JP2010256075A - Flowmeter and method of measuring flow rate - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a flowmeter for stably measuring a standard flow rate, etc. and a method of measuring a flow rate. <P>SOLUTION: An ultrasonic flowmeter 10 measures a flow velocity V and temperature T1 of a gas in a measuring tube 13 by using first and second ultrasonic transmitter-receivers 14 and 15 while measuring hydrostatic pressure P1 of the gas in the measuring tube 13 by using a static pressure meter 17. A dynamic pressure P2 of the gas is calculated from the flow velocity V while a total pressure P3 is calculated by using the sum of the hydrostatic pressure P1 and the dynamic pressure P2. By using the measured or calculated actual total pressure P3, actual temperature T1, and actual total pressure P3, and a relational expression based on the Boyle-Charle's law, the actual flow velocity V is output by calculating a standard unit flow rate Qx and the standard flow rate Q. The flow rate Qx is of the gas flowing through a unit area in the measuring tube 13 at previously determined standard temperature T0 and standard total pressure P0. The flow rate Q is found by multiplying the flow rate Qx by the inside cross-section of the measuring tube 13. <P>COPYRIGHT: (C)2011,JPO&INPIT

Description

  The present invention converts the flow velocity of a gas flowing through a measuring tube at an arbitrary temperature and pressure into a standard flow rate flowing at a predetermined standard temperature and pressure using a relational expression based on Boyle-Charles' law. The present invention relates to a flow meter to measure and a flow measurement method.

  Conventionally, as this type of flow meter, the temperature and pressure detected by the temperature sensor and the pressure sensor and the flow velocity measured by the flow meter body are substituted into the relational expression based on Boyle-Charles' law, and the standard flow rate is calculated. Those are known (for example, see Patent Document 1).

JP 2007-187506 A (paragraph [0003])

  However, if the conventional flowmeters described above are attached to, for example, a plurality of positions in a city gas piping network, the sum of a standard flow rate detected at a gas supply source and a standard flow rate detected at a plurality of positions at the end of the piping network is shifted. May occur. That is, the conventional flow meter described above cannot accurately measure the standard flow rate.

  The present invention has been made in view of the above circumstances, and an object of the present invention is to provide a flow meter and a flow rate measuring method capable of measuring a standard flow rate stably and accurately.

  Analysis of the measurement error of a conventional flow meter revealed that the measurement error increased as the flow velocity increased. From this point, the following invention for measuring the standard flow rate and the like by performing calculation in consideration of the influence of the flow velocity has been completed.

  The invention of claim 1 is a flow rate detection unit capable of detecting a flow rate of gas in a measurement tube, a static pressure detection unit capable of detecting a static pressure of gas in the measurement tube, and a dynamic pressure for calculating the dynamic pressure of the gas from the flow rate. A calculation unit, a total pressure calculation unit that calculates the total pressure by the sum of static pressure and dynamic pressure, a temperature detection unit that can detect the temperature of the gas in the measurement tube, a flow rate detection unit, a temperature detection unit, and a total pressure calculation unit Using the actual flow velocity, actual temperature, and actual total pressure detected in Step 1, and the relational expression based on Boyle-Charles' law, the actual flow velocity is measured at a predetermined standard temperature and standard total pressure. A flow meter characterized by comprising a standard conversion unit for converting to a standard unit flow rate of gas flowing in a unit area or converting to a standard flow rate obtained by multiplying the standard unit flow rate by the inner cross-sectional area of the measuring tube. is there.

  In the invention of claim 2, the standard temperature is T0, the standard total pressure is P0, the standard temperature which is the density of the gas under the standard temperature T0 and the standard total pressure P0 is ρ0, the actual temperature is T1, the static pressure is P1, Assuming that the pressure is P2, the actual temperature T1 and the measured density which is the density of the gas under the actual total pressure is ρ1, and the actual flow velocity is V, the dynamic pressure calculation unit is based on the following equations (1) and (2). The flowmeter according to claim 1, wherein the density during measurement ρ1 and the dynamic pressure P2 are calculated.

  According to a third aspect of the present invention, the flow velocity detectors are arranged at two different positions in the axial direction of the measurement tube, and the first and second ultrasonic transducers capable of transmitting and receiving ultrasonic waves in both directions, A propagation time measuring unit for measuring the first propagation time of the ultrasonic wave from the first to the second ultrasonic transducer and the second propagation time of the ultrasonic wave from the second to the first ultrasonic transducer. If the distance in the axial direction of the measuring tube between the first and second ultrasonic transducers is L, the first propagation time is t1, and the second propagation time is t2, the following equation (3) is used. It is configured to calculate the flow velocity V, and when the ultrasonic sound velocity is C, the sound velocity calculation unit that calculates the ultrasonic sound velocity C based on the following equation (4), and the inside of the measurement tube based on the sound velocity C are calculated. The flowmeter according to claim 2, further comprising a standard density specifying unit that specifies a standard density according to a type of flowing gas. That.

  According to a fourth aspect of the present invention, the flow velocity detectors are arranged at two different positions in the axial direction of the measurement tube, and the first and second ultrasonic transducers capable of transmitting and receiving ultrasonic waves in both directions, A propagation time measuring unit for measuring the first propagation time of the ultrasonic wave from the first to the second ultrasonic transducer and the second propagation time of the ultrasonic wave from the second to the first ultrasonic transducer. When the distance in the axial direction of the measuring tube between the first and second ultrasonic transducers is L, the first propagation time is t1, the second propagation time is t2, and the actual flow velocity is V, the above formula ( 3) The flow velocity V is configured to be calculated based on 3), and the sound velocity calculation section for calculating the ultrasonic sound velocity C based on the above equation (4), and the temperature of the gas, where C is the ultrasonic sound velocity. And a sound speed / temperature data table that correlates the sound speed according to the temperature, and the temperature measurement section uses the sound speed calculated by the sound speed calculation section. A flow meter according to any one of claims 1 to 3, characterized in that to determine the actual temperature from the sound velocity and temperature data table based on.

  The invention of claim 5 detects the flow velocity, static pressure, dynamic pressure and temperature of the gas in the measuring tube, and the actual total pressure and the actual flow velocity which are the sum of the detected actual static pressure and the actual dynamic pressure. And the actual temperature and the relational expression based on Boyle-Charles' law, the actual flow velocity is converted into the standard unit flow rate of the gas flowing in the unit area in the measuring tube at the predetermined standard temperature and standard total pressure. Alternatively, the flow rate measurement method is characterized in that it is converted into a standard flow rate obtained by multiplying the standard unit flow rate by the inner cross-sectional area of the measurement tube.

  In the invention of claim 6, the standard temperature is T0, the standard total pressure is P0, the standard temperature which is the density of the gas under the standard temperature T0 and the standard total pressure P0 is ρ0, the actual temperature is T1, the static pressure is P1, When the pressure is P2, the actual total pressure is P3, the actual temperature T1 and the density at the time of measurement, which is the density of the gas under the actual total pressure P3, is ρ1, and the actual flow velocity is V, the above formulas (1) and (2 6 is a flow rate measurement method according to claim 5, wherein the measurement-time density ρ1 and the dynamic pressure P2 are calculated based on.

  According to the seventh aspect of the present invention, the first and second ultrasonic transducers are arranged at two different positions in the axial direction of the measuring tube, and the ultrasonic waves from the first to the second ultrasonic transducers are transmitted. The first propagation time and the second propagation time of the ultrasonic wave from the second to the first ultrasonic transducer are measured, and the distance in the axial direction of the measuring tube between the first and second ultrasonic transducers Is L, the first propagation time is t1, the second propagation time is t2, and the sound velocity of the ultrasonic wave is C, the flow velocity V is calculated based on the above equation (3), and the superfluidity based on the above equation (4) is calculated. The flow rate measuring method according to claim 6, wherein the sound velocity C of the sound wave is calculated, and the standard density corresponding to the type of gas flowing in the measurement tube is specified based on the sound velocity C.

  In the invention according to claim 8, the first and second ultrasonic transducers are arranged at two different positions in the axial direction of the measuring tube, and the first ultrasonic wave to the second ultrasonic transducer is transmitted. The first propagation time and the second propagation time of the ultrasonic wave from the second to the first ultrasonic transducer are measured, and the distance in the axial direction of the measuring tube between the first and second ultrasonic transducers Is L, the first propagation time is t1, the second propagation time is t2, the actual flow velocity is V, and the ultrasonic sound velocity is C, the flow velocity V is calculated based on the above equation (3), and the above equation ( 4) The sound speed C of the ultrasonic wave is calculated based on 4), and a sound speed / temperature data table in which the gas temperature and the sound speed corresponding to the temperature are associated with each other is provided. Based on the sound speed C calculated by the sound speed calculation unit. The actual temperature is specified from the sound speed / temperature data table. The claim according to any one of claims 5 to 7, Which is a flow rate measurement method.

  “Temperature” in the specification and claims attached to the application of the present invention means “absolute temperature” unless it is expressed as Celsius or “° C.” is added.

[Inventions of Claims 1 and 5]
According to the first and fifth aspects of the present invention, the standard unit flow rate or the standard flow rate is calculated using the total pressure that is the sum of the dynamic pressure and the static pressure that change depending on the magnitude of the flow velocity. Regardless, the standard unit flow rate and the standard flow rate can be measured stably and accurately. Further, in the flow meter according to the invention of claim 1, since the dynamic pressure is calculated using the flow velocity, compared to a configuration in which a device such as a Pitot tube for measuring the dynamic pressure is separately provided in order to obtain the dynamic pressure. The flow meter becomes compact.

[Inventions of Claims 2 and 6]
In the inventions of claims 2 and 6, in the calculation of the dynamic pressure, the gas measurement density ρ1 is calculated using the total pressure as in the above formula (1), so the accuracy of the measurement density ρ1 is also increased. Since the dynamic pressure is calculated using the measurement density ρ1 as in the above equation (2), the dynamic pressure can be calculated accurately.

[Inventions of Claims 3 and 7]
In the inventions of claims 3 and 7, the first and second ultrasonic transducers for detecting the flow velocity are used to calculate the sound speed of the ultrasonic wave, the calculation result of the sound speed and the measurement tube are passed through. The standard density can be determined from the sound velocity / density data table corresponding to the sound speed according to the type of gas to be obtained and the standard density according to the type of gas, so that different types of gas can flow through the measurement tube. Even in this case, the standard unit flow rate and the standard flow rate can be measured stably and accurately.

[Inventions of Claims 4 and 8]
In the inventions of claims 4 and 8, the first and second ultrasonic transducers for detecting the flow velocity are used to calculate the sound speed of the ultrasonic wave, and the calculation result of the sound speed and the measurement pipe are passed through. Since the actual temperature is specified from the sound speed / temperature data table in which the temperature of the gas to be obtained and the sound speed according to the temperature are associated with each other, the flow meter is more compact than a configuration in which a thermometer is separately provided.

The block diagram of the ultrasonic flowmeter concerning one embodiment of the present invention. Controller block diagram Diagram explaining the relationship between sound speed and temperature

[First Embodiment]
Hereinafter, an embodiment in which the present invention is applied to an ultrasonic flowmeter will be described with reference to FIGS. As shown in FIG. 1, the ultrasonic flowmeter 10 of this embodiment includes a measurement main body 11 and a controller 20. The measurement main body 11 has, for example, a cylindrical measurement tube 13 attached in the middle of the gas tube 12, and includes first and second ultrasonic transducers 14 and 15 on the inner surface of the measurement tube 13. ing. The first and second ultrasonic transducers 14 and 15 are arranged on a straight line that obliquely intersects the central axis of the measurement tube 13. Note that any one of air, city gas, and LP gas flows through the gas pipe 12 to which the ultrasonic flowmeter 10 of the present embodiment is connected.

  The measuring tube 13 is integrally provided with a static pressure gauge 17 for detecting the static pressure inside thereof. Specifically, the branch path 16 is extended from the center position between the first and second ultrasonic transducers 14 and 15 in the axial direction of the measuring tube 13 toward the side perpendicular to the axial direction. The hydrostatic pressure gauge 17 is connected to the end of the branch path 16. The static pressure gauge 17 incorporates, for example, a diaphragm (not shown) that deforms in accordance with the static pressure in the measuring tube 13, and changes the deformation amount of the diaphragm into an electrical signal and outputs it.

  The controller 20 includes a wave transmission / reception control circuit 21, a static pressure detection circuit 25, and a signal processing unit 30. The static pressure detection circuit 25 converts the electrical signal output from the static pressure gauge 17 into a detected value of static pressure and outputs it. In the present embodiment, the “static pressure detector” according to the present invention is constituted by the static pressure gauge 17 and the static pressure detection circuit 25.

  The transmission / reception control circuit 21 corresponds to the “propagation time measurement unit” of the present invention, and includes an oscillation circuit (not shown) that outputs pulses at a predetermined period, and the first and second ultrasonic transducers 14 and 15. And a wave receiving circuit (not shown) for detecting that the first and second ultrasonic transducers 14 and 15 have received the ultrasonic wave. I have. Then, the first ultrasonic transducer 14 is connected to the transmission circuit, while the second ultrasonic transducer 15 is connected to the reception circuit, and the first ultrasonic transducer 14 outputs the ultrasonic wave. Until the second ultrasonic transducer 15 receives the ultrasonic wave, the number of pulses output by the oscillation circuit is measured as the first propagation time of the ultrasonic wave, and the first ultrasonic transducer 14 is measured. Is switched to a state in which the second ultrasonic transmitter / receiver 15 is connected to the transmitter circuit, and the second ultrasonic transmitter / receiver 15 outputs an ultrasonic wave. The number of pulses output by the oscillation circuit until reception by the first ultrasonic transducer 14 is measured as the second propagation time of the ultrasonic wave.

  The signal processing unit 30 includes a CPU 21A, a ROM 21B, and a RAM 21C. The signal processing unit 30 functions as a control system shown in the block diagram of FIG. 2 by executing a data processing program (not shown) stored in the ROM 21B. .

  2 calculates the sum of the reciprocal of the first propagation time measured by the transmission / reception control circuit 21 and the reciprocal of the second propagation time. The frequency difference calculation unit shown is configured to calculate a value obtained by subtracting the reciprocal of the second propagation time from the reciprocal of the first propagation time. Here, the distance in the axial direction of the measurement tube 13 between the first and second ultrasonic transducers 14 and 15 (that is, the gas flow direction) is L, the first propagation time is t1, and the second propagation time. T2, the actual flow velocity of the gas flowing through the measuring tube 13 is V, the ultrasonic velocity is C, and the first ultrasonic transducer 14 is disposed upstream of the second ultrasonic transducer 15. Then, the following equations (5) and (6) are established.

  Therefore, the frequency sum calculation unit 31 calculates (2C / L) as a substitute value of the sound velocity C as shown in the above equation (5) by calculating the sum of the reciprocals of the first and second propagation times. ing. That is, the frequency sum calculation unit 31 calculates a substantial sound speed Cx multiplied by a constant (2 / L). Further, the frequency difference calculation unit 32 calculates (2V / L) as a substitute value of the flow velocity V as shown in the above equation (6) by calculating the difference between the reciprocals of the first and second propagation times. is doing. That is, the frequency difference calculation unit 32 calculates a substantial flow velocity Vx multiplied by a constant (2 / L).

  In the control system of FIG. 2, the flow velocity calculation unit denoted by reference numeral 33 multiplies the calculation result of the frequency difference calculation unit 32 by L / 2 to calculate a true flow velocity V that is not a substitute value. In the present embodiment, the frequency difference calculation unit 32 and the flow velocity calculation unit 33, the above-described transmission / reception control circuit 21, and the first and second ultrasonic transducers 14 and 15 according to the present invention. A “flow velocity detection unit” is configured.

  In the control system of FIG. 2, the gas type identification unit indicated by reference numeral 34 is based on the substantial sound velocity Cx calculated by the frequency sum calculation unit 31 and the gas flowing through the measurement tube 13 is air, city gas, LP gas. Is specified. Here, the speed of sound when the ultrasonic wave propagates through the gas varies depending on the type of the gas and also on the temperature. In the present embodiment, the temperature of the gas flowing through the gas pipe 12 is 253.1 [K] (−20 [° C.]) or higher at the lowest, and 333.1 [K] (60 [° C.] at the highest. ]) It is as follows. Furthermore, in FIG. 3, the change of the sound speed with respect to the temperature of -20-60 [degreeC] is shown for every air, city gas, and LP gas. As shown in the figure, in the range of 253.1 to 333.1 [K] (−20 to 60 [° C.]), the value of sonic velocity does not become the same among air, city gas, and LP gas. . Therefore, the gas type identification unit 34, based on the characteristics shown in FIG. 3, the first lower limit determination value and the upper limit determination value, the second lower limit determination value and the upper limit determination value, or the third lower limit determination value. Value and upper limit determination value are set, and the substantial sound speed Cx falls between any of the lower limit determination value and the upper limit determination value among the first to third lower limit determination values and the upper limit determination value. Whether the gas flowing through the measuring tube 13 is air, city gas, or LP gas is specified.

  The temperature specifying unit indicated by reference numeral 35 in the control system of FIG. 2 acquires information on the gas type of the gas flowing through the measuring tube 13 from the gas type specifying unit 34, and the substantial sound speed Cx from the frequency sum calculating unit 31. Are obtained, and the temperature of the gas is specified based on them. Specifically, the ROM 21B (see FIG. 1) of the controller 20 includes a first sound speed / temperature data table 41 that associates the temperature of air with a substantial sound speed Cx corresponding to the temperature, and the city gas. The second sonic velocity / temperature data table 42 in which the temperature and the substantial sonic velocity Cx corresponding to the temperature are associated with each other, and the LP gas temperature and the substantial sonic velocity Cx corresponding to the temperature are associated with each other. The sound speed / temperature data table 43 is stored. And the temperature specific | specification part 35 accesses one of the 1st-3rd sound speed and temperature data tables 41, 42, and 43 according to the kind of gas which flows through the measurement pipe | tube 13 based on the information of gas type, and is substantially The gas temperature is specified from the sound speed / temperature data table based on the typical sound speed Cx.

  The standard density specifying unit denoted by reference numeral 36 in the control system of FIG. 2 acquires information on the gas type of the gas from the temperature specifying unit 35, and sets a standard temperature set in advance based on the information on the gas type of the gas. And the standard density as the density of the gas under standard total pressure. Here, in the ultrasonic flowmeter 10 of the present embodiment, 273.1 [K] (0 degrees Celsius) as the standard temperature and 101.3 [kPa] (1 atmosphere) as the standard total pressure are preset, The data of the standard temperature 273.1 [K] and the standard total pressure 101.3 [kPa] are incorporated in the data processing program (not shown) and stored in the ROM 21B (see FIG. 1). The ROM 21B stores a density database 44 in which information on gas types is associated with standard densities of air, city gas, and LP gas. And the standard density specific | specification part 36 acquires the standard density of the gas which flows through the inside of the measurement pipe | tube 13 from the density database 44 of ROM21B based on the information of gaseous gas type.

  Further, the standard density specifying unit 36 acquires the calculation result of the gas flow velocity from the flow velocity calculation unit 33 and also acquires the detection result of the static pressure from the static pressure detection circuit 25, and the following equations (1) and (2) are obtained. Utilizing this, the density at the time of measurement, which is the actual temperature in the measuring tube 13 and the actual gas density under the total pressure, is calculated. That is, assuming that the standard temperature is T0, the standard total pressure is P0, the standard density is ρ0, the actual temperature is T1, the static pressure is P1, the dynamic pressure is P2, the measurement density is ρ1, and the actual flow velocity is V, Expressions (1) and (2) are established.

  Specifically, the standard density specifying unit 36 first calculates the measurement density ρ1 with P2 = 0 in the equation (1). Next, the dynamic pressure P2 is calculated from the measured density ρ1 and the equation (2), and the measured density ρ1 is calculated again from the obtained dynamic pressure P2 and the equation (1). In this way, the measurement density ρ1 is calculated by repeatedly using the equations (1) and (2).

  Note that the following formula (7) is obtained by modifying the formulas (1) and (2). The standard density specifying unit 36 may calculate the measurement density ρ1 from the equation (7).

  Further, the standard density specifying unit 36 may simply calculate the measurement density ρ1 by setting P2 = 0 in the equation (1), that is, without repeatedly using the equations (1) and (2).

  The dynamic pressure calculation unit indicated by reference numeral 37 in the control system of FIG. 2 acquires the measured density ρ1 from the standard density specifying unit 36 and the flow velocity V from the flow velocity calculation unit 33, and the above equation (2). From this, the gas dynamic pressure P2 is calculated.

  The total pressure calculation unit denoted by reference numeral 38 in the control system of FIG. 2 acquires the dynamic pressure P2 from the dynamic pressure calculation unit 37, acquires the static pressure P1 from the static pressure detection circuit 25, and generates the static pressure P1 and The total pressure P3 (= P1 + P2) is calculated by the sum of the dynamic pressure P2.

  The standard unit flow rate calculation unit indicated by reference numeral 39 in the control system of FIG. 2 acquires the total pressure P3 from the total pressure calculation unit 38, acquires the flow rate V from the flow rate calculation unit 33, and the temperature T1 from the temperature specifying unit 35. The standard unit flow rate Qx is calculated from the following equation (8) based on Boyle-Charles' law. Here, the standard unit flow rate Qx is the flow rate of the gas flowing in the unit area in the measuring tube 13 at the above-described standard temperature and standard total pressure at the actual flow velocity of the gas flowing at an arbitrary temperature and pressure. That is, the standard unit flow rate Qx is also the flow velocity of the gas flowing in the measurement tube 13 under the standard temperature and the standard total pressure.

  2 obtains the standard unit flow rate Qx from the standard unit flow rate computation unit 39, multiplies the standard unit flow rate Qx by the inner cross-sectional area of the measuring tube 13, The standard flow rate Q is calculated. Then, the standard unit flow rate Qx and the standard flow rate Q are given from the signal processing unit 30 to the output circuit 22 of the controller 20 shown in FIG. 1 and output from the output circuit 22 to the outside of the ultrasonic flow meter 10.

  As described above, in the ultrasonic flow meter 10 of the present embodiment, the standard unit flow rate Qx and the standard flow rate Q are obtained using the total pressure that is the sum of the dynamic pressure P2 and the static pressure P1 that change depending on the magnitude of the gas flow velocity V. Therefore, regardless of the flow velocity V, the standard unit flow rate Qx and the standard flow rate Q can be stably and accurately measured. Moreover, since the first and second ultrasonic transducers 14 and 15 transmit and receive ultrasonic waves across the entire measurement tube 13 and detect the flow velocity V, the average flow velocity V of the entire measurement tube 13 is detected. In this respect, the standard unit flow rate Qx and the standard flow rate Q can be accurately measured. Furthermore, since the measurement density ρ1 of the gas is calculated using the total pressure P3, the accuracy of the measurement density ρ1 is also increased, and the dynamic pressure P2 is calculated using the measurement density ρ1. The dynamic pressure P2 can be calculated with high accuracy.

  Further, the first and second ultrasonic transducers 14 and 15 for detecting the flow velocity V are used to calculate the ultrasonic sound velocity C, and the type of gas flowing in the measuring tube 13 from the sound velocity C is calculated. Therefore, even when different types of gases can flow through the measurement tube 13, the standard unit flow rate Qx and the standard flow rate Q can be stably and accurately measured. In addition, since the dynamic pressure P2 is calculated using the flow velocity V, the ultrasonic flowmeter 10 is compared with a configuration in which a device such as a Pitot tube for measuring the dynamic pressure is separately provided in order to obtain the dynamic pressure P2. It becomes compact. Furthermore, since the actual temperature T1 is specified from the calculation result of the sound velocity C, the ultrasonic flowmeter 10 is more compact than a configuration in which a thermometer is separately provided.

[Other Embodiments]
The present invention is not limited to the above-described embodiment. For example, the embodiments described below are also included in the technical scope of the present invention, and various other than the following can be made without departing from the scope of the invention. It can be changed and implemented.

  (1) In the above embodiment, the actual temperature T1 is specified from the calculation result of the sound velocity C. However, the actual temperature T1 may be measured by a thermometer. Even with such a configuration, the standard unit flow rate Qx and the standard flow rate Q can be stably measured regardless of the magnitude of the flow velocity V.

  (2) In the above-described embodiment, an alarm or the like is issued when the substantial sound speed Cx does not belong to any of the lower limit determination value and the upper limit determination value of the first to third lower limit determination values and the upper limit determination value. It is good also as a structure provided with the alarm device. Thereby, gas mixture detection other than air, city gas, and LP gas can be aimed at.

DESCRIPTION OF SYMBOLS 10 Ultrasonic flowmeter 14 1st ultrasonic transducer 15 2nd ultrasonic transducer 17 Static pressure meter 21 Transmission / reception control circuit 25 Static pressure detection circuit 33 Flow velocity calculating part 34 Gas type specific | specification part 35 Temperature specific part 36 Standard density Specific unit 37 Dynamic pressure calculation unit 38 Total pressure calculation unit 39 Standard unit flow rate calculation unit 40 Standard flow rate calculation unit

Claims (8)

A flow rate detector that can detect the flow rate of the gas in the measurement tube;
A static pressure detector capable of detecting the static pressure of the gas in the measuring tube;
A dynamic pressure calculator that calculates the dynamic pressure of the gas from the flow velocity;
A total pressure calculation unit that calculates a total pressure by the sum of the static pressure and the dynamic pressure;
A temperature detector capable of detecting the temperature of the gas in the measuring tube;
Using the actual flow velocity detected by the flow velocity detection unit, the temperature detection unit, and the total pressure calculation unit, the actual temperature and the actual total pressure, and the relational expression based on Boyle-Charles' law, Is converted to a standard unit flow rate of gas flowing in a unit area in the measurement tube at a predetermined standard temperature and standard total pressure, or a standard obtained by multiplying the standard unit flow rate by an inner cross-sectional area of the measurement tube. A flow meter comprising a standard conversion unit for converting into a flow rate. The standard temperature is T0, the standard total pressure is P0, the standard density that is the density of the gas under the standard temperature T0 and the standard total pressure P0 is ρ0, the actual temperature is T1, the static pressure is P1, the dynamic When the pressure is P2, the actual temperature T1 and the density at the measurement, which is the density of the gas under the actual total pressure, is ρ1, and the actual flow velocity is V,
The dynamic pressure calculator is

The flowmeter according to claim 1, wherein the measurement density ρ <b> 1 and the dynamic pressure P <b> 2 are calculated based on the following formula. The flow velocity detectors are arranged at two different positions in the axial direction of the measuring tube, and are capable of transmitting and receiving ultrasonic waves in both directions, and the first to second ultrasonic transducers. A propagation time measuring unit for measuring the first propagation time of the ultrasonic wave to the ultrasonic transducer and the second propagation time of the ultrasonic wave from the second to the first ultrasonic transducer;
When the distance in the axial direction of the measurement tube between the first and second ultrasonic transducers is L, the first propagation time is t1, and the second propagation time is t2,

The flow velocity V is calculated on the basis of the equation (2), and the sound velocity of the ultrasonic wave is C.

A sound speed calculation unit that calculates the sound speed C of the ultrasonic wave based on the equation (1), and a standard density specifying unit that specifies the standard density corresponding to the type of gas flowing in the measurement tube based on the sound speed C. The flow meter according to claim 2, wherein The flow velocity detectors are arranged at two different positions in the axial direction of the measuring tube, and are capable of transmitting and receiving ultrasonic waves in both directions, and the first to second ultrasonic transducers. A propagation time measuring unit for measuring the first propagation time of the ultrasonic wave to the ultrasonic transducer and the second propagation time of the ultrasonic wave from the second to the first ultrasonic transducer;
When the distance in the axial direction of the measuring tube between the first and second ultrasonic transducers is L, the first propagation time is t1, the second propagation time is t2, and the actual flow velocity is V. ,

The flow velocity V is calculated on the basis of the equation (2), and the sound velocity of the ultrasonic wave is C.

A sound speed calculation unit for calculating the sound speed C of the ultrasonic wave based on the equation, and a sound speed / temperature data table in which the temperature of the gas and the sound speed corresponding to the temperature are associated with each other.
The temperature measurement unit identifies the actual temperature from the sound speed / temperature data table based on the sound speed C calculated by the sound speed calculation unit. The flow meter described in 1.   The flow velocity, static pressure, dynamic pressure, and temperature of the gas in the measuring tube are detected, and the actual total pressure, the actual flow velocity, the actual temperature, and the boil, the sum of the detected actual static pressure and the actual dynamic pressure are detected. Using the relational expression based on Charles' law, the actual flow velocity is converted into a standard unit flow rate of a gas flowing in a unit area in the measuring tube at a predetermined standard temperature and standard total pressure, or A flow rate measuring method, wherein the flow rate is converted into a standard flow rate obtained by multiplying the standard unit flow rate by the inner cross-sectional area of the measuring tube. The standard temperature is T0, the standard total pressure is P0, the standard density that is the density of the gas under the standard temperature T0 and the standard total pressure P0 is ρ0, the actual temperature is T1, the static pressure is P1, the dynamic When the pressure is P2, the actual temperature T1 and the density at the measurement, which is the density of the gas under the actual total pressure, is ρ1, and the actual flow velocity is V,

The flow rate measuring method according to claim 5, wherein the measurement density ρ1 and the dynamic pressure P2 are calculated based on the following formula. The first and second ultrasonic transducers are arranged at two different positions in the axial direction of the measurement tube, and the first propagation time of the ultrasonic waves from the first to the second ultrasonic transducers and the Measuring the second propagation time of the ultrasonic wave from the second to the first ultrasonic transducer;
The distance between the first and second ultrasonic transducers in the axial direction of the measuring tube is L, the first propagation time is t1, the second propagation time is t2, and the ultrasonic sound velocity is C. Then

And calculating the flow velocity V based on the formula

The flow rate according to claim 6, wherein a sound velocity C of the ultrasonic wave is calculated based on the formula, and the standard density corresponding to the type of gas flowing in the measuring tube is identified based on the sound velocity. Measurement method. The first and second ultrasonic transducers are arranged at two different positions in the axial direction of the measurement tube, and the first propagation time of the ultrasonic waves from the first to the second ultrasonic transducers and the Measuring the second propagation time of the ultrasonic wave from the second to the first ultrasonic transducer;
The distance in the axial direction of the measurement tube between the first and second ultrasonic transducers is L, the first propagation time is t1, the second propagation time is t2, the actual flow velocity is V, If the ultrasonic velocity is C,

And calculating the flow velocity V based on the formula

The sound speed C of the ultrasonic wave is calculated on the basis of the equation, and a sound speed / temperature data table in which the temperature of the gas is associated with the sound speed corresponding to the temperature is prepared.
The flow rate measuring method according to claim 5, wherein the actual temperature is specified from the sound speed / temperature data table based on a calculation result of the sound speed calculation unit.

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