method to measure the electromotive force generated between the electrodes 4a and 4b by the excitation magnetic field C of the sine wave. A method is adopted in which the + side and one side of the sine wave are smoothed independently, and the difference between them is used as an output value. This method makes it possible to eliminate the influence of detection time.

8 is input kakizade, 9 is recorder, ]0 is telemeter,
"l" indicates the /pull-up power supply.

In the arithmetic processing unit 7, the flow tube calculation is performed based on the above equation (3) (2), but in reality it is difficult to keep the magnetic flux density constant C2, so the magnetic field distribution In other words, based on the water level measurement result by the water level gauge 5, the average value of the magnetic field in the cross section of the waterway at the center of the magnetic field is calculated, and then (correction using a magnetic field correction function that converts it into the magnetic flux density of the second lowest riverbed) This method can be expressed as a relational expression for the electromotive force E to be measured as follows.

B=f(h)　φB.

Bo=C11■.

,',B=c・ENG.・f (h) ... (4) Here, f (h) is the magnetic field correction function, C is a constant, Bo is the magnetic flux density of the river bed, ■. indicates the current flowing through the coil (-).

Substituting equation (4) into equation (3) equation 1; r(h〕I.　　　　　-1,31 It is expressed as

If the river bed is electrically insulated, the direct fluid (
Second, the generated electromotive force is measured, and the current tQ is determined by equation (5).

However, in case C2 where the river bed is not insulated, the open channel itself and the surrounding soil are conductive, so it is necessary to correct the measured electromotive force by taking into account the conductivity of the river bed and flowing water. For this reason, the conductivity of the riverbed is measured in advance and input to the arithmetic processing unit 7, and the conductivity of the flowing water, which changes sequentially, is constantly measured and the measured signal is input to the arithmetic processing unit 7C. I made it.

The basic idea of this correction is that from the relationship between the electromotive force generated by the fluid, the internal resistance of the fluid itself, and the external resistance of the river bed, the total resistance (internal resistance +
Therefore, these resistances are calculated and converted into the total electromotive force C2 generated in the fluid. If we discuss this in more detail, it will be as follows.

Considering a thin flow in a rectangular channel l: with river bed current as the measurement object, the internal resistance, that is, the electrical resistance r of the flowing water, is
and the external resistance, i.e., the electrical resistance r of the river bed, can be expressed as follows. Here σ1. σ2 represents the conductivity of running water and riverbed, respectively.

Further, the relationship between the current 5 and the total electromotive force E is expressed as i/(r1+r2)=E.multidot.-(81).

Next, the measured electromotive force Eo between the poles 4a and 4b installed on both banks of C is actually (2 shows only the value due to the external resistance corresponding to the riverbed, and this is BO=i・rz=l '''' (Represented as 91σ weight, it is from equations (6) to (9), and considering equation 0).

It can be expressed as

Also, since Q is shown by (21), +2
1. (From Equation 11,
■ Substituting the formula C2, Now consider the condition that the waterway is a thin flow, and if V, then C0・h C2・b, and 0■ Formula is b C2
・E.

f(h) 1. -　I. It can be expressed as °°αJ.

Equation 0 is a general equation for the flow rate in a rectangular waterway with riverbed energization, but it can also be derived using C2 in the same manner as above for a trapezoidal waterway or its narrow-shaped waterway.

Although the excitation coil 2 is arranged above the open channel 1 in the embodiment shown in FIG. 2, it may be arranged below the open channel 1. It may also be placed above and below the open channel as shown in Figure 3A (2), in which case synchronized magnetic fields can be generated from above and below (from 2, a relatively uniform magnetic field distribution can be obtained. In addition, as shown in Fig. 30, the C double excitation coil 2
Make it U-shaped and make it an open channel! It is also possible to use a C2 device that wraps the waterway from below, and in this case, it has the same advantages as the one shown in FIG. 3A, but can generate a magnetic field without blocking the upper part of the waterway. Furthermore, although not shown, the waterway is shaped into a trapezoid or the like, and the excitation coil overflows the waterway surface? May be placed.

(Effects of the Invention) As described above (2. According to this invention, a magnetic field is generated in an open channel, the electromotive force and water level generated thereby are measured, and the flow rate is calculated based on the measured values. Since it is a water treatment device, it is possible to perform stable real-time flow rate measurement, and water resources can be effectively managed without the need for human labor.

[Brief explanation of the drawing]

FIG. 1 is a diagram showing the measurement principle of the device of this invention, FIG. 2 is a block diagram showing one embodiment of the invention, and FIG. 3 is a schematic diagram showing another example of arrangement of excitation coils.

Claims (1)

[Claims] 1. An excitation coil that generates a magnetic field in an open channel in a direction perpendicular to the flow velocity of the flowing water, an electromotive force measuring member that measures the electromotive force generated in the direction perpendicular to the flow velocity and the magnetic field, and the water level of the water stream. A flow rate measuring device for an open channel, comprising: a water level measuring member for measuring the flow rate; and a calculating member for inputting each output signal of the electromotive force measuring member and the water level measuring member and calculating the flow rate based on these output signals. 2. Claim 1, comprising a conductivity measuring member for measuring the conductivity of flowing water, the output signal of which is input to a calculation member.
Flow rate measuring device as described in section. 3. Claim 2, comprising a conductivity measuring member for measuring the conductivity of a river bed, and an output signal thereof is input to a calculation member.
Flow rate measuring device as described in section.