JPH0611368A - Karman's vortex flowmeter - Google Patents

Abstract

PURPOSE:To obtain a Karman's vortex flowmeter which can perform highly accurate flow rate measurement over a wide flow rate range without limiting the object to be measured. CONSTITUTION:The pressure difference between two points which changes in corresponding to a Karman's vortex B generated near pillar-like bodies 3 and 4 inserted into a flow passage is detected and, at the same time, a flow caused by the pressure difference is detected by using a thermal detecting means. The flow rate flowing through the flow passage is measured from the two kinds of detecting signals.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a Karman vortex flowmeter for detecting a flow rate of a fluid by detecting a Karman vortex generated on a downstream side surface of a columnar object inserted into a fluid flow. .

[0002]

2. Description of the Related Art FIG. 8 shows, for example, JP-A-60-22081.
It is sectional drawing which shows the conventional Karman vortex flowmeter shown by the 9th publication. In the figure, 2 is a flow path, 4 is a columnar body, 6 is a pressure guiding tube, 8 is a silicon chip, and 9 is a piezoresistive gauge.

The conventional Karman vortex flowmeter is constructed as described above, and the pressure change due to the Karman vortex generated by the columnar body 4 is introduced to the thin portion of the silicon chip 8 using the pressure guiding tube 6, and the thin portion due to this pressure difference. Was detected by the change in the resistance value of the piezoresistive gauge 9, and the flow velocity or the flow rate was measured from the fluctuation frequency of the resistance value. Such a Karman vortex flowmeter is characterized by relatively high measurement accuracy.

[0004]

However, in general, the Karman vortex flowmeter of the type in which a plate-shaped member is deflected by a pressure change due to a vortex to detect a strain has the following problems in principle. Since the change in pressure is proportional to the square of the flow velocity, it is difficult to achieve both sensitivity and rangeability. That is, since the Karman vortex street becomes extremely weak in the low flow rate region, it is necessary to make the plate member thin in order to increase the sensitivity in this region, but in this case, the pressure due to the vortex becomes large in the high flow rate region. Excessive displacement and force are applied, and vortices cannot be detected accurately. On the contrary, when the plate member is thickened, the vibration resistance in the high flow rate range is improved, but the sensitivity in the low flow rate range is lowered. Also, because it is a so-called positive displacement type, when measuring the gas flow rate, insert a temperature detection element to correct the density change due to temperature and pressure at a position that can accurately measure the fluid temperature without affecting the generation of vortices. Had to do. Therefore, as a vortex detector that has high sensitivity in the low-speed flow rate range and has sufficient response in the high-speed flow rate range, for example, there is a system that uses cooling of the heat wire. However, there is a problem that it is easily affected by adhesion. As described above, in the conventional Karman vortex flowmeter, in order to obtain sufficient measurement accuracy depending on the vortex detection method and measurement element, the measurement target and measurement area are limited, and the output of the measurement element is abnormal. There was a problem in guaranteeing the function when the occurrence occurred. Generally, in fluid measurement, it is rare that only one of various physical quantities of fluid is required, and simultaneous measurement of a plurality of physical quantities such as flow rate, absolute pressure, and temperature is often required. However, such measurement is impossible with the conventional vortex flowmeter.

The present invention has been made in order to solve the above problems, and provides a Karman vortex flowmeter capable of highly accurate flow rate measurement over a wide flow rate range without limiting the measurement object. It is an object.

Another object of the present invention is to obtain a compound Karman vortex flowmeter capable of simultaneously measuring the absolute pressure and the flow rate of the fluid in the flow channel.

[0007]

In the Karman vortex flowmeter according to the present invention, a pressure measuring element and a heating element are used together to detect pressure fluctuation due to Karman vortex, and the flow rate is measured from these two detection signals. It is a thing.

In the Karman vortex flowmeter, a thin portion formed by etching and a through hole are provided on one semiconductor chip, a pressure measuring element is formed on the thin portion, and both ends are formed in the through hole. The supported heat generating element may be formed with a temperature measuring element on the surface of the semiconductor chip near the through hole.

In the Karman vortex flowmeter, a pressure measuring element, a pressure guiding chamber in which a heating element and a temperature measuring element are pressure-separated, a pressure guiding tube connecting the pressure guiding chamber and a flow path, and a thin portion are provided. A reference pressure chamber that keeps airtightness may be provided.

[0010]

When the measurement fluid is flown through the flow path, Karman vortices are generated by the columnar body. The pressure difference caused by the pressure fluctuation caused by the Karman vortex is detected by the pressure measuring element formed in the thin portion, and the flow rate of the measurement fluid is measured. On the other hand, when the heating element controlled to generate heat at a temperature higher than the fluid temperature measured by the temperature detecting element is cooled by the flow of the fluid caused by the pressure fluctuation due to the Karman vortex, the heating current flowing through the heating element is The flow rate of the measuring fluid is measured from the magnitude or the fluctuating frequency. Then, according to the flow rate range, or an output abnormality is detected, and each of the above measurement results is selected and taken out. As a result, it is possible to perform high-accuracy and wide-range measurements by taking advantage of the merits of each element, and it is possible to prevent the function of the flowmeter from being paralyzed even if an abnormality occurs in one of the measuring elements.

Further, a thin portion and a through hole formed by etching are formed on one semiconductor chip, a pressure measuring element is formed on the thin portion, and a heating element supported at both ends in the through hole is formed. When a Karman vortex flowmeter is formed by forming a temperature measuring element on the surface of the semiconductor chip in the vicinity of the through hole, the Karman vortex flowmeter can be formed with high accuracy and small size, and furthermore, a pressure measuring element, a temperature detecting element, a heating element, etc. Since it can be integrally formed by semiconductor manufacturing technology, mass production is possible,
Therefore, the cost can be reduced.

Further, a pressure guiding chamber in which the pressure measuring element and the heating element and the temperature measuring element are pressure-separated, a pressure guiding tube connecting the pressure guiding chamber and the flow path, and a reference pressure chamber for keeping the thin portion airtight. With the configuration including, it is possible to simultaneously measure the absolute pressure of the fluid in the flow path, and it is possible to obtain the mass flow rate of the fluid, energy, etc.

[0013]

【Example】

Example 1. Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings. 1 is an overall configuration diagram showing an embodiment of the present invention, and FIG. 2 is a sectional view taken along the line AA of FIG. In each figure, 2 is a flow path, and the rectifying grid 1 is provided on the upstream side thereof. Further, 3 and 4 constitute a pair of vortex generators, and as shown in FIG. 2, an upstream side columnar body 3 having an isosceles triangular cross section and a downstream side having an isosceles trapezoidal cross section. The columnar body 4 is inserted and fixed perpendicularly to the flow with a certain gap. The pressure fluctuation of the Karman vortex B generated by the upstream columnar body 3 is
It is introduced from the pressure guiding hole 5 provided in the inside through the pressure guiding tubes 6a and 6b. 7 is a pedestal made of Pyrex glass or the like. The silicon chip 8 is bonded to the pedestal 7 by anodic bonding or the like. The silicon chip 8 is made of (100) plane single crystal silicon, and has a thin portion 14,
The through holes 15 are formed side by side. The pressure guiding tube 6a branches into two in the middle, communicates with the thin portion 14 and the through hole 15, and then converges again into one pressure guiding tube 6b which is led out to the side surface on the opposite side of the downstream side columnar body 4. It

Next, FIG. 3 shows the silicon chip 8 of FIG. 2, (a) is a perspective view thereof, and (b) is CC of FIG. 3 (a).
It is sectional drawing which followed the line. The silicon chip 8 has a thin portion 14 that is etched from the back surface. This thin part 14
A pressure detecting element 9 is provided on the surface of the element, and a piezoresistive gauge is used in this embodiment, and is formed in the (110) direction by a semiconductor technique such as impurity diffusion.
The four piezoresistive gauges form a Wheatstone bridge. Reference numeral 10 is an aluminum bonding pad for taking out the wiring. Reference numeral 11 is a temperature detecting element, and a platinum thin film resistor is used in this embodiment. Reference numeral 12 is an aluminum wiring. Reference numeral 13 is a heating element, which uses a platinum thin film resistor in this embodiment, and the periphery thereof is punched by etching to form a rectangular through hole 15.

Next, the operation of the Karman vortex flowmeter having the above structure will be described with reference to FIGS. When the measurement fluid Q flows into the flow path, Karman vortices are generated by the upstream columnar body 3. Now, assuming that the vortex is at the position B in the figure, positive pressure and negative pressure are generated near the openings of the pressure guiding tubes 6a and 6b, respectively. As a result, a fluid flow R that flows in from the pressure guiding tube 6a and flows out through the pressure guiding tube 6b is generated. This pressure fluctuation and flow R are guided to the thin portion 14 and the through hole 15 on the silicon chip. The thin portion 14 vibrates due to pressure fluctuation due to Karman vortex. Due to the stress variation due to this vibration, the resistance value of the piezoresistive gauge 9 formed on the surface of the thin portion changes. This resistance value change is detected by configuring a bridge. Since the fluctuation frequency is proportional to the flow velocity,
The flow velocity or flow rate can be measured from this frequency. On the other hand, the heat-generating platinum thin-film resistor 13 protruding into the through hole 15 is controlled to generate heat at a constant temperature higher than the fluid temperature measured by the temperature-detecting platinum thin-film resistor 11. When the flow R flows in there, the platinum thin film resistor 13 for heat generation
Is cooled. At this time, the flow velocity or flow rate can be measured by detecting the fluctuating frequency of the heating current flowing through the platinum thin film resistor 13. As described above, the output signal is obtained from both the piezoresistive gauge 9 and the platinum thin film resistor 13, but the output signal is switched by the external control circuit. That is, when high sensitivity is required in a minute flow rate range, or when an abnormality is detected in the output due to contaminants in the fluid adhering to the platinum thin film resistor 13, the output signal from the piezoresistive gauge 9 is taken out and set to a large value. When high-speed response is required in the flow rate range or when an abnormal pressure is detected on the thin-walled portion and the output of the piezoresistive gauge is detected, the output signal of the platinum thin-film resistor 13 for heat generation is taken out. As a result, it is possible to perform high-accuracy and wide-range measurements by taking advantage of the merits of each element, and it is possible to prevent the function of the flowmeter from being paralyzed even if an abnormality occurs in one of the measuring elements.

Example 2. Although four piezoresistive gauges are arranged in the (110) direction on the silicon substrate having the (100) plane in the first embodiment, the arrangement and the number may be arbitrary. For example, the same effect can be obtained by arranging piezoresistive gauges in the (110) direction on a (110) plane silicon substrate. Further, although the platinum thin film resistor 11 is used as the temperature detecting element, the same effect can be obtained by using a diode driven by a constant current. Further, although the platinum thin film resistor 13 is used as the heating element, a diffused resistor, a transistor or the like may be used.

Embodiment 3. In the first and second embodiments, the silicon chip 8 is installed inside the downstream columnar body 4, but it can be placed outside the flow path 2 to facilitate maintenance and inspection.

Example 4. FIG. 4 is an overall configuration diagram showing an embodiment configured to measure the absolute pressure of the flow path by the pressure measuring element 9. 1 to 15 are exactly the same as those in Examples 1 to 3 above. Reference numeral 16 is a pressure guiding tube, and 17 is a vortex detector. FIG. 5 is an enlarged cross-sectional view of the vortex detector as seen from the flow direction, and FIG. 6 is a side sectional view of the vortex detector. In this embodiment, the pressure measuring element 9 is installed in a pressure guiding chamber 18 that is pressure-separated from the temperature measuring element 11 and the heating element 13, and the pressure guiding chamber 18 and the flow path 2 are connected by a pressure guiding tube 16. There is. Also, the thin portion 1
The back surface of 4 is hermetically bonded to the base 7 by anodic bonding or the like to form a reference pressure chamber 19. Since the inside of the reference pressure chamber 19 is sealed, the influence of humidity can be minimized. According to such an embodiment, the absolute pressure of the fluid flowing through the flow path 2 can be measured by the pressure measuring element 9. On the other hand, the flow velocity or flow rate can be measured by the heating element as in the first to third embodiments. That is, two physical quantities that are important in fluid measurement, that is, the absolute pressure of the flow path and the flow rate, can be measured simultaneously.

Example 5. Although the piezoresistive gauge is used as the pressure detecting element in the fourth embodiment, the intended purpose can be achieved by forming the pressure detecting element by the method shown in FIG. That is, the impurity diffusion layer 20 is formed in the thin portion 14 of the silicon chip, and this is used as a movable electrode, and the aluminum electrode 21 is vapor-deposited on the surface of the pedestal 7 in the reference pressure chamber 19, and this is used as a fixed electrode. It is possible to configure a capacitive pressure detecting element that utilizes the change in the capacitance of the capacitor due to the displacement of the part.

[0020]

As described above, according to the present invention, the pressure measuring element and the heating element are used together to detect the pressure fluctuation due to the Karman vortex, and the flow rate is measured from these two detection signals. When high sensitivity is required in the flow rate range, or when abnormalities in the output are detected due to contaminants in the fluid adhering to the heating element, the output signal is taken out from the pressure detection element and high-speed response is achieved in the large flow rate range. Is required, or when an excessive pressure is applied to the thin portion and an abnormality is detected in the output of the pressure detection element, the output signal is taken from the heating element,
These two detection methods can be used together, making it possible to perform high-accuracy and wide-range measurements by taking advantage of their respective strengths, and even if one of the detection methods fails, the other function is completely paralyzed. There is also an effect that it can be avoided.

Further, a thin portion and a through hole formed by etching are provided on one semiconductor chip, a pressure measuring element is formed on the thin portion, and a heat generating element supported at both ends in the through hole is formed. If a Karman vortex flowmeter is formed by forming a temperature measuring element on the surface of the semiconductor chip in the vicinity of the through hole, the Karman vortex flowmeter can be formed with high accuracy and small size, and further, the pressure measuring element, the temperature detecting element, and the heat generating element. Etc. can be integrally formed by semiconductor manufacturing technology, so mass production is possible,
There is an effect that it can be made cheap. Good to do.

Further, a pressure guiding chamber in which the pressure measuring element and the heating element and the temperature measuring element are pressure-separated, a pressure guiding tube connecting the pressure guiding chamber and the flow path, and a reference pressure chamber for keeping the thin portion airtight. By including the configuration, it is possible to simultaneously measure the absolute pressure, flow velocity, and temperature of the fluid, which are important physical quantities in fluid measurement, and the mass flow rate, energy, etc. of the fluid that cannot be obtained by measuring individual physical quantities. Can be obtained.

[Brief description of drawings]

FIG. 1 is an overall configuration diagram showing a first embodiment of the present invention.

FIG. 2 is a sectional view taken along the line AA of FIG.

FIG. 3 is a perspective view and a cross-sectional view of a silicon chip according to a first embodiment of the present invention.

FIG. 4 is an overall configuration diagram showing a fourth embodiment of the present invention.

FIG. 5 is an enlarged cross-sectional view of a vortex detector according to a fourth embodiment of the present invention as viewed in the fluid flow direction.

FIG. 6 is a side sectional view of a vortex detector in a fourth embodiment of the present invention.

FIG. 7 is a sectional view of a silicon chip and a pedestal according to a fifth embodiment of the present invention.

FIG. 8 is an overall configuration diagram of a conventional vortex flowmeter.

[Explanation of symbols]

 2 flow path 3 upstream columnar body 4 downstream columnar body 6a pressure guiding tube 6b pressure guiding tube 8 silicon chip 9 pressure measuring element 11 temperature measuring element 13 heat generating element 14 thin portion 15 through hole 16 pressure guiding tube 18 pressure guiding chamber 19 reference pressure chamber

Claims (3)

[Claims] 1. A pressure difference between two points, which changes corresponding to a Karman vortex generated near a columnar body inserted in a flow path, is detected, and a flow generated by the pressure difference is detected by a thermal detection means. Karman vortex flowmeter that detects the flow rate and measures the flow rate from these two detection signals. 2. A thin portion, a pressure measuring element formed in the thin portion, a through hole formed in the vicinity of the thin portion,
The Kalman according to claim 1, wherein a heating element, which is supported at both ends in the through hole and generates heat at a constant temperature higher than the fluid temperature, and a temperature measuring element formed near the through hole are integrally formed on one semiconductor chip. Vortex flow meter. 3. A pressure guiding chamber in which a pressure measuring element and a heating element and a temperature measuring element are pressure-separated, a pressure guiding tube connecting the pressure guiding chamber and a flow path, and a reference pressure chamber for keeping a thin portion airtight. The Karman vortex flowmeter according to claim 1 or 2, further comprising: