JPH0572220A - Detecting apparatus of velocity of fluid - Google Patents

Abstract

PURPOSE:To enable execution of highly precise detection by a method wherein a pressure of an internal space of a surrounding body provided on the upper side of a flow passage and having a hole bored in the wall surface is made to fluctuate at a prescribed frequency and the velocity of a fluid is calculated on the basis of a change in the pressure generated. CONSTITUTION:A surrounding body 7 covers a hole 2 bored in the wall surface of a pipe 1 from outside in an airtight manner. A sound pressure generating means 10 such as a thin-type speaker is fitted to the wall surface of the surrounding body 7 so that it forms a part of the wall surface. The means 10 is driven in a sine wave manner by a drive circuit 11 of which an output frequency is set to be a Helmholtz resonance frequency determined by the capacity V10 of the surrounding body 7, the dimension of the diameter 2r of the hole 2, etc., and an internal pressure in the surrounding body 7 is made to change at the Helmholtz resonance frequency. A capacitor-microphone 8 is fitted inside the surrounding body 7 and detects the pressure in the surrounding body 7. A coeffi cient circuit 9 amplifies a detection output from the microphone 8 at a prescribed amplification rate, detects the flow velocity of a gas in the pipe 1 and outputs it.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a fluid velocity detecting device for detecting the velocity (flow velocity) of a fluid flowing through a pipe or the like.

[0002]

2. Description of the Related Art As a conventional fluid velocity detecting device, an air flow sensor will be described as an example. That is, the air flow sensor arranges a thin heater wire in the flow of gas so as to be orthogonal to the flow direction of the gas, supplies a constant current to the heater wire in a pulsed manner to generate heat, and the heat is radiated by the heater wire. The flow velocity of the fluid was detected by detecting the resistance change.

[0003]

However, in such a conventional fluid velocity detecting device, since the heater wire is in direct contact with the fluid, dust, chemical vapor, etc. are mixed into the fluid. If it is attached to the heater wire, or the surface of the heater wire is in direct contact with the chemical vapor in the fluid for a long period of time, the heat dissipation state changes over time, There was a possibility that the thermal relationship between the fluid and the heater wire would change and the error would gradually increase.

Further, since a very thin heater wire is used in order to obtain a large change in the resistance value of the heater wire, when the dust is large and it moves at a high speed, the heater wire is very Since a large external force may cause plastic deformation, it is necessary to provide a filter on the windward side.

Furthermore, since an external force proportional to the velocity of the fluid hits the thin heater wire and the heater wire always acts on the fluid as a flow resistance, when the fluid with high velocity is to be measured, the heater is used. There is a risk that the wire will be stretched and the measurement error will increase, and if an external force that exceeds the elastic limit of the heater wire is applied, the heater wire will have a resistance value different from the initial resistance value.

The present invention solves the above-mentioned problems by adapting the principle of acoustic technology, that is, a research field of a completely different student from the above-mentioned technical field, for example, as an acoustic component. It is an object of the present invention to provide a fluid velocity detecting device which is easy to maintain and uses, which is cheaper and more accurate than ever before, by using a generally well-known speaker and microphone.

[0007]

SUMMARY OF THE INVENTION According to the present invention, there is provided an enclosure provided on an upper side of a fluid passage and having a hole formed in a wall surface in contact with the passage, and a pressure in an inner space of the enclosure. A configuration for calculating the velocity of the fluid, comprising sound pressure generating means for varying the fluid at a predetermined frequency, and flow velocity detecting means for calculating the velocity of the fluid based on the pressure change generated in the internal space of the enclosure. And

[0008]

In the fluid velocity device according to the present invention, the pressure of the gas in the enclosure is changed at the Helmholtz resonance frequency determined by the actual space volume of the enclosure, the size of the hole, etc., and the fluid is passed through the hole of the enclosure. The velocity of the fluid is simply measured by acting on the measurement fluid and detecting the pressure fluctuation in the enclosure at that time.

[0009]

DESCRIPTION OF THE PREFERRED EMBODIMENTS An outline of the theory of the basic principle of the present invention will be described with reference to FIG. In FIG. 1, reference numeral 1 denotes a pipe having a wall thickness h, in which a gas (fluid) to be measured flows from one end A to the other end B at a flow velocity V _f . Reference numeral 2 denotes a small-diameter hole 2r having a diameter 2r formed in the wall surface of the pipe 1, and reference numeral 3 denotes sound pressure generation of a speaker or the like which is opposed to the hole 2 formed in the wall surface of the pipe 1 at a predetermined interval. It is driven at a predetermined frequency by means. Reference numeral 4 denotes a diffracted wave of a sound wave generated by the sound pressure generating means 3 (which has the same meaning as the sound pressure here) becomes a compressional wave and is diffused and formed in an arc shape after passing through the hole 2.

Next, the principle of obtaining the flow velocity V _f based on the above basic configuration will be described with reference to FIGS. 2 to 4. First, as shown in FIG. 2, a cylinder of air (density ρ) having a diameter 2r and a thickness (wall thickness) h is formed in a portion of the hole 2 formed in the wall surface of the pipe 1 as shown by the diagonal lines. It is considered that the acoustic tube 5 having a diameter 2r and a length h in terms of acoustics is formed thereby. The sound pressure generating means 3 is arranged so as to face the acoustic tube 5 from below (see FIG. 1), and the sound pressure generating means 3 is driven by a sine wave at a predetermined frequency.

Here, when the sound pressure generating means 3 is driven by a sine wave at a predetermined frequency, at the upper open end of the acoustic tube 5,
As shown in FIG. 3, a cylindrical air portion (mass: m) 6 of air (density ρ) having a radius r and a thickness (πr) / 2 is generated by the sound pressure generating means 3 and the air spring (in the acoustic tube 5). It is considered that the air spring 1c in FIG. 6 and the single vibration up and down at a velocity V _v (t) (displacement: X (t)). At this time, the mass m of the cylindrical air portion 6 (hereinafter referred to as additional mass) is expressed by the following equation.

[0012]

[Equation 1]

However, (π · r) / 2 can be theoretically calculated. Also, the kinetic energy of this vibration system is
(1/2) m · v _v ² .

Here, as shown in FIG. 1, the gas flows in the pipe 1 from the direction A to the direction B at the flow velocity V _f , and the gas also flows at the upper end surface of the acoustic tube 5 at the velocity V _f . Assuming that, the cylindrical air portion 6 in the portion of the additional mass m shown by the diagonal lines in FIG. 3 receives an external force by the gas flowing from the A direction, and the velocity V _f is shown by the diagonal lines C and D in FIG. Is flowed downstream (direction B) by an amount proportional to (indicated by L in FIG. 4). As a result, the cylindrical air portion 6 in the portion shown by the solid line in FIG. The energy stored in the portion of the additional mass m of is also carried away by the flow of air in the leeward direction, that is, in the B direction.
In other words, energy dissipation occurs. Therefore, when a displacement amount (displacement amount) L occurs during the time t and the plane sectional area of the portion of the additional mass m is A

[0015]

[Equation 2] Becomes However, K is a constant. The amount of energy D · t dissipated during time t is

[0016]

[Equation 3]

Energy amount D dissipated per unit time
Is

[0018]

[Equation 4]

However, d = (mKV _f ) / (πr ² ). Substituting equation 1 into equation 4

[0020]

[Equation 5]

At this time, the velocity V _f of the fluid is

[0022]

[Equation 6]

[0023] That is, if the damper coefficient d of the acoustic tube 5 is known, the flow velocity V _f can be known.

Next, each specific configuration will be shown, and how to obtain the damper coefficient d and how to obtain the flow velocity V _f will be described with reference to FIGS. 5 and 6. First, it demonstrates based on FIG. In the figure, the same components as those in FIG. 1 or their equivalents are designated by the same reference numerals and the description thereof will be omitted.

In the figure, 7 is a hole 2 formed in the wall surface of the pipe 1.
Airtight housing that covers the outside from the outside (enclosure)
A sound pressure generating means 10 such as a thin speaker is attached to the wall surface of the housing 7 so as to form a part of the wall surface. The sound pressure generating means 10 has a volume V _{0 of the} housing 7 and a hole 2 Drive circuit 1 in which the output frequency is set to the Helmholtz resonance frequency determined by the size of the diameter 2r of the
1 drives a sine wave to change the internal pressure in the housing 7 at the Helmholtz resonance frequency.

In FIG. 5, a hole is formed on the wall surface of the pipe 1.
2 was drilled, but the part of the wall surface of the housing 7
A part of the wall surface of Ip 1 is formed and a hole 2 is formed on the wall surface.
May be pierced and shared with the wall surface.
The shape of the hole 2 is not only circular but also rectangular such as rectangular and square.
The size and shape of the
Needless to say, it can be decided by the situation. 8 is
With a condenser microphone (sound pressure detection means),
Mounted in the housing 7 to provide pressure (sound
Pressure) fluctuation is detected. 9 is a coefficient circuit including an amplifier circuit, etc.
Then, the detection output from the microphone 8 is set to a predetermined amplification factor.
And the flow velocity V of the gas in the pipe 1 _fTo detect
Output.

Next, the calculation logic of the damper coefficient d of the acoustic tube 5 based on the configuration shown in FIG. 5 will be described with reference to FIG.

First, in FIGS. 5 and 6, P ₀ is the atmospheric pressure, ΔP (t) is the change amount of the pressure (sound pressure) in the housing 7 generated by the driving of the sound pressure generating means 10, and X (t ) Is the vertical displacement of the cylindrical air portion 6 forming the additional mass m generated in the hole 2 of the pipe 1, and U (t) is the pressure receiving surface of the sound pressure generating means 10 (for example, the cone paper of the speaker). Equivalent to)
, R is the radius of the hole 2 of the pipe 1 (also the radius of the cylindrical air portion 6 forming the additional mass m), V ₀ is the actual space volume in the housing 7, and S is the sound pressure generating means 10. Area of pressure receiving surface, γ is specific heat ratio of gas (1.4 in case of air), V _f
Is the flow velocity of the gas to be measured, A is the cross-sectional area of the cylindrical air portion 6 forming the additional mass m (opening area of the hole 2), m is the mass of the cylindrical air portion 6 (additional mass), and d is the acoustic tube. 5 can be considered equivalent to the physical model of the vibration system shown in FIG. 6.

That is, the portion of the cylindrical air portion 6 in the physical model is the additional mass m of the cylindrical air portion 6 itself,
An air spring generated in the housing 7 (or generated in the housing 7 through the acoustic tube 5 and a cylindrical air portion 6).
Therefore, it can be said that it is generated in the acoustic tube 5) 1c,
It is composed of a control element such as a damper 1b generated in the acoustic tube 5. Therefore, in FIG. 6, the following equations 7 and 8 are established.

[0030]

[Equation 7]

[0031]

[Equation 8]

The above equations 7 and 8 are Laplace transformed and arranged. Here, since it is a prerequisite that the flow velocity V _f of the gas in the pipe 1 and the damper coefficient d are in a proportional relationship, when the drive frequency of the sound pressure generating means 10 is set to the Helmholtz resonance frequency as described above. , Its resonance angular frequency ω _r is

[0033]

[Equation 9]

By

[Equation 10]

Can be set. Ie

[0036]

[Equation 11]

Is satisfied. Next, from the above equation 11, ΔP
The transfer function from (s) to U (s) is

[0038]

[Equation 12]

In Equation 12, the drive frequency (or drive angular frequency) of the sound pressure generating means 10 is set to the Helmholtz resonance frequency (or Helmholtz resonance angular frequency), and the drive voltage is set to a sine wave having a constant peak value. Therefore, U (iω) = constant value and ΔP (iω) = output voltage value of the microphone 8 can be set.

Therefore, from the above equation 12, the damper coefficient d
Is calculated by arithmetic calculation, and the result is substituted into Equation 6 to calculate the flow velocity V _f of the fluid to be measured.

Next, an embodiment will be described based on the apparatus shown in FIG. In FIG. 7, the same components as those shown in FIG. 5 or equivalent components are designated by the same reference numerals, and the description thereof will be omitted.

That is, in the figure, the pipe 1 is extended horizontally in the left-right direction, and a hole 2 is bored at the top of the pipe 1.
In addition, a state is shown in which the housing 7 is installed so as to cover the hole 2 from above, and the details and the detection circuit are as follows. Reference numeral 13 is a partition plate for partitioning the housing 7 into the same volume on the left and right, and the central portion of the partition plate 13 alternately presses the first and second housings 7a, 7b formed by the partition plate 13. It is formed by the sound pressure generating means 10 such as a thin speaker. Also, the first housing 7a partitioned by the partition plate 13
Communicates with the internal space of the pipe 1 through the hole 2, and the second housing 7b is completely sealed, and the first and second
Microphones 8 and 14 having the same characteristics are provided in the housings 7a and 7b, respectively, and an output signal from the microphone 8 is added to the adding circuit 21, and an output signal from the microphone 14 is output to the first absolute value circuit 20 and the adding circuit. 21 are respectively connected.

The sound pressure generating means 10 is driven by the drive circuit 11 which outputs the sine wave set to the Helmholtz resonance frequency described above.

Next, the logic by which the damper coefficient d and the flow velocity V _f are calculated by using the structure shown in FIG. 7 will be described. In other words, ΔP ₁ (t) is generated by driving the sound pressure generating means 10 and ΔP ₂ (t) is generated by driving the sound pressure generating means 10. The amount of change in internal pressure in the second housing 7b, X (t) is the amount of vertical displacement of the cylindrical air portion 6 generated in the hole 2 of the pipe 1, and U (t) is the pressure receiving surface of the sound pressure generating means 10. In the left-right direction, r is the radius of the hole 2 of the pipe 1, V ₀ is the actual space volume of the first and second housings 7a and 7b, S is the area of the pressure receiving surface of the sound pressure generating means 10, and γ is gas Specific heat ratio (1.4 in the case of air), V _f is the flow velocity of the gas flowing in the pipe 1,
A is a cross-sectional area of the columnar air portion 6, m is the columnar air portion 6
, D is the damper coefficient generated in the acoustic tube 5, and C ₀ is the sound velocity.

[0045]

[Equation 13]

[0046]

[Equation 14]

Here, the absolute value of the amplitude of ΔP ₂ (s) and ΔP 2
Taking the ratio of the absolute value of the amplitude of ₁ (s) + ΔP ₂ (s),

[0048]

[Equation 15]

In Expression 15, | ΔP ₂ (s) | is the absolute value of the output of the microphone 14, that is, the output of the first absolute value circuit 20, and | ΔP ₁ (s) + ΔP ₂ (s) | is an adder circuit 21 for adding the respective outputs of the microphones 8 and 14.
In absolute value of the sum, that is, those taking the absolute value of the sum output from each of the adder circuit 22 of the microphone 8 and 14 in the second absolute value circuit 22, and V _0,
Since each of A, π, γ, K and C ₀ is a constant and is set as a coefficient of the coefficient circuit 24, V _f can be obtained.

That is, the outputs of both microphones 8 and 14 are supplied to the second absolute value circuit 22 via the adder circuit 21 connected to each output side, and the absolute value output is
First absolute value circuit 2 to which the output of the microphone 14 is connected
The output of 0 is divided in the division circuit 23 at the next stage, and the division result is multiplied by a coefficient in the coefficient circuit 24 to obtain the flow velocity V.
Calculate _f . The coefficient of the coefficient circuit 24 is expressed by
It is set according to the situation by the magnitudes of the constants V ₀ , A, π, γ, K and C ₀ in 5.

Further, as shown in FIG. 8 for the details of the main part of the structure described in FIG. 7, the inner bottom surface of the first housing 7a is formed in a saddle shape, and the hole 2 is formed at the top thereof.
, The inner bottom surface is formed with a tapered surface 26 that is inclined toward the hole 2 as shown in FIG.
When water drops or the like are generated in the housing 7a, the water drops fall on the tapered surface 26 and are collected in the direction of the hole 2.
A configuration may be adopted in which water droplets and the like are easily discharged into the pipe 1 through the hole 2.

Next, FIG. 10 shows the positions and shapes of the holes formed in the pipe 1, and the description thereof will be given. Figure 10
In, the hole 25 is provided in the vicinity of the attachment portion where the housing 7 is attached to the pipe 1. In other words,
By providing the pipe 1 at the lowest position within the portion forming the bottom wall of the housing 7, as shown in FIG.
Water droplets and the like generated in the housing 7 will drop in the direction of the arrow toward the hole 25.

[0053]

As described above, according to the present invention, there is provided an enclosure provided on the upper side of a fluid passage and having a hole formed in a wall surface in contact with the passage, and an inner space of the enclosure. The sound pressure generating means for changing the pressure at a predetermined frequency, and the flow velocity detecting means for calculating the velocity of the fluid based on the pressure change generated in the internal space of the enclosure are provided. Since it is a fluid velocity detecting device, the measuring device is inexpensive, and water droplets can be prevented from entering the housing, so that maintenance and management can be simplified, which is a very significant effect.

Further, since it can be produced by a small-scale manufacturing facility, it has an extremely great industrial effect that the capital investment is small.

[Brief description of drawings]

FIG. 1 is a configuration explanatory view for explaining the principle of the present invention.

FIG. 2 is an operation explanatory view for explaining FIG.

FIG. 3 is an operation explanatory view for explaining FIG. 1.

FIG. 4 is an operation explanatory view for explaining FIG. 1.

FIG. 5 is a configuration explanatory diagram embodying the configuration explanatory diagram of FIG. 1 shown for explaining the principle of the present invention.

FIG. 6 is a physical model of a vibration system equivalent to the model of the configuration explanatory diagram shown in FIG.

FIG. 7 is a diagram for explaining an example of the present invention.

8 is an enlarged view of a main part of the embodiment shown in FIG.

FIG. 9 is an explanatory view of another embodiment of the portion shown in FIG.

FIG. 10 is a diagram for explaining another embodiment of the present invention.

FIG. 11 is a cross-sectional explanatory view of the main parts of FIG.

[Explanation of symbols]

 1 pipe 2, 25 hole 3, 10 speaker (sound pressure generating means) 7 housing 8, 14 microphone (sound pressure detecting means) 9, 24 coefficient circuit 11 drive circuit 13 partition plate 20, 22 absolute value circuit 21 adder circuit 23 division Circuit 17 Housing 26 Tapered surface

[Equation 16]

[Equation 17]

[Equation 18]

[Formula 19]

[Equation 20]

[Equation 21]

[Equation 22]

[Equation 23]

Claims (1)

[Claims] 1. An enclosure provided on an upper side of a fluid passage and having a hole formed in a wall surface in contact with the passage, and a pressure for varying a pressure of an inner space of the enclosure at a predetermined frequency. A fluid velocity detecting device comprising: a sound pressure generating unit; and a flow velocity detecting unit that calculates a velocity of the fluid based on a pressure change generated in the inner space of the enclosure.