JP7174574B2 - Ultrasonic flowmeter and determination method of zero-crossing time in ultrasonic flowmeter - Google Patents

Description

The present invention relates to an ultrasonic flowmeter that measures the flow rate of a fluid using ultrasonic waves and a method for determining zero-crossing time in the ultrasonic flowmeter.

2. Description of the Related Art Conventionally, an ultrasonic flowmeter that measures the flow rate of a fluid using ultrasonic waves has been used as a flowmeter that measures the flow rate of the fluid.

In this ultrasonic flowmeter, as shown in the schematic diagram of FIG. 25, a first ultrasonic transmitter/receiver (upstream transducer) 2 is arranged on the outer peripheral surface of the upstream side of the pipe 1 through which the fluid to be measured flows, A second ultrasonic transmitter/receiver (downstream transducer) 3 is arranged on the outer circumferential surface on the downstream side, and ultrasonic waves are transmitted between the first ultrasonic transmitter/receiver 2 and the second ultrasonic transmitter/receiver 3 via fluid. A measurement process for transmitting and receiving signals in both directions is performed multiple times, and the flow velocity v of the fluid is measured based on the propagation time difference of the ultrasonic signals in both directions obtained for each measurement process. The flow rate Q of the fluid is obtained from the cross-sectional area S (see Patent Document 1, for example).

In FIG. 25, θ is the angle between the axis of the pipe 1 and the propagation direction of the ultrasonic signal. Ultrasonic signals emitted from the first ultrasonic transmitter/receiver 2 and received by the second ultrasonic transmitter/receiver 3 (ultrasonic signals propagating from the upstream side to the downstream side (forward propagating ultrasonic signals) ) is represented by the following equation (1).
t1=L/(c+vcos θ) (1)
Here, L is the propagation distance [m] of the ultrasonic signal, and c is the speed of sound in the fluid [m/s]. Since ultrasonic waves propagate along with the flow of fluid, the faster the flow, the shorter the propagation time.

Similarly, ultrasonic signals emitted from the second ultrasonic transmitter/receiver 3 and received by the first ultrasonic transmitter/receiver 2 (ultrasonic signals propagating from the downstream side to the upstream side (ultrasonic signals propagating in the opposite direction) The propagation time t2 (reverse propagation time) of the sound wave signal)) is represented by the following equation (2).
t2=L/(c-vcosθ) (2)
Ultrasonic waves propagate against the flow of fluid, so the faster the flow, the longer it takes to propagate.

The inverses of the forward and backward propagation times are:
1/t1=(c+vcos θ)/L (3)
1/t2=(c−vcos θ)/L (4)

The sum of the reciprocal of the forward propagation time and the reciprocal of the backward propagation time is:
1/t1+1/t2=2c/L=2/t0 (5)
By transforming the equation (5), an equation for obtaining the speed of sound c is obtained.
c=(L/2)(1/t1+1/t2)=L/t0 (6)

Similarly, the difference between the inverse of the forward propagation time and the inverse of the backward propagation time is:
1/t1-1/t2=2v cos θ/L (7)
By modifying the equation (7), an equation for obtaining the flow velocity v is obtained.
v=(L/2 cos θ)·(1/t1−1/t2) (8)

Once the flow velocity is determined, it can be multiplied by the cross-sectional area S to determine the volumetric flow rate, or further multiplied by the density to determine the mass flow rate.

Even if it is difficult to accurately obtain the propagation time itself, the propagation time difference (the difference between the forward propagation time and the backward propagation time) can be obtained with high accuracy as the difference between the zero-crossing times. The zero-crossing time will be described later. In such a case, the flow velocity v is obtained according to the following calculation.

From the above formulas (1) and (2),
Δt=t2−t1=L/(c−vcos θ)−L/(c+vcos θ)=2 vL cos θ/(c ² −v ² cos ² θ)≈2 vL cos θ/c ² (9)
therefore,
v≈(c ² /2Lcos θ)·(t2−t1)=(c ² /2Lcos θ)·Δt (10)
(propagation time difference method).

Also, if the propagation time when the flow velocity is 0 is t0, from the above equation (1) or (2),
t0=L/c (11)
so that
t1=L/(c+vcos θ)=L/c·(1/(1+vcos θ/c))≈L/c·(1−vcos θ/c)=L/c−vLcos θ/c ² =t0−Δt/2 . (12)
t2=L/(c−vcos θ)=L/c·(1/(1−vcos θ/c))≈L/c·(1+vcos θ/c)=L/c+vLcos θ/c ² =t0+Δt/2 (13)
can be written as

From the above formulas (12) and (13),
t0≈(t1+t2)/2 (14)
becomes.
From the above formulas (11) and (14),
t1+t2≈2L/c (15)
can be written as

FIG. 26(a) shows a waveform diagram (schematic diagram) of the reception signal (forward reception signal) output from the second ultrasonic transmitter/receiver 3, and FIG. 26(b) shows the waveform of the first ultrasonic wave. FIG. 2 shows a waveform diagram (schematic diagram) of a reception signal (reverse reception signal) output from the transmitter/receiver 2. FIG. FIGS. 27(a) and 27(b) show enlarged views of the horizontal axis (time axis) of the received signal shown in FIGS. 26(a) and 26(b). FIG. 28 shows a waveform diagram (schematic diagram) in which the forward received signal and the backward received signal are superimposed. FIG. 29 shows an enlarged view of the horizontal axis (time axis) of the received signal shown in FIG.

In FIG. 25, the first ultrasonic transmitter/receiver 2 and the second ultrasonic transmitter/receiver 3 are alternately pulse-driven for a certain period of time. As a result, the pulsed ultrasonic signal (forward transmission signal) emitted from the first ultrasonic transmitter/receiver 2 is received by the second ultrasonic transmitter/receiver 3 via the fluid, and the second ultrasonic wave A pulsed ultrasonic signal (reverse transmission signal) emitted from the transmitter/receiver 3 is received by the first ultrasonic transmitter/receiver 2 via the fluid.

30(a) shows transmission signals output from the ultrasonic transmitter/receivers 2 and 3, and FIG. 30(b) shows reception signals output from the ultrasonic transmitter/receivers 2 and 3. FIG. In addition, in FIG. 30(a), the horizontal axis is reduced. Also, in FIG. 30(a), tu indicates the period of the transmission signal.

After the pulse-like ultrasonic signal is emitted, the received signal is still small at the reception timing tr of the first pulse-like ultrasonic signal. Therefore, after a short time from the reception timing tr, when the received signal becomes large to some extent, the timing of the next zero crossing exceeding a predetermined threshold voltage (reference voltage) Vs is set as the target zero crossing time Z, and this zero crossing Time Z is often used to calculate the propagation time t (=t1 or t2) from the transmission start timing ts of the ultrasonic signal to the reception timing tr.

The zero-crossing time Z is considered to exist after a predetermined time dly with respect to the reception timing tr. Therefore, by subtracting the predetermined time dly from the zero-crossing time Z, the propagation time t is obtained.
t=Z-dly (16)

The predetermined time dly is calculated in advance as the difference between the ideal propagation time (calculated by dividing the propagation path length by the speed of sound) and the target zero-crossing time Z. FIG.

Japanese Patent No. 5228462

However, in such an ultrasonic flowmeter, the amplitude of the received signal may change due to fluctuations in the flow rate, etc., and the received signal may exceed the threshold voltage Vs at unintended timing, or may not exceed the threshold voltage Vs at intended timing. sometimes

As a result, it may be erroneously determined that the zero-cross time Z is the target zero-cross time shifted by one or more periods of the ultrasonic waves. Using an erroneous zero-crossing time will result in a calculated propagation time that is erroneous by an integer multiple of the ultrasound period (tu).

For example, in FIG. 30, a change occurs in the amplitude of the received signal, and the zero-cross time Z′ one cycle before the target zero-cross time Z may be erroneously determined as the target zero-cross time Z, or the zero-cross time one cycle after Z″ may be erroneously determined to be the desired zero-crossing time Z.

In this case, the propagation time t obtained from the correct zero-crossing time Z is t=Z-dly, whereas the propagation time t obtained from the erroneous zero-crossing time Z' is t=Z'-dly=Z-tu −dly=t−tu≠t. Also, the propagation time t obtained from the erroneous zero-crossing time Z″ is t=Z″−dly=Z+tu−dly=t+tu≠t.

In this way, in conventional ultrasonic flowmeters, when the amplitude of the received signal changes, an incorrect zero-crossing time is selected as the desired zero-crossing time, and an incorrect propagation time is calculated, resulting in an incorrect flow rate. There was a time when I was lost.

The present invention was made to solve such problems, and its object is to always select the correct zero-crossing time in both the forward and reverse directions, and to calculate the correct propagation time. The object of the present invention is to provide an ultrasonic flowmeter and a method for determining the zero-crossing time in the ultrasonic flowmeter.

In order to achieve such an object, the present invention comprises a pipe (1) through which a fluid to be measured flows, a first ultrasonic transmitter/receiver (2) arranged upstream of this pipe, and a pipe downstream of the pipe. a second ultrasonic transmitter/receiver (3) positioned in the In an ultrasonic flowmeter (100) configured to perform a plurality of steps and measure the flow rate of a fluid based on the propagation time difference of ultrasonic signals in both directions obtained for each measurement step, a first The received signal output from the second ultrasonic transmitter/receiver that received the ultrasonic signal from the ultrasonic transmitter/receiver is taken in as a forward received signal, and the forward received signal exceeds a preset threshold voltage. After that, a plurality of timings at which the forward received signal zero-crosses are detected as zero-crossing times, and each of the detected zero-crossing times is acquired as a candidate for the current forward zero-crossing time. A candidate acquisition unit (41) acquires a received signal output from a first ultrasonic transmitter/receiver that has received an ultrasonic signal from a second ultrasonic transmitter/receiver as a reverse received signal, and receives this reverse direction reception. After the signal exceeds a preset threshold voltage, multiple zero-crossing timings of the received signal in the reverse direction are detected as zero-crossing times, and each of the detected zero-crossing times is used as a candidate for the current reverse-direction zero-crossing time. a backward zero-crossing time candidate acquisition unit (42) configured to acquire, the current forward zero-crossing time candidate acquired by the forward zero-crossing time candidate acquisition unit, and For all combinations with the current reverse zero-cross time candidate, the difference between the current forward zero-cross time candidate and the current reverse zero-cross time candidate is obtained as the current propagation time difference candidate. The configured propagation time difference candidate calculation unit (43), the current forward zero-crossing time candidate acquired by the forward zero-crossing time candidate acquisition unit, and the current reverse zero-crossing time candidate acquired by the backward zero-crossing time candidate acquisition unit Propagation time configured to obtain the sum of the current forward zero-crossing time candidate and the current reverse zero-crossing time candidate as the current propagation time sum candidate for all combinations of zero-crossing time candidates A sum candidate calculator (44) and a forward zero-crossing time A previous propagation time difference calculating unit (45) configured to obtain a difference between a previous fixed value and a previous fixed value of the backward zero crossing time as the previous propagation time difference, and a previous fixed of the forward zero crossing time. A previous propagation time sum calculation unit (46) configured to obtain the sum of the value and the previous fixed value of the zero crossing time in the opposite direction as the previous propagation time sum, and the current propagation time difference candidate calculation unit (46) configured to obtain a propagation time difference change calculation unit (47) configured to calculate a change from the previous propagation time difference calculated by the previous propagation time difference calculation unit for all of the propagation time difference candidates; a propagation time sum change calculation unit configured to calculate a change from the previous propagation time sum calculated by the previous propagation time sum calculation unit for all candidates for the current propagation time sum calculated by the unit (48), and based on the change from the previous propagation time difference obtained by the propagation time difference change calculation unit and the change from the previous propagation time sum obtained by the propagation time sum change calculation unit, The current forward zero-crossing time is selected from among the current forward zero-crossing time candidate acquired by the direction zero-crossing time candidate acquisition unit and the current backward zero-crossing time candidate acquired by the backward zero-crossing time candidate acquisition unit. and a zero-crossing time determination unit (49) configured to determine the time and the current reverse zero-crossing time.

Further, the present invention comprises a pipe (1) through which a fluid to be measured flows, a first ultrasonic transmitter/receiver (2) arranged upstream of the pipe, and a second ultrasonic transmitter/receiver (2) arranged downstream of the pipe. an ultrasonic transmitter/receiver (3), performing a plurality of measurement steps of transmitting/receiving ultrasonic signals in both directions through a fluid between the first ultrasonic transmitter/receiver and the second ultrasonic transmitter/receiver; A method for determining a zero-crossing time in an ultrasonic flowmeter (100) configured to measure the flow rate of a fluid based on the propagation time difference of ultrasonic signals in both directions obtained for each of these measurement steps, comprising: The received signal output from the second ultrasonic transmitter/receiver that received the ultrasonic signal from the second ultrasonic transmitter/receiver is taken as a forward received signal, and the forward received signal exceeds a preset threshold voltage A forward zero-crossing time candidate acquisition step ( S101), the received signal output from the first ultrasonic transmitter/receiver that received the ultrasonic signal from the second ultrasonic transmitter/receiver is captured as a reverse received signal, and this reverse received signal is set in advance. After exceeding the set threshold voltage, a plurality of zero-crossing timings of the received signal in the reverse direction are detected as zero-crossing times, and each of the detected zero-crossing times is acquired as a candidate for the current reverse-direction zero-crossing time. A zero-crossing time candidate obtaining step (S102), the current forward zero-crossing time candidate obtained by the forward zero-crossing time candidate obtaining step, and the current reverse zero-crossing time candidate obtained by the backward zero-crossing time candidate obtaining step. a propagation time difference candidate calculation step (S103) for obtaining, as a candidate for the current propagation time difference, the difference between the current forward zero-crossing time candidate and the current backward zero-crossing time candidate for all combinations with candidates; For all combinations of the current forward zero-crossing time candidate acquired by the direction zero-crossing time candidate acquisition step and the current backward zero-crossing time candidate acquired by the backward zero-crossing time candidate acquisition step, the current order A propagation time sum candidate calculation step (S104) for obtaining the sum of a direction zero-crossing time candidate and a current reverse zero-crossing time candidate as a current propagation time sum candidate; a previous propagation time difference calculating step (S105) of obtaining the difference between the previous fixed value of the zero crossing time in the forward direction and the previous fixed value of the zero crossing time in the reverse direction as the previous propagation time difference; All of the current propagation time difference candidates obtained by the previous propagation time sum calculation step (S106), in which the sum of the zero-crossing time in the opposite direction and the previous fixed value is obtained as the previous propagation time sum, and the propagation time difference candidate calculation step. , a propagation time difference change calculation step (S107) for obtaining a change from the previous propagation time difference obtained by the previous propagation time difference calculation step, and a current propagation time sum candidate obtained by the propagation time sum candidate calculation step For all of the above, a propagation time sum change calculation step (S108) for obtaining a change from the previous propagation time sum obtained by the previous propagation time sum calculation step, and a propagation time difference change calculation step obtained by the previous propagation time difference change calculation step Current forward zero-crossing time obtained by the forward zero-crossing time candidate obtaining step based on the change from the propagation time difference and the change from the previous propagation time sum obtained by the propagation time sum change calculating step The zero-cross time determination step ( S109 to S112).

In the present invention, the forward received signal output from the second ultrasonic transmitter/receiver (3) that has received the ultrasonic signal from the first ultrasonic transmitter/receiver is compared with the threshold voltage (Vs). After the forward received signal exceeds the threshold voltage, the zero crossing time (Z1) at which the forward received signal crosses zero is detected a plurality of times, and each of the detected zero crossing times is used as a candidate for the current forward zero crossing time. (Z1ij). In addition, the reverse received signal output from the first ultrasonic transmitter/receiver (2) that received the ultrasonic signal from the second ultrasonic transmitter/receiver is compared with the threshold voltage (Vs), and the reverse direction after the received signal exceeds the threshold voltage, the zero-crossing times (Z2) at which the reverse received signal crosses zero are detected multiple times, and each of the detected zero-crossing times is used as a candidate for the current reverse-direction zero-crossing time (Z2ik ).

Then, for all combinations of the current forward zero-crossing time candidate (Z1ij) and the current reverse zero-crossing time candidate (Z2ik), the current forward zero-crossing time candidate and the current reverse zero-crossing time candidate The difference (Z2ik-Z1ij) from the candidate for the zero-crossing time of , is obtained as the candidate (αijk) for the current propagation time difference. For all combinations of the current forward zero-crossing time candidate (Z1ij) and the current reverse zero-crossing time candidate (Z2ik), the current forward zero-crossing time candidate and the current reverse zero-crossing time candidate The sum (Z1ij+Z2ik) with the candidate for the zero-crossing time is obtained as the candidate (βijk) for the current sum of propagation times.

Then, the difference (Z2i-1-Z1i-1) between the previous fixed value of the zero-crossing time in the forward direction (Z1i-1) and the previous fixed value of the zero-crossing time in the reverse direction (Z2i-1) is the previous propagation time difference. (αi−1), and for all the current propagation time difference candidates (αijk), the amount of change (Δαijk) from the previous propagation time difference (αi−1) is calculated. In addition, the sum (Z1i-1+Z2i-1) of the previous fixed value of the zero-crossing time in the forward direction (Z1i-1) and the previous fixed value of the zero-crossing time in the previous direction (Z2i-1) is the sum of the previous propagation times ( βi−1), and for all the current propagation time sum candidates (βijk), the amount of change (Δβijk) from the previous propagation time sum (βi−1) is obtained.

Based on the change (Δαijk) from the previous propagation time difference and the change (Δβijk) from the previous propagation time sum, the current forward zero-crossing time candidate (Z1ij) and the current reverse zero-crossing time candidate (Z1ij) are determined. The current forward zero-crossing time (Z1i) and the current backward zero-crossing time (Z2i) are determined from among the direction zero-crossing time candidates (Z2ik). For example, the combination of the smallest change (Δαijk) from the previous propagation time difference and the smallest change (Δβijk) from the previous propagation time sum is determined as the current forward zero-crossing time (Z1i) and the reverse zero-crossing time (Z2i). ).

In the above description, as an example, constituent elements on the drawings corresponding to constituent elements of the invention are indicated by parenthesized reference numerals.

As described above, according to the present invention, the difference between the previous fixed value of the zero-cross time in the forward direction and the previous fixed value of the zero-cross time in the reverse direction is used as the previous propagation time difference, and candidates for the current propagation time difference are determined. Calculate the amount of change from the previous propagation time difference for all, the sum of the previous fixed value of the forward zero crossing time and the previous fixed value of the backward zero crossing time is the sum of the previous propagation time, and the current propagation time sum. Based on the change from the previous propagation time difference and the previous propagation time sum, the current forward zero crossing time is calculated for all of the candidates. and the current reverse zero-crossing time candidates, the current forward zero-crossing time and the current reverse zero-crossing time are determined. The correct zero-crossing time is always selected for both the forward and reverse directions by determining the combination with the smallest change from the previous propagation time sum as the current forward zero-crossing time and reverse zero-crossing time. , it is possible to calculate the correct propagation time.

FIG. 1 is a diagram showing a current (i-th) forward propagation time candidate t1ij and a zero-crossing time candidate Z1ij. FIG. 2 is a diagram showing the current (i-th) backward propagation time candidate t2ik and the zero-crossing time candidate Z2iK. FIG. 3 is a diagram showing the previous (i−1) forward zero-crossing time definite value Z1i-1 and the propagation time definite value t1i-1. FIG. 4 is a diagram showing the previous (i−1) backward zero-crossing time definite value Z2i-1 and the propagation time definite value t2i-1. FIG. 5 is a diagram showing a main part of an ultrasonic flowmeter according to an embodiment of the invention. FIG. 6 is a diagram showing an outline of the hardware configuration of the flow rate computing device in this ultrasonic flowmeter. FIG. 7 is a flow chart for explaining a first example (embodiment 1) of the processing operation executed by the CPU of the flow rate computing device in this ultrasonic flowmeter. FIG. 8 is a flowchart following FIG. FIG. 9 is a diagram illustrating previous fixed values Z1i-1 and Z2i-1 of the zero-crossing time. FIG. 10 is a diagram illustrating the previous propagation time difference αi-1 and the propagation time sum βi-1. FIG. 11 is a diagram illustrating candidates Z1ij for the current forward zero-crossing time. FIG. 12 is a diagram exemplifying the current reverse zero-cross time candidate Z2ik. FIG. 13 is a diagram illustrating candidates αijk for the current propagation time difference. FIG. 14 is a diagram illustrating candidates βijk for the current propagation time sum. FIG. 15 is a diagram illustrating the variation Δαijk from the previous propagation time difference. FIG. 16 is a diagram illustrating the change Δβijk from the previous propagation time sum. FIG. 17 is a diagram showing determined values of the current forward zero-crossing time Z1i and backward zero-crossing time Z2i. FIG. 18 is a flow chart for explaining a second example (embodiment 2) of the processing operation executed by the CPU of the flow computing device. FIG. 19 is a flowchart following FIG. FIG. 20 is a diagram showing an example of obtaining the average value of the variation Δαijk from the previous propagation time difference with the same kj. FIG. 21 is a diagram showing an example of obtaining an average value of changes Δβ ijk from the previous sum of propagation times with the same j+k. FIG. 22 is a diagram showing determined values of the current forward zero-crossing time Z1i and backward zero-crossing time Z2i. FIG. 23 is a functional block diagram of the essential parts of the flow rate computing device. FIG. 24 is a diagram showing an example in which the zero-crossing timing is detected as the zero-crossing time every half cycle. FIG. 25 is a schematic diagram of an ultrasonic flowmeter. FIG. 26 is a waveform diagram (schematic diagram) of forward and backward received signals output from the ultrasonic transmitter/receiver. FIG. 27 is an enlarged view of the horizontal axis (time axis) of the received signal shown in FIG. FIG. 28 is a waveform diagram (schematic diagram) in which a forward received signal and a backward received signal are superimposed. FIG. 29 is an enlarged diagram of the horizontal axis (time axis) of the received signal shown in FIG. FIG. 30 is a diagram showing transmission signals and reception signals output from an ultrasonic transmitter/receiver.

BEST MODE FOR CARRYING OUT THE INVENTION Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings. First, the principle of the present invention will be described before describing the embodiments.

[Principle of Invention]
It may sometimes be assumed that the fluid composition, temperature, and flow velocity each do not change abruptly. For example, if there is a pipe or a buffer tank in front of the flow rate measurement unit, changes in the composition, temperature, and flow velocity of the fluid will be mitigated, and if the measurement interval is sufficiently short, these physical quantities will change slowly. can be regarded as In addition, since the speed of sound in the fluid can also be regarded as a function of the components, temperature, pressure, etc. of the fluid, it can be regarded that the speed of sound does not change abruptly with respect to the measurement interval.

By using this assumption that "the sonic velocity (c) and flow velocity (v) of the fluid do not change abruptly", it is possible to select an appropriate zero-crossing time as follows.

Since the speed of sound (c) does not change abruptly from the above equation (15), it can be assumed that the sum of the propagation times does not abruptly change.
From the above equation (9), the fact that the speed of sound (c) and the flow velocity (v) do not change abruptly means that the difference in propagation time does not change abruptly.
Therefore, "the speed of sound (c) and the flow velocity (v) do not change suddenly" means that the difference and the sum of the propagation times do not change suddenly.

Let the forward and backward propagation times be t1 and t2, respectively. The propagation times t1 and t2 change from moment to moment due to changes in flow rate (flow velocity) and temperature (sound velocity). The propagation times t1 and t2 are measured discretely, and the i-th measured propagation times t1 and t2 are t1i and t2i, respectively. Further, let Z1 and Z2 be the zero-cross times in the forward direction and Z2, respectively, and let Z1i and Z2i be the i-th acquired zero-cross times Z1 and Z2.

The i-th measured propagation times t1i and t2i have a plurality of candidates according to the measured zero-crossing times Z1i and Z2i. Further, for the zero-crossing times Z1i and Z2i, there are a plurality of candidates obtained by adding/subtracting integral multiples of one cycle to/from the target zero-crossing times Z1i and Z2i.

Let t1ij be the candidate for the propagation time t1i, and Z1ij be the candidate for the zero-crossing time Z1i (see FIG. 1). Let t2ik be the candidate for the propagation time t2i, and Z2ik be the candidate for the zero-crossing time Z2i (see FIG. 2). Also, the target zero-crossing times Z1i and Z2i are assumed to be Z1it and Z2it. Note that j and k are numbers indicating candidates, and in this example, j is an integer of j≧0, and k is an integer of k≧0.

In this case, t1ij and t2ik are
t1ij=Z1ij-dly
t2ik = Z2ik - dly
It can be expressed as.

Also, Z1ij and Z2ik are
Z1ij=Z1it+tuj
Z2ij = Z2it + tuk
It can be expressed as.

When αijk is a candidate for the i-th (current) propagation time difference t2i-t1i,
αijk=t2ik-t1ij=Z2ik-Z1ij=Z2it-Z1it+(kj)tu
can be summarized as

Let t1i-1 be the definite value of the i-1-th (previous) forward propagation time (see FIG. 3), t2i-1 be the definite value of the backward propagation time (see FIG. 4), and the propagation time difference When t2i-1-t1i-1 is αi-1,
αi-1 = t2i-1 - t1i-1 = Z2i-1 - Z1i-1
is represented.

Here, for all candidates αijk of the current propagation time difference, the change from the previous propagation time difference αi-1 is obtained as Δαijk (Δαijk = αijk - αi-1), and the change Δαijk from the previous propagation time difference is the minimum A combination of j and k that satisfies is obtained, and k−j=d obtained from this combination is set as the first condition. At this stage, there are multiple candidates for the combination of j and k that satisfies k−j=d.

Similarly, when a candidate for the i-th (current) propagation time sum t1i + t2i is βijk,
βijk=t1ij+t2ik=Z1ij+Z2ik-2dly=Z1it+Z2it-2dly+(j+k)tu
can be summarized as

Let t1i-1 be the definite value of the i-1-th (previous) forward propagation time (see FIG. 3), t2i-1 be the definite value of the backward propagation time (see FIG. 4), and the propagation time difference When t1i-1 + t2i-1 is βi-1,
βi-1=t1i-1+t2i-1=Z1i-1+Z2i-1-2dly
is represented.

Here, for all candidates βijk of the current propagation time sum, the variation from the previous propagation time sum βi-1 is obtained as Δβijk (Δβijk = βijk - βi-1), and the variation from the previous propagation time difference Δβijk A combination of j and k that minimizes is determined, and j+k=a determined from this combination is used as the second condition. At this stage, there are multiple candidates for the combination of j and k that satisfies j+k=a.

Then, j and k that satisfy both conditions of "kj=d (first condition)" and "j+k=a (second condition)" are obtained. In this case, when d and a are determined, j and k are uniquely determined by j=(ad)/2 and k=(a+d)/2.

Then, the forward zero-crossing time candidate Z1ij and the backward zero-crossing time Z2ik indicated by the obtained j and k are determined as the current forward zero-crossing time Z1i and the backward zero-crossing time Z2i.

By doing so, the variation Δαijk from the previous propagation time difference and the variation Δβijk from the previous propagation time sum are the most among the forward zero-crossing time candidate Z1ij and the backward zero-crossing time candidate Z2ik. A small combination is determined as the current forward zero-crossing time Z1i and backward zero-crossing time Z2i. This makes it possible to always select correct zero-crossing times Z1i and Z2i in both forward and reverse directions and to calculate correct propagation times t1 and t2.

In order to realize the present invention, the threshold voltage vs is sufficiently low with respect to the wave height immediately before the target zero-crossing time, so that the target zero-crossing time can be reliably achieved even if there is a fluctuation in the amplitude of the received signal. make it detectable.

In this case, since the threshold voltage vs is low, a zero-cross time that is earlier than the target zero-cross time may also be detected. make sure it is fixed.

[Embodiment]
FIG. 5 shows a main part of an ultrasonic flowmeter 100 according to an embodiment of the invention. In the figure, the same reference numerals as in FIG. 25 denote the same or equivalent components as those described with reference to FIG. 25, and the description thereof will be omitted.

In this ultrasonic flowmeter 100, for the first ultrasonic transmitter/receiver (upstream transducer) 2 and the second ultrasonic transmitter/receiver (downstream transducer) 3, "first ultrasonic transmitter/receiver 2 and A measurement step of transmitting and receiving ultrasonic signals in both directions through fluid between the second ultrasonic transmitter/receiver 3 is performed a plurality of times, and based on the propagation time difference of the ultrasonic signals in both directions obtained for each measurement step A flow rate calculation device 4 is provided which measures the flow velocity v of the fluid using the flow velocity v and obtains the flow rate Q of the fluid from the measured flow velocity v and the cross-sectional area S of the pipe 1 .

As shown in FIG. 6, the flow calculation device 4 includes a central processing unit (CPU) 4-1, a random access memory (RAM) 4-2, a read-only memory (ROM) 4-3, and a hard disk. It comprises a storage device 4-4, input/output interfaces 4-5 and 4-6, and a bus line 4-7 connecting them.

A flow rate calculation program is installed in the flow rate calculation device 4 as a program specific to the present embodiment. This flow rate calculation program is provided in a state recorded on a recording medium such as a CD-ROM. installed.

In this flow rate calculation device 4, the CPU 4-1 processes the input information via the interface 4-5, and accesses the RAM 4-2, ROM 4-3, and storage device 4-4 while installing the It operates according to the flow rate calculation program. A first example (embodiment 1) of the processing operation executed by the CPU 4-1 according to this flow rate calculation program will be described below with reference to the flow charts divided into FIGS. 7 and 8. FIG.

[Embodiment 1]
The CPU 4-1 takes in the reception signal (see FIG. 1) output from the second ultrasonic transmitter/receiver 3 via the interface 4-5 as the current forward reception signal, and this forward reception signal is After exceeding the set threshold voltage Vs, the timing at which the forward received signal zero-crosses is detected a plurality of times as zero-crossing times, and each of the detected zero-crossing times is used as a candidate Z1ij for the current forward zero-crossing time. acquire (step S101). The acquired candidate Z1ij for the current forward zero-crossing time is stored in the storage device 4-4.

In this example, the zero-crossing time is detected as the zero-crossing timing at which the forward received signal shifts from the plus side to the minus side (the timing at which it crosses the zero potential). That is, after the forward received signal exceeds the threshold voltage Vs, a plurality of timings at which the forward received signal crosses zero every one cycle (tu) are detected as zero-crossing times, and each of the detected zero-crossing times is detected this time. is acquired as a candidate Z1ij for the forward zero-crossing time.

Next, the CPU 4-1 takes in the reception signal (see FIG. 2) output from the first ultrasonic transmitter/receiver 2 via the interface 4-5 as the current reception signal in the opposite direction, and After the signal exceeds a preset threshold voltage Vs, the timing at which the reverse received signal zero-crosses is detected a plurality of times as zero-crossing times, and each of the detected zero-crossing times is used as the current reverse zero-crossing time. It is acquired as a candidate Z2ik (step S102). The acquired candidate Z2ik for the current reverse zero-crossing time is stored in the storage device 4-4.

In this example, the zero-crossing time is detected as the zero-crossing timing at which the reverse received signal shifts from the plus side to the minus side (the timing at which it crosses the zero potential). That is, after the reverse received signal exceeds the threshold voltage Vs, a plurality of timings at which the reverse received signal crosses zero every one cycle (tu) are detected as zero crossing times, and each of the detected zero crossing times is detected this time. is obtained as a candidate Z2ik for the zero-crossing time in the opposite direction.

Next, the CPU 4-1 determines the current forward zero-cross time candidate Z1ij obtained in step S101 and the current reverse zero-cross time candidate Z2ik obtained in step S102. The difference "Z2ik-Z1ij" between the current zero-crossing time candidate Z1ij and the current reverse zero-crossing time candidate Z2ik is obtained as the current propagation time difference candidate αijk (step S103).

Further, the CPU 4-1 determines the current forward zero-cross time candidate Z1ij acquired in step S101 and the current backward zero-cross time candidate Z2ik acquired in step S102. The sum "Z1ij+Z2ik" of the zero-crossing time candidate Z1ij and the current reverse zero-crossing time candidate Z2ik is obtained as the current propagation time sum candidate βijk (step S104).

In addition, the CPU 4-1 propagates the difference "Z2i-1-Z1i-1" between the previous fixed value Z1i-1 of the forward zero-crossing time and the previous fixed value Z2i-1 of the backward zero-crossing time. The time difference αi-1 is obtained (step S105), and the sum "Z1i-1+Z1i-1" of the previous fixed value Z1i-1 of the forward zero-crossing time and the previous fixed value Z2i-1 of the reverse zero-crossing time is obtained. is obtained as the propagation time sum βi-1 (step S106).

Then, the CPU 4-1 calculates the change Δαijk (Δαijk=αijk−αi-1) from the previous propagation time difference αi-1 obtained in step S105 for all the current propagation time difference candidates αijk obtained in step S103. (step S107).

Further, the CPU 4-1 determines the change Δβijk (Δβijk=βijk−βi-1 ) is obtained (step S108).

Then, the CPU 4-1 finds the combination of j and k that minimizes the absolute value of the variation Δαijk from the previous propagation time difference found in step S107, and k−j=d calculated from this combination of j and k. is obtained as a first condition (step S109). Also, the combination of j and k that minimizes the absolute value of the change Δβijk from the previous propagation time sum obtained in step S108 is obtained, and j+k=a obtained from this combination of j and k is used as the second condition. (step S110).

Then, the CPU 4-1 obtains j and k that satisfy both conditions of "kj=d (first condition)" and "j+k=a (second condition)" (step S111). That is, k−j=d and j+k=a are simultaneously solved to obtain j and k as j=(ad)/2 and k=(a+d)/2.

Then, the CPU 4-1 selects the forward zero-cross time candidates Z1ij and Z2ij for the current forward zero-cross time and Z2ij, respectively, for the forward zero-cross time indicated by j and k obtained in step S111. The candidate Z1ij and backward zero-crossing time Z2ik are determined as the current forward zero-crossing time Z1i and backward zero-crossing time Z2i (step S112).

[Specific example of Embodiment 1]
Next, a specific example of Embodiment 1 will be described. In the specific example of the first embodiment, the previous fixed value Z1i-1 of the forward zero-crossing time is "229.17 µs", and the previous fixed value Z2i-1 of the backward zero-crossing time is "229.91 µs". ” (see FIG. 9).

In this case, the difference (previous propagation time difference) αi-1 between the previous fixed value Z1i-1 of the forward zero-crossing time and the previous fixed value Z2i-1 of the backward zero-crossing time is Z2i-1-Z1i- 1=074 [μs], the sum of the previous fixed value Z1i-1 of the forward zero-crossing time and the previous fixed value Z2i-1 of the backward zero-crossing time (previous propagation time sum) βi-1 is obtained as Z1i-1+Z2i-1=459.08 [.mu.s] (see FIG. 10).

In addition, Z1i0 is acquired as "225.37 μs", Z1i1 as "227.28 μs", and Z1i2 as "229.23 μs" as candidate Z1ij for the current forward zero-crossing time (see FIG. 11). Z2i0 is "228.00 μs", Z2i1 is "229.93 μs", and Z2i2 is "231.82 μs" as zero-crossing time candidates Z2ik (see FIG. 12).

In this case, for all combinations of the current forward zero-cross time candidate Z1ij and the current reverse zero-cross time candidate Z2ik, the current forward zero-cross time candidate Z1ij and the current reverse zero-cross time candidate Z1ij If the difference "Z2ik-Z1ij" with the candidate Z2ik is obtained as the current propagation time difference candidate αijk, the current propagation time difference candidate αijk is as shown in FIG.

For all combinations of the current forward zero-cross time candidate Z1ij and the current reverse zero-cross time candidate Z2ik, the current forward zero-cross time candidate Z1ij and the current reverse zero-cross time candidate When the sum "Z1ij+Z2ik" with Z2ik is obtained as the current propagation time sum candidate βijk, the current propagation time sum candidate βijk is as shown in FIG.

Then, for all the current propagation time difference candidates αijk, if the variation Δαijk from the previous propagation time difference αi-1 is obtained as “αijk−αi-1”, the variation Δαijk from the previous propagation time difference is shown in FIG. as shown. Also, for all candidates βijk of the current propagation time sum, if the change Δβijk from the previous propagation time sum βi-1 is obtained as "βijk - βi-1", the change Δβijk from the previous propagation time sum is It comes to show in FIG.

In FIG. 15, the combination of j and k that minimizes the absolute value of the change .DELTA..alpha.ijk from the previous propagation time difference is j=1 and k=0 (hatched cells in the figure). From the combination of j and k, kj=d is obtained as the first condition. In this case, d=-1 is obtained from the combination of j=1 and k=0, and kj=-1 is the first condition. Note that combinations of j and k with d=-1 include k=1 and j=2 (cells indicated by hatched lines in the figure), and this combination of j and k is also a candidate.

In FIG. 16, the combination of j and k that minimizes the absolute value of the change .DELTA..beta.ijk from the previous sum of propagation times is j=1 and k=2 (hatched cells in the figure). From the combination of j and k, j+k=a is obtained as the second condition. In this case, a=3 is obtained from the combination of j=1 and k=2, and j+k=3 is the second condition. There are also combinations of j and k where a=3, k=1 and j=2 (cells indicated by hatched lines in the figure), and this combination of j and k is also a candidate.

In the specific example of the first embodiment, the two conditions obtained assuming that the difference in the zero-crossing times and the change in the sum are small are "k−j=−1" (first condition) and "j+k=3". (Second condition), j=2 as a combination of j and k that satisfy both conditions, that is, the combination that has the smallest change Δαijk from the previous propagation time difference and the smallest change Δβijk from the previous propagation time sum. , k=1.

As a result, the forward zero-crossing time candidate Z1i2 and the backward zero-crossing time candidate Z2i1 indicated by j=2 and k=1 thus obtained are converted to the current forward zero-crossing time Z1i and the backward zero-crossing time Z1i. It is determined as time Z2i (see FIG. 17).

[Embodiment 2]
Next, a second example (embodiment 2) of the processing operation executed by the CPU 4-1 according to the flow rate calculation program will be described with reference to the flow charts divided into FIGS. 18 and 19. FIG.

18 and 19, the processing of steps S201 to S208 is the same as the processing of steps S101 to S108 in the flowchart divided into FIGS. omitted. It should be noted that in the second embodiment, the minimum value is calculated by one-dimensionalizing the difference of the zero-crossing times and the change in the sum using the average.

In the second embodiment, the CPU 4-1 obtains the average value of the variation Δαijk from the previous propagation time difference obtained in step S207 for the same k−j, and determines the k− Obtain j=d as the first condition (step S209). Further, regarding the variation Δβijk from the previous propagation time sum obtained in step S208, the average value of the same j+k is obtained, and the absolute value of the average value j+k=d is obtained as the second condition (step S210).

Then, the CPU 4-1 obtains j and k that satisfy both conditions of "kj=d (first condition)" and "j+k=a (second condition)" (step S211). That is, k−j=d and j+k=a are simultaneously solved to obtain j and k as j=(ad)/2 and k=(a+d)/2.

Then, the CPU 4-1 selects the forward zero-cross time candidate Z1ij and the current reverse zero-cross time candidate Z2ij from the current forward zero-cross time candidate Z1ij and the current reverse zero-cross time candidate Z2ij, respectively. The candidate Z1ij and backward zero-crossing time Z2ik are determined as the current forward zero-crossing time Z1i and backward zero-crossing time Z2i (step S212).

[Specific example of Embodiment 2]
Next, a specific example of the second embodiment will be described. Also in the specific example of the second embodiment, in the same way as in the first embodiment, in step S207, the variation Δαijk from the previous propagation time difference as shown in FIG. 15 is obtained, and in step S208, It is assumed that a change Δβijk from the previous sum of propagation times as shown in (1) is obtained.

In Embodiment 1, the combination of j and k that minimizes the absolute value of the change Δαijk from the previous propagation time difference is obtained, and from this combination of i and k, k−j=d is obtained as the first condition. I made it On the other hand, in the second embodiment, the average value of the variation Δαijk from the previous propagation time difference is calculated for the same k−j, and the absolute value of the average value k−j=d is the smallest. 1 condition (see FIG. 20). In the example shown in FIG. 20, the absolute value of the average value is minimum when kj=-1. Therefore, kj=-1 is taken as the first condition.

Further, in Embodiment 1, the combination of j and k that minimizes the absolute value of the change Δβijk from the previous propagation time sum is obtained, and from this combination of i and k, j+k=a is set as the second condition. I asked for it. On the other hand, in the second embodiment, the average value of the change Δβijk from the previous propagation time sum is calculated for the same j+k, and the absolute value of the average value j+k=a is the second condition. (See FIG. 21). In the example shown in FIG. 21, the absolute value of the average value is minimum when j+k=3. Therefore, j+k=3 is the second condition.

In the specific example of the second embodiment, the two conditions obtained assuming that the difference in the zero-crossing times and the change in the sum are small are k−j=−1 (first condition) and j+k=3 (second condition). condition), j=2 and k=1 as j and k satisfying both conditions, that is, as a combination where the change Δαijk from the previous propagation time difference and the change Δβijk from the previous propagation time sum are the smallest. is required.

As a result, the forward zero-crossing time candidate Z1i2 and the backward zero-crossing time candidate Z2i1 indicated by j=2 and k=1 thus obtained are converted to the current forward zero-crossing time Z1i and the backward zero-crossing time Z1i. It is determined as time Z2i (see FIG. 22).

FIG. 23 shows a functional block diagram of the main part of the flow rate computing device 4 in the ultrasonic flowmeter 100. As shown in FIG. The flow rate calculation device 4 includes, as the processing functions of the CPU 4-1, a forward zero-crossing time candidate acquisition unit 41, a backward zero-crossing time candidate acquisition unit 42, a propagation time difference candidate calculation unit 43, and a propagation time sum candidate calculation unit 44. , a previous propagation time difference calculator 45, a previous propagation time sum calculator 46, a propagation time difference change calculator 47, a propagation time sum change calculator 48, and a zero crossing time determination unit 49.

In this flow rate calculation device 4, the forward zero-crossing time candidate acquisition unit 41 receives the ultrasonic signal from the first ultrasonic transmitter/receiver 2 and outputs the received signal output from the second ultrasonic transmitter/receiver 3 in the forward direction. After this forward received signal exceeds the threshold voltage Vs, the timing at which this forward received signal crosses zero (in this example, the timing at which the forward received signal crosses zero every cycle) are detected as zero-crossing times, and each of the detected zero-crossing times is acquired as a candidate Z1ij for the current forward zero-crossing time.

The backward zero-crossing time candidate acquiring unit 42 acquires the received signal output from the first ultrasonic transmitter/receiver 2 that has received the ultrasonic signal from the second ultrasonic transmitter/receiver 3 as a backward received signal, and obtains this After the reverse received signal exceeds the threshold voltage Vs, a plurality of timings at which the reverse received signal crosses zero (in this example, the timing at which the reverse received signal crosses zero every cycle) are detected as zero crossing times. , each of the detected zero-crossing times is obtained as a candidate Z2ik for the current reverse zero-crossing time.

The propagation time difference candidate calculation unit 43 calculates the current forward zero-cross time candidate Z1ij acquired by the forward zero-cross time candidate acquisition unit 41 and the current reverse zero-cross time acquired by the backward zero-cross time candidate acquisition unit 42. For all combinations with candidates Z2ik of , the difference "Z2ik-Z1ij" between the current forward zero-crossing time candidate Z1ij and the current backward zero-crossing time candidate Z2ik is obtained as the current propagation time difference candidate αijk.

The propagation time sum candidate calculation unit 44 calculates the current forward zero-crossing time candidate Z1ij acquired by the forward zero-crossing time candidate acquiring unit 41 and the current reverse zero-crossing time candidate Z1ij acquired by the backward zero-crossing time candidate acquiring unit 42. For all combinations with time candidates Z2ik, the sum of the current forward zero-crossing time candidate Z1ij and the current backward zero-crossing time candidate Z2ik, "Z1ij+Z2ik", is obtained as the current propagation time sum candidate βijk.

The previous propagation time difference calculator 45 obtains the difference between the previous fixed value Z1i-1 of the forward zero-crossing time and the previous fixed value Z2i-1 of the backward zero-crossing time as the previous propagation time difference αi-1, The previous propagation time sum calculation unit 46 sets the sum of the previous fixed value Z1i-1 of the forward zero-crossing time and the previous fixed value Z2i-1 of the backward zero-crossing time as the previous propagation time sum βi-1. Ask.

The propagation time difference change calculation unit 47 calculates all of the current propagation time difference candidates αijk obtained by the propagation time difference candidate calculation unit 43 from the previous propagation time difference αi-1 obtained by the previous propagation time difference calculation unit 45. A change amount Δαijk (Δαijk=αijk−αi−1) is obtained, and the propagation time sum change calculation unit 48 calculates all of the current propagation time sum candidates βijk obtained by the propagation time sum candidate calculation unit 44 from the previous A change Δβijk (Δβijk=βijk−βi-1) from the previous propagation time sum βi-1 obtained by the propagation time sum calculator 46 is obtained.

The zero-crossing time determination unit 49 supplies the change Δαijk from the previous propagation time difference obtained by the propagation time difference change calculation unit 47 to the propagation time difference change calculation unit 47 and the change from the previous propagation time sum obtained by the propagation time sum change calculation unit 48 . Determine the current forward zero-crossing time Z1i and the current reverse zero-crossing time Z2i from the current forward zero-crossing time candidate Z1ij and the current backward zero-crossing time candidate Z2ik based on Δβijk. do.

In this case, the zero-crossing time determination unit 49 selects the current forward zero-crossing time candidate Z1ij and the current backward zero-crossing time candidate Z2ik as in the first and second embodiments described above. , the combination of the smallest change Δαij from the previous propagation time difference and the smallest change Δβij from the previous total propagation time is determined as the current forward zero-crossing time Z1i and the current backward zero-crossing time Z2i. The determined zero-cross times Z1i and Z2i are used as the previous determined values Z1i-1 and Z2i-1 of the zero-cross times when measuring the next propagation time difference.

In the above-described embodiment, in the forward zero-crossing time candidate acquiring unit 41 and the backward zero-crossing time candidate acquiring unit 42, the timing at which the forward received signal and the backward received signal zero-cross each cycle (tu) is detected as the zero-crossing time, it is also possible to detect the zero-crossing timing every half cycle (tu/2) as the zero-crossing time (see FIG. 24).

Even if the zero-crossing timing is detected every half cycle as the zero-crossing time, the correct zero-crossing times Z1i and Z2i are always selected in both the forward and reverse directions in the same manner as in the above-described embodiment, and the correct propagation time is obtained. It becomes possible to calculate t1 and t2.

Further, in the zero-crossing time determining unit 49, the average of the current determined forward zero-crossing time Z1i and a plurality of forward zero-crossing time candidates Z1ij contiguous to this zero-crossing time Z1i is obtained, and this average is used as the current forward zero-crossing time Z1i. The forward zero-crossing time used for calculation of the propagation time t1 is determined as the current reverse zero-crossing time Z2i and the average of a plurality of backward zero-crossing time candidates Z2ik following this zero-crossing time Z2i is calculated. The backward zero-crossing time used for calculating the current backward propagation time t2 may be used. By doing so, it is possible to reduce variations in the measured propagation time in the same manner as in Patent Document 1.

[Expansion of Embodiment]
Although the present invention has been described with reference to the embodiments, the present invention is not limited to the above embodiments. Various changes that can be understood by those skilled in the art can be made to the configuration and details of the present invention within the scope of the technical idea of the present invention.

1... Piping, 2... First ultrasonic transmitter/receiver (upstream transducer), 3... Second ultrasonic transmitter/receiver (downstream transducer), 4... Flow calculation device, 4-1... Central processing unit (CPU ), 4-2... random access memory (RAM), 4-3... dedicated memory (ROM), 4-4... storage device, 4-5, 4-6... interface, 4-7... bus line, 41... forward direction Zero-crossing time candidate acquisition unit 42 Reverse zero-crossing time candidate acquisition unit 43 Propagation time difference candidate calculation unit 44 Propagation time sum candidate calculation unit 45 Previous propagation time difference calculation unit 46 Previous propagation time sum calculation Part 47... Propagation time difference change calculation part 48... Propagation time sum change calculation part 49... Zero cross time determination part 100... Ultrasonic flow meter.

Claims (11)

a pipe through which a fluid to be measured flows; a first ultrasonic transmitter/receiver arranged upstream of the pipe; and a second ultrasonic transmitter/receiver arranged downstream of the pipe; The measurement step of transmitting and receiving ultrasonic signals in both directions through the fluid between the ultrasonic transmitter and receiver of and the second ultrasonic transmitter and receiver is performed a plurality of times, and in the two directions obtained for each of these measurement steps In an ultrasonic flowmeter configured to measure the flow rate of the fluid based on the propagation time difference of the ultrasonic signal,
A received signal output from the second ultrasonic transmitter/receiver that received the ultrasonic signal from the first ultrasonic transmitter/receiver is taken as a forward received signal, and the forward received signal is set in advance. After exceeding the current threshold voltage, multiple timings at which the forward received signal crosses zero are detected as zero-crossing times, and each of the detected zero-crossing times is acquired as a candidate for the current forward zero-crossing time. a forward zero-crossing time candidate acquiring unit;
A received signal outputted from the first ultrasonic transmitter/receiver that received the ultrasonic signal from the second ultrasonic transmitter/receiver is taken as a reverse received signal, and the reverse received signal is set in advance. After exceeding the current threshold voltage, a plurality of timings at which the reverse received signal crosses zero are detected as zero-crossing times, and each of the detected zero-crossing times is acquired as a candidate for the current reverse-direction zero-crossing time. a backward zero-crossing time candidate acquiring unit;
For all combinations of the current forward zero-crossing time candidate acquired by the forward zero-crossing time candidate acquiring unit and the current backward zero-crossing time candidate acquired by the backward zero-crossing time candidate acquiring unit, a propagation time difference candidate calculation unit configured to obtain a difference between a current forward zero-crossing time candidate and a current backward zero-crossing time candidate as a current propagation time difference candidate;
For all combinations of the current forward zero-crossing time candidate acquired by the forward zero-crossing time candidate acquiring unit and the current backward zero-crossing time candidate acquired by the backward zero-crossing time candidate acquiring unit, a propagation time sum candidate calculation unit configured to obtain the sum of the current forward zero-crossing time candidate and the current backward zero-crossing time candidate as a current propagation time sum candidate;
a previous propagation time difference calculating unit configured to obtain, as a previous propagation time difference, a difference between a previous fixed value of the forward zero-crossing time and a previous fixed value of the backward zero-crossing time;
a previous propagation time sum calculation unit configured to calculate a sum of a previous fixed value of the forward zero-crossing time and a previous fixed value of the backward zero-crossing time as a previous propagation time sum;
A propagation time difference change configured to obtain a change from a previous propagation time difference obtained by the previous propagation time difference calculation unit for all current propagation time difference candidates obtained by the propagation time difference candidate calculation unit. a calculation unit;
For all the current propagation time sum candidates obtained by the propagation time sum candidate calculation unit, a change from the previous propagation time sum obtained by the previous propagation time sum calculation unit is calculated. a propagation time sum variation calculator;
The forward zero-crossing is performed based on the change from the previous propagation time difference calculated by the propagation time difference change calculator and the change from the previous propagation time sum calculated by the propagation time sum change calculator. The current forward zero-crossing time is selected from among the current forward zero-crossing time candidate acquired by the time candidate acquiring unit and the current backward zero-crossing time candidate acquired by the backward zero-crossing time candidate acquiring unit. and a zero-cross time determination unit configured to determine the current reverse zero-cross time. The ultrasonic flowmeter according to claim 1,
The zero-crossing time determination unit
A combination having the smallest change from the previous propagation time difference and the smallest change from the previous propagation time sum is selected from the current forward zero-crossing time candidate and the current backward zero-crossing time candidate. , as the current forward zero-cross time and the current reverse zero-cross time. The ultrasonic flowmeter according to claim 1,
The forward zero-crossing time candidate acquisition unit includes:
With i being the number indicating the current time and j being the number indicating the candidate, the current forward zero-crossing time candidate is extracted as Z1ij,
The backward zero-crossing time candidate acquisition unit,
With i being the number indicating the current time and k being the number indicating the candidate, the candidate for the zero crossing time in the reverse direction is extracted as Z2ik,
The propagation time difference candidate calculation unit,
For all combinations of the current forward zero-cross time candidate Z1ij and the current reverse zero-cross time candidate Z2ik, the current forward zero-cross time candidate Z1
The difference between ij and the current reverse zero-crossing time candidate Z2ik is defined as the current propagation time difference candidate αijk
as
The propagation time sum candidate calculation unit,
For all combinations of the current forward zero-cross time candidate Z1ij and the current reverse zero-cross time candidate Z2ik, the current forward zero-cross time candidate Z1ij
and the current reverse zero-crossing time candidate Z2ik as the current propagation time sum candidate βijk,
The previous propagation time difference calculator,
Obtaining a difference between the previous fixed value Z1i of the forward zero-crossing time and the previous fixed value Z2i of the backward zero-crossing time as a previous propagation time difference αi-1,
The previous propagation time sum calculation unit,
obtaining the sum of the previous fixed value Z1i of the forward zero-crossing time and the previous fixed value Z2i of the backward zero-crossing time as the previous propagation time sum βi-1;
The propagation time difference variation calculator,
Obtaining as Δαijk the amount of change from the previous propagation time difference αi-1 for all of the current propagation time difference candidates αijk,
The propagation time sum change calculation unit,
Obtaining as Δβijk the amount of change from the previous propagation time sum βi−1 for all of the current propagation time sum candidates βijk ,
The zero-crossing time determination unit
A change Δαij from the previous propagation time difference obtained by the propagation time difference change calculator
Find the combination of j and k that minimizes the absolute value of k, and k-
With j=d as the first condition, the combination of j and k that minimizes the absolute value of the change Δβijk from the previous sum of propagation times obtained by the sum of propagation time changes calculated by the sum of propagation time change calculation section is determined, and from this combination Using the obtained j+k=a as a second condition, obtaining j and k that satisfy both the first condition and the second condition, and obtaining the forward zero crossing indicated by the obtained j and k An ultrasonic flowmeter characterized in that the time candidate Z1ij and the backward zero-cross time candidate Z2ik are determined as the current forward zero-cross time Z1i and the backward zero-cross time Z2i. The ultrasonic flowmeter according to claim 1,
The forward zero-crossing time candidate acquisition unit includes:
With i being the number indicating the current time and j being the number indicating the candidate, the current forward zero-crossing time candidate is extracted as Z1ij,
The backward zero-crossing time candidate acquisition unit,
With i being the number indicating the current time and k being the number indicating the candidate, the candidate for the zero crossing time in the reverse direction is extracted as Z2ik,
The propagation time difference candidate calculation unit,
For all combinations of the current forward zero-cross time candidate Z1ij and the current reverse zero-cross time candidate Z2ik, the current forward zero-cross time candidate Z1
The difference between ij and the current reverse zero-crossing time candidate Z2ik is defined as the current propagation time difference candidate αijk
as
The propagation time sum candidate calculation unit,
For all combinations of the current forward zero-cross time candidate Z1ij and the current reverse zero-cross time candidate Z2ik, the current forward zero-cross time candidate Z1ij
and the current reverse zero-crossing time candidate Z2ik as the current propagation time sum candidate βijk,
The previous propagation time difference calculator,
Obtaining a difference between the previous fixed value Z1i of the forward zero-crossing time and the previous fixed value Z2i of the backward zero-crossing time as a previous propagation time difference αi-1,
The previous propagation time sum calculation unit,
obtaining the sum of the previous fixed value Z1i of the forward zero-crossing time and the previous fixed value Z2i of the backward zero-crossing time as the previous propagation time sum βi-1;
The propagation time difference variation calculator,
Obtaining as Δαijk the amount of change from the previous propagation time difference αi-1 for all of the current propagation time difference candidates αijk,
The propagation time sum change calculation unit,
Obtaining as Δβijk the amount of change from the previous propagation time sum βi−1 for all of the current propagation time sum candidates βijk ,
The zero-crossing time determination unit
A change Δαij from the previous propagation time difference obtained by the propagation time difference change calculator
For k, find the average value of the same kj, let d be the kj with the smallest absolute value of the average value, and the change from the previous propagation time sum calculated by the propagation time sum change calculation unit Calculate the average value of the same j + k for the minute Δβijk, and the absolute value of the average value is the minimum j
Letting +k be a, find j and k that satisfy both the conditions of k−j=d and j+k=a, and find the forward zero-crossing time candidate Z1ij and the backward zero-crossing time candidate Z1ij indicated by the found j and k. , the candidate zero-crossing times Z2ik are determined as the current forward-direction zero-crossing time Z1i and the current backward-direction zero-crossing time Z2i. In the ultrasonic flowmeter according to any one of claims 1 to 4,
The forward zero-crossing time candidate acquisition unit includes:
A received signal output from the second ultrasonic transmitter/receiver that received the ultrasonic signal from the first ultrasonic transmitter/receiver is taken as a forward received signal, and the forward received signal is set in advance. A plurality of timings at which the forward received signal crosses zero every cycle after exceeding the threshold voltage, are detected as zero-crossing times, and each of the detected zero-crossing times is acquired as a candidate for the current forward zero-crossing time. ,
The backward zero-crossing time candidate acquisition unit,
A received signal outputted from the first ultrasonic transmitter/receiver that received the ultrasonic signal from the second ultrasonic transmitter/receiver is taken as a reverse received signal, and the reverse received signal is set in advance. A plurality of zero-crossing times are detected as zero-crossing times for each cycle of the received signal in the reverse direction after exceeding the threshold voltage, and each of the detected zero-crossing times is acquired as a candidate for the current reverse-direction zero-crossing time. An ultrasonic flowmeter characterized by: In the ultrasonic flowmeter according to any one of claims 1 to 4,
The forward zero-crossing time candidate acquisition unit includes:
A received signal output from the second ultrasonic transmitter/receiver that received the ultrasonic signal from the first ultrasonic transmitter/receiver is taken as a forward received signal, and the forward received signal is set in advance. A plurality of zero-crossing times are detected at every half cycle after the forward received signal exceeds the threshold voltage, and each of the detected zero-crossing times is acquired as a candidate for the current forward zero-crossing time. ,
The backward zero-crossing time candidate acquisition unit,
A received signal outputted from the first ultrasonic transmitter/receiver that received the ultrasonic signal from the second ultrasonic transmitter/receiver is taken as a reverse received signal, and the reverse received signal is set in advance. A plurality of timings at which the reverse received signal crosses zero every half cycle after exceeding the threshold voltage, are detected as zero-crossing times, and each of the detected zero-crossing times is acquired as a candidate for the current reverse-direction zero-crossing time. An ultrasonic flowmeter characterized by: In the ultrasonic flowmeter according to any one of claims 1 to 6,
The zero-crossing time determination unit
Obtaining the average of the determined current forward zero-crossing time and a plurality of candidates for forward zero-crossing times that are continuous with this zero-crossing time, and using this average for calculating the current forward propagation time. year,
Obtaining the average of the fixed current reverse zero-cross time and a plurality of candidates for the reverse zero-cross time successive to this zero-cross time, and using this mean when calculating the current reverse propagation time. An ultrasonic flowmeter characterized by: a pipe through which a fluid to be measured flows; a first ultrasonic transmitter/receiver arranged upstream of the pipe; and a second ultrasonic transmitter/receiver arranged downstream of the pipe; The measurement step of transmitting and receiving ultrasonic signals in both directions through the fluid between the ultrasonic transmitter and receiver of and the second ultrasonic transmitter and receiver is performed a plurality of times, and in the two directions obtained for each of these measurement steps A method for determining a zero crossing time in an ultrasonic flowmeter that measures the flow rate of the fluid based on the propagation time difference of the ultrasonic signal,
A received signal output from the second ultrasonic transmitter/receiver that received the ultrasonic signal from the first ultrasonic transmitter/receiver is taken as a forward received signal, and the forward received signal is set in advance. A plurality of zero-crossing times are detected as the zero-crossing times of the forward received signal after exceeding the current threshold voltage, and each of the detected zero-crossing times is acquired as a candidate for the current forward zero-crossing time. a candidate acquisition step;
A received signal outputted from the first ultrasonic transmitter/receiver that received the ultrasonic signal from the second ultrasonic transmitter/receiver is taken as a reverse received signal, and the reverse received signal is set in advance. After exceeding the current threshold voltage, multiple zero-crossing times are detected as the zero-crossing times of the received signal in the reverse direction, and each of the detected zero-crossing times is acquired as a candidate for the current reverse zero-crossing time. a candidate acquisition step;
For all combinations of the current forward zero-crossing time candidates acquired by the forward zero-crossing time candidate acquiring step and the current backward zero-crossing time candidates acquired by the backward zero-crossing time candidate acquiring step, a propagation time difference candidate calculation step of obtaining a difference between a current forward zero-crossing time candidate and a current backward zero-crossing time candidate as a current propagation time difference candidate;
For all combinations of the current forward zero-crossing time candidates acquired by the forward zero-crossing time candidate acquiring step and the current backward zero-crossing time candidates acquired by the backward zero-crossing time candidate acquiring step, a propagation time sum candidate calculation step of obtaining, as a current propagation time sum candidate, the sum of the current forward zero-crossing time candidate and the current reverse zero-crossing time candidate;
a previous propagation time difference calculating step of obtaining, as a previous propagation time difference, a difference between a previous fixed value of the forward zero-crossing time and a previous fixed value of the backward zero-crossing time;
a previous propagation time sum calculating step of obtaining a sum of a previous fixed value of the forward zero-crossing time and a previous fixed value of the backward zero-crossing time as a previous propagation time sum;
a propagation time difference variation calculation step of obtaining a variation from the previous propagation time difference obtained by the previous propagation time difference calculation step for all current propagation time difference candidates obtained by the propagation time difference candidate calculation step;
A change in propagation time sum obtained by obtaining a change from the previous sum of propagation times obtained by the previous sum of propagation times calculating step for all candidates of the current sum of propagation times obtained by the sum of propagation times calculating step. a calculation step;
The forward zero-crossing is performed based on the change from the previous propagation time difference obtained by the propagation time difference change calculation step and the change from the previous propagation time sum obtained by the propagation time sum change calculation step. The current forward zero-crossing time is selected from the current forward zero-crossing time candidate acquired by the time candidate acquiring step and the current backward zero-crossing time candidate acquired by the backward zero-crossing time candidate acquiring step. and a zero-cross time determination step of determining the current reverse zero-cross time. In the method for determining the zero crossing time in the ultrasonic flowmeter according to claim 8,
The zero-crossing time determination step includes:
A combination having the smallest change from the previous propagation time difference and the smallest change from the previous propagation time sum is selected from the current forward zero-crossing time candidate and the current backward zero-crossing time candidate. , a current forward zero-crossing time and a current reverse zero-crossing time. In the method for determining the ultrasonic flowmeter zero-crossing time according to claim 8,
The forward zero-crossing time candidate obtaining step includes:
With i being the number indicating the current time and j being the number indicating the candidate, the current forward zero-crossing time candidate is extracted as Z1ij,
The backward zero-crossing time candidate obtaining step includes:
With i being the number indicating the current time and k being the number indicating the candidate, the candidate for the zero crossing time in the reverse direction is extracted as Z2ik,
The propagation time difference candidate calculation step includes:
For all combinations of the current forward zero-cross time candidate Z1ij and the current reverse zero-cross time candidate Z2ik, the current forward zero-cross time candidate Z1
The difference between ij and the current reverse zero-crossing time candidate Z2ik is defined as the current propagation time difference candidate αijk
as
The propagation time sum candidate calculation step includes:
For all combinations of the current forward zero-cross time candidate Z1ij and the current reverse zero-cross time candidate Z2ik, the current forward zero-cross time candidate Z1ij
and the current reverse zero-crossing time candidate Z2ik as the current propagation time sum candidate βijk,
The previous propagation time difference calculation step includes:
Obtaining a difference between the previous fixed value Z1i of the forward zero-crossing time and the previous fixed value Z2i of the backward zero-crossing time as a previous propagation time difference αi-1,
The previous propagation time sum calculation step includes:
obtaining the sum of the previous fixed value Z1i of the forward zero-crossing time and the previous fixed value Z2i of the backward zero-crossing time as the previous propagation time sum βi-1;
The propagation time difference variation calculation step includes:
Obtaining as Δαijk the amount of change from the previous propagation time difference αi-1 for all of the current propagation time difference candidates αijk,
The propagation time sum change calculation step includes:
Obtaining as Δβijk the amount of change from the previous propagation time sum βi−1 for all of the current propagation time sum candidates βijk ,
The zero-crossing time determination step includes:
A combination of j and k that minimizes the absolute value of the variation Δαijk from the previous propagation time difference obtained by the propagation time difference variation calculation step is obtained, and k−j=d obtained from this combination is set as the first condition. Then, the combination of j and k that minimizes the absolute value of the change Δβijk from the previous propagation time sum obtained by the propagation time sum change calculation step is obtained, and j+k=a obtained from this combination is the second and find j and k that satisfy both the first condition and the second condition. A method for determining a zero-crossing time in an ultrasonic flowmeter, characterized in that the zero-crossing time candidate Z2ik of the current time is determined as a current forward zero-crossing time Z1i and a current backward zero-crossing time Z2i. In the method for determining the zero crossing time in the ultrasonic flowmeter according to claim 8,
The forward zero-crossing time candidate obtaining step includes:
With i being the number indicating the current time and j being the number indicating the candidate, the current forward zero-crossing time candidate is extracted as Z1ij,
The backward zero-crossing time candidate obtaining step includes:
With i being the number indicating the current time and k being the number indicating the candidate, the candidate for the zero crossing time in the reverse direction is extracted as Z2ik,
The propagation time difference candidate calculation step includes:
For all combinations of the current forward zero-cross time candidate Z1ij and the current reverse zero-cross time candidate Z2ik, the current forward zero-cross time candidate Z1
The difference between ij and the current reverse zero-crossing time candidate Z2ik is defined as the current propagation time difference candidate αijk
as
The propagation time sum candidate calculation step includes:
For all combinations of the current forward zero-cross time candidate Z1ij and the current reverse zero-cross time candidate Z2ik, the current forward zero-cross time candidate Z1ij
and the current reverse zero-crossing time candidate Z2ik as the current propagation time sum candidate βijk,
The previous propagation time difference calculation step includes:
Obtaining a difference between the previous fixed value Z1i of the forward zero-crossing time and the previous fixed value Z2i of the backward zero-crossing time as a previous propagation time difference αi-1,
The previous propagation time sum calculation step includes:
obtaining the sum of the previous fixed value Z1i of the forward zero-crossing time and the previous fixed value Z2i of the backward zero-crossing time as the previous propagation time sum βi-1;
The propagation time difference variation calculation step includes:
Obtaining as Δαijk the amount of change from the previous propagation time difference αi-1 for all of the current propagation time difference candidates αijk,
The propagation time sum change calculation step includes:
Obtaining as Δβijk the amount of change from the previous propagation time sum βi−1 for all of the current propagation time sum candidates βijk ,
The zero-crossing time determination step includes:
For the variation Δαijk from the previous propagation time difference obtained by the propagation time difference variation calculation step, the average value of the same k−j is obtained, and the absolute value of the average value is the minimum k
Let -j be d, find the average value of the change Δβ ijk from the previous propagation time sum obtained by the propagation time sum change calculating step for the same j+k, and determine the j+k that minimizes the absolute value of the average value. a, find j and k that satisfy both the conditions of k−j=d and j+k=a, and find the forward zero-crossing time candidate Z1ij and the backward zero-crossing time indicated by the found j and k A method for determining a zero-crossing time in an ultrasonic flowmeter, comprising determining a candidate time Z2ik as a current forward zero-crossing time Z1i and a current backward zero-crossing time Z2i.

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