Ultrasonic flow sensor

Abstract

To provide a more practical ultrasonic flow rate sensor.SOLUTION: Ultrasonic elements 15A and 15B transmit and receive ultrasonic waves. A first flow rate value of a fluid in a pipe is calculated on the basis of the propagation time difference of ultrasonic wave signals, a measured value corresponding to the rate of ultrasonic waves in the fluid in the pipe, and a parameter for specifying the inner diameter of the pipe. A second flow rate value of the fluid in the pipe is calculated on the basis of the frequency shift of an ultrasonic signal reflected in the fluid and the parameter. The first flow rate value is calculated by using a propagation time of an ultrasonic wave signal as a measured value according to the correspondence relation among the distance of a route where an ultrasonic wave propagate in the fluid in the pipe, the time of propagation of the ultrasonic wave in the route, and the rate of the ultrasonic wave.SELECTED DRAWING: Figure 2

Description

Technical Field

[0001] The present invention relates to an ultrasonic flow sensor for measuring the flow rate of a fluid flowing in a pipe.

Background Art

[0002] Ultrasonic flow sensors for measuring the flow rate of a fluid flowing in a pipe based on a plurality of methods are known. For example, Patent Document 1 describes an ultrasonic measuring device that performs measurement by a transmission method and measurement by a reflection method. In the transmission method, a first flow rate signal indicating the flow rate of the fluid is obtained by performing an operation on a reception signal of ultrasonic waves that have passed through the fluid. In the reflection method, a second flow rate signal indicating the flow rate of the fluid is obtained by performing a correlation operation on a reception signal of ultrasonic waves reflected by bubbles or the like contained in the fluid.

[0003] The correction coefficient storage unit stores a first correction coefficient used for correcting the first flow rate signal and a second correction coefficient used for correcting the second flow rate signal. The amount of bubbles contained in the fluid is determined, and depending on the determined amount of bubbles, either the first flow rate signal corrected using the first correction coefficient or the second flow rate signal corrected using the second correction coefficient is output.

Prior Art Documents

Patent Documents

[0004]

Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0005] The flow rate of the fluid is calculated using parameters such as the speed of sound in the fluid or the inner diameter of the pipe input by the user. Even if the parameters are the same, the degree to which the parameters contribute to the calculated flow rate differs depending on the flow rate measurement method. When the parameters are accurate, the flow rates calculated based on a plurality of measurement methods are consistent with each other.

[0006] However, inputting accurate parameters is not easy. If the parameters entered by the user are inaccurate, the calculated flow rate will vary significantly depending on the measurement method. Therefore, even if the actual flow rate through the piping does not change, the calculated flow rate may fluctuate discontinuously. This reduces the practicality of ultrasonic flow sensors.

[0007] The objective of this invention is to provide an ultrasonic flow sensor with improved practicality. [Means for solving the problem]

[0008] (1) The ultrasonic flow sensor according to the first invention comprises: a plurality of ultrasonic elements that transmit and receive ultrasonic signals, at least one of them; a first measuring unit that measures the propagation time of an ultrasonic signal and the difference in the propagation time of an ultrasonic signal by transmitting and receiving an ultrasonic signal that penetrates the fluid in the pipe between a pair of ultrasonic elements among the plurality of ultrasonic elements; a propagation time determination unit that determines the fluid propagation time, which is the time it takes for an ultrasonic signal to propagate in the path through the fluid in the pipe, based on the propagation time of the ultrasonic signal measured by the first measuring unit; a first calculation unit that calculates a first flow rate value of the fluid in the pipe based on the difference in the propagation time of the ultrasonic signal measured by the first measuring unit, a measured value corresponding to the ultrasonic velocity in the fluid in the pipe, and the square of a parameter for determining the inner diameter of the pipe; a second measuring unit that measures the frequency shift of an ultrasonic signal by transmitting an ultrasonic signal toward the fluid in the pipe and receiving an ultrasonic signal reflected in the fluid using one or a pair of ultrasonic elements among the plurality of ultrasonic elements; and a second calculation unit that calculates a second flow rate value of the fluid in the pipe based on the frequency shift of the ultrasonic signal measured by the second measuring unit and the square of a parameter. When a first flow rate value is calculated by the first calculation unit and a second flow rate value is calculated by the second calculation unit, the flow rate value is determined using at least one of the first flow rate value and the second flow rate value, based on the stability of the flow rate calculation. The first calculation unit calculates a first flow rate value using the fluid propagation time as a measured value, according to the correspondence between the path distance, the fluid propagation time, and the ultrasonic velocity.

[0009] (2) The ultrasonic flow sensor according to the second invention comprises: a plurality of ultrasonic elements that transmit and receive ultrasonic signals, at least one of them; a first measuring unit that measures the propagation time of an ultrasonic signal and the difference in the propagation time of an ultrasonic signal by transmitting and receiving an ultrasonic signal that penetrates the fluid in the pipe between a pair of ultrasonic elements among the plurality of ultrasonic elements; a propagation time determination unit that determines the fluid propagation time, which is the time it takes for an ultrasonic signal to propagate in the path through the fluid in the pipe, based on the propagation time of the ultrasonic signal measured by the first measuring unit; a first calculation unit that calculates a first flow rate value of the fluid in the pipe based on the difference in the propagation time of the ultrasonic signal measured by the first measuring unit, a measured value corresponding to the ultrasonic velocity in the fluid in the pipe, and a parameter for determining the inner diameter of the pipe; a second measuring unit that measures the frequency shift of an ultrasonic signal by transmitting an ultrasonic signal toward the fluid in the pipe and receiving an ultrasonic signal reflected in the fluid using one or a pair of ultrasonic elements among the plurality of ultrasonic elements; and a second calculation unit that calculates a second flow rate value of the fluid in the pipe based on the frequency shift of the ultrasonic signal measured by the second measuring unit and a parameter. When a first flow rate value is calculated by the first calculation unit and a second flow rate value is calculated by the second calculation unit, the flow rate value is determined using at least one of the first flow rate value and the second flow rate value, based on the stability of the flow rate calculation. The first calculation unit calculates the first flow rate value using the fluid propagation time as a measured value, such that the difference in the influence of parameters on the first flow rate value and the second flow rate value is minimized.

[0010] (3) The ultrasonic flow sensor according to the third invention is an ultrasonic flow sensor for measuring the flow rate of a fluid flowing in a pipe, comprising: a first ultrasonic element for transmitting and receiving ultrasonic waves; a second ultrasonic element for transmitting and receiving ultrasonic waves; a first calculation unit for calculating a first flow rate value indicating the fluid flow rate based on the difference in ultrasonic wave propagation time between the first ultrasonic element and the second ultrasonic element; and a second calculation unit for calculating a second flow rate value indicating the fluid flow rate based on the frequency shift of ultrasonic waves received by the first ultrasonic element when the first ultrasonic element transmits ultrasonic waves. When a first flow rate value is calculated by the first calculation unit and a second flow rate value is calculated by the second calculation unit, the flow rate value is determined using at least one of the first flow rate value and the second flow rate value, based on the stability of the flow rate calculation.The first flow rate value and the second flow rate value are calculated by the first calculation unit and the second calculation unit, respectively, using calculation formulas such that the correlation between the first flow rate value and the parameters included in the calculation formula for the first flow rate value and input by the user is the same, and the correlation between the second flow rate value and the parameters included in the calculation formula for the second flow rate value and input by the user is the same. [Effects of the Invention]

[0011] According to the present invention, the practicality of ultrasonic flow sensors can be improved. [Brief explanation of the drawing]

[0012] [Figure 1] This is a side view of an ultrasonic flow sensor according to one embodiment of the present invention. [Figure 2] This is a schematic cross-sectional view showing the configuration of the sensor head in Figure 1. [Figure 3] Figure 2 is a block diagram showing the configuration of the control unit. [Figure 4] This diagram illustrates the operation of the sensor head using the propagation time difference method. [Figure 5] This is a diagram illustrating how to identify values ​​related to the speed of sound. [Figure 6] This diagram illustrates the operation of the sensor head in the pulsed Doppler method. [Figure 7] This diagram illustrates the operation of the sensor head in a more specific way using the pulsed Doppler method. [Figure 8] This figure shows the Doppler signals detected over time. [Figure 9] This figure shows the Doppler signal detected when the microbubble density is high. [Figure 10] This figure shows the fluid flow rate calculated using the propagation time difference method and the pulsed Doppler method. [Figure 11] Figure 3 is a flowchart showing an example of an algorithm for the flow rate calculation process executed in hybrid mode by the control unit. [Figure 12]It is a flowchart showing an example of the algorithm of the flow rate calculation process executed in the hybrid mode by the control unit of FIG. 3.

Embodiments for Carrying Out the Invention

[0013] (1) Schematic Configuration of Ultrasonic Flow Sensor Hereinafter, an ultrasonic flow sensor according to an embodiment of the present invention will be described with reference to the drawings. FIG. 1 is a side view showing the configuration of the ultrasonic flow sensor in an example of the present invention. The ultrasonic flow sensor 100 includes a sensor head 10, a clamp portion 20, and a display 30. The sensor head 10 is attached to the pipe P and calculates the flow rate value of the fluid flowing through the pipe P. The clamp portion 20 is attached to the pipe P, and the sensor head 10 is attached to the pipe P by being attached to the clamp portion 20. The display 30 is attached to the sensor head 10 and performs display output and output to an external device according to the flow rate value calculated by the sensor head 10. In this embodiment, the maximum inner diameter (diameter) of the pipe P corresponds to, for example, the inner diameter corresponding to the pipe nominal diameter “50A” defined in the JIS standard. For example, the inner diameter of a steel pipe with a pipe nominal diameter of “50A” is 52.9 mm. In the following description, an example in which the sensor head 10 is attached to the upper surface of the horizontally extending pipe P will be described.

[0014] The sensor head 10 has a connector 12, an indicator lamp 18, and sensor fixing screws 101. The connector 12 and the indicator lamp 18 are provided on the upper surface of the sensor head 10. The sensor fixing screws 101 are inserted into holes provided at both ends of the sensor head 10 in the direction along the pipe P.

[0015] The clamp portion 20 includes an upper clamp member 21, a lower clamp member 22, and a clamp fixing screw 23. The upper clamp member 21 is attached from above the pipe P, the lower clamp member 22 is attached from below the pipe P, and the upper clamp member 21 and the lower clamp member 22 are coupled to each other by a plurality of clamp fixing screws 23 so as to sandwich the pipe P. Thereby, the clamp portion 20 is attached to the outer peripheral surface of the pipe P. As shown by the dashed arrow in FIG. 1, two sensor fixing screws 101 are screwed into holes provided in the upper surface of the upper clamp member 21. Thereby, the sensor head 10 is held by the clamp portion 20 in a state where the lower surface is in contact with the pipe P.

[0016] The display 30 includes a housing portion 31, a connector 32, a control unit 33, a memory element 34, an operation unit 35, a display unit 36, an indicator light 37, a first connection port 38, a second connection port 39, and a power circuit 40.

[0017] The housing portion 31 has a substantially rectangular parallelepiped shape and is attached to the upper surface of the sensor head 10 as shown by the dotted arrow in FIG. 1. The housing portion 31 houses the control unit 33, the memory element 34, and the power circuit 40.

[0018] The connector 32 is provided on the lower surface of the housing portion 31. When the connector 12 and the connector 32 are connected, the display 30 and the sensor head 10 can communicate with each other. The connector 12 and the connector 32 are directly connected when the housing portion 31 is attached to the upper surface of the sensor head 10. Also, the connector 12 and the connector 32 are connected via a cable not shown, and at this time, the housing portion 31 is removed from the sensor head 10. Thus, the connector 12 and the connector 32 of this embodiment can be connected by a predetermined method whether the housing portion 31 is attached to the sensor head 10 or the housing portion 11 is removed from the sensor head 10. That is, the connector 32 of the display 30 and the connector 12 of the sensor head 10 are connected in a state where the display 30 is detachable from the sensor head 10.

[0019] The control unit 33 includes, for example, a CPU (Central Processing Unit) as a processor, memory, and other storage means, and controls each part of the display unit 30 according to a program stored in memory. The control unit 33 receives the flow rate value calculated by the sensor head 10 from the sensor head 10 via the connector 32, and also receives parameters specified by the user by operating the operation unit 35. The control unit 33 controls the memory element 34 to store the flow rate value. Furthermore, the control unit 33 compares the flow rate value with a predetermined threshold. Based on the comparison result, the control unit 33 controls the operation of the display unit 36 ​​and indicator lights 37. The control unit 33 also generates a switching signal based on the comparison result and outputs the switching signal to an external device via the second connection port.

[0020] The memory element 34 is a ring buffer. The memory element 34 sequentially stores log data at predetermined time intervals, which associates the flow rate value calculated by the sensor head 10 with the time the flow rate value was input. The log data may include the maximum flow rate, minimum flow rate, integrated flow rate, or the level of the switching signal. When log data is stored in the entire storage area of ​​the memory element 34, the first stored log data is overwritten with the latest log data. Therefore, log data stored in the memory element 34 is retained for a certain period of time until it is overwritten by the latest log data.

[0021] The control unit 35 is provided on the upper surface of the housing unit 31. The user inputs threshold values ​​and parameters to be compared with the flow rate value by operating the control unit 35. The user may select the desired parameter from the options displayed on the display unit 36, or may directly indicate the value of the desired parameter. The parameters input from the control unit 35 include parameters related to initial settings for calculating the flow rate, frequently used parameters, and infrequently used parameters. Parameters related to initial settings include the material of the piping and the outer diameter of the standard piping P. The outer diameter of the standard piping P is a parameter that the user can specify based on the standard, and the nominal diameter specified in the given standard is input. A list of standard nominal diameters and outer diameters corresponding to the standard nominal diameters may be displayed, and the user may select from among them. Frequently used parameters include response time, display resolution, hysteresis, zero-cut flow rate, direction of fluid flow, and the period for detecting the density of microbubbles, which will be described later. These frequently used parameters are related to the control unit 33 generating a switching signal based on the flow rate value and outputting a switching signal. Therefore, it is assumed that these are frequently used parameters, as it is easy for the user to input each parameter while referring to the actual output results in order to obtain the desired output from the ultrasonic flow sensor 100. In contrast, parameters that are used less frequently include the flow rate calculation mode, the outer diameter of the pipe P, the thickness of the pipe P, the velocity of sound in the pipe P, or the kinematic viscosity of the fluid. These parameters are related to the sensor head 10 calculating the flow rate value. Therefore, these parameters are input by users who want to obtain the desired output from the ultrasonic flow sensor 100, and in particular by users who want to adjust the flow rate value calculated by the sensor head 10, and are therefore assumed to be used relatively less frequently. The parameters related to the dimensions of the pipe P, which are input as parameters that are used less frequently, are parameters whose values ​​are changed when the user further fine-tunes the value corresponding to the standard nominal diameter. The parameters input from the operation unit 35 are provided to the sensor head 10.

[0022] The display unit 36 ​​is provided on the upper surface of the housing unit 31. The display unit 36 ​​displays the fluid flow rate value calculated by the sensor head 10, the comparison result between the flow rate value and the threshold value, and the parameter items input by operating the operation unit 35. As described above, the display unit 30 is detachable from the sensor head 10, so the user can place the display unit 30 in a suitable position. This allows the user to visually check the flow rate status of the piping P even when they are at a distance from the part of the piping P to which the sensor head 10 is attached.

[0023] The indicator light 37 has multiple light-emitting diodes that emit light in different colors and is provided on the upper surface of the housing 31. The indicator light 37 lights up or flashes in a manner that allows identification of the level of the switching signal generated by the control unit 33. That is, the indicator light 37 lights up or flashes in a manner that allows identification of an indication that the flow rate of the fluid flowing through the pipe P is above a certain amount and an indication that the flow rate of the fluid flowing through the pipe P is below a certain amount. Similar to the display unit 36, the indicator light 37 is provided on the display unit 30 so that the user can visually check the flow rate status of the pipe P from a suitable position. In the following description, the fluid flowing through the pipe P is assumed to fill the cross-section of the pipe P, and the fluid flowing through the pipe P is referred to as the fluid inside the pipe P.

[0024] The connection port 38 is a USB (Universal Serial Bus) port and is located on the side of the housing 31. When the connection port 38 is connected to an external information processing device via a cable (not shown), the log data stored in the memory element 34 is output to the information processing device.

[0025] The connection port 39 is an M12 port and is provided on the end face of the housing 31. The connection port 39 is connected to an external device such as a personal computer or a programmable logic controller by a cable (not shown). The switching signal generated by the control unit 33 and output to the external device via the connection port 39 is a signal indicating one of two states: the flow rate value calculated by the sensor head 10 is greater than or equal to a predetermined threshold value, or the flow rate value is less than a predetermined threshold value. In other words, it is a signal in which the flow rate of the fluid in the pipe P is binarized by comparison with a threshold value. The switching signal is used by an external device capable of controlling other devices to switch the on and off states of those other devices according to the flow rate of the fluid in the pipe P. Thus, when other devices are controlled according to the flow rate of the fluid in the pipe P, the ultrasonic flow sensor 100 can be said to function as a flow switch that switches the operating state of other devices by comparing the flow rate of the fluid in the pipe P with a threshold value.

[0026] In this embodiment, the switching signal is generated by comparing the flow rate value calculated by the sensor head 10 with a predetermined threshold value. However, it is sufficient that the switching signal reflects whether the fluid flow rate in the pipe P is above a certain amount or below a certain amount. As will be described later, the sensor head 10 in this embodiment calculates the flow rate value based on the fluid velocity value and the cross-sectional area of ​​the pipe P. Therefore, the switching signal may be generated by comparing the velocity value with a threshold value related to the velocity.

[0027] The power supply circuit 40 converts the voltage supplied by the external commercial power supply into a voltage suitable for the ultrasonic flow sensor 100, and supplies the converted voltage to the control unit 33, memory element 34, display unit 36, and indicator light 37. The power supply circuit 40 also supplies the converted voltage to each part of the sensor head 10 via the connector 32.

[0028] Figure 2 is a schematic cross-sectional view showing the configuration of the sensor head 10 in Figure 1. The sensor head 10 includes a housing 11, a connector 12, a control unit 13, two wedge members 14, two ultrasonic elements 15, an acoustic couplant 16, an ultrasonic shielding plate 17, and an indicator light 18.

[0029] The housing 11 has a roughly rectangular parallelepiped shape with an open bottom. A connector 12 is provided on the top surface of the housing 11. A wedge material 14 is housed in the opening at the bottom of the housing 11, exposing the acoustic couplant 16. The housing 11 houses the control unit 13 and the ultrasonic element 15.

[0030] The connector 12 is provided on the upper surface of the housing 11. As described above, the connector 12 is positioned so that it can be connected to the connector 32 when the housing 31 is attached to the housing 11.

[0031] The control unit 13 includes, for example, a CPU (Central Processing Unit) as a processor, memory, and other storage means, and controls each part of the sensor head 10 according to a program stored in memory. The control unit 13 acquires parameters input to the control unit 33 via the connector 12. The control unit 13 also controls the two ultrasonic elements 15 to transmit and receive ultrasonic signals from the ultrasonic elements 15, and measures the measured values ​​related to the transmission and reception of ultrasonic signals. Furthermore, the control unit 13 calculates the flow rate of the fluid flowing through the piping P based on the measured values ​​obtained by controlling the ultrasonic elements 15 and the parameters acquired from the control unit 33. Details of the flow rate calculation method will be described later.

[0032] The wedge material 14 is positioned between the ultrasonic element 15 and the pipe P when the sensor head 10 is attached to the clamp portion 20. The wedge material 14 is made of a non-metallic material that has high rigidity and high acoustic transparency. Preferably, the wedge material 14 is made of a material with high environmental resistance. In this embodiment, the wedge material 14 is made of PPS (polyphenylene sulfide) resin and PEEK (polyether ether ketone) resin, but it may also be made of ULTEM® resin. The wedge material 14 has an element coupling surface 14a that faces diagonally upward and a pipe coupling surface 14b that faces downward.

[0033] In the following description, when distinguishing between the two wedge materials 14, one wedge material 14 will be referred to as wedge material 14A, and the other wedge material 14 as wedge material 14B. The wedge materials 14A and 14B are arranged in the longitudinal direction of the housing 11 with their element coupling surfaces 14a facing diagonally upward and outward, and are attached to the opening at the bottom of the housing 11. This creates a space inside the housing 11 that prevents the ingress of liquids such as water and oil.

[0034] The ultrasonic element 15 is capable of transmitting and receiving ultrasonic signals. The control unit 13 selectively operates the ultrasonic element 15 in a transmission mode for transmitting ultrasonic signals and in a reception mode for receiving ultrasonic signals. The ultrasonic element 15 is a composite element. Therefore, the reverberation time of the transmitted ultrasonic waves is short, and noise is reduced when the same ultrasonic element 15 is operated in transmission mode and then in reception mode. In particular, in the pulse Doppler method described later, it is preferable that the ultrasonic element 15 that transmits ultrasonic waves and the ultrasonic element 15 that receives the reflected ultrasonic signal are the same ultrasonic element 15 in order to receive the ultrasonic signal reflected by a reflector in a fluid at a position where the intensity of the ultrasonic signal is high. At this time, if there is reverberation when transmitting an ultrasonic signal, it will affect the reception accuracy, so it is preferable that the ultrasonic element 15 that operates in the Doppler method is a composite element with a short reverberation time. Therefore, the measurement accuracy in the pulse Doppler method is improved by the ultrasonic element 15 being a composite element. In the propagation time difference method described later, ultrasonic signals are propagated in two directions: one along the direction of fluid flow in the pipe P, and the other against the direction of flow. If the ultrasonic element 15 that transmits the ultrasonic signal when propagating in one direction and the ultrasonic element 15 that receives the ultrasonic signal when propagating in the other direction are the same ultrasonic element 15, the number of ultrasonic elements 15 required is reduced. Therefore, even in the propagation time difference method, the measurement accuracy is improved when the number of ultrasonic elements 15 is reduced because the ultrasonic element 15 is a composite element.

[0035] In the following explanation, when distinguishing between the two ultrasonic elements 15, one ultrasonic element 15 will be referred to as ultrasonic element 15A, and the other ultrasonic element 15 will be referred to as ultrasonic element 15B. Ultrasonic element 15A is joined to the element bonding surface 14a of the wedge material 14A, and ultrasonic element 15B is joined to the element bonding surface 14a of the wedge material 14B. As a result, ultrasonic elements 15A and 15B are housed in the housing 11 at a predetermined angle with respect to the piping P.

[0036] The acoustic couplant 16 has a solid shape and is made of a soft elastic material such as polymer rubber or a gel-like substance. The acoustic couplant 16 is provided at the lower part of the housing 11 so as to contact the pipe coupling surface 14b of the wedge material 14. The lower surface of the acoustic couplant 16 protrudes slightly below the lower surface of the housing 11. The sensor head 10 is fixed to the clamp part 20 by two sensor fixing screws 101, so that the acoustic couplant 16 is pressed against the pipe P and the sensor head 10 is attached to the pipe P. The acoustic couplant 16 matches the acoustic impedance of the wedge material 14 and the pipe P by its lower surface contacting the pipe P. Therefore, it is preferable that the acoustic couplant 16 has an acoustic impedance value between the acoustic impedance value of the wedge material 14 and the acoustic impedance value of the pipe P.

[0037] The ultrasonic shielding plate 17 is made of, for example, foamed rubber and has a flat plate shape. The ultrasonic shielding plate 17 is positioned between the wedge materials 14A and 14B so as to penetrate the acoustic couplant 16 with its plate surface aligned vertically. In this case, it is prevented that ultrasonic components that do not pass through the pipe P are directly transmitted between the wedge materials 14A and 14B.

[0038] The indicator light 18 has, for example, multiple light-emitting diodes and lights up or flashes in a manner that allows for identification of the switching signal level, similar to the indicator light 37 of the display unit 30. Therefore, when the display unit 30 is attached to the sensor head 10, the user can understand the status of the piping P by looking at the indicator light 37 of the display unit 30. On the other hand, as described above, the display unit 30 can be removed from the sensor head 10 by connecting the connector 12 and the connector 32 with a cable, thereby separating the display unit 30 from the sensor head 10. Therefore, even when the display unit 30 is separated from the sensor head 10, the user can understand the status of the piping P by looking at the indicator light 18 of the sensor head 10, and can also understand the status of the piping P by looking at the indicator light 37 of the display unit 30 which is placed in a suitable position.

[0039] (2) Operation of the sensor head Referring to Figure 3, the functional configuration of the sensor head 10 and the display unit 30 will be explained.

[0040] The control unit 13 includes, for example, a CPU (Central Processing Unit) as a processor and a storage unit 131, and controls each part of the sensor head 10 according to a program stored in the storage unit 131.

[0041] The control unit 13 executes processing according to the flow rate calculation mode selected by the user operating the operation unit 35 in Figure 1, and outputs the flow rate value to the display unit 30. More specifically, the flow rate calculation mode for the sensor head 10 can be selected from propagation time difference mode, pulse Doppler mode, and hybrid mode. In propagation time difference mode, the flow rate value calculated by the propagation time difference method is output to the display unit 30. In pulse Doppler mode, the flow rate value calculated by the pulse Doppler method is output to the display unit 30. In hybrid mode, the flow rate value obtained by combining the flow rate value calculated by the propagation time difference method and the flow rate value calculated by the pulse Doppler method is output to the display unit 30.

[0042] The control unit 13 includes a storage unit 131, a first measurement unit 132, a propagation time determination unit 133, a first calculation unit 134, a second measurement unit 135, a second calculation unit 136, a cycle skip determination unit 137, a microbubble detection unit 138, and a flow rate value synthesis unit 139.

[0043] The memory unit 131 stores parameters used for various controls of the control unit 13. For example, parameters such as velocity C', incidence angle θ', incidence angle θ, and Blasius coefficient, which will be described later, are stored in advance. Furthermore, the memory unit 131 also stores the wedge propagation time τ1 and the couplant propagation time τ2 as known parameters.

[0044] The first measuring unit 132 is a measuring unit for calculating the flow rate of fluid in pipe P using a propagation time difference method. The first measuring unit 132 controls ultrasonic elements 15A and 15B to measure the propagation time ta, which is the time it takes for an ultrasonic signal transmitted from ultrasonic element 15A toward pipe P to be reflected off the inner wall of pipe P and propagate to ultrasonic element 15B; the propagation time tb, which is the time it takes for an ultrasonic signal transmitted from ultrasonic element 15B toward pipe P to be reflected off the inner wall of pipe P and propagate to ultrasonic element 15A; and the propagation time difference Δt, which is the difference between propagation time ta and propagation time tb. Propagation time ta, propagation time tb, and propagation time difference Δt are measured values ​​measured by the first measuring unit 132.

[0045] Referring to Figure 4, the operation of the sensor head 10 when the first measuring unit 132 measures a measurement value will be explained. First, the first measuring unit 132 controls the ultrasonic element 15A to transmit an ultrasonic signal from the ultrasonic element 15A toward the pipe P. The ultrasonic signal transmitted by the ultrasonic element 15A propagates through the wedge material 14A in the direction of arrow A1, passes through the acoustic couplant 16 and enters the fluid in the pipe P, and propagates through the fluid in the pipe P in the direction of arrow A2. The ultrasonic signal that has propagated through the fluid is reflected by the inner wall of the pipe P, propagates through the fluid in the direction of arrow A3, passes through the acoustic couplant 16 and enters the wedge material 14B, propagates through the wedge material 14B in the direction of arrow A4 and is received by the ultrasonic element 15B. In this way, the first measuring unit 132 measures the propagation time ta from when the ultrasonic signal transmitted by the ultrasonic element 15A is received by the ultrasonic element 15B.

[0046] Next, the first measuring unit 132 controls the ultrasonic element 15B to transmit ultrasonic waves. The ultrasonic signal transmitted by the ultrasonic element 15B propagates through a path including the wedge material 14, the acoustic couplant 16, the piping P, and the fluid inside the piping P, similar to the path taken by the ultrasonic signal transmitted from the ultrasonic element 15A, as shown by arrows B1, B2, B3, and B4, and is received by the ultrasonic element 15A. In this way, the first measuring unit 132 measures the propagation time tb from the ultrasonic signal transmitted by the ultrasonic element 15B until it is received by the ultrasonic element 15A.

[0047] Then, the first measuring unit 132 measures the propagation time ta and propagation time tb, and then measures the propagation time difference Δt.

[0048] Thus, the measurement required to calculate the flow rate using the propagation time difference method requires an ultrasonic element that transmits and receives an ultrasonic signal that propagates along the direction of fluid flow, and an ultrasonic element that transmits and receives an ultrasonic signal that propagates against the direction of fluid flow. In this embodiment, since the measurement for the propagation time difference method is performed by two ultrasonic elements 15, the number of ultrasonic elements required to calculate the flow rate using the propagation time difference method is minimized, which has a certain effect on miniaturizing the sensor head 10. The number of ultrasonic elements for the propagation time difference method is not limited to two, and may be realized with three or more ultrasonic elements.

[0049] Furthermore, in this embodiment, each ultrasonic element 15 is provided on the upper side of the pipe P, and the ultrasonic signal propagation path is a path that reflects off the lower inner wall of the pipe P. Since multiple ultrasonic elements 15 are provided on one side of the pipe P, the user can easily position the ultrasonic elements with access from one side of the pipe P. In particular, in this embodiment, since the housing 11 accommodates two ultrasonic elements 15, the user can position multiple ultrasonic elements on the pipe P even more easily. The ultrasonic signal propagation path in measurement for the propagation time difference method is not limited to a configuration in which the ultrasonic element is reflected off the inner wall on the opposite side from where the ultrasonic element is placed, but may also be a configuration in which the ultrasonic signal is propagated from an ultrasonic element provided on one side of the pipe P to an ultrasonic element provided on the other side of the pipe P. For example, in this embodiment, ultrasonic element 15B is provided on the lower side of the pipe P, and the ultrasonic signal is propagated from ultrasonic element 15A provided on the upper side to ultrasonic element 15B. In this case, since the path in which the ultrasonic signal is propagated does not include reflection off the inner wall of the pipe P, the ultrasonic element receiving the ultrasonic signal can receive an ultrasonic signal of relatively high intensity.

[0050] Returning to Figure 3, the control unit 13 has a propagation time determination unit 133. The propagation time determination unit 133 determines the fluid propagation time τ4 of the ultrasonic signal that propagates through the fluid in the pipe P when the propagation time ta is measured by the first measurement unit 132. The fluid propagation time τ4 determined by the propagation time determination unit 133 is the time it takes for the ultrasonic signal to propagate along the path indicated by arrows A2 and A3 in Figure 3.

[0051] Referring to Figure 5, the determination of the fluid propagation time τ4 by the propagation time determination unit 133 will be explained. The path through which the ultrasonic signal propagates from ultrasonic element 15A to ultrasonic element 15B includes the wedge material 14, the acoustic couplant 16, the pipe P, and the fluid in the pipe P. The propagation time ta measured by the first measurement unit 132 is the time it takes for the ultrasonic signal to propagate through the path including the wedge material 14, the acoustic couplant 16, the pipe P, and the fluid in the pipe P. Therefore, the propagation time ta (τ0 in Figure 5) consists of the wedge propagation time τ1 propagating through the wedge material 14, the couplant propagation time τ2 propagating through the acoustic couplant 16, the pipe propagation time τ3 propagating through the pipe P, and the fluid propagation time τ4 propagating through the fluid in the pipe P. The wedge propagation time τ1 and the couplant propagation time τ2 are known values ​​that have been measured in advance and are stored in the storage unit 131 when the ultrasonic flow sensor 100 is shipped. Furthermore, the pipe propagation time τ3 is determined by the user referring to a table that associates pipe material with pipe sound velocity and inputting the pipe sound velocity as a parameter. Therefore, the propagation time determination unit 133 determines the fluid propagation time τ4 by subtracting the wedge propagation time τ1, the couplant propagation time τ2, and the pipe propagation time τ3 from the propagation time t0.

[0052] Returning to Figure 3, the control unit 13 has a first calculation unit 134. The first calculation unit 134 calculates the flow rate of the fluid in the pipe P using the propagation time difference method. More specifically, the flow rate value V1 is calculated by the following equation (1), which includes the propagation time difference Δt, which is a measured value by the first measurement unit 132, and the fluid propagation time T. In this embodiment, the fluid propagation time T is the fluid propagation time τ4 specified by the propagation time specification unit 133.

[0053]

number

[0054] In equation (1) above, C' is the velocity of the ultrasonic waves in the wedge material 14, and θ' is the angle of incidence of the ultrasonic waves onto the wedge material 14. d is the inner diameter of the pipe P, and λ is the pipe friction coefficient (Blasius coefficient). The velocity C', the angle of incidence θ', the angle of incidence θ, and the Blasius coefficient are known and are stored in advance in the memory unit 131 of the control unit 13. The inner diameter d is a parameter that the user inputs by operating the operation unit 35. Therefore, the first calculation unit 134 calculates the flow rate value V1 based on the propagation time difference Δt, which is a measured value measured by the first measurement unit 132, the fluid propagation time τ4, which is determined by the propagation time determination unit 133, the parameter for determining the inner diameter d of the pipe, and the value stored in advance in the memory unit 131. Note that d in equation (1) or equations (2) to (4) described later 2 π / 4 is the cross-sectional area of ​​pipe P, and the value obtained by dividing the flow rate by the cross-sectional area is the flow velocity of the fluid flowing through pipe P.

[0055] The second measuring unit 135 is a measuring unit for calculating the flow rate of fluid in the pipe P using the pulse Doppler method. The second measuring unit 135 controls the ultrasonic element 15B to transmit a pulsed ultrasonic signal from the ultrasonic element 15B toward the pipe P, and receives the ultrasonic signal reflected by a reflector contained in the fluid, and measures the frequency shift Δf between the transmitted ultrasonic signal and the reflected ultrasonic signal. In other words, the frequency shift Δf is a measured value measured by the second measuring unit 135.

[0056] Referring to Figure 6, the operation of the sensor head 10 when the second measuring unit 135 measures the measurement value will be explained. First, the second measuring unit 135 controls the ultrasonic element 15B to transmit a pulsed ultrasonic signal of several pulses from the ultrasonic element 15B toward the pipe P. At this time, the second measuring unit 135 controls the ultrasonic element 15B so that the ultrasonic signal is transmitted at a frequency f stored in the memory unit 131. The ultrasonic signal transmitted by the ultrasonic element 15B propagates through the wedge material 14B in the direction of arrow C1, passes through the acoustic couplant 16, enters the fluid in the pipe P, and propagates through the fluid in the pipe P in the direction of arrow C2.

[0057] Here, the fluid flowing through pipe P contains microbubbles as reflectors that reflect the ultrasonic signals transmitted from the ultrasonic element 15B in the control by the second measuring unit 135. Microbubbles are, for example, tiny bubbles with a diameter of 10 μm to 50 μm. Fluids that easily contain microbubbles include, for example, coolant fluids such as water-soluble cutting oils used to cool the machining points of machine tools. Coolant fluids contain surfactants, and since they are circulated and reused after coming into contact with air, a large amount of microbubbles are generated in the coolant fluid flowing through pipe P.

[0058] The ultrasonic signal propagates through the fluid in pipe P in the direction of arrow C2, and the ultrasonic signal reflected by the microbubbles acting as reflectors propagates through the fluid in pipe P in the direction of arrow C3. The ultrasonic signal is reflected in multiple directions by the microbubbles contained in the fluid, but the direction with the highest intensity among the reflected ultrasonic signals is in the direction of arrow C3. The ultrasonic signal propagating in the direction of arrow C3 passes through the acoustic couplant 16, propagates through the wedge material 14B in the direction of arrow C4, and is received by the ultrasonic element 15B. In this way, the second measuring unit 135 measures the frequency shift Δf, which is the difference between the frequency of the ultrasonic signal transmitted by the ultrasonic element 15B and the frequency of the ultrasonic signal received by the ultrasonic element 15B. The frequency shift Δf is proportional to the movement speed of the microbubbles contained in the fluid in pipe P, that is, the flow velocity of the fluid in pipe P.

[0059] Thus, measuring the flow rate using the pulsed Doppler method requires an ultrasonic element that transmits an ultrasonic signal towards the fluid and an ultrasonic element that receives the ultrasonic signal reflected by reflectors contained in the fluid. As mentioned above, in the pulsed Doppler method, the accuracy of ultrasonic signal reception is higher if the ultrasonic element that transmits the ultrasonic signal and the ultrasonic element that receives the ultrasonic signal are the same; therefore, ultrasonic element 15B performs both the transmission and reception of the ultrasonic signal. In particular, in this embodiment, the ultrasonic element used in the pulsed Doppler method is a composite element, which improves the measurement accuracy. Note that the number of ultrasonic elements for the pulsed Doppler method is not limited to one, and may be implemented with two or more ultrasonic elements. When the ultrasonic element that receives the ultrasonic signal in the pulsed Doppler method is provided separately from the ultrasonic element that transmits the ultrasonic signal, there is no need to consider reverberation, which improves the reception accuracy.

[0060] Furthermore, in this embodiment, the ultrasonic element 15B is controlled for both the propagation time difference method measurement, i.e., measurement by the first measurement unit 132, and the pulsed Doppler method measurement, i.e., measurement by the second measurement unit 135. For this reason, measurements for the propagation time difference method and measurements for the pulsed Doppler method are performed using two ultrasonic elements 15, but a separate ultrasonic element may be provided for each measurement method. For example, the first measurement unit 132 may control a pair of ultrasonic elements to measure the measurement value, and the second measurement unit 135 may measure the measurement value using a different pair of ultrasonic elements or a single ultrasonic element than the pair of ultrasonic elements controlled by the first measurement unit 132.

[0061] Furthermore, the second measuring unit 135 controls the ultrasonic element 15B to measure the frequency shift Δf as a measured value, although the ultrasonic element 15A may also be used. In this embodiment, because the housing 11 is small, the distance between the control unit 13 and the ultrasonic element 15 is small. In particular, a power supply circuit 40 is provided near the part of the control unit 13 to which the connector 12 is connected, and the frequency of the ultrasonic signal received by the ultrasonic element is easily affected by the power supply circuit 40. For this reason, in this embodiment, the second measuring unit 135 controls the ultrasonic element 15B, which is relatively far from the connector 12, to measure the frequency shift Δf.

[0062] Returning to Figure 3, the control unit 13 has a second calculation unit 136. The second calculation unit 136 calculates the flow rate of the fluid in the pipe P using the pulse Doppler method. More specifically, the flow rate value V2 is calculated by the following equation (2), which includes the frequency shift Δf, a measured value obtained by the second measurement unit 135, as a parameter. The frequency f is the frequency of the ultrasonic signal transmitted by the ultrasonic element 15B, and as described above, it is stored in the storage unit 131.

[0063]

number

[0064] In equation (2), frequency f is the frequency of the ultrasonic signal transmitted from the ultrasonic element 15B under the control of the second measuring unit 135, and is stored in the memory unit 131 as described above. Also, as described above, velocity C', incident angle θ', incident angle θ, and Blasius coefficient are known and are stored in advance in the memory unit 131 of the control unit 13, and inner diameter d is a parameter input by the user. Therefore, the second calculation unit 136 calculates the flow rate value V2 based on the frequency shift Δf, which is a measured value measured by the second measuring unit 135, the parameter for identifying the inner diameter d of the pipe, and the value stored in advance in the memory unit 131.

[0065] In addition, equation (2) has been simplified so that the flow rate value V2 is calculated using a single measured frequency shift Δf, for the purpose of comparing the flow rate value V2 calculated by the second calculation unit 136 with the flow rate value V1 calculated by the first calculation unit 134. In this embodiment, in order to improve the accuracy of the flow rate value V2, the second measurement unit 135 measures the frequency shift Δf of the fluid in the pipe P at multiple points, and the second calculation unit 136 calculates the flow rate value V2 based on the multiple measured frequency shifts Δf.

[0066] Figure 7 illustrates the details of the measurement of the frequency shift Δf by the second measuring unit 135. Figure 7 shows a more specific operation of the sensor head 10 in the pulse Doppler method. As shown in Figure 7, the fluid does not flow at a uniform velocity within the flow path of the pipe P, but rather flows with a predetermined velocity distribution. The flow velocity of the fluid flowing near the center of the flow path of the pipe P is greater than the flow velocity of the fluid flowing near the inner wall of the pipe P. The Δf measured by the second measuring unit 135 is a measurement value corresponding to one point in the inner diameter direction d of the fluid in the pipe P. Therefore, when the flow rate value V2 is calculated based on only one frequency shift Δf, the calculated flow rate value V2 will differ depending on whether the frequency shift Δf is the frequency shift Δf of the frequency signal reflected near the center of the pipe P or the frequency shift Δf of the frequency signal reflected near the inner wall of the pipe P.

[0067] In the pulsed Doppler method, the time it takes for the ultrasonic waves transmitted by the ultrasonic element 15B to reach the microbubbles, and the time it takes for the ultrasonic waves reflected by the microbubbles to reach the ultrasonic element 15B, differ for each position in the radial direction of the pipe P where the microbubbles flow. Therefore, the second measuring unit 135 measures the frequency shift Δf for each time interval from when the ultrasonic signal is transmitted from the ultrasonic element 15B until the ultrasonic signal reflected by the microbubbles is received by the ultrasonic element 15B. Hereafter, the position in the radial direction of the pipe P where the microbubbles flow will be referred to as the microbubble flow depth.

[0068] Figure 8 shows the ultrasonic signals (Doppler signals) detected over time. The horizontal axis in Figure 8 represents frequency. The vertical axis in Figure 8 represents the intensity of the Doppler signals. In the example in Figure 8, multiple Doppler signals s1 to s4 are shown by solid lines, dotted lines, dashed lines, and double-dash lines, respectively. Doppler signals s1 to s4 are Doppler signals detected for ultrasonic waves reflected by microbubbles flowing at depths d1 to d4 in Figure 7, and are detected at multiple different times t1 to t4. The second measurement unit 135 measures the frequency shift Δf corresponding to depths d1 to d4, using the centroid position of the Doppler signals s1 to s4 as the Doppler frequency corresponding to depths d1 to d4. The second calculation unit 136 calculates the flow velocity of the microbubbles at each depth d1 to d4 based on the multiple measured frequency shifts Δf. Based on this, the second calculation unit 136 can identify the velocity distribution of the fluid in the pipe P. Furthermore, the second calculation unit 136 averages the velocity distribution of the identified fluid, and multiplies the averaged flow velocity by the cross-sectional area to calculate the flow rate value V2, which is the fluid flow velocity in the pipe P.

[0069] As described above, the pulse Doppler method allows for spatial resolution of the fluid's position and identification of its velocity distribution. In this embodiment, the fluid velocity is calculated for each depth d1 to d4, but the number of depth points may be appropriately determined according to the diameter of the pipe P or the processing speed of the control unit 13.

[0070] As described above, the pulsed Doppler method makes it possible to calculate the flow rate with high accuracy even when the density of microbubbles in the fluid is relatively high. However, when the density of microbubbles is higher than the value v2 in Figure 10, which will be described later, the accuracy of the flow rate calculation decreases. The reason for this is explained below.

[0071] Returning to Figure 3, the control unit 13 has a cycle skip determination unit 137. The cycle skip determination unit 137 determines whether or not a cycle skip has occurred in the Doppler frequency measured by the second measurement unit 135. A cycle skip is a phenomenon in the calculation of the Doppler frequency in which, if the amount of shift of the transmitted ultrasonic frequency is greater than one phase cycle, the shift amount to the phase one cycle after the original phase is calculated as the frequency shift, rather than the original phase. This occurs relatively often when the phase interval of the ultrasonic is short, i.e., when the ultrasonic frequency is high, as in this embodiment. When a cycle skip occurs, a Doppler frequency smaller than the original value is calculated, resulting in a flow rate smaller than the original value. Therefore, the cycle skip determination unit 137 determines that a cycle skip has occurred when the flow velocity calculated for each depth d1 to d4 deviates from the previous value by a predetermined value or more. The flow rate value V2 calculated based on the frequency shift Δf corresponding to the Doppler frequency in which the cycle skip determination unit 137 has determined that a cycle skip has occurred is treated as a flow rate value with low stability. For example, in pulse Doppler mode, where the flow rate value V2 is output to the display unit 30, the second calculation unit 136 outputs the flow rate value calculated based on the previous measurement as the flow rate value V2 to the display unit 30, rather than the flow rate value V2 with low stability that was determined to have caused a cycle skip. Also, in hybrid mode, the flow rate value synthesis unit 139 reduces the synthesis ratio of the flow rate value V2 with low stability that was determined to have caused a cycle skip.

[0072] Furthermore, the second calculation unit 136 may be configured to correct the flow rate value V2 if it is determined that a cycle skip has occurred. For example, the second calculation unit 136 may correct the flow rate value to the value it would be when no cycle skip occurs. This correction may be made by adding a correction value determined to correspond to the ultrasonic frequency, or by multiplying it by a correction rate determined to correspond to the ultrasonic frequency.

[0073] The microbubble detection unit 138 detects the density of microbubbles contained in the fluid based on predetermined indicators. The detection period can be set by the user by inputting information into the operation unit 35 in Figure 2. The indicators for detecting the microbubble density include, for example, the intensity or width of the Doppler signal detected at each depth in the pipe P. The storage unit 131 also stores in advance a table showing the relationship between the microbubble density detected by the microbubble detection unit 138 and the correction value.

[0074] The horizontal axis in Figure 9 represents frequency. The vertical axis in Figure 9 represents the intensity of the detected Doppler signal. In the example in Figure 9, we consider the Doppler signal detected at time t4. In this case, the Doppler signal s4 is received for the ultrasound reflected by the microbubbles flowing at depth d4 in Figure 7 (see Figure 8).

[0075] However, when the density of microbubbles is high, the attenuation of ultrasound increases, so the intensity of the Doppler signal for ultrasound from microbubbles flowing at a depth d4 decreases. Also, the amount of ultrasound reflected from microbubbles flowing at a depth shallower than d4 increases. Here, when ultrasound is diffusely reflected by microbubbles flowing at a depth shallower than d4, the diffusely reflected ultrasound reaches the ultrasonic element 15 with a delay compared to when it is directly reflected. The signal for ultrasound that has been diffusely reflected and reaches the ultrasonic element 15 in this way is called a false signal.

[0076] When diffusely reflected ultrasonic waves reach the same time t4 as the ultrasonic waves reflected by microbubbles flowing at depth d4, a Doppler signal is detected that is a combination of the Doppler signal s4 that should be detected and the false signals. In the example in Figure 9, the Doppler signal s4 and the false signals sa~sd overlap, resulting in the detection of a Doppler signal s4' that is larger and thicker than the Doppler signal s4. For ease of visualization, the false signals sa~sd are shown by thin dotted lines, thin dashed lines, thick dotted lines, and thick dashed lines, respectively. The Doppler signals s4 and s4' are shown by thin solid lines and thick solid lines, respectively.

[0077] In this case, the Doppler frequency corresponding to the depth d4 is measured based on the Doppler signal s4' rather than the Doppler signal s4. Using the Doppler frequency measured in this way will result in a lower average fluid velocity than the original value. Consequently, the calculated fluid flow rate will also be lower than the original value. As a result, the accuracy of the flow rate calculation will decrease.

[0078] To prevent such a decrease in accuracy, the memory unit 131 stores a table showing the relationship between the correction amount of the flow rate value calculated based on the false signal and the density of microbubbles detected by the microbubble detection unit 138. The second calculation unit 136 corrects the flow rate value based on the density of microbubbles and the table stored in the memory unit 131.

[0079] Returning to Figure 3, the control unit 13 has a flow rate value synthesis unit 139. In hybrid mode, the flow rate value synthesis unit 139 synthesizes the flow rate value V1 and the flow rate value V2 at a predetermined ratio. In the hybrid mode of this embodiment, the period during which the first measurement unit 132 operates to calculate the flow rate value V1 and the period during which the second measurement unit 135 operates to calculate the flow rate value V2 are both 150 ms, and measurements by the first measurement unit 132 and measurements by the second measurement unit 135 are performed alternately. The flow rate value synthesis unit 139 synthesizes the flow rate value V1 and the flow rate value V2 and outputs the result of the synthesis as the flow rate value V4 to the display unit 30. In this embodiment, the operating period of the first measurement unit 132 and the operating period of the second measurement unit 135 are both 150 ms, but the embodiment is not limited to this. The operating period of the first measurement unit 132 or the operating period of the second measurement unit 135 may be shorter than 150 ms or longer than 150 ms. Furthermore, the operating periods of the first measuring unit 132 and the second measuring unit 135 may be of different lengths.

[0080] Figure 10 shows the fluid flow rates calculated using the time difference propagation method and the pulsed Doppler method. The horizontal axis of Figure 10 represents the density of microbubbles contained in the fluid. The vertical axis of Figure 10 represents the relative value of the calculated flow rate to the actual fluid flow rate. The flow rate measured using the time difference propagation method is shown by a thick solid line, and the flow rate measured using the pulsed Doppler method is shown by a thin solid line.

[0081] As shown in Figure 10, in the propagation time difference method, 100% of the flow rate can be calculated when the microbubble density is relatively low. However, when the microbubble density is relatively high, the flow rate cannot be calculated. On the other hand, in the pulsed Doppler method, a flow rate close to 100% can be calculated when the microbubble density is relatively high. In particular, the flow rate can be calculated with relatively high accuracy when the microbubble density is between value v1 and value v2, which is higher than value v1.

[0082] Therefore, in hybrid mode, the flow rate value synthesis unit 139 synthesizes the flow rate value V1 calculated by the propagation time difference method and the flow rate value V2 calculated by the pulse Doppler method at a predetermined ratio based on the stability of the flow rate calculation, and outputs the synthesized flow rate value V4 to the display unit 30 as the calculated flow rate value. Accordingly, in hybrid mode, the switching signal is generated based on the synthesized flow rate value V4, and the indicator light 37 lights up or blinks based on the synthesized flow rate value V4. The stability of the flow rate calculation is, for example, the intensity of the detected Doppler signal. In addition, the flow rate value V2 calculated by the second calculation unit 136 based on the measured value in which a cycle skip is determined to have occurred is treated as a flow rate value with low stability of flow rate calculation. (3) Calculation of flow rate using the propagation time difference method Let's explain equations (1) and (2).

[0083] In the conventional propagation time difference method, the flow rate value V3 has been calculated using the following equation (3).

[0084]

number

[0085] Compared to equation (1), equation (3) differs in the terms enclosed in boxes. In equation (3), C is the fluid sound velocity, which indicates the speed of ultrasonic waves in the fluid, and θ is the angle of incidence of ultrasonic waves into the fluid. Velocity C corresponds to the speed of ultrasonic waves in the fluid. Since the angle of incidence θ is known, it is stored in the memory unit 131 like other known values, but velocity C is a value that fluctuates depending on the material of the fluid and the temperature of the fluid, and therefore it is a parameter that requires input by the user. Accordingly, in calculating the flow rate value V3 using equation (3), the parameters velocity C and inner diameter d, which are input by the user, are referenced. Therefore, if the velocity C parameter differs from the actual value, or if the inner diameter d parameter differs from the actual value, the flow rate value V3 will also deviate from the actual flow rate. In equation (3), the flow rate value V3 is proportional to velocity C and inner diameter d, so the difference between the flow rate value V3 and the actual flow rate is proportional to the difference between the input velocity C and the actual value, and the difference between the input inner diameter d and the actual value.

[0086] While equation (3) is used to calculate the flow rate value V3, in the pulsed Doppler method, the flow rate value V2 is calculated using equation (2) above. Equation (2) includes the inner diameter d as a parameter input by the user. Therefore, in calculating the flow rate value V2 using equation (2), the inner diameter d, which is a parameter input by the user, is referenced. Consequently, if the inner diameter d parameter differs from the actual value, the flow rate value V2 will also deviate from the actual flow rate. In equation (2), the flow rate value V2 is proportional to the square of the inner diameter d, so the difference between the flow rate value V3 and the actual flow rate is proportional to the square of the difference between the inner diameter d parameter and the actual value.

[0087] The relationship between the flow rate value V3 and the parameters in equation (3) is different from the relationship between the flow rate value V2 and the parameters in equation (2). For example, if there is a difference between the inner diameter parameter d and the actual value, the flow rate value V3 deviates from the actual flow rate in proportion to that difference, while the flow rate value V2 deviates from the actual flow rate in proportion to the square of that difference. For this reason, even if the inner diameter parameter d is not changed when calculating the flow rate value V3 and the flow rate value V2, and the actual flow rate is the same, a difference is likely to occur between the flow rate value V2 and the flow rate value V3. Similarly, if there is a difference between the velocity parameter C and the actual value, the flow rate value V3 deviates from the actual flow rate in proportion to that difference in velocity C, while the flow rate value V2 does not deviate from the actual flow rate due to the difference in velocity C. Therefore, even if the parameters are not changed when calculating the flow rate value V2 and the flow rate value V3, and the actual flow rate is the same, a difference is likely to occur between the flow rate value V3 and the flow rate value V2. In a configuration that allows for the calculation of flow rates using the propagation time difference method with the conventional equation (3) and the pulse Doppler method with equation (2), there was a problem in that when the flow rate calculation method was switched, the flow rate would fluctuate rapidly due to the difference between flow rate value V3 and flow rate value V2.

[0088] In particular, in a configuration like this embodiment, where the flow rate value is calculated alternately using the propagation time difference method and the pulse Doppler method, and a combined flow rate value is output, there is a risk that the output flow rate value may change according to the combined ratio of the flow rates, even if the actual flow rate does not change. Furthermore, a change in the output flow rate value may cause the switching signal, which is the result of comparing with a threshold, to change, even if the actual flow rate does not change.

[0089] In particular, it is difficult to use measured values ​​as the velocity C included in equation (1). This velocity C is the speed of sound when the fluid velocity is 0, and it is a value that fluctuates with changes in the fluid temperature. Therefore, in order to actually measure velocity C and improve the accuracy of the velocity C parameter, the user would need to measure the speed of sound with the fluid flowing through pipe P stopped and at the same temperature as when it flows through pipe P, which is extremely difficult.

[0090] Therefore, in calculating the flow rate value using the propagation time difference method in this embodiment, the fluid propagation time T, which is determined based on the propagation time ta measured by the first measuring unit 132, is used as a measured value related to velocity C to calculate the flow rate value. Since equation (1) is an equation in which velocity C in equation (3) is determined based on the fluid propagation time T, the flow rate value V1 is the flow rate value calculated using the fluid propagation time T as a measured value related to velocity C. According to equation (1), the flow rate value V1 is calculated based on the propagation time difference Δt measured by the first measuring unit 132 and the fluid propagation time T determined by the propagation time determination unit 133 based on the propagation time ta, so the velocity C parameter is not referenced.

[0091] We will now explain in detail how to determine the velocity C included in equation (3) using the fluid propagation time T. First, the velocity C input to the user in equation (3) is the speed of sound when the fluid velocity is 0. In the propagation time difference method, the speed of sound in the fluid is affected by the fluid velocity, and the fluid velocity and flow rate are calculated by measuring the difference between the propagation time when ultrasonic waves propagate along the direction of fluid flow and the propagation time when ultrasonic waves propagate against the direction of fluid flow. At this time, since the difference between velocity C and the speed of sound in the fluid affected by the fluid velocity is small, even if the flow rate is calculated using the speed of sound in the fluid affected by the fluid velocity instead of velocity C, a value close to the flow rate calculated using velocity C will be obtained.

[0092] In this embodiment, the velocity Ca of the ultrasonic signal transmitted from ultrasonic element 15A to ultrasonic element 15B in the fluid during measurement by the first measuring unit 132 is treated as a value approximating the velocity C. Here, velocity Ca is calculated based on the correspondence between the length of the path, the propagation time of the ultrasonic waves in the path, and the propagation speed of the ultrasonic waves in the path. The path corresponding to velocity Ca is the path in the fluid within the pipe P through which the ultrasonic signal is propagated from the first ultrasonic element 15A to the second ultrasonic element 15B, and is therefore expressed as 2d / cosθ. The propagation time corresponding to velocity Ca is the fluid propagation time τ4, which is determined as the fluid propagation time T by the propagation time determination unit 133 based on the propagation time ta measured by the first measuring unit 132. For this reason, in this embodiment, in addition to the first measuring unit 132 that measures the propagation time difference Δt, a propagation time determination unit 133 is provided that determines the fluid propagation time τ4 based on the propagation time ta measured by the first measuring unit 132. Velocity Ca is calculated based on the relationship between the length of the path, the propagation time of the path, and the propagation velocity of the path. Therefore, velocity Ca is the value obtained by dividing the corresponding path length 2d / cosθ by the fluid propagation time T. In this embodiment, velocity Ca is a value that replaces velocity C. Accordingly, velocity C in equation (3) is replaced by velocity Ca, that is, the value obtained by dividing 2d / cosθ by T, and equation (3) is transformed into equation (1). Here, the fluid propagation time T is a measured value because it is a value determined based on the propagation time ta measured by the first measuring unit 132. Therefore, calculating the flow rate using equation (1) means calculating the flow rate using the fluid propagation time T as a measured value related to velocity C. Furthermore, equation (1) can be said to be an equation in which velocity C in equation (3) is determined by the fluid propagation time T as a measured value.

[0093] As shown in equation (1), the flow rate value V1 calculated by equation (1) is calculated from measured values ​​except for the inner diameter d, and is proportional to the square of the inner diameter d. The flow rate value V2 calculated by equation (2) is also calculated from measured values ​​except for the inner diameter d, and is proportional to the square of the inner diameter d. For this reason, both the flow rate value V1 and the flow rate value V2 fluctuate similarly according to the error in the inner diameter d parameter. Therefore, when the inner diameter d parameter when the flow rate value V1 is calculated and the inner diameter d parameter when the flow rate value V2 is calculated are the same, and the actual flow rate is the same, it is unlikely that there will be a difference between the flow rate value V1 and the flow rate value V2. For this reason, in a configuration that allows for the calculation of flow rate values ​​using both the propagation time difference method and the pulse Doppler method, the fluctuation of the flow rate value when switching between methods can be reduced.

[0094] Furthermore, it is preferable that the fluid propagation time T, which is a measured value related to velocity C, is the value obtained by dividing 2d / cosθ, which is the path length of the ultrasonic waves in the fluid, by a velocity that approximates velocity C, that is, a value that approximates the time it takes for an ultrasonic signal propagating at velocity C to propagate along the path length of the ultrasonic waves in the fluid. When such a value is used as the measured value related to velocity C, equation (3) is converted into a calculation formula in which the calculated flow rate value is proportional to the square of the inner diameter d, as in equation (1), and the relationship between the flow rate value and the inner diameter d becomes the same as in equation (2) of the pulsed Doppler method. Therefore, fluctuations in the flow rate value due to parameter errors when switching between calculation by the propagation time difference method and calculation by the pulsed Doppler method can be reduced.

[0095] The fluid propagation time T may be calculated not only by subtracting the wedge propagation time τ1, couplant propagation time τ2, and pipe propagation time τ3 from the propagation time ta, but also by subtracting the wedge propagation time τ1, couplant propagation time τ2, and pipe propagation time τ3 from the propagation time tb. Alternatively, the value obtained by subtracting the wedge propagation time τ1, couplant propagation time τ2, and pipe propagation time τ3 from the average value of propagation time ta and propagation time tb may be used.

[0096] (3) Flow rate calculation process Figures 11 and 12 are flowcharts showing an example of an algorithm for the flow rate calculation process executed in hybrid mode by the control unit 13 in Figure 3. The flow rate calculation process in hybrid mode will be explained below using the control unit 13 in Figure 3 and the flowcharts in Figures 11 and 12.

[0097] In the flowchart shown in Figure 11, the flow rate value V1 is calculated using the propagation time difference method. First, the first measuring unit 132 controls the ultrasonic element 15A to transmit an ultrasonic signal and controls the ultrasonic element 15B to receive the ultrasonic signal transmitted from ultrasonic element 15A (step S1). Next, the first measuring unit 132 measures the propagation time ta of the ultrasonic signal from ultrasonic element 15A to ultrasonic element 15B in step S1 (step S2).

[0098] Subsequently, the first measuring unit 132 controls the ultrasonic element 15B to transmit an ultrasonic signal and controls the ultrasonic element 15A to receive an ultrasonic signal (step S3). Next, the first measuring unit 132 measures the propagation time tb of the ultrasonic signal from the ultrasonic element 15B to the ultrasonic element 15A in step S3 (step S4). Steps S1, S2 and steps S3, S4 may be performed in any order.

[0099] Next, the first measuring unit 132 measures the propagation time difference Δt based on the propagation times measured in steps S2 and S4 (step S5). The propagation time identification unit 133 identifies the fluid propagation time τ4 based on the propagation time ta measured in step S2 (step S6). Furthermore, the first calculation unit 134 calculates the flow rate value V1 of the fluid flowing through the pipe P based on the propagation time difference Δt calculated in step S5, the fluid propagation time τ4 identified in step S6 as the fluid propagation time T, and equation (1) (step S7). Steps S1 to S7 correspond to the processing in the propagation time difference method.

[0100] After step S7, the second measuring unit 135 controls the ultrasonic element 15B to sequentially transmit and receive pulsed ultrasonic signals (step S8). Next, the second measuring unit 135 measures the frequency shift Δf, which is the difference between the frequency of the ultrasonic signal transmitted in step S8 and the Doppler frequency of the received ultrasonic signal (step S9). The second calculation unit 136 then calculates the fluid velocity flowing through the pipe P based on the frequency shift Δf measured in step S9 and equation (2) (step S10).

[0101] The cycle skip determination unit 137 determines whether or not a cycle skip has occurred based on the frequency shift corresponding to each depth d1 to d4 (step S11). If it is determined that no cycle skip has occurred, the process in step S13 is performed. If it is determined that a cycle skip has occurred, the flow rate value V2 output as a pulse Doppler flow rate value, that is, the flow rate value V2 corrected in step S15 described later, is treated as a flow rate value with low stability (step S12). The second calculation unit 136 averages the flow velocity in the pipe P based on the flow velocity distribution identified based on the flow velocity at each depth d1 to d4, and calculates the flow rate based on the averaged flow velocity. That is, in steps S10 and S13, the flow rate value corresponding to equation (2) is calculated.

[0102] The microbubble detection unit 138 detects the density of microbubbles contained in the fluid at a set period (step S14). Step S14 may be executed in parallel with steps S8 to S10, or it may be executed before step S11. The second calculation unit 136 corrects the flow rate value V2 calculated in step S13 based on the microbubble density detected in step S14 and a predetermined table (step S15). Steps S8 to S15 correspond to processing in the pulse Doppler method. In hybrid mode, steps S1 to S7 and steps S8 to S15 may be executed in any order.

[0103] In this embodiment, the determination of whether or not a cycle skip has occurred in step S11, and the detection of the density of microbubbles contained in the fluid in step S14, are both processes to further improve the accuracy of the flow rate calculated using the pulsed Doppler method. Therefore, the processes in steps S11 and S14 are not limited to the processing order shown in Figure 12, as long as they can be reflected in the flow rate calculated using the pulsed Doppler method.

[0104] After step S15, the flow rate value synthesis unit 139 determines the synthesis ratio of the flow rate value V1 calculated in step S7 and the flow rate value V2 calculated in step S15 based on the stability of the flow rate calculation, such as the intensity of the Doppler signal detected in step S8 (step S16). Subsequently, the flow rate value synthesis unit 139 calculates the flow rate value V4 of the fluid flowing through pipe P by synthesizing the flow rate value V1 calculated in step S7 and the flow rate value V2 corrected in step S15 at the synthesis ratio determined in step S16 (step S17). After that, the calculation unit 2 outputs the flow rate value V4 calculated in step S17 to the control unit 33 of the display unit 30 (step S18), and returns to step S1. The control unit 33 of the display unit 30 compares the flow rate output by the algorithm shown in Figures 11 and 12 with a predetermined threshold value and generates a switching signal.

[0105] In the propagation time difference mode, steps S1 to S7 are executed, and in step S18, the flow rate value V1 calculated in step S7 is output to the display unit 30. The control unit 33 of the display unit 30 compares the flow rate value V1 calculated in step S7 with a predetermined threshold. In this embodiment, the flow rate value V1 is calculated by equation (1) in all propagation time difference modes, but in the propagation time difference mode, the flow rate value V3 may be calculated by equation (3). In this case, steps S1 to S5 are executed, and step S6 is not executed.

[0106] On the other hand, in pulse Doppler mode, steps S1 to S7, S16, and S17 are not executed, and steps S8 to S15 are executed first, followed by step S18, in which the flow rate value V2 calculated in step S15 is output to the display unit 30. The control unit 33 of the display unit 30 compares the flow rate value V2 corrected in step S15 with a predetermined threshold value.

[0107] (4) Effects In the ultrasonic flow sensor 100 according to this embodiment, ultrasonic signals are transmitted and received by ultrasonic element 15A. Ultrasonic signals are also transmitted and received by ultrasonic element 15B. In the propagation time difference method, the flow rate of the fluid flowing through the pipe P is calculated by the first calculation unit 134 based on the propagation time difference of the ultrasonic signals between ultrasonic element 15A and ultrasonic element 15B. In the pulsed Doppler method, the flow rate of the fluid flowing through the pipe P is calculated by the second calculation unit 136 based on the frequency shift of the ultrasonic signal received by ultrasonic element 15B when ultrasonic element 15B transmits a pulsed ultrasonic signal.

[0108] In the propagation time difference method, the flow rate is calculated using equation (1), in which a value corresponding to the ultrasonic velocity in the fluid is determined by measurement, such that the relationship between the flow rate and the value included in the calculation formula and input by the user is the same as the relationship between the flow rate and the value included in the calculation formula and input by the user.

[0109] The known calculation formula (3) used for calculating flow rate using the propagation time difference method and the known calculation formula (2) used for calculating flow rate using the pulse Doppler method use different reference input values, resulting in different degrees of dependence of the user-input values ​​on the calculated flow rate between the two formulas. However, with this configuration, the parameter corresponding to the ultrasonic velocity in the fluid is determined based on the value measured by the sensor head 10, so the degree of dependence of the user-input values ​​on the calculated flow rate becomes the same between the two formulas. As a result, when the flow rate of the fluid flowing through pipe P is the same and the parameters set by the user are the same, there is less likely to be a difference between the flow rate calculated using the propagation time difference method and the flow rate calculated using the pulse Doppler method. Therefore, when the parameters are the same and the flow rate flowing through pipe P does not change, the possibility of discontinuous fluctuations in the calculated flow rate is reduced. This improves the practicality of the ultrasonic flow sensor 100.

[0110] Furthermore, in hybrid mode, the flow rate value synthesis unit 139 determines the composite ratio of the time-difference flow rate and the pulsed Doppler flow rate based on the stability of the flow rate calculation. The fluid flow rate is then calculated by the calculation unit 2 by combining the time-difference flow rate value V1 and the pulsed Doppler flow rate value V2 based on the determined composite ratio. In this case, it becomes easier to accurately measure the fluid flow rate regardless of the density of microbubbles contained in the fluid. Additionally, the flow rate can be corrected by the calculation unit 2 based on parameters such as the outer diameter of the pipe P or the kinematic viscosity of the fluid. In this case, the fluid flow rate can be measured even more accurately.

[0111] Furthermore, the control unit 33 of the display unit 30 generates a switching signal indicating either that the flow rate is above a predetermined threshold or below a predetermined threshold. In this case, the ultrasonic flow sensor 100 operates as a flow switch. Here, in a practical flow switch, it is required to calculate the actual flow rate with high reproducibility rather than calculating the actual flow rate with absolute accuracy. Therefore, in hybrid mode, the ultrasonic flow sensor 100 can be operated as a practical flow switch.

[0112] (5) Other embodiments (a) In the above embodiment, the flow rate is calculated by multiplying the flow velocity by the cross-sectional area of ​​the pipe P, so the inner diameter d of the pipe P is referenced when calculating the flow rate. In particular, in the above embodiment, the dimensions of the pipe P to which the sensor head 10 is attached are not limited to a single specific dimension, so the inner diameter d of the pipe P needs to be input by the user. Also, in the above embodiment, since it is attached from outside the pipe P, unlike a flow sensor that includes a part that constitutes a portion of the pipe P, the inner diameter d of the pipe P needs to be input by the user. For this reason, in the above embodiment, equation (1) was used in which the effects of deviations in the velocity C parameter are eliminated, and sound velocity-related values ​​are applied so that all flow rates deviate similarly with respect to deviations in the inner diameter d parameter. In contrast, in ultrasonic flow sensors that can only be attached to a specific diameter by design, or ultrasonic flow sensors that include a part of the pipe through which the fluid flows, the inner diameter d is a predetermined value and does not require user input. In these configurations as well, in order to prevent the flow rate of the propagation time difference method and the flow rate of the pulse Doppler method from diverging due to a discrepancy in the input velocity C, equation (1), in which the velocity C is determined based on measured values, may be used.

[0113] (b) In the above embodiment, regardless of whether it is hybrid mode or propagation time difference mode, the fluid flow rate value V1 in the propagation time difference method is calculated by equation (1) instead of equation (3), but the embodiment is not limited to this. Equation (1) may be applied only in hybrid mode, and in propagation time difference mode, the flow rate value V3 calculated by equation (3) may be output. Alternatively, the fluid flow rate value V in the pulse Doppler method may be calculated by the following equation (4) instead of equation (2). Here, T is the fluid propagation time as described above and is determined based on actual measurements.

[0114]

number

[0115] In this case, the pulse Doppler method's flow rate is calculated using equation (4), which is an equation in which the value included in equation (2) is determined based on measured values, so that the relationship between the flow rate and the value included in equation (3) and input by the user is the same as the relationship between the flow rate and the value included in equation (2). Specifically, the flow rate value V calculated using the pulse Doppler method in equation (4) is proportional to the velocity C and also proportional to the inner diameter d of the pipe P, similar to the flow rate value V calculated using the propagation time difference method in equation (3). In other words, the degree of dependence of the value input by the user on the calculated flow rate value V is made the same for both the propagation time difference method and the pulse Doppler method. Therefore, the possibility of a large discrepancy between the flow rate value V calculated using the pulse Doppler method and the flow rate value V calculated using the propagation time difference method due to deviations between the value input by the user and the actual value is reduced.

[0116] (c) In the above embodiment, in hybrid mode, flow rate calculation using the propagation time difference method and pulse Doppler method flow rate calculation are performed at predetermined time intervals, and a value obtained by combining the calculated flow rates is output. However, the configuration may switch the flow rate calculation method to be performed depending on the stability. For example, when the amount of microbubbles is small, a flow rate value using the propagation time difference method is output, and when the amount of microbubbles is large, a flow rate value obtained by combining the flow rate value using the propagation time difference method and the flow rate value using the pulse Doppler method is output.

[0117] (d) In the above embodiment, the fluid flow rate in the pulse Doppler method is calculated based on the average value of the velocity distribution of the fluid flowing through the pipe P, but the embodiment is not limited thereto. The fluid flow rate in the pulse Doppler method may be calculated based on a representative value other than the average value, such as the median, which is determined by the velocity distribution of the fluid flowing through the pipe P.

[0118] (e) In the above embodiment, the ultrasonic element 15A and the ultrasonic element 15B are arranged above the pipe P and aligned along the direction in which the pipe P extends, but the embodiment is not limited to this. The ultrasonic element 15A and the ultrasonic element 15B may be arranged opposite each other with the pipe P in between. That is, one ultrasonic element may be arranged above the pipe P and the other ultrasonic element may be arranged below the pipe P.

[0119] (6) Correspondence between each component of the claim and each part of the embodiment The following describes examples of the correspondence between each component of the claims and each part of the embodiments, but the present invention is not limited to the following examples. Various other elements having the configuration or function described in the claims can also be used as each component of the claims.

[0120] In the above embodiment, piping P is an example of piping, ultrasonic flow sensor 100 is an example of an ultrasonic flow sensor, and ultrasonic elements 15B and 15A are examples of first and second ultrasonic elements, respectively. The first measuring unit 132 is an example of a first measuring unit, the propagation time specification unit 133 is an example of a propagation time specification unit, the first calculation unit 134 is an example of a first calculation unit, the second measuring unit 135 is an example of a second measuring unit, and the second calculation unit 136 is an example of a second calculation unit. The wedge material 14 or acoustic couplant 16 is an example of a path member. The memory unit 131 is an example of a memory unit, the flow rate value synthesis unit 139 is an example of a flow rate value synthesis unit, the control unit 33 is an example of a control unit, the operation unit 35 is an example of an operation unit, and the indicator lights 18 and 37 are examples of indicator lights. [Explanation of Symbols]

[0121] 10...Sensor head, 11, 31...Housing, 12, 32...Connector, 13, 33...Control unit, 14, 14A, 14B...Wedge material, 14a...Element coupling surface, 14b...Pipe coupling surface, 15, 15A, 15B...Ultrasonic element, 16...Acoustic couplant, 17...Ultrasonic shielding plate, 20...Clamp section, 21...Upper clamp member, 22...Lower clamp member, 23...Clamp fixing screw, 30...Display unit, 34...Memory element, 35...Operation unit, 36...Display 37...Indicator light, 38, 39...Connection port, 40...Power supply circuit, 100...Ultrasonic flow sensor, 101...Sensor fixing screw, 131...Memory unit, 132...First measurement unit, 133...Propagation time determination unit, 134...First calculation unit, 135...Second measurement unit, 136...Second calculation unit, 137...Cycle skip determination unit, 138...Microbubble detection unit, 139...Flow rate value synthesis unit, P...Piping, s1~s4, s4'...Doppler signal, sa~sd...False signal

Claims

1. A plurality of ultrasonic elements that transmit and receive ultrasonic signals, A first measuring unit measures the propagation time of an ultrasonic signal and the difference in the propagation time of an ultrasonic signal by transmitting and receiving ultrasonic signals that penetrate the fluid inside the pipe between a pair of ultrasonic elements from among the plurality of ultrasonic elements. A propagation time determination unit that determines the fluid propagation time, which is the time it takes for an ultrasonic signal to propagate along a path through the fluid inside a pipe, based on the propagation time of the ultrasonic signal measured by the first measurement unit, A first calculation unit calculates a first flow rate value of the fluid in the pipe based on the propagation time difference of the ultrasonic signal measured by the first measurement unit, a measured value corresponding to the ultrasonic velocity in the fluid in the pipe, and the square of a parameter for determining the inner diameter of the pipe. A second measuring unit measures the frequency shift of an ultrasonic signal by transmitting an ultrasonic signal to the fluid inside a pipe and receiving an ultrasonic signal reflected in the fluid, using one or a pair of ultrasonic elements from among the plurality of ultrasonic elements. The system includes a second calculation unit that calculates a second flow rate value of the fluid in the piping based on the frequency shift of the ultrasonic signal measured by the second measurement unit and the square of the parameter, When the first calculation unit calculates a first flow rate value and the second calculation unit calculates a second flow rate value, the flow rate value is determined using at least one of the first flow rate value and the second flow rate value based on the stability of the flow rate calculation. The first calculation unit calculates a first flow rate value using the fluid propagation time as the measured value, according to the correspondence between the distance of the path, the fluid propagation time, and the ultrasonic velocity, in an ultrasonic flow sensor.

2. A plurality of ultrasonic elements that transmit and receive ultrasonic signals, A first measuring unit measures the propagation time of an ultrasonic signal and the difference in the propagation time of an ultrasonic signal by transmitting and receiving ultrasonic signals that penetrate the fluid inside the pipe between a pair of ultrasonic elements from among the plurality of ultrasonic elements. A propagation time determination unit that determines the fluid propagation time, which is the time it takes for an ultrasonic signal to propagate along a path through the fluid inside a pipe, based on the propagation time of the ultrasonic signal measured by the first measurement unit, A first calculation unit calculates a first flow rate value of the fluid in the pipe based on the propagation time difference of the ultrasonic signal measured by the first measurement unit, a measured value corresponding to the ultrasonic velocity in the fluid in the pipe, and a parameter for identifying the inner diameter of the pipe. A second measuring unit measures the frequency shift of an ultrasonic signal by transmitting an ultrasonic signal to the fluid inside a pipe and receiving an ultrasonic signal reflected in the fluid, using one or a pair of ultrasonic elements from among the plurality of ultrasonic elements. The system includes a second calculation unit that calculates a second flow rate value of the fluid in the piping based on the frequency shift of the ultrasonic signal measured by the second measurement unit and the parameters, When the first calculation unit calculates a first flow rate value and the second calculation unit calculates a second flow rate value, the flow rate value is determined using at least one of the first flow rate value and the second flow rate value based on the stability of the flow rate calculation. The first calculation unit calculates the first flow rate value using the fluid propagation time as the measured value, such that the difference in influence of the parameter on the first flow rate value and the second flow rate value is small.

3. A path member located between the plurality of ultrasonic elements and the piping, which constitutes a part of the ultrasonic transmission path, The system includes a storage unit that pre-stores information related to the speed of ultrasonic signals in the aforementioned path member, The ultrasonic flow sensor according to claim 1 or 2, wherein the propagation time determination unit determines the fluid propagation time based on the propagation time measured by the first measurement unit and information related to the velocity of the ultrasonic signal in the path member stored in the storage unit.

4. The ultrasonic flow sensor according to claim 3, wherein the propagation time determination unit determines the fluid propagation time based on information related to the speed of ultrasonic waves in the piping.

5. The ultrasonic flow sensor according to claim 4, wherein the propagation time determination unit determines the fluid propagation time based on information relating to the velocity of ultrasonic waves in the pipe, which is determined based on at least one of the material of the pipe and the thickness of the pipe.

6. The first measuring unit measures the propagation time of the ultrasonic signal, specifically the propagation time of the ultrasonic signal propagating along the direction of fluid flow in the pipe and the propagation time of the ultrasonic signal propagating against the direction of fluid flow in the pipe. The ultrasonic flow sensor according to any one of claims 1 to 5, wherein the propagation time determination unit determines the fluid propagation time based on the average time of the propagation time of an ultrasonic signal propagating along the direction of fluid flow in the pipe and the propagation time of an ultrasonic signal propagating in the opposite direction of fluid flow in the pipe.

7. It is equipped with an operating unit that accepts user input, The ultrasonic flow sensor according to claim 1 or 3, wherein the operating unit selects a mode in which a first flow rate value is output as a flow rate value and a mode in which a second flow rate value is output as a flow rate value based on the user's operation received by the operating unit.

8. The ultrasonic flow sensor according to any one of claims 1 to 7, further comprising a flow rate value synthesis unit that synthesizes the first flow rate value and the second flow rate value and outputs the synthesized flow rate value.

9. The ultrasonic flow sensor according to claim 8, wherein the flow rate value synthesis unit synthesizes the first flow rate value and the second flow rate value based on the stability of the flow rate calculation.

10. The ultrasonic flow sensor according to any one of claims 7 to 9, further comprising a control unit that generates a switching signal indicating either that the output flow rate value is greater than or equal to a predetermined threshold or that it is less than the predetermined threshold.

11. The ultrasonic flow sensor according to claim 10, further comprising an operation unit for receiving the setting of a predetermined threshold.

12. The ultrasonic flow sensor according to claim 10 or 11, further comprising an indicator light that displays the result of comparing the output flow rate value with the predetermined threshold value.

13. The ultrasonic flow sensor according to any one of claims 10 to 12, wherein the first calculation unit or the second calculation unit corrects the output flow rate value based on predetermined parameters set.

14. An ultrasonic flow sensor for measuring the flow rate of fluid flowing inside a pipe, A first ultrasonic element that transmits and receives ultrasonic waves, A second ultrasonic element that transmits and receives ultrasonic waves, A first calculation unit calculates a first flow rate value indicating the flow rate of the fluid based on the difference in ultrasonic wave propagation time between the first ultrasonic element and the second ultrasonic element, The system includes a second calculation unit that calculates a second flow rate value indicating the flow rate of the fluid based on the frequency shift of the ultrasonic waves received by the first ultrasonic element when the first ultrasonic element transmits ultrasonic waves, When the first calculation unit calculates a first flow rate value and the second calculation unit calculates a second flow rate value, the flow rate value is determined using at least one of the first flow rate value and the second flow rate value based on the stability of the flow rate calculation. An ultrasonic flow sensor in which the first flow rate value and the second flow rate value are each calculated by the first calculation unit and the second calculation unit, respectively, using calculation formulas such that the correlation between the first flow rate value and the parameter included in the calculation formula for the first flow rate value and input by the user is the same, and the correlation between the second flow rate value and the parameter included in the calculation formula for the second flow rate value and input by the user is the same.

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