JPH10253413A - Ultrasonic flowmeter - Google Patents

Abstract

PROBLEM TO BE SOLVED: To miniaturize an ultrasonic flowmeter, enhance its accuracy, and widen the range of flow rates to be measured. SOLUTION: A transceiver (1 or 2) on the transmitting side is driven by the algebraic sum E-F of the output voltage E of an OR circuit 8 and the output voltage F of an OR circuit 9. When T is a fixed period, drive is carried out for the first (T/2)×4 period of the driving voltage of E-F at (b) to excite the transceiver. In the following (T/2)×4 period, drive is carried out to excite the transceiver. In the following (T/2)×2 period, a voltage of the opposite phase is applied for braking. Reverberation is thereby eliminated.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention relates to an improvement of an ultrasonic flow meter.

[0002]

2. Description of the Related Art An ultrasonic flowmeter which measures the propagation time of ultrasonic waves in the forward and reverse directions with respect to a flow, calculates the flow velocity from this propagation time to determine the flow rate, and further calculates the integrated flow rate. It is well known.

In FIG. 5, if the sound velocity in a stationary fluid is C and the velocity of the fluid flow is V, the propagation velocity is C + V when the propagation direction of the sound wave is the same as the flow direction, and the velocity is opposite to the flow. In the case of the direction, it becomes CV.

Accordingly, a pair of ultrasonic transducers 1 and 2 are disposed at a distance L from each other upstream and downstream of the flow tube 3, and an ultrasonic pulse is transmitted from one transducer 1 in the forward direction. When transmitting, the arrival time required for the ultrasonic pulse to reach the other transducer 2 is t ₁ , and when the ultrasonic pulse is transmitted from the transducer 2 in the reverse direction, the ultrasonic pulse is transmitted to the transducer 1. Assuming that the arrival time required for arrival is t ₂ , t ₁ = L / (C + V) (1) t ₂ = L / (C−V) (2)

The flow velocity V is determined from the above equations (1) and (2) as V = L {(1 / t ₁ ) − (1 / t ₂ )} / 2 (3)

In order to improve the accuracy of propagation time measurement, instead of measuring _one arrival time t ₁ , t ₂ from transmission to reception, the next transmission is performed a plurality of times (n times) in the same direction at the same time as reception. ) By repeating, arrival time (propagation time) t
₁ and t ₂ are repeated n times, and the time nt ₁ and nt ₂ from the first (first) transmission to the last (n-th) reception
Was measured.

The arrival time of the ultrasonic pulse is, as shown in FIG. 6, a time t from the transmission drive signal P for exciting the transmitter / receiver on the transmission side to the head a of the received wave. Since the amplitude grows and attenuates after the maximum amplitude elapses, the head a affected by noise cannot be accurately detected. Also, the waveform may fluctuate due to the flow of the fluid.

Therefore, a well-known received wave detection unit determines a threshold value V _TH as a reference for reception, and detects a zero cross point C at which a wave that first reaches this level passes through a zero level to obtain τ from a time measured. , The arrival time t was determined.

The threshold value V _TH is set so that the zero cross point of a certain specific wave (third wave in FIG. 6) can be always detected. It is stored, and it is obtained by subtracting τ from the time at the zero cross point C.

In the example of FIG. 6, the third wave of the received wave first reaches the threshold value V _TH at the point indicated by the symbol b, and the point indicated by the symbol C is the zero cross point of the third wave. If the zero-cross point of the wave immediately before or immediately after the specific wave (eg, the third wave) is incorrectly detected,
The arrival time differs by one period of the ultrasonic wave, and causes a large measurement error.

Particularly, in an ultrasonic flowmeter in which transmission and reception are repeated a plurality of times (n times) continuously in the same direction in order to improve the measurement accuracy of the arrival time, n times of the arrival time are collectively measured. If all the n receptions do not reliably capture the aimed wave, an error will occur. An error will occur if a wave targeted at any one of n times is removed, and the probability that accurate measurement can be performed may be reduced.

In order to reduce this error factor, it is necessary to sufficiently increase the ultrasonic pulse signal. This is because if the signal is sufficiently larger than the noise, the margin for the waveform fluctuation becomes large.

The only way to increase the reception signal is to increase the oscillation drive power of the transmitter / receiver on the transmission side. However, transmission and reception are performed by a method of transmitting the next at the same time as receiving the ultrasonic wave.
In an ultrasonic flowmeter that measures nt in a continuous manner and collectively measures nt (especially in a small flowmeter), there is a problem that even if a large drive is performed, the effect is small.

That is the problem of reverberation. Since ultrasonic waves are emitted to a space partitioned by a tube wall or the like, there is inevitably reverberation, and if the next received wave arrives before the reverberation disappears, the reverberation becomes noise.

As a countermeasure, it is conceivable that the next transmission is performed after the reverberation becomes sufficiently small. However, in principle, the transmission interval is determined by the distance L and the propagation speed C and cannot be long. In particular, a small meter has a small distance L and a short transmission interval.

In order to sufficiently increase the received signal with respect to noise, even if the transmission power is increased, the reverberation also increases in proportion to the power. Therefore, when the reverberation becomes larger than the noise other than the reverberation, the power is further increased. S / E
No improvement in N ratio is observed.

In order to ensure the accuracy of the ultrasonic flowmeter, it is indispensable to always catch a specific wave, but it is difficult to maintain the accuracy because the S / N ratio is limited as described above. Another problem due to the inability to use large power for transmission is the difference in τ depending on the transmission direction of ultrasonic waves.

As described above, in the arrival time measurement, t and τ are measured together (actually, n times the measurement), and τ is subtracted later to obtain t. Therefore, τ is a problem in realizing an accurate flowmeter. In particular, when τ in the forward direction and τ in the reverse direction are stored as the same value, the difference between the actual value and the actual value is the movement of the zero point, which causes a large error in the minute flow rate range.

What determines τ is the transmitting frequency of the transmitting side. The accuracy in the micro flow rate range depends on how to correctly control or control this transmission frequency.

However, in the method of detecting the rising of the received wave as in the present method, it is only necessary to transmit the ultrasonic element of the transmitter / receiver for a moment, so that one rectangular pulse (or a period equivalent thereto) is required. (No pulse). In this case, the transmission frequency cannot be controlled, and it is determined by the natural frequency of the transmitting ultrasonic element.

Since the natural frequency slightly varies from element to element, and varies depending on the temperature and the like, and the manner of the change varies from individual to individual, it is difficult to always correctly grasp τ. For this reason, it is conceivable to vibrate the transmitting side element with several rectangular pulses having a constant period in order to control the transmitting frequency to some extent. However, to control the frequency to some extent, it is necessary to apply a large power to the element.

However, it is difficult to control the frequency because a large power cannot be used for transmission for the above-mentioned reason, and thus it has been difficult to realize a flowmeter with high accuracy even in a minute flow rate range.

Accordingly, an object of the present invention is to realize a small and accurate ultrasonic flowmeter from a large flow rate range to a minute flow rate range.

[0024]

In order to achieve the above object, according to the first aspect of the present invention, at least one pair of ultrasonic transducers, which work on both a transmitting side and a receiving side, are provided, and the flow of the fluid is controlled. An ultrasonic flowmeter that transmits and receives ultrasonic waves from upstream to downstream and from downstream to upstream, and obtains the flow velocity and the flow rate from the arrival time in each direction.First, the transmitter on the transmission side is transmitted, and the transmission and reception on the transmission side is performed. When the received wave detection unit which receives a signal from the wave detector detects a received wave, the transmitting / receiving wave transmitter on the transmitting side is transmitted again at the same time.
The time from the first transmission to the reception of the fixed number of times (the n-th time), that is, n times of the arrival time, is collectively measured, and the arrival time is obtained from the result. The unit comprises an amplifying unit and a comparing unit. The signal from the transmitter / receiver is amplified first and then compared with a reference voltage level (V _TH ). The point at which the crossed wave passes through the next zero level is set as the point at which the received wave is detected, and the reference voltage level is set so that some predetermined wave always crosses first. And after driving the transmitter / receiver on the transmitting side several times with a waveform having a fixed period,
An ultrasonic flowmeter characterized in that braking is performed so as to forcibly stop subsequent vibration.

The ultrasonic flowmeter according to the present invention captures the rise of the received wave, and it is preferable that the zero cross point of the third wave, the fourth wave, the fifth wave, or the like at the relatively front end is set as the reception detection point. Therefore, there is no effect on the reception detection regardless of the size of the subsequent waves.

However, it can be said that reverberation increases as the peak value of the received wave increases. As for the drive waveform, the voltage waveform applied first from the normal state in which no voltage is applied is referred to as the first drive, and the subsequent reverse voltage waveform is referred to as the second drive in the subsequent drive (see FIG. 3). ).

For example, considering the case of capturing the third wave of the received wave, if it is assumed that the speed at which the information of the drive waveform is transmitted is the same as the sound speed, the drive waveform that affects the third wave of the received wave is the same. Up to the third drive. It is up to the fourth drive to affect the zero-cross point of the third wave. Therefore, the shape of the drive waveform after the end of the fourth drive does not affect the reception detection point.

In the present invention, the peak value of the received wave is not so increased by devising the waveform after the end of the fourth driving, and the reverberation is relatively reduced.
In the prior art, the reception waveform is such that the first wave is smaller than the second wave,
The wave gradually becomes larger, and peaks at several waves or tens of waves from the head as shown in FIG. This is the same even when the drive is a single drive of only the first drive. This means that the transmitter element does not vibrate once with one drive, but vibrates several times continuously, emits ultrasonic waves continuously to some extent, and makes a peak when the drive ends. This indicates that the vibration is continuous after the vibration.

Therefore, if the excessive vibration that does not affect the reception wave detection point after the driving is forcibly stopped or reduced, the peak of the reception wave is reduced and the reverberation is also reduced.

The amplitude of the received wave increases sharply until the reception is detected, and thereafter does not increase so much. Therefore, the peak is relatively small, and the reception without reverberation can be realized. The wave aimed at the flow rate region can be reliably captured, and thus a flow meter with less error can be realized.

The first drive or the first drive and the second drive
It is not possible to control the frequency of transmission by driving alone because there is no element that determines the period. However, if the first drive to the fourth drive are performed, the frequency of transmission can be controlled to some extent because it includes the element of period. (See FIG. 3).

The fact that the frequency of transmission can be controlled means that the period of reception can be controlled.
Is to be able to control Thus, if τ in the forward direction and the reverse direction can be made the same, accurate measurement in a minute flow rate region is possible.

Conventionally, when a certain amount of power is applied to a transmitting element with a driving waveform having a period in order to aim for such an effect, there is reverberation as described above. Nt is continuously measured and nt is collectively measured.
It was not possible to increase the resolution of the measurement.

According to the present invention, if the extra vibration is stopped or reduced, the reverberation can be reduced without affecting the reception detection point. Claim 2
According to the invention, in the ultrasonic flowmeter according to the first aspect, the transmitter / receiver on the transmission side is driven several times with a waveform having a fixed period, and then a voltage having a phase opposite to that of the drive is applied for a short time to forcibly vibrate. It is characterized by stopping.

The third aspect of the present invention provides the first or second aspect.
In the ultrasonic flowmeter described above, the number of the several times of driving is set to a number obtained by adding one to the number corresponding to the number of the predetermined wave.

In the present invention, the number of drives of the transmitter / receiver on the transmitting / receiving side is set to be the strongest for determining the zero cross point of the received wave, and unnecessary free vibration thereafter can be rapidly attenuated. For example, when capturing the m-th wave
The determination of the zero cross point of the wave may be considered up to the (m + 1) th drive. Therefore, the drive after that is only harmful because the reverberation is increased.

[0037]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS Next, a preferred embodiment of the present invention will be described with reference to a first embodiment shown in FIGS.
In this embodiment, a pair of ultrasonic transducers for transmitting and receiving ultrasonic waves in the same or oblique direction in the flow of the fluid, and a transducer on the receiving side are connected and receive when a received wave is detected. A reception wave detection unit that outputs a wave detection signal, and drives the transmitter / receiver on the transmission side every time the measurement on / off signal changes from the off side to the on side, and thereafter drives the reception wave detection signal for each, n
The transmitter driver that stops driving when the received wave detection signal is input or the measurement on / off signal is turned off, and the received wave detection signal from the received wave detector is Counting starts from zero each time the OFF signal turns on,
a first counter for detecting the nth received wave detection signal and outputting the nth received wave detection signal, and a time (n) from when the measurement ON / OFF signal is turned on to the nth received wave detection signal
A second counter for measuring (t ₁ + τ) and (t ₂ + τ), and switching between transmission and reception at a fixed timing to change the direction of the ultrasonic wave, and each time the measurement ON / OFF signal is changed from the OFF side to the ON side In the ultrasonic flowmeter having a control unit for reading the measured value of the second counter when receiving the n-th received wave signal and calculating the flow velocity, flow rate, and the like, the main part of the transmitter drive unit is shown in FIG. It is configured as shown in FIG.

That is, the transmitter driving section 10 is mainly constructed by connecting four one-shot circuits 4, 5, 6, 7 and two OR circuits 8, 9 as shown in FIG. It is.
One-shot circuit 4 outputs a pulse having a time width determined by the trigger signal. As shown in FIG. 2, the trigger signal is configured to be input as a trigger of the one-shot circuit 4 when the measurement ON / OFF signal changes from the OFF side to the ON side and when the received wave detection signal is input. I have. No trigger signal is input after the nth received wave detection signal is input.

Each of the one-shot circuits 5, 6, 7 is configured to output a pulse having a predetermined time width triggered by the rise of the output pulse from each of the one-shot circuits 4, 5, and 6.

In this example, an unnecessary trigger signal is input together with the n-th received wave detection signal (FIG. 2). It is also possible to prevent a trigger from being input.

The outputs A and C of the one-shot circuits 4 and 6 are O
The signal R is output to one end of the transmitter / receiver 1 or 2 on the transmission side, and the outputs B and D of the one-shot circuits 5 and 7 are ORed and applied to the other end of the transmitter / receiver 1 or 2 on the transmission side.

The output pulse widths of the three one-shot circuits 4, 5, 6 are set to the same T / 2, and the output pulse width of the other one-shot circuit 7 is set to Τ which is larger than T / 2. is there.

Accordingly, the driving voltage EF applied to the transmitter / receiver 1 or 2 on the transmitting side is as shown in FIG. 1 (b). The first half of the drive on the minus side determined by the one-shot circuit 7 constitutes the fourth drive (see FIG. 3) following the drive determined by the one-shot circuits 4 to 6, while the second half includes the first to fourth drive voltages. And acts in the direction to forcibly stop and stop the vibration of the transmitting / receiving transducer.

FIGS. 4A and 4B show a second embodiment in which a transmitter driving circuit 10 is composed of five one-shot circuits 4, 5, 6, 7, 11 and OR circuits 8, 9. FIG. 1 (a) (b)
It is suitable for a flow meter for detecting the zero-cross point of the third wave as in the embodiment of FIG.

The drive voltage applied to the transmitter / receiver 1 or 2 becomes the voltage indicated by FG in FIG. 4B, which is excited by the first four drives (T / 2) × 4, and is subsequently driven (T / 2) ×
Forcibly braking between the two.

[0046]

Since the ultrasonic flow meter of the present invention is constructed as described above, it can transmit with a large power, so that the amplitude of the received wave can be margined, and the fluctuation of the received wave can be increased. m waves can be captured.

Also, since the power is large, the frequency of oscillation can be controlled, and τ can be controlled, so that τ can be equalized in the forward and reverse directions. Therefore, the arrival time can be measured with high accuracy, and a small, high-accuracy ultrasonic flowmeter having a wide measurement flow range can be realized.

[Brief description of the drawings]

FIG. 1A is a block diagram of a main part of a transmitter driving circuit according to a first embodiment of the present invention, and FIG. 1B is a diagram showing a voltage waveform thereof.

FIG. 2 is a timing chart of the first embodiment of the present invention.

FIG. 3 is a diagram of a driving voltage waveform according to the first embodiment of the present invention.

FIG. 4A is a block diagram of a main part of a transmitter driving circuit according to a second embodiment of the present invention, and FIG. 4B is a diagram showing a voltage waveform thereof.

FIG. 5 is a schematic diagram illustrating the principle of an ultrasonic flowmeter.

FIG. 6 is a diagram illustrating detection points of a reception wave of the ultrasonic flowmeter.

FIG. 7 is a diagram illustrating a waveform of a received wave according to the related art.

[Explanation of symbols]

1, 2 Ultrasonic transducer C Zero cross point (Received wave detection point) Τ Constant period V _TH reference voltage level (threshold)

Claims (3)

[Claims] At least one pair of ultrasonic transducers that work on both a transmitting side and a receiving side are provided to transmit and receive ultrasonic waves in a fluid flow from upstream to downstream and from downstream to upstream. An ultrasonic flowmeter that determines the flow velocity and the flow rate from the arrival time of the ultrasonic wave.First, the transmitter on the transmitting side is transmitted, and the received wave detector that receives the signal from the transmitter on the transmitting side detects the received wave. At the same time, the transmitter / receiver on the transmitting side is transmitted again, and this is repeated a certain number of times (n times).
The time from the first transmission to the reception of a certain number of times (the n-th time), that is, n times of the arrival time, is collectively measured, and the arrival time is obtained from the result. The reception wave detection unit is an amplification unit. The signal from the transmitter / receiver is amplified first and then compared with the reference voltage level (V _TH ). The point passing through the zero level is set as the point at which the received wave is detected, and the reference voltage level is always set so that some predetermined wave is first passed, and the transmission An ultrasonic flowmeter characterized in that, after driving a transducer on the side several times with a waveform having a fixed period, braking is performed so as to forcibly stop subsequent vibration. 2. The method according to claim 1, wherein the transmitter / receiver on the transmitting side is driven several times with a waveform having a fixed period, and then a voltage having a phase opposite to that of the driving is applied for a short time to forcibly stop the vibration. 1
An ultrasonic flowmeter as described. 3. The ultrasonic wave according to claim 1, wherein the number of times of driving is set to a number obtained by adding one to the number corresponding to the number of the predetermined wave. Flowmeter.