JP3628308B2 - Flowmeter - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention relates to a flow meter, and more particularly to a flow meter capable of detecting a critical state of a fluid to be measured.
[0002]
[Prior art]
There are various types of flowmeters that measure the flow rate or flow velocity of fluid, but especially in flowmeters that have a mechanism for constricting the fluid, the gas that flows at high speed may be in a critical state due to the throttling mechanism. . As the gas is gradually expanded, the velocity increases, the temperature decreases, and thus the local sound velocity also decreases. For this reason, the local Mach number M increases more rapidly than the increase in speed and reaches a state of M = 1. This state is called a critical state. Moreover, the pressure at this time is called a critical pressure. The liquid can be handled as incompressible (Mach number less than 0.3) without exception. In the critical state, a shock wave may be generated inside the flow tube, and the sensor (pickup) signal for detecting the flow of the fluid to be measured is disturbed, and accurate measurement cannot be performed. Even if a shock wave does not occur, it cannot be said that the temperature in the measurement tube is uniformly distributed, and an accurate measurement value cannot be obtained in a flow meter that measures the flow rate by performing temperature correction.
[0003]
Typical examples of flowmeters with a mechanism for constricting fluid are nozzles, venturi pipes, and orifice flowmeters. However, in order to increase the flow detection capability of Coriolis mass flowmeters, in many cases, thin and thin A curved measuring tube is used, and a curved structure that is structurally easy to twist is often selected so that Coriolis force can be easily detected. For this reason, the flow may be restricted by a narrow tube or the flow may be restricted by bending. It is sufficient if there is such a constricted part where the sensor is not affected, but the Coriolis mass flowmeter has a constricted part of the measuring tube itself, and if a shock wave is generated in the measuring tube as described above The effect on the measurement results is great. Furthermore, even if the flow is not restricted upstream and downstream of the sensor, the restriction of the sensor itself may be a factor that determines the critical flow rate of the line.
[0004]
In conventional Coriolis flowmeters and other flowmeters, there is no means to detect the critical state in gas measurement, and the critical flow velocity is obtained from experiments, or used roughly from the sound velocity obtained from temperature and pressure under the operating conditions. The critical flow velocity (flow rate) under the conditions was obtained. However, in many cases, the sound speed of the fluid measured by the user (user) is unknown, or even if the critical flow velocity is obtained in advance, the information obtained from the user such as temperature, pressure, and physical properties of the fluid is not accurate. There was a possibility that it would become critical when installed.
[0005]
If the flow meter reaches the critical state during measurement with a flow meter, and the flow meter is a type of flow meter that measures the instantaneous flow rate, it may be caused by vibration caused by shock waves generated in or near the flow tube (flow tube) or abnormal output due to temperature gradients. Although it is easy to notice the state, in the case of a type of flow meter that measures the integrated flow rate, it is often overlooked.
[0006]
[Problems to be solved by the invention]
This invention is made | formed in view of the above actual condition, and it aims at providing the flowmeter which can detect a critical state.
[0007]
[Means for Solving the Problems]
According to a first technical means of the present invention, in the flowmeter for measuring the flow rate or flow velocity of the fluid to be measured, the temperature difference or the temperature ratio between the upstream side and the downstream side of the throttle part of the flow tube through which the fluid to be measured flows. a temperature difference detecting means for detecting, for notifying the user and the critical state detecting means for detecting a critical state of the fluid to be measured, the critical state detected by the critical state detecting means based on the output of the temperature difference detecting means And a notification means.
[0008]
The second technical means is the first technical means, wherein the temperature difference detecting means includes a first temperature sensor provided on the upstream side, a second temperature sensor provided on the downstream side, and the first temperature sensor. Means for calculating a difference or ratio of the temperature detected by the second temperature sensor with respect to the temperature detected by the temperature sensor, and the critical state detecting means is critical when the difference or ratio is greater than a predetermined value. It is characterized by detecting as a state.
[0009]
A third technical means is a flow meter for measuring the flow rate or flow speed of the test fluid, the temperature difference or temperature of the vicinity of the downstream side of the throttle portion of the flow tube fluid to be measured flows, a downstream side of the vicinity of the downstream side a temperature difference detecting means for detecting the ratio, the critical state detecting means for detecting a critical state of the fluid to be measured based on the output of the temperature difference detecting means, the user of the critical state detected by the critical state detecting means And a notification means for notifying.
[0010]
A fourth technical means is the third technical means, wherein the temperature difference detection means includes a first temperature sensor provided in the downstream vicinity of the second temperature sensor provided downstream of the downstream side near And a means for calculating the difference or ratio of the temperature detected by the second temperature sensor with respect to the temperature detected by the first temperature sensor, and the critical state detecting means has a predetermined value for the difference or ratio. When it is larger, it is detected as a critical state.
[0011]
A fifth technical means according to any one of the first to fourth technical means is characterized in that the throttle portion is a position that can be closed according to the shape and / or operating state of the flow tube. It is.
[0013]
DETAILED DESCRIPTION OF THE INVENTION
The present invention is provided with a means for detecting a critical state in a flow meter, a Coriolis flow meter, or other flow meter using a throttle mechanism such as a nozzle, an orifice, or a venturi tube. Hereinafter, Coriolis mass flowmeters, Venturi tubes, and orifice flowmeters will be described as examples of the embodiments, and the details will be described. However, the present invention can be applied to other configuration examples of these flowmeters and other flowmeters. And at least the position of the flow tube where the fluid to be measured may become critical by circulating the fluid to be measured, near the upstream side and the downstream side (or near the downstream side and its downstream side). Any flow meter configured to detect a temperature difference (or temperature ratio), compare the detected data with a predetermined value, detect a critical state based on the comparison result, and notify the user of the critical state.
[0014]
FIG. 1 is a perspective view for explaining an example of a Coriolis mass flow meter, showing a configuration of a flow meter according to an embodiment of the present invention. In the figure, 1 is a support tube, 2 and 3 are flanges, 4 and 5 are support plates, 6 and 7 are U-shaped flow tubes, 8 is a coil, 9 is a core, 10 and 12 are magnets, and 11 and 13 are coils. 14, 15 are support plates, and 21, 22 are temperature sensors.
[0015]
A Coriolis mass flowmeter supports one or both ends of a flow tube through which a fluid to be measured flows, and vibrates the flow tube around a support point in a direction perpendicular to the flow direction of the fluid flowing in the flow tube. A phase difference proportional to the Coriolis force is generated between the excitation portion and the both end support portions, and the Coriolis force is proportional to the mass flow rate. Therefore, the mass flow rate is obtained by detecting the phase difference. The flow tubes (tubes) are classified into a single tube method and a multiple tube method (mainly two tubes) according to the number of tubes, and are classified into a straight tube shape, a bending shape, a loop shape, and the like according to the tube shape. In FIG. 1, the Coriolis type | mold mass flowmeter which used the flow tubes 6 and 7 which used two bending type tubes (U shape etc.) as a measuring tube is illustrated.
[0016]
The Coriolis type mass flow meter of the present embodiment includes a support tube 1, a drive unit composed of parallel U-shaped flow tubes 6 and 7 opening in the support tube 1, a coil 8 and a core 9, a magnet 10 and a coil 11. And a support plate (vibration fulcrum plate) 14 and 15 as supports, and upstream of the throttle part of the flow tube through which the fluid to be measured flows. The temperature difference or temperature between the two temperature sensors 21, 22 and the temperature sensors 21, 22 as temperature difference detecting means for detecting the temperature difference or temperature ratio between the temperature sensor and the downstream side (or the vicinity of the downstream side and the downstream side) A means for calculating a ratio (not shown), and a notification means (not shown) for notifying the user of the flow meter by an alarm or display if the temperature difference or the temperature ratio is equal to or greater than a predetermined value And Flanges 2 and 3 are attached to both ends of the support tube 1, and supporting plates 4 and 5 are respectively fixed to the shaft MM of the support tube 1 while being inclined. The U-shaped flow tubes 6 and 7 are circular tubes of the same shape and the same size, and both ends are opened in the support tube 1 and fixed in parallel. At this time, the symmetry axes Oa-Oa and Ob-Ob of the U-shaped flow tubes 6 and 7 are perpendicular to the axis MM of the support tube 1. At the symmetry axis of the U-shaped flow tubes 6, 7, for example, at the tip of the U-shaped flow tubes 6, 7, there is a drive means comprising a coil 8 and a core 9 that drives the U-shaped flow tubes 6, 7 so It is arranged. The driving means includes a coil 8 fixed on a base attached to the U-shaped flow tubes 6 and 7 and excited at a resonance frequency, and a core 9 inserted into the coil 8. 7 is driven by the electromagnetic force of the drive means. One sensor is composed of a magnet 10 and a coil 11, and the other is composed of a magnet 12 and a coil 13. Each of the sensors is arranged near the tip of the U-shaped flow tubes 6 and 7 at a symmetrical position of the axis Oa-Oa (Ob-Ob). It is installed. Here, the magnet 10 (12) is mounted on the U-shaped flow tube 6 and the coil 11 (13) is mounted on the U-shaped flow tube 7.
[0017]
The Coriolis mass flow meter configured as described above is interposed by the flanges 2 and 3 of the support tube 1 in a flow tube (not shown) through which the fluid to be measured flows. The fluid flows into the support tube 1, is blocked by the support plate 5, and flows through the U-shaped flow tubes 6 and 7 at an equal flow rate. When an alternating current having a resonance frequency for vibration is applied to the coil 8, the core 9 is attracted and repelled, and the U-shaped flow tubes 6 and 7 are vibrated in a tuning fork shape. A phase difference detection sensor including the magnet 10 and the coil 11 and the magnet 12 and the coil 13 outputs a sine wave signal having a phase difference proportional to the Coriolis force on the inflow side and the outflow side. The mass flow rate is determined by detecting this phase.
[0018]
FIG. 2 is a diagram illustrating a configuration of a data processing unit in the flow meter according to the embodiment of the present invention, and is a diagram for supplementarily explaining the Coriolis mass flow meter of FIG. 1.
The flowmeter according to the present embodiment relates to the data processing, the temperature difference detecting means for detecting a temperature difference (or temperature ratio) at two locations on the flow tube satisfying at least a predetermined condition, and the detected temperature difference (or temperature). It is assumed that there is provided means for calculating (ratio) and critical state detecting means for detecting the critical state by comparing the calculated value with a predetermined value. Here, the predetermined value is a value determined in advance according to two positions on the flow tube and the shape / motion (what kind of motion part, etc.) between them. Furthermore, it is assumed that notification means is provided for notifying the user of the critical state detected by the critical state detection means by warning or display. This notification means may be a means for transmitting a notification signal for restricting the valve in order to reduce the flow rate of the fluid to be measured. Referring to the embodiment of FIG. 1, as the temperature difference detection means, for example, temperature sensors 21 and 22 and means for calculating the temperature difference or temperature ratio between the temperature sensors 21 and 22 may be provided, and the critical state As a detection means, a critical state detector 23 for detecting a critical state by comparing the calculated value with a predetermined value may be provided. The temperature difference detecting means may be a means for directly detecting a temperature difference (or temperature ratio) from two temperature difference (or temperature ratio) extraction sections. As a notification means, an indicator 24 is provided in FIG. 2 for allowing the user to detect the critical state detected by the critical state detector 23. Note that a converter 25 that performs processing such as amplification and filtering on the output signal from the phase difference detection sensor, a flow rate calculator 26 for calculating a flow rate or a flow velocity based on the output signal from the converter 25, a coil 8 and It is assumed that various devices such as a power source for driving the core 9 and a power source for a phase difference detection sensor including the coils 11 and 13 and the magnets 10 and 12 are connected via the support tube 1, for example. In FIG. 2, the indicator 24 is shown as displaying the output from the flow rate calculator 26 together with the notification of the critical state.
[0019]
3 and 4 are diagrams for explaining the principle of the position of the temperature sensor in the flow meter according to the present invention. FIGS. 3A and 3B are temperature sensors in the Coriolis mass flow meter of FIG. FIG. 4 is a diagram showing the internal flow of the nozzle when the flow at the throat portion of the nozzle has reached a critical level.
[0020]
FIG. 3 shows an outline of a cross section of one flow tube (flow tube) 6 among the measurement tubes in the Coriolis mass flow meter of FIG. 1, and this flow tube 6 has regions R ₁ , R ₂ , R _3. , R ₄ , and there is a possibility that the fluid to be measured becomes a critical state between the region R ₁ and the region R ₄ . Since the flow tube 6 can be said to be a tube that narrows the flow in the support tube 1, the portion where the cross-sectional area decreases is the nozzle, the portion where the cross-sectional area increases is the diffuser, and the portion where the nozzle moves from the diffuser or from the diffuser to the nozzle is the throat. , region R ₁ is a nozzle, the region R ₄ has a diffuser. Hereinafter, the possibility of becoming a critical state will be described with reference to FIG.
[0021]
In general, at subsonic speeds (M <1), the gas expands / decreases / accelerates at the nozzle, and the gas compresses / increases / decreases at the diffuser. On the other hand, at supersonic speed (M> 1), the gas is compressed, heated, and decelerated by the nozzle, and the gas is expanded, decreased, and accelerated by the diffuser. To increase the flow from subsonic speed to supersonic speed, a throat is always required, and M = 1 in the throat. Conversely, a throat is also required when decelerating the flow from supersonic to subsonic speed, but only in the case of deceleration, a shock wave with a discontinuous pressure rise occurs and decelerates from supersonic to subsonic speed without throat. You can also. A vertical shock wave always reduces the flow from supersonic to subsonic. When a shock wave is generated, it is no longer an isentropic flow. Theoretically, in a diffuser connected to a throat that reaches M = 1 at the throat, either compression / expansion can occur. If compression occurs, the flow velocity decreases again as a subsonic velocity and approaches the flow velocity value upstream of the throat. Conversely, if expansion occurs, the flow rate will increase further and the flow will remain supersonic. Actually, the compression / expansion is determined by the back pressure after the diffuser. FIG. 4 is a schematic diagram when a Laval tube 30 having a diffuser attached to a nozzle has an airflow in the direction of the arrow, in which 31 is a throat portion, 32 is a subsonic region, 33 is a sonic surface, and 34 is a supersonic region. , 35 are shock wave fronts, and 36 is a subsonic region. As the internal flow of the nozzle when the flow at the throat portion 31 of the nozzle is sufficiently critical, the airflow in the subsonic region 32 becomes supersonic at the supersonic region 34 at the throat portion 31, and a shock wave (wavefront 35 at the diffuser portion). ) Occurs, and the subsonic velocity becomes subsonic in the subsonic velocity region 36.
[0022]
On the other hand, the mass flow rate has a relationship of increasing with increasing pressure ratio, reaching a maximum value in a critical state, and decreasing with further increasing pressure ratio with respect to the pressure ratio. In addition, since the mass flow rate depends on the temperature of the fluid to be measured, the flowmeter normally corrects by temperature, but this temperature correction is applied to the fluid to be measured in a state where the critical state is reached or not reached. However, it cannot be said that the actual accurate mass flow rate is output as a measurement value, and if it is reversed, it cannot be determined whether or not the fluid to be measured has reached a critical state. Further, since the mass flow rate increases without limit by increasing the upstream pressure, it is not noticed that it is in a critical state. For example, in a sonic nozzle that is always used in a critical state, it is routine to raise the upstream pressure in order to increase the mass flow rate. When in the critical state, the mass flow rate is output with many errors. Whether a mass flow rate or a volumetric flow rate is required, this determination is particularly difficult in the case of a flow meter that measures an integrated flow rate. The present invention makes use of the fact that a temperature difference occurs before and after the critical state, i.e., the temperature in the supersonic region is lower than the temperature in the subsonic region when the fluid to be measured changes from subsonic to supersonic. The determination is made based on a temperature difference (or temperature ratio) between two predetermined locations on the flow tube.
[0023]
Since the flow of gas is accelerated and thermal energy is converted into kinetic energy from the flow restricting portion (throat portion 31) to the shock wave generation position (wavefront 35), the temperature and pressure of the gas decrease. Assuming that no shock wave is generated for reference, the state of the flowing gas is isentropically changed, and T ₀ and p ₀ are set to the static state (stagnation point) of temperature, pressure, T and p from that state, etc. Assuming the temperature and pressure after entropy change, the relationship T / T ₀ = (p / p ₀ ) ^ ((κ−1) / κ) is established. For example, when air at 25 ° C. and 1 atm is sucked, the temperature and pressure at that point become about −25 ° C. and 0.5 atm when the specific heat ratio κ = 1.4. In general, if the expansion is rapid after the restriction, the kinetic energy is converted back into thermal energy and the fluid temperature recovers to the state before the flow is restricted, but the restricted part like the flow tube of the Coriolis flow meter is long. There may be a state like a so-called supersonic wind tunnel that does not recover pressure between a plurality of chokings (occlusions) and, in some cases, upstream and downstream chokings. In any case, a phenomenon occurs in which a temperature distribution occurs in the flow direction that cannot be seen in a flow of less than M = 0.3 that can be treated as an incompressible flow. In the present invention, temperature sensors are installed upstream and downstream of the choking position, and the critical state is detected based on the measured temperature difference.
[0024]
Referring to FIG. 3 (A), in the Coriolis mass flow meter of the present embodiment, the region R ₁ flowing from the supporting plate 5 into the U-shaped flow tubes 6 and 7 is contracted. Further, in addition to the region R ₁ , the curved portions indicated by R ₂ and R ₃ may generate a vertical shock wave or a pseudo shock wave, and further, as illustrated by the development of the velocity boundary layer in the interval indicated by a to b. A pointed velocity distribution may result, resulting in spurious throats. In this way, there is a possibility that the temperature becomes supersonic at any location and the temperature is lowered. FIG. 3A illustrates a case where the temperature sensor 21 is installed in front of the sections a and b and the temperature sensor 22 is installed in the section. The installation position is premised on the occurrence of a pseudo throat state due to a sharp velocity distribution (shown). In this case, the difference between the temperature T ₂ in the temperature sensor 22 and the temperature T ₁ in the temperature sensor 21 occurs even in the region R ₁ , R ₂ , R ₃ or the supersonic region in the section between them. There is no problem with the installation positions of the sensors 21 and 22 as they are.
[0025]
FIG. 3B shows an example of installation locations of two temperature sensors when the section from a to c can be in the supersonic range. After the first temperature sensor 21 is in the region _{R 1,} the second temperature sensor 22 so that 'is placed after the _{R 3,} their temperature difference _T 1 -T _2' Request. However, when a critical state occurs in a measuring tube in which the fluid to be measured that has cooled down in front of the region R ₂ does not become the same temperature as the temperature sensor 21 that is familiar in the region R ₅ or the like, that is, in the region R ₁ or later. A measuring tube having a structure in which up to c is a supersonic region is necessary.
[0026]
Although not shown, it is considered even flow region R ₁ is a throat portion, and the R ₁ before, may be installed respectively temperature sensor after R _1. In practice, one temperature sensor may be provided in the support tube 1 and one flow sensor in the flow tube 6 in FIG. Of course, since it is preferable that the difference between the two temperature sensors is clearly displayed in the critical state, the above description shows an example in which temperature sensors are installed in the subsonic region and the supersonic region before the supersonic region. Two locations may be provided in the supersonic region, or two locations may be provided in the supersonic region and in the subsonic region after the supersonic region. Actually, it is better to determine the position of the temperature sensors 21 and 22 after ascertaining which throttle in the flow tube 6 is an element that determines the critical state. In addition, even if the temperature sensors 21 and 22 are multi-tube type flow meters, it is possible to detect a critical state if at least one set is installed, and an example in which only the flow tube 6 is installed is shown. You may install in both the pipes 6 and 7.
[0027]
FIG. 5 is a diagram showing a configuration of a flow meter according to an embodiment of the present invention, and is a cross-sectional view for explaining an example of a differential pressure flow meter using a conical venturi tube. In the figure, 40 is a conical venturi, 41 is an inlet cylinder, 42 is an inlet cone, 43 is a throat, 44 is an outlet cone, 45 is an outlet cylinder, 46 and 47 are differential pressure extraction sections, 48, Reference numeral 49 denotes a temperature sensor. In FIG. 5, the diameter of the inlet cylindrical portion 41 and the outlet cylindrical portion 45 is D, the diameter of the throat portion 43 is d (<D), and the differential pressure extracting portion 46 is connected to the inlet conical portion 41 and another differential pressure extracting portion. 47 is provided in the throat portion 43, and the flow rate or flow velocity is obtained from the differential pressure. The temperature sensors 48 and 49 are also installed at the same locations as the differential pressure extraction sections 46 and 47, respectively. In addition, description regarding the flow rate calculation, the temperature sensor, and the critical state is omitted.
[0028]
FIG. 6 is a diagram showing a configuration of a flow meter according to an embodiment of the present invention, and is a cross-sectional view for explaining an example of a differential pressure flow meter using an orifice. In the figure, 50 is an orifice flow meter, 51 is a measuring tube, 52 is an orifice plate, 53 is a throttle hole, 54 and 55 are differential pressure take-out portions, and 56 and 57 are temperature sensors. The differential pressure take-out portion 54 is provided in front of the orifice plate 52, and another differential pressure take-out portion 55 is provided after the orifice plate 52, and the flow rate or flow velocity is obtained from the differential pressure. The temperature sensors 56 and 57 are also installed at the same locations as the differential pressure extraction sections 54 and 55, respectively. In addition, description regarding the flow rate calculation, the temperature sensor, and the critical state is omitted.
[0029]
Further, the temperature sensor probe may be installed in consideration of the velocity boundary layer and the temperature boundary layer. That is, when the probe is installed on the upstream side of the throttle, the flow pattern at the throttle is not affected and the height of the temperature boundary layer thickness or more is required. Further, on the downstream side of the throttle, for example, in the case of the Venturi tube of FIG. 5, the temperature / velocity boundary layer is thin, so that it is not necessary to extend the probe to the center, and the probe may be attached to the inside of the tube wall. However, in the case of the orifice of FIG. 6, it is preferable to install the orifice at a position where the jet from the throttle portion directly hits the probe.
[0030]
Note that the temperature correction of the flow rate measuring sensor may be performed using the output of one of the two temperature sensors or using the average value of the two temperature sensors. In the Coriolis type mass flow meter, a temperature sensor that has been conventionally installed to correct the spring multiplier of the flow tube may be used in combination with a temperature sensor that is related to the detection of the critical state. The average value with the temperature sensor may be used for correcting the spring multiplier. FIG. 6 shows an example in which the temperature sensor is installed extending to the center of the flow tube in consideration of this. This is effective in the following cases. In particular, when the temperature is changed, if the gas measurement with a small heat capacity is performed and the flow velocity is low, the temperature boundary layer is thick, and therefore there is a long time between the temperature of the flow tube and the fluid temperature. In this case, rather than using only the temperature sensor on the upstream pipe wall as the representative temperature of the flow tube, use the average value with the temperature sensor on the downstream side, or weight the temperature measurement values from multiple temperature sensors. A more accurate measurement result can be obtained by performing temperature correction with the representative temperature calculated by the function.
[0031]
【The invention's effect】
According to the present invention, a critical state can be detected in a flow meter. According to the present invention, an erroneous measurement result is not adopted by this detection.
[Brief description of the drawings]
FIG. 1 is a diagram showing the configuration of a flow meter according to an embodiment of the present invention, and is a perspective view for explaining an example of a Coriolis type mass flow meter.
2 is a diagram showing a configuration of a data processing unit in a flow meter according to an embodiment of the present invention, and is a diagram for supplementarily explaining the Coriolis mass flow meter of FIG.
3 is a view for explaining the principle of the position of the temperature sensor in the flow meter according to the present invention, and is a view showing the position of the temperature sensor in the Coriolis mass flow meter of FIG. 1;
FIG. 4 is a diagram for explaining the principle of the installation position of the temperature sensor in the flowmeter according to the present invention, and shows the state of internal flow of the nozzle when the flow at the throat portion of the nozzle has reached a sufficiently critical level. FIG.
FIG. 5 is a diagram showing a configuration of a flow meter according to an embodiment of the present invention, and is a cross-sectional view for explaining an example of a differential pressure flow meter using a conical venturi tube.
FIG. 6 is a diagram showing a configuration of a flow meter according to an embodiment of the present invention, and is a cross-sectional view for explaining an example of a differential pressure flow meter using an orifice.
[Explanation of symbols]
DESCRIPTION OF SYMBOLS 1 ... Support tube, 2, 3 ... Flange, 4, 5 ... Supporting plate, 6, 7 ... U-shaped flow tube, 8 ... Coil, 9 ... Core, 10, 12 ... Magnet, 11, 13 ... Coil, 14, DESCRIPTION OF SYMBOLS 15 ... Support plate, 21, 22, 48, 49, 56, 57 ... Temperature sensor, 23 ... Critical state detector, 24 ... Indicator, 25 ... Converter, 26 ... Flow rate calculator, 31, 43 ... Throat part, 32 ... Subsonic region, 33 ... Sonic surface, 34 ... Supersonic region, 35 ... Shock wavefront, 36 ... Subsonic region, 40 ... Conical venturi, 41 ... Inlet cylindrical portion, 42 ... Inlet cone portion, 44 ... Outlet cone 45, outlet cylindrical part, 46, 47, 54, 55 ... differential pressure extraction part, 50 ... orifice flow meter, 51 ... measuring tube, 52 ... orifice plate, 53 ... throttle hole.

Claims (5)

In flow meter for measuring the flow rate or flow velocity of the fluid to be measured, and the temperature difference detecting means for detecting an upstream side of the narrowed portion of the flow tube fluid to be measured flows, a temperature difference or temperature ratio between the downstream, the temperature A critical state detection unit that detects a critical state of the fluid to be measured based on an output of the difference detection unit, and a notification unit that notifies a user of the critical state detected by the critical state detection unit. Flowmeter. The temperature difference detecting means includes a first temperature sensor provided on the upstream side, a second temperature sensor provided on the downstream side, and the second temperature sensor for the temperature detected by the first temperature sensor. 2. A means for calculating a temperature difference or ratio detected by the sensor, wherein the critical state detection means detects a critical state when the difference or ratio is greater than a predetermined value. Flowmeter. In flow meter for measuring the flow rate or flow rate of the measurement fluid, and the vicinity of the downstream side of the throttle portion of the flow tube fluid to be measured flows, temperature difference detection for detecting a temperature difference or temperature ratio between the downstream side of the vicinity of the downstream side comprising means and a critical state detecting means for detecting a critical state of the fluid to be measured based on the output of the temperature difference detecting means, and notification means for notifying the user of the critical state detected by the critical state detecting means A flow meter characterized by that. It said temperature difference detection means, said first temperature sensor provided in the downstream vicinity of a second temperature sensor provided downstream from the vicinity of the downstream side, relative to the first temperature detected by the temperature sensor of Means for calculating a temperature difference or ratio detected by the second temperature sensor, and the critical state detection means detects a critical state when the difference or ratio is greater than a predetermined value. The flow meter according to claim 3. The flowmeter according to any one of claims 1 to 4, wherein the throttle portion is a position that can be closed according to a shape and / or an operating state of the flow tube.

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