JP2006275814A - Ultrasonic flowmeter - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To achieve high measurement accuracy without being affected by characteristics changes of an ultrasonic oscillator and a difference in propagation time caused by a difference in the characteristics between ultrasonic oscillators placed upstream and downstream. <P>SOLUTION: The ultrasonic flowmeter comprises a transmission circuit 104 for generating a driving pulse signal, a first ultrasonic oscillator 101 which is placed in a channel 100 and generates an ultrasonic wave in response to the driving pulse signal from the transmission circuit, a second ultrasonic oscillator 102 which is placed facing the first ultrasonic oscillator with a predetermined distance therefrom in the channel, receives the ultrasonic wave generated by the first ultrasonic oscillator, and outputs as a reception signal, a level detection circuit 107 for detecting the level of the reception signal output from the second ultrasonic oscillator, correction means 108 to 110, 112 for collecting the level of the reception signal on the basis of the detected level of the reception signal, and a flow measurement circuit 114 which measures the propagation time of the ultrasonic wave from the first ultrasonic oscillator to the second ultrasonic oscillator on the basis of the corrected reception signal and measures the flow of a fluid flowing through the channel on the basis of the measured propagation time. <P>COPYRIGHT: (C)2007,JPO&INPIT

Description

  The present invention relates to an ultrasonic flowmeter that measures the flow rate of a fluid using ultrasonic waves, and more particularly to a technique that eliminates measurement errors due to secular changes and the like.

  Conventionally, a pair of ultrasonic transducers are provided at a certain distance on the upstream side and downstream side of the fluid flow path, and ultrasonic signals are repeatedly transmitted and received between them, and the ultrasonic signal from the upstream side to the downstream side There is known an ultrasonic flowmeter that obtains a flow rate based on the difference between the propagation accumulated time of the current and the propagation accumulated time from the downstream side to the upstream side.

  In such an ultrasonic flow meter, the electrical characteristics of the ultrasonic vibrator change due to aging, temperature change, and the like. When the electrical characteristics of the ultrasonic vibrator change, the amplitude of the received signal changes, and the time position of the zero cross point used as the arrival point of the ultrasonic wave changes. Further, when the flow rate from the upstream side to the downstream side increases, the amplitude of the received signal changes. As a result, the problem of measuring the wrong arrival time has occurred.

  As a countermeasure against this problem, when the ratio of erroneous measurements, that is, the ratio of error occurrences, exceeds a certain value, an alarm is displayed to inform the time of maintenance or replacement of the ultrasonic flowmeter. (For example, refer to Patent Document 1).

As a technique of a conventional ultrasonic flowmeter, for example, a flow rate measuring device described in Patent Document 2 is known. This flow measuring device includes a transmitter / receiver that transmits / receives ultrasonic waves in a fluid, a repetitive unit that transmits the ultrasonic waves again after receiving the ultrasonic waves, transmission from the upstream side to the downstream side of the flow, or transmission from the downstream side to the upstream side. Time measuring means for measuring accumulated time during repetition, flow rate calculating means for calculating a flow rate based on ultrasonic propagation time, automatic gain means for varying the signal amplification degree according to the signal level of the receiver, and the automatic gain Frequency setting means for changing the number of repetition means according to the value of the means. According to this, since the number of repetitions is changed according to the reception voltage, the flow rate accuracy can be maintained even if the reception sensitivity changes.
JP-A-9-236463 JP 2000-329596 A

  By the way, in the above-described conventional ultrasonic flowmeter, it is known that the ultrasonic vibrator changes internal impedance and the like due to temperature change and secular change, and changes the electrical characteristics of the ultrasonic vibrator. For example, the sound pressure output from the ultrasonic transducer is attenuated even when the level of the drive signal applied to the ultrasonic transducer on the transmission side is constant, or is applied to the ultrasonic transducer on the reception side. Although the transmitted sound pressure level is constant, the sensitivity of the ultrasonic transducer changes. For this reason, the level of the electrical signal (reception signal) output from the ultrasonic transducer on the reception side is attenuated.

  Due to these attenuations, the voltage change per unit time of the received signal obtained as an analog signal changes, and the cross point at the threshold level when the analog signal is converted into a digital signal changes with time. As a result, there is a problem that the flow rate measurement value changes even though the flow rate does not change.

  In the method disclosed in Patent Document 1 described above, it is difficult to determine whether the measurement is a temporary wrong measurement due to a lifetime or temperature due to aging, and it is difficult to quantitatively calculate the occurrence rate of the wrong measurement. difficult.

  Further, in the flow rate measuring device disclosed in Patent Document 2 described above, the amplification factor of the automatic gain means is changed according to the magnitude of the reception level of the receiver, and from the amplification factor to the upstream, the downstream to the upstream The number of times of transmission (reception) is changed to maintain the measurement accuracy, but there is no disclosure about the point that the automatic gain means makes the level of the received signal constant regardless of the level of the received signal. Absent.

  The present invention achieves high measurement accuracy without being affected by changes in the characteristics of ultrasonic transducers caused by temperature changes or changes over time, and differences in propagation times due to differences in the characteristics of upstream and downstream ultrasonic transducers. An ultrasonic flow meter is provided.

  In order to solve the above problems, an ultrasonic flowmeter according to the present invention is arranged in a transmission circuit that generates a drive pulse signal and a flow path, and generates an ultrasonic wave according to the drive pulse signal from the transmission circuit. The first ultrasonic transducer is disposed opposite to the first ultrasonic transducer at a predetermined distance in the flow path, receives the ultrasonic wave generated by the first ultrasonic transducer, and outputs it as a received signal. A second ultrasonic transducer; a level detection circuit for detecting a level of the reception signal output from the second ultrasonic transducer; and a level of the reception signal based on the level of the reception signal detected by the level detection circuit The ultrasonic wave propagation time from the first ultrasonic transducer to the second ultrasonic transducer is measured and measured based on a correction unit that corrects the level and the received signal whose level is corrected by the correction unit. Based on the propagation time It characterized by comprising a flow rate measuring circuit for measuring the flow rate of the fluid.

  According to the ultrasonic flowmeter of the present invention, the level of the received signal generated by the characteristic change of the first ultrasonic transducer and the second ultrasonic transducer is corrected and made constant. Stable measurement of propagation time required from transmission to reception is possible. Propagation time due to changes in characteristics of ultrasonic transducers due to changes over time, temperature changes, etc., and differences in characteristics between upstream and downstream ultrasonic transducers Therefore, it is possible to provide an ultrasonic flowmeter capable of obtaining high measurement accuracy without being affected by the difference between the two.

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

  FIG. 1 is a block diagram showing the configuration of the ultrasonic flowmeter according to the first embodiment of the present invention. The ultrasonic flowmeter includes a first ultrasonic transducer 101, a second ultrasonic transducer 102, a transmission / reception switching circuit 103, a transmission circuit 104, a reception circuit 105, a filter circuit 106, a level detection circuit 107, and a reference value holding circuit 108. , A comparator 109, a gain setting circuit 110, a delay circuit 111, an amplifier circuit 112, a comparator 113, a flow rate measuring circuit 114, and a repeating circuit 115. The correction means of the present invention comprises a reference value holding circuit 108, a comparator 109, a gain setting circuit 110, and an amplifier circuit 112.

  The 1st ultrasonic transducer | vibrator 101 is arrange | positioned in the upstream of the inside of the flow path 100 through which fluids, such as gas and air, flow. The second ultrasonic transducer 102 is disposed on the downstream side in the flow channel 100 and at a position separated from the first ultrasonic transducer 101 by a distance L so as to face the first ultrasonic transducer 101. Has been. Further, the first ultrasonic transducer 101 and the second ultrasonic transducer 102 are arranged coaxially in the flow channel 100.

  The first ultrasonic transducer 101 generates an ultrasonic wave according to the drive pulse signal sent from the transmission / reception switching circuit 103 and transmits the ultrasonic wave toward the second ultrasonic transducer 102. The first ultrasonic transducer 101 receives the ultrasonic wave from the second ultrasonic transducer 102, converts it into an electrical signal, and sends it to the transmission / reception switching circuit 103 as a received signal.

  The second ultrasonic transducer 102 generates an ultrasonic wave according to the drive pulse signal from the transmission / reception switching circuit 103 and transmits the ultrasonic wave toward the first ultrasonic transducer 101. The second ultrasonic transducer 102 receives the ultrasonic wave from the first ultrasonic transducer 101, converts it into an electrical signal, and sends it to the transmission / reception switching circuit 103 as a received signal.

  The transmission / reception switching circuit 103 sends the drive pulse signal sent from the transmission circuit 104 to the first ultrasonic transducer 101 to generate an ultrasonic wave, and from the second ultrasonic transducer 102 that has received this ultrasonic wave. The obtained reception signal is sent to the reception circuit 105, or conversely, the drive pulse sent from the transmission circuit 104 is sent to the second ultrasonic transducer 102 to generate an ultrasonic wave, and this ultrasonic wave is received. Whether to send the reception signal obtained from the first ultrasonic transducer 101 to the reception circuit 105 is switched.

  The transmission circuit 104 generates a drive pulse signal for driving the first ultrasonic transducer 101 or the second ultrasonic transducer 102 in response to the transmission signal sent from the repetition circuit 115. The drive pulse signal generated by the transmission circuit 104 is sent to the transmission / reception switching circuit 103.

  The reception circuit 105 amplifies the reception signal Rs transmitted from the first ultrasonic transducer 101 or the second ultrasonic transducer 102 via the transmission / reception switching circuit 103 with a constant gain. The reception signal amplified by the reception circuit 105 is sent to the filter circuit 106.

  The filter circuit 106 removes noise components included in the reception signal sent from the reception circuit 105. The reception signal from which noise has been removed by the filter circuit 106 is sent to the level detection circuit 107 and the delay circuit 111.

  The level detection circuit 107 detects the level (amplitude) of the received signal, for example, the peak level. The level of the reception signal detected by the level detection circuit 107 is sent to the comparator 109.

  The reference value holding circuit 108 holds a reference level that the received signal should have. The reference level held in the reference value holding circuit 108 is sent to the comparator 109.

  The comparator 109 compares the level of the received signal detected by the level detection circuit 107 with the reference level held in the reference value holding circuit 108, and outputs a difference level between the level of the received signal and the reference level. The difference level from the comparator 109 is sent to the gain setting circuit 110 as a difference signal.

  The gain setting circuit 110 calculates a gain to be set in the amplifier circuit 112 based on the difference signal sent from the comparator 109. The gain setting circuit 110 includes a gain setting table in which a difference value based on the difference signal is associated with a gain to be set, and a gain corresponding to the difference signal is read from the gain setting table. The gain calculated by the gain setting circuit 110 is set in the amplifier circuit 112.

  The delay circuit 111 delays the reception signal sent from the filter circuit 106 by a fixed time (delay time). Details of the delay time in the delay circuit 111 will be described later. The reception signal delayed by the delay circuit 111 is sent to the amplifier circuit 112.

  The amplifier circuit 112 amplifies the reception signal sent from the delay circuit 111 according to the gain set by the gain setting circuit 110. The reception signal amplified by the amplifier circuit 112 is sent to the comparator 113.

  The comparator 113 converts the analog reception signal sent from the amplifier circuit 112 into a digital reception signal by slicing the analog reception signal at a predetermined threshold voltage Vc. A digital reception signal obtained by the conversion in the comparator 113 is sent to the flow rate measurement circuit 114 and the repetition circuit 115.

  Every time a digital reception signal is sent from the comparator 113 in a state where it is detected that the transmission signal from the repetition circuit 115 has been received, the flow rate measurement circuit 114 performs a known algorithm based on the digital reception signal. The flow rate of the fluid flowing through the flow path 100 is calculated. The flow rate measurement circuit 114 has a propagation time for the ultrasonic wave to reach the second ultrasonic transducer 102 on the downstream side from the first ultrasonic transducer 101 on the upstream side and an upstream side from the second ultrasonic transducer 102 on the downstream side. The fluid flow rate is measured based on the difference from the propagation time for the ultrasonic wave to reach the first ultrasonic transducer 101.

  The repetition circuit 115 counts the number of repetitions in which ultrasonic waves should be transmitted from the first ultrasonic transducer 101 or the second ultrasonic transducer 102. Specifically, the number of repetitions is incremented every time a reception signal is obtained from the comparator 113. Each time the count is up, a transmission signal is sent to the transmission circuit 104 and the flow rate measurement circuit 114.

  Next, the operation of the ultrasonic flowmeter according to the first embodiment of the present invention configured as described above will be described. In the following, a case where the first ultrasonic transducer 101 on the upstream side is set to the ultrasonic wave transmission side and the second ultrasonic transducer 102 on the downstream side is set to the ultrasonic wave reception side will be described as an example.

  When the drive pulse signal generated by the transmission circuit 104 is applied to the first ultrasonic transducer 101 via the transmission / reception switching circuit 103, the first ultrasonic transducer 101 has the magnitude of the applied drive pulse signal. A corresponding ultrasonic wave is generated and transmitted toward the second ultrasonic transducer 102 on the downstream side. The ultrasonic wave reaches the second ultrasonic transducer 102 on the downstream side with a propagation time t multiplied by the sound velocity V and the distance L. The second ultrasonic transducer 102 converts the received ultrasonic wave into an electrical signal and outputs it as a reception signal Rs.

  The reception signal Rs output from the second ultrasonic transducer 102 is input to the reception circuit 105 via the transmission / reception switching circuit 103, amplified at a constant gain in the reception circuit 105, and transmitted to the filter circuit 106. Then, the noise component is removed by the filter circuit 106 and sent to the delay circuit 111 and the level detection circuit 107.

  The level detection circuit 107 detects and holds the level of the received signal Rs, that is, the peak value Wh as shown in FIG. The comparator 109 inputs and compares the peak value Wh held in the level detection circuit 107 and the reference value Vr held in the reference value holding circuit 108. Then, the comparator 109 outputs a difference signal corresponding to the comparison result to the gain setting circuit 110. The gain setting circuit 110 sets the gain of the amplifier circuit 112 according to the difference signal received from the comparator 109.

  For example, when the received signal is Rs indicated by a solid line in FIG. 2, the peak value Wh is the same as the reference value Vr, and therefore the comparator 109 outputs a differential signal having a value of zero to the gain setting circuit 110. To do. As a result, the gain setting circuit 110 does not change the gain of the amplifier circuit 112 and maintains the original state.

  When the received signal is Rs-a indicated by a broken line in FIG. 2, the peak value Wh-a is lower than the reference value Vr, so that the comparator 109 compares the difference value ΔVd between the peak value Wh-a and the reference value Vr. Is output to the gain setting circuit 110. Thereby, the gain setting circuit 110 reads the gain according to the difference value ΔVd from the gain setting table, increases the gain of the amplifier circuit 112 according to the difference value ΔVd, and the peak value Wh-a of the received signal Rs-a is obtained. Control is performed to be the same as the reference value Vr.

  Further, when the received signal is Rs-b indicated by a one-dot chain line in FIG. 2, the peak value Wh-a is larger than the reference value Vr, so that the comparator 109 calculates the difference value between the peak value Wh-b and the reference value Vr. Is output to the gain setting circuit 110. Thereby, the gain setting circuit 110 reads the gain according to the difference value from the gain setting table, decreases the gain of the amplifier circuit 112 according to the difference value, and the peak value Wh-b of the reception signal Rs-b is the reference. Control is made to be the same as the value Vr.

  As described above, the gain setting circuit 110 increases the gain of the amplifier circuit 112 when the level of the received signal output from the filter circuit 106 is lower than the reference value Vr, and increases the gain of the amplifier circuit 112 when the level is higher than the reference value Vr. Operates to reduce the gain. Further, the degree of increase or decrease of the gain is controlled according to the magnitude of the difference value from the reference value Vr.

  The delay time of the delay circuit 111 is set to be longer than the time required until the gain is set in the amplifier circuit 112 via the level detection circuit 107, the comparator 109, and the gain setting circuit 110. Thus, after the gain setting circuit 110 sets the gain of the amplifier circuit 112, the received signal from the filter circuit 106 is input to the amplifier circuit 112 via the delay circuit 111. The set gain can be set to the same level as the reference value Vr.

  Note that an ultrasonic flowmeter can be configured without using the delay circuit 111. That is, a preliminary measurement is performed before the main measurement for transmitting and receiving ultrasonic waves to measure the flow rate of the fluid flowing in the flow channel 100, and the gain setting circuit is based on the peak value of the received signal detected by the preliminary measurement. It is possible to determine the gain of the amplifier circuit 112 by 110 and perform this measurement using the determined gain. According to this configuration, since the delay circuit 111 is not necessary, the configuration of the ultrasonic flowmeter can be simplified and the price can be reduced.

  If the gain in the amplifier circuit 112 is not controlled now, whether the amplitude of the received signal is the secular change or temperature change of the first ultrasonic transducer 101 and the second ultrasonic transducer 102, or the upstream side. It varies depending on whether it is downstream. In this case, when the analog received signal is converted into a digital signal by the comparator 113, the received signals Rs, Rs-a, and Rs-c have different amplitudes as shown in FIG. The inclination changes, and the cross point of the threshold voltage Vc of the comparator 113 changes with time. As a result, the arrival time from the output of the transmission signal until the reception signal is converted into a digital signal by the comparator 113 changes, and the flow rate is measured by the flow rate measurement circuit 114 even though the flow rate is the same. The flow rate measurement value changes or varies.

  On the other hand, according to the ultrasonic flowmeter according to the first embodiment of the present invention, the ultrasonic waves output from the first ultrasonic transducer 101 and the second ultrasonic transducer 102 due to secular change and temperature change. Since it is configured to correct and change the amplitude of the received signal due to changes in sound pressure or reception sensitivity, it is possible to stably measure the propagation time required from transmission to reception of ultrasonic waves. Ultrasonic flow rate enables high measurement accuracy without being affected by the difference in propagation time due to changes in the characteristics of the ultrasonic transducer due to changes in temperature and temperature, and differences in the characteristics of the upstream and downstream ultrasonic transducers Can provide a total.

  The ultrasonic flowmeter according to the second embodiment of the present invention controls the drive voltage of the drive pulse signal output from the transmission circuit 104 by the output of the gain setting circuit 110 in the ultrasonic flowmeter according to the first embodiment. It is a thing.

  FIG. 4 is a block diagram showing the configuration of the ultrasonic flowmeter according to the second embodiment of the present invention. In the following, the same or corresponding components as those of the ultrasonic flowmeter according to the first embodiment are denoted by the same reference numerals as those used in the description of the first embodiment, and the description thereof is omitted or simplified. The correction means of the present invention comprises a reference value holding circuit 108, a comparator 109, a gain setting circuit 110a, and a transmission circuit 104a.

  The gain setting circuit 110a generates a drive voltage control signal for controlling the drive voltage of the drive pulse signal output from the transmission circuit 104a based on the difference signal sent from the comparator 109 as a comparison result. The drive voltage control signal generated by the gain setting circuit 110a is sent to the transmission circuit 104a.

  The transmission circuit 104a is a drive pulse signal for driving the first ultrasonic transducer 101 or the second ultrasonic transducer 102 until the number of repetitions set by the repetition circuit 115 is completed, and is a gain setting circuit 110a. A drive pulse signal in which the drive voltage is controlled according to the drive voltage control signal generated in the above is output. The drive pulse signal output from the transmission circuit 104 a is sent to the transmission / reception switching circuit 103.

  Next, the operation of the ultrasonic flowmeter according to the second embodiment of the present invention configured as above will be described. As described in the ultrasonic flowmeter according to the first embodiment, the comparator 109 includes the peak value (level) of the received signal held in the level detection circuit 107 and the reference held in the reference value holding circuit 108. The value Vr is input and compared. Then, the comparator 109 outputs a signal corresponding to the comparison result to the gain setting circuit 110a. The gain setting circuit 110a generates a drive voltage control signal according to the signal received from the comparator 109 and sends it to the transmission circuit 104a, thereby controlling the drive voltage of the drive pulse signal output from the transmission circuit 104a.

  For example, when the level of the received signal is the same as the reference value Vr, the comparator 109 outputs a differential signal having a value of zero to the gain setting circuit 110a. The gain setting circuit 110a supplies a drive voltage control signal corresponding to the difference signal to the transmission circuit 104a, maintains the drive voltage of the drive pulse signal output from the transmission circuit 104a as it is, and the first ultrasonic wave The signal amplitude applied to the transducer 101 or the second ultrasonic transducer 102 is maintained.

  When the level of the received signal is lower than the reference value Vr, the comparator 109 outputs a difference signal having the difference value to the gain setting circuit 110a. The gain setting circuit 110a supplies a drive voltage control signal corresponding to the difference signal to the transmission circuit 104a, and increases the drive voltage of the drive pulse signal output from the transmission circuit 104a to increase the first ultrasonic transducer 101 or The signal amplitude applied to the second ultrasonic transducer 102 is increased.

  When the level of the received signal is higher than the reference value Vr, the comparator 109 outputs a difference signal having the difference value to the gain setting circuit 110a. The gain setting circuit 110a supplies a drive voltage control signal corresponding to the difference signal to the transmission circuit 104a, and reduces the drive voltage of the drive pulse signal output from the transmission circuit 104a to reduce the first ultrasonic transducer 101 or The signal amplitude applied to the second ultrasonic transducer 102 is reduced. With the above operation, the amplitude of the reception signal input to the comparator 113 can be made constant as in the ultrasonic flow meter according to the first embodiment. Similar effects can be obtained.

  In the ultrasonic flowmeter according to Example 1 or Example 2 described above, due to deterioration or failure of the first ultrasonic transducer 101, the second ultrasonic transducer 102, circuit components, etc. due to aging or temperature change, When it is detected that the received signal Rs is less than the predetermined reference value, an alarm circuit (not shown) that issues an alarm to the outside and notifies the abnormality of the flow meter can be further provided.

  Also, in the ultrasonic flow meter according to the second embodiment, the ultrasonic flow meter can be configured without using the delay circuit 111, similarly to the ultrasonic flow meter according to the first embodiment described above. According to this configuration, since the delay circuit 111 is not necessary, the configuration of the ultrasonic flowmeter can be simplified and the price can be reduced.

  As described above, according to the ultrasonic flowmeters according to the first and second embodiments of the present invention, the increase or decrease in the amplitude of the ultrasonic reception signal is detected from the comparison with the reference value, and the difference between them is detected. Accordingly, by changing the gain of the amplifier circuit 112 or the amplitude of the drive pulse signal output from the transmission circuit 104, the amplitude of the received signal input to the comparator 113 is made constant, so that the threshold voltage Vc in the comparator 113 is set. The cross-point between and does not change, and stable propagation time can be measured.

  In addition, this invention is not limited to Example 1 and Example 2 which were mentioned above. For example, the peak value of the reception level of the received signal from the filter circuit 106 is held by a peak detection circuit constituted by an operational amplifier (op amp), and the held peak value and the reference voltage are input to the differential amplifier, and this difference is obtained. A difference voltage between the peak value and the reference voltage may be obtained by a dynamic amplifier, and the gain of the gain setting circuit 110 may be set in accordance with the difference voltage.

  The ultrasonic flowmeter of the present invention can be applied to an ultrasonic gas meter or the like.

It is a block diagram which shows the structure of the ultrasonic flowmeter which concerns on Example 1 of this invention. It is a wave form diagram of a received signal for demonstrating operation | movement of the ultrasonic flowmeter which concerns on Example 1 of this invention. It is a figure for demonstrating the transition of the cross point of the received signal in the ultrasonic flowmeter which concerns on Example 1 of this invention. It is a block diagram which shows the structure of the ultrasonic flowmeter which concerns on Example 1 of this invention.

Explanation of symbols

100 Flow path 101 First ultrasonic transducer 102 on the upstream side Second ultrasonic transducer 103 on the downstream side Transmission / reception switching circuits 104, 104a Transmission circuit 105 Reception circuit 106 Filter circuit 107 Level detection circuit 108 Reference value holding circuit 109 Comparator 110, 110a Gain setting circuit 111 Delay circuit 112 Amplifier circuit 113 Comparator 114 Flow measurement circuit 115 Repetition circuit

Claims (7)

A transmission circuit for generating a drive pulse signal;
A first ultrasonic transducer disposed in a flow path and generating an ultrasonic wave in response to a drive pulse signal from the transmission circuit;
A second ultrasonic transducer that is disposed opposite to the first ultrasonic transducer at a certain distance in the flow path, receives the ultrasonic wave generated by the first ultrasonic transducer, and outputs it as a received signal;
A level detection circuit for detecting a level of a reception signal output from the second ultrasonic transducer;
Correction means for correcting the level of the received signal based on the level of the received signal detected by the level detection circuit;
An ultrasonic propagation time from the first ultrasonic transducer to the second ultrasonic transducer is measured based on the received signal whose level is corrected by the correcting means, and the flow is measured based on the measured propagation time. A flow rate measurement circuit for measuring the flow rate of the fluid flowing in the path,
An ultrasonic flowmeter comprising: The correction means includes
An amplification circuit for amplifying the reception signal output from the second ultrasonic transducer;
A comparator that compares the level of the received signal detected by the level detection circuit with a predetermined reference value and outputs the comparison result as a difference signal;
A gain setting circuit for setting a gain for the amplifier circuit such that the level of the received signal becomes a predetermined level based on the differential signal from the comparator;
The ultrasonic flowmeter according to claim 1, further comprising: The correction means includes
A comparator that compares the level of the received signal detected by the level detection circuit with a predetermined reference value and outputs the comparison result as a difference signal;
Based on the difference signal from the comparator, the drive voltage of the drive pulse signal generated by the transmitter circuit is controlled by sending a drive voltage control signal to the transmitter circuit so that the level of the received signal becomes a predetermined level. A gain setting circuit;
The ultrasonic flowmeter according to claim 1, further comprising: A delay circuit that delays a reception signal output from the second ultrasonic transducer by a time required for correction by the correction unit;
The ultrasonic flowmeter according to claim 1, wherein the correction unit corrects a level of a reception signal output from the delay circuit.   The gain setting circuit is configured so that the level of the reception signal supplied to the flow rate measurement circuit becomes a predetermined level based on the level of the reception signal obtained by performing a preliminary measurement before the main measurement for measuring the propagation time. The ultrasonic flowmeter according to claim 2, wherein a gain is set for the amplifier circuit.   The gain setting circuit is configured so that the level of the reception signal supplied to the flow rate measurement circuit becomes a predetermined level based on the level of the reception signal obtained by performing a preliminary measurement before the main measurement for measuring the propagation time. 4. The ultrasonic flowmeter according to claim 3, wherein the driving voltage control signal is sent to the transmitting circuit to control the driving voltage of the driving pulse signal generated by the transmitting circuit.   An alarm circuit is provided to notify the outside that an abnormality has occurred when it is detected that the level of the received signal output from the second ultrasonic transducer is less than a predetermined reference value. The ultrasonic flowmeter according to any one of claims 1 to 6.

Images