JPH0552614A - Karman vortex-type flow meter - Google Patents

Abstract

PURPOSE:To increase measurement accuracy of flow by measuring the flow with good response and accurately even when the flow rate of fluid varies, to stabilize the form of a vortex producing body. CONSTITUTION:When a Karman vortex 4 is made into contract with a heat- sensitive resistant wire 16, the heat-sensitive resistant wire 16 is cooled to vary its resistance value. A control unit 17 forms signal waveforms as frequency signals from variation in resnstant value, obtauns produce frequency of the karman vortex 4 from the signal waves, and calculates the flow rate V of air. Also a temperature measuring circuit reads out characteristic curves in a temperature map from the flow rate V, and measures the temperature of air by means of the resistance values read out from the characteristic curves and signal wave forms. By this, the control unit 17 measures the flow of mass by means of a flow of volume obtained from the product of the flow rate V and flow path area S and the density of air at the measured air temperature. Also a vortex producing body 11 produces heat by current from a battery power 13 for each start of an engine to burn out and remove foreign matter adhered on its surface.

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 suitable for measuring the flow rate of gas such as air and gas, and liquid such as water and fuel.

[0002]

2. Description of the Related Art FIG. 7 shows an example in which a conventional Karman vortex flowmeter is used as an air flow meter for detecting the intake air amount of an automobile engine.

In the figure, reference numeral 1 denotes a stepped cylindrical casing provided in the middle of an intake manifold (not shown). The casing 1 has an inlet 1A side formed to have an enlarged diameter. A rectifying net 2 that rectifies the intake air is attached to the.

Reference numeral 3 denotes a vortex generator formed in the shape of a triangular prism, which is provided on the axial line of the casing 1 and is provided in the intermediate portion of the casing 1. The vortex generator 3 is a rectifier flowing in the direction of the arrow. By contacting the air in the state, Karman vortices 4, 4, ... Which are in proportion to the flow velocity of the air are alternately generated on the downstream side.

Reference numerals 5, 5, ... Denote a plurality of flat plate-shaped vortex stabilizers which are provided in the casing 1 at the downstream side of the vortex generator 3, and each of the vortex stabilizers 5 is air. It is installed so that it is orthogonal to the flow of. Each of the vortex stabilizers 5 stabilizes the Karman vortex 4 generated by the vortex generator 3.

Reference numeral 6 denotes an ultrasonic sensor mounted on the wall portion of the casing 1. The ultrasonic sensor 6 is located downstream of the vortex stabilizer 5 and fixed to the casing 1, and the front surface thereof is inside the casing 1. Ultrasonic transmitter 6 provided to face
A and an ultrasonic receiver 6B fixed to the casing 1 so as to face the ultrasonic transmitter 6A. The transmitter 6A and the receiver 6B are connected to the lead wires 7A, 7
It is connected to a control unit 8 described later via B. Then, the ultrasonic sensor 6 is an ultrasonic transmitter 6A.
By receiving the ultrasonic wave transmitted from the casing 1 into the casing 1 by the ultrasonic wave receiver 6B, the Karman vortex 4 is detected from the phase shift of the ultrasonic wave and the vortex detection signal is sent to the control unit 8 as an on / off pulse signal. It is output.

Reference numeral 8 denotes a control unit composed of a CPU and the like as a microcomputer. The control unit 8 has an output side to which an ultrasonic wave transmitter 6A of an ultrasonic wave sensor 6 is connected via a lead wire 7A and an input. The receiver 6B of the ultrasonic sensor 6 is connected to the side via a lead wire 7B. Also, the control unit 8
In a storage area 8A composed of a RAM or the like, the arithmetic expression shown in the following Expression 1 is stored.

[0008]

[Equation 1]

Then, the control unit 8 obtains the flow velocity V of the intake air flowing in the casing 1 in the direction of the arrow from the vortex detection signal from the ultrasonic receiver 6B by the above mathematical expression 1, and stores this flow velocity V in advance. From the flow passage area S of the casing 1 stored in the area 8A, the volume flow rate A of air is

[0010]

## EQU2 ## This is obtained as A = V.multidot.S.

The Karman vortex flowmeter according to the prior art has the above-mentioned structure, and its operation will be described below.

First, the air flowing into the casing 1 is
It is rectified by the rectifying net 2 and contacts the vortex generator 3. Since the vortex generator 3 is an obstacle to the air, Karman vortices 4, 4, ... Which are proportional to the flow velocity V of the air are regularly and alternately generated on the downstream side of the vortex generator 3. Each Karman vortex 4 moves toward the downstream side while being stabilized by each vortex stabilizer 5. Next, when the control unit 8 applies a high frequency voltage to the ultrasonic transmitter 6A of the ultrasonic sensor 6 via the lead wire 7A, the ultrasonic transmitter 6A transmits an ultrasonic wave according to the high frequency voltage, The ultrasonic waves are received by the ultrasonic receiver 6B.

When the Karman vortex 4 crosses this ultrasonic wave, the ultrasonic wave reception state (ultrasonic wave phase shift, etc.) by the ultrasonic wave receiver 6B changes, so that the ultrasonic wave receiver 6B The passage of the Karman vortex 4 is detected as an on / off pulse signal, and this pulse signal is output to the control unit 8 as a vortex detection signal.

Next, the control unit 8 reads the vortex detection signal from the ultrasonic receiver 6B, and the Karman vortex 4
Is calculated, and the flow velocity V of the air is obtained from the vortex generation frequency f based on the above equation 1. As a result, the control unit 8 uses the flow velocity V and the flow passage area S of the casing 1 to calculate the volumetric flow rate A of the air based on the equation 2.
Is calculated, and this volume flow rate A is displayed and output to the outside.

[0015]

In the Karman vortex flowmeter according to the above-mentioned conventional technique, the ultrasonic sensor 6 is used.
Since the Karman vortex 4 is detected from the phase shift of the ultrasonic wave received by the ultrasonic receiver 6B, the frequency change, etc., it is hardly affected by the temperature change of the air. However, the detection by the ultrasonic sensor 6 has a problem that when the flow velocity V of the air changes, not only the response becomes low and the accuracy also deteriorates, but also the entire ultrasonic sensor 6 becomes large in size. Further, since the volume flow rate A can be measured, if the mass flow rate is required, a separate temperature sensor must be provided in the casing 1 to correct the density of air,
There is a problem that the overall configuration becomes complicated.

Further, when the flowmeter is used for a long time, foreign matter in the air gradually adheres to the surface of the vortex generator 3 to form deposits 9, 9, and the deposits 9 cause the vortex generator 3 to deposit. The shape changes. In particular, when it is used for measuring the intake air amount of an automobile engine, the shape of the vortex generator 3 is likely to change because a lot of foreign substances such as gum and carbon are mixed in the air. However, in the Karman vortex flowmeter, the accuracy of the flow rate measurement is determined by the accuracy of the shape and size of the vortex generator 3, so if the shape of the vortex generator 3 changes,
There is a problem that the volumetric flow rate A cannot be measured accurately and the reliability is significantly reduced.

The present invention has been made in view of the above-mentioned problems of the prior art. Even if the flow velocity of the fluid changes, the flow rate of the fluid can be accurately measured with good responsiveness, and the shape of the vortex generator can be maintained for a long period of time. It is an object of the present invention to provide a Karman vortex flowmeter which is stabilized over a period of time and is capable of improving flow rate measurement accuracy.

[0018]

In order to solve the above-mentioned problems, the structure adopted by the present invention is a cylindrical casing through which a fluid flows, and is provided in the casing perpendicularly to the flow direction of the fluid. A vortex generator that generates a Karman vortex on the downstream side by the flow of a fluid, and a silicon carbide fiber that is provided on the casing located on the downstream side of the vortex generator and has a resistance value that changes depending on the presence of the Karman vortex Temperature sensitive resistance wire, a signal detecting means for detecting a change in resistance value of the temperature sensitive resistance wire as a frequency signal, and a flow velocity / flow rate operation for calculating a flow velocity or a flow rate based on a detection signal detected by the signal detecting means. And means.

Further, temperature measuring means for measuring the temperature of the fluid based on the detection signal detected by the signal detecting means and the flow velocity or flow rate of the fluid calculated by the flow velocity / flow rate calculating means, and the temperature measuring means. The mass flow rate of the fluid is calculated from the density calculating means for calculating the density of the fluid from the temperature of the fluid, and the density of the fluid calculated by the density calculating means and the flow velocity or flow rate of the fluid calculated by the flow velocity / flow rate calculating means. It is preferable to provide a mass flow rate calculation means for calculation.

Further, the vortex generator is made of a heat-generating material that generates heat with an electric current, and a burnout means is provided for burning foreign matter attached to the vortex generator by supplying an electric current to the vortex generator. Good.

[0021]

When the fluid flows in the casing and comes into contact with the vortex generator, Karman vortices are alternately generated on the downstream side of the vortex generator, and the resistance value of the temperature-sensitive resistance wire changes depending on the presence or absence of the Karman vortex. .. The signal detecting means detects the change in the resistance value as a frequency signal, and the flow velocity / flow rate calculating means can calculate the flow velocity or flow rate of the fluid based on the detection signal.

Further, temperature measuring means for measuring the temperature of the fluid based on the detection signal detected by the signal detecting means and the flow velocity or flow rate of the fluid calculated by the flow velocity / flow rate calculating means, and the fluid measured by the temperature measuring means. Density calculation means for calculating the density of the fluid from the temperature of, and mass flow rate calculation for calculating the mass flow rate of the fluid from the density of the fluid calculated by the density calculation means and the flow velocity or flow rate of the fluid calculated by the flow velocity / flow rate calculation means By providing the means, the mass flow rate of the fluid flowing in the casing can be calculated and obtained.

Further, if the vortex generator is made of a heat-generating material that generates heat by an electric current, and electric current is supplied to the vortex generator, a burnout means for burning foreign matter attached to the vortex generator is provided. Foreign matter attached to the surface of the vortex generator can be burned and removed to prevent the shape of the vortex generator from changing.

[0024]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT An embodiment of the present invention will be described below with reference to FIGS. In the embodiment, the same components as those of the conventional technique shown in FIG. 7 described above are designated by the same reference numerals, and the description thereof will be omitted.

In the figure, reference numeral 11 denotes a vortex generator according to the present embodiment, which is located on the axis of the casing 1 in substantially the same manner as the vortex generator 3 described in the prior art. 1, which is provided in the middle part of the vortex generator 1
As shown in FIG. 2, 1 is formed into a long columnar shape from silicon carbide fiber as a heat generating material. In addition, the lead wires 12A and 12B are provided on the axially upper and lower ends of the vortex generator 11, respectively.
Is connected to the battery power source 13 and the energizing switch 14 which will be described later via the respective lead wires 12A and 12B. Here, the silicon carbide fiber forming the vortex generator 11 has a thermistor characteristic in which its resistance value decreases as the temperature rises. And the vortex generator 1
1 is a Karman vortex 4, 4, 4 downstream due to the flow of air
Are alternately generated, and when a current is supplied from the battery power source 13 via the energizing switch 14 or the like, the current generates heat to a predetermined temperature (for example, about 1000 ° C.).

Reference numeral 13 denotes a battery power source mounted on the automobile,
14 is provided between the plus side of the battery power source 13 and the upper end side of the vortex generator 11 and is provided in the middle of the lead wire 12A. The energizing switch is shown, and the energizing switch 14 is a normally open relay. The energizing switch 14 is connected to a burnout circuit 18, which will be described later, via a lead wire 15, is closed by a control signal from the burnout circuit 18, and supplies a current from the battery power source 13 to the vortex generator 11. To do.

Reference numeral 16 denotes a temperature-sensitive resistance wire which is provided on the casing 1 at the downstream side of the vortex generator 11 and is made of a small-diameter silicon carbide fiber. The temperature-sensitive resistance wire 16 is a control unit 17 described later. Connected with. The temperature-sensitive resistance wire 16 has a thermistor characteristic in which, when the flow velocity V of air increases or when it contacts the Karman vortex 4, the temperature of itself decreases and the resistance value increases.

Reference numeral 17 denotes a control unit composed of a CPU and the like as a microcomputer, and the control unit 17 is composed of a burning circuit 18 and a flow rate measuring unit 20 described later.

Reference numeral 18 denotes a burnout circuit provided in the control unit 17. The burnout circuit 18 is connected to the energizing switch 14 at its output side, and has a key switch 19 for starting an automobile engine at its input side. Are connected. When the key switch 19 is turned on, the burn-out circuit 18 outputs a control signal to the energizing switch 14 to close the energizing switch 14 for a predetermined time (about 2 seconds), and the vortex generator 11 is closed. A current is supplied from the battery power source 13 to heat the vortex generator 11 to about 1000 ° C.

Reference numeral 20 denotes a flow rate measuring unit provided in the control unit 17, and the flow rate measuring unit 20 has a resistance value detecting circuit 21 and a flow velocity calculating circuit 2 which will be described later as shown in FIG.
5, a temperature measuring circuit 26, a mass flow rate calculating circuit 30 and the like.

Reference numeral 21 denotes a resistance value detecting circuit provided on the input side of the flow rate measuring unit 20 and connected to the temperature-sensitive resistance wire 16. The resistance value detecting circuit 21 is a resistance value R of the temperature-sensitive resistance wire 16.
Is detected and a detection signal is output. Reference numeral 22 denotes a waveform detection circuit as signal detection means provided on the output side of the resistance value detection circuit 21. The waveform detection circuit 22 stores the detection signal from the resistance value detection circuit 21 in a memory such as a RAM. 4 according to the time change.
Signal waveform 23 of the resistance value R as a frequency signal as shown in FIG.
Is to detect. Here, the signal waveform 23 is
When the Karman vortex 4 comes into contact with the temperature sensitive resistance wire 16, the temperature sensitive resistance wire 16 is cooled by the Karman vortex 4 and its resistance value R increases. It has a sinusoidal shape that increases and decreases.

Reference numeral 24 denotes a generated frequency detection circuit provided on the output side of the waveform detection circuit 22. The generated frequency detection circuit 24 uses the signal waveform 23 detected by the waveform detection circuit 22 as shown in FIG. The number of occurrences of 4 per time, that is, the generation frequency f of the Karman vortex 4 is detected. Reference numeral 25 denotes a flow velocity calculation circuit that constitutes flow velocity / flow rate calculation means together with the generation frequency detection circuit 24 and a volume flow rate calculation circuit 29 described later. The flow velocity calculation circuit 25 determines the generation frequency f detected by the generation frequency detection circuit 24. On the basis of this, the flow velocity V of the air is calculated from the following equation 3 which is almost the same as the equation shown in the above equation 1.

[0033]

[Formula 3] V = (d1 / s) · f, where d1: diameter of vortex generator 11

Reference numeral 26 denotes a temperature measuring circuit which is located in the flow rate measuring unit 20 and is connected to the waveform detecting circuit 22 as a temperature measuring means. The temperature map 27 shown in FIG. Is remembered. Then, the temperature measuring circuit 26 sets the resistance value of the valley portion 23A of the signal waveform 23 detected by the waveform detecting circuit 22 as the minimum resistance value R0 in the state where the temperature sensitive resistance wire 16 is not in contact with the Karman vortex 4. The temperature T of the air is read based on the temperature map 27 by reading the resistance value R0 and the flow velocity V obtained by the flow velocity calculating circuit 25.
Is to measure. Here, the temperature map 27
Is a plurality of flow velocities V1, V2, V3 ... (3
The resistance value R of the temperature-sensitive resistance wire 16 and the temperature T of the air are stored as a map according to (only the book is shown).

Reference numeral 28 denotes a density calculation circuit as a density calculation means provided on the output side of the temperature measurement circuit 26. The density calculation circuit 28 is based on the temperature T from the temperature measurement circuit 26 and has a density map (not shown). No.), the air density ρ at that temperature T is calculated, and this air density ρ is output to the mass flow rate calculation circuit 30. Here, in the density map, the relationship between the fluid temperature and the fluid density is stored as a map according to the type of fluid such as air and gasoline.

Reference numeral 29 denotes a volume flow rate calculation circuit which is provided on the output side of the flow rate calculation circuit 25 and constitutes a flow rate / flow rate calculation means together with the flow rate calculation circuit 25. The arithmetic expression shown is stored. The volumetric flow rate calculation circuit 29 calculates the volumetric flow rate A from the flow velocity V calculated by the flow velocity calculation circuit 25 based on the equation (2).

Reference numeral 30 denotes a mass flow rate calculation circuit as a mass flow rate calculation means provided in the flow rate measurement unit 20, and the memory of the mass flow rate calculation circuit 30 stores the calculation formula shown in the following equation 4. .. Then, the mass flow rate calculation circuit 30
Is for calculating the mass flow rate B based on the volume flow rate A from the volume flow rate calculation circuit 29 and the air density ρ from the density calculation circuit 28.

[0038]

[Equation 4] B = A · ρ

Reference numeral 31 denotes an output switching circuit provided between the volume flow rate calculation circuit 29 and the mass flow rate calculation circuit 30. The output switching circuit 31 is switched to a volume flow rate A by being switched by an operator. One of the mass flow rates B is selected and switched, and the respective flow rates A and B are output to the display 32 and displayed.

The Karman vortex flowmeter according to this embodiment has the above-mentioned structure, and its operation will be described below.

First, when the air rectified by the rectifying net 2 flows into the casing 1, the air comes into contact with the vortex generator 11, and the Karman vortices 4 are alternately arranged regularly on the downstream side of the vortex generator 11. Occur. When the Karman vortex 4 contacts the temperature-sensitive resistance wire 16, the temperature-sensitive resistance wire 1
Since 6 is cooled by the Karman vortex 4, the temperature of itself decreases and the resistance value R increases. Next, the resistance value detection circuit 2
1 detects the resistance value R of the temperature sensitive resistance wire 16, and the waveform detection circuit 22 forms a signal waveform 23 based on the detected resistance value R from the resistance value detection circuit 21. Then, the generation frequency detection circuit 24 detects the generation frequency f of the Karman vortex 4 from the signal waveform 23, and the flow velocity calculation circuit 25 calculates the flow velocity V of air from the equation 3 based on the generation frequency f. Further, as shown in FIG. 6, when the air temperature T changes from the low temperature T1 to the high temperature T2 or the flow velocity V increases, the temperature-sensitive resistance line increases as the flow velocity V of the air increases. 16
The resistance value R changes. However, the waveform detection circuit 22
The change in resistance value of the temperature-sensitive resistance wire 16 is arranged in time series to form a signal waveform 23.
Since the generated frequency f is detected from 3, the air temperature T,
The generated frequency f can be detected without being affected by the change in the flow velocity V.

On the other hand, the temperature measuring circuit 26 reads the resistance value of the valley 23A of the signal waveform 23 from the waveform detecting circuit 22 as the minimum resistance value R0, and also reads the flow velocity V of the air from the flow velocity calculating circuit 25. Then, the temperature measuring circuit 26
Selects the closest flow velocity among the flow velocity V1, V2, V3, ... Stored in advance from the flow velocity V from the flow velocity calculation circuit 25, and the temperature at which the lowest resistance value R0 appears at this flow velocity is the air temperature T. To the density calculation circuit 28, and the density calculation circuit 28 reads the density map and outputs the temperature T
The density ρ of the air at is calculated.

Next, the volume flow rate calculation circuit 29 calculates the volume flow rate A from the flow rate V output from the flow rate calculation circuit 25 based on the above equation 2, and the mass flow rate calculation circuit 30 calculates the volume flow rate A and the density. From the air density ρ output from the circuit 28, the mass flow rate B is calculated based on the equation (4). Then, the output switching circuit 31 switches the volume flow rate calculation circuit 29 and the mass flow rate calculation circuit 30 according to the operator's selection to output the volume flow rate A and the mass flow rate B to the display 32 for display.

When the key switch 19 is turned on, the burnout circuit 18 outputs a control signal to the energizing switch 14 to close the energizing switch 14 for a predetermined time so that the current from the battery power source 13 is changed. Lead wire 12A,
Is supplied to the vortex generator 11 via 12B,
Is heated to about 1000 ° C. As a result, foreign substances such as gum and carbon attached to the surface of the vortex generator 11 are
The vortex generator 11 is burnt and removed by heat generation.

Thus, according to this embodiment, the vortex generator 1
The Karman vortex 4 generated by 1 can be reliably detected as a change in the resistance value of the temperature-sensitive resistance wire 16, a signal waveform 23 is generated from this change in the resistance value, and the generation frequency f is detected from the signal waveform 23. Thus, the flow rate V can be obtained and the volumetric flow rate A can be reliably calculated. As a result,
As described in the prior art, even when the flow velocity V of air changes, the resistance value of the temperature-sensitive resistance wire 16 quickly follows this change in flow velocity as shown in FIG. 6, so that the flow velocity V has high responsiveness. Can be obtained, and the volumetric flow rate A can be accurately measured.

Further, the temperature measuring circuit 26 can measure the air temperature T corresponding to the flow velocity V based on the temperature map 27, and the density calculating circuit 28 can calculate the air density ρ at the temperature T. As a result, the air temperature T can be effectively measured from the resistance value change of the single temperature-sensitive resistance wire 16 and the flow velocity V without using a separate temperature sensor, and the air density at that temperature T can be measured. The mass flow rate B can be accurately calculated by reliably calculating ρ, and the overall configuration can be made compact.

Further, the vortex generator 11 is formed of silicon carbide fiber as a heating element, and the burnout circuit 18 closes the energizing switch 14 to turn the vortex generator 11 on when the key switch 19 is turned on. Since the current is supplied from the battery power source 13, the vortex generator 11 can be made to generate heat every time the engine is started, and foreign matter adhering to the surface of the vortex generator 11 can be burned off and reliably removed. it can. As a result,
Even when the flowmeter is used for a long time, it is possible to effectively prevent the deposits 9 described in the prior art from being generated on the surface of the vortex generator 11 and prevent the shape of the vortex generator 11 from changing. ,
The volume flow rate A and the mass flow rate B of air can be measured with high accuracy over a long period of time, and the reliability can be significantly improved.

In the above embodiment, the vortex generator 11 is
Although the heat-generating material is described as being formed in a columnar shape from silicon carbide fibers having thermistor characteristics, it may be formed in another shape such as a triangular shape or a quadrangular shape instead. Depending on the case, other heat generating materials such as nichrome wire and platinum may be used instead of the silicon carbide fiber.

Further, in the above-described embodiment, the vortex generator 11 is supplied with current for about 2 seconds, and the vortex generator 11 is heated to 1000
Although it has been described that the heat is generated at about ℃, instead of this, for example, the vortex generator 11 may be supplied with an electric current for 2 seconds or less, or for 2 seconds or more.
It may be configured to generate heat at 00 ° C or lower, or 1000 ° C or higher.

Further, in the above embodiment, the output switching circuit 31
According to the volume flow rate calculation circuit 29 and the mass flow rate calculation circuit 30,
Although it has been described as switching between and, the configuration may be such that only the mass flow rate is displayed instead. Further, the output switching circuit 31 may be eliminated and the volume flow rate and the mass flow rate may be displayed at the same time, and the temperature T calculated by the temperature measuring circuit 26 may be displayed.
May be displayed.

Further, in the above embodiment, a plurality of vortex stabilizers 5, 5, ... Are arranged on the downstream side of the vortex generator 11, but in some cases, each vortex stabilizer 5 is omitted. May be.

Further, in the above-mentioned embodiment, the case where the Karman vortex flowmeter is used for the air flow meter of the automobile engine has been described as an example, but the present invention is not limited to this, and an industrial gas such as CFC gas, It can be widely applied to flow rate measurement of various fluids such as fuels such as gasoline and factory water.

[0053]

As described in detail above, according to the present invention, the resistance value of the temperature-sensitive resistance wire made of silicon carbide fiber which is brought into contact with the Karman vortex and changes in temperature is detected as a frequency signal by the signal detecting means, The flow velocity / flow rate calculation means can calculate the flow rate or flow rate of the fluid based on the detection signal detected by the signal detection means. As a result, even when the flow velocity or flow rate of the fluid changes, the resistance value of the temperature-sensitive resistance wire can be changed according to the presence or absence of the Karman vortex, and the flow velocity or flow rate of the fluid can be accurately calculated.

The temperature measuring means accurately detects the temperature of the fluid on the basis of the detection signal from the signal detecting means and the flow velocity or flow rate from the flow velocity / flow rate calculating means, and the density calculating means determines the temperature of the fluid at this temperature. The density of the fluid can be calculated, and the flow rate calculation means can reliably calculate and determine the mass flow rate of the fluid from the fluid density and the flow velocity or flow rate. As a result, the fluid temperature can be measured without using a separate temperature sensor, and the mass flow rate of the fluid can be effectively obtained.

Further, since the vortex generator is made of a heat-generating material that generates heat by an electric current, and a current is supplied to the vortex generator, the foreign matter attached to the vortex generator is burned out. It is possible to reliably remove foreign matter attached to the surface of the body. As a result, even when the flow meter is used for a long time, it is possible to effectively prevent foreign matter from adhering to the surface of the vortex generator and changing the shape of the vortex generator, and to keep the flow rate of the fluid for a long time. It is possible to perform accurate measurement over a range and improve reliability.

[Brief description of drawings]

FIG. 1 is a circuit configuration diagram showing an overall circuit configuration of a Karman vortex flowmeter according to an embodiment of the present invention.

FIG. 2 is an electric circuit diagram showing an electric circuit in FIG.

3 is a block circuit diagram showing a circuit configuration of a flow rate measuring unit 20 in FIG.

FIG. 4 is an explanatory diagram showing signal waveforms.

FIG. 5 is an explanatory diagram showing a temperature map.

FIG. 6 is an explanatory diagram showing a state in which the resistance value changes when the flow velocity and the air temperature change.

FIG. 7 is a circuit configuration diagram showing an overall configuration of a Karman vortex flowmeter according to a conventional technique.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Casing 4 Karman vortex 11 Vortex generator 14 Energizing switch (burning-out means) 16 Temperature-sensitive resistance wire 22 Waveform detection circuit (signal detection means) 25 Flow velocity calculation circuit (flow velocity / flow rate calculation means) 26 Temperature measurement means (temperature measurement means) ) 28 density calculation circuit (density calculation means) 29 volume flow calculation circuit 30 mass flow calculation circuit (mass flow calculation means)

Claims (3)

[Claims] 1. A cylindrical casing through which a fluid flows, and a casing provided in the casing perpendicularly to the flow direction of the fluid,
A vortex generator that generates a Karman vortex on the downstream side by the flow of a fluid, and a silicon carbide fiber that is provided on the casing located on the downstream side of the vortex generator and has a resistance value that changes depending on the presence of the Karman vortex Temperature sensitive resistance wire, a signal detecting means for detecting a change in resistance value of the temperature sensitive resistance wire as a frequency signal, and a flow velocity / flow rate operation for calculating a flow velocity or a flow rate based on a detection signal detected by the signal detecting means. Karman vortex flowmeter consisting of means. 2. A temperature measuring means for measuring the temperature of the fluid based on the detection signal detected by the signal detecting means and the flow velocity or flow rate of the fluid calculated by the flow velocity / flow rate calculating means, and the temperature measuring means measures the temperature. The mass flow rate of the fluid is calculated from the density calculating means for calculating the density of the fluid from the temperature of the fluid, and the density of the fluid calculated by the density calculating means and the flow velocity or flow rate of the fluid calculated by the flow velocity / flow rate calculating means. The Karman vortex flowmeter according to claim 1, further comprising a mass flow rate calculation means for performing a calculation. 3. The vortex generator is formed of a heat-generating material that generates heat with an electric current, and a burn-out means for burning foreign matter attached to the vortex generator by supplying an electric current to the vortex generator is provided. The Karman vortex flowmeter according to claim 1 or 2, characterized in that.