JP4580178B2 - Ultrasonic flowmeter and flow velocity measurement method - Google Patents

Description

  The present invention relates to an ultrasonic velocimeter and a flow velocity measuring method for measuring a flow velocity of a fluid using ultrasonic waves.

  Conventionally, as this type of ultrasonic current meter, for example, there is one described in Japanese Patent Application Laid-Open No. 2002-340642 by the present applicant.

  The ultrasonic current meter described in this publication includes a burst signal generating means for generating a burst signal, and a pair of transmission / reception ultrasonic probes arranged on the upstream side and the downstream side of the fluid to be measured, The transmission / reception ultrasonic probe converts the burst signal generated from the burst signal generation means into ultrasonic waves and transmits it to the fluid to be measured, and the other transmission / reception ultrasonic probe receives the ultrasonic waves propagated through the fluid to be measured. ing. The downstream propagation time transmitted from the upstream transmitting / receiving ultrasonic probe and received by the downstream transmitting / receiving ultrasonic probe using the received signals received by the upstream / downstream transmitting / receiving ultrasonic probes, and , A signal corresponding to a difference in propagation time from the upstream propagation time transmitted from the downstream transmission / reception ultrasonic probe and received by the upstream transmission / reception ultrasonic probe, and the upstream propagation time and the downstream propagation time Signals corresponding to the average ultrasonic propagation time are obtained, and the flow velocity is obtained from these signals.

  A signal corresponding to the propagation time difference and a signal corresponding to the ultrasonic propagation time are passed through a low-pass filter to obtain a DC level.

Specifically, a configuration for obtaining a conventional ultrasonic wave propagation time will be described with reference to a timing chart shown in FIG. As shown in FIG. 7, the transmission trigger signal is generated every predetermined period T ₀ , and the upstream and downstream transmission signals (burst signals) are synchronized with the transmission trigger signal (FIG. 7A). FIGS. 7B and 7C are generated, and these signals are respectively sent to the upstream transmitting / receiving ultrasonic probe and the downstream transmitting / receiving ultrasonic probe and converted into ultrasonic waves. These ultrasonic waves are received by the downstream transmission / reception ultrasonic probe and the upstream transmission / reception ultrasonic probe, converted into electrical signals, and become downstream and upstream reception signals. Actually, the received signal on the downstream side and the upstream side differ depending on the flow velocity of the fluid to be measured, but for the sake of explanation, the difference is ignored in the figure, and the transmitted signal and the received signal have the same shape on both the upstream side and the downstream side. It represents.

Also, latch signals (FIGS. 7 (f) and (g)) that become high level by the transmission trigger signal and low level by the reception signal are generated, and each latch signal is converted into a DC signal by a low-pass filter (FIG. 7 (h), (i)) The propagation time signal V ₀ (FIG. 7 (j)), which is an average signal of each DC signal, is obtained so that the voltage represents the propagation time, and ultrasonic propagation is performed from the average signal. Seeking time.

In this case, the propagation time signal V ₀ is

で表されるので、超音波伝搬時間ｔ_０は、

Therefore, the ultrasonic wave propagation time t ₀ is

の式から求めることができる。

It can be obtained from the following formula.

As described above, in the conventional ultrasonic flow rate meter, the ultrasonic propagation time _{t 0 required,} but proportional to T 0 _{/ V cc,} the greater the value of this _T 0 _{/ V cc, t 0} There is a problem that cannot be obtained with high accuracy.

JP 2002-340642 A

  The present invention has been made in view of such a problem, and provides an ultrasonic current meter and a flow velocity measuring method capable of obtaining a measured value such as an ultrasonic propagation time with high accuracy and achieving low power consumption. Is the purpose.

In order to achieve the above object, an ultrasonic anemometer according to the invention of claim 1 comprises:
A transmission signal generating means for generating a transmission signal;
At least two ultrasonic probes arranged on the upstream side and the downstream side of the fluid to be measured, the upstream ultrasonic probe receiving the transmission signal from the transmission signal generating means and transmitting the ultrasonic wave into the fluid to be measured The downstream ultrasonic probe receives the ultrasonic wave and outputs a reception signal (referred to as a downstream reception signal), and the downstream ultrasonic probe receives the transmission signal from the transmission signal generating means to be measured. An ultrasonic probe that transmits ultrasonic waves into the fluid, and an upstream ultrasonic probe receives the ultrasonic waves and outputs a reception signal (referred to as an upstream reception signal);
Latch means for generating a reception state change signal whose state changes at the timing of reception of at least one of the upstream reception signal and the downstream reception signal;
Switch means for conducting the reception state change signal in a predetermined period before and after the reception state change signal changes;
Switch control signal generating means for generating a switch control signal for switching conduction / non-conduction of the signal of the switch means;
DC signal converting means for converting a signal conducted in the switch means into a DC signal;
The voltage of the DC signal from the DC signal conversion unit, based on the time from the predetermined time period and the transmission switching means is conductive until the start of the predetermined period, determined between the time ultrasonic wave propagation ultrasound propagates, ultra A calculation means for calculating the flow velocity of the fluid to be measured using the sound wave propagation time;
It is characterized by providing.

According to a second aspect of the invention, in what according to claim 1, wherein said switch control signal generating means, and generating a switch control signal based on the sound velocity of ultrasonic wave propagation distance and the criteria.

According to a third aspect of the invention, in what according to claim 1, characterized in that said switch control signal generating means, the voltage of the DC signal from the DC signal conversion means generates a switch control signal to be constant And

According to a fourth aspect of the present invention, in any one of the first to third aspects, the transmission signal is a burst signal,
Binarization means for binarizing the upstream reception signal and the downstream reception signal;
A phase difference measuring means for measuring a phase difference between the upstream side received signal and the downstream side received signal respectively binarized by the binarizing means;
Further comprising
The calculating means calculates the flow velocity of the fluid to be measured based on the ultrasonic wave propagation time and the phase difference signal from the phase difference measuring means.

According to a fifth aspect of the present invention, the latch means according to any one of the first to third aspects, wherein the latch means is in a reception state in which the state changes at the reception timing of the upstream side received signal and the downstream side received signal. Generate a change signal,
The DC signal converting means converts the reception state change signal of each of the upstream reception signal and the downstream reception signal from the latch means conducted in the switch means into a DC signal,
The calculation means is configured to determine the ultrasonic propagation time from the ultrasonic probe on the upstream side to the ultrasonic probe on the downstream side and the ultrasonic wave on the downstream side based on the respective DC signals from the DC signal conversion means and the conduction timing of the switch means. An ultrasonic propagation time from the probe to the upstream ultrasonic probe is obtained, and the flow velocity of the fluid to be measured is calculated.

The method for measuring the flow velocity of the fluid to be measured according to claim 6,
Place ultrasonic probes upstream and downstream of the fluid to be measured,
The ultrasonic wave is propagated from the upstream ultrasonic probe to the downstream ultrasonic probe to obtain the reception signal (referred to as the downstream reception signal), and from the downstream ultrasonic probe to the upstream ultrasonic probe. Obtain the received signal (called upstream received signal) by propagating the ultrasonic wave,
Generating a reception state change signal whose state changes at the timing of reception of at least one of the upstream reception signal and the downstream reception signal;
Generate a switch control signal corresponding to a predetermined period before and after the state change signal at the time of reception changes,
On the basis of the switch control signals, and conducting the received time status change signal in the predetermined period before and after the reception time of the state change signal is changed, and converted into a DC signal,
The voltage of the DC signal, the predetermined period and based on the time from transmission until the start of the predetermined time period, between ultrasonic wave propagation time to the between the upstream side of the ultrasonic probe and the downstream side of the ultrasonic probe ultrasound propagates And the flow velocity of the fluid to be measured is calculated based on the ultrasonic wave propagation time.

  In addition, it is also possible to comprise the ultrasonic flowmeter which calculates | requires the flow volume of to-be-measured fluid using the ultrasonic flowmeter of this invention.

According to the present invention, the reception state change signal whose state changes at the timing of reception of at least one of the upstream reception signal and the downstream reception signal is converted into a DC signal in a predetermined period before and after the state change. . In this case, the voltage V _{0 of the} DC signal is expressed as follows: t _{g1 is} the time from transmission to the start of the predetermined period, t _g2 is the predetermined period in which the switch means is conducted, and t ₀ is the ultrasonic propagation time.

となり、ｔ_ｇ２／Ｖ_ｃｃに比例する項を持つが、この係数ｔ_ｇ２／Ｖ_ｃｃの値を従来よりも小さくすることができるため（ｔ_ｇ２＜Ｔ_０）、ｔ_０を高精度に求めることができるようになる。 Therefore, the ultrasonic wave propagation time t ₀ is

_Next, but having a term proportional to _{t g2 / V cc, (t} g2 <T 0) for values can be smaller than conventional the coefficient _t g2 _{/ V cc,} to seek _{t 0} with high accuracy Will be able to.

Unlike the conventional case, since the ultrasonic propagation time t ₀ can be obtained regardless of the cycle of the transmission signal, the accuracy does not deteriorate even if the cycle of the transmission signal is increased. Therefore, the cycle of the transmission signal is increased. Power consumption can be reduced.

  According to the fifth aspect of the present invention, the ultrasonic propagation time from the upstream ultrasonic probe to the downstream ultrasonic probe and the downstream are based on the DC signal from the DC signal converting means and the conduction timing of the switch means. By obtaining the ultrasonic wave propagation time from the ultrasonic probe on the side to the ultrasonic probe on the upstream side, the flow velocity can be obtained with a simple circuit configuration.

Hereinafter, embodiments of the present invention will be described with reference to the drawings.
(First embodiment)
FIG. 1 is a block diagram of an ultrasonic current meter 10 according to the first embodiment of the present invention. In this embodiment, the ultrasonic velocimeter 10 includes a burst signal generation unit 110 that generates a burst signal, a pair of transmission / reception ultrasonic probes 6 and 7, and reception signals from the transmission / reception ultrasonic probes 6 and 7. A binarization unit 112 that performs binarization, a phase difference measurement unit 116 that calculates a phase difference between binarized received signals, an ultrasonic propagation time measurement unit 117 that calculates an ultrasonic propagation time, and an ultrasonic propagation A flow velocity measurement unit 118 that measures the flow velocity and the flow rate of the fluid to be measured based on the propagation time signal from the time measurement unit 117 and the phase difference signal from the phase difference measurement unit 116; The pair of transmitting / receiving ultrasonic probes 6 and 7 are attached to a tube 8 through which a fluid to be measured flows. A fluid to be measured 9 whose flow rate and flow rate are to be measured flows through the pipe 8.

  Hereinafter, each part will be described with reference to the detailed block diagram of FIG.

  The burst signal generation unit 110 includes a trigger circuit 1, a transmission signal generation circuit 2, and a timing circuit 3. The trigger circuit 1 generates a transmission trigger signal S1 at a set transmission repetition interval. This signal S1 is an ultrasonic propagation time measuring unit 117 described later in addition to the transmission signal generation circuit 2 and the timing circuit 3. Sent to. The timing circuit 3 outputs a switch control signal S2 (described later) and a sample and hold circuit control signal S4 based on the transmission trigger signal S1. The transmission signal generation circuit 2 generates a transmission signal A and a transmission signal B, which are burst signals, based on the transmission trigger signal S1, and constitutes transmission signal generation means. These two burst signals can be signals having phases different from each other as disclosed in Japanese Patent Laid-Open No. 2002-340642.

  The transmission signal A and the transmission signal B are sent to the transmission / reception ultrasonic probe 6 and the transmission / reception ultrasonic probe 7, respectively. The transmission / reception ultrasonic probe 6 and the transmission / reception ultrasonic probe 7 convert an electric signal and an ultrasonic signal, and convert the transmission signal A and the transmission signal B, which are burst signals, into ultrasonic waves. In addition to being transmitted into the fluid 9 to be measured, the ultrasonic waves propagated through the fluid 9 to be measured are received, converted into a received signal A and a received signal B, respectively, and output. One transmitting / receiving ultrasonic probe (ultrasonic probe 6 in the case of the figure) is on the upstream side, and the other transmitting / receiving ultrasonic probe (ultrasonic probe 7 in the case of the figure) is on the downstream side. Placed in. The ultrasonic probe may be provided with separate ultrasonic probes for transmission and reception.

  These transmission / reception ultrasonic probes 6 and 7 may be attached to the outside of the tube 8 or to the inside of the tube 8. However, in order to appropriately transmit and receive ultrasonic waves, Therefore, the transmission / reception ultrasonic probes 6 and 7 are arranged so that the angle formed between the ultrasonic wave propagation direction and the tube axis direction is almost always constant. Mounted. Therefore, when the tube diameter is determined, the propagation distance of the ultrasonic wave can be obtained. That is, if the angle between the ultrasonic propagation direction and the tube axis direction is θ and the tube diameter is D, the propagation distance L is

となる。

It becomes.

  The reception signals A and B from these transmission / reception ultrasonic probes 6 and 7 are input to the binarization unit 112. The binarization unit 112 includes amplification circuits 14 and 15 and binarization circuits 16 and 17. The amplifier circuits 14 and 15 amplify the received signals A and B, but the bandwidth must be set appropriately in order to remove unnecessary noise components. However, the amplifier circuits 14 and 15 can be omitted in some cases due to the low power consumption, in other words, high sensitivity, which is a feature of the present invention. The outputs of the amplifier circuit 14 and the amplifier circuit 15 are input to the binarization circuit 16 and the binarization circuit 17, respectively. The binarization circuits 16 and 17 binarize the outputs of the amplifier circuit 14 and the amplifier circuit 15, and are composed of a comparison circuit or the like. The outputs of the amplifier circuit 14 and the amplifier circuit 15 are connected to a voltage around 0V. Are compared by a comparison circuit.

  Next, the received signals binarized by the binarization circuits 16 and 17 are input to the phase difference measuring unit 116. The phase difference measuring unit 116 includes an exclusive OR circuit 30, a sample and hold circuit 31, a low-pass filter 33, and an A / D conversion circuit 35.

  The exclusive OR circuit 30 outputs an exclusive OR signal from the received signals from the binarization circuits 16 and 17. This exclusive OR changes according to the phase difference between the two received signals, and its output is input to the sample and hold circuit 31. The sample and hold circuit 31 receives the sample and hold circuit control signal S4 from the timing circuit 3, and the sample and hold circuit 31 is exclusive while the control signal S4 is at the high level. The logical sum signal is sampled and held, and the value is maintained while the control signal S4 is at the low level. The output from the sample and hold circuit 31 is sent to the low pass filter 33. The low-pass filter 33 removes a high-frequency component and converts it into a low-frequency signal (DC voltage), and the DC voltage level corresponds to the phase difference of the received signal. The output is A / D converted by the A / D conversion circuit 35.

  The reception signals binarized by the binarization circuits 16 and 17 are also input to the ultrasonic propagation time measuring unit 117. The ultrasonic propagation time measurement unit 117 includes latch circuits 21 and 22, switches 23 and 24, an adder 25, a low-pass filter 26, and an A / D conversion circuit 27.

  The latch circuits 21 and 22 output signals that are set by the transmission trigger signal S1 and reset by rising from the binarization circuits 16 and 17, respectively, and signals whose state changes at the timing of receiving the reception signal. Is constituted. The width of this signal corresponds to the ultrasonic propagation time from transmission to reception. Outputs from these latch circuits 21 and 22 are input to switches 23 and 24. The switches 23 and 24 are ON / OFF controlled by the switch control signal S2 from the timing circuit 3, and outputs from the latch circuits 21 and 22 to the adder 25 while the switch control signal S2 is at a high level. When the switch control signal S2 is at a low level, it is made non-conductive and maintained at a high impedance, thereby constituting a switch means that does not change the output voltage of the adder 25. The adder 25 adds the respective voltages from the latch circuits 21 and 22 that conduct the switches 23 and 24.

  The low pass filter 26 removes a high frequency component and converts it into a low frequency signal (DC voltage), and constitutes a DC signal converting means. The output of the low-pass filter 26 is A / D converted by the A / D conversion circuit 27.

  The signals A / D converted by the A / D conversion circuit 35 and the A / D conversion circuit 27 are input to the flow velocity measuring unit 118. The flow velocity measuring unit 118 includes an arithmetic circuit 36, a display unit 42, and an input unit 43 such as a keyboard. The arithmetic circuit 36 can be constituted by a microcomputer having a CPU, a memory, and the like. From the output from the ultrasonic propagation time measuring unit 117 and the output from the phase difference measuring unit 116, the flow velocity and flow rate of the fluid to be measured. Is what you want.

  With reference to the timing chart of the signal in FIG. 3, the operation of the ultrasonic wave velocity meter configured as described above mainly regarding the measurement of the ultrasonic wave propagation time in the ultrasonic wave propagation time measuring unit 117 will be described.

First, as shown in FIG. 3 (a), the trigger circuit 1, and transmits the trigger signal S1 is transmitted repetition interval T _0, which is set is generated in synchronization with the transmission signal generated in the transmission trigger signal S1 A transmission signal A and a transmission signal B are generated from the circuit 2 (FIGS. 3B and 3C). Are shown with the same waveform in the figure, the transmission signal B and the transmission signal A may be a burst pulse whose phase is different, the transmission pulse width T ₁ is substantially equal. Received signal A and the reception signal B is received from a transmission start timing from via the ultrasonic propagation time t _0. When there is a flow inside the tube 8, a time difference corresponding to the flow velocity occurs in the time when the reception signal A and the reception signal B appear (FIGS. 3D and 3E), but the time difference is clearly shown in the figure. Absent). Received signals A and B are amplified by amplification circuits 14 and 15, respectively.

  The outputs of the amplifier circuits 14 and 15 are binarized by the binarization circuits 16 and 17.

  On the other hand, the output from the latch circuits 21 and 22 includes a signal that remains high until the binarization circuits 16 and 17 become high level from the start of transmission, in other words, until the reception signal A and the reception signal B appear. Appears (FIGS. 3 (f) and (g)).

  The switch control signal S2 is a signal that is at a high level in the vicinity of the reception signal (FIG. 3 (h)), and the outputs from the switches 23 and 24 are added during the period of the high level. After being added by the unit 25 (FIG. 3 (i)), it is sent to the low-pass filter 26 and converted into a DC signal (FIG. 3 (j)). The value of the DC voltage is A / D converted by the A / D conversion circuit 27 and input to the arithmetic circuit 36.

The output of the latch circuit 21 and the output of the latch circuit 22 have a difference in pulse width depending on the speed of the fluid 9 to be measured flowing inside the tube 8, but the adder 25 outputs the latch circuit 21 output and the latch circuit 22 output. The sum of the pulse widths is a function of the ultrasonic propagation time t ₀ when there is no flow inside the tube 8. In addition, the switch control signal S2 is a function of the time _tg1 from the transmission trigger signal S1 until the switches 23 and 24 are turned on and the time _{tg2 during} which the switches are on. Specifically, the ultrasonic propagation time signal voltage V _{0 that} is ½ of the output signal from the low-pass filter 26 after being added by the adder 25 is the ultrasonic propagation time t ₀ , and the latch circuit 21 and the latch circuit 21 are latched. When the power supply voltage level of the circuit 22 is V _cc and the constant is t _c ,

となる。この式から、超音波伝搬時間ｔ_０は、

It becomes. From this equation, the ultrasonic wave propagation time t ₀ is

It becomes. The first item of the right side of this equation _is proportional to t g2 _{/ V cc,} which is small when compared to the conventional coefficient _T 0 _{/ V cc,} the change in _{V 0} with respect to the change in _{t 0} is conventionally Can be seen to be larger. This means that t ₀ can be measured with higher accuracy than in the past.

Next, the switch control signal S2 will be described. As described above, the time for which the switch control signal S2 is at the high level needs to be in the vicinity of the presence of the reception signal, in other words, the period that extends over the reception time. Although the time at which the received signal appears, that is, the ultrasonic propagation time changes depending on the temperature, it is an approximate value if the ultrasonic propagation distance between the transmitting / receiving ultrasonic probes 6 and 7 and the speed of sound in the fluid to be measured are known. Can be predicted. That is, assuming that the sound velocity v at room temperature, the predicted ultrasonic propagation time t _0p is

By setting in advance the tube diameter D and the ultrasonic propagation distance between the transmission / reception ultrasonic probes 6 and 7, the time t _g1 from the transmission trigger signal S1 to the high level can be calculated as a predicted ultrasonic wave. It can be determined as a time a little earlier than the propagation time _t0p .

Time t _g1 decided as described above, which may be a fixed value at all times, the ultrasonic propagation time signal voltage V ₀ changes the t _g1 to a predetermined value, for example, V _{cc / 2} You can also. The arithmetic circuit 36 may control the switch control signal S2 generated from the timing circuit 3 serving as a switch control signal generating unit so that the ultrasonic propagation time signal voltage V ₀ is always V _cc / 2. In this case, equation (2) is

となり、ｔ_ｇ２、ｔ_ｃは定数、ｔ_ｇ１は変数となる。

T _g2 and t _c are constants, and t _g1 is a variable.

In this example, the adder 25 is used to add the upstream side received signal A and the downstream side received signal B to obtain the ultrasonic wave propagation time t _0. It is also possible to add. The time difference between the received signal A and the received signal B, if it is determined that significantly smaller than the ultrasonic propagation time t ₀ to be determined, without using the adder 25, either one only of the latch circuit it is also seeking ultrasonic propagation time t ₀ from the low-pass filter directly using the signal no problem will be readily understood. It will also be readily understood that the ultrasonic wave propagation time t ₀ is related to the temperature of the fluid 9 inside the tube 8 so that the temperature of the fluid can be measured by this device. .

  Next, in the phase difference measuring unit 116, the exclusive OR circuit 30 is exclusive of the upstream side received signal A and the downstream side received signal B binarized by the binarization circuits 16 and 17, respectively. The logical sum is taken, and the signal is converted into a DC signal by the low pass filter 33 via the sample and hold circuit 31. The sample and hold circuit 31 is configured to take an exclusive OR in the central portion of the received pulse in order to stably take the exclusive OR by the exclusive OR circuit 30. The circuit control signal S4 is generated based on the transmission trigger signal S1 in the timing circuit 3 like the switch control signal S2 so as to cut out only the vicinity of the center of the pulse of the output of the exclusive OR circuit 30. It is generated at a timing approximately corresponding to the vicinity of the center of the received signal.

  While the sample and hold circuit control signal S4 is at the high level, the sample and hold circuit 31 cuts out the output of the exclusive OR circuit 30, and when the sample and hold circuit control signal S4 is at the low level, the sample and hold circuit 31 The AND hold circuit 31 is in a high impedance state and holds the output of the low pass filter 33.

The output of the low pass filter 33 is obtained by removing the high frequency component of the output of the sample-and-hold circuit 31, i.e., the DC voltages V ₁ outputted by the low-pass filter 33, the upstream reception signals A and the downstream side reception Since this is a function of time t _Δ corresponding to the phase difference of the signal B, the value of the DC voltage V ₁ is A / D converted by the A / D conversion circuit 35 and input to the arithmetic circuit 36.

The flow velocity F _{1 of the} fluid 9 flowing in the pipe 8 is generally determined by using the ultrasonic propagation time t _{1 in the} direction along the flow, the ultrasonic propagation time t _{2 in the} direction against the flow, and the signal propagation time τ outside the fluid. ,

Can be obtained as Here, K is a constant. According to the method described so far, t ₁ −t ₂ can be measured as t _Δ and (t ₁ + t ₂ ) / 2 can be measured as t ₀ , and K and τ can be measured under the measurement conditions. it is possible to know the like, as a result, the flow rate F _l of the fluid 9 flowing in the pipe 8 can be accurately obtained.

The arithmetic circuit 36, K obtained in advance, by storing the value of tau, it can be determined the flow rate F _l.

(Second Embodiment)
Next, FIG. 4 is a diagram illustrating a second embodiment of the present invention. In the figure, the same components as those in the first embodiment are denoted by the same reference numerals, and detailed description thereof is omitted.

  In this embodiment, a propagation time measurement unit 119 is provided instead of the phase difference measurement unit 116 and the ultrasonic propagation time measurement unit 117 in the first embodiment.

  The propagation time measurement unit 119 includes latch circuits 51 and 52, switches 53 and 54, low-pass filters 55 and 56, and A / D conversion circuits 57 and 58.

  The operations of the latch circuits 51 and 52 and the switches 53 and 54 are the same as those of the latch circuits 21 and 22 and the switches 23 and 24 of the first embodiment, and constitute latch means and switch means, respectively. The low-pass filters 55 and 56 constitute direct-current signal conversion means for removing the high-frequency components of the respective signals from the latch circuits 51 and 52 that conduct the switches 53 and 54 and converting them into low-frequency signals (DC voltages). The A / D conversion circuits 57 and 58 perform A / D conversion on the DC voltages from the low-pass filters 55 and 56 and input them to the arithmetic circuit 36.

  The operation of the propagation time measuring unit 119 of the ultrasonic current meter configured as described above will be described with reference to the timing chart of signals in FIG.

  The latch circuits 51 and 52 operate in the same manner as in the previous embodiment, are set by the transmission trigger signal S1, and are reset by signals from the binarization circuits 16 and 17. That is, the output from the latch circuits 51 and 52 includes a signal that remains high until the binarization circuits 16 and 17 become high level from the start of transmission, in other words, until the reception signal A and the reception signal B appear. Appears (FIGS. 5 (f) and (g)).

  The switch control signals S2 and S3 are signals that are at a high level in the vicinity of the reception signal (FIGS. 5 (h) and (i)). The signals (FIGS. 5 (j) and (k)) are sent to the low-pass filters 55 and 56 and converted into DC signals (FIGS. 5 (l) and (m)). The value of the DC voltage is A / D converted by the A / D conversion circuit 53 and input to the arithmetic circuit 36.

Although not explicitly shown in the figure, the output of the latch circuit 51 and the output of the latch circuit 52 have a difference in pulse width depending on the velocity of the fluid 9 to be measured flowing inside the tube 8. DC voltage is converted into DC signals, ultrasonic propagation time t _u from the transmitting and receiving ultrasonic probe 7 of the respective downstream to the transmitting and receiving ultrasonic probe 6 on the upstream _side, the upstream side downstream from the transmitting and receiving ultrasonic probe 6 the ultrasonic wave propagation function of the time t _d to transmit and receive ultrasound probe 7 side. _Also , functions of the time t _g1u and t _g1d from the transmission trigger signal S1 to the time when the switches 53 and 54 are turned ON by the switch control signals S2 and S3, and the time t _g2u and t _g2d while the switch is ON. It also becomes. Specifically, the output signal V _u from the low-pass filter 55 and the output signal V _d from the low-pass filter 56 are expressed as follows, assuming that the power supply voltage level of the latch circuit 51 and the latch circuit 52 is V _cc and the constant is t _c .

となる。この式から、超音波伝搬時間ｔ_ｕ、ｔ_ｄは、

It becomes. From this equation, the ultrasonic wave propagation times t _u and t _d are

となる。

It becomes.

In this way, as in the first embodiment, the switch control signals S2 and S3 are set based on the digital values of V _u and V _d input to the arithmetic circuit 36 or so that V _u and V _d become V _cc / 2. When the timings t _g1u and t _g1d that become the high level are controlled, the ultrasonic propagation times t _u and t _d can be obtained from the values of the t _g1u and t _g1d . Ultrasonic propagation time _t u, _{t d as t u = t 2, t d} = t 1, by inputting the equation (3), can be obtained flow rate _{F 1.}

  In the second embodiment, since a high-speed counter or the like is not required for obtaining the propagation time difference, a low power consumption apparatus can be obtained.

  FIG. 6 is a modification of the second embodiment. In this example, the circuit is further simplified, and an analog switch 60 is provided in front of the amplifier circuit 14 of the binarization unit 112. The binarization unit 112 includes one amplification circuit 14 and one binarization circuit 16, and the propagation time measurement unit 120 includes one latch circuit 51.

  The switch 60 selects whether the reception signal captured by the binarization unit 112 is upstream or downstream, and the switch signal S5 from the timing circuit 3 outputs the trigger signal S1. The switch 60 is switched every time, or the switch 60 is switched every time two or more trigger signals S1 are sent. Further, in synchronization with the switching signal of the switch switching signal S5, when the upstream side is selected by the switch switching signal S5, only the switch control signal S2 has a high level in the vicinity of the received signal. When the downstream side is selected by the switch switching signal S5, only the switch control signal S3 becomes a high level signal in the vicinity of the received signal.

  When the upstream side is selected in the switch 60, the output from the low-pass filter 56 is not changed and maintains the value at the previous measurement, and when the downstream side is selected, the output from the low-pass filter 55 is changed. Without maintaining the value of the previous measurement.

  Even in this case, the flow velocity can be obtained by performing the calculation of the expression (3) in the calculation circuit 36.

Furthermore, in the above embodiments, the following modifications are possible.
A three-state buffer can be used as the switches 23, 24, 53, and 54 in each of the above embodiments, thereby enabling a circuit to be configured at low cost.
In the binarization circuits 16 and 17 in each of the above embodiments, when the fluid is a liquid, since the rising of the reception signal is steep, the reception signal can be directly binarized. In the case of gas, since the rising of the reception signal tends to be dull, an envelope detection circuit is provided in front of the binarization circuits 16 and 17, and when the output from the envelope detection circuit exceeds a predetermined value, It is also possible to start binarization.
· If the flow rate F _l is determined, the flow rate of the fluid 9 flowing in the flow rate F _l with a tube 8 can be accurately obtained.
The obtained flow velocity _Fl or flow velocity _Fl and flow rate can be displayed on the display unit 42.
-Furthermore, this anemometer can also be connected to a two-wire control loop.

According to the above embodiments, the following effects can be obtained.
Rather than converting the output from the latch circuit that represents the time from transmission to reception into a DC signal using a low-pass filter as in the past, the output from the latch circuit that represents reception near the received signal is converted to a DC signal using a low-pass filter. By doing so, it is possible to obtain the reception time, that is, the ultrasonic wave propagation time with higher accuracy than in the past.

In the case of the first embodiment, if t _g2 / T ₀ = _1/50 , the ultrasonic wave propagation time influences the flow velocity by the square from the equation (3), so the accuracy is 2 It is theoretically possible to obtain 100 times the accuracy, and it has been confirmed that the accuracy of 20 times or more can be obtained in the experiment.
- In the past, in order to decrease the accuracy by increasing the transmission repetition interval T _0, since it was not possible to increase the transmission repetition interval T _0, in the present invention, the transmission repetition interval T ₀ is no effect on the accuracy a, it is possible to increase the transmission repetition interval T _0, by reducing the number of occurrences of the transmission signal, it is possible to reduce the power consumption more.

1 is an overall block diagram of an ultrasonic current meter according to a first embodiment of the present invention. It is a detailed block diagram of FIG. It is a timing chart showing the measurement principle of the ultrasonic propagation time by 1st Embodiment of this invention. It is a detailed block diagram of the ultrasonic velocimeter by 2nd Embodiment of this invention. It is a timing chart showing the measurement principle by 2nd Embodiment of this invention. It is a detailed block diagram of the ultrasonic velocity meter by the modification of 2nd Embodiment of this invention. It is a timing chart showing the measurement principle of the conventional ultrasonic propagation time.

Explanation of symbols

2 Transmission signal generation circuit (transmission signal generation means)
3 Timing circuit (switch control signal generation means)
6, 7 Transmission / reception ultrasonic probe 21, 22, 51, 52 Latch circuit (latch means)
23, 24, 53, 54 Switch (switch means)
26, 55, 56 Low-pass filter (DC signal conversion means)
36 Arithmetic circuit (calculation means)

Claims (6)

A transmission signal generating means for generating a transmission signal;
At least two ultrasonic probes arranged on the upstream side and the downstream side of the fluid to be measured, the upstream ultrasonic probe receiving the transmission signal from the transmission signal generating means and transmitting the ultrasonic wave into the fluid to be measured The downstream ultrasonic probe receives the ultrasonic wave and outputs a reception signal (referred to as a downstream reception signal), and the downstream ultrasonic probe receives the transmission signal from the transmission signal generating means to be measured. An ultrasonic probe that transmits ultrasonic waves into the fluid, and an upstream ultrasonic probe receives the ultrasonic waves and outputs a reception signal (referred to as an upstream reception signal);
Latch means for generating a reception state change signal whose state changes at the timing of reception of at least one of the upstream reception signal and the downstream reception signal;
Switch means for conducting the reception state change signal in a predetermined period before and after the reception state change signal changes;
Switch control signal generating means for generating a switch control signal for switching conduction / non-conduction of the signal of the switch means;
DC signal converting means for converting a signal conducted in the switch means into a DC signal;
The voltage of the DC signal from the DC signal conversion unit, based on the time from the predetermined time period and the transmission switching means is conductive until the start of the predetermined period, determined between the time ultrasonic wave propagation ultrasound propagates, ultra A calculation means for calculating the flow velocity of the fluid to be measured using the sound wave propagation time;
An ultrasonic velocimeter characterized by comprising. The ultrasonic flowmeter according to claim 1, wherein the switch control signal generating means generates a switch control signal based on an ultrasonic propagation distance and a reference sound speed. The ultrasonic flowmeter according to claim 1, wherein the switch control signal generating unit generates the switch control signal so that the voltage of the DC signal from the DC signal converting unit is constant. The transmission signal is a burst signal;
Binarization means for binarizing the upstream reception signal and the downstream reception signal;
A phase difference measuring means for measuring a phase difference between the upstream side received signal and the downstream side received signal respectively binarized by the binarizing means;
Further comprising
The said calculating means calculates the flow velocity of the fluid to be measured based on the said ultrasonic propagation time and the phase difference signal from the said phase difference measuring means. Ultrasonic anemometer. The latch means generates a reception state change signal whose state changes at the reception timing of the upstream reception signal and the downstream reception signal,
The DC signal converting means converts the reception state change signal of each of the upstream reception signal and the downstream reception signal from the latch means conducted in the switch means into a DC signal,
The calculation means is configured to determine the ultrasonic propagation time from the ultrasonic probe on the upstream side to the ultrasonic probe on the downstream side and the ultrasonic wave on the downstream side based on the respective DC signals from the DC signal conversion means and the conduction timing of the switch means. The ultrasonic flowmeter according to any one of claims 1 to 3, wherein the ultrasonic wave propagation time from the probe to the ultrasonic probe upstream is calculated and the flow velocity of the fluid to be measured is calculated. Place ultrasonic probes upstream and downstream of the fluid to be measured,
The ultrasonic wave is propagated from the upstream ultrasonic probe to the downstream ultrasonic probe to obtain the reception signal (referred to as the downstream reception signal), and from the downstream ultrasonic probe to the upstream ultrasonic probe. Obtain the received signal (called upstream received signal) by propagating the ultrasonic wave,
Generating a reception state change signal whose state changes at the timing of reception of at least one of the upstream reception signal and the downstream reception signal;
Generate a switch control signal corresponding to a predetermined period before and after the state change signal at the time of reception changes,
On the basis of the switch control signals, and conducting the received time status change signal in the predetermined period before and after the reception time of the state change signal is changed, and converted into a DC signal,
The voltage of the DC signal, the predetermined period and based on the time from transmission until the start of the predetermined time period, between ultrasonic wave propagation time to the between the upstream side of the ultrasonic probe and the downstream side of the ultrasonic probe ultrasound propagates And calculating the flow velocity of the fluid to be measured based on the ultrasonic wave propagation time.

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