JP2006343292A - Ultrasonic flowmeter - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an ultrasonic flowmeter capable of detecting stably reception timing of a reception side ultrasonic wave. <P>SOLUTION: A propagation time of an ultrasonic pulse propagated in a measured fluid is detected stably by changing a threshold value for detecting arrival, to a reception side ultrasonic sensor 3b, of the ultrasonic pulse propagated in the measured fluid, in response to a level of an acoustic noise in a measured flow passage measured by the reception side ultrasonic sensor 3b, at the time other than a time when the ultrasonic pulse transmitted from the reception side ultrasonic sensor 3b into the measured fluid arrives at the reception side ultrasonic sensor 3b. <P>COPYRIGHT: (C)2007,JPO&INPIT

Description

  The present invention relates to an ultrasonic flowmeter that measures the flow rate of a fluid to be measured using ultrasonic waves.

  As an example of a conventional ultrasonic flowmeter, at least a pair of ultrasonic sensors having a predetermined inclination angle with respect to the flow direction is arranged in a pipe (measured flow path) through which a measured fluid such as gas flows. Between the pair of ultrasonic sensors, the forward direction of the flow of the fluid to be measured (when the upstream ultrasonic sensor is used as the transmission sensor and the downstream ultrasonic sensor is used as the reception sensor), the reverse direction (downstream) When the ultrasonic sensor on the side is used as the transmitting sensor and the ultrasonic sensor on the upstream side is used as the receiving sensor), ultrasonic pulses are sent and received alternately using the measured fluid as the medium, and the ultrasonic pulses change into the flow of the measured fluid. On the other hand, the difference in propagation time between the case of propagating in the forward direction and the case of propagating in the reverse direction is measured, and the flow velocity (flow rate per unit time) of the fluid to be measured is obtained based on this difference in propagation time. Ultrasound configured to calculate flow rate from The amount meter is known.

  In this type of ultrasonic flowmeter, each propagation time is calculated based on the time difference between the transmission timing of the ultrasonic pulse from the transmission side ultrasonic sensor and the reception timing of the ultrasonic pulse by the reception side ultrasonic sensor. ing.

  In this case, the reception timing of the ultrasonic pulse propagating in the fluid to be measured is detected by directly receiving the reception signal waveform of the reception-side ultrasonic sensor by high-speed A / D conversion processing and DSP (Digital Signal Processing) calculation. The reception signal of the reception-side ultrasonic sensor is pulsed by performing correlation processing or comparison processing with an electrical threshold value. However, the method of capturing the reception signal waveform of the reception-side ultrasonic sensor as it is becomes very complicated and expensive.

  Therefore, in this type of ultrasonic flowmeter, as an inexpensive structure, the reception signal voltage of the reception-side ultrasonic sensor is propagated through the fluid under measurement by smoothing it with an integration circuit and comparing it with a fixed threshold value. A method for simply detecting the reception timing of the ultrasonic pulse is employed.

In this simple detection method, several threshold values for detecting the reception timing of ultrasonic pulses are prepared in advance with fixed values, that is, values that can be used to pulse the received signal in a stable manner within the estimated arrival time. In addition, a method is employed in which a microcomputer as a measurement calculation control circuit selects a fixed threshold value used at the time of detection from these prepared values as needed.
JP 7-311062 A

  However, when an ultrasonic flow meter that employs the simple detection method described above is attached to a pipe that is subject to vibration, for example, acoustic noise due to vibration that is not a problem under normal ultrasonic flow meter installation conditions Need to be considered.

  Specifically, when an ultrasonic flowmeter is attached to a pipe where the flow rate of the fluid flowing through the pipe fluctuates greatly, the acoustic noise in the pipe also changes as needed. Thus, it may be difficult to pulse the received signal using a fixed threshold that the measurement arithmetic control circuit selects from time to time.

  In addition, since the propagation efficiency of ultrasonic waves propagating in the measured fluid is proportional to the pressure in the pipe, the reception level of the received ultrasonic waves and acoustic noise received by the receiving ultrasonic sensor changes depending on the pressure of the measured fluid itself. The S / N ratio between the received ultrasonic wave and the acoustic noise changes. Therefore, in the case of a simple detection method in which a microcomputer as a measurement calculation control circuit selects a fixed threshold at any time, there is a possibility that the reception signal of the reception side ultrasonic sensor cannot be stably pulsed. A complicated circuit such as an AGC (Automatic Gain Control) amplifier is used to adjust the reception level.

  However, even with such a configuration, if the arrival of ultrasonic waves propagating in the measured fluid cannot be detected on a scheduled basis and the reception timing of the ultrasonic pulses propagating in the measured fluid cannot be detected, the flow rate output will be sudden. It may change or output an inappropriate value (incorrect output), which may make the operation of the control system at the latter stage using the flow meter output unstable.

  In addition, acoustic noise in the pipe is also generated in uneven portions such as a bent portion or a portion of the pipe, and the pipe is in a resonance state, and the acoustic noise in the pipe is periodically increased. In particular, when the flow rate of the fluid to be measured is in a high flow rate (high flow velocity) region, the S / N between the received ultrasonic wave and the acoustic noise is caused by the acoustic noise generated in the uneven portion for attaching the ultrasonic sensor. There is a possibility that the ratio becomes worse and the ultrasonic wave propagated through the fluid to be measured cannot be stably received and detected.

  In such a situation, when selecting a fixed threshold value, it may be possible to predict the acoustic noise magnitude in advance and set the threshold value to a sufficiently high voltage value. As the signal level gradually increases due to the characteristics of the signal, changes in the reception level and phase are likely to occur due to interference between propagating ultrasonic waves where high reception levels are obtained. Prone to occur. Therefore, in order to reduce the reading error, it is desired to detect ultrasonic waves that are not affected by interference with a threshold value as low as possible in a low flow rate region where acoustic noise is small.

  The present invention has been made in view of the above-described problems, and an object of the present invention is to provide an ultrasonic flowmeter that can stably detect the reception timing of reception-side ultrasonic waves.

  In order to solve the above problems, the present invention alternately connects at least a pair of ultrasonic sensors arranged at a predetermined angle with respect to the flow direction in the measured flow path, and the transmission side and the reception side. An ultrasonic flowmeter comprising: a flow rate calculation means for calculating a flow velocity of a fluid to be measured flowing in a measured flow path based on a difference in propagation time of ultrasonic waves transmitted and received between the ultrasonic sensors using the measured fluid as a medium The detection output of the ultrasonic sensor on the receiving side is compared with a threshold value in order to cause the flow rate calculation means to acquire the propagation time of the ultrasonic wave transmitted and received between the ultrasonic sensors using the measured fluid as a medium. The ultrasonic reception determination means for detecting that the ultrasonic wave propagating through the fluid to be measured has been received by the ultrasonic sensor on the receiving side and supplying the detection result to the flow rate calculation means, and the ultrasonic reception determination means. Threshold value of acoustic noise in the measured channel Characterized in that it comprises an adjusting means for adjusting fit to be.

  Further, in the present invention, the adjusting means acquires the magnitude of acoustic noise in the measured channel based on a detection output that excludes the time of ultrasonic reception detection by the reception-side ultrasonic sensor. .

  Further, in the present invention, the adjusting means monitors the adjusted threshold value in comparison with a predetermined specified value, and when the adjusted threshold value exceeds the specified value, the flow rate calculating means Flow rate calculation stop means for stopping the calculation of the flow velocity of the fluid to be measured or its external output is provided.

  In the present invention, the flow rate calculation means is provided with a correction means for correcting the propagation time of the acquired ultrasonic wave based on the threshold value adjusted by the adjustment means or the flow velocity of the fluid under test calculated by itself. It is characterized by being.

  According to the present invention, the threshold for detecting that the ultrasonic pulse propagating in the fluid to be measured has reached the ultrasonic sensor on the receiving side is adjusted to the magnitude of the acoustic noise in the channel to be measured. Therefore, even in a measurement environment where a large acoustic noise with the same frequency as an ultrasonic pulse propagating in the measured fluid occurs in a high flow rate region, etc. Stable detection of a sound wave pulse is possible, and a stable flow rate measurement of a fluid to be measured can be performed with an inexpensive configuration.

  Furthermore, the threshold value for detecting the arrival of the ultrasonic pulse propagating in the measured fluid reaches the ultrasonic sensor on the receiving side is automatically set according to the acoustic noise in the measured flow channel. In this case, the detection time error when detecting the arrival of the ultrasonic pulse at the receiving ultrasonic sensor is corrected by adjusting the propagation time of the ultrasonic pulse according to the adjusted value. Even when the acoustic noise in the flow path is large, the propagation time of the ultrasonic pulse in the measured flow path can be obtained accurately, and it is calculated regardless of the acoustic noise level in the measured flow path. The flow rate error can be reduced.

  Further, according to the present invention, the threshold value for detecting that the acoustic noise in the measured flow path is too large and the ultrasonic pulse propagating in the measured fluid has reached the receiving-side ultrasonic sensor. If it is impossible to stably measure the flow rate of the fluid under measurement even if it is automatically adjusted, detect the sign in advance and do not perform unstable flow rate output to the subsequent controller. By holding the output, it is possible to avoid sudden changes in the operation of the control system at the subsequent stage or instability.

An ultrasonic flowmeter according to an embodiment of the present invention will be described with reference to the drawings.
FIG. 1 is a schematic cross-sectional view and a system block diagram of an ultrasonic flowmeter according to an embodiment of the present invention.

  In FIG. 1, an ultrasonic flow meter 1 transmits and receives a pair of ultrasonic pulses to and from a flow meter body 3 provided with a pipe 3p that forms a flow path 2 through which a gas (gas) or liquid as a fluid to be measured flows. The possible ultrasonic sensors 3a and 3b that are used for both transmission and reception are arranged at positions that are acoustically opposed to each other at an angle θ with respect to the flow direction of the fluid to be measured. In the illustrated embodiment, the ultrasonic sensors 3a and 3b that are used for both transmission and reception are separated by a predetermined interval along the flow direction of the fluid to be measured, and on one side of the flow path 2 of the pipe line 3p. A reflected wave of an ultrasonic pulse transmitted from one ultrasonic sensor 3a (3b), propagated in the fluid to be measured and reflected by the other pipe wall sandwiching the flow path 2, The ultrasonic sensor 3b (3a) can be received.

  Each of the ultrasonic sensors 3 a and 3 b is configured by a piezoelectric element or the like, and is connected to the sensor driving circuit 5 and the sensor receiving circuit 6 via the switching circuit 4.

  The switching circuit 4 switches and connects one of the ultrasonic sensors 3a (3b) to the sensor driving circuit 5 based on a transmission / reception switching instruction supplied from a measurement calculation control circuit 10 to be described later as an ultrasonic transmission sensor. The other ultrasonic sensor 3b (3a) is switched and connected to the sensor receiving circuit 6 to function as an ultrasonic receiving sensor, and the transmission / reception side between the ultrasonic sensors 3a and 3b is switched.

  The sensor drive circuit 5 generates an impulse (that is, a drive pulse) for driving the ultrasonic sensor 3a or the ultrasonic sensor 3b based on an ultrasonic pulse generation instruction supplied from a measurement calculation control circuit 10 described later. . The drive pulse generated by the sensor drive circuit 5 is supplied to the ultrasonic sensor 3a (3b) selected as the transmission side via the switching circuit 4, and is sent from the ultrasonic sensor 3a (3b) to the fluid to be measured. An ultrasonic pulse is emitted. The emitted ultrasonic pulse is modulated under the influence of the flow velocity vector component of the fluid to be measured, propagates through the fluid to be measured, and is received by the ultrasonic sensor 3b (3a) selected as the receiving side. .

  The sensor receiving circuit 6 detects the sound pressure (including the above-described sound pressure due to the ultrasonic pulse) that propagates through the fluid to be detected, which is detected by the ultrasonic sensor 3b (3a) selected as the receiving side. (In this case, it is converted to a voltage signal), amplified and waveform-shaped, and then output to the detection circuit 7 as a detection signal.

  The detection circuit 7 performs full-wave rectification on the detection signal from the sensor reception circuit 6 and detects the detection signal, and outputs the detected detection signal to the integration circuit 8.

  The integration circuit 8 integrates the detection signal subjected to the full-wave rectification detection from the detection circuit 7 and converts it into a detection signal composed of an envelope waveform of the peak value, and the detection signal of the converted envelope waveform is output from the comparison circuit 9. The data is output to the comparison input terminal and one addition input terminal of the filter / adder circuit 14 described later.

  The filter / adder circuit 14 smoothes the detection signal of the envelope waveform from the integration circuit 8, and uses the detection signal voltage of the smoothed envelope waveform to generate a fixed voltage as a preset comparison reference. 13 is added to the output voltage, and this added output signal is output to the sample input terminal of the sample hold circuit 15 and simultaneously supplied to the second monitoring input terminal of the measurement calculation control circuit 10.

  The reference potential circuit 13 receives the ultrasonic pulse transmitted from the ultrasonic sensor 3a (3b) selected as the transmission side and propagated through the measured fluid when no acoustic noise is generated in the pipe line 3p. On the basis of the received sound pressure when received by the ultrasonic sensor 3b (3a) selected as a reference, a comparison reference voltage (fixed voltage) for ultrasonic pulse reception determination at that time is generated and output. .

  In the sample hold circuit 15, the addition output signal from the filter / adder circuit 14 is input to the sample input terminal, the hold signal from the measurement arithmetic control circuit 10 is input to the hold input terminal, and the output is supplied to the comparison circuit 9. The other comparison input terminal is supplied as a threshold reference voltage signal for discrimination of ultrasonic pulse reception timing. The output of the sample hold circuit 15 is also supplied to the first monitoring input terminal of the measurement calculation control circuit 10 at the same time.

  The comparison circuit 9 compares the detection signal of the envelope waveform from the integration circuit 8 input to one of the comparison input terminals with the threshold reference voltage signal from the sample and hold circuit 15 to detect the detection signal of the envelope waveform. When the magnitude (voltage value) exceeds the threshold reference voltage signal from the sample and hold circuit 15, the reception timing pulse signal of the ultrasonic pulse is output to the measurement calculation control circuit 10.

  The measurement calculation control circuit 10 is constituted by a so-called microcomputer, and controls the operation of each part of the ultrasonic flow meter 1 such as the switching circuit 4, the sensor drive circuit 5, and the sample hold circuit 15 for measuring the flow rate of the fluid to be measured. .

  In addition, the measurement calculation control circuit 10 receives an ultrasonic pulse transmitted from one ultrasonic sensor 3a (3b) functioning as an ultrasonic transmission sensor into the measured fluid in order to calculate the flow rate of the measured fluid. The ultrasonic pulse propagation time t required to propagate through the fluid measurement and reach the other ultrasonic sensor 3b (3a) functioning as the ultrasonic reception sensor is, for example, an ultrasonic pulse generation instruction to the sensor drive circuit 5 described above. Of the measured fluid and the input timing of the reception timing pulse signal supplied from the comparison circuit 9, and based on the measured ultrasonic pulse propagation time t, the flow velocity of the fluid to be measured (the flow rate per unit time). Size) and, if necessary, the integrated flow rate of the fluid to be measured is calculated from the calculated flow velocity. Flow rate data such as a flow rate and an integrated flow rate measured and calculated by the measurement calculation control circuit 10 is supplied to the output circuit 11 and the display circuit 12.

  Furthermore, the measurement calculation control circuit 10 is based on the output level of the sample hold circuit 15 supplied to the first monitoring input terminal and the output level of the filter / addition circuit 14 supplied to the second monitoring input terminal. The measurement control of the propagation time t of the ultrasonic pulse in the fluid to be measured and the execution of the flow rate data measurement calculation based on the measured propagation time t are controlled.

  The output circuit 11 outputs flow rate data such as a flow rate and an integrated flow rate of the fluid to be measured supplied from the measurement calculation control circuit 10 to a control system (not shown). Further, the display circuit 12 omits the flow rate data such as the flow rate and the integrated flow rate of the fluid to be measured supplied from the measurement calculation control circuit 10 and outputs the flow rate data to the display.

  Next, the measurement of the fluid under test by the ultrasonic flowmeter 1 of the present embodiment configured as described above will be described.

FIG. 2 is a flowchart of flow rate measurement by the ultrasonic flowmeter of the present embodiment.
FIG. 3 is a more specific flowchart of the flow rate data calculation portion in the flow rate measurement flowchart shown in FIG.

  The measurement computation control circuit 10 determines the transmission direction of the ultrasonic pulse at the current measurement based on the transmission direction of the ultrasonic pulse at the previous measurement (whether forward or reverse with respect to the flow direction of the fluid to be measured). In order to measure the propagation time of the ultrasonic pulse propagating through the fluid, a measurement start process is performed at the start of ultrasonic pulse flow measurement, such as resetting a reception detection counter provided therein (step S101).

  Then, the measurement calculation control circuit 10 supplies a transmission / reception switching instruction corresponding to the transmission direction of the ultrasonic pulse at the time of the current measurement to the switching circuit 4 and selects one of the ultrasonic sensors 3a and 3b (for example, an ultrasonic wave). It is set to function the ultrasonic sensor 3a) as an ultrasonic transmission sensor and the other (for example, the ultrasonic sensor 3b) as an ultrasonic reception sensor (step S102).

  Thereafter, the measurement calculation control circuit 10 supplies an ultrasonic pulse generation instruction to the sensor drive circuit 5 to send out ultrasonic pulses from the ultrasonic sensor 3a on the ultrasonic transmission side toward the fluid to be measured. Then, the time counting of the propagation time t by the reception detection counter (internal timer counter) for measuring the propagation time t of the ultrasonic pulse in the fluid to be measured is started (step S103).

  In addition, the measurement calculation control circuit 10 receives the magnitude (voltage value) of the threshold reference voltage signal for determining the reception timing of the ultrasonic pulse simultaneously with or prior to the ultrasonic pulse generation instruction to the sensor drive circuit 5 described above. ) Setting processing (step S104), its monitoring / confirmation processing (steps S104 and S105), and reception timing discrimination permission processing (step S106).

  Here, before describing each of the above processes (steps S104, S105, and S106) in detail, problems in measuring the propagation time t of the ultrasonic pulse propagating through the fluid to be measured will be described with reference to FIGS. .

FIG. 4 is an explanatory diagram of signal waveforms of each part of the ultrasonic flow meter when acoustic noise in the measured channel is small.
FIG. 5 is an explanatory diagram of signal waveforms of each part of the ultrasonic flow meter when acoustic noise in the measured channel is large. Here, the inside of the measured flow path refers to the inside of the pipe 3 p of the ultrasonic flowmeter 1.

  4 and 5, (a) represents the waveform of the pulse generation instruction signal supplied from the measurement calculation control circuit 10 to the sensor drive circuit 5. Further, (b) shows the fluid to be measured from the ultrasonic sensor 3a selected as the transmitting ultrasonic sensor based on the output of the pulse generation instruction signal shown in (a) at the time of the current switching at the above-described step S102. When an ultrasonic pulse waveform (indicated by a solid line) transmitted toward the inside and the ultrasonic pulse propagates through the fluid to be measured and reaches the ultrasonic sensor 3b selected as the receiving ultrasonic sensor 2 represents a virtual waveform (indicated by a broken line) of the ultrasonic pulse. Further, (c) shows a detection signal waveform (smooth waveform) of the envelope waveform output from the integration circuit 8 based on the reception signal output of the ultrasonic sensor 3b selected as the reception ultrasonic sensor at the time of switching this time. It is a thing. Further, (d) represents the waveform of the reception timing pulse signal output from the comparison circuit 9 (reception timing pulse signal waveform). This reception timing pulse signal is obtained by converting a detection signal of an envelope waveform as an output of the integration circuit 8 shown in (c) to a threshold reference voltage signal (in FIG. Corresponds to the comparison result of size comparison.

  In FIG. 4 showing the case where the acoustic noise in the measured channel is small, the reception timing pulse signal shown in (d) is the detection signal of the envelope waveform as the output of the integrating circuit 8 shown in (c). Based on the relationship between the magnitude and the magnitude of the threshold reference voltage signal supplied from the sample and hold circuit 15, it is almost the same as the virtual waveform of the ultrasonic pulse that has reached the ultrasonic sensor 3 b indicated by the broken line in FIG. It is generated at a timing with a one-to-one correspondence.

  However, in FIG. 5 showing a case where the acoustic noise in the measured channel is large, the acoustic noise is assumed to be as shown in FIG. When it is fixed to the same size as the small case, the ultrasonic sensor 3b detects this acoustic noise, and therefore, as shown in (c), the envelope waveform as the output of the integration circuit 8 is detected. The magnitude of the detection signal is affected by the influence of the acoustic noise. As a result, the reception timing pulse signal output from the comparison circuit 9 is small in the magnitude of the detection signal of the envelope waveform as the output of the integration circuit 8 shown in (c) and the acoustic noise supplied from the sample hold circuit 15. Based on the relationship with the magnitude of the threshold reference voltage signal that remains fixed according to the case, even if the magnitude of the detection signal of the envelope waveform exceeds the magnitude of the threshold reference voltage signal due to this acoustic noise, The comparison circuit 9 generates a reception timing pulse signal. Therefore, as shown in (d), the comparison circuit 9 generates a plurality of reception timing pulse signals for one ultrasonic pulse sent from the ultrasonic sensor 3a, or (b). There is a possibility that a reception timing pulse signal having a one-to-one correspondence relationship may not be generated at substantially the same timing as the virtual waveform of the ultrasonic pulse reaching the ultrasonic sensor 3b indicated by the broken line in FIG.

  As a result, the measurement calculation control circuit 10 cannot accurately measure the propagation time t of the ultrasonic pulse propagating through the fluid under measurement based on the reception timing pulse signal supplied from the comparison circuit 9. The calculation output of the flow rate data for the fluid to be measured in step S110 of FIG.

  Returning to FIG. 2, in the ultrasonic flowmeter 1 of the present embodiment, the above-described threshold reference voltage signal magnitude (voltage value) setting process (step S104) and its monitoring / confirmation process (step S104). , S105), a reception timing discrimination permission process (step S106) is executed, and the propagation time of the ultrasonic pulse propagating through the fluid to be measured can be accurately measured.

  That is, in the ultrasonic flowmeter 1 of the present embodiment, the measurement calculation control circuit 10 supplies the hold control input terminal of the sample hold circuit 15 almost simultaneously with or prior to the ultrasonic pulse generation instruction to the sensor drive circuit 5. The held signal is temporarily deactivated, and the output of the sample and hold circuit 15, that is, the threshold reference voltage signal supplied to the comparison circuit 9 is set or updated (step S104). Note that the end of the temporary deactivation period of the hold signal by the measurement arithmetic control circuit 10 is such that the ultrasonic pulse transmitted from the ultrasonic sensor 3a on the transmission side propagates through the fluid to be measured, and the ultrasonic sensor on the reception side. The period is set before arriving at 3b, and the period length is set based on the measured flow velocity of the previous fluid to be measured.

  By temporarily deactivating the hold signal supplied from the measurement calculation control circuit 10, the sample hold circuit 15 changes to the threshold reference voltage signal held so far, and supplies the sample input terminal at the time of deactivation. In this case, the output voltage of the filter / adder circuit 14 is fetched, and the fetched output voltage is held as a new threshold reference voltage signal based on the supply return of the hold signal supplied from the measurement calculation control circuit 10. Become.

  At this time, the magnitude of the output voltage of the filter / adder circuit 14 is equal to the magnitude of the detection signal voltage obtained by smoothing and averaging the detection signal of the envelope waveform from the integration circuit 8, and acoustic noise in the pipe 3p in advance. A value obtained by adding the magnitude of the output voltage of the reference potential circuit 13 that generates a comparison reference voltage (fixed voltage) for determining the reception of the ultrasonic pulse when it does not occur.

  Therefore, since the timing at the time of deactivation corresponds to a situation where the ultrasonic pulse transmitted from the ultrasonic sensor 3a has not been received by the ultrasonic sensor 3b, the magnitude of the output voltage of the filter / adder circuit 14 is The comparison reference voltage for discrimination of ultrasonic pulse reception when no acoustic noise is generated in the measured channel is used as the magnitude of the detection signal of the envelope waveform supplied from the integration circuit 8, that is, the current pipeline 3p. The value is corrected according to the size of the acoustic noise. As a result, the measurement calculation control circuit 10 makes a comparison for the reception discrimination of the ultrasonic pulse according to the current magnitude of the acoustic noise in the measured channel by temporarily deactivating the hold signal to the sample hold circuit 15. The reference voltage is held in the sample hold circuit 15 as an updated threshold reference voltage signal.

  The measurement calculation control circuit 10 takes in the magnitude of the newly set and held threshold reference voltage signal from the first monitoring input terminal (step S105), and compares it with a preset specified value. (Step S106).

  This specified value makes it impossible to stably transmit and receive ultrasonic pulses between the pair of ultrasonic sensors 3a and 3b using the measured fluid as a medium alternately in the forward and reverse directions with respect to the flow of the measured fluid. Is a preset value (voltage value). For example, as shown in FIG. 4C, this specified value is an envelope waveform output in response to reception of an ultrasonic pulse from the integration circuit 8 in a state where acoustic noise in the measured channel is small. It is set to a value in a range that does not exceed the magnitude of the detection signal, and corresponds to the set upper limit value of the threshold reference voltage signal.

  As a result of the comparison with respect to the specified value, the measurement calculation control circuit 10 is able to determine whether or not the ultrasonic pulse is stably received when the newly set threshold reference voltage signal does not exceed the specified value. The reception gate of its own reception timing pulse signal is opened (opened) so as to allow the acquisition of the reception timing pulse signal supplied from the comparison circuit 9 (step S107). Further, when the threshold reference voltage signal newly set and held exceeds the specified value, the measurement calculation control circuit 10 performs measurement abnormality processing shown in steps S111 to S114 described later.

  Then, when the reception timing pulse signal is supplied from the comparison circuit 9 to the open reception gate (step S108), the measurement calculation control circuit 10 performs the above-described step S103 based on the input timing of the reception timing pulse signal. The time counting of the propagation time t by the reception detection counter started in step S109 is stopped (step S109).

  When the reception timing pulse signal is supplied from the comparison circuit 9 to the measurement arithmetic control circuit 10 in step S108, the sample hold circuit 15 is set by the threshold value reference voltage signal magnitude setting process in step S104 described above. The current pipeline is started before the ultrasonic pulse generation instruction to the sensor drive circuit 5 or at the same time or in advance and is held before the ultrasonic pulse transmitted by the instruction is propagated to the ultrasonic sensor 3b. A comparison reference voltage for reception determination of an ultrasonic pulse corresponding to the magnitude of acoustic noise in 3p is held as a threshold reference voltage signal.

  Therefore, even if the acoustic noise in the measured channel as shown in FIG. 5 is large, the comparison circuit 9 has almost the same timing as the virtual waveform of the ultrasonic pulse reaching the ultrasonic sensor 3b. A reception timing pulse signal having a one-to-one correspondence can be generated.

  FIG. 6 is an explanatory diagram of signal waveforms of each part of the ultrasonic flow meter when the acoustic noise in the measured flow path is large in the ultrasonic flow meter of the present embodiment. In addition, since the description about the signal waveform of each part of (a)-(d) in FIG. 6 is the same as the description about the signal waveform of each part of (a)-(d) in FIG. 4 and FIG. The description about is omitted.

  As shown in FIG. 6, in the ultrasonic flowmeter 1 of the present embodiment, acquired simultaneously with or in advance of a pulse generation instruction supplied from the measurement calculation control circuit 10 shown in (a) to the sensor drive circuit 5, The magnitude of the detection signal of the envelope waveform immediately before or immediately before the propagation time measurement of the integration circuit 8 shown in (c), and reception of ultrasonic pulses when no acoustic noise is generated in the preset channel to be measured A value obtained by adding the magnitude of the output voltage of the reference potential circuit 13 that generates a comparison reference voltage (fixed voltage) for determination is supplied from the sample hold circuit 15 to the comparison circuit 9 as a threshold reference voltage signal. Yes. Therefore, the magnitude of the threshold reference voltage signal of the comparison circuit 9 depends on the magnitude of the acoustic noise in the measured channel compared to the case where the acoustic noise in the measured channel shown in FIG. 4 is small. Thus, it is configured to automatically adjust to a large value.

  As a result, as shown in FIGS. 5C and 5D, the magnitude of the detection signal of the envelope waveform output from the integration circuit 8 is the threshold reference voltage from the sample hold circuit 15 due to acoustic noise. It is possible to prevent the signal size from being exceeded as much as possible. Therefore, as shown in (c) and (d) of FIG. 6, a plurality of reception timing pulse signals are measured from the comparison circuit 9 with respect to one ultrasonic pulse sent from the ultrasonic sensor 3a. The reception timing pulse signal having a one-to-one correspondence is generated at substantially the same timing as the virtual waveform of the ultrasonic pulse that has reached the ultrasonic sensor 3b indicated by the broken line in (b). This can be supplied to the measurement calculation control circuit 10.

  As a result, the measurement calculation control circuit 10 performs the propagation time of the ultrasonic pulse propagating in the fluid to be measured based on the reception timing pulse signal supplied from the comparison circuit 9 in the flow rate data calculation output process shown in step S110. t can be measured accurately, and even if there is some acoustic noise in the measured flow path, the calculation output of the flow rate data for the measured fluid can be executed accurately.

  Here, details of the flow rate data calculation output process shown in step S110 by the measurement calculation control circuit 10 described above will be described with reference to FIG.

  The measurement calculation control circuit 10 transmits the ultrasonic sensor 3a this time for transmission based on the count value of the reception detection counter whose time count is stopped by the reception timing pulse signal supplied from the comparison circuit 9 in step S109 described above. As the ultrasonic sensor, the ultrasonic pulse propagation time t using the measured fluid in the transmission / reception of the ultrasonic pulse using the ultrasonic sensor 3b as the receiving ultrasonic sensor is acquired (step S1101).

  In the present embodiment, the measurement calculation control circuit 10 further performs a correction process for the acquired propagation time t (step S1102). Here, the correction process of the propagation time t will be described with reference to FIG.

  FIG. 7 is an explanatory diagram that is described based on the signal waveform of each part of the ultrasonic flowmeter for correcting the propagation time of the acquired ultrasonic pulse in the ultrasonic flowmeter of the present embodiment.

  In FIG. 7, (4a) corresponds to the waveform of the ultrasonic pulse generation signal shown in FIGS. 4 and 6 (a), and (4c) shows the measured current shown in FIG. 4 (c). This corresponds to the detection signal waveform of the envelope waveform output from the integration circuit 8 when the acoustic noise in the road is small, and (4d) is a reception timing pulse signal output from the comparison circuit 9 shown in FIG. This corresponds to the waveform. Further, (6c) corresponds to the detection signal waveform of the envelope waveform output from the integration circuit 8 when the acoustic noise in the measured flow path shown in FIG. 6 (c) is large, and (4d) is the figure. This corresponds to the waveform of the reception timing pulse signal output from the comparison circuit 9 shown in 4 (d).

  As shown in FIG. 7, even if the flow direction and the propagation direction of the ultrasonic pulse flow direction are the same with the same fluid to be measured, the integration circuit 8 when the acoustic noise in the flow channel to be measured shown in (6c) is large. Is output from the comparison circuit 9 based on the comparison between the magnitude of the detection signal of the envelope waveform output from the voltage value Vh of the threshold reference voltage signal supplied from the sample hold circuit 15 (6d). The supply timing of the received reception timing pulse signal to the measurement calculation control circuit 10 is the magnitude of the detection signal of the envelope waveform output from the integration circuit 8 when the acoustic noise in the measured channel is small as shown in (4c). Based on the comparison with the voltage value Vl of the threshold reference voltage signal supplied from the sample hold circuit 15, the reception shown in (4d) is output from the comparison circuit 9. The supply timing of the measuring operation control circuit 10 of the timing pulse signal, voltage value Vh of the threshold reference voltage signal is greater by minute than the voltage value Vl of the threshold reference voltage signal, a delay of Δt occurs.

  This delay in Δt does not increase even if the value of the threshold reference voltage signal is changed when the mechanical Q of the ultrasonic sensors 3a and 3b is low and the rise of the received signal waveform is fast, but it depends on the flow rate. When the amplitude of the received signal voltage changes when the ultrasonic pulse is flowed downstream, or when the mechanical Q of the ultrasonic sensors 3a and 3b is high and the rising of the received signal waveform is slow, the signal becomes large and remarkable. become.

  As a result, the propagation time tl of the ultrasonic pulse acquired based on the count value of the reception detection counter when the acoustic noise is small and the ultrasonic pulse acquired based on the count value of the reception detection counter when the acoustic noise is large. An error Δt occurs between the propagation time th and the same propagation time t cannot be obtained, and an error may occur in the calculation result of the flow rate data.

  Therefore, returning to FIG. 3, in the ultrasonic flowmeter 1 of the present embodiment, the same flow rate and the propagation direction related to the flow direction of the ultrasonic pulse are the same regardless of the magnitude of the acoustic noise. Based on the voltage value of the threshold reference voltage signal supplied from the sample hold circuit 15, that is, the magnitude of acoustic noise in the pipe 3 p, so that the propagation time t is reached. Then, the propagation time t of the ultrasonic pulse acquired based on the count value of the reception detection counter is corrected (step S1102). More specifically, the measurement calculation control circuit 10 determines the voltage value of the threshold reference voltage signal supplied from the sample hold circuit 15 or the flow rate of the next step S1103 at the previous transmission / reception of the ultrasonic pulse. By adding or subtracting the error Δt with respect to the acquired propagation time t according to the flow velocity obtained by performing the data calculation process, the error from the original propagation time t becomes the acoustic noise in the pipe line 3p. It is not caused by the size of the.

  In this way, when the measurement calculation control circuit 10 corrects the propagation time t of the acquired ultrasonic pulse, the measurement calculation control circuit 10 changes the ultrasonic sensor from the ultrasonic sensor 3b performed immediately before this time based on the corrected propagation time t. If the propagation time t obtained by transmitting / receiving ultrasonic pulses in the opposite direction to 3a is already stored in the internal memory, the flow rate data is calculated based on the propagation time difference between the two (step S1103), the output processing of the calculated flow rate data to the display circuit 12 or the output circuit 11 is performed (step S1104). Then, the measurement calculation control circuit 10 stores the propagation time t and the propagation direction of the ultrasonic pulse acquired in the current transmission / reception in the internal memory as the propagation time t and the propagation direction of the ultrasonic pulse acquired in the previous transmission / reception. After that, the transmission / reception side of the ultrasonic sensors 3a and 3b is changed from this time, and the series of measurement processing from step S101 is repeated again.

  On the other hand, if it is determined in step S106 that the threshold reference voltage signal newly set and held in the sample hold circuit 15 in step S105 in FIG. Performs the measurement abnormality process shown in steps S111 to S114.

  In this case, the measurement operation control circuit 10 increments the count value of the abnormality counter in the internal memory and counts up (step S111), and then compares the updated count value with a preset specified number of times. (Step S112).

  As a result of the comparison, if the count value of the abnormality counter has not reached the specified number, the measurement calculation control circuit 10 outputs the output voltage of the filter / adder circuit 14 supplied to its second monitoring input terminal. (Step S113), and the comparison reference for determining the magnitude of the detection signal of the envelope waveform of the integrating circuit 8 and the reception of the ultrasonic pulse when no acoustic noise is generated in the preset measured channel The magnitude of the output voltage obtained by adding the magnitude of the output voltage of the reference potential circuit 13 that generates the voltage (fixed voltage) becomes equal to or less than a preset specified value, and the influence of acoustic noise in the pipe line 3p is reduced. If confirmed (step S114), the transmitting / receiving side of the ultrasonic sensors 3a and 3b is changed from this time, and a series of measurement processes from step S101 is started again.

  In this case, calculation of flow rate data by actual measurement of the propagation time t until the acoustic noise in the pipe 3p does not significantly affect the measurement of the propagation time t related to transmission / reception of the ultrasonic pulse using the fluid to be measured as a medium. If the flow is interrupted and stable flow rate measurement cannot be performed, unstable flow rate data is not output, and the output can be retained or updated based on the flow rate data calculated before that time. It is possible to avoid sudden changes (steep changes) in the operation of the control system at the subsequent stage of the ultrasonic flowmeter 1 or instability.

  The measurement calculation control circuit 10 outputs a measurement abnormality to the display circuit 12 or the output circuit 11 when the count value of the abnormality counter in step S112 is equal to or larger than the predetermined number in the comparison. The flow rate measurement is stopped and automatic return is not performed (step S115).

  By executing the measurement abnormality process shown in steps S111 to S114, the flow rate detection (received sound wave detection) is stopped in order to avoid erroneous detection, and the next ultrasonic transmission / reception operation is performed, and at the same time, the flow rate output is immediately before. The value that was able to stably measure the flow rate is maintained to avoid sudden change in output, and an abnormality is notified to indicate that the flow rate measurement is unstable.

  In step S115 described above, when the generation of normal acoustic noise continues continuously for a specified number of times and the arrival of the received sound wave cannot be detected stably, the measurement calculation control circuit 10 performs sensor driving. The circuit 5 is controlled so as to increase the drive voltage of the ultrasonic sensors 3a and 3b on the transmission side so that the received level of the received ultrasonic pulse is larger than the acoustic noise, and even in this state, the sound wave is continuously received. It is also possible to detect an abnormality when it is not possible to detect.

  The ultrasonic flow meter of the present embodiment is configured as described above, but the embodiment of the ultrasonic flow meter of the present invention is not limited to this. For example, in the above description, the measurement of the propagation time of the ultrasonic pulse of the ultrasonic flowmeter provided with a pair of transmission / reception ultrasonic sensors has been described, but the measurement of the propagation time of the ultrasonic pulse propagating in the fluid to be measured. Any flowmeter that performs the calculation of flow rate data by performing the above.

1 is a schematic cross-sectional view and a system block diagram of an ultrasonic flowmeter according to an embodiment of the present invention. It is a flowchart of the flow measurement by the ultrasonic flowmeter of this Embodiment. It is a more specific flowchart about the flow volume data calculation part in the flowchart of the flow volume measurement shown in FIG. It is explanatory drawing of the signal waveform of each part of ultrasonic flowmeter when the acoustic noise in a to-be-measured flow path is small. It is explanatory drawing of the signal waveform of each part of ultrasonic flowmeter when the acoustic noise in a to-be-measured flow path is large. In the ultrasonic flowmeter of this Embodiment, it is explanatory drawing of the signal waveform of each part of ultrasonic flowmeter when the acoustic noise in a to-be-measured flow path is large. In the ultrasonic flowmeter of this Embodiment, it is explanatory drawing demonstrated based on the signal waveform of each part of the ultrasonic flowmeter for correct | amending the propagation time of the acquired ultrasonic pulse.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Ultrasonic flow meter 2 Flow path 3 Flowmeter main body 3p Pipe line 3a, 3b Ultrasonic sensor 4 Switching circuit 5 Sensor drive circuit 6 Sensor receiving circuit 7 Detection circuit 8 Integration circuit 9 Comparison circuit 10 Measurement calculation control circuit 11 Output circuit 12 Display circuit 13 Reference potential circuit 14 Filter / adder circuit 15 Sample hold circuit

Claims (4)

At least a pair of ultrasonic sensors arranged at a predetermined angle with respect to the flow direction in the measured flow path;
A flow rate for calculating the flow velocity of the measured fluid flowing in the measured flow path based on the difference in propagation time of the ultrasonic waves transmitted and received between the ultrasonic sensors using the measured fluid as a medium by alternately switching between the transmitting side and the receiving side An ultrasonic flowmeter comprising a computing means,
In order for the flow rate calculation means to acquire the propagation time of ultrasonic waves transmitted and received between the ultrasonic sensors using the measured fluid as a medium, the detection output of the ultrasonic sensor on the receiving side is compared with a threshold value to be measured. Ultrasonic reception determination means for detecting that the ultrasonic wave propagated in the fluid is received by the ultrasonic sensor on the receiving side and supplying the detection result to the flow rate calculation means;
An ultrasonic flowmeter comprising: an adjustment unit that adjusts a threshold value of the ultrasonic wave reception determination unit in accordance with the magnitude of acoustic noise in the measured channel. The said adjustment means acquires the magnitude | size of the acoustic noise in a to-be-measured flow path based on the detection output remove | excluded at the time of the ultrasonic reception detection by the said ultrasonic sensor of the receiving side. Ultrasonic flow meter. The adjusting means monitors the adjusted threshold value in comparison with a predetermined specified value, and when the adjusted threshold value exceeds the specified value, the flow rate of the fluid to be measured by the flow rate calculating means The ultrasonic flowmeter according to claim 1 or 2, further comprising a flow rate calculation stop means for stopping the calculation of or the external output thereof. The flow rate calculation means is provided with a correction means for correcting the propagation time of the acquired ultrasonic wave based on the threshold value adjusted by the adjustment means or the flow velocity of the fluid under test calculated by itself. The ultrasonic flowmeter according to any one of claims 1 to 3.

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