JPH0688836A - Fluid velocity detector - Google Patents

Abstract

PURPOSE:To obtain an inexpensive but highly accurate fluid velocity detector having a simple constitution by using loudspeakers and microphones. CONSTITUTION:A hole 12 has a diameter larger than the diameter 2r of another hole 2 and the straight line connecting the centers of the holes 2 and 12 is made parallel to the center line of a pipe 1. Both holes 2 and, 12 are respectively closed from the outside of the pipe 1 by means of separately provided housings 7 and 13 and sound pressure generating means, such as loudspeakers, etc., and sound pressure detecting means 8 and 14, such as microphones, etc., are respectively provided in the housings 7 and 13. A second factor circuit 15 is set at an amplification factor which is different from that of a first factor circuit 9 and amplifies the output signal of the microphone 14 at the amplification factor. A switching circuit 16 alternately selects the output signals of the circuits 9 and 15 based on switching signals from a switching timing signal generation circuit and outputs the selected signals.

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 such as air.

[0002]

2. Description of the Related Art An air flow sensor will be described as an example of a conventional fluid velocity detecting device. That is, the air flow sensor is arranged so that a thin heater wire is orthogonal to the gas flow direction in the gas flow, and a constant current is supplied in a pulsed manner to the heater wire to generate it. The flow velocity of the fluid is 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 if the surface of the heater wire is directly in contact with the vapor etc. of the drug in the fluid for a long time, it changes and the heat dissipation state changes over time. There is a possibility that the temperature may change and the thermal relationship between the fluid and the heater wire may change and the error may gradually increase.

Further, in order to increase the resistance value change of the heater wire while achieving the power saving, a very thin heater wire having a large resistance value per unit length is used, so that the dust is large and it is large. In the case of moving at high speed, a very large external force acts on the heater wire, which may cause plastic deformation, so that it is necessary to provide a filter on the windward side.

Further, 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 possibility that the wire will be stretched and the measurement error will be large, 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 problems by adapting the principle of acoustic technology, which is a completely different research field from the above-mentioned technical field, and is, for example, as an acoustic component. It is an object of the present invention to propose a fluid velocity detecting device that is cheaper than ever, can be simplified, and has a wide measurement range by using a generally well-known speaker and microphone.

[0007]

According to the present invention, a first hole disposed so as to contact a fluid flow passage and a second hole having a diameter or a length different from that of the first hole are bored. Surrounding means, driving means for varying the pressure in the surrounding means at a predetermined frequency, detecting means for detecting a pressure change in the internal space of the surrounding means caused by the operation of the driving means, and the detecting means. And a calculating means for obtaining the velocity of the fluid based on the detection output from the means.

[0008]

In the fluid velocity detecting device according to the present invention, the gas in the plurality of enclosures is brought into contact with the flow of the fluid through the holes provided in the respective enclosures, and the pressure in the enclosures is increased. A change (sound pressure change) is generated, and the velocity of the fluid is measured by detecting the pressure change in the surrounding means at that time.

[0009]

DESCRIPTION OF THE PREFERRED EMBODIMENTS 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 . 2 is a small-diameter hole having a diameter of 2r formed in the wall surface of the pipe 1; 3 is the pipe 1
It is driven at a predetermined frequency by a sound pressure generating means such as a speaker, which is disposed so as to face the hole 2 formed in the wall surface at a predetermined interval. Reference numeral 4 denotes a diffracting wave of a sound wave generated by the sound pressure generating means 3 (which is synonymous with sound pressure here) becomes a compressional wave, and is diffused and formed in an arc in the pipe 1 after passing through the hole 2. is there.

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 (thickness) h is formed in a portion of the hole 2 formed in the wall surface of the pipe 1 as shown by diagonal lines. It is considered that the acoustic tube 5 having a diameter 2r and a length h in terms of acoustics is thereby formed. 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 having a radius r and a thickness (πr) / 2 (density ρ) is formed in the sound pressure generating means 3 and the acoustic tube 5. The velocity Vv (t) (displacement: X (t)) by the air spring (air spring 1c in FIG. 6)
It is thought that a single vibration can be made in the vertical direction. 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, (πr) / 2 can be theoretically calculated. Also, the kinetic energy of this vibration system is
(1/2) mv _v ² .

Here, as shown in FIG. 1, air flows in the pipe 1 from the direction A to the direction B at a flow velocity V _f , and the air also flows at the upper end surface of the acoustic tube 5 at a velocity V _f . Assuming that, the columnar air portion 6 in the portion of the additional mass m shown by hatching in FIG. 3 receives an external force by the air flowing from the direction A, and the velocity V _f is shown by hatching C and D in FIG. Is flowed downstream (in the B direction) by an amount proportional to (indicated by L in FIG. 4). As a result, the columnar air portion 6 indicated by the solid line in FIG. 4 is displaced along the upper end surface of the acoustic tube 5 by L in the leeward B direction to the columnar air portion 6 ′ indicated by the broken line. 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, assuming that a displacement amount (displacement amount) L occurs during the time t and the plane cross-sectional area of the portion of the additional mass m (the area of the portion indicated by the diagonal line D in FIG. 4) 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 is

[0022]

[Equation 6]

It becomes That is, if the damper coefficient d of the acoustic tube 5 is known, the velocity V _f can be known.

Next, each concrete 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 FIG. 5, the same components as those shown 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.
Housing for airtightly covering the outside (enclosing means)
Then, 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, and the sound pressure generating means 10 has a space volume V _{0 of} the housing 7 and a hole. The sine wave drive is performed by the drive circuit 11 whose output frequency is set to match the Helmholtz resonance frequency determined by the size of the diameter 2r of 2 and the internal pressure in the housing 7 is changed at the Helmholtz resonance frequency. .

Although the hole 2 is formed in the wall surface of the pipe 1 in FIG. 5, a part of the wall surface of the housing 7 forms a part of the wall surface of the pipe 1, and the hole 2 is formed in the wall surface.
May be provided and the wall surface may be shared. In addition to the above-mentioned factors, the Helmholtz resonance frequency also varies depending on the length of the hole 2. Therefore, this is also a factor for determining the Helmholtz resonance frequency.

Reference numeral 8 denotes a condenser microphone (sound pressure detecting means) which is mounted in the housing 7 and detects pressure (sound pressure) fluctuations in the housing. Reference numeral 9 is a coefficient circuit including an amplifier circuit and the like, which amplifies the detection output from the microphone 8 with a predetermined amplification factor to detect and output the flow velocity V _f of the gas in the pipe 1.

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 FIG. 5 and FIG. 6, P ₀ is atmospheric pressure, ΔP (t) is a pressure (sound pressure) change amount in the housing 7 generated by driving 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 air 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.

[0031]

[Equation 7]

[0032]

[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 air 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 frequency ω _r is

[0034]

[Equation 9]

By

[Equation 10]

Can be set. Ie

[0037]

[Equation 11]

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

[0039]

[Equation 12]

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

Therefore, from the above equation 12, the damper coefficient d
Is obtained by arithmetic calculation, and the result is substituted into the equation 6 to obtain the fluid V _f to be measured.

Although the hole 2 is formed in a circular shape in the above structure, it may be a rectangular shape such as a rectangle as shown in FIGS. 7 and 8. The long sides of the rectangle may be arranged so as to be parallel to the flow direction of the fluid flowing from the A direction to the B direction. In that case, the flow velocity V of the fluid is V.
_The shape must be set according to the measurement range of _f , its size, etc. It should be noted that the reason why the rectangular hole is described here is that the description is simpler and clearer than that of the circular hole.

Here, the differences shown in FIGS. 7 and 8 will be described below by comparing them. That is, what is shown in FIG.
_If the fluid is flowing at a certain flow velocity V _f , the air portion (indicated by the solid line) is longer than the one shown in FIG. (Shown in agreement with the shown hole 6) 6 is displaced in the B direction by approximately 30% with respect to the length L1 of the hole 2. 8 shows that the flow velocity V _{f of the} fluid is the same as that shown in FIG. 7 and that the air portion 6 is displaced during the same time, the displacement of that shown in FIG. The quantity is shown to be displaced by approximately 65% with respect to the length L2 of the hole 2.

The following can be said from these both figures.
That is, when the flow velocity V _f exceeds a certain level, measurement cannot be performed with an apparatus having a hole having a small dimension in the fluid flow direction, such as the hole 6 having the shape shown in FIG. It has been shown that a device with large pores of V is effective for widely varying flow rates V _f . Also, the energy amount D that is carried away by the fluid flow per unit time and dissipated is set so that the side orthogonal to the fluid flow direction is set longer in comparison with that shown in FIG. Since it is large, it has been shown to be effective in detecting small flow velocity changes. It should be noted that, for the sake of description, the square hole is used for the sensitivity and the measurement range, but it goes without saying that the hole may be a circular hole as described above.

Next, an embodiment according to the present invention will be described with reference to FIGS.
A description will be given based on 0. Of the configurations in FIGS. 9 and 10, only the points different from those shown in FIG. 5 will be described, and the same configurations or equivalent portions will be denoted by the same reference numerals and the description thereof will be omitted. 9 and 10, 1
Reference numeral 2 is another hole formed in the pipe 1 having a diameter larger than the diameter 2r of the hole 2 and is in the flow direction (A to B) of the fluid.
The straight line that is provided along the direction) and connects the centers of the holes 2 and 12 is set to be parallel to the center line M of the pipe 1. Further, each of the holes 2 and 12 on both sides is provided with the housings 7 and 1 which are separately provided.
3 is sealed from the outside of the pipe 1, and in the housings 7 and 13, sound pressure generating means such as a speaker and sound pressure detecting means 8 and 1 such as a microphone as shown in FIG.
4 is attached. Reference numeral 15 is a second coefficient circuit which is set to an amplification factor different from that of the first coefficient circuit 9 and amplifies the output signal from the microphone 14 by the amplification factor. The output signals from 15 and 15 are selectively selected and output based on a switching signal from a switching timing signal generating circuit (not shown).

With the above structure, the sound pressure generating means is driven in the housings 7 and 13 at different Helmholtz resonance frequencies set uniquely to change the sound pressure. It flows from A to B direction. Here, when the fluid velocity V _f changes in a large velocity range from low speed to high velocity, the fluid velocity V _f
Is detected by the microphone 8 in the housing 7 within a certain range from low speed to a certain medium speed as described above, and is detected by the microphone 14 installed in the other housing 13 for the speed range higher than that. The detection signal of is selectively output by the switching circuit 16 through the first coefficient circuit 9 and the second coefficient circuit 15 which are respectively connected, and only one of the signals is selected and output. The switching timing of the switching circuit 16 is set when the magnitude of the output signal of the first coefficient circuit 9 is constantly monitored by a switching timing signal generating circuit (not shown) and the magnitude of the output signal exceeds a predetermined magnitude. A switching signal is supplied from the switching timing signal generating circuit to the switching circuit 16.

Further, in FIGS. 9 and 10, both holes 2 are formed.
If the distances of 12 and 12 are arranged close to each other, if the design is such that turbulent flow is generated by the hole 2 on the upstream side, there is a possibility that it will be affected, so do not be affected. It is necessary to arrange them at a certain interval.

Next, a second embodiment will be described with reference to FIG. 11, but only parts different from FIG. 9 will be described. In this embodiment, the hole positions in FIG. 9 are changed. That is, hole 1
The position of the housing 13 is changed so that the position of the hole 2 is shifted to the position rotated by 180 ° with respect to the position of the hole 2, and the housing 13 is changed accordingly. With such a structure, even if a slight turbulent flow is generated in the hole 2, there is no hole 12 in the downstream thereof, so that the dimension in the length direction can be set small. Further, since the other hole 12 is not located on the downstream side of the hole 2, unless the inner diameter of the pipe 1 is small and the cylindrical air portions 6 formed at the positions of both holes 2 and 12 are not affected by each other, the disorder occurs in the hole 2. The flow does not affect the measurement. The other parts are the same as or substantially equivalent to those in FIG. 9, and therefore description thereof will be omitted.

Next, a third embodiment will be described with reference to FIG. 12, but only parts different from FIG. 11 will be described. In this embodiment, the other hole 12 is positioned upstream of the one hole 2 in the structure shown in FIG. 11 and is rotated by an angle smaller than 180 ° to be displaced, and the other part is shown in FIG. It is the same as or equivalent to the one shown, and the description thereof will be omitted. This is shown in FIG. 11 when the inner diameter of the pipe 1 is small.
When the holes 2 and 12 face each other as described above, the columnar air portions 6 act on each other, which is effective for a thin pipe.

Next, a fourth embodiment will be described with reference to FIG. 13, but only parts different from those of FIG. 12 will be described. In this embodiment, in the structure shown in FIG. 12, the position of the other hole 12 is located downstream of the one hole 2 so that a turbulent flow is unlikely to occur and a small-diameter hole 2 that is easy to design is located on the upstream side. A hole 12 having a large diameter is formed by piercing, and a turbulent flow is likely to be generated on the downstream side, that is, a turbulent flow is unlikely to occur and a design is difficult. Further, center lines M1 and M2 that pass through the centers of the holes 2 and 12 and are parallel to the flow direction of the fluid do not coincide with each other, and are separated by a distance P.

[0051]

As described above, according to the present invention, the first hole and the first hole arranged so as to be in contact with the flow passage of the fluid are provided.
Of the second hole having a diameter or a length different from that of the hole, driving means for varying the pressure in the enclosure at a predetermined frequency, and the driving means for generating the pressure. A fluid velocity detecting device comprising: a detecting unit that detects a pressure change in the inner space of the enclosure; and a calculating unit that obtains the velocity of the fluid based on a detection output from the detecting unit. The flow rate can be accurately measured by a simple method in a large measurement range, and the measurement apparatus can be inexpensive, and maintenance and management can be simplified, which is extremely effective. Also, since it can be created with a small-scale manufacturing facility, it has an extremely large industrial effect that requires less capital investment.

[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 structural explanatory view showing an embodiment in which the structural explanatory view of FIG. 1 shown for explaining the principle of the present invention is embodied.

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 an explanatory view of the action when the shape of the hole is an elongated hole in order to explain the embodiment of the present invention.

FIG. 8 shows a shape of a hole for explaining an embodiment of the present invention.
FIG. 8 is an explanatory view of the operation when a long hole different from FIG.

FIG. 9 is an explanatory diagram showing a first embodiment according to the present invention.

10 is a plan cross-sectional explanatory view for explaining a positional relationship between holes formed in the pipe 1 shown in FIG.

FIG. 11 is an essential part cross-sectional explanatory view for explaining a second embodiment of the present invention.

FIG. 12 is an explanatory cross-sectional view of an essential part for explaining a third embodiment of the present invention.

FIG. 13 is an essential part cross-sectional explanatory view for explaining a fourth embodiment of the present invention.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Pipes 2, 12, Holes 3 Speaker (sound pressure generating means) 7, 13 Housing 8, 14 Microphone (sound pressure detecting means) 9, 15 Coefficient circuit 11 Drive circuit 16 Switching circuit

Claims (1)

[Claims] 1. Enclosing means having a first hole and a second hole having a diameter or a length different from that of the first hole, the first hole being arranged in contact with a fluid passage, and the surrounding means. Drive means for varying the internal pressure at a predetermined frequency, detection means for detecting a pressure change in the internal space of the surrounding means generated by the operation of the drive means, and based on the detection output from the detection means A fluid velocity detecting device, comprising: a calculating unit that obtains the velocity of the fluid.