Frequency selection method for frequency-mixing ultrasonic flowmeters

Abstract

To provide a frequency selection method for a frequency-mixing ultrasonic flowmeter that can dynamically adapt to the measurement of flow velocity and flow rate of various liquids with different properties.SOLUTION: A first sensor and a second sensor are controlled to respectively transmit frequency-mixing wave signals in a pipe, and a first flow velocity of the liquid in the pipe is calculated based on a time-difference method, where the frequency-mixing wave signal includes three different frequencies. By controlling either the first sensor or the second sensor to transmit a waveform signal containing a fixed frequency in the pipe, a second flow velocity of the liquid in the pipe is calculated based on a Doppler method, and the intensity of the Doppler signal is determined. When the intensity of the Doppler signal is smaller than a first threshold, the first flow velocity is output. When the intensity of the Doppler signal is greater than a second threshold, the second flow velocity is output. When the intensity of the Doppler signal is between the first and second thresholds, it is determined, by referring to a table, whether to output the first or second flow velocity.SELECTED DRAWING: Figure 5

Description

[Technical Field]

[0001] This claim relates to an ultrasonic flow meter, and more particularly to a method for frequency selection in an ultrasonic flow meter. [Background technology]

[0002] Conventional ultrasonic flow meters use the Time of Flight (ToF) method to measure the flow velocity and volume of liquid in a pipe, and can also use the Pulsed Wave Doppler (PWD) method to measure the flow velocity and volume of liquid in a pipe. The difference between the two is that the Time of Flight (ToF) method uses the time difference between multiple received signals to perform measurements and is a time domain measurement method, while the Doppler method uses the difference in signal frequency to perform measurements and is a frequency domain measurement method.

[0003] Both the time difference method and the Doppler method can measure the flow velocity and flow rate of a liquid, but the time difference method is not suitable for all liquids that contain foreign matter (such as bubbles or particles) or are opaque. If the liquid in the pipe contains bubbles, particles, or is opaque, when using the time difference method with an ultrasonic flow meter to measure, the measured flow velocity and flow rate will be inaccurate. In contrast, the Doppler method can only measure accurately if the liquid contains a sufficient amount of bubbles. If the liquid in the pipe is free of bubbles and particles, when using the Doppler method with an ultrasonic flow meter to measure, the measured flow velocity and flow rate will also be inaccurate.

[0004] Liquid flowing through a pipe does not maintain the same state forever, so for example, bubble-free liquid in a pipe may suddenly start to produce bubbles after flowing for a certain period of time. If an ultrasonic flowmeter were to measure this pipe using a fixed time difference method, accurate measurement data would no longer be obtained after bubbles appeared.

[0005] In summary, conventional ultrasonic flow meters are in need of improvement because they are not dynamically adaptable to measuring the flow rate and volume of various liquids with different properties. Summary of the Invention [Problem to be solved by the invention]

[0006] This claim discloses a frequency selection method for a frequency-mixing ultrasonic flow meter, which can dynamically determine whether the time difference method or the Doppler method needs to be adopted based on real-time signal strength to calculate the liquid flow rate. [Means for solving the problem]

[0007] In an embodiment, the claimed frequency selection method for a frequency-mixing ultrasonic flowmeter is applied to an ultrasonic flowmeter having a first sensor, a second sensor, and a processing circuit, and includes the following steps: step a) controlling the first sensor and the second sensor by the processing circuit to emit frequency-mixing wave signals in a pipe, respectively, to measure time-of-flight (ToF) signals, and calculating a first flow velocity of the liquid in the pipe based on the time-of-flight method, wherein the frequency-mixing wave signals are complex waves sequentially including at least three different frequencies; step b) controlling one of the first sensor and the second sensor by the processing circuit to emit a waveform signal including a fixed frequency in the pipe, to measure a Doppler (Pulse Wave Doppler, PWD) signal, and calculating a second flow velocity of the liquid in the pipe based on the Doppler method; step c) outputting the first flow velocity calculated based on the ToF signal if the signal strength of the PWD signal is less than a first threshold. Step d) if the signal strength of the PWD signal is greater than a second threshold, output the second flow velocity calculated based on the PWD signal, where the second threshold is greater than the first threshold; and step e) if the signal strength of the PWD signal is between the first threshold and the second threshold, determine whether to output the first flow velocity or the second flow velocity by referring to an intensity correspondence table in the processing circuit. [Effects of the Invention]

[0008] Compared to the related art, the present invention can determine which measurement method needs to be adopted based on the current state of the liquid in the pipe to measure the flow rate, thereby obtaining more accurate and reliable measurement results. [Brief explanation of the drawings]

[0009] [Figure 1] FIG. 1 is a first schematic diagram of a sensor installation configuration. [Figure 2] FIG. 2 is a second schematic diagram of the sensor installation configuration. [Figure 3] 1 is a circuit block diagram of a specific embodiment of the frequency-mixing ultrasonic flowmeter of the present invention. [Figure 4] FIG. 10 is a signal transmission sequence diagram of a frequency mixed ultrasonic flowmeter. [Figure 5] 1 is a specific example of the frequency selection method of the present invention. [Figure 6A] FIG. 10 is a first sequence diagram of the measurement pattern of the present invention. [Figure 6B] FIG. 10 is a second sequence diagram of the measurement pattern of the present invention. [Figure 6C] FIG. 10 is a third sequence diagram of the measurement pattern of the present invention. [Figure 7A] 1 is a first example of a frequency mixing signal for ToF measurement according to the present invention. [Figure 7B] 10 is a second example of a frequency mixing wave signal for ToF measurement according to the present invention. [Figure 7C] 1 is a flowchart of the ToF measurement of the present invention. [Figure 8A] 1 is a specific example of a waveform signal including a fixed frequency for PWD measurement according to the present invention. [Figure 8B] 1 is a flowchart of the PWD measurement of this claim. DETAILED DESCRIPTION OF THE INVENTION

[0010] This claim discloses a frequency selection method for a frequency-mixing ultrasonic flow meter, which simultaneously uses the Time of Flight (ToF) method and the Pulsed Wave Doppler (PWD) method to measure the flow rate of the liquid, and determines which measurement method is suitable for the current state of the liquid in the pipe, and then dynamically uses the appropriate measurement method to measure the flow rate of the liquid, thereby obtaining more accurate and reliable measurement results.

[0011] Specifically, commonly used ultrasonic flow meters use the time difference method or the Doppler method to measure the flow velocity and volume of liquid in a pipe, but the application areas suitable for these two measurement methods are by no means the same. More specifically, the time difference method is more suitable for measuring the flow velocity of liquids without foreign matter (e.g., without bubbles or particles) (also called single-phase liquids), while the Doppler method is more suitable for measuring the flow velocity of liquids with foreign matter (e.g., with bubbles or particles) (also called multi-phase liquids). Because ultrasonic flow meters generally measure the flow velocity of a liquid and then calculate the volume of the liquid, the accuracy of the flow velocity measurement is extremely important to those skilled in the art.

[0012] To facilitate understanding of the present invention, the measurement principles of the time difference method and the Doppler method will now be explained.

[0013] Please refer to Figure 1. This is a first schematic diagram of a sensor installation configuration. In the embodiment of Figure 1, a liquid flows in a pipe 10 and has a flow direction 13 from left to right. A first sensor (transducer) 11 and a second sensor 12 of the ultrasonic flowmeter are installed at different positions on the same side of the outer wall of the pipe 10. The first sensor (transducer) 11 and the second sensor 12 each function as a transmitting end, capable of transmitting a signal of a specific frequency (i.e., an ultrasonic signal) into the pipe, and each function as a receiving end, capable of receiving an echo signal of the ultrasonic signal transmitted by the other sensor.

[0014] Specifically, the first sensor 11 and the second sensor 12 can be controlled to simultaneously emit signals 111 and 121 of the same frequency (e.g., 3 MHz). The signal 111 emitted by the first sensor 11 propagates through the pipe 10 and is received by the second sensor 12 after a certain time. Similarly, the signal 121 emitted by the second sensor 12 also propagates through the pipe 10 and is received by the first sensor 11 after a certain time. In the embodiment, the first sensor 11 and the second sensor 12 are controlled to function as transmitting ends to simultaneously emit the signals 111 and 121, and after emitting the signals 111 and 121, are controlled to switch to receiving ends and wait for an echo signal of the signals 111 and 121 emitted by the other sensor.

[0015] Although the direction of flow of the liquid and the propagation direction of the signal 111 emitted by the first sensor 11 are the same (for example, both are pointing to the right side of the pipe 10), they are opposite to the propagation direction of the signal 121 emitted by the second sensor 12, so the time at which the second sensor 12 receives the echo signal of the signal 111 is earlier than the time at which the first sensor 11 receives the echo signal of the signal 121. Based on the time difference between the time at which the second sensor 12 receives the echo signal and the time at which the first sensor 11 receives the echo signal, and taking into account the frequencies used for the emitted signals 111, 121 of the first sensor 11 and the second sensor 12, a processor (not shown) of the ultrasonic flowmeter can calculate the flow velocity of the liquid in the pipe 10.

[0016] It should be noted that the installation locations of the first sensor 11 and the second sensor 12 in FIG. 1 are merely one example of various installation configurations; that is, the two sensors 11 and 12 are installed on the same side of the outer wall of the pipe 10, spaced apart. In this manner, signals 111 and 121 are emitted into the pipe 10 by the sensors, reflected by the inner wall of the pipe 10, and reach the other sensor. In another embodiment, the first sensor 11 and the second sensor 12 may be installed on opposite sides of the outer wall of the pipe 10. In this embodiment, the signal 111 emitted by the first sensor 11 reaches the second sensor 12 directly through the liquid, without being reflected by the inner wall of the pipe 10 in between. Similarly, the signal 121 emitted by the second sensor 12 reaches the first sensor 11 directly through the liquid, without being reflected by the inner wall of the pipe 10 in between. Specifically, when the claimed multi-frequency ultrasonic flowmeter performs measurement using the time difference method, the installation locations of the two sensors on the pipe are not limited in any way.

[0017] Please refer to Figure 2, which shows a second schematic diagram of a sensor installation configuration. In the embodiment of Figure 2, a liquid flows in a pipe 10 and has a flow direction 13 from left to right. A single sensor (for example, a first sensor 11) of the ultrasonic flow meter is installed on one side of the outer wall of the pipe 10, and the first sensor 11 can emit an ultrasonic signal into the pipe 10 and receive an echo signal of the ultrasonic signal it has emitted.

[0018] Specifically, the first sensor 11 first transmits a signal 131 of a specific frequency (e.g., 3.33 MHz) into the pipe 10 as a transmitting end. If the liquid is a multiphase liquid containing foreign matter (air bubbles, oil droplets, sand and gravel, foreign solids, and other substances that do not dissolve in the liquid to be measured), the signal 131 is reflected when it comes into contact with the foreign matter, and the reflected echo signal is received by the first sensor 11, which has been switched to the receiving end.

[0019] The foreign matter is mixed in the liquid and flows through the pipe 10 along with the liquid. Because the volume of the foreign matter is extremely small (e.g., approximately 0.3 millimeters (mm) in diameter), the speed of the foreign matter's movement can be considered to match the flow velocity of the liquid. Based on the Doppler effect, the frequency of the signal 131 emitted by the first sensor 11 and the received echo signal forms a Doppler shift. Therefore, when the Doppler method is adopted, the ultrasonic flowmeter can calculate the flow velocity of the liquid in the pipe 10 based on the frequency shift (also called the frequency difference value) between the signal 131 emitted by the first sensor 11 and the received echo signal.

[0020] Under some circumstances, the state of the liquid in the pipe 10 may change as the liquid flows. If a user selects a first flow meter and combines it with the time difference method to measure the flow velocity of a single-phase liquid in the pipe, the flow velocity measured by the first flow meter will lose accuracy as foreign matter begins to appear in the liquid over time. Similarly, if a user selects a second flow meter and combines it with the Doppler method to measure the flow velocity of a multiphase liquid in the pipe, the flow velocity measured by the second flow meter will lose accuracy as foreign matter disappears over time. In light of this, the present claim describes a frequency-mixed ultrasonic flow meter and its frequency selection method that can dynamically switch between different measurement methods. Regardless of how the state of the liquid in the pipe changes (e.g., whether or not foreign matter is present), this frequency-mixed ultrasonic flow meter can accurately measure the flow velocity of the liquid by combining the following frequency selection method to select the optimal measurement method.

[0021] Please refer to Figure 3, which shows a circuit block diagram of a specific embodiment of the claimed mixed-frequency ultrasonic flowmeter. Figure 3 discloses the claimed mixed-frequency ultrasonic flowmeter (hereinafter referred to as "flowmeter 3" in the specification), which includes a first sensor 311, a second sensor 312, a switch 32, a signal emitting module 33, a signal receiving module 34, and a processing circuit 35. The first sensor 311 and the second sensor 312 are connected to the switch 32, which is connected to the signal emitting module 33, the signal receiving module 34, and the processing circuit 35, and the signal emitting module 33 and the signal receiving module 34 are connected to the processing circuit 35, respectively. The first sensor 311 and the second sensor 312 correspond to the first sensor 11 and the second sensor 12 in Figures 1 and 2 and are used to be installed on the outer wall of a pipe to be measured, thereby emitting ultrasonic signals toward the inside of the pipe and measuring the flow rate of the liquid in the pipe by a time difference method or a Doppler method.

[0022] When performing measurement using the time difference method (hereinafter referred to as "ToF measurement"), the processing circuit 35 issues a control signal to the switch 32, thereby switching the first sensor 311 and the second sensor 312 to the transmitting end of the ToF measurement. Furthermore, the processing circuit 35 controls the first sensor 311 and the second sensor 312 through the signal transmitting module 33 to simultaneously transmit frequency mixed wave signals (details will be described later). After transmitting the frequency mixed wave signals, the processing circuit 35 issues another control signal to the switch 32, thereby switching the first sensor 311 and the second sensor 312 to the receiving end of the ToF measurement. Furthermore, the processing circuit 35 controls the first sensor 311 and the second sensor 312 through the signal receiving module 34 to receive and respond to the echo signals of the frequency mixed wave signals transmitted by the other sensor. For example, the second sensor 312 receives the echo signal of the first frequency mixed wave signal transmitted by the first sensor 311, and the first sensor 311 receives the echo signal of the second frequency mixed wave signal transmitted by the second sensor 312.

[0023] In an embodiment, the processing circuit 35 calculates the flow velocity and the flow rate of the liquid in the pipe based on the time difference between the two echo signals received by the first sensor 311 and the second sensor 312, respectively.

[0024] When performing measurements using the Doppler method (hereinafter referred to as "PWD measurements"), the flow meter 3 only needs to use one of the first sensor 311 and the second sensor 312. For ease of understanding, the following description will be given taking the first sensor 311 as an example, but the same technical means can also be applied to the second sensor 312.

[0025] When performing PWD measurement, the processing circuit 35 issues a control signal to the switch 32, thereby switching the first sensor 311 to the transmitting end of the PWD measurement. Furthermore, the processing circuit 35 controls the first sensor 311 through the signal transmitting module 33 to transmit a waveform signal including a fixed frequency. After transmitting the waveform signal including the fixed frequency, the processing circuit 35 issues another control signal to the switch 32, thereby switching the first sensor 311 to the receiving end of the PWD measurement. Furthermore, the processing circuit 35 controls the first sensor 311 through the signal receiving module 34 to receive and respond to an echo signal of the waveform signal including the fixed frequency. In this embodiment, the processing circuit 35 can calculate the flow velocity and flow rate of the liquid in the pipe based on the frequency shift (also referred to as the frequency difference value) between the waveform signal transmitted by the first sensor 311 and the received echo signal.

[0026] It is worth noting that when applied to ToF measurement, the signal receiving module 34 includes at least a low-noise amplifier, a programmable gain amplifier, and a filter, and when applied to PWD measurement, the signal receiving module 34 includes at least a low-noise amplifier, a programmable gain amplifier, a filter, and a comparator, but the above is only one embodiment of the present invention and is not limited thereto.

[0027] The technical feature of this claim is that the flowmeter 3 performs one or more ToF measurements and one or more PWD measurements, then estimates the current state of the liquid in the pipe (for example, whether it is a single-phase liquid or a multiphase liquid) based on the measurement results, and determines whether it needs to output the flow velocity obtained based on the ToF measurement or the flow velocity obtained based on the PWD measurement. When it cannot directly determine which measurement method's flow velocity needs to be output, the flowmeter 3 of this claim further refers to a pre-created intensity correspondence table 351 and determines whether it needs to output the flow velocity obtained based on the ToF measurement or the flow velocity obtained based on the PWD measurement based on the signal intensity (details will be described later).

[0028] Please refer to FIG. 4, which is a signal transmission sequence diagram of a frequency-mixed ultrasonic flowmeter. As shown in FIG. 4, the flowmeter 3 performs a ToF measurement period C1 and a PWD measurement period C2 at intervals. Specifically, the flowmeter 3 repeatedly transmits a signal using the first sensor 311 as the ToF measurement transmitting end (Tx), reacts to the signal using the second sensor 312 as the ToF measurement receiving end (Rx), transmits a signal using the second sensor 312 as the ToF measurement transmitting end (Tx), and reacts to the signal using the first sensor 311 as the ToF measurement receiving end (Rx). This process is considered to be one ToF measurement period C1. Furthermore, the flowmeter 3 repeatedly transmits a signal using the first sensor 311 (or the second sensor 312) as the PWD measurement transmitting end (Tx), and reacts to the signal using the same first sensor 311 (or the same second sensor 312) as the PWD measurement receiving end (Rx). This process is considered to be one PWD measurement period C2.

[0029] In this claim, the flowmeter 3 calculates a measurement result based on the time difference method using at least two echo signals in one ToF measurement period C1, and calculates another measurement result based on the Doppler method using one echo signal in one PWD measurement period C2. It is noteworthy that the flowmeter 3 can obtain two echo signals (i.e., one ToF measurement), four echo signals (i.e., two ToF measurements), or six echo signals (i.e., three ToF measurements) in one ToF measurement period C1, and can obtain one echo signal (i.e., one PWD measurement), two echo signals (i.e., two PWD measurements), or three echo signals (i.e., three PWD measurements) in one PWD measurement period C2, depending on whether the user selects a ToF-oriented pattern (e.g., the liquid in the pipe is a multiphase liquid), a PWD-oriented pattern (e.g., the liquid in the pipe is a single-phase liquid), or a balanced pattern (i.e., the number of ToF measurements is the same as the number of PWD measurements), but is not limited to the above.

[0030] Please refer to Fig. 5, which shows a specific embodiment of the claimed frequency selection method. Fig. 5 discloses a specific implementation procedure of the claimed frequency selection method. The above frequency selection method is mainly applicable to the flow meter 3 shown in Fig. 3.

[0031] 5, after the first sensor 311 and the second sensor 312 of the flowmeter 3 are respectively installed at corresponding positions on the pipe to be measured, the processing circuit 35 controls the first sensor 311 and the second sensor 312 to perform ToF measurement, and can further control one of the first sensor 311 and the second sensor 312 to perform PWD measurement (step S51). There is no set order for the ToF measurement and the PWD measurement, and it is determined by the measurement pattern set by the user.

[0032] For example, during one ToF measurement period C1, the processing circuit 35 first controls the first sensor 311 and the second sensor 312 to emit a frequency-mixed wave signal into the pipe, thereby measuring a time-of-flight (ToF) signal. Next, during one PWD measurement period C2, the processing circuit 35 controls one of the first sensor 311 and the second sensor 312 to emit a waveform signal containing a fixed frequency into the pipe, thereby measuring a Doppler (PWD) signal. Specifically, the ToF signal collectively refers to the frequency-mixed wave signals emitted by the two sensors 311 and 312 and the corresponding echo signals, and the PWD signal collectively refers to the waveform signal containing a fixed frequency emitted by one of the two sensors 311 and 312 and the corresponding echo signals. In this claim, the processing circuit 35 can directly calculate the flow velocity of the liquid based on the ToF signal and the PWD signal.

[0033] After acquiring at least two ToF signals, the processing circuitry 35 can calculate a first flow velocity of the liquid in the pipe based on the time difference method (step S52). After acquiring at least one PWD signal, the processing circuitry 35 can determine the signal strength of the PWD signal (step S53) and can calculate a second flow velocity of the liquid in the pipe based on the Doppler method (step S54).

[0034] It is worth noting that in step S51, the flowmeter 3 performs one or more ToF measurements during one ToF measurement period C1 and one or more PWD measurements during one PWD measurement period C2 according to a measurement pattern set by the user, and the order and number of ToF and PWD measurements performed correspond to the properties of the liquid in the piping. For example, the user of the flowmeter 3 or the processing circuitry 35 may determine the number of ToF measurements that must be performed during one ToF measurement period C1, the number of PWD measurements that must be performed during one PWD measurement period C2, and the order in which the ToF and PWD measurements are performed, depending on whether the liquid is a single-phase liquid without bubbles or particles, or a multiphase liquid with bubbles or particles.

[0035] Please refer to Figures 6A, 6B and 6C at the same time, which are first, second and third sequence diagrams of the measurement pattern of the present invention, respectively.

[0036] FIG. 6A discloses a ToF-focused pattern in which the number of ToF measurements is greater than the number of PWD measurements. In the embodiment of FIG. 6A, the flowmeter 3 can perform three ToF measurements during one ToF measurement period C1, and then two PWD measurements during one PWD measurement period C2. After the PWD measurement period C2 ends, the flowmeter 3 can again perform three ToF measurements during the next ToF measurement period C1, and so on. Alternatively, the flowmeter 3 can repeat the ToF measurement period C1 N times, and then repeat the PWD measurement period C2 M times.

[0037] Specifically, because multiphase liquids provide good signal quality for PWD measurements, the number of PWD measurements can be slightly less than the number of ToF measurements when measuring the flow velocity of multiphase liquids. Therefore, the ToF-weighted pattern shown in Figure 6A is mainly applicable to measurements of multiphase liquids.

[0038] FIG. 6B illustrates a PWD-focused pattern in which the number of PWD measurements is greater than the number of ToF measurements. In the example of FIG. 6B, the flowmeter 3 can perform three PWD measurements during one PWD measurement period C2, and then two ToF measurements during one ToF measurement period C1. After the ToF measurement period C1 ends, the flowmeter 3 can perform three PWD measurements during the next PWD measurement period C2, and so on. Alternatively, the flowmeter 3 can repeat the PWD measurement period C2 M times, and then repeat the ToF measurement period C1 N times.

[0039] Specifically, because single-phase liquids provide good signal quality for ToF measurements, the number of ToF measurements can be slightly less than the number of PWD measurements when measuring the flow velocity of single-phase liquids. Therefore, the PWD-focused pattern shown in Figure 6B is mainly applicable to measurements of single-phase liquids.

[0040] FIG. 6C discloses a balance pattern in which the number of PWD measurements is equal to the number of ToF measurements. In the embodiment of FIG. 6C, the flowmeter 3 can perform one PWD measurement during one PWD measurement period C2, followed by one ToF measurement during one ToF measurement period C1. After the ToF measurement period C1 ends, the flowmeter 3 can perform another PWD measurement during the next PWD measurement period C2, and so on. Alternatively, the flowmeter 3 can repeat the PWD measurement period C2 M times, followed by the ToF measurement period C1 N times.

[0041] By using one of the three measurement patterns, the processing circuit 35 of the flowmeter 3 can acquire the ToF signal and PWD signal, and further calculate the flow velocity of the liquid in the pipe based on the time difference method and the Doppler method in steps S52 and S54, respectively.

[0042] One technical feature of the present invention is that the frequency mixed wave signals emitted by the first sensor 311 and the second sensor 312 during ToF measurement are a complex wave (e.g., the frequency mixed wave signals 7 and 7' shown in FIG. 7A or 7B) that sequentially include at least three different frequencies. The special characteristics of the complex wave (i.e., a single waveform corresponding to three consecutive and different frequencies) can improve the discrimination level in signal processing in the processing circuit 35 and also improve noise resistance (details will be described later).

[0043] In this embodiment, after acquiring the PWD signal by PWD measurement, the processing circuitry 35 first determines the signal strength of the PWD signal (step S53), and then compares the PWD signal with a plurality of predefined thresholds (step S55). Generally, the signal strength of the PWD signal obtained by PWD measurement is more accurate than the signal strength of the ToF signal obtained by ToF measurement, and the faster the liquid flow velocity, the stronger the signal strength of the PWD signal tends to be. Therefore, in this embodiment, when the signal strength of the PWD signal is less than a predefined first threshold, the processing circuitry 35 outputs a first flow velocity calculated based on the ToF signal (step S56). When the signal strength of the PWD signal is greater than a predefined second threshold, the processing circuitry 35 outputs a second flow velocity calculated based on the PWD signal (step S57).

[0044] In an embodiment, the second threshold is greater than the first threshold.

[0045] In an embodiment, the second threshold is 30,000, and the first threshold is 10,000.

[0046] If it is determined in step S55 that the signal strength of the PWD signal is between the first threshold and the second threshold, the processing circuit 35 further uses the PWD signal to refer to the intensity correspondence table 351 (step S58), and thereby determines, based on the table reference result, whether it is necessary to output the first flow velocity obtained based on the ToF measurement or the second flow velocity obtained based on the PWD measurement (step S59).

[0047] Table 1 below discloses one specific embodiment of the intensity correspondence table 351 of the present invention. Experimental tests have shown that the reliability of the ToF signal is higher than that of the PWD signal. Therefore, when the signal strength is lower, the flowmeter 3 refers to the intensity correspondence table 351 to preferentially select the result obtained by the ToF measurement (i.e., the first flow velocity). Furthermore, as the flow velocity increases, the signal strength of the PWD signal becomes stronger. Therefore, by referring to the intensity correspondence table 351, the flowmeter 3 can change to select the result obtained by the PWD measurement (i.e., the second flow velocity) after the signal strength of the PWD signal reaches a certain value (e.g., exceeds 6N+10,000).

[0048] [Table 1]

[0049] In the above Table 1, T refers to ToF measurement, D refers to PWD measurement, and N is (30000-10000) / 12, that is, the lower limit value of signal strength in intensity correspondence table 351 is 10000 and the upper limit value is 30000. In an embodiment, the lower limit value of signal strength in intensity correspondence table 351 is equal to the first threshold value used by processing circuit 35 in step S55 of Fig. 5, and the upper limit value of signal strength is equal to the second threshold value used by processing circuit 35 in step S55 of Fig. 5, and the first and second threshold values ​​are not limited to the above 10000 and 30000. In this claim, the user of flowmeter 3 can further specify the signal selection based on the actual situation on site, so as to better meet the reliability of actual application on site.

[0050] It is worth noting that the data in the intensity correspondence table 351 may have a hysteresis band, i.e., the colored range in the above table 1. Specifically, within the hysteresis band, the flowmeter 3 repeatedly switches between PWD measurement and ToF measurement as the signal strength of the PWD signal increases or decreases, which causes a decrease in measurement efficiency and measurement accuracy. For this reason, the frequency selection method of the present invention further provides a technical means of delayed switching.

[0051] 5, when the processing circuit 35 determines that the signal strength of the current PWD signal is between the first threshold and the second threshold, the processing circuit 35 determines whether to output the first flow velocity obtained through the ToF measurement or the second flow velocity obtained through the PWD measurement by referring to the intensity correspondence table 351. During the next period, if the signal strength of the PWD signal is still between the first threshold and the second threshold, the processing circuit 35 similarly determines whether to output the first flow velocity or the second flow velocity by referring to the intensity correspondence table 351. After the processing circuit 35 determines the output mode for the current period, it first determines whether the current output mode (i.e., whether the first flow velocity obtained through the ToF measurement or the second flow velocity obtained through the PWD measurement is currently being output) is the same as the output mode determined for the current period.

[0052] If the current output method and the output method determined in this cycle are the same, the processing circuit 35 does not need to switch the output method, that is, it directly outputs the first flow rate or the second flow rate determined in this cycle.

[0053] If the current output method differs from the output method determined in this cycle, for example, if the current output method outputs a first flow velocity obtained through ToF measurement but the output method determined in this cycle outputs a second flow velocity obtained through PWD measurement, the processing circuit 35 will not immediately switch the output method for a while, but will first determine whether the number of times the output method differs exceeds a preset number (for example, 3 or 5 times, but is not limited to this).

[0054] If the current output mode and the output mode determined for this cycle are different but the number of times they differ has not reached a preset number, the processing circuit 35 continues to output one of the first flow rate and the second flow rate in the current output mode. For example, suppose the current output mode is to output the first flow rate obtained through ToF measurement, and the output mode determined for this cycle is to output the second flow rate obtained through PWD measurement, but it is initially determined that a different output mode should be used for this cycle. In this case, the processing circuit 35 does not directly switch the output mode, but waits for one or more more cycles, thereby preventing the flowmeter 3 from repeatedly switching between ToF measurement and PWD measurement, which would affect measurement efficiency and accuracy.

[0055] If the current output method and the output method determined in this cycle are different and the number of times they have differed has already reached a preset number, the processing circuit 35 switches from the current output method (e.g., outputting the first flow velocity obtained through ToF measurement) to the output method determined in this cycle (e.g., outputting the second flow velocity obtained through PWD measurement), thereby outputting the other of the first flow velocity and the second flow velocity.

[0056] Through the claimed method, the flow meter can dynamically perform frequency selection based on signal strength (i.e., select whether to use the ToF measurement result or the PWD measurement result), thereby making the flow meter applicable to single-phase and multiphase liquids simultaneously.

[0057] 7A, 7B, and 7C are respectively a first embodiment, a second embodiment, and a flowchart of the ToF measurement of the frequency mixed wave signal of the present invention.

[0058] As mentioned above, when the flowmeter 3 of the present invention performs ToF measurement, the signal emitting module 33 controls the first sensor 311 and the second sensor 312 to emit a frequency mixed wave signal 7, respectively. The frequency mixed wave signal 7 is a complex wave having at least three consecutive and different frequencies. As shown in Figure 7A, in this embodiment, the complex wave includes, in order, a noise frequency f1, a measurement frequency f2, and a cut-off frequency f3. When the processing circuit 35 of the flowmeter 3 calculates the ToF signal, the ToF signal is obtained by mainly measuring a signal at a position corresponding to the measurement frequency f2.

[0059] Specifically, the noise frequency f1 is lower than the lowest frequency to which the first sensor 311 and the second sensor 312 of the flowmeter 3 can respond, and the cutoff frequency f3 is higher than the highest frequency to which the first sensor 311 and the second sensor 312 of the flowmeter 3 can respond. In other words, after the first sensor 311 emits the frequency mixed wave signal 7, the second sensor 312 does not receive an echo signal at the position corresponding to the noise frequency f1 and the cutoff frequency f3. Similarly, after the second sensor 312 emits the frequency mixed wave signal 7, the first sensor 311 does not receive an echo signal at the position corresponding to the noise frequency f1 and the cutoff frequency f3. The measurement target frequency f2 is between the noise frequency f1 and the cutoff frequency f3 and is a frequency to which the first sensor 311 and the second sensor 312 can respond. In other words, in the frequency mixed wave signal 7, the measurement target frequency f2 is the main frequency that the flowmeter 3 needs to measure, and the signal at the position corresponding to the measurement target frequency f2 is the major signal that the flowmeter 3 needs to measure.

[0060] Experimental tests have shown that when the transmitting end transmits a single-pulse waveform, the signal propagates through the liquid and the signal received by the receiving end has a relatively small amplitude. Conversely, when the transmitting end transmits a multi-pulse waveform, the signal received by the receiving end has a relatively large amplitude, i.e., a relatively strong signal strength. This invention makes the first sensor 311 and the second sensor 312 transmit a frequency mixed wave signal 7, thereby enhancing the signal strength of the measured ToF signal. Furthermore, since the flowmeter 3 does not employ signals corresponding to the noise frequency f1 and the cutoff frequency f3, the use of a multi-pulse waveform does not affect the content of the ToF signal at all.

[0061] 7B shows another frequency mixed wave signal 7', which differs from FIG. 7A in that the frequency mixed wave signal 7' includes a plurality of target frequencies f2 between the noise frequency f1 and the cutoff frequency f3. In the embodiment of FIG. 7B, the frequency mixed wave signal 7' includes, in order, the noise frequency f1, the first target frequency f21, the second target frequency f22, and the cutoff frequency f3. In this embodiment, when the processing circuit 35 of the flowmeter 3 calculates the ToF signal, it mainly measures a first signal at a position corresponding to the first target frequency f21 and a second signal at a position corresponding to the second target frequency f22, and then calculates the average value of the first and second signals to obtain the ToF signal.

[0062] Because the claimed flowmeter 3 is used to measure the flow velocity and flow rate of a liquid in a pipe, its accuracy may vary depending on the response capabilities of the first sensor 311 and the second sensor 312, the installation positions of the first sensor 311 and the second sensor 312 on the pipe, and the dimensions and wall thickness of the pipe. In this case, it is necessary to adjust the parameters of the flowmeter 3, thereby achieving better measurement accuracy. Therefore, in the above embodiment, the user can set the number of target frequencies f2 in the mixed frequency signals 7, 7' based on the actual situation, for example, one, two, or more, but is not limited to those shown in FIGS. 7A and 7B. The number of target frequencies f2 corresponds to the dimensions and wall thickness of the pipe, or the specifications of the first sensor 311 and the second sensor 312, and the multiple target frequencies f2 are the same and consecutive.

[0063] By increasing the number of frequencies f2 to be measured, the present invention can improve measurement accuracy when the flowmeter 3 is used on special piping (for example, piping with joints or bends).

[0064] It is worth noting that in order to accommodate different sized pipes, the flowmeter 3 may need to select and use sensors with different sizes and specifications, and the frequency bands to which sensors with different sizes and specifications can respond also differ. Therefore, the claimed flowmeter 3 can dynamically set the noise frequency f1, the measurement target frequency f2 (or the first measurement target frequency f21 and the second measurement target frequency f22), and the cutoff frequency f3 in the frequency mixed wave signals 7, 7' according to the actual situation (i.e., the type of sensor used and the size of the installed pipe), making it possible to apply the claimed method to various situations.

[0065] 7C discloses a specific procedure for performing ToF measurement with the claimed flowmeter 3. As shown in FIG. 7C, when performing ToF measurement, the processing circuit 35 first transmits a signal to the switch 32 to switch the first sensor 311 and the second sensor 312 to the transmitting end of the ToF measurement (step S71), and then controls the first sensor 311 and the second sensor 312 via the signal transmitting module 33 to transmit a frequency mixed wave signal into the piping (step S72). Next, the processing circuit 35 transmits a signal to the switch 32 to switch the first sensor 311 and the second sensor 312 to the receiving end of the ToF measurement (step S73), and then controls the first sensor 311 and the second sensor 312 via the signal receiving module 34 to receive an echo signal of the frequency mixed wave signal (step S74).

[0066] Next, for each of the first sensor 311 and the second sensor 312, the processing circuit 35 determines whether or not there are echo signals at all frequencies of the frequency mixed wave signal (step S75). If there are no echo signals at all frequencies of the frequency mixed wave signal, the processing circuit 35 can acquire a ToF signal by directly measuring a signal at a position corresponding to the measurement target frequency f2 (step S76). More specifically, the processing circuit 35 can obtain a ToF signal by measuring a signal at a position corresponding to one measurement target frequency f2, or can obtain a ToF signal by measuring signals at positions corresponding to multiple measurement target frequencies f2 (e.g., first measurement target frequency f21 and second measurement target frequency f22) and calculating an average value of the multiple signals.

[0067] In step S75, if it is determined that echo signals exist at all frequencies of the frequency mixed wave signal (for example, there are echo signals at both the noise frequency f1 and the cutoff frequency f3), the processing circuit 35 determines that noise exists in the echo signal (step S77). In this situation, the processing circuit 35 must perform secondary processing on the echo signal, and obtains the ToF signal by extracting the main signal required for calculation (i.e., the signal at the position corresponding to the measurement target frequency f2) from the echo signal (step S78). In the embodiment, the secondary processing may be, for example, automatic gain control (AGC), but is not limited thereto.

[0068] After acquiring the ToF signal, the processing circuit 35 further demodulates the ToF signal, and calculates the flow velocity and flow rate of the liquid based on the time difference method using the ToF signal received by the first sensor 311 and the ToF signal received by the second sensor 312.

[0069] Please refer to Figures 8A and 8B, in which Figure 8A is a specific example of a waveform signal including a fixed frequency in the PWD measurement of the present invention, and Figure 8B is a flowchart of the PWD measurement of the present invention.

[0070] As mentioned above, when the flowmeter 3 of the present invention performs PWD measurement, the signal transmitting module 33 controls the sensor (take the first sensor 311 as an example) to transmit a waveform signal 8 having a fixed frequency f0, and then the signal receiving module 34 controls the first sensor 311 to receive an echo signal of this waveform signal 8, thereby obtaining the PWD signal.

[0071] FIG. 8B shows a specific procedure for measuring PWD using the claimed flowmeter 3. As shown in FIG. 8B, when measuring PWD, processing circuit 35 first transmits a signal to switch 32 to switch one of the sensors (e.g., first sensor 311) to the transmitting end of PWD measurement (step S81). Then, processing circuit 35 controls first sensor 311 via signal transmitting module 33 to transmit waveform signal 8 containing the fixed frequency into the piping (step S82). Processing circuit 35 then transmits a signal to switch 32 to switch first sensor 311 to the receiving end of PWD measurement (step S83). Processing circuit 35 then controls first sensor 311 via signal receiving module 34 to receive an echo signal of waveform signal 8 and calculates the frequency difference between waveform signal 8 and the echo signal to obtain the PWD signal. After obtaining the PWD signal, processing circuit 35 demodulates the PWD signal and calculates the flow velocity and flow rate of the liquid based on the Doppler method.

[0072] The claimed method allows the flow meter to simultaneously perform ToF and PWD measurements, and determines which measurement method's flow velocity / flow rate should be used based on signal strength. Thus, by dynamically switching between measurement methods, it is possible to apply the method to different liquids, and obtain more accurate and reliable measurement results. [Explanation of symbols]

[0073] 10 Piping 11 First Sensor 12 Second Sensor 111, 121, 131 signals 13 Flow direction 14 Foreign object 3 Ultrasonic flowmeter 311 First Sensor 312 Second Sensor 32 Switch 33 Signal Transmitting Module 34 Signal Receiving Module 35 Processing circuit 351 Strength Correspondence Table 7, 7' frequency mixed wave signal 8 Fixed frequency waveform C1 ToF measurement cycle C2 PWD measurement cycle S51~S59 Measurement procedure S71~S78 ToF measurement procedure S81~S84 PWD measurement procedure

Claims

1. A frequency selection method for a frequency-mixing ultrasonic flow meter, the method being applied to an ultrasonic flow meter having a first sensor, a second sensor, and a processing circuit, and further comprising: Step a) controlling the first sensor and the second sensor by the processing circuit to respectively emit frequency mixed wave signals in the pipe, thereby measuring time of flight (ToF) signals, and calculating a first flow velocity of the liquid in the pipe based on the time difference method, wherein the frequency mixed wave signals are complex waves including at least three consecutive and different frequencies; Step b) controlling one of the first sensor and the second sensor by the processing circuit to emit a waveform signal having a fixed frequency in the pipe, thereby measuring a Pulse Wave Doppler (PWD) signal, and calculating a second flow velocity of the liquid in the pipe based on the Doppler method. Step c) if the signal strength of the PWD signal is smaller than a first threshold, outputting the first flow velocity calculated based on the ToF signal; Step d) outputting the second flow velocity calculated based on the PWD signal when the signal strength of the PWD signal is greater than a second threshold, wherein the second threshold is greater than the first threshold; and step e) when the signal intensity of the PWD signal is between the first threshold value and the second threshold value, determining whether the first flow velocity or the second flow velocity is to be output by referring to an intensity correspondence table that determines whether the first flow velocity or the second flow velocity is to be output depending on the signal intensity of the PWD signal and the flow velocity of the liquid; A frequency selection method for a frequency-mixing ultrasonic flow meter, comprising the steps of:

2. 2. The frequency selection method for a frequency mixed ultrasonic flowmeter according to claim 1, wherein the composite wave includes a noise frequency, a measurement target frequency, and a cutoff frequency in that order, and step a) is a step of obtaining the ToF signal by measuring a signal at a position corresponding to the measurement target frequency.

3. 3. The method for selecting a frequency for a frequency-mixing ultrasonic flowmeter according to claim 2, wherein the noise frequency is lower than the lowest frequency to which the first sensor and the second sensor can respond, the cutoff frequency is higher than the highest frequency to which the first sensor and the second sensor can respond, and the measurement target frequency is between the noise frequency and the cutoff frequency and is a frequency to which the first sensor and the second sensor can respond.

4. The composite wave includes, in order, the noise frequency, the first target frequency, the second target frequency, and the cutoff frequency, and step a) is a step of measuring a first signal at a position corresponding to the first target frequency and a second signal at a position corresponding to the second target frequency, and calculating an average value of the first signal and the second signal to obtain the ToF signal. The frequency selection method for a frequency mixed ultrasonic flowmeter according to claim 3.

5. 4. The frequency selection method for a frequency mixed ultrasonic flowmeter according to claim 3, wherein the composite wave includes one or more target frequencies between the noise frequency and the cutoff frequency, and the number of target frequencies corresponds to the dimensions, wall thickness or specifications of the pipe or the first sensor and the second sensor.

6. Step e) further comprises: Step e1) After determining that the first flow rate or the second flow rate needs to be output, it is determined whether the current output method is the same as the output method determined for this cycle. Step e2) If the current output method and the output method determined in this cycle are the same, output the first flow rate or the second flow rate based on the current output method. Step e3) If the current output method differs from the output method determined in this cycle, it is determined whether the number of times the current output method differs exceeds a preset number of times. Step e4) If it is determined that the number of different times has not reached the preset number of times, maintaining the output of one of the first flow rate and the second flow rate in the current output mode; and Step e5) When it is determined that the number of different times has reached the preset number of times, the output method is switched to the output method determined in this cycle, and the other of the first flow rate and the second flow rate is output.

3. The method for selecting frequencies for a frequency-mixing ultrasonic flowmeter according to claim 2, comprising:

7. The step a) includes: Step a1) switching the first sensor and the second sensor to a transmission end by the processing circuit; Step a2) controlling the first sensor and the second sensor by the processing circuit to emit the frequency mixed wave signals in the piping, respectively; Step a3) switching the first sensor and the second sensor to a receiving end by the processing circuit; Step a4) controlling the first sensor and the second sensor by the processing circuit to receive echo signals of the frequency mixed wave signal, respectively; Step a5) determining whether the echo signal exists at all frequencies of the frequency mixed wave signal for the first sensor and the second sensor, respectively; and Step a6) If it is determined that the frequency mixed wave signal does not indicate that the echo signal exists at all frequencies, the ToF signal is acquired by measuring a signal at a position corresponding to the frequency to be measured.

3. The method for selecting frequencies for a frequency-mixing ultrasonic flowmeter according to claim 2, comprising:

8. The step a) further comprises: Step a7) if it is determined that the echo signal exists at all frequencies of the frequency mixed wave signal, it is determined that noise exists in the echo signal; and Step a8) After step a7), a secondary processing is performed on the echo signal to extract a signal at a position corresponding to the frequency to be measured, thereby obtaining the ToF signal.

3. The method for selecting frequencies for a frequency-mixing ultrasonic flowmeter according to claim 2, comprising:

9. The step b) includes: Step b1) switching the first sensor or the second sensor to a transmission end by the processing circuit; Step b2) controlling the transmission end by the processing circuit to emit a waveform signal including the fixed frequency in the piping; Step b3) switching the transmitting end to a receiving end by the processing circuit; and Step b4) controlling the receiving end to receive an echo signal of the waveform signal by the processing circuit, and calculating a frequency difference value to obtain the PWD signal; 3. The method for selecting frequencies for a frequency-mixing ultrasonic flowmeter according to claim 2, comprising:

10. 3. The frequency selection method for a frequency mixed ultrasonic flowmeter according to claim 2, wherein the ultrasonic flowmeter performs step a) once or a plurality of times, and then performs step b) once or a plurality of times, and then performs steps c) to e), wherein the order and number of times steps a) and b) are performed correspond to the properties of the liquid, and wherein the liquid is a single-phase liquid without bubbles and particles, or a multi-phase liquid with bubbles or particles.

Images