JPS6410785B2 - - Google Patents

Description

[Detailed Description of the Invention] [Field to which the invention pertains] The present invention relates to a method and device for measuring the flow velocity of fluid, and in particular to groundwater, ports, etc. that exhibit minute movements.
The present invention relates to a fluid flow velocity measurement method and device suitable for measuring the dynamics of an actual or model river.

[Prior art and its problems]

In recent years, decisions have been made as to whether or not to adopt freezing construction methods, and
Accurately measuring flow velocity and direction is an important issue when conducting surveys of pollution in rivers, etc.

However, the conventionally commonly used tracer method requires drilling a large number of boreholes for groundwater investigation, which is extremely expensive, and if the flow rate of groundwater is slow, it takes a long time to measure and causes measurement errors. There was an inconvenience caused by this.

Furthermore, even with a propeller-type current meter that has improved the drawbacks of the prior art described above, it is impossible to measure the flow velocity in a minute flow velocity region of 1 [cm] per second or less. Measurement means using the Doppler effect have disadvantages in that the equipment is expensive and large, and is not suitable for measuring flow velocity in groundwater, rivers, etc. due to safety issues and the need for special qualifications.

In contrast, the inventors have recently proposed a method for measuring the flow velocity and flow direction of flowing water by generating an annular ion layer around a measurement electrode using electric pulses.

However, with such ion generation methods, it takes a long time for the peak of the generated ion layer to reach the measurement electrode.
Due to the diffusion of the ion layer that occurs during this period, measurement sensitivity is low, making it difficult to detect peak values.

[Purpose of the invention]

SUMMARY OF THE INVENTION An object of the present invention is to provide an omnidirectional fluid flow rate measuring method and apparatus that can improve the disadvantages of the conventional method and measure the fluid flow rate relatively quickly.

[Means for solving problems]

Therefore, in the present invention, a measurement electrode section and an ion generation electrode section are arranged at the same location in the fluid to be measured, and then a predetermined pulse voltage is applied to the ion generation electrode section to perform a predetermined measurement in the measurement area. An ionic layer consisting of a starting level of ion concentration is formed. after that,
A configuration is adopted in which the application of pulse voltage to the ion generating electrode section is stopped, measurement of the degree of decrease in ion concentration is started, and the flow rate of the fluid is specified in accordance with the level change. This aims to achieve the above-mentioned purpose.

[First Embodiment of the Invention] Hereinafter, a first embodiment of the present invention will be described based on FIGS. 1 to 9.

First, the measurement principle of flow rate measurement, which forms the background of the present invention, will be explained.

When ion masses are generated locally in a fluid to measure flow velocity, a concentration difference occurs between the ion concentration and the average ion concentration in the fluid, which causes diffusion.

When the concentration gradient of a substance participating in diffusion changes over time, the diffusion becomes unsteady diffusion.
The following formula is satisfied.

∂c/∂t=D∂ ² c/∂x ² …where c is the concentration of the substance participating in the diffusion, D is the diffusion coefficient, t is the time, and x is the displacement.

In order to solve this equation, as an initial condition, the concentration c(0 _, x) at time t=0 is a function f(x) of the displacement 2≦x≦h/2) f(x)=0(x<-h/2, h/2<x)... Consider the case given by a rectangular function.

At this time, the concentration c(t, x) at displacement x can be calculated by solving the equation: However, A=-(x-α) ² /4Dt.

Here, assuming that h→0, that is, concentrated in a small interval, and giving the initial condition as a delta function, c ₀ h=Q, However, B=-x ² /4Dt.

The formula is, when the initial condition is t=0, the time t and the displacement x when given by the concentration Q on the x=0 plane.
represents the concentration at

Next, we will consider diffusion in a fluid system, that is, diffusion in which ion particles themselves move in a fluid with a velocity that corresponds to the flow velocity.

Now let the flow velocity be u. When the initial conditions of the equation are given, the ion concentration given at t = 0, x = 0 will be diffused at t = t ₁ , as shown in Figure 1, and the distribution of ion concentration with respect to displacement will be averaged. , the peak value decreases. The displacement at which this ion concentration peaks is the moving distance of the ion mass ``u・t ₁ ''
be equivalent to. That is, it can be seen that diffusion in a fluid system is equivalent to the initial concentration input plane (x=0 plane) moving with the flow velocity in a stationary system. At this time, the displacement x ₁ in the fluid system is the displacement x ₁ in the stationary system
−u・t ₁ ”. From this, the ion concentration at displacement x and time t in the fluid system is given by the following equation.

However, E=-(x-ut) ² /4Dt FIG. 2 shows the relationship between ion concentration C(t, x) and time t when x is fixed and velocity u is used as a parameter. From this figure, as the speed decreases,
It can be seen that the time when the ion concentration reaches its peak is delayed, and the peak value tends to decrease accordingly. That is, the ion concentration distribution is averaged, resulting in a decrease in sensitivity.

In addition, the figure also shows the time ``t=x/u'' at which the ion reaches the displacement x when no diffusion phenomenon occurs.
It is shown below. This shows that when a diffusion phenomenon occurs, the time at which the concentration reaches its peak tends to be earlier than when the diffusion phenomenon does not occur. This causes an error in the measurement time.

In order to eliminate this drawback, the present invention adopts a method of setting the ion concentration measurement point at the ion mass generation point.

In this case, by substituting x=0 into the equation, the ion concentration C(t,0) becomes the following equation.

However, G=-u ² t/4D FIG. 3 shows the relationship between time t and ion concentration C(t,0) when speed u is used as a parameter. From the figure, it can be seen that as the speed u increases, the rate of decrease in ion concentration tends to increase. Further, the ion concentration monotonically decreases with respect to time t, so that both ion concentration measurement and time measurement can be performed.

When the flow velocity u is determined from the formula, the following formula is obtained.

If the value of Q and one of C and t in the formula is set in advance from the formula, the flow velocity u can be determined by measuring the time until the ion concentration reaches C or by measuring the ion concentration after time t has elapsed. Understand what is required. That is, the rate of change in ion concentration is equal to the flow rate u
Correlates with

Next, an embodiment of a fluid flow rate measuring device constructed based on the above measurement principle will be described with reference to FIGS. 4 to 9.

FIG. 4 is an explanatory diagram showing an example of actual measurement using a flow rate measuring device.

In FIG. 4, reference numeral 1 denotes a measurement borehole drilled in the ground E from the ground surface to a predetermined depth into the groundwater layer (sand layer, gravel layer, etc.). A measurement probe (hereinafter referred to as a "probe") 3 suspended via a boring rod 2 is inserted into the borehole 1 down to the test depth. In the groundwater layer in the ground E, there is a flow of groundwater as shown by the arrow F in the figure, so that groundwater W gushes out into the borehole 1 below the groundwater level.
The probe 3 is submerged in this groundwater W. The probe 3 is electrically connected to an external measuring device (not shown) by a cable 5 extending inside the boring rod 2, and thereby the groundwater flow velocity can be measured and recorded. It is becoming more and more popular.

FIG. 5 specifically shows the configuration of the probe 3 described above, which has a cylindrical probe body 6 that is detachably screwed onto the rod 2.
The probe body 6 has a disk-shaped head 7 attached to the lower open end of the probe body 6, and a bottom plate 8 disposed below the head 7 at a predetermined distance.
The head 7 is screwed to the lower end of the probe body 6 at the upper ends of the four struts 9, thereby being hermetically attached to the probe body 6. Also, pillar 9
By fixing the bottom plate 8 to the lower end of the head with nuts 10, a predetermined space (observation part) 11 is formed between the head 7 and the bottom plate 8, and groundwater can flow into this observation part 11. It is completed.

The head 7 is made of an insulating material. An electrode rod 20 for measurement is set and fixed at the center of this head 7. A board (not shown) equipped with an electric circuit for measuring flow velocity, which will be described later, is provided inside the probe body 6 on the top side of the head 7, and a cable 5 is connected to this board for predetermined wiring. It is designed to be done. The bottom plate 8 prevents the electrode rod 20 from being damaged even if the probe 3 accidentally collides with the bottom of the borehole when lowering the entire probe 3 into the borehole 1, and also prevents the flow of groundwater in the observation section 11. It performs functions such as making safety.

A cylindrical wire mesh 12 is disposed between the peripheral end of the head 7 and the peripheral end of the bottom plate 8. This wire mesh 12 prevents foreign matter from entering the observation section 11 due to collapse of the side wall of the borehole 1, etc., and also electrically shields the electrode rod 20 to eliminate the influence of external noise due to earth currents, etc. It is for.

As shown in FIG. 6, the electrode rod 20 includes a rod-shaped electrode rod main body 22 made of an insulating member that penetrates the head 7 and protrudes downward, and a lower end portion of the electrode rod main body 22 that is arranged coaxially at predetermined intervals. Annular first electrodes 23 to 4th electrodes 26 as ion concentration measurement electrodes disposed in
First and second ion generation electrodes 30 as ion formation means each provided below the electrode 26;
31.

The first ion generation electrode 30 is a ground electrode formed in a relatively wide annular shape, whereas the second ion generation electrode 31 is fixed to the lower end of the electrode rod body 22 and has a thin disk shape. These first and second
By arranging the ion generation electrodes 30, 31 and the first to fourth electrodes 23 to 26 on the same axis along the vertical direction and at approximately the same point, the sixth
It is designed to allow non-directional flow velocity measurements in the horizontal plane of the figure.

A positioning collar 27 is provided on the lower end surface of the head 7 of the electrode body 22, and a ring 28 interposed between the collar 27 and the head 7 seals the space between the two. There is.

The upper end of this electrode rod body 22 is fixed to the upper end surface of the head with a nut 21, as shown in FIG. And the first to fourth electrodes 23 to 2
6 and first and second ion generation electrodes 30, 31
is configured to be connected to the substrate by a lead wire through a wiring hole 32 bored in the electrode rod main body 22.

Of the electrode rods 20 configured in this way, the first,
The second ion generation electrodes 30 and 31 form an ion layer (lump) locally around the first to fourth electrodes 23 to 26 based on a pulse voltage applied from the outside.
It is intended to form a

On the other hand, the first to fourth electrodes 23 to 26 measure changes in ion concentration caused by movement (including diffusion) of this ion layer with the flow rate.
Since there is a proportional relationship between ion concentration and electrical conductivity, the first to fourth electrodes 23 to 26 constitute the so-called four-electrode method, which is one of the methods for measuring the electrical conductivity of a liquid. That is, the first and fourth electrodes 23 and 26 have the function of current electrodes, and the second and third electrodes 24 and 25
have a function as a voltage electrode for voltage detection, and these form a set of measurement electrodes. Generally, the electrical conductivity (i.e., ion concentration) of a measured object is determined from the relationship between the voltage and current applied to the measured object, but when a current is passed through a liquid, an electrode reaction occurs and the current gradually becomes difficult to flow. This will cause measurement errors. The four-electrode method adjusts the voltage applied to a pair of current electrodes so that the voltage applied between a pair of voltage electrodes is always constant, thereby eliminating the above measurement error.

Next, the electrical configuration for driving and measuring the electrode group 20 described above will be explained with reference to FIG. 1st,
A pulse generator 35 is connected to the two ion generation electrodes 30 and 31. This pulse generator 35
has the function of outputting a single pulse at a predetermined level for a short period of time. When this single pulse is applied to the first and second ion generation electrodes 30 and 31, the first
- A local ion layer (OH etc.) is formed in the vicinity of the fourth electrodes 23 to 26 in a short time. By forming this ion layer, the ion concentration near the first to fourth electrodes 23 to 26 increases to a predetermined level. This 1st to 4th
An ion concentration detection circuit 40 is connected to the electrodes 23-26.

To explain this in more detail, the first and fourth electrodes 2
3 and 26, a predetermined voltage is applied from the AC power supply 41 via the voltage control section 42, and the electrode rod 20
It is designed to energize the surrounding liquid. Also, the voltage between the second and third electrodes 24 and 25 (the voltage that occurs when the area around the electrode rod 20 is energized)
is sent to the voltage control section 42 via an amplifier 43. This voltage control section 42 controls the voltage applied between the first and fourth electrodes so that the detected voltage input from the amplifier 43 is always constant. A resistor R for current measurement is inserted in series between the voltage control section 42 and the fourth electrode 26, and the current flowing through this resistor R is converted into a voltage between both ends, and the amplifier circuit 44 and the rectifier circuit 4
It is designed to be output via 5.

Therefore, the current I flowing through the resistor R and the voltage electrode 2
The electrical conductivity of the liquid, that is, the ion concentration C, is determined by the voltage V between 4 and 25. In this case, since V is constant, changes in current I can directly measure changes in ion concentration. This ion concentration detection circuit 4
The output of 0 is sent to a comparison circuit 47.

A predetermined ion concentration signal is input to this comparison circuit 47 by manual operation from a reference concentration setting circuit 48 that is separately provided in advance. This comparison circuit 47 connects the first to fourth electrodes 2 described above.
An ion layer is formed around 3 to 26, and the measurement is started after the concentration reaches the measurement start level,
It has a function to immediately output a coincidence signal when the concentration drops to the reference concentration for ending the measurement. This coincidence signal is output to timer 50.

The timer 50 is configured to receive a pulse output end signal from the pulse generator 35 separately. Therefore, the time required from the time when the pulse generator 35 finishes outputting pulses (i.e., the time when the ion layer is formed at the measurement start level) until the comparison circuit 47 outputs a matching signal, that is, the concentration changes to the reference concentration for ending the measurement. A timer 50 measures the time required to do so. If the Q at the time of ion layer formation is measured or calculated in advance from the above-mentioned formula, the flow velocity can be determined based on the set value in the reference concentration setting circuit 48 and the time measured by the timer 50.

Figure 8 shows the flow velocity determined by the above measurement method and timer 5.
An example of the relationship between 0 and the measured time is shown in comparison with a theoretical value. Moreover, FIG. 9 shows the relationship between absolute flow velocity (actual flow velocity) and measured flow velocity.

According to this first embodiment, the flow velocity is measured by forming ion masses in the fluid and detecting the concentration changes accompanying the flow of the fluid, so the extremely small flow velocity can be measured at a single measurement point with a simple configuration. In addition, since the ion mass generation point and the measurement point are the same, accurate measurement can be performed with less measurement error. In addition, since the ion generation electrode and measurement electrode are arranged symmetrically in the horizontal plane, omnidirectional measurement is possible, and once the device is installed, it can be repeated semi-permanently by simply applying pulses to the ion generation electrode. It has the advantage of being able to perform measurements.

In the above embodiment, the flow rate is determined by detecting the time when the reference concentration for completing the measurement is reached, but the flow rate may also be determined by detecting the ion concentration after a predetermined time has elapsed since ion generation. Furthermore, the flow rate may be measured by continuously recording the concentration change after the formation of the ion mass using a plotter or the like. In addition, if the observation section is filled with granular material having almost the same soil properties as the ground to be measured (for example, sand collected from the ground to be measured) and buried around the observation section, the same flow rate measurement as described above can be achieved. More accurate flow rate measurements can be made based on the measurement method.

[Second Embodiment] Next, a second embodiment will be described based on FIGS. 10 and 11. In this second embodiment, the measurement probe includes a substantially cylindrical connecting member 61 that is removably screwed to the lower end of the boring rod 2 described above, and a connecting member 61 that is implanted in the bottom surface 61A of the connecting member 61. It consists of a fixed measuring electrode rod 60.
This measurement electrode rod 60 includes a rod-shaped electrode support rod 62 made of an insulating material, an annular ground electrode 64 and an insulating tube 63 disposed coaxially at the lower end of the electrode support 62 at a predetermined interval. , measurement electrode 65,
It is composed of an insulating cylinder and an ion generating electrode 66 having a conical portion 66A at the tip.

The ion generation electrode 66 is used to generate a local ion layer by a pulse voltage applied between the ion generation electrode 66 and the earth electrode 64. The measurement electrode 65 is the earth electrode 64
This is used to measure ion concentration, that is, conductivity in a liquid.

The outer peripheral side of the connecting member 61 is equipped with fins 70, 70, which protrude radially in the horizontal direction, and by backfilling the fins 70, 70,..., the measuring probe 60 partial hull can be rotated. It is designed to be fixed in place. 80 is a cable for connecting each electrode of the electrode rod 62 to an external device.

The probe constructed in this way is first lowered into the borehole 1 via the boring rod 2, and then pushed down toward the bottom wall of the borehole. At this time, the measuring electrode rod 60 portion is inserted into the ground (see FIG. 10). Next, the area around the connecting member 61 remaining on the bottom wall of the hole is backfilled with sand or the like as shown by the two-dot chain line A in FIG. 10 to fix the entire probe non-rotatably. 2
is removed, and the entire inside of the borehole 1 is backfilled to the ground level. Through this work, the probe part is completely buried within the layer to be measured in the ground, making it possible to accurately measure the actual flow of groundwater.

FIG. 11 is an explanatory diagram showing the ion concentration measuring circuit in the second embodiment. This ion concentration measurement circuit 90 consists of three fixed resistors as shown in the figure.
R ₁ to R ₃ , the measurement electrode 65 and the ground electrode 64
A variable resistance RX _, which is a liquid resistance, is bridge _- connected to The voltage V between the resistors R ₁ and R ₂ and the terminal P is measured to measure the variable resistor RX, that is, the change in conductivity of the liquid. By configuring the measurement circuit 90 in this way, the concentration change of the ion layer formed locally between the measurement electrode 65 and the ground electrode 64 at the ion generation electrode 66 with the flow of groundwater can be detected using the measurement voltage V. This can be seen as a change in Then, by performing calculations substantially similar to those in the first embodiment for this concentration change, the flow velocity of groundwater can be determined.

According to this second embodiment, the probe and measurement circuit can be configured extremely easily, and the entire device can therefore be miniaturized, and the actual groundwater flow velocity can be measured accurately over a long period of time. Become.

〔Effect of the invention〕

As described above, according to the present invention, since the measurement start point is already at or near the maximum level point of the ion concentration, there is no need to detect the maximum level point, and at the same time, the influence of diffusion is small, so measurement errors are reduced. The size of the device is significantly smaller, which improves measurement accuracy, and measurement can be performed at a single measurement point, making it possible to further miniaturize the device and improve work efficiency. It is possible to provide an unprecedented and excellent fluid flow rate measurement method and device.

[Brief explanation of the drawing]

Figures 1 to 3 are explanatory diagrams explaining the measurement principle of the present invention, Figure 4 is an explanatory diagram showing the first embodiment of the present invention, and Figure 5 is a partially cutaway diagram showing the probe of Figure 4. 6 is a partially cutaway front view showing an electrode rod according to a part of FIG. 5, FIG. 7 is a block diagram showing an example of the configuration of an electric circuit used for measurement, and FIGS. 8 and 9. 10 is a diagram showing an example of a measurement result, FIG. 10 is a front view showing a probe according to a second embodiment of the present invention, and FIG. 11 is an explanatory diagram showing the measurement circuit of FIG. 10. 20, 60...Measurement electrode rod, 23-26...
...first to fourth electrodes as electrodes for measuring ion concentration,
30, 31, 66...Ion generation electrode as ion forming means, 35...Pulse generating section, 40...
...Ion concentration detection circuit, 47...Comparison circuit, 50
...Timer, 64... Earth electrode, 65... Measuring electrode, 90... Ion concentration measuring circuit.

Claims (1)

[Claims] 1. A measurement electrode section and an ion generation electrode section are disposed at the same location in the fluid to be measured, and then a predetermined pulse voltage is applied to the ion generation electrode section to define a predetermined measurement area. An ion layer with an ion concentration at the measurement starting level is formed, and then the application of pulse voltage to the ion generating electrode section is stopped, measurement of the degree of decrease in ion concentration is started, and the fluid is adjusted according to the level change. A fluid flow velocity measurement method characterized by determining the flow velocity of a fluid. 2. An ion concentration measuring electrode disposed in the fluid to be measured, an ion forming means consisting of a pair of electrode members separately installed at one end and the other end of the ion concentration measuring electrode, and It has a pulse generator that applies a predetermined pulse voltage until the ion concentration between the electrodes reaches a predetermined measurement start level, and starts timing immediately upon receiving a pulse output end signal output from the pulse generator. a timer to
and an ion concentration detection circuit that converts the ion concentration detected by the concentration measurement electrode into an electrical signal and outputs it, and when the signal output from the ion concentration detection circuit drops to a predetermined reference value for ending the measurement. 1. A fluid flow rate measuring device, characterized in that a comparison circuit that immediately outputs a timing stop signal to the timer when the ion concentration detection circuit is installed is attached to the ion concentration detection circuit.