JPS59155718A - Flow velocity detecting apparatus - Google Patents

Abstract

PURPOSE:To measure the flow velocity of a liquid, especially, the liquid having viscosity or the liquid comprising muddy matter flowed through a pipe at a low speed, by selecting the operation of either one of three systems by an apparatus comprising the combination of an air bubble injector, an electrostatic capacity detecting electrode and a flow velocity operator. CONSTITUTION:An air bubble injector 2 capable of injecting a minute amount of air bubbles into a pipe 1 is provided to the pipe 1 while an electrostatic capacity detecting electrode 3 is provided behind said injector 2 so as to leave a distance L2 therefrom and connected to a converter 4 for converting electrostatic capacity to an electric signal. A flow velocity operator 5 inputting this electric signal and the injection signal generated when air bubbles are injected by the injector 2 measures an air bubble passing time and divides the distance L2 by a measuring time to calculate a flow velocity. The electrode 3 is determined by the properties of the substance to be detected flowed through the pipe 1 or the selection of an operation system and, when the dielectric constant of the substance to be detected may be large and the electrode may be small, a detection electrode 7 and an opposed electrode 8 are opposedly provided on the insulating sheet 6 fixed to a part of the pipe 1 and the electrostatic capacity of the detection electrode 7 to the opposed electrode 8 is calculated.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a liquid flow rate detection device for detecting the flow rate of a highly viscous liquid or an abrasive muddy liquid.

Conventionally, various methods have been proposed for flowmeters and current meters, but ultrasonic flowmeters and electromagnetic flowmeters, which have little interference with the flow, have poor accuracy at low speeds, and are not capable of measuring the flow rate of low-speed fluids. The various mechanical types had the disadvantage that they could not be applied to highly viscous liquids or abrasive muddy liquids. For this reason, there is still no suitable measuring device for detecting the flow rate of highly viscous liquids that are often sent through pipes at low speeds, or muddy liquids that contain highly abrasive stone powder or metal powder. This is the current situation.

This invention was made in view of the above circumstances, and it is possible to inject a very small amount of air bubbles that do not change the chemical composition of the fluid and do not pose a risk of impeding the flow, without worrying about changing the flow rate. It is an object of the present invention to provide a liquid flow rate detection device that can measure the flow rate of the fluid by detecting the propagation of the bubbles together with the fluid using a capacitance detector.

The present invention will be described below based on embodiments shown in the accompanying drawings.

As shown in FIG. 1, a pipe 1 is provided with a bubble injector 2 that can inject a small amount of bubbles into the pipe 1. Behind (downstream) of this bubble injector 2, there is a distance L1 between the bubble injector 2 and the bubble injector 2. A capacitance detection electrode 3 is provided at a distance, and the capacitance detection electrode 3 is connected to a converter 4 that converts capacitance into an electrical signal. The flow rate calculator 5, which receives this electric signal and the injection signal emitted by the bubble injector 2 when injecting bubbles, connects the capacitance detection electrode 3 and the converter after the bubbles are injected and the injection signal is emitted. 4, the time until the passage of the bubble is detected is measured, and the flow velocity is calculated by dividing the distance by the measurement time.

The capacitance detection electrode 3 is determined by the nature of the object to be detected flowing in the pipe 1 and the selection of the calculation method, and an example thereof will be shown below. First, if the dielectric constant of the object to be detected is large and the electrode can be small, especially if it is necessary to detect local capacitance changes, a part of the pipe 1 as shown in FIG. An insulating sheet 6” fixed to a detection electrode 7
and a counter electrode 8 are provided to face each other, and the capacitance of the detection electrode 7 with respect to the counter electrode 8 is determined.

Second, if the electrode is small and the capacitance change is small,
Alternatively, if it is difficult to capture bubbles locally, as shown in FIG. It is sufficient to detect the capacitance between. However, in this case, using the counter electrode 8a as a guard electrode and detecting the capacitance between the detection electrode 7a and the pipe 1 yields almost the same results, and has the advantage that one of the detection electrodes is grounded. It is preferable that there is. Note that the guard electrode is installed for the purpose of limiting the detection location to one location by making it the same potential as the detection electrode 7a and blocking the current flowing between the detection electrode 7a and the pipe wall on the guard electrode side. , is not necessarily required and may be omitted.

Thirdly, if the capacitance is to be detected over a wide range, and the shape of the bubble is large, or if it is necessary to detect the pulsation of a collection of fine bubbles, as shown in Fig. 4,
An insulating sheet 6b is wrapped around the pipe 1, and this insulating sheet 6b
Detection electrodes 7 are arranged on the pipe 1 at predetermined intervals in the longitudinal direction.
b and the counter electrode 81) are fixed, and the capacitance between the detection electrode 7b and the counter electrode 8b is measured. Note that, if particular precision is not required, the capacitance between the pipe 1 and the detection electrode 71 may be measured by short-circuiting the pipe 1 and the counter electrode 8b.

In addition, in the capacitance detection electrode mentioned above, the table shows that the capacitance is CO when all the space except the part facing each other via an insulator is air, and the inside of the pipe 1 is filled with the detection object. If the relative permittivity of the object to be detected is ε, then the capacitance C8 becomes C1-εCO, and since the relative permittivity ε is always larger than ], the capacitance C8 is
5 is larger than the capacitance. By the way, when a bubble passes through a place where a capacitance detection electrode exists, the relative dielectric constant of the bubble is 1, so it is not easy to provide a quantitative formula, but the capacitance decreases and the bubble's dielectric constant is 1. Passage can be detected.

Note that what is needed here is not quantitative detection of bubbles, but
Since the purpose is to detect the passage of air bubbles, the following two detections are sufficient.

In addition, if the inside of the pipe 1 is not filled with the object to be detected, there is a problem in detecting the amount of the object passing through in addition to the flow rate for flow rate measurement. The passage cross section can be detected by First, as shown in Fig. 5, the capacitance per unit area is calculated when an object with a dielectric constant of ε and a thickness of a is inserted into the parallel electrodes 9, 9 separated by a distance cl ii, ilj. If C2 is the capacitance per unit area when the space between the parallel electrodes 9 and 9 is all air, then the capacitances C2 and C are as follows: εd C2-a-+g (d-a) 0 holds true, and the capacitance @C2 becomes an increasing function with respect to the thickness 1.

If the capacitance detection electrode has a shape as shown in Figure 4 and the cross-sectional shape of the object to be detected becomes complicated, it will be difficult to formulate a precise mathematical formula, but as long as the fluid is not biased to the left or right in the pipe 1. It is assumed that a certain functional relationship holds true for the quantity, regardless of the shape or position of the detected object. In fact, experimentally the fourth
When capacitance is measured using the capacitance detection electrode shown in the figure, a reproducible function is obtained for the amount of the detected object, and the value corresponding to the amount of the detected object is obtained from the obtained capacitance meter value. This can be achieved by using a function generator or a memory in which the function is stored in advance. By using the capacitance detection electrode shown in Fig. 5, the cross-sectional area of the object passing through the pipe 1 can be measured, and the flow rate can be easily determined from this cross-sectional area and the flow velocity. This is the advantage of using capacitance detection to detect bubbles.

Next, it will be shown that the flow rate of the object to be detected can be measured using the bubble injector 2, the capacitance detection electrode 3, and the like.

The first method calculates the propagation velocity by directly measuring the time it takes for the bubble to pass between two points. This means that the bubble injector 2 injects bubbles into the pipe 1 at a period longer than the time it takes for one bubble to pass the distance L1. Therefore, if the bubble injection time is r1, and the time when the bubble is detected by the capacitance detection electrode 3 is r2, then the time r for the bubble to travel after being injected is r = 'r2-'r. ,
Therefore, the propagation speed of the bubble is V.

It is obtained as V= □. If the pipe 1 is installed horizontally, the propagation velocity V of the bubbles and the flow velocity of the object to be detected are equal, so the flow velocity of the object to be detected is V. In addition, in this measurement, the bubble injection interval needs to be longer than the passage time f. This is because it cannot be confirmed that the bubble detected by the capacitance detection electrode 3 is the bubble injected immediately before.

Therefore, taking into account expected fluctuations in flow rate, the injection interval would be set to a value larger than the slowest case, but this would take longer to obtain − measurements and accommodate rapid fluctuations in flow rate. In addition, the risk of erroneous measurements increases.

In order to eliminate the above-mentioned drawbacks, there are methods that control the bubble injection interval based on the obtained measurement results. That is, the response speed and accuracy of measurement are improved by controlling the injection interval to be a value greater than the measurement time r by shortening the injection interval when the flow rate is high and increasing it when the flow rate is slow. A simple and reliable means to achieve this is to activate the bubble injector 2 at the moment when a bubble is detected by the capacitance detection electrode 3, and inject the bubble into the pipe 1. This has the advantage that the flow velocity calculator 5 is extremely simple. However, in this measurement, once a false detection is made, the bubble injection interval will be controlled based on the false result, and there is a risk of false measurement, so it is necessary to provide a compensator in case of any false detection. There is.

Therefore, in order to further reduce the risk of erroneous measurements, it is possible to distinguish between bubbles injected at a certain time and bubbles injected before and after that time.

For example, the size of bubbles that are sequentially injected may be changed, or a plurality of bubbles may be injected in succession, and the number of bubbles injected may be changed. If this is repeated a sufficient number of times to return to the original state, the converter 4 or the flow rate calculator 5 is equipped with a means for identifying it, and the passage time of the same bubble can be measured to avoid erroneous measurements. will disappear.

Note that the above flow rate measurement was performed on the premise that the injection time from the bubble injector 2 could be specified, but even if this is not possible, the flow rate can be measured.

The second method has a faster response speed than the first method, making it possible to measure even when the flow velocity is very slow. This method does not directly measure the propagation speed of a bubble between two points, but rather modulates the bubble injection interval or the number of injections per unit time, and calculates the bubble passing signal from the capacitance detection electrode by appropriately modulating the bubble injection interval or the number of injections per unit time. This modulation signal is demodulated, and the propagation time between two points of the bubble is indirectly measured from the relationship between the modulation signal and the demodulation signal.

An example of the second method is to increase the number of injections per unit time at a constant rate △ in proportion to time, and after a sufficiently long time relative to the flow rate, decrease and return to the original number of injections r. It produces repeating sawtooth frequency modulation.In the increasing section, the number of injections per unit time is ``.When time [ has elapsed, the number of injections f is f = fo + △[・On the other hand, when the number of passages per unit time is demodulated from the detection signal of a bubble passing through the capacitance detection electrode, it is delayed by the time E' required for the bubble to propagate from the injection point to the detection point. Therefore, the number of passes f' per unit time in the same time becomes f' = fo + △ "・(t-t'), as shown in Figure 6. Therefore, the difference between the modulated signal and the demodulated signal is taken. Then, f-"'-△f-t'f-f't'=□△" Since the value △f is constant, the propagation time 1' can be found, and 'Similar to the first method, The bubble propagation velocity V is determined from the equation LE', and if the pipe 1 is horizontal, this becomes the flow velocity.

Note that the number of injections is f. The output signal of the difference f - f' between the modulated signal and the demodulated signal is disturbed near the boundary where it returns to Then, it will show a constant value of △f·E' which is proportional to the flow velocity.

Also, the number of injections F. The repetition interval for returning to ``.'' must be sufficiently longer than the propagation time L', so similarly to the first method, the repetition frequency of bubble injection, the number of injections ``.'', and the variable value △f are fed back from the obtained flow velocity. Accuracy may be improved by controlling.

Next, the other side of the second method will be shown. This adds sinusoidal frequency modulation to the number of injections per unit time (1).If the sinusoidal modulation signal S is 5=sin ω・[, then the number of injections of modulated bubbles per unit time is f=[ o+△f-sinω・[ Since the number of days f' in which a bubble passes per unit time detected by the capacitance detection electrode is delayed by the time E' as in the previous example, f'==fo+△f-sinω- (t-t'),
When the sine wave signal is demodulated from this, the demodulated signal S' becomes S'=sinω·(t-t'). The time t' can be easily determined from the relationship between the two signals s and s' using digital or analog delay measurement or phase measurement means since the two signals are sine waves of the same frequency. From this, the flow velocity V can be measured.

The above is a frequency modulation that modulates the number of injections per unit time using sawtooth and sine wave signals, but as shown in Figure 7, in addition to the standard bubbles injected at regular intervals, Various modulation methods can be applied, such as phase modulation in which a bubble is added with similar modulation to the phase P, and various waveforms can be considered for improving the accuracy of the modulated signal.

In the third method, air bubbles are mixed in the detection object, and the first method. In the second method, it is impossible to distinguish between injected bubbles and mixed bubbles, leading to the risk of erroneous measurements, and it is not possible to inject a single bubble at any time as desired due to the pipe installation situation and the nature of the detected object. This will be adopted in certain cases. This method is based on the first method.
This is the opposite of the second method, injecting completely irregular bubbles.
If there is regular periodicity, measurement becomes difficult, so if necessary, a stirring device may be provided to disperse bubbles irregularly after injection. This stirring device is preferably of a stationary type so that it is effective for viscous substances to be detected.

This third method cannot be measured with the measuring device shown in FIG. 1, so as shown in FIG.
The first one is located behind (downstream) of the I-large vessel 2. The second electrostatic waste amount detection electrodes 10.11 are provided at a predetermined distance L2 apart, and each electrode 1
0.11 is connected to a converter 12 that converts capacitance into an electric signal, and this converter 12 is connected to a flow velocity calculator 13. Note that even if there are multiple electrodes io and ii, there is no need for multiple converters; if you measure while switching multiple electrodes with a single converter, the electrostatic field M
can be detected. By combining a high-speed switch and a corresponding analogue blowfish or digital memory, it is possible to perform multi-point measurements sufficient for a flow velocity measurement system. Further, the capacitance detection electrode 11 detects air bubbles and emits an injection signal indicating that air bubbles have been artificially injected.

-1- Section 1. Assuming that the capacitances detected by the second capacitance detection electrodes 10 and 11 are respectively C3+''4, the capacitances C3 and C4 fluctuate irregularly with time, but their waveforms are as shown in FIG. As shown in a), the time E' for the bubbles to propagate through both electrodes 10 and 11 is similar by 8, so C4(L)#C3(LL').Here, the electrostatic field ...The correlation φ between C3 and C4 is taken, and this has a peak point as shown in Figure 9 (1) when τ-['.Therefore, this peak point is the expected flow rate. The correlation φ is obtained for an appropriate range of τ corresponding to the value of τ, and when this is differentiated, the value of τ when the differential value becomes zero is obtained.

In this way, if the time (') is determined, the propagation velocity V of the bubble becomes 2 E', and if the pipe is horizontal, this value becomes the flow velocity.

The second calculation process can be performed using a digital calculator by converting the capacitances C3 and C4 into digital values, or can be performed in an analog manner.

Explaining the calculation system for analog flow rate measurement based on Fig. 10, advancing the measured electrostatic field [WC+(t) and delaying the capacitance C31t) have the same result, so the electrostatic Capacitor C4 (1) is connected to analog delay circuit 1
5 is delayed by a time τ, and the time [ is controlled in inverse proportion to the oscillation frequency of the clock generator 16.
t ) is multiplied by the multiplier 17, and then the integrator 1
B is integrated over a sufficient period r, and the correlation φ−+5
TC3(t-t)·C,,(t),dt is output. When this output is differentiated with respect to time τ through the differentiator 19 while changing the frequency f, the time τ at which the differential output becomes zero is the sought time L', so this time τ
is measured indirectly by the frequency f. That is, the frequency f at the moment when the differential output becomes zero. Since it represents the period, it can be directly determined by calculating the period.

Note that determining the differential value while greatly changing the time τ has the disadvantage that the total time will be extended by 1111j and the response speed to changes in flow velocity will be slow. It is desirable to feedback control the clock generator 16 so that it varies in the vicinity. Further, it is desirable to perform feedback control on the bubble injector 2 so that the distribution frequency of irregular fluctuations of bubbles varies within an appropriate range from the obtained flow rate value.

In the above embodiments, the embodiment shown in FIG. The flow velocity can also be measured using the second method.

As described above, this invention is a device that combines a bubble injector, a capacitance detection electrode, a flow velocity calculator, etc. by selecting one of the three calculation methods, and is capable of handling liquids, especially at low speeds, in pipes. It becomes possible to measure viscous liquids or muddy liquids flowing inside. If the pipe is not filled with fluid, an insulating sheet is wrapped around the pipe, and a detection electrode and a counter electrode are fixed on the insulating sheet at a predetermined distance in the longitudinal direction of the pipe.
Since it is possible to determine the cross-sectional area of the object to be detected as it flows through the pipe, there is an advantage that not only the flow velocity but also the flow rate can be measured extremely easily.

[Brief explanation of the drawing]

FIG. 1 is a block diagram showing an example of this invention, and FIG.
The figure is a perspective view showing an example of a capacitance detection electrode, Fig. 5 is a front view showing parallel electrodes, Fig. 6 is a waveform diagram explaining an example of the first method, and Fig. 7 is an example of the second method. FIG. 8 is a block diagram showing the other side of the invention, and FIG.
a), (+3) are waveform diagrams illustrating an example of the third method,
FIG. 10 is a circuit diagram showing an example of an arithmetic system for performing the third method. 1...Pipe, 2...Bubble injector, 3,10.11
... Capacitance detection electrode, 4, 12 ... Converter, 5,
13... Flow rate calculator, 6, 6a, 6b... Insulating sheet, 7° 7a, 7b... Detection electrode, s, sa, sb.
...Counter electrode, 9...Parallel electrode, N Figure 6 Figure 9 (b) Figure 10 Figure 8

Claims (1)

[Claims] (1) A bubble injector for injecting bubbles into a pipe; a first capacitance detection electrode provided on the pipe behind the bubble injector for detecting bubbles; A flow velocity detector consisting of a converter that converts into an electrical signal, and a flow velocity calculator that calculates the propagation velocity of the bubbles by determining the propagation time for the bubbles injected from the bubble injector to pass through the capacitance detection electrode. . (2) The bubble injector is composed of a bubble injector and a second capacitive slip detector for detecting bubbles from the bubble injector, and emits an injection signal when the bubbles pass through the second capacitance detector. A flow velocity detection device according to claim 1, characterized in that: f3) J- The capacitance detection electrode is characterized in that a detection electrode and a counter electrode are provided on an insulating sheet measured on a part of a pipe. Flow rate detection device described in Section 1. (4) The capacitance detection electrode is characterized in that the detection electrode and the counter electrode are wound at a predetermined distance with an insulating sheet interposed therebetween. flow velocity detection device. (5) The above-mentioned capacitance detection electrode is a patent characterized in that the detection electrode and the opposing electrode are provided on an insulating sheet wrapped around the pipe at a predetermined interval in the longitudinal direction of the pipe. A flow rate detection device according to claim 1 or 2.