JP2001249038A - Flow-rate measuring apparatus - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a flow-rate measuring apparatus by which the zero point can be corrected precisely. SOLUTION: The flow-rate measuring apparatus is composed of a first ultrasonic sensor TD1, a second ultrasonic sensor TD2 and a flow-rate measuring part 3. The measuring part 3 is provided with a first oscillation means 34, a second oscillation means 35, a reception means 36, a flow-rate measuring means 31-1, a comparison means 31-2 and a control means 31-3. In the comparison means 3102, in a state that a flow rate is zero, a first reception amplitude at a time when an ultrasonic signal from the ultrasonic sensor TD1 is received by the ultrasonic sensor TD2 and a receiving circuit 36 after a definite time t3 is compared with a second reception amplitude at a time when an ultrasonic signal from the ultarsonic sensor TD2 is received by the ultrasonic sensor TD1 after the definite time t3. The control means 31-3 makes the gain or the oscillation frequency of the oscillation means 34 or the oscillation means 35 variable on the basis of the comparison result of the comparison means 31-2, and it controls the first reception amplitude so as to agree with the second reception amplitude.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a flow rate measuring device for measuring a flow rate of a gas or the like using ultrasonic waves, and more particularly to a technique for correcting a zero flow rate.

[0002]

2. Description of the Related Art FIG.
An ultrasonic flowmeter having a configuration shown in FIG.
The ultrasonic flow meter is disposed at a predetermined distance L in a gas flow path 2 formed in a housing 1 having a gas inlet 1a and an outlet 1b, and operates at an ultrasonic frequency, for example, a piezoelectric vibrator. Ultrasonic sensors TD1 and TD2 comprising
Having. An operation of causing the other ultrasonic sensor TD2 or TD1 to receive an ultrasonic signal generated from one ultrasonic sensor TD1 or TD2 alternately is performed, and the ultrasonic signal is propagated between the ultrasonic sensors TD1 and TD2 in the gas flow direction. Time t1 and time t2 of propagation in the direction opposite to the gas flow direction were measured, and the two measured propagation times t
The flow velocity V of the gas flowing in the gas flow path 2 is intermittently obtained based on the propagation time difference between 1 and t2.

[0003] Specifically, assuming that the propagation speed (sound speed) of sound in a stationary gas is c, the propagation speed of the ultrasonic signal in the forward direction of the gas flow is (c + V). The time t1 when the ultrasonic signal from the ultrasonic sensor TD1 advances in the same direction as the gas flow and reaches the ultrasonic sensor TD2, and the ultrasonic signal from the ultrasonic sensor TD2 advances in the opposite direction to the gas flow. T
The time t2 to reach D1 is t1 = L / (c + V) (1) t2 = L / (c−V) (2) From the equations (1) and (2), V = (L / 2) · (1 / t1-1 / t2) = (L / 2) · ((t2−t1) / (t2 · t1)) (3) , L are known, the flow velocity V can be obtained by measuring t1 and t2.

When the flow velocity V is obtained, the instantaneous flow rate Q
i is given by: Qi = A · (L / 2) · ((t2−t1) / (t2 · t1)) (4) where A is the cross-sectional area of the gas flow path 2.

The passing flow rate Qt is obtained by multiplying the instantaneous flow rate Qi obtained as described above by the intermittent time, and the integrated flow rate Q obtained by integrating the passing flow rate Qt is displayed on a display (not shown). Thereby, an ultrasonic flowmeter can be configured. The housing 1 houses a flow rate measuring unit 3 composed of a microcomputer or the like, controls the generation and reception of the ultrasonic waves by the above-described ultrasonic sensors TD1 and TD2, and has a propagation time t1 based on the received ultrasonic waves. , T2, and calculation of the flow velocity, instantaneous flow rate, passing flow rate, integrated flow rate, and the like based on the measured propagation time.

On the other hand, in the state where the flow rate is zero, if the characteristics of the ultrasonic sensors TD1 and TD2 are the same, t1 = t2. However, due to the aging of the ultrasonic sensors TD1 and TD2, their reception amplitudes change. As a result, the measurement of the propagation time is not performed correctly, so that t1 ≠ t2, and a time difference of Δt may occur.

That is, for example, as shown in FIG.
In a state where the flow rate is zero, the ultrasonic sensor TD1 is driven, and an ultrasonic signal emitted from the ultrasonic sensor TD1 is received by the ultrasonic sensor TD2, and a propagation time t1 until the reception amplitude Vth is obtained, and the ultrasonic sensor TD2 is transmitted. When driven, the ultrasonic signal emitted from the ultrasonic sensor TD2 is
1 and a propagation time t until the reception amplitude Vth is obtained.
2 do not match, and a time difference of Δt may occur (Δt
= T1-t2). At this time, as shown in FIG. 12, the time difference Δt shows a characteristic (initial value characteristic A) that increases linearly in proportion to the increase in the flow rate value, and when t1> t2, the time difference Δt becomes positive from the initial value. The characteristic is shifted in the direction (characteristic B).
When t1 <t2, the characteristic is shifted in the negative direction (characteristic C).

In such a case, the measured flow value does not become zero by the deviation width due to the time difference of Δt, so that correct flow measurement cannot be performed. Therefore, the zero flow rate correction is performed by correcting the deviation from the initial value measured when the flow rate is zero and applying the deviation to the actual measured flow rate value.

[0009]

However, FIG.
As shown in the above, when the time difference Δt based on the temporal change of the ultrasonic sensors TD1 and TD2 has the same deviation width from the initial value at any flow rate, the zero point correction can be performed by the above-described method. If the deviation width from the initial value (characteristic A) is different depending on the flow rate value, there is a problem that if the zero point is corrected by the above-described method, the deviation when there is a flow rate increases.

[0010] Therefore, an object of the present invention is to provide a flow rate measuring apparatus capable of performing accurate zero point correction in view of the above-mentioned problems.

[0011]

In view of the above-mentioned object,
As shown in the basic configuration diagram of FIG. 1, the first and second ultrasonic sensors TD1 and TD1, which are arranged at predetermined intervals in a flow path through which a fluid flows, as shown in the basic configuration diagram of FIG. T
D2 and a flow rate measuring unit 3 comprising the first ultrasonic sensor TD
A first oscillator 34 for generating a signal for driving the first ultrasonic sensor 1, a second oscillator 35 for generating a signal for driving the second ultrasonic sensor TD2, and the first and second ultrasonic sensors TD1. , Receiving means for receiving signals from TD2
And a first propagation in which an ultrasonic signal from the first ultrasonic sensor TD1 driven by a signal from the first oscillating means 34 is received by the second ultrasonic sensor TD2 and the receiving means 36 At time t1, an ultrasonic signal from the second ultrasonic sensor TD2 driven by a signal from the second oscillating means 35 is received by the first ultrasonic sensor TD1 and the receiving means 36. Flow rate measuring means 31-1 for measuring the flow rate of the fluid based on the propagation time t2 of
When the flow rate is zero, the first ultrasonic sensor TD
The first reception amplitude when the ultrasonic signal from the first ultrasonic sensor 1 is received by the second ultrasonic sensor TD2 and the receiving means 36 after a predetermined time t3, and the ultrasonic signal from the second ultrasonic sensor TD2. Is a comparison result between the first ultrasonic sensor TD1 and the second reception amplitude when the second reception amplitude is received by the reception unit 36 after the predetermined time t3, and a comparison result of the comparison unit 31-2. Control means 32-3 for varying the gain or oscillation frequency of the first oscillating means 34 or the second oscillating means 35 on the basis of the above, and controlling the first received amplitude and the second received amplitude to coincide. And characterized in that:

According to the first aspect of the present invention, the flow rate measuring device includes the first and second ultrasonic sensors TD1 and TD2 arranged at predetermined intervals in the flow path through which the fluid flows, and the flow rate measuring apparatus. And part 3. The flow measuring unit 3 includes a first oscillating unit 34, a second oscillating unit 35, a receiving unit 36, a flow measuring unit 31-1, a comparing unit 31-2, and a control unit 32-3. ing. The first oscillating means 34 has a first
For driving the ultrasonic sensor TD1. Second
Oscillating means 35 generates a signal for driving the second ultrasonic sensor TD2. The receiving means 36 receives signals from the first and second ultrasonic sensors TD1, TD2. The flow rate measuring unit 31-1 is configured to receive the ultrasonic signal from the first ultrasonic sensor TD1 driven by the signal from the first oscillating unit 34, 1 and the ultrasonic signal from the second ultrasonic sensor TD2 driven by the signal from the second oscillating means 35, the first ultrasonic sensor TD1 and the receiving means 3
Then, the flow rate of the fluid is measured based on the second propagation time t2 received in step S6. In the state where the flow rate is zero, the comparing unit 31-2 performs the first operation when the ultrasonic signal from the first ultrasonic sensor TD1 is received by the second ultrasonic sensor TD2 and the receiving unit 36 after a predetermined time t3. The reception amplitude is compared with a second reception amplitude when the ultrasonic signal from the second ultrasonic sensor TD2 is received by the first ultrasonic sensor TD1 and the receiving means 36 after a predetermined time t3. Control means 32
-3 varies the gain or the oscillation frequency of the first oscillating means 34 or the second oscillating means 35 based on the comparison result of the comparing means 31-2, and the first received amplitude and the second received amplitude match. To control.

According to a second aspect of the present invention, in the flow rate measuring device of the first aspect, a shutoff valve 4 for shutting off the flow path 2 is provided. There is a feature.

According to the second aspect of the present invention, the shut-off valve 4 for shutting off the flow path 2 is provided. When the flow rate is zero, the shut-off valve 4 is closed.

According to a third aspect of the present invention, in the flow rate measuring device of the first aspect, the pressure sensor 5 is provided. It is characterized in that it is in a state where it is in a predetermined range equal to or close to the closing pressure and the flow rate measured by the flow rate measuring means 31-1 is in a predetermined range close to zero.

According to the third aspect of the present invention, the pressure sensor 5 is provided, and when the flow rate is zero, the pressure in the flow path is equal to or smaller than the closing pressure based on the detection output of the pressure sensor 5. And the flow rate measured by the flow rate measuring means 31-1 is within a predetermined range close to zero.

[0017]

Embodiments of the present invention will be described below with reference to the drawings.

FIG. 2 and FIG. 3 are a configuration diagram and a block diagram showing an embodiment of the flow rate measuring device according to the present invention. In the figure, the same reference numerals are given to the same parts as those in the conventional example in FIG. 10, and detailed description thereof will be omitted in the following description.

In FIG. 2, the flow rate measuring device according to the present invention comprises:
As an example, an electronic gas meter is configured, is disposed at a fixed distance L in a flow path 2 formed in a housing 1 having a gas inlet 1a and an outlet 1b, and operates at an ultrasonic frequency, for example, a piezoelectric vibrator. A first ultrasonic sensor TD1 and a second ultrasonic sensor TD2.

Further, a flow velocity measuring unit 3 is housed in the housing 1 to control the generation and reception of ultrasonic waves by the ultrasonic sensors TD1 and TD2, and a propagation time t1 based on the received ultrasonic waves. , T2, and calculation of the flow velocity, instantaneous flow rate, passing flow rate, integrated flow rate, and the like based on the measured propagation time.

In the vicinity of the gas inlet 1a, a shutoff valve 4 for shutting off a gas flow and a pressure sensor 5 for detecting a gas pressure are arranged.

FIG. 3 is a block diagram showing an example of the configuration of the flow rate measuring section 3. The microcomputer (μCOM) 31 as flow rate detecting means, comparing means and control means, amplifiers 32 and 33, and the first oscillator It comprises an ultrasonic sensor oscillating circuit 34 as a means, an ultrasonic sensor oscillating circuit 35 as a second oscillating means, and a receiving circuit 36 as a receiving means. The ultrasonic sensor TD1 is driven by an oscillation signal in the form of a pulse burst from the ultrasonic sensor oscillating circuit 34 to generate ultrasonic waves, and receives the ultrasonic signal emitted from the ultrasonic sensor TD2 and Send to Similarly, the ultrasonic sensor TD2 includes an ultrasonic sensor oscillation circuit 35
Is driven by an oscillation signal in the form of a pulse burst from the controller, generates an ultrasonic wave, and receives an ultrasonic signal emitted from the ultrasonic sensor TD1 and sends it to the receiving circuit.

The receiving circuit 13 receives a signal from the other ultrasonic sensors TD1 and TD2 which has received the ultrasonic signal transmitted through the flow path 2 and has a preamplifier (not shown) for processing the ultrasonic signal. Built-in.

The μCOM 31 includes ultrasonic sensors TD1, T
While controlling generation and reception of ultrasonic waves by D2, measurement of propagation times t1 and t2 based on the received ultrasonic waves, flow velocity, instantaneous flow rate, passing flow rate based on the measured propagation times,
Performs calculations such as integrated flow. Also, μCOM31
Performs processing based on the gas pressure detection signal from the pressure sensor 4 and controls the shutoff valve 5.

Next, the flow rate zero point correction processing of the present invention in the above configuration will be described. In the present invention, in summary, the flow rate zero point is corrected by correcting a change in the reception amplitude due to a change with time of the ultrasonic sensor.
That is, the reception amplitude levels of the ultrasonic sensors TD1 and TD2 at a certain time t (s) in the zero flow state are measured and compared, and the ultrasonic sensor oscillation circuit is set so that the amplitudes of the respective reception waveforms become the same. The zero point is corrected by changing the drive voltage or the oscillation frequency of the drive 34, 35.

Hereinafter, the flow rate zero point correction processing will be described in detail. First, the μCOM 31 closes the shut-off valve 5 to stop the gas flow, and creates a state where the flow rate is zero. Next, μCO
M31 drives the ultrasonic oscillation circuit 34 to generate a pulse burst signal, and supplies the pulse burst signal to the ultrasonic sensor TD1 to generate an ultrasonic signal. The ultrasonic signal transmitted from the ultrasonic sensor TD1 is received by the ultrasonic sensor TD2, and a signal from the ultrasonic sensor TD2 based on the ultrasonic signal is received by the receiving circuit. The μCOM 31 takes in a signal generated by the receiving circuit 13 in response thereto. At this time, μ
As shown in FIG. 4, the COM 31 includes an ultrasonic sensor TD1 based on a pulse burst signal of the ultrasonic sensor oscillation circuit 34.
After a certain period of time t3 from the drive, the amplitude value y (v) of the received waveform received by the ultrasonic sensor TD2 and the receiving circuit 36 is measured.

Next, the μCOM 31 is connected to the ultrasonic oscillation circuit 3.
5 is driven to generate a pulse burst signal, which is supplied to the ultrasonic sensor TD2 to generate an ultrasonic signal. The ultrasonic signal transmitted from the ultrasonic sensor TD2 is received by the ultrasonic sensor TD1, and a signal from the ultrasonic sensor TD1 based on the ultrasonic signal is received by the receiving circuit. μC
The OM 31 captures a signal generated by the receiving circuit 13 in response. At this time, as shown in FIG. 4, the μCOM 31 outputs the amplitude of the received waveform received by the ultrasonic sensor TD1 and the receiving circuit 36 after a fixed time t3 from the driving of the ultrasonic sensor TD2 by the pulse burst signal of the ultrasonic sensor oscillating circuit 35. Measure the value z (v).

Next, the μCOM 31 calculates both reception amplitude values y
(V) and z (v) are compared, and as shown in FIG.
If (v) is smaller than z (v), the μCOM 31 changes the gain of the ultrasonic sensor oscillation circuit 34 to
Control is performed so that y (v) matches z (v). In detail, the μCOM 31 increases the gain of the amplifier 32, and thereby increases the drive voltage of the ultrasonic oscillation circuit 34, thereby increasing the gain. Therefore, the amplitude of the pulse burst signal of the ultrasonic oscillation circuit 34 increases, thereby increasing the level of the ultrasonic signal from the ultrasonic sensor TD1.
D2 and the reception amplitude y (v) of the reception circuit 36 increase, and as a result, control is performed so as to match z (v).

On the other hand, if z (v) is smaller than y (v), the μCOM 31 controls the ultrasonic sensor oscillation circuit 35 to change z (v) to y (v) by changing the gain. . Specifically, the μCOM 31 increases the gain of the amplifier 33, and thereby the ultrasonic oscillation circuit 3
The gain is increased by increasing the drive voltage of No. 5.
Therefore, the amplitude of the pulse burst signal of the ultrasonic oscillation circuit 35 increases, thereby increasing the level of the ultrasonic signal from the ultrasonic sensor TD2, and the ultrasonic sensor TD1 and the receiving circuit 36 receiving this after a predetermined time t3. The reception amplitude z (v) increases, and as a result, control is performed so as to match y (v).

In this manner, the gain of the ultrasonic sensor oscillation circuit 34 or 35 is variably controlled so that the two reception amplitudes y (v) and z (v) after the fixed time t3 coincide with each other. By maintaining the gain, at the time of the flow rate measurement described above, t1 = t2 in the state of the zero flow rate, which means that the zero flow rate correction has been performed.

In this case, as shown in FIG. 5, even when the deviation width of the time difference Δt from the initial value (characteristic A) is not constant (characteristic B or C), the reception amplitude values y (v) and z (v) Are corrected to be the same, so that there is no deviation from the initial value. Therefore, even when there is a flow rate, correct flow rate measurement can be performed.

In the above description, the zero point correction is performed by changing the gain of the ultrasonic sensor oscillation circuit 34 or 35. Alternatively, the ultrasonic sensors TD1, TD
The oscillation frequency of the ultrasonic sensor oscillation circuit 34 or 35 may be varied by using the impedance characteristic of No. 2.

The ultrasonic sensors TD1 and TD2 generally have a characteristic that the impedance z changes with respect to the excitation frequency f, as shown in FIG. Excitation frequency value C actually used in the ultrasonic sensor for transmitting and receiving ultrasonic signals
Is set between the series resonance point A and the parallel resonance point B. At the time of transmission, when the excitation frequency value C approaches the series resonance point A,
Although it vibrates greatly, it is easily broken, and the maximum sensitivity can be obtained by bringing the excitation frequency value C closer to the parallel resonance point B during reception.

Therefore, μCOM 31 calculates both reception amplitude values y
(V) is compared with z (v). If y (v) is smaller than z (v), the gain of the amplifier 32 is increased, thereby increasing the frequency of the pulse burst signal of the ultrasonic oscillation circuit 34. Thereby, the excitation frequency of the ultrasonic sensor TD2 that has received the ultrasonic signal emitted from the ultrasonic sensor TD1 excited by the pulse burst signal approaches the parallel resonance point B in FIG. Therefore, the amplitude of the signal sent from the ultrasonic sensor TD2 to the receiving circuit 36 increases, and the receiving amplitude y (v) of the receiving circuit 36 increases, and as a result, z
Control is performed so as to coincide with (v).

On the other hand, if z (v) is smaller than y (v), the gain of the amplifier 33 is increased, thereby increasing the frequency of the pulse burst signal of the ultrasonic oscillation circuit 35. As a result, the excitation frequency of the ultrasonic sensor TD1, which has received the ultrasonic signal emitted from the ultrasonic sensor TD2 excited by the pulse burst signal, approaches the parallel resonance point B in FIG. Therefore, the amplitude of the signal sent from the ultrasonic sensor TD1 to the receiving circuit 36 increases, and the receiving circuit 36
Is increased, and as a result, it is controlled to match y (v).

In this way, the oscillation frequency of the ultrasonic sensor oscillation circuit 34 or 35 is variably controlled so that the reception amplitudes y (v) and z (v) after a certain time t3 coincide with each other.
By maintaining the oscillation frequency after the change, t1 = t2 in the zero flow state at the time of the flow rate measurement described above, which means that the zero flow rate correction has been performed.

Next, the above-mentioned zero point correction processing will be described with reference to the flowchart of FIG. First, a state where the flow rate is zero is confirmed by closing the shutoff valve 5 (step S1). Next, an ultrasonic signal is emitted from the ultrasonic sensor TD1, and the time t
The reception amplitude y (v) in the ultrasonic sensor TD2 and the receiving circuit 36 at 3 (s) and the ultrasonic signal from the ultrasonic sensor TD2, and the ultrasonic sensor TD1 and the receiving circuit 36 at time t3 (s) Is measured at step (2) (step S2).

Next, y (v) and z (v) are compared, and it is determined whether or not both match (step S3). If the answer to step S3 is no, the ultrasonic sensor oscillation circuit 3
The gain or transmission frequency of 4 or 35 is varied (step S4). Next, it is determined whether y (v) and z (v) match (step S5). If the answer is no, the process returns to step S4, and the operation of changing the gain or transmission frequency of the ultrasonic sensor oscillation circuit 34 or 35 is continued.

If the answer in step S5 is yes,
Alternatively, if the answer to step S3 is yes, t1 = t2 (step S6) and Q = 0 (step S6).
7).

Next, FIG. 8 shows a step S1 in FIG.
9 is a flowchart illustrating an example of a subroutine for performing a zero flow rate confirmation process. First, μCOM31 is
Learn the gas usage pattern by measuring the flow rate (step S
11) Check the time period when no use is made. Then, control is performed such that the shut-off valve 5 is closed in the time period when the flow is not used (step S12), and a state of zero flow is created (step S13).

Further, in the above-described process of confirming the zero flow state in step S1, instead of the shut-off valve 5 shown in FIG. 8, the detection of gas pressure confirms that there is no turbulent flow, and the flow rate varies. Confirmation that the value is equal to or less than the value may be included. FIG. 9 is a flowchart showing an example of a subroutine for performing the process of confirming the zero flow in this case. First, μ
The COM 31 learns the gas usage pattern by measuring the flow rate (step S21), and measures the gas pressure with the pressure sensor 4 when the usage is small (step S22). Next, it is determined whether or not the detected gas pressure is equal to the closing pressure (step S23). If the answer is yes, increasing the resolution of the pressure sensor 4 (step S24), and then, the difference P (= P ₁ -P ₀₎ of occlusion pressure P ₀ and the gas pressure P ₁ detected
Is the absolute value | P |
≦ | P | ≦ a) It is determined whether or not.

If the answer is yes, the ultrasonic sensor TD
1 and TD2 to measure the flow rate (step S26),
It is determined whether or not the obtained absolute value | Q | of the flow rate value is within a predetermined range close to zero (b ≦ | Q | ≦ c) (step S27). Here, b is the minimum value of the measured flow rate error, and c is the maximum value of the flow rate set not to be used by the user. If the answer is yes, it is determined that the flow rate is zero (step S28).

On the other hand, if the answer to step S23 or S25 or S27 is NO, the timer is counted for a predetermined time T (step S29), and thereafter, the process returns to step S22, and the operations after step S22 are repeated again. Here, the predetermined time T for counting the timer is a waiting time for repeating the operation from step S22 onward again.
The specific value is determined by learning of the μCOM 31 in step S21.

[0044]

According to the first aspect of the present invention, the flow rate can be accurately corrected to zero, and the flow rate can be correctly measured without erroneously determining that there is a flow rate when the flow rate is zero. There is no charge. Also, when there is a flow rate, correct measurement can be performed.

According to the second aspect of the present invention, a completely zero flow state can be created for zero flow rate correction.

According to the third aspect of the invention, it is possible to perform the zero correction of the flow rate without affecting the use of the user.

[Brief description of the drawings]

FIG. 1 shows a basic configuration diagram of a flow measurement device according to the present invention.

FIG. 2 is a configuration diagram showing an embodiment of a flow measurement device according to the present invention.

FIG. 3 is a block diagram illustrating a configuration example of a flow measurement unit in FIG. 2;

FIG. 4 is a signal waveform diagram showing a state of reception amplitude of the ultrasonic sensor in FIG. 2 after a predetermined time.

FIG. 5 is a diagram showing a flow rate versus propagation time difference characteristic of an ultrasonic signal in FIG. 2;

FIG. 6 is a diagram showing frequency versus impedance characteristics of the ultrasonic sensor in FIG.

FIG. 7 is a flowchart showing a zero point correction process in FIGS. 2 and 3;

FIG. 8 is a flowchart showing an example of a subroutine for confirming a zero flow state in the flowchart of FIG. 7;

FIG. 9 is a flowchart showing another example of a subroutine for confirming a zero flow state in the flowchart of FIG. 8;

FIG. 10 is a configuration diagram illustrating an example of a conventional flow measurement device.

11 is a signal waveform diagram showing a state of reception amplitude of the ultrasonic sensor in FIG.

12 is a diagram showing a flow rate versus propagation time difference characteristic of an ultrasonic signal in FIG. 10;

[Explanation of symbols]

 2 Flow path 3 Flow velocity measuring unit 4 Shut-off valve 5 Pressure sensor 31-1 Flow rate detection means (μCOM) 31-2 Comparison means (μCOM) 31-3 Control means (μCOM) 34 First oscillation means (ultrasonic sensor oscillation circuit) ) 35 second oscillating means (ultrasonic sensor oscillation circuit) 36 receiving means (receiving circuit) TD1 first ultrasonic sensor TD2 second ultrasonic sensor TD3 third ultrasonic sensor

Claims (3)

[Claims] 1. A flow rate measuring apparatus comprising: first and second ultrasonic sensors arranged at predetermined intervals in a flow path through which a fluid flows; and a flow rate measuring unit, wherein the flow rate measuring unit is Generating a signal for driving the first ultrasonic sensor;
Oscillating means, and a second means for generating a signal for driving the second ultrasonic sensor
Oscillating means; receiving means for receiving signals from the first and second ultrasonic sensors; and an ultrasonic signal from the first ultrasonic sensor driven by a signal from the first oscillating means. The first propagation time received by the second ultrasonic sensor and the receiving unit and the ultrasonic signal from the second ultrasonic sensor driven by the signal from the second oscillating unit are the same as those of the second ultrasonic sensor. Flow rate measuring means for measuring a flow rate of the fluid based on the first ultrasonic sensor and the second propagation time received by the receiving means; and an ultrasonic wave from the first ultrasonic sensor in a state of zero flow rate A first reception amplitude when a signal is received by the second ultrasonic sensor and the reception unit after a predetermined time;
Comparing means for comparing an ultrasonic signal from the second ultrasonic sensor with a second reception amplitude when the ultrasonic signal is received by the first ultrasonic sensor and the receiving means after the predetermined time; Control means for varying the gain or the oscillating frequency of the first oscillating means or the second oscillating means on the basis of the comparison result, and controlling the first reception amplitude and the second reception amplitude to match. A flow rate measuring device comprising: 2. The flow rate measuring device according to claim 1, further comprising a shut-off valve for shutting off the flow path, wherein the zero flow state is a state in which the shut-off valve is closed. 3. A state in which a pressure sensor is provided and the flow rate is zero is
Based on the detection output of the pressure sensor, the pressure in the flow path is equal to or close to a closing pressure, and falls within a predetermined range close to the closing pressure, and the flow rate measured by the flow rate measuring unit is within a predetermined range close to zero. The flow measurement device according to claim 1, wherein the flow measurement device is in a state.