JPH1073464A - Ultrasonic flowmeter - Google Patents

Abstract

PROBLEM TO BE SOLVED: To improve the measuring accuracy of a flowmeter by acquiring the specified wave of a received wave correctly even if the amplitude of the received wave is changed in a sing-around type, and acquiring the specified wave of the received wave accurately without errors even if there is the amplitude change in the received wave caused by temperature irregularity or the like. SOLUTION: A time t11 from the transmission to the reception at the first time at the time of forward direction measurement or at the time of reverse direction measurement is measured. A time α, which is slightly shorter than the half cycle of an ultrasonic wave, is determined. At the second time, a time t12 to the first zero-crossing point after the elapse of t11 -α from the transmitting time, is measured and made to serve for t12 -α for the next third time. This is repeated by (n) times. The time from the first transmission to the detection of the received wave at the (n)-th time is otherwise measured, and the flow speed and the flowrate are operated.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention relates to an improvement of an ultrasonic flowmeter.

[0002]

2. Description of the Related Art In FIG. 11, if the sound velocity in a stationary fluid is C and the flow velocity of a fluid is V, if the propagation direction of the sound wave coincides with the direction along the flow (hereinafter referred to as forward direction), The propagation speed is C + V, and is C-V in the direction opposite to the flow (hereinafter referred to as the reverse direction).

A pair of transducers 1 and 2 are arranged at a distance L from the upstream and downstream of a flow tube 3 and an ultrasonic wave is transmitted (transmitted) from one transducer 1 in a forward direction. When the time required for the ultrasonic wave to reach the other transducer 2 is t, when the ultrasonic wave is transmitted (transmitted) in the opposite direction from the transducer 2,
The arrival time required for the ultrasonic wave to reach the transducer 1 is represented by t '.
Then, t = L / (C + V) (1) t '= L / (C−V) (2)

The arrival times t, of the ultrasonic waves in the forward and reverse directions,
t ′ is measured, and the flow velocity V is calculated from the measured t ′.
The flow rate and the integrated flow rate (volume) were calculated. The flow velocity V was calculated from the above equations (1) and (2) as V = L {(1 / t)-(1 / t ')} / 2 (3).

[0005] arrival time t, to measure t ', etc., for example, as shown in FIG. 12, reception on the reception side of the transducer the transmission side of the transducer from the transmission driving signals P ₁ to excite (drive) It is good to directly measure the time t until the wave arrives, but in practice this is not possible.

This is because the received wave attenuates after its amplitude gradually increases. Although FIG. 12 shows only a part of the received waveform while the amplitude is increasing, it is impossible to detect the leading “A” which is the arrival point of the received wave.

In order to detect the arrival time of the received wave,
First, V _TH as a reference level for reception is determined, and a zero-cross point at which a wave that first reaches this level passes through a zero level is detected to detect a received wave.

[0008] The reference level V _TH is determined so as to catch some specific waves of the received wave. In FIG. 12, the third wave of the received wave is captured. That is, the reference level V at the point "b"
The third wave reaches _TH and is caught. Then, a zero-cross point "c" at which the third wave passes through the zero level is detected and set as a reception point.

However, since the actual arrival time is the head "A" of the received wave, the time τ from the point "A" to "C" is experimentally obtained in advance and stored, and the transmission drive signal P ₁ The arrival time t is obtained by subtracting τ from the actual measurement time from the time when the transmitter / receiver on the transmission side is driven to the zero-cross point “c” of the third wave of the reception wave.

As is apparent from FIG. 12, the time τ is a value corresponding to approximately 1.5 times the period of the ultrasonic wave. When the flow velocity V is obtained by the equation (3) from the single forward arrival time t or the reverse arrival time t ′ shown in the above equations (1) and (2), and the flow rate and the integrated flow rate are further obtained, the flow meter Is determined by the resolution of the reference clock of the counter that measures the time t + τ or t ′ + τ.

Therefore, in order to realize a flowmeter with higher accuracy even when a reference clock having the same resolution is used, at the time of measurement in the forward direction, the ultrasonic transmitter / receiver on the receiving side receives the received wave (specific wave of the specified wave). At the same time as detecting the (zero cross point), the ultrasonic transmitter / receiver on the transmitting side is driven and the next transmission is repeated, and the transmission / reception is repeated a plurality of times (n). The sing-around, in which the wave detector detects a received wave (a zero-cross point of a specific wave) and simultaneously drives the ultrasonic transmitter / receiver on the transmitting side to perform the next transmission, thereby performing transmission / reception a plurality of (n) times Ultrasonic flow meters of the type are well known.

In this flow meter, at the time of forward measurement and at the time of reverse measurement, the time from the first transmission to the plurality of (n) receptions, that is, the arrival times t and t ', is respectively determined using a reference clock. By measuring a plurality of times nt and nt ', a value corresponding to the average of a plurality of (n) times of arrival is obtained.

In FIG. 12, a reference symbol P ₂ indicates a transmission drive signal for detecting the zero-cross point “c” of the third wave of the received wave and transmitting (driving) the ultrasonic transducer on the transmitting side again at the same time. By doing so, the accuracy of the flowmeter is improved to a multiple (n) times higher than in the case where the flow rate is obtained from the single arrival times t and t '. For example, if n is 100, the measurement accuracy of the flow meter becomes 100 times.

However, the waveform of the received wave is not necessarily the one shown in FIG.
A clean waveform as shown by the solid line in 2 is not always obtained with a stable amplitude every time, and a constant level of noise is always present, and when the fluid flow is turbulent, especially when the fluid is a gas, In addition, the amplitude of the received wave may fluctuate greatly due to uneven temperature.

For example, when the amplitude of the received wave becomes small as shown by a broken line in FIG. 12, the third wave does not reach the reference level _VTH , so that the target third wave cannot be caught and the fifth wave cannot be captured. The zero-cross point “d” is erroneously detected as the arrival time of the received wave, and the time t for one cycle of the ultrasonic wave is detected.
An error occurs in which an error e occurs.

[0016] At this, as shown at P _'2, disadvantageously resulting in the next outgoing drive signal at a timing of the zero-crossing point of the fifth wave "d" appears occurs in FIG.

[0017]

Therefore, there has been proposed a method for detecting that a specific wave of a received wave, that is, a targeted wave, has been removed, that is, for detecting an error. For example, a method of detecting a peak value of a received wave has been proposed. Monitoring is performed, and when this value is out of a certain range, an error is determined.

In these methods, if there is an error, if a target wave is removed, it is detected. Therefore, it is assumed that almost no errors occur. Therefore, if the received wave always fluctuates greatly, the sing-around type ultrasonic flowmeter may cause an error in one of a plurality of (n) measurements at the time of forward measurement or at the time of backward measurement, and There was a problem that it became impossible.

As a method of reducing the error, the peak value of the immediately preceding received wave is stored and a value obtained by multiplying the peak value by a constant value smaller than 1, that is, a value proportional to the peak value of the immediately preceding received wave is stored. Although a method of using as a reference level V _TH has been proposed, since a peak value hold circuit is required,
There has been a problem that the current consumption becomes large, and it is not suitable for a battery-driven ultrasonic flowmeter.

SUMMARY OF THE INVENTION It is an object of the present invention to provide a sing-around type ultrasonic flow meter which can stably and accurately determine the arrival time even if the received wave is slightly disturbed, instead of detecting an error. .

Still another object of the present invention is to provide a sing-around type ultrasonic flow meter which can be driven by a battery while reducing current consumption.

[0022]

In order to achieve the above-mentioned object, according to the first aspect of the present invention, a pair of ultrasonic transducers (1) and (2) which function on both a transmitting side and a receiving side are provided in a flow tube. (3) The ultrasonic flow meter is provided separately at the upstream and the downstream, transmits and receives ultrasonic waves from the upstream to the downstream and from the downstream to the upstream in the fluid flow, and obtains flow velocity and flow rate from arrival time in each direction. First, the transmitter / receiver (1 or 2) on the transmitting side is transmitted, and the received wave detector (4) for inputting the signal of the transmitter / receiver (2 or 1) on the receiving side detects the received wave and again. The transmission from the transmitter / receiver (1 or 2) on the transmission side is configured to be repeated a plurality of times (n) times, and the time from the first transmission to the reception of the certain plurality (n) times using the reference clock. The first time was obtained by measuring the arrival time of one time. Detection of the received wave, a zero-cross point of the wave initially reaching the predetermined reference level (V _TH) crosses the zero level, the detection point of the reception wave of the second and subsequent times, until the reception wave detection from the transmission of the last The ultrasonic flow meter is characterized in that the first zero-cross point after the transmission has been performed for a time obtained by subtracting a predetermined time (α) from the time of (1) is set as a reception wave detection point.

When the distance L between the pair of ultrasonic transducers (1) and (2) is 0.2 m, for example, and the sound velocity C in the stationary fluid is 440 m / S in this ultrasonic flow meter, the fluid stops. Is reached, that is, one arrival time t when the flow rate is zero is t = L / C = 0.2 / 440 ≒ 454 μS, which is an extremely short time.

Therefore, in each of the plural (n) transmissions and receptions in the forward measurement and the backward measurement, the difference between the arrival times of adjacent transmissions and receptions can be considered to be almost zero compared to the time of 454 μS. Further, if the frequency of the ultrasonic wave is, for example, 250 kHz, the period is 4 μS, and the difference between the arrival times of the adjacent transmission and reception is an extremely small value compared to the period of 4 μS. Cycle 4
It is only a small value of a few% of μS.

[0025] Therefore, as shown in FIG. 1, among the plurality of transmitting and receiving a continuous, from the first transmission drive signals (transmission) P _1, the time until the reception or first receiver was t ₁₁ case, the second received wave arrives is the time has passed the second transmission P ₂ after approximately time t ₁₁ which is performed simultaneously with the first receiver. Therefore, the zero cross point closest to that point is a good point as the second received wave detection point.

The same applies to the third transmitting and receiving, in turn, we anticipate the third received wave detection points using the second time t ₁₂ of transmission and reception of that obtained as described above, by detecting the zero-cross point Then, in the same manner, a zero cross point, which is the next reception wave detection point, is sequentially obtained in the same manner.

[0027] Therefore, in the present invention, when generally expressed as t _{1 i} the arrival time from the previous transmission and reception, the received wave the first zero-cross point after passed t _{1 i-.alpha.} from the transmission time of the round The detection point was set (see FIG. 1B).

However, α is a value smaller than half of one period of the ultrasonic wave, and is preferably set to 20 to 40% of the period of the ultrasonic wave. Note that the measurement accuracy of the time nt from the first first transmission to the last n-th reception is directly related to the accuracy of the flowmeter, and the transmission / reception times t ₁₁ , t ₁₂ , and t 1, t 1, t ₁₂ , t 1, t 1, t 2, t 1, t 2, t 1, t 2, t 1, t 2, t 1, t 2, t 1, t 2, t 3, …, T
_{Since 1 i} ,..., Tn have no relation to the measurement accuracy of the flow meter, it is not necessary to measure with such high accuracy.

According to the present invention, even when the zero-cross point of the first received wave is detected, if the targeted wave can be reliably captured, the subsequent received waves can capture the targeted wave regardless of the magnitude of the amplitude. The zero cross point can be detected.

In FIG. 1, the time t ₁₁ from the _first transmission P ₁ to the reception (detection of the zero-cross point of the third wave) is compared with the second transmission P ₂ from the first reception time to t _11. The first zero-cross point after the point of time -α is set as the second received wave detection point (particularly, see FIG. 3B).

As shown in FIG. 1B, even if the third wave, which is the target wave of the second received wave, does not reach the reference level V _TH , the zero-cross point of the target third wave can be reliably determined. Can be detected. Contrary to the case shown in FIG. 1B, even if the wave before the third wave, which is the target wave of the second received wave, exceeds the reference level _VTH , the zero-cross point of the third wave is definitely reached. Clearly, it can be detected.

[0032] In the prior art, when transmitting and receiving the plurality (n) of times in the forward direction during measurement and reverse measurement, as by n times every reception captures waves aimed, with respect to the reference level V _TH In contrast to the need for the amplitude of the targeted wave to fall within an appropriate range, in the present invention, only the first received wave needs to be captured in relation to the reference level _VTH, and The probability of error is very small. That is, the reliability of the measurement is improved.

By the way, in the first aspect of the present invention, the first
Is the wave aimed at the reference level V _TH , for example, the third wave
Since the target wave is caught by the arrival of the wave, when the amplitude of the first received wave greatly changes out of a predetermined range, the received wave is detected at the zero cross point of the first received wave. There is a possibility that the time point is shifted by one period of the ultrasonic wave from the true value, and an error is caused by that amount.

Therefore, the second aspect of the present invention eliminates such an error. According to a second aspect of the present invention, a pair of ultrasonic transducers (1) and (2) acting on both the transmitting side and the receiving side are provided at a position upstream and downstream of the flow tube (3), respectively. Is an ultrasonic flowmeter that transmits and receives ultrasonic waves from upstream to downstream and from downstream to upstream, and obtains flow velocity and flow rate from arrival time in each direction, and firstly, a transmitter / receiver (1 or 2) on the transmission side.
Is transmitted, and the received wave detector (4), which inputs the signal of the receiving side transducer (2 or 1), detects the received wave and simultaneously transmits the transmitting side transducer (1 or 2) again. Is repeated a fixed number of times (n) times, and the time from the first transmission to the fixed plurality of (n) times of reception is measured using the reference clock, so that the arrival time for one time is obtained. In the detection of the reception wave, the detection of the reception wave is performed at a zero crossing point where the wave that first reaches a certain reference level (V _TH ) crosses the zero level, and the time from each transmission to the detection of the reception wave is monitored every time. When the time difference between adjacent times becomes equal to or less than a certain time for a certain number of consecutive times, it is determined that the received wave has been accurately captured, and the detection points of the received waves thereafter are received from the previous transmission. Fixed time from time to wave detection The first zero-crossing point after the lapse of the transmission for the time obtained by subtracting (α) is set as the reception wave detection point, and the transmission / reception determined to have been accurately captured or the transmission of any subsequent transmission / reception is defined as the first transmission. An ultrasonic flowmeter characterized by the following.

The reference level V _TH is naturally set to a voltage which is most suitable for catching a specific wave aimed at, for example, the third wave. Therefore, even if the target wave is caught using the reference level V _TH as in the prior art, the probability that the target wave is caught correctly is the highest, but there is a possibility that the wrong wave is caught. However, there is a high possibility that an error of one cycle of the ultrasonic wave will occur, and in the invention of claim 1, there is a possibility that such an error will occur in the first reception.

According to the second aspect of the present invention, in order to avoid such an error, when it is determined that the target wave, for example, the third wave has been reliably caught, the zero-cross point (received wave) of the wave caught from the transmission at that time is determined. The subsequent measurement is performed based on the time until the detection point).

As described above, there is almost no difference between adjacent transmission / reception times as long as the target wave is captured. On the other hand, if the target wave cannot be caught,
There will be a difference for the period. If there is a time difference close to one cycle when comparing the two measurement times, it cannot be determined which one has correctly caught the aimed wave, but it can be determined that the measurement is to be performed several times continuously.

That is, as described above, the reference level V _TH is designed and adjusted so as to catch the aimed wave with the maximum probability. In most cases, the aimed wave can be captured. Therefore, it is most likely that some measurements are correct. As long as it is a correct measurement that captures the target wave, each measurement time obtained is almost the same value. Conversely, if the measurement time of almost the same value continues, they have a large probability that the target wave is correctly captured. Can be said.

According to the second aspect of the present invention, it is determined that the target wave has been correctly caught when a measurement time of a close value is obtained continuously for a plurality of times, and the subsequent procedure is the first aspect. In the same manner as in the invention of

When it is determined that the target wave has been correctly caught, the transmission performed simultaneously with the detection of the received wave at that time has been completed.
(First) transmission / reception.

Then, the first zero-cross point after a time obtained by subtracting a certain time α from the previous measurement time with reference to the immediately preceding measurement time is set as the next reception wave detection point. In the following, the operation of the second aspect of the invention, particularly the operation up to the first transmission, will be described in more detail with reference to FIG.

Transmission. In the measurement time t _'11 is obtained.
| T ′ ₁₁ −t ′ ₁₂ |> β for a fixed time β of less than one cycle of the ultrasonic wave for which the measurement time t ′ ₁₂ is obtained by

The measurement time t _'13 is obtained in. | T ′ ₁₂ −t ′ ₁₃ |> β. In the measurement time t _'14 is obtained.

| T ′ ₁₃ −t ′ ₁₄ | <β. Since the measurement time t _'13, t' of ₁₄ and difference less handset are continuous, at that point, the transmission of the measurement, the first transmission regarded for n times of sing around method a transmission of the previous i.e. Then, the next reception is t ′ ₁₄ −α from this first transmission.
The first zero-cross point after the point of time elapses is set as the reception wave detection point. Thereafter, the same operation is repeated.

According to the second aspect of the present invention, first, it is confirmed that the target wave has been correctly caught, and then it is assumed that no large change in the arrival time occurs suddenly. Since the zero cross point near the measurement time is set as the reception detection point, accurate measurement can be reliably performed even if the amplitude of the received wave changes thereafter.

[0046] As the invention of the claim 2, necessarily consecutively several times about the same measuring time (t _'13),
It is not necessary to assume that (t ′ ₁₄ ) occurs. For example, several measurement times t ′ ₁₁ , t ′ ₁₂ ,... Are measured, and the measurement time that appears most frequently is correct. It is possible to achieve the object of the present invention by determining that the transmission performed simultaneously with the detection of the received wave when it is determined to be correct is the first transmission out of n times. 3
Invention.

According to a third aspect of the present invention, a pair of ultrasonic transducers (1) and (2) acting on both the transmitting side and the receiving side are provided at the upstream and downstream of the flow tube (3), respectively. An ultrasonic flowmeter that transmits and receives ultrasonic waves from upstream to downstream and from downstream to upstream in a flow, and obtains flow velocity and flow rate from arrival time in each direction. The ultrasonic flowmeter (1 or 2) ) Is transmitted, and the received wave detector (4), which receives a signal from the transmitter / receiver (2 or 1) on the receiving side, detects the received wave and simultaneously transmits the transmitter / receiver (1 or 2) again. This is repeated a certain number of times (n) times, and the time from the first transmission to the certain number of (n) times reception is measured using the reference clock to determine the arrival time for one time. The detection of the received wave first _reaches a certain reference level (V _TH ). The arrival time from the transmission of each time to the detection of the received wave is monitored multiple times continuously, and the measured value that appears the most times among the arrival times of the multiple times is correct. Value and
Thereafter, when the arrival time matches the value determined to be correct, it is determined that the received wave has been accurately captured, and the detection point of the received wave thereafter is fixed from the time from the previous transmission to the reception wave detection. The first zero-cross point after a lapse of the transmission (α) by the time obtained by subtracting the time (α) is set as the reception wave detection point, and the transmission / reception determined to have been accurately captured or the transmission of any subsequent transmission / reception is determined as the first transmission. An ultrasonic flowmeter characterized by transmission.

The invention of claim 4 is based on claims 1 and 2.
Or in the ultrasonic flowmeter according to 3, the predetermined time (α)
Is a value shorter than half the period of the ultrasonic wave.

[0049]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS Next, preferred embodiments of the present invention will be described with reference to some examples. Embodiment 1 Embodiment 1 shown in FIGS. 3 to 5 corresponds to the first aspect of the present invention.

In FIGS. 3 and 4, reference numerals 1 and 2 denote a pair of ultrasonic transducers, which are disposed upstream and downstream of the flow tube 3 as in the prior art shown in FIG. By using 1 as a transmitting side and using the other transducer 2 as a receiving side, ultrasonic waves are transmitted and received in the fluid in the forward direction from upstream to downstream.

In addition, using the transducer 2 as a transmitting side,
By using the transmitter / receiver 1 as a receiving side, ultrasonic waves are transmitted and received in the fluid in the reverse direction from downstream to upstream. The two ultrasonic transducers 1 and 2 are constituted by ultrasonic transducers.

Reference numeral 4 denotes a reception wave detector, to which the transmitter / receiver 2 or 1 on the reception side selected by the signal switch 5 is connected to its input to detect a specific wave of the reception wave, that is, the zero cross point of the third wave. Then, a reception wave detection signal is output.

Reference numeral 6 denotes a transmitter drive unit, which receives the first transmission command signal from the control unit 7 and drives the transmitter / receiver 1 or 2 on the transmission side, and thereafter detects the reception wave from the reception wave detection unit 4. Each time a signal is received, the transmitter / receiver 1 or 2 on the transmission side is driven.

When receiving the n-th received wave detection signal from the first counter 8, the control unit 7
Until the first transmission command signal is received, the driving of the transducer is stopped.

In this embodiment, the meaningless (n + 1) -th driving is designed, but there is no problem because it is ignored on the receiving side. To eliminate the (n + 1) -th drive, the circuit configuration becomes slightly complicated, so this design was adopted.

Reference numeral 8 denotes a first counter, to which a received wave detection signal from the received wave detection unit 4 is input, and reset from the first transmission command signal from the control unit 7 to change the number of received wave detection signals from zero to zero. Is counted, and at each of the forward measurement and the backward measurement, the nth received wave detection signal is detected and the nth received wave detection signal is output.

Reference numeral 9 denotes a second counter, which counts the reference clocks of a built-in reference clock oscillator.
The time from the first transmission command signal to the nth received wave detection signal is counted and measured. The control unit 7 reads this time (count value).

In this embodiment, the count value (measurement time) of the second counter 9 is cleared to zero by the first transmission command signal, and the counting of the reference clock is started.

The control unit 7 inverts the transmission / reception switching signal at fixed time intervals, thereby switching the signal switch 5 and the changeover switch 10 in synchronization, and switching the transmission / reception role of each transmitter / receiver.

That is, at the time of forward measurement, the signal switch 5 and the changeover switch 10 are set in the illustrated state, the transducer 1 is used as a transmitting side, and the transducer 2 is used as a receiving side. Then, at the time of reverse measurement, the signal switch 5 and the changeover switch 10 are switched from the illustrated state, and the transducer 2 is used as the transmitting side, and the transducer 1 is used as the receiving side.

After switching the signal switch 5 and the changeover switch 10, the control section 7 outputs the first transmission command signal after waiting for a time during which noise or the like due to the changeover is settled down every time. When the nth received wave detection signal is input, the second
And the flow rate / flow rate of the fluid is calculated from the count value (measurement time) of the second counter 9 in the opposite direction by reading the count value (measurement time) of the counter 9 immediately before.

FIG. 4 shows a specific circuit configuration of the received wave detector 4 of FIG. 3, which is connected as shown. Hereinafter, the configuration and operation of the circuit of FIG. 4 will be described with reference to the timing chart of FIG.

Reference numeral 12 denotes an amplifier for amplifying a signal from the transmitter / receiver 2 or 1 on the receiving side, and reference numeral 13 denotes a first analog comparison unit.
It is configured to output a short pulse at the moment when the output of the amplifier 12 as the + input becomes larger than the reference level V _TH as the − input.

The output of the second analog comparison section 15 is input to the S input of the RS-FF 14. This output is
Since the zero-cross point from the plus to the minus of the received wave is detected and is output without slack, RS-FF1
The output Q of 4 is always "H".

The rising edge detector 16 at the subsequent stage of the RS-FF 14 changes the Q output of the RS-FF 14 from “L” to “H”.
And outputs a short pulse.
Reference numeral 17 denotes a counter for measuring time by counting the clock of the oscillator 18. The counter 17 is reset by a first transmission command signal input via the OR gate 19 and starts counting from zero.

When the first transmission command signal is input, DF
F20 is reset, the Q output thereof becomes "L", and the changeover switch SW enters the state shown in the figure to select the first analog comparison unit 13.

When the received wave arrives and the amplified signal exceeds the reference level _VTH , a signal is output from the first analog comparison section 13. This signal is provided by the switch S
Since the signal is input to the R input of the RS-FF 14 via W, the output Q of the RS-FF 14 becomes “L”.

Further, a signal output from the second analog comparing section 15 is input to the S input of the RS-FF 14 at a zero crossing point where the received wave passes through the zero level, the output Q becomes "H", and the rising edge detecting section 16 outputs the signal as a received wave detection signal.

This received wave detection signal is the CK of the D-FF 20
Since it is an input, the output Q of the D-FF 20 is “H”.
As a result, the changeover switch SW is switched from the state shown in the figure, and the digital comparison unit 21 is connected to the R input of the RS-FF 14.
A = B output is input.

The received wave detection signal also serves as a latch input of the storage unit 22, and the value of the counter 17 at the moment when the received wave detection signal is input to the latch input, that is, the first reception command signal, The time t ₁₁ (=
A) is stored in the storage 22 (see FIG. 5).

In FIG. 4, the time measurement value of the counter 17 is generally indicated by A. As described above, the reception wave detection signal latches the memory 22 and stores the time t ₁₁ (= A) from the transmission to the reception wave detection (the zero-cross point of the third wave), and then the count value of the counter 17. Is reset, and the process proceeds to the measurement of the time until the next reception wave detection (zero-cross point of the third wave).

Reference numeral 23 denotes a subtractor, which is a value A− obtained by subtracting the predetermined time α from the time A (= t ₁₁ ) stored in the storage 22.
α (= t ₁₁ −α) is output, and this output is input to the B input of the digital comparison unit 21.

The time measurement value A of the counter 17 is also input to the A input of the digital comparison section 21, and when both inputs are equal, a signal is output from the A = B output. When the count of the counter 17 advances and becomes equal to t ₁₁ −α, the A = B output becomes “H”, the output Q of the RS-FF 14 becomes “L”, and a state for waiting for the next zero crossing is set.

When the zero crossing actually occurs, the RS-FF 14 is set by the output of the second analog comparing section 15, the output Q of the RS-FF 14 becomes "H", and the received wave detection signal is output again.

Here, the time measurement value t ₁₂ of the counter 17 is stored in the storage unit 22. Thereafter, the same operation is repeated. Note that the oscillator 18 can use the reference clock of the reference clock oscillator built in the second counter 9 of FIG. 3 directly or by dividing the frequency.

Then, when the n-th received wave detection signal is input, the control unit 7 in FIG. 3 counts the value of the second counter 9, that is, from the first transmission to the n-th zero-cross point of the third wave. The time is read and the flow velocity / flow rate is calculated.

[Embodiment 2] Embodiment 2 shown in FIGS. 6 to 10 corresponds to the second aspect of the present invention. The second embodiment is different from the first embodiment.
Since many parts have the same configuration as in the first embodiment, the following description will be made in the first embodiment.
The differences from the above are mainly described in detail.

The first counter 8 is reset by a restart signal from the control unit 7.
Thereafter, the (n + 1) th received wave detection signal is detected and the nth
Outputs the reception wave detection signal.

The second counter 9 measures the time from the first received wave detection signal to the nth received wave detection signal after the input of the restart signal, and outputs the count value (time measurement value) to the control unit 7. It has become.

The count storage value output from the storage unit 22 of the reception wave detection unit 4 is input to the control unit 7.
The reception wave detector 4 is provided with an OR gate 24 so that a logical sum signal of the first transmission command signal and the restart signal is input to the reset input R of the D-FF 20.

In this embodiment, a microcomputer is used as the control unit 7. 1). First, after setting the transmission / reception direction to a predetermined forward or reverse direction, the first command signal is output after noise or the like during switching is reduced. At this time, a restart signal is also output with a slight delay. At this time, the reception detection interrupt is permitted.
Enter zero for the previous value.

2). The received wave detection signal is input to the control unit 7 as an interrupt signal. FIG. 8 is a flowchart showing the movement at that time. 3). It is the first of the interrupt t _'11 is read. Since zero is set as the previous value, the difference naturally becomes larger than the count value β corresponding to about a half cycle of the ultrasonic wave, and the continuous number is cleared to zero. Then, the control section 7 outputs a restart signal.

4). Therefore, the changeover switch SW of the received wave detection unit 4 is temporarily switched to the “H” side for selecting A = B output of the digital comparator 21, but is returned to the output side “L” of the first analog comparison unit 13. It is.

5). Further, the first counter 8 which has started counting upon receiving the reception wave detection signal is again in the original standby state.
A state in which a reception wave detection signal serving as a count start signal is provided.

6). The t _'11 is stored as the previous value. 7). When the restart signal is output, the received wave at that time is sufficiently small and does not exceed the reference level _VTH .

8). Read the next interrupt time t _'12.
Here, the reference level V _TH does not capture the third wave aimed at. Therefore, | t ′ ₁₁ −t ′ ₁₂ | becomes larger than the aforementioned β. | T ′ ₁₁ −t ′ ₁₂ |> β Therefore, as in the previous case, the continuous number is cleared to zero, and a restart signal is output. t _'12 is stored.

9). The same applies to the next interrupt. t ′ ₁₃ is stored. 10). In the next interrupt, t _'14 is _{read, | t' 13 -t '14} | becomes smaller than beta.

| T ′ ₁₃ −t ′ ₁₄ | <β Since m = 1 in the present embodiment, the number of continuations is increased by 1 to 1, and it is determined that the targeted third wave has been captured. When m is set to a larger value, a restart signal is output until the number of consecutive times does not reach m.

When it is determined that the targeted third wave has been caught, this interrupt, that is, the reception wave detection signal interrupt is masked and disabled. Do not.

11). The actual measurement will be started upon receipt of t _'14. 12). Subsequent steps are the same as in the first embodiment. It should be noted that at the beginning of t ₁₁ is 't from the time of reception of the measurement of the _14' t ₁₄
The first zero cross point after -α.

Further, since the first counter 8 counts the reception detection signal at the start time as 1, the (n + 1) -th time corresponds to the n-th time in the first embodiment. Also, the reference level V
_TH can be set on the minus side (negative side) as shown in FIG. In this case, the zero cross point as the reception wave detection point is the first zero cross point on the minus side or the plus side.

In the timing chart of FIG. 9, the time indicated by the symbol Τ is the time required for processing from the reception wave detection signal to the output of the restart signal. During this time T, the reception wave attenuates and becomes small. Has become.

In the second embodiment, m is set to 1. However, if m is limited to 2 or more, when the number of continuations becomes m-1, the restart signal is not output so that the wave can be correctly generated. The transmission / reception determined to have been captured can be set as the first first transmission / reception.

[0094]

Since the ultrasonic flowmeter of the present invention is constructed as described above, even if the amplitude of the received wave is disturbed due to noise, turbulence of the flow, uneven temperature, etc., the zero-cross point of the predetermined wave can be set. Accurate detection is possible, and so-called errors are eliminated.

As a result, it is not necessary to repeat the measurement and the current consumption can be reduced, which is useful for the practical use of a battery-driven ultrasonic flowmeter. Also, since a certain amount of noise can be tolerated, it is not necessary to increase the amplification of the amplifier, and at low cost,
In addition, current consumption can be reduced, and from this aspect also, the feasibility of a battery-driven ultrasonic flowmeter can be improved.

Then, the reliability of the measured value increases.

[Brief description of the drawings]

FIG. 1 is a diagram for explaining the operation of the invention of claim 1;
(A) is a time chart, and (b) is an enlarged detail view of a part of FIG.

FIG. 2 is a time chart for explaining the operation of the invention of claim 2;

FIG. 3 is a block diagram of a first embodiment of the present invention.

FIG. 4 is a diagram showing a specific electric circuit of a main part of FIG. 3;

FIG. 5 is a time chart for explaining the operation of FIGS. 3 and 4;

FIG. 6 is a block diagram of a second embodiment of the present invention.

7 is a diagram showing a specific electric circuit of a main part of FIG. 6;

FIG. 8 is a flowchart illustrating the operation of FIGS. 6 and 7.

FIG. 9 is a time chart for explaining the operation of FIGS. 6 and 7;

FIG. 10 is a diagram illustrating a relationship between a received wave and a reference level _VTH .

FIG. 11 is a schematic diagram illustrating the principle of the prior art.

FIG. 12 is a diagram showing electric signal waveforms for explaining the operation of a reception wave detection unit according to the related art.

[Explanation of symbols]

1, 2 Ultrasonic transducer 3 Flow tube 4 Received wave detector V _TH reference level α Constant time C Zero cross point

Claims (4)

[Claims] 1. A pair of ultrasonic transducers (1) and (2) acting on both a transmitting side and a receiving side are provided at an upstream side and a downstream side of a flow tube (3), respectively. An ultrasonic flowmeter that transmits and receives ultrasonic waves from downstream to upstream and from downstream to upstream, and obtains the flow velocity and flow rate from the arrival time in each direction, and first transmits a transmitter / receiver (1 or 2) on the transmission side, A certain number of times that the reception wave detector (4) for inputting the signal of the reception side transducer (2 or 1) detects the reception wave and simultaneously transmits the transmission side transducer (1 or 2) again. (N) times, and measuring the time from the first transmission to a certain (n) times reception using a reference clock to determine the arrival time for one time, The first detection of the received wave is performed at a fixed reference level (V
_TH ) is the zero crossing point where the first wave crosses the zero level, and the detection point of the second and subsequent received waves is a certain time (α) subtracted from the time from the previous transmission to the detection of the received wave. An ultrasonic flowmeter characterized in that the first zero-cross point after a lapse of time from the current transmission is set as a reception wave detection point. 2. A pair of ultrasonic transducers (1) and (2) acting on both a transmitting side and a receiving side are provided at an upstream side and a downstream side of a flow tube (3), respectively. An ultrasonic flowmeter that transmits and receives ultrasonic waves from downstream to upstream and from downstream to upstream, and obtains the flow velocity and flow rate from the arrival time in each direction, and first transmits a transmitter / receiver (1 or 2) on the transmission side, A certain number of times that the reception wave detector (4) for inputting the signal of the reception side transducer (2 or 1) detects the reception wave and simultaneously transmits the transmission side transducer (1 or 2) again. (N) times, and measuring the time from the first transmission to a certain (n) times reception using a reference clock to determine the arrival time for one time, detection of received waves, waves first reach a predetermined reference level (V _TH) is Zerorebe The time between transmission and detection of the received wave is monitored every time.When the difference between adjacent times of these times becomes less than or equal to a certain time continuously for a certain number of times, the received wave is accurately detected. And the detection point of the received wave after that is the first point after the lapse of that time from the time from the previous transmission to the detection of the received wave minus a certain time (α). The ultrasonic flowmeter according to claim 1, wherein the zero-cross point is used as a reception wave detection point, and the transmission / reception determined to have been accurately captured or the transmission of any subsequent transmission / reception is defined as the first transmission. 3. A pair of ultrasonic transducers (1) and (2) acting on both a transmitting side and a receiving side are provided at an upstream side and a downstream side of a flow tube (3), respectively. An ultrasonic flowmeter that transmits and receives ultrasonic waves from downstream to upstream and from downstream to upstream, and obtains the flow velocity and flow rate from the arrival time in each direction, and first transmits a transmitter / receiver (1 or 2) on the transmission side, A certain number of times that the reception wave detector (4) for inputting the signal of the reception side transducer (2 or 1) detects the reception wave and simultaneously transmits the transmission side transducer (1 or 2) again. (N) times, and measuring the time from the first transmission to a certain (n) times reception using a reference clock to determine the arrival time for one time, detection of received waves, waves first reach a predetermined reference level (V _TH) is Zerorebe , And the arrival time from the transmission of each time to the detection of the received wave is continuously monitored a plurality of times, and the measurement value that appears most frequently among the arrival times of the plurality of times is determined to be a correct value, Thereafter, when the arrival time matches the value determined to be correct, it is determined that the received wave has been accurately captured, and the detection point of the received wave thereafter is fixed from the time from the previous transmission to the reception wave detection. The first zero-cross point after a lapse of the transmission (α) by the time obtained by subtracting the time (α) is set as the reception wave detection point, and the transmission / reception determined to have been accurately captured or the transmission of any subsequent transmission / reception is determined as the first transmission. An ultrasonic flowmeter characterized by transmission. 4. The ultrasonic flowmeter according to claim 1, wherein said predetermined time (α) is a value shorter than half the period of the ultrasonic wave.