JP2008170211A - Ultrasonic flowmeter - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an ultrasonic flowmeter capable of stably measuring a flow rate over a long period by preventing mixing of electrical noise into a signal line connecting an ultrasonic transducer with an amplifier circuit. <P>SOLUTION: The ultrasonic flowmeter comprises: a pair of ultrasonic transducer circuits 22 disposed at a predetermined distance from each other on upstream and downstream sides of a passage in which a fluid to be measured flows; a time measuring means for measuring propagation time of ultrasonic signals that are transmitted and received between the pair of ultrasonic transducer circuits 22; and a flow rate measuring means for measuring a flow rate of a fluid to be measured based on propagation time measured by the time measuring means, wherein, each of the pair of ultrasonic transducer circuits 22 includes: an ultrasonic transducer 22a; a signal changeover switch 22b for switching transmission and reception signals transmitted and received between the pair of ultrasonic transducers 22a; and an amplification circuit 22c for amplifying the reception signal by a predetermined gain. <P>COPYRIGHT: (C)2008,JPO&INPIT

Description

  The present invention relates to an ultrasonic flowmeter capable of measuring a flow rate with high accuracy while preventing the influence of electrical noise.

  Conventionally, a pair of ultrasonic transducers are provided at a certain distance on the upstream side and downstream side of the flow path, and the ultrasonic signal is transmitted and received between them repeatedly. 2. Description of the Related Art An ultrasonic flowmeter that obtains a flow rate based on a difference between a propagation integration time of a sound wave signal and a propagation integration time from a downstream side to an upstream side is known.

  In such conventional ultrasonic flow measurement, because the distance between the ultrasonic transducer and the amplifier is large, a weak signal immediately after conversion when the ultrasonic signal received by the ultrasonic transducer is converted into an electrical signal. There is a problem that electrical noise is mixed in, and the S / N ratio is lowered, and the accurate propagation time cannot be measured.

  Therefore, compare the average value of the propagation time in the flow velocity direction and the propagation time in the reverse flow direction at the time of flow rate measurement, and the average value of the propagation time in the flow velocity direction and the propagation time in the reverse flow direction during normal measurement set in advance, There is an ultrasonic flowmeter that includes an erroneous measurement determination means that determines that there is a difference of a predetermined size or more as erroneous measurement, thereby preventing measurement accuracy from being lowered due to erroneous measurement due to electrical noise (for example, , See Patent Document 1).

  FIG. 4 is a configuration diagram of an ultrasonic flow meter disclosed in Patent Document 1. The ultrasonic flowmeter includes an ultrasonic transducer 2 installed in a measurement flow path 1 through which a fluid flows, a drive circuit 3 that drives the ultrasonic transducer 2, and a control unit 4 that outputs a start signal to the drive circuit 3. A propagation time measurement unit 5 that measures the propagation time of ultrasonic waves, a calculation unit 6 that receives measurement data from the propagation time measurement unit 5, an ultrasonic transducer 7 that receives ultrasonic waves transmitted from the ultrasonic transducer 2, An amplifier 8 that amplifies the output of the ultrasonic transducer 7, a reception detection circuit 9 that compares the output of the amplifier 8 with a reference voltage and stops the propagation time measurement unit 5 when the magnitude relationship is reversed, and an output of the ultrasonic wave Alternatively, a changeover switch 10 that switches the operation of the ultrasonic transducer to either reception or an erroneous measurement determination unit 11 is provided. The ultrasonic transducers 2 and 7 are capable of transmitting and receiving. Further, by providing the changeover switch 10, the propagation time in the flow direction and the reverse flow direction can be measured.

  In the ultrasonic flowmeter, the drive circuit 3 that has received the start signal from the control unit 4 performs pulse driving of the ultrasonic transducer 2 for a certain period of time, and at the same time, the propagation time measurement unit 5 measures time according to the signal from the control unit 4. Begin to. Ultrasound is transmitted from the pulse-driven ultrasonic transducer 2. The ultrasonic wave transmitted from the ultrasonic transducer 2 propagates through the fluid to be measured and is received by the ultrasonic transducer 7. The reception output of the ultrasonic transducer 7 is amplified by the amplification factor set by the control unit 4 in the amplifier 8. Then, the reception detection circuit 9 receiving the output of the amplifier 8 determines reception of the ultrasonic wave and stops the propagation time measuring unit 5. Then, the control unit 4 obtains the flow velocity from the time information obtained from the propagation time measurement unit 5.

Next, the operation of the erroneous measurement determination unit 11 will be described. First, an average value of propagation times in the flow direction and the reverse flow direction measured by the propagation time measurement unit 5 is obtained, and a difference from a preset average value of propagation times during normal measurement is obtained. Although the propagation time varies depending on the flow size, the average value in the flow velocity direction and the reverse flow direction is constant regardless of the flow size. Therefore, if the average value changes significantly, it is considered that there is some abnormality in the measurement system. Therefore, if the difference between the average values is larger than a predetermined value, it can be determined that the measurement is incorrect.
JP 2001-183195 A

  However, although the ultrasonic flowmeter shown in FIG. 4 determines erroneous measurement due to electrical noise, since the ultrasonic transducer and the amplifier circuit that amplifies the received signal are separated, the ultrasonic transducer and the amplifier circuit are separated. This is a structure in which electrical noise is likely to be mixed into the signal line to be connected, and there is a problem that the S / N ratio is lowered.

  Further, there are the following problems in shortening the transmission path length of the amplifier circuit and the ultrasonic transducer. When outputting an ultrasonic wave, the ultrasonic transducer outputs an ultrasonic signal to be transmitted to the front surface of the ultrasonic transducer and outputs an ultrasonic signal to the rear. Therefore, when an amplifier circuit is installed behind the ultrasonic transducer, the ultrasonic signal output backward is reflected by the circuit board of the amplifier circuit and affects the vibration operation of the ultrasonic transducer in the front. Output to the front of the sound wave transducer. For this reason, the reflected signal affects the signal received by the other ultrasonic transducer, lowers the S / N ratio of the signal, and consequently reduces the measurement accuracy of the propagation time.

  The present invention solves the above-mentioned problems of the prior art, and prevents electric noise from entering the signal line connecting the ultrasonic transducer and the amplifier circuit, and enables stable flow rate measurement over a long period of time. It is an object to provide an ultrasonic flowmeter.

  In order to solve the above problems, an ultrasonic flowmeter according to the present invention is a pair of the invention according to claim 1 that is installed at a certain distance from the upstream side and the downstream side of the flow path through which the fluid to be measured flows. Based on the propagation time measured by the time measuring means, the time measuring means for measuring the propagation time of the ultrasonic signal transmitted and received between the pair of ultrasonic vibrator circuits, and the time measuring means An ultrasonic flowmeter having a flow rate measuring means for measuring a flow rate of the fluid to be measured, wherein each of the pair of ultrasonic transducer circuits is between an ultrasonic transducer and the pair of ultrasonic transducers And a signal changeover switch for switching between a transmission signal and a reception signal transmitted and received, and an amplifier circuit for amplifying the reception signal with a predetermined gain.

  According to a second aspect of the present invention, in the first aspect, each of the ultrasonic transducer circuits includes an integrated circuit in which the ultrasonic transducer, the signal changeover switch, and the amplifier circuit are housed in the same package. Features.

  According to a third aspect of the present invention, in the first or second aspect, each of the ultrasonic transducer circuits includes a circuit board independent of the time measuring unit and the flow rate measuring unit.

  According to a fourth aspect of the present invention, in any one of the first to third aspects, each of the ultrasonic transducer circuits is provided between the ultrasonic transducer, the signal changeover switch, and the amplifier circuit. A sound absorbing material that absorbs ultrasonic waves propagating to the signal changeover switch side is provided.

  A fifth aspect of the present invention is characterized in that, in the fourth aspect, the sound absorbing material is made of a fibrous material.

  A sixth aspect of the present invention is characterized in that, in the fourth or fifth aspect, the sound absorbing material has an uneven shape on the surface.

  According to the first aspect of the present invention, since the ultrasonic transducer circuit includes the ultrasonic transducer and the amplifier circuit, the transmission line length of the signal line connecting the two is shortened, and electrical noise is generated. Mixing can be prevented. As a result, the S / N ratio can be improved, and variations due to noise can be reduced. Therefore, highly accurate propagation time measurement and flow rate measurement are possible. Further, the amplitude of the pulse signal applied to the ultrasonic transducer on the transmission side can be reduced, and the power consumption can be reduced.

  According to the second aspect of the present invention, by constructing the ultrasonic transducer, the signal changeover switch, and the amplifier circuit with an integrated circuit of the same package, signals are exchanged inside the integrated circuit, Since the transmission path length can be shortened and it is difficult to receive disturbance, the S / N ratio can be improved.

  According to the third aspect of the present invention, since the ultrasonic transducer circuit is an independent circuit board, it is possible to prevent digital noise from being mixed into the received signal.

  According to the fourth aspect of the present invention, since the sound absorbing material that absorbs the ultrasonic wave propagating to the signal changeover switch side is provided, the reflection of the ultrasonic signal can be prevented and the measurement accuracy can be prevented from being lowered.

  According to the fifth aspect of the present invention, since the sound absorbing material is made of a fibrous material, the energy of the ultrasonic signal output from the ultrasonic transducer can be absorbed as the vibration of the fiber. .

  According to the sixth aspect of the present invention, since the sound absorbing material has an uneven shape on the surface, the sound absorbing effect can be enhanced.

  Hereinafter, embodiments of the ultrasonic flowmeter of the present invention will be described in detail with reference to the drawings.

  Embodiments of the present invention will be described below with reference to the drawings. FIG. 1 is a block diagram showing the internal configuration of the ultrasonic transducer circuit according to the first embodiment of the present invention, and FIG. 2 is a block diagram showing the overall configuration of the ultrasonic flowmeter.

  First, the configuration of the present embodiment will be described. As shown in FIG. 1, the ultrasonic transducer circuit 22 of the ultrasonic flowmeter according to the present embodiment includes an ultrasonic transducer 22a, a changeover switch 22b, and an amplification circuit. 22c. The configuration of the ultrasonic transducer circuit 24 shown in FIG. 2 is the same as that of the ultrasonic transducer circuit 22. The ultrasonic transducer circuit 22 includes an integrated circuit in which the ultrasonic transducer 22a, the changeover switch 22b, and the amplifier circuit 22c are housed in the same package.

  The changeover switch 22b corresponds to the signal changeover switch of the present invention, and switches between a transmission signal and a reception signal transmitted and received between the pair of ultrasonic transducers 22a. The amplification circuit 22c amplifies the reception signal sent from the ultrasonic transducer 22a via the changeover switch 22b with a predetermined gain.

  Further, as shown in FIG. 2, the entire configuration of the ultrasonic flowmeter according to the present embodiment includes a flow path 20, an ultrasonic transducer circuit 22, an ultrasonic transducer circuit 24, a transmission circuit 26, a repetition circuit 28, and a comparator. The circuit 30 includes a propagation time measurement unit 32, a flow rate measurement unit 34, an oscillation circuit 36, and a timing generation circuit 38.

  A fluid to be measured such as air or gas flows through the flow path 20. The ultrasonic transducer circuit 22 and the ultrasonic transducer circuit 24 are installed at a certain distance on the upstream side and the downstream side of the flow path 20 through which the fluid to be measured flows. Between the ultrasonic transducer circuit 22 and the ultrasonic transducer circuit 24, the operation of transmitting and receiving ultrasonic waves to and from each other in the forward direction and the reverse direction of the fluid flow is repeatedly performed. The flow rate is calculated based on the difference. The ultrasonic transducer circuit 22 and the ultrasonic transducer circuit 24 are formed of a circuit board independent of other components such as the propagation time measuring unit 32 and the flow rate measuring unit 34.

  The transmission circuit 26 is connected to the ultrasonic transducer circuit 22 and the ultrasonic transducer circuit 24 and generates a pulse signal that drives the ultrasonic transducer circuit 22 or 24. The repetition circuit 28 is connected to the transmission circuit 26 and the propagation time measurement unit 32, and sets the number of times that an ultrasonic signal is repeatedly transmitted from the ultrasonic transducer circuit 22 or 24.

  The comparator circuit 30 is connected to the ultrasonic transducer circuit 22, the ultrasonic transducer circuit 24, and the propagation time measuring unit 32, and converts an analog signal into a digital signal.

  The propagation time measuring unit 32 corresponds to the time measuring means of the present invention, and propagates ultrasonic signals transmitted and received between the ultrasonic transducer circuit 22 and the ultrasonic transducer circuit 24 based on the output signal of the comparator circuit 30. Measure time.

  The flow rate measurement unit 34 corresponds to the flow rate measurement unit of the present invention, and measures the flow rate of the fluid to be measured based on the propagation time measured by the propagation time measurement unit 32.

  The oscillation circuit 36 generates a clock signal used in the signal processing of the propagation time measurement unit 32 and the timing generation circuit 38.

  The timing generation circuit 38 is connected to the ultrasonic transducer circuit 22, the ultrasonic transducer circuit 24, and the repetition circuit 28, and outputs a switching signal to control the switching timing of the selector switch 22b.

  Next, the operation of the ultrasonic flowmeter according to the first embodiment will be described. When transmitting an ultrasonic signal, the transmission circuit 103 generates a pulse signal and outputs the pulse signal to the ultrasonic transducer circuit 22 (or the ultrasonic transducer circuit 24). The generated pulse signal is applied as a transmission signal to the ultrasonic transducer 22a via the changeover switch 22b in the ultrasonic transducer circuit 22. The ultrasonic transducer 22a outputs an ultrasonic signal corresponding to the intensity of the applied pulse signal toward the other ultrasonic transducer (here, the ultrasonic transducer inside the ultrasonic transducer circuit 24).

  When receiving the output ultrasonic signal, the ultrasonic transducer 22a converts the received ultrasonic signal into an electric signal and outputs the electric signal. The output electrical signal is input to the amplifier circuit 22c via the changeover switch 22b. The amplifier circuit 22c amplifies the input electric signal with a predetermined gain and outputs it as a received signal. The output reception signal is input to the comparator circuit 30 and converted into a digital signal. Further, the comparator circuit 30 outputs the converted digital signal to the propagation time measuring unit 32. The propagation time measuring unit 32 measures the propagation time of the ultrasonic signal transmitted / received between the ultrasonic transducer circuit 22 and the ultrasonic transducer circuit 24 based on the signal output from the comparator circuit 30, and displays the measurement result. Output to the flow rate measuring unit 34. The flow rate measuring unit 34 measures the flow rate of the fluid to be measured based on the bidirectional propagation time between the upstream and downstream measured by the propagation time measuring unit 32.

  As described above, according to the ultrasonic flowmeter of the first embodiment of the present invention, the ultrasonic transducer circuit 22 includes the ultrasonic transducer 22a that receives the ultrasonic wave and the amplification circuit 22c. The transmission line length of the signal line connecting the ultrasonic transducer 22a and the amplifier circuit 22c can be shortened, and electrical noise can be prevented from being mixed into the signal line of the weak ultrasonic reception signal. In addition, since the amplification circuit 22c amplifies the received signal and outputs it to the comparator circuit 30, it is possible to improve the S / N ratio, reduce variation due to noise with respect to the signal output from the comparator circuit 30, and consequently high-accuracy propagation time. Measurement and flow rate measurement are possible.

  Further, since the S / N ratio can be improved, the amplitude of the pulse signal applied to the ultrasonic transducer 22a on the transmission side can be reduced, and the power consumption can be reduced.

  Furthermore, by constructing the ultrasonic transducer 22a, the changeover switch 22b and the amplifier circuit 22c with an integrated circuit of the same package, signals can be exchanged inside the integrated circuit, the signal transmission path length can be shortened, and disturbances can be received. Therefore, the S / N ratio of the signal and noise can be improved. Moreover, power consumption can be reduced for the reasons described above.

  In addition, the ultrasonic transducer circuit 22 is an independent circuit board, and is configured by a circuit board separate from the other transmission circuit 26, the comparator circuit 30, the propagation time measurement unit 32, the flow rate measurement unit 34, and the like. It is possible to prevent digital noise from being mixed into the ultrasonic reception signal.

  FIG. 3 is a block diagram showing the internal configuration of the ultrasonic transducer circuit according to the second embodiment of the present invention. The difference from the configuration of the first embodiment is that a sound absorbing material 22d is newly provided between the ultrasonic transducer 22a and the changeover switch 22b. The sound absorbing material 22d absorbs ultrasonic waves propagating from the ultrasonic transducer 22a to the changeover switch 22b side. The sound absorbing material 22d is made of a fibrous material such as glass fiber, ceramic fiber, or carbon fiber. Furthermore, the sound absorbing material 22d has a concavo-convex shape on the surface on the side receiving the ultrasonic signal.

  Next, the operation of the ultrasonic flowmeter according to the embodiment 2 will be described. The basic operation is the same as that of the ultrasonic flowmeter described in the first embodiment. However, when outputting ultrasonic waves, the ultrasonic transducer 22a outputs an ultrasonic signal to be transmitted to the front surface of the ultrasonic transducer 22a and outputs an ultrasonic signal to the rear. The sound absorbing material 22d absorbs the ultrasonic signal output rearward and prevents reflection of the ultrasonic signal.

  As described above, according to the ultrasonic flow meter according to the second embodiment of the present invention, the sound absorbing material 22d is provided to prevent the reflection of the ultrasonic wave, and the vibration operation and the ultrasonic wave of the ultrasonic vibrator 22a. It is possible to prevent the ultrasonic signal output to the front surface of the transducer 22a from being affected. Moreover, since the sound absorbing material 22d is made of a fibrous material such as glass fiber, ceramic fiber, or carbon fiber, the energy of the ultrasonic signal output from the ultrasonic transducer 22a is absorbed as fiber vibration. Can do. Furthermore, since the sound absorbing material 22d has an uneven shape on the surface receiving the ultrasonic signal, the sound absorbing effect can be enhanced.

  The ultrasonic flow meter according to the present invention can be used for an ultrasonic flow meter such as an ultrasonic gas meter capable of measuring a gas flow rate.

It is a block diagram which shows the internal structure of the ultrasonic transducer circuit of Example 1 of this invention. It is a block diagram which shows the structure of the whole ultrasonic flowmeter of the form of Example 1 of this invention. It is a block diagram which shows the internal structure of the ultrasonic transducer circuit of Example 2 of this invention. It is a block diagram which shows the structure of the conventional ultrasonic flowmeter.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Measurement flow path 2 Ultrasonic vibrator 3 Drive circuit 4 Control part 5 Propagation time measurement part 6 Calculation part 7 Ultrasonic vibrator 8 Amplifier 9 Reception detection circuit 10 Changeover switch 11 Incorrect measurement determination means 20 Flow path 22 Ultrasonic vibrator Circuit 22a Ultrasonic vibrator 22b Changeover switch 22c Amplifying circuit 22d Sound absorbing material 24 Ultrasonic vibrator circuit 26 Transmission circuit 28 Repeat circuit 30 Comparator circuit 32 Propagation time measurement unit 34 Flow rate measurement unit 36 Oscillation circuit 38 Timing generation circuit

Claims (6)

A pair of ultrasonic transducer circuits installed at a certain distance from the upstream side and the downstream side of the flow path through which the fluid to be measured flows;
Time measuring means for measuring the propagation time of an ultrasonic signal transmitted and received between the pair of ultrasonic transducer circuits;
An ultrasonic flowmeter having flow measurement means for measuring the flow rate of the fluid to be measured based on the propagation time measured by the time measurement means,
Each of the pair of ultrasonic transducer circuits includes:
An ultrasonic transducer,
A signal changeover switch for switching between a transmission signal and a reception signal transmitted and received between the pair of ultrasonic transducers;
An amplifying circuit for amplifying the received signal with a predetermined gain;
An ultrasonic flowmeter characterized by comprising:   2. The ultrasonic flowmeter according to claim 1, wherein each of the ultrasonic transducer circuits comprises an integrated circuit in which the ultrasonic transducer, the signal changeover switch, and the amplifier circuit are housed in the same package.   3. The ultrasonic flowmeter according to claim 1, wherein each of the ultrasonic transducer circuits includes a circuit board independent of the time measuring unit and the flow rate measuring unit.   Each of the ultrasonic transducer circuits includes a sound absorbing material that absorbs ultrasonic waves propagating to the signal changeover switch side between the ultrasonic transducer, the signal changeover switch, and the amplification circuit. The ultrasonic flowmeter according to any one of claims 1 to 3.   The ultrasonic flowmeter according to claim 4, wherein the sound absorbing material is made of a fibrous material.   6. The ultrasonic flowmeter according to claim 4, wherein the sound absorbing material has an uneven shape on a surface.

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