JP2011202999A - Vortex flowmeter and comparator threshold setting method - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a vortex flowmeter capable of automatically setting a comparator threshold for determining the presence of a gas flow.SOLUTION: The vortex flowmeter 1 includes: a vortex generating body disposed in a flow channel through which a fluid to be measured flows; a bypass flow channel in which an alternating flow is generated by a vortex generated by the vortex generating body; a pressure sensor 6 detecting a pressure value of the fluid to be measured in the flow channel; and a flow sensor 10 detecting an amplitude and a frequency of the alternating flow, and calculates a flow rate of the fluid to be measured on the basis of the frequency of the alternating flow when the amplitude of the alternating flow detected by the flow sensor 10 exceeds a comparator threshold. The vortex flowmeter includes: a memory 7 recording pressure threshold information defining correlation between a pressure value of the fluid to be measured in the flow channel and the comparator threshold; and a central control unit 8 automatically setting the comparator threshold on the basis of the pressure value detected by the pressure sensor 6 and the pressure threshold information recorded in the memory 7.

Description

  The present invention relates to a vortex flowmeter and a comparator threshold value setting method.

  Conventionally, a vortex generator (Kalman vortex) is generated by a vortex generator placed in a gas pipe in which a predetermined flow path for gas flow is formed to generate gas vibration, and the measurement is performed based on the frequency of this gas vibration. A vortex flowmeter that measures (calculates) the flow rate of gas has been proposed and put into practical use. In addition, at present, a bypass flow path perpendicular to the flow direction of the gas to be measured is formed on the downstream side of the vortex generator, and a thermal flow sensor is disposed in the bypass flow path. A flow meter that detects the frequency of gas vibration and calculates the volume flow rate of the gas to be measured has been proposed and put into practical use. Furthermore, a vortex flowmeter that converts this volume flow rate into a mass flow rate has been proposed (see, for example, Patent Document 1).

  Further, in recent years, a vortex generation frequency component of a Karman vortex generated by a vortex generator arranged in a gas flow channel is detected by a flow sensor arranged in a bypass channel formed in the vortex generator. A Karman vortex flowmeter comprising a detector and a converter that calculates a vortex generation frequency based on the detection output from the flow sensor and calculates a mass flow rate based on the vortex generation frequency and the fluid pressure in the bypass flow path. It has been introduced (for example, see Patent Document 2).

JP 2004-93349 A JP 2004-117158 A

  By the way, in the above-described vortex flowmeter that detects the vortex frequency of the gas by the flow sensor, the amplitude of the detected sensor signal is a comparator threshold value (a signal amplitude threshold value for determining whether or not the gas is flowing in the flow path). ) Is exceeded, it is determined that the frequency of the sensor signal is significant (gas is flowing in the flow path) and the flow rate calculation is performed.

  If the comparator threshold value for determining the presence or absence of such a gas flow is set to a relatively small value, it is possible to detect a low pressure / low flow rate flow. However, fluctuations and electrical noise generated in the flow path can be detected. This is likely to be affected, and may cause erroneous detection of the flow rate (displaying the flow rate even though the fluid to be measured is not circulating). For this reason, when the conventional vortex flowmeter is employed, it is necessary for the user to manually reset the comparator threshold value according to the use situation, which is troublesome.

  The present invention has been made in view of such circumstances, and an object thereof is to provide a vortex flowmeter capable of automatically setting a comparator threshold value for determining the presence or absence of a gas flow.

  In order to achieve the above object, the vortex flowmeter according to the present invention has a vortex generator disposed in a flow path through which a fluid to be measured flows, and an alternating flow is generated inside the vortex generated by the vortex generator. The bypass flow path, the pressure sensor for detecting the pressure value of the fluid to be measured in the flow path, the flow sensor for detecting the amplitude and frequency of the alternating flow, and the amplitude of the alternating flow detected by the flow sensor A flow rate calculation means for calculating a flow rate of a fluid to be measured based on an alternating flow frequency when a comparator threshold is exceeded, wherein the pressure value of the fluid to be measured in the flow path and the comparator threshold value A threshold setting for automatically setting a comparator threshold based on information recording means for recording pressure threshold information for defining a correlation between the pressure threshold value and pressure value detected by the pressure sensor and pressure threshold information recorded on the information recording means. Those comprising a means.

  The comparator threshold value setting method according to the present invention includes a vortex generator disposed in a flow path through which a fluid to be measured flows, and a bypass flow in which an alternating flow is generated by the vortex generated in the vortex generator. A vortex flowmeter comparator threshold value for calculating a flow rate of the fluid under measurement based on the frequency of the alternating flow when the amplitude of the alternating flow exceeds the comparator threshold value. A pressure detection step for detecting a pressure value of the fluid to be measured in the channel; pressure threshold value information defining a correlation between the pressure value detected in the pressure detection step and the pressure value of the fluid to be measured in the flow channel and the comparator threshold value And a threshold value setting step for automatically setting a comparator threshold value based on the above.

  When such a configuration and method are employed, a comparator threshold value for determining the presence or absence of a gas flow can be automatically set according to the pressure value of the fluid to be measured in the flow path. In other words, it has been experimentally confirmed that when the pressure value of the fluid under measurement in the flow path increases, the amplitude of the alternating flow increases even at the same flow rate. Therefore, there is a correlation between the pressure value of the fluid under measurement and the comparator threshold value. (A relation in which the comparator threshold value increases when the pressure value of the fluid to be measured increases) is recorded in advance as pressure threshold value information, and the comparator threshold value is automatically set based on the detected pressure value and the recorded pressure threshold value information. be able to. Accordingly, it is possible to suppress erroneous detection of the flow rate without being affected by noise.

  In the vortex flowmeter, a flow having a heating resistor disposed in the bypass flow path and a temperature sensor that is installed in the vicinity of the heating resistor and measures a temperature change of a fluid to be measured heated by the heating resistor. A sensor can be employed.

  When such a configuration is adopted, information relating to the frequency of the alternating flow generated in the bypass flow path is obtained by detecting the temperature change of the fluid to be measured heated by the heating resistor using the temperature sensor. Can do.

  ADVANTAGE OF THE INVENTION According to this invention, it becomes possible to provide the vortex flowmeter which can set the comparator threshold value for discriminating the presence or absence of a gas flow automatically.

It is a front view of the vortex flowmeter concerning the embodiment of the present invention. It is the side view which looked at the vortex flowmeter shown in FIG. 1 from the arrow II direction shown in FIG. It is a fragmentary sectional view of the vortex flowmeter shown in FIG. It is a fragmentary sectional view of the vortex flowmeter shown in FIG. It is explanatory drawing of the internal structure of the vortex generator of the vortex flowmeter shown in FIG. It is sectional drawing along the VI-VI line shown in FIG. It is a perspective view of the thermal type flow sensor carried in the vortex flowmeter concerning the embodiment of the present invention. It is sectional drawing along the VIII-VIII line shown in FIG. It is a block diagram which shows the functional structure of the vortex flowmeter which concerns on embodiment of this invention. It is a time chart which shows the time history of the sensor signal of measured gas. It is a graph which shows the correlation of the flow velocity of to-be-measured gas, and a sensor signal amplitude for every pressure. It is a map used for the comparator threshold value setting of the vortex flowmeter which concerns on embodiment of this invention. It is a flowchart for demonstrating operation | movement of the vortex flowmeter which concerns on embodiment of this invention.

  Hereinafter, a vortex flowmeter according to an embodiment of the present invention will be described with reference to the drawings. In each figure, the thickness and size of each member, the enlargement / reduction ratio, etc. are shown without matching with the actual ones for easy understanding. In addition, embodiment described below is the illustration for demonstrating this invention, and this invention is not limited to this embodiment.

  The vortex flowmeter 1 according to the present embodiment is disposed in a fluid pipe 2 and a flow path 2a that form a flow path 2a through which a gas to be measured flows, as shown in FIGS. 1, 2, 6, and 9 and the like. Vortex generator 3, bypass flow path 4 formed inside the vortex generator 3, thermal flow sensor 10 disposed in the bypass flow path 4, heater 14 of the thermal flow sensor 10 (heating resistor) Drive circuit 5 for generating heat by applying a current to the gas, pressure sensor 6 for detecting the pressure of the gas to be measured, memory 7 for recording various information and control programs, central control unit for calculating various physical quantities and controlling the drive circuit 5 8. A display unit 9 for displaying various information is provided.

  As shown in FIGS. 1 and 2, the fluid pipe 2 is a short cylindrical member. As shown by broken lines in FIG. 1, pipes 100 for circulating the gas to be measured are connected to both ends of the fluid pipe 2. As shown in FIGS. 2 and 3, the vortex generator 3 is a columnar member longer than the diameter of the fluid pipe 2, and the diameter of the vortex generator 3 enters the fluid pipe 2 from the through hole 2 b formed in the wall portion of the fluid pipe 2. It is inserted so as to cross in the direction. Between the outer periphery of the vortex generator 3 and the through hole 2 b of the fluid pipe 2, an O-ring 21 that maintains the hermeticity of the fluid pipe 2 is disposed. Further, the vortex generator 3 is fixed to the fluid pipe 2 by a fixing plate 22.

  The bypass channel 4 is formed so as to extend in a direction (direction of arrow B in FIG. 6) orthogonal to the flow direction of the gas to be measured (direction of arrow A in FIGS. 1 and 6). Both ends thereof are openings 4a. An alternating flow is generated inside the bypass channel 4 by a vortex street (Karman vortex) generated by the vortex generator 3. As shown in FIGS. 3 and 5, the flow direction of the gas to be measured (in the direction of arrow A) and the bypass flow from the middle of the bypass flow path 4 to above the vortex generator 3, as shown in FIGS. A small-diameter hole 3a is formed so as to extend in a direction orthogonal to the extending direction of the path 4 (arrow B direction). A pipe 23 having an outer diameter smaller than the inner diameter of the small diameter hole 3a is detachably inserted into the small diameter hole 3a. A sensor assembly 24 on which the thermal flow sensor 10 is mounted is fixed to the tip 23 a of the pipe 23.

  The thermal flow sensor 10 is a flow sensor having a semiconductor diaphragm disposed so as to come into contact with a gas to be measured flowing through the bypass flow path 4. As shown in FIGS. 7 and 8, the thermal flow sensor 10 is provided on the substrate 11 provided with the cavity 12, the insulating film 13 disposed on the substrate 11 so as to cover the cavity 12, and the insulating film 13. The heater 14 includes a first resistance temperature sensor 15 and a second resistance resistance element 16 disposed on both sides of the heater 14, an ambient temperature sensor 17, and the like.

  A portion of the insulating film 13 covering the cavity 12 constitutes a heat insulating diaphragm. The ambient temperature sensor 17 detects the temperature of the gas to be measured flowing through the bypass flow path 4. The heater 14 is disposed at the center of the insulating film 13 covering the cavity 12 and functions as a heating resistor that generates heat due to current supplied from the drive circuit 5. In the present embodiment, the drive circuit 5 generates heat by applying current to the heater 14 so that the temperature of the heater 14 is higher than the temperature of the gas under measurement measured by the ambient temperature sensor 17.

  The first resistance temperature detector 15 is used to detect the temperature on one side of the heater 14, and the second resistance temperature detector 16 is used to detect the temperature on the other side of the heater 14. Both function as a temperature sensor. Sensor signals corresponding to the temperature difference between the two sides of the heater 14 are detected by the first and second resistance temperature measuring elements 15, 16 and related to the amplitude and frequency of the alternating flow generated in the bypass flow path 4. Information can be obtained. That is, the thermal flow sensor having the heater 14 and the first and second resistance temperature measuring elements 15 and 16 functions as a flow sensor in the present invention. Information regarding such a frequency is input to the central control unit 8 and used for calculation of a volume flow rate of the gas to be measured.

Note that silicon (Si) or the like can be used as the material of the substrate 11 shown in FIGS. As a material of the insulating film 13, silicon oxide (SiO ₂ ) or the like can be used. The cavity 12 is formed by anisotropic etching or the like. Platinum (Pt) or the like can be used for each material of the heater 14, the first resistance temperature detector 15, the second resistance temperature detector 16, and the ambient temperature sensor 17, and can be formed by a lithography method or the like. .

  As shown in FIG. 3, such a thermal flow sensor 10 is disposed at a position facing the bypass flow path 4 by inserting the tip 23 a of the pipe 23 to the deepest portion of the small diameter hole 3 a. It becomes. As shown in FIG. 3, the pipe 23 inserted into the small diameter hole 3a of the vortex generator 3 is formed above the small diameter hole 3a and is inserted into the large diameter hole 3b having an inner diameter larger than that of the small diameter hole 3a. 25 is fixed.

  Further, as shown in FIG. 4, a pressure sensor 6 for detecting the pressure of the gas to be measured is disposed above the fixed member 25.

  A signal amplifying printed circuit board (not shown) for the thermal flow sensor 10 and the pressure sensor 6 is provided on the outer peripheral surface of the fixing member 25, and the connection line 18 of the thermal flow sensor 10 is connected to the inside of the pipe 23. The printed wiring board is connected through the space. The space surrounding the printed wiring board and the pressure sensor 6 is protected by a cylindrical case 27 attached to the outside of the vortex generator 3 via an O-ring 26. A housing 28 is attached above the case 27 as shown in FIGS. As shown in FIG. 4, a terminal 29 is built in the housing 28, and a printed wiring board 30 provided with the memory 7, the central control unit 8, and the like is disposed in the terminal 29. A cover 31 is screwed into the opening 28a of the housing 28, and a display unit 9 for displaying various information such as the mass flow rate of the gas to be measured is provided on the opposite side of the opening 28a.

  The memory 7 defines the correlation between the pressure value of the gas to be measured in the flow path 2a and the comparator threshold value (signal amplitude threshold value for determining whether or not the gas is flowing in the flow path). Pressure threshold information is recorded in advance. The correlation between the pressure value of the gas to be measured and the comparator threshold value will be described with reference to FIGS.

  The alternating flow of the gas to be measured generated in the bypass flow path 4 of the vortex flowmeter 1 is a sensor signal having a waveform as shown in FIG. 10 via the first and second resistance temperature detectors 15 and 16. Detected as (voltage). In a general vortex flowmeter, when the amplitude A of the sensor signal exceeds a predetermined comparator threshold, it is determined that the frequency of the sensor signal is significant (gas is flowing in the flow path). Flow rate calculation is performed.

Here, it has been experimentally confirmed that when the pressure of the gas to be measured increases, the amplitude of the sensor signal increases even at the same flow rate as shown in FIG. Therefore, in the present embodiment, a linear map M ₁ as shown in FIG. 12 is given as an example of pressure threshold information that defines the correlation between the pressure value of the gas to be measured and the comparator threshold. The memory 7 functions as information recording means in the present invention.

The central control unit 8 automatically sets the comparator threshold value based on the pressure value detected by the pressure sensor 6 and the linear map M ₁ (FIG. 12) recorded in the memory 7. In addition, when the amplitude of the alternating flow sensor signal generated in the bypass flow path 4 exceeds the set comparator threshold, the central control unit 8 determines the frequency of the alternating flow sensor signal and the ambient temperature sensor 17. The mass flow rate of the gas to be measured is calculated based on the information detected by the pressure sensor 39. That is, the central control unit 8 functions as a threshold setting unit and a flow rate calculation unit in the present invention.

  Next, operation | movement of the vortex flowmeter 1 which concerns on embodiment of this invention is demonstrated with reference to the flowchart shown in FIG. In the vortex flowmeter 1 according to the present embodiment, a “comparator threshold setting method” in which the comparator threshold is automatically set according to the pressure value of the gas to be measured flowing in the flow path 2a can be implemented.

  First, in step S1, a vortex is generated in the flow path 2a through which the gas to be measured flows by the vortex generator 3, and then the process proceeds to step S2, where an alternating flow is generated in the bypass flow path 4 by the vortex. Next, the process proceeds to step S3, where the temperature of the gas to be measured is detected using the ambient temperature sensor 17, and the center of the heater 14 disposed in the bypass channel 4 is set to a constant temperature higher than the detected temperature. The controller 8 controls the drive circuit 5 to give a current to the heater 14 to generate heat.

Subsequently, it progresses to step S4, and after detecting the pressure of to-be-measured gas using the pressure sensor 6, it progresses to step S5. In step S <b> 5, the central control unit 8 automatically sets a comparator threshold based on the pressure value detected in step S <b> 4 and the pressure threshold information recorded in the memory 7. For example, when the pressure value detected by the pressure sensor 6 is 300 kPa, the central control unit 8 sets the comparator threshold value to “3.0 (V)” using the linear map M ₁ in FIG. Step S4 corresponds to the pressure detection step in the present invention, and step S5 corresponds to the threshold setting step in the present invention.

  Then, it progresses to step S6 and the sensor signal of the alternating flow produced | generated in the bypass flow path 4 is detected using the thermal type flow sensor 10. Then, it progresses to step S7. In step S7, the central control unit 8 determines whether the amplitude of the sensor signal detected in step S6 exceeds the comparator threshold automatically set in step S5, and a positive determination is obtained (step S7: If yes), proceed to step S8. On the other hand, if a negative determination is obtained in step S7 (step S7: NO), the process returns from step S4 to repeat the steps from pressure detection to amplitude determination.

  In step S8, the central control unit 8 calculates the volume flow rate of the gas to be measured by multiplying the frequency of the sensor signal detected in step S6 by a predetermined coefficient, and this volume flow rate and the temperature detected in step S3, Based on the pressure value detected in step S4, the mass flow rate of the gas to be measured is calculated. The mass flow rate calculated in this way is displayed on the display unit 9.

  In the vortex flowmeter 1 in the embodiment described above, the comparator threshold value for determining the presence or absence of the gas flow can be automatically set according to the pressure value of the gas to be measured in the flow path 2a. That is, since it has been experimentally confirmed that when the pressure value of the gas to be measured in the flow path 2a increases, the amplitude of the sensor signal in the alternating flow increases even at the same flow rate, the pressure value of the gas to be measured and the comparator threshold value. Can be recorded in advance as a specific map (FIG. 12), and the comparator threshold value can be automatically set based on the detected pressure value and the recorded map. Accordingly, it is possible to suppress erroneous detection of the flow rate without being affected by noise.

  In this embodiment, an example in which temperature sensors (first and second resistance temperature measuring elements 15 and 16) that detect the frequency of the alternating flow generated in the bypass flow path 4 are arranged on both sides of the heater 14. Although shown, the temperature sensor does not necessarily have to be arranged on both sides of the heater 14, and the temperature sensor may be arranged on one side of the heater 14 to detect the frequency. Further, the frequency of the alternating flow generated in the bypass flow path 4 can be detected by the temperature change of the heater 14 itself.

In the present embodiment, an example in which a linear map M ₁ as shown in FIG. 12 is given as the pressure threshold information that defines the correlation between the pressure value of the gas to be measured and the comparator threshold is shown. The information is not limited to this, and can be appropriately changed according to the specifications of the thermal flow sensor. For example, it is also possible to employ a non-linear map M3 shown a stepwise map M ₂ and two-dot chain line indicated by the one-dot chain line in FIG. 12 as the pressure threshold information.

  In the above embodiment, an example in which the columnar vortex generator 3 is disposed by being inserted from the through hole 2b of the fluid pipe 2 has been described. However, the columnar vortex generator 3 is directly incorporated into the fluid pipe 2. A configuration can also be adopted. In addition, the present invention can be variously modified and implemented without departing from the scope of the invention.

DESCRIPTION OF SYMBOLS 1 ... Eddy flow meter 2a ... Flow path 3 ... Vortex generator 4 ... Bypass flow path 5 ... Drive circuit 6 ... Pressure sensor 7 ... Memory (information recording means)
8: Central control unit (threshold setting means, flow rate calculating means)
10 ... Thermal flow sensor (flow sensor)
14 ... Heater (heating resistor)
15 ... 1st resistance temperature sensor (temperature sensor)
16 ... 2nd resistance temperature sensor (temperature sensor)

Claims (4)

A vortex generator disposed in a flow path through which the fluid to be measured flows, a bypass flow path in which an alternating flow is generated by the vortex generated in the vortex generator, and the fluid to be measured in the flow path A pressure sensor for detecting the pressure value, a flow sensor for detecting the amplitude and frequency of the alternating flow, and the frequency of the alternating flow when the amplitude of the alternating flow detected by the flow sensor exceeds a comparator threshold. A vortex flowmeter comprising: a flow rate calculation means for calculating a flow rate of the fluid to be measured based on
Information recording means for recording pressure threshold information defining a correlation between a pressure value of a fluid to be measured in the flow path and a comparator threshold;
Threshold setting means for automatically setting a comparator threshold based on the pressure value detected by the pressure sensor and the pressure threshold information recorded in the information recording means,
Vortex flow meter. The flow sensor is
A heating resistor disposed in the bypass flow path, and a temperature sensor that is installed in the vicinity of the heating resistor and measures a temperature change of a fluid to be measured heated by the heating resistor.
The vortex flowmeter according to claim 1. The pressure threshold information defines a relationship in which the comparator threshold increases when the pressure value of the fluid to be measured in the flow path increases.
The vortex flowmeter according to claim 1 or 2. A vortex generator disposed in a flow path through which the fluid to be measured flows, and a bypass flow path in which an alternating flow is generated by the vortex generated in the vortex generator, the amplitude of the alternating flow Is a method of setting a comparator threshold value of a vortex flowmeter that calculates a flow rate of a fluid to be measured based on the frequency of the alternating flow when a comparator threshold value is exceeded,
A pressure detection step of detecting a pressure value of the fluid to be measured in the flow path;
A threshold setting step for automatically setting a comparator threshold based on the pressure value detected in the pressure detection step, and pressure threshold information defining a correlation between the pressure value of the fluid to be measured in the flow path and the comparator threshold; Comprising
Comparator threshold setting method.

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