JP4789182B2 - Ultrasonic flow meter - Google Patents

Description

  The present invention relates to an ultrasonic flowmeter.

JP 2004-239868 A

  2. Description of the Related Art Conventionally, an ultrasonic flowmeter using ultrasonic waves is known as a flow rate measuring device that measures a flow rate of city gas or water. For example, the following method is employed for measuring the flow rate. That is, a pair of ultrasonic elements is provided on the upper and lower sides in the flow direction of the flow path, and ultrasonic waves (from one ultrasonic element (transmitting-side ultrasonic element) to the other ultrasonic element (receiving-side ultrasonic element) ( The direct propagation wave time that the direct wave reaches) is measured, and the reflected propagation wave time until the direct wave is reflected and returned from the surface of the receiving ultrasonic element is measured, and the flow rate is measured using these propagation times. Measurement is performed.

  As the ultrasonic element, a piezoelectric element is often used. A piezoelectric element is an element that emits an ultrasonic wave when a drive signal is input. In order to accurately measure the flow rate over a long period of time, the time from when the drive signal is input until the ultrasonic wave is transmitted (transmission delay time) Ideally, it should be constant without aging.

  However, it has been found that each ultrasonic element has its own electrical load (for example, impedance), and the transmission delay time varies depending on the electrical load. Since the electrical load deteriorates over time, the transmission delay time will change if the ultrasonic flowmeter has been used for many years. Therefore, there has been a problem that it is difficult to accurately measure the flow rate over a long period of time.

  Describing in more detail with reference to FIG. 9, a conventional ultrasonic flowmeter 101 is provided with ultrasonic transducers 103 and 104 on the upper and lower sides of a flow path 102 through which a fluid flows, and a transmitter for transmitting a drive signal thereto. 105 is provided. Then, by alternately switching the transmission side switch 108 and the reception side switch 109, ultrasonic waves are transmitted from one ultrasonic transducer, and ultrasonic waves are received by the other ultrasonic transducer. That is, transmission of ultrasonic waves from the upper side to the lower side (forward direction) and transmission of ultrasonic waves from the lower side to the upper side (reverse direction) are performed alternately. Then, the flow rate of the fluid is measured according to the time when the ultrasonic wave reaches. As described above, when the ultrasonic transducers 103 and 104 are alternately switched to transmit and receive ultrasonic waves, when the electrical load of each of the ultrasonic transducers 103 and 104 changes with time, the emission delay time of the ultrasonic waves Changes, and the propagation time cannot be measured accurately. As a result, the flow rate could not be measured accurately.

  The present invention has been made in the background as described above. In particular, it is an object of the present invention to provide an ultrasonic flowmeter that can be used accurately over a long period of time.

Means for Solving the Problems and Effects of the Invention

The present invention includes a flow path through which a fluid passes;
A pair of ultrasonic elements disposed at the upper and lower sides of the flow path, each having a predetermined electrical load, and a composite of an ultrasonic transmission function and an ultrasonic reception function;
A transmitter that is electrically connected to the pair of ultrasonic elements and transmits a drive signal for transmitting ultrasonic waves to the ultrasonic elements;
A time measuring means for measuring a time during which the ultrasonic wave propagates between the pair of ultrasonic elements;
An arithmetic means for calculating a flow rate of the fluid flowing through the flow path based on the measured time;
With
Wherein said pair of ultrasonic elements and the transmitting unit, the connected in series when transmitting ultrasonic waves, electrical load of the pair of ultrasonic elements is an ultrasonic flowmeter according to claim Rukoto synthesized.

  According to the present invention, since a pair of ultrasonic elements are connected in series when transmitting ultrasonic waves, it is possible to transmit ultrasonic waves simultaneously from both ultrasonic elements. That is, by connecting ultrasonic elements in series, each ultrasonic element is connected in a form in which its own electrical load (for example, impedance) and the electrical load of the counterpart ultrasonic element are combined. Therefore, the delay time when transmitting the ultrasonic wave is common. In addition, even when the electrical load of the ultrasonic element changes with time, it is possible to transmit ultrasonic waves at the same time, and it is possible to perform highly accurate flow rate measurement over a long period of time.

The present invention also provides
In order to detect a reception signal generated when the ultrasonic element receives an ultrasonic wave, a receiving unit for the ultrasonic element located on the upper side of the flow path and a reception for the ultrasonic element located on the lower side part can be an ultrasound flowmeter provided. For example, a receiving unit for the upper ultrasonic element and a receiving unit for the lower ultrasonic element can be provided separately. Thereby, each ultrasonic element can receive ultrasonic waves separately and almost simultaneously. Therefore, the measurement accuracy can be further improved without being affected by the flow rate fluctuation or temperature change that occurs between the upper side measurement and the lower side measurement.

Furthermore, the present invention provides
A receiving unit for detecting a reception signal generated when the ultrasonic element receives ultrasonic waves is used for an ultrasonic element located on the upper side of the flow path and for an ultrasonic element located on the lower side. It is good also as an ultrasonic flowmeter provided in common. By sharing the receiving unit in this way, simultaneous drive reception is possible without providing an extra circuit configuration and the cost can be reduced. In addition, since the receiving unit consumes a large amount of current, it is possible to reduce the current by sharing the receiving unit as described above. For example, a battery used in a gas meter can be used for a long time.

The present invention also provides:
A flow path through which the fluid passes;
A pair of ultrasonic elements disposed at the upper and lower sides of the flow path, each having a predetermined electrical load, and a composite of an ultrasonic transmission function and an ultrasonic reception function;
A transmitter that is electrically connected to the pair of ultrasonic elements and transmits a drive signal for transmitting ultrasonic waves to the ultrasonic elements;
A receiving unit for detecting a reception signal generated when the ultrasonic element receives ultrasonic waves;
When transmitting ultrasonic waves, the pair of ultrasonic elements are connected in series and driven simultaneously, and the electrical connection is switched while the transmitted ultrasonic waves are propagating, and the ultrasonic elements receive the ultrasonic waves. Switching control means for allowing the reception signal to be output when input to the reception unit;
Time measuring means for measuring a time from when the ultrasonic element is driven until the receiving unit detects the received signal;
An arithmetic means for calculating a flow rate of the fluid flowing through the flow path based on the measured time;
It is an ultrasonic flowmeter characterized by providing.

Next, embodiments of the present invention will be described with reference to the drawings.
FIG. 1 is a schematic block diagram showing an embodiment of an ultrasonic flow meter 1 according to the present invention. Thus, the ultrasonic transducer (ultrasonic element of the present invention) 3 is provided on the upper side in the flow path 2 through which the measurement medium such as gas flows, and the ultrasonic transducer 4 is provided on the lower side. These ultrasonic transducers 3 and 4 are composed of, for example, a piezoelectric element and the like. An ultrasonic transmission function for transmitting an ultrasonic wave when a drive signal is applied and an electric signal (received signal) when an ultrasonic wave is received. It combines with the ultrasonic reception function to generate.

  The ultrasonic flowmeter 1 includes a control unit 7 and a transmission unit 5 that transmits a drive signal for emitting ultrasonic waves to the ultrasonic transducers 3 and 4 under the control of the control unit 7. Further, the transmission unit 5 sends signals to the reception units 6a and 6b to inform the timing when the ultrasonic transducers 3 and 4 are driven.

  On the other hand, the ultrasonic flowmeter 1 includes switches 8 to 10 that are switched ON / OFF under the control of the control unit 7. First, the ultrasonic transducers 3 and 4 are connected in series by switching the switches 8 to 10 to the 1 side. Thereafter, a drive signal is input from the transmission unit 5 and ultrasonic waves are simultaneously transmitted from the ultrasonic transducers 3 and 4. The ultrasonic wave propagates through the flow path 2 and reaches the ultrasonic transducer on the other side. While the ultrasonic wave is propagating through the flow path 2, the switches 8, 9, and 10 are switched to the second side by the control of the control unit 7, whereby the upper ultrasonic transducer 3 is connected to the receiving unit 6a, The lower ultrasonic transducer 4 is connected to the receiver 6b. The ultrasonic transducers 3 and 4 that have received the ultrasonic waves generate reception signals, and the reception signals are detected by the reception units 6 a and 6 b through the switches 8 and 10. In this way, the receiving units 6a and 6b can detect direct propagation waves in the forward and reverse directions. Following this, the reflected propagation wave can also be detected.

  Here, the forward direction is a direction from the upper ultrasonic transducer 3 to the lower ultrasonic transducer 4, and the reverse direction is a direction from the lower ultrasonic transducer 4 to the upper ultrasonic transducer 3. . Direct propagation waves (hereinafter also referred to as direct waves) are ultrasonic waves that are transmitted directly to the other ultrasonic transducer without being reflected, and reflected propagation waves (hereinafter referred to as reflected waves). (Note) is the ultrasonic wave reflected back by the other ultrasonic transducer.

  In the embodiment of FIG. 1, two receiving units are provided. As a result, the ultrasonic waves simultaneously emitted from the ultrasonic transducers 3 and 4 can be simultaneously received by both ultrasonic elements 3 and 4. When only one receiving unit is provided, there are cases where the ultrasonic waves are transmitted in two portions and the upper side measurement and the lower side measurement are performed separately. However, as in the embodiment of FIG. 1, since ultrasonic waves can be received at the same time, it is not affected by temperature changes or flow rate changes that occur between upper-side measurement and lower-side measurement, and measurement accuracy is further improved. It becomes possible to make it.

  On the other hand, a time measuring means (not shown) is connected to the receiving units 6a and 6b, and measures the time until the direct propagation wave arrives and the time until the reflected propagation wave arrives. The timing when the ultrasonic wave is transmitted is based on the signal sent from the transmission unit 5 to the reception units 6a and 6b. Then, the flow rate of the fluid flowing through the flow path 2 is calculated using the direct propagation time and reflection propagation time in the forward direction and the direct propagation time and reflection propagation time in the reverse direction. This calculation is performed by the calculation means (control unit 7) of the present invention. Details of the calculation method will be described later.

  As described above, the ultrasonic flowmeter 1 of the present invention is connected to the transmission unit 5 in a form in which electrical loads (for example, impedances) of the ultrasonic transducers 3 and 4 are combined when transmitting ultrasonic waves (series connection). Therefore, ultrasonic waves can be transmitted simultaneously. In addition, when the ultrasonic flowmeter 1 has been used for many years, the electrical load of each of the ultrasonic transducers 3 and 4 changes over time. Sound waves can be transmitted. As a result, accurate flow measurement can be performed.

  Next, the control unit 7 will be described with reference to FIG. The control unit 7 includes, for example, a microcomputer, and includes a CPU 16, a RAM 17, a ROM 18, an I / O, and a bus line 19 that connects them. The ROM 18 stores a transmitter control program 18a, a switching control program 18b, and an arithmetic program 18c. The CPU 16 controls the transmission unit 5 by executing the transmission unit control program 18a. Further, the switching control means and the calculation means of the present invention are realized by executing the switching control program 18b and the calculation program 18c.

  Next, another embodiment of the ultrasonic flowmeter 1 according to the present invention is shown in FIG. In this embodiment, switches 8 to 12 that are switched by the control unit 7 are provided, and when transmitting ultrasonic waves, the switches 8, 9, and 10 are set to the 1 side, and the ultrasonic transducers 3 and 4 are connected in series. And when receiving an ultrasonic wave, switch 8,9,10 is set to 2 side, and switch 11,12 is set to 1 side. Thereby, the reverse direct propagation wave received by the ultrasonic transducer 3 can be detected by the reception unit 6a, and the forward direct propagation wave received by the ultrasonic transducer 4 can be detected by the reception unit 6b.

  Thereafter, the ultrasonic waves are reflected from the surfaces of the ultrasonic transducers 3 and 4 to become reflected waves and propagate through the flow path 2. Then, the switches 11 and 12 are switched to the second side while the reflected wave is propagating. Accordingly, the forward reflected propagation wave received by the ultrasonic transducer 3 can be detected by the receiving unit 6b, and the backward reflected propagation wave received by the ultrasonic transducer 4 can be detected by the receiving unit 6a.

  Next, timing when transmitting and receiving ultrasonic waves will be described with reference to FIG. First, as described above, the ultrasonic transducers 3 and 4 are connected in series, and a drive signal is sent from the transmitter 5. As a result, a voltage is applied to the ultrasonic transducers 3 and 4 and ultrasonic waves are transmitted simultaneously. When the ultrasonic transducer on the other side receives the ultrasonic wave, a reception signal is generated. The reception units 6a and 6b detect the reception signal, and a waveform appears at the timing shown in FIG. In the example of FIG. 3, since the fluid flows in the flow path 2, the ultrasonic wave transmitted from the upper side first reaches the lower side, and thereafter, the ultrasonic wave transmitted from the lower side reaches the upper side.

  The time measuring means described above measures the time from when the driving signal is input to the upper ultrasonic transducer 3 until the direct propagation wave (1) is detected as the forward direct propagation wave arrival time. Next, the time from when the driving signal is input to the lower ultrasonic transducer 4 until the direct propagation wave (2) is detected is measured as the backward direct propagation wave arrival time. Each direct propagation wave is reflected on the surface of the ultrasonic transducers 3 and 4 to become a reflected propagation wave, and reaches the upper-side ultrasonic transducer 3 and the lower-side ultrasonic transducer 4, respectively. The time measuring means measures the time from when the drive signal is input to the upper ultrasonic transducer 3 until the reflected wave (3) is detected as the forward reflected propagation wave arrival time. Further, the time from when the drive signal is input to the lower ultrasonic transducer 4 until the reflected wave (4) is detected is measured as the backward reflected propagation wave arrival time.

Next, a method for calculating the flow rate will be described. First, each symbol shown in FIG. 4 is defined as follows.
t1 Time for the ultrasonic wave to reach from the surface of the upper ultrasonic transducer 3 to the surface of the lower ultrasonic transducer 4 t2 Time for the ultrasonic wave to reach the surface of the upper ultrasonic transducer 3 from the surface of the lower ultrasonic transducer 4 tT1 Transmission delay time from when a drive signal is input to the upper ultrasonic transducer 3 to when an ultrasonic wave is transmitted from the surface of the upper ultrasonic transducer 3 tR1 An ultrasonic wave is generated on the surface of the upper ultrasonic transducer 3 Reception delay time tT2 from arrival to detection of received signal tT2 Transmission from input of drive signal to lower ultrasonic transducer 4 until transmission of ultrasonic waves from the surface of lower ultrasonic transducer 4 Delay time tR2 After ultrasonic waves reach the surface of the lower ultrasonic transducer 4 Reception delay time T1 until a transmission signal is detected The order from when a drive signal is input to the upper ultrasonic transducer 3 to when the reception unit 6 detects that the lower ultrasonic transducer 4 has received a direct wave. Directional direct propagation wave arrival time T2 Reverse direct propagation wave arrival time from when a drive signal is input to the lower ultrasonic transducer 4 until the receiving unit 6 detects that the upper ultrasonic transducer 3 has received the direct wave Time τ1 Forward reflected propagation wave arrival time τ2 from the time when the driving signal is input to the upper ultrasonic transducer 3 until the receiving unit 6 detects that the upper ultrasonic transducer 3 has received the reflected wave. Until the receiving unit 6 detects that the lower ultrasonic transducer 4 has received the reflected wave after the drive signal is input to the sonic transducer 4. Reverse reflection propagation wave arrival time L at the distance between ultrasonic transducers 3 and 4 (propagation distance)
S Cross-sectional area of channel 2

Each measurement time is
T1 = tT1 + t1 + tR2 (1)
T2 = tT2 + t2 + tR1 (2)
τ1 = tT1 + t1 + t2 + tR1 (3)
τ2 = tT2 + t1 + t2 + tR2 (4)
The true propagation times t1 and t2 necessary for actually calculating the flow rate can be expressed as (1) from (3)-(2). T1 = τ1-T2- (tT1-tT2) (5)
From (4)-(1), t2 = τ2−T1 + (tT1−tT2) (6)
It is expressed. As described above, the ultrasonic transducers 3 and 4 are connected (series connected) so as to synthesize their electric loads and are driven simultaneously. Therefore, the transmission delay times tT1 and tT2 in the expressions (5) and (6) have the same value. When this value is expressed as tT3, equations (5) and (6) are as follows.
t1 = τ1-T2- (tT3-tT3) = τ1-T2 (7)
t2 = τ2-T1 + (tT3-tT3) = τ2-T1 (8)
After obtaining t1 and t2,
Flow velocity V = (L / 2) × (1 / t1-1 / t2)
The flow rate can be calculated as Q = S × V.

  Thus, by using the equations (7) and (8), t1 and t2 can be obtained without being affected by the transmission delay times tT1 and tT2 of the ultrasonic transducers 3 and 4 at all.

  That is, by connecting the ultrasonic transducers 3 and 4 in series and simultaneously driving them, the influence of the delay term in the equations (5) and (6) is eliminated. When the ultrasonic transducers 3 and 4 are used for a long period of time, their electrical loads (impedance and the like) change over time. For this reason, the transmission delay times tT1 and tT2 change. However, by simultaneous driving as described above, even if tT3 changes to tT3 ', it is not affected. Therefore, it becomes possible to perform highly accurate flow rate measurement over a long period of time.

  Here, a comparison with a conventional ultrasonic flowmeter is made. As shown in FIG. 9, the conventional ultrasonic flowmeter 101 switches one of the transmission side switch 108 and the reception side switch 109 so that one of the ultrasonic transducers 103 and 104 is used for transmission and the other is used for reception. Were used alternately. For this reason, the transmission delay times tT1 and tT2 of the ultrasonic transducers 103 and 104 are not the same value, and the above equations (5) and (6) have to be used when obtaining t1 and t2. The transmission delay times tT1 and tT2 were previously stored in the control means 7 as initial values. However, when the electrical load of the ultrasonic transducers 103 and 104 deteriorates over time, the transmission delay times tT1 and tT2 change. t2 could not be determined accurately. On the other hand, the present invention can use the above formulas (7) and (8) to drive the ultrasonic transducers 103 and 104 simultaneously, and the transmission delay times tT1 and tT2 change as the electrical load changes over time. However, t1 and t2 can be obtained accurately without being affected by the above.

  Next, another embodiment of the present invention is shown in FIG. In this embodiment, only one receiving unit 6 is provided, and the one receiving unit 6 serves as the receiving unit of the upper-side ultrasonic transducer 3 and the receiving unit of the lower-side ultrasonic transducer 4. For example, the receiving unit is composed of a voltage detection circuit, and the current consumption is relatively large. Therefore, by using one receiving unit 6 as shown in FIG. 5, the entire current consumption can be suppressed. In particular, it is possible to suppress instantaneous current consumption when detecting reception signals from the ultrasonic transducers 3 and 4.

  When detecting ultrasonic waves, for example, the method shown in FIG. 6 can be employed. That is, first, ultrasonic waves are emitted from both the upper-side ultrasonic transducer 3 and the lower-side ultrasonic transducer 4 by the first simultaneous driving. Then, the ultrasonic wave emitted from the upper ultrasonic transducer 3 is received as (5) by the lower ultrasonic transducer 4, and the ultrasonic wave reflected from the surface of the lower ultrasonic transducer 4 is further received by the upper ultrasonic transducer 4. By receiving as (7) by the sonic transducer 3, the forward direct propagation wave arrival time T1 and the forward reflected propagation wave arrival time τ1 are measured. In the first simultaneous driving, the direct wave (6) and the reflected wave (8) from the lower ultrasonic transducer 4 are not measured.

  Thereafter, ultrasonic waves are simultaneously emitted again from both the upper-side ultrasonic transducer 3 and the lower-side ultrasonic transducer 4 again by the second simultaneous driving. Then, the ultrasonic wave emitted from the lower ultrasonic transducer 4 is received by the upper ultrasonic transducer 3 as (9), and the ultrasonic wave reflected from the surface of the upper ultrasonic transducer 3 is further transmitted to the lower ultrasonic transducer 3. By receiving as (11) by the sonic transducer 4, the backward direct propagation wave arrival time T2 and the backward reflected propagation wave arrival time τ2 are measured.

  Further, as shown in FIG. 7, the ultrasonic transducers 3 and 4 may be connected in parallel. In this embodiment, switches 13, 14, and 15 are provided, and these switches are controlled to be switched by the control unit 7. When emitting ultrasonic waves, first, the switch 13 is turned on, and the switches 14 and 15 are turned off, so that the ultrasonic transducers 3 and 4 are connected in parallel, and a drive signal is input from the transmission unit 5. The first ultrasonic simultaneous transmission is performed from the sonic transducers 3 and 4. Thereafter, the switch 13 is turned off, the switch 14 is turned off, and the switch 15 is turned on while the ultrasonic wave is propagating. Then, the forward direct propagation wave received by the ultrasonic transducer 4 is detected by the receiving unit 6. Thereafter, the switch 14 is turned on while the switch 13 is turned off, the switch 15 is turned off, and the forward reflected propagation wave received by the ultrasonic transducer 3 is detected by the receiving unit 6. Subsequently, the switch 13 is turned on, the switches 14 and 15 are turned off, the ultrasonic transducers 3 and 4 are connected in parallel, and the second simultaneous ultrasonic transmission is performed. Thereafter, the switch 13 is turned off, the switch 14 is turned on, and the switch 15 is turned off to detect the backward direct propagation wave. Further, the switch 13 is turned off, the switch 14 is turned off, and the switch 15 is turned on to produce the backward reflected propagation wave. Detect. In this way, the forward propagation wave arrival time and the reflected propagation wave arrival time in the forward direction and the reverse direction can be measured at the timing shown in FIG.

  Even when the ultrasonic transducers 3 and 4 are connected in parallel as shown in FIG. 7, the transmission delay times of the ultrasonic transducers 3 and 4 can be made common. Therefore, the above formulas (7) and (8) can be used, and high-precision flow rate measurement can be performed over a long period of time.

Block diagram of ultrasonic flowmeter 1 according to the present invention Embodiment further provided with switches 11 and 12 Timing chart when sending and receiving ultrasound Diagram for explaining how to calculate flow measurement Embodiment with only one receiver Timing chart used in the ultrasonic flowmeter 1 of FIG. Embodiment in which ultrasonic transducers 3 and 4 are connected in parallel Example of control unit 7 Conventional example

Explanation of symbols

1 Ultrasonic flow meter 2 Flow path 3 Upper-side ultrasonic transducer (ultrasonic element)
4 Lower ultrasonic transducer (ultrasonic element)
5 Transmitters 6a and 6b Receiver 7 Control unit (switching control means, calculation means)
8-15 switch

Claims (4)

A flow path through which the fluid passes;
A pair of ultrasonic elements disposed at the upper and lower sides of the flow path, each having a predetermined electrical load, and a composite of an ultrasonic transmission function and an ultrasonic reception function;
A transmission unit for transmitting a driving signal for transmitting ultrasonic waves to the ultrasonic element,
A time measuring means for measuring a time during which the ultrasonic wave propagates between the pair of ultrasonic elements;
An arithmetic means for calculating a flow rate of the fluid flowing through the flow path based on the measured time;
With
Wherein said pair of ultrasonic elements and the transmitting unit, the connected in series when transmitting ultrasonic waves, an ultrasonic flowmeter electrical load of the pair of ultrasonic elements and wherein Rukoto synthesized. In order to detect a reception signal generated when the ultrasonic element receives an ultrasonic wave, a receiving unit for the ultrasonic element located on the upper side of the flow path and a reception for the ultrasonic element located on the lower side The ultrasonic flowmeter according to claim 1, further comprising a portion.   A receiving unit for detecting a reception signal generated when the ultrasonic element receives ultrasonic waves is used for an ultrasonic element located on the upper side of the flow path and for an ultrasonic element located on the lower side. The ultrasonic flowmeter according to claim 1, which is provided in common. A flow path through which the fluid passes;
A pair of ultrasonic elements disposed at the upper and lower sides of the flow path, each having a predetermined electrical load, and a composite of an ultrasonic transmission function and an ultrasonic reception function;
A transmitter that is electrically connected to the pair of ultrasonic elements and transmits a drive signal for transmitting ultrasonic waves to the ultrasonic elements;
A receiving unit for detecting a reception signal generated when the ultrasonic element receives ultrasonic waves;
When transmitting ultrasonic waves, the pair of ultrasonic elements are connected in series and driven simultaneously, and the electrical connection is switched while the transmitted ultrasonic waves are propagating, and the ultrasonic elements receive the ultrasonic waves. Switching control means for allowing the reception signal to be output when input to the reception unit;
Time measuring means for measuring a time from when the ultrasonic element is driven until the receiving unit detects the received signal;
An arithmetic means for calculating a flow rate of the fluid flowing through the flow path based on the measured time;
An ultrasonic flowmeter comprising:

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