JP2006038709A - Ultrasonic flowmeter - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To carry out a flow measurement on the basis of the following property of a reception wave frequency of each reception wave pulse being known beforehand, without waiting an elapse of time until the oscillation of an ultrasonic transducer on the reception side approaches to its antiresonant frequency. <P>SOLUTION: In an ultrasonic flowmeter 1 wherein a pair of ultrasonic transducers 2a, 2b are respectively disposed on upstream and downstream sides along a flow direction in a flow channel 3 in which fluid flows, only one specific pulse is selected from a reception wave pulse group output by the ultrasonic transducer on the reception side in a receiving means 5 by using a lock wave number counter 16, based on the emission timing of a transmission wave pulse group output by the ultrasonic transducer on the transmission side, whereby the clock frequency of the transmission wave pulse group is controlled. <P>COPYRIGHT: (C)2006,JPO&NCIPI

Description

The present invention relates to an ultrasonic flow meter, and more particularly to an ultrasonic flow meter that measures the flow velocity and flow rate of a fluid such as city gas, LPG, and water using ultrasonic waves.

As an example of a conventional ultrasonic flowmeter, one using a phase-locked loop (PLL) is known (see, for example, Patent Document 1). The measurement principle in this type of ultrasonic flowmeter is that a pair of ultrasonic transducers is provided on the upper side and lower side in the fluid flow direction of the flow path, and ultrasonic waves are predetermined between the pair of ultrasonic transducers by the PLL. The number of waves (hereinafter referred to as the lock wave number) is controlled so that the ultrasonic transducer on the upper side in the flow direction (hereinafter referred to as the forward ultrasonic transducer) and the ultrasonic transducer on the lower side in the flow direction (hereinafter referred to as the super Transmission wave frequency (hereinafter referred to as the forward transmission wave frequency) when the ultrasonic wave is emitted toward the ultrasonic transducer) and when the ultrasonic wave is emitted from the reverse ultrasonic transducer toward the forward ultrasonic transducer. Measure the transmission wave frequency (hereinafter referred to as the reverse transmission wave frequency) and measure the measured forward transmission frequency. Determine the average flow velocity of the fluid flowing through the flow path based on the fine reverse transmission wave frequencies, a method of obtaining the flow rate by multiplying the flow path cross-sectional area more average flow velocity.

Now, as shown in FIG. 2, the lock wave number is N, the forward transmission wave frequency is f _j , the reverse transmission wave frequency is f _g , and the distance between the forward ultrasonic transducer 2a and the reverse ultrasonic transducer 2b (hereinafter referred to as “f _g”) . , The propagation length) is L, and the flow velocity of the fluid is V. In the measurement when the ultrasonic wave is propagated from the forward ultrasonic transducer 2a to the reverse ultrasonic transducer 2b (hereinafter referred to as forward measurement), Expression (1) is obtained, and the following expression (2) is obtained by measurement when ultrasonic waves are propagated from the backward ultrasonic transducer 2b to the forward ultrasonic transducer 2a (hereinafter referred to as reverse direction measurement).

L / (C + V) = N / f j → Lf j / N = C + V ··· (1)
L / (C−V) = N / f _g → Lf _g / N = C−V (2)

The following formula (3) is obtained from the formula (1) -the formula (2), and the following formula (4) is obtained from the formula (1) + the formula (2).

V = (L / 2N) × (f _j −f _g ) (3)
C = (L / 2N) × (f _j + f _g ) (4)

Then, the flow rate Q is obtained by the following equation (5) using the cross-sectional area S of the flow path and the correction coefficient H.

Q = V · S · H (5)

Furthermore, when the fluid is air from the sound velocity C obtained by the equation (4), the temperature τ can be obtained by the simple equation C = 331.68 + 0.61τ, and therefore the correction for the temperature τ is possible.

In the conventional ultrasonic flowmeter, in order to measure an accurate ultrasonic propagation time, for example, as shown in FIG. 8, the number of drive pulses (in the transmission interval of FIG. 8A) from the ultrasonic transducer on the transmission side is measured. In the example, when the transmission wave pulse group 3) (see FIG. 8A) is fired, propagates through the medium and reaches the reception-side ultrasonic transducer as a reception wave pulse group, the reception wave in the reception-side ultrasonic transducer is received. With respect to the received wave conversion signal (see FIG. 8B) obtained by the mechanical-electrical conversion of the pulse group, the mask release signal (see FIG. 8C) is turned on after waiting for a preset mask time, Only a received wave conversion signal (see FIG. 8B) having a predetermined number of pulses (usually more than the number of drive pulses) is binarized to obtain a binarized received wave conversion signal (see FIG. 8D), This binarized received wave converted signal (Fig. See (d)) and the transmission wave clock phase comparison output signal of the (see FIG. 8 (a) refer) was obtained (FIG. 8 (e) refer). Then, after waiting for the elapsed time required for the mechanical vibration to rise due to the ultrasonic wave of the ultrasonic transducer on the receiving side, the frequency of the clock of the transmission wave pulse group at the point where the phase comparison output signal (see FIG. 8E) disappears. (Transmission wave frequency) was locked.

Instead of turning on the mask release signal after waiting for a preset mask time and using only the received wave conversion signal of a predetermined number of pulses as a phase comparison target, an ultrasonic wave is transmitted from the transmitting ultrasonic transducer. An ultrasonic flowmeter is known in which the zero cross point of the ultrasonic transducer on the reception side is detected while the gate time is sequentially updated to accurately measure the ultrasonic propagation time (see Patent Document 2).

Furthermore, the first ultrasonic propagation time is measured, a time α slightly shorter than the half-cycle of the ultrasonic wave is determined, and the second and subsequent times are the first after the previous ultrasonic propagation time −α has elapsed. There is also known an ultrasonic flowmeter that measures the ultrasonic propagation time up to the zero cross point by repeatedly measuring the ultrasonic propagation time a plurality of times (see Patent Document 3).
Japanese Patent Publication No. 3-39246 JP 2002-277301 A JP 10-73464 A

By the way, in the conventional ultrasonic flowmeter that performs control as shown in FIG. 8, the phase comparison output signal disappears after waiting for the elapsed time required for the mechanical vibration to rise due to the ultrasonic wave of the ultrasonic transducer on the receiving side. Because the transmission wave frequency of the clock of the transmission wave pulse group was locked at, the transmission wave frequency cannot be locked unless the elapsed time until the vibration of the ultrasonic transducer on the receiving side approaches the anti-resonance frequency cannot be locked. There was a problem that the wave frequency could not be quickly controlled. Further, it is necessary to perform phase comparison at least several times with one transmission of ultrasonic waves. If five phase comparisons are performed with one transmission of ultrasonic waves, 3000 transmissions are performed per second. When this is done, 5 × 3000 = 15000 times, and the number of phase comparisons is very large, which hinders low power consumption.

In addition, in the conventional ultrasonic flowmeter described in Patent Document 2, ultrasonic waves are transmitted from the ultrasonic transducer on the transmission side, and the zero cross point of the ultrasonic transducer on the reception side is detected while sequentially updating the gate time. Therefore, it is necessary to propagate ultrasonic waves several times before obtaining an accurate zero cross point, and there is a problem in that unnecessary ultrasonic waves are wasted repeatedly. In particular, a new gate time is set by calculation from the previous measurement time, which complicates calculation processing and makes circuit control difficult.

Furthermore, in the conventional ultrasonic flowmeter described in Patent Document 3, the first ultrasonic propagation time is used, and the second and subsequent times are times obtained by subtracting α from the first ultrasonic propagation time. Since it was necessary to set the mask time and repeat the time measurement, similarly to the ultrasonic flowmeter described in Patent Document 2, there was a problem that the arithmetic processing was complicated and circuit control was difficult.

Even if the vibration of the ultrasonic transducer on the reception side at the initial stage of reception deviates from the anti-resonance frequency that cannot be detected at the transmission wave frequency, the reception-side ultrasonic transducer for each received wave pulse in the reception-side ultrasonic transducer is known in advance. It is an object of the present invention to provide an ultrasonic flowmeter capable of quickly controlling the transmission wave frequency based on the follow-up property of the reception wave frequency.

Means for Solving the Problems and Effects of the Invention

The ultrasonic flowmeter according to claim 1 is provided with a pair of ultrasonic transducers on the upper side in the flow direction and the lower side in the flow direction in the flow path through which the fluid flows, and ultrasonic waves are predetermined between the pair of ultrasonic transducers. In an ultrasonic flowmeter that controls a transmission wave frequency so as to obtain a predetermined lock wave number and obtains a flow velocity and a flow rate based on the transmission wave frequency, based on the emission timing of a transmission wave pulse group from an ultrasonic transducer on the transmission side Thus, the transmission side frequency is controlled by using only one specific pulse of the reception wave pulse group in the ultrasonic transducer on the reception side. According to the ultrasonic flowmeter of the first aspect, the transmission wave frequency can be quickly controlled by comparing the phase with the clock of the transmission wave pulse group using only one specific pulse of the reception wave pulse group. And low power consumption can be expected.

The ultrasonic flowmeter according to claim 2 is the ultrasonic flowmeter according to claim 1, wherein the specific pulse of the received wave pulse group is binarized in one cycle of the clock of the transmitted wave pulse group. A frequency of the clock of the transmission wave pulse group by performing phase comparison between the binarization means and a specific pulse of the reception wave pulse group binarized by the binarization means and the clock of the transmission wave pulse group And a phase-locked loop for controlling. According to the ultrasonic flowmeter of claim 2, the specific one pulse of the reception wave pulse group is binarized in one cycle of the clock of the transmission wave pulse group, and the binarized specific pulse and the transmission wave are binarized. By controlling the transmission wave frequency by comparing the phase with the clock of the pulse group, only one specific pulse of the reception wave pulse group can be used to control the transmission wave frequency, and the transmission wave frequency can be controlled quickly. Can be done.

The ultrasonic flowmeter according to claim 3 is the ultrasonic flowmeter according to claim 1 or 2, wherein a lock wave number counter that counts a clock of the transmission wave pulse group, and a specific number of the reception wave pulse group are specified. Receiving means for setting a mask release time for extracting one pulse to one cycle of the clock of the transmission wave pulse group after the lock wave number counter has counted up to an arbitrary count value set in advance. According to the ultrasonic flow meter of claim 3, one period of the clock of the transmission wave pulse group after the lock wave number counter counts the lock wave number until the mask release time for taking out one specific pulse of the reception wave pulse group is counted. Thus, one specific pulse can be easily extracted. Further, since the clock of the transmission wave frequency is only counted up to a predetermined lock wave number, it is not necessary to perform calculations such as the previous measurement time, and calculation processing and circuit control are facilitated.

The ultrasonic flowmeter according to claim 4 is the ultrasonic flowmeter according to any one of claims 1 to 3, wherein the received wave conversion signal for one specific pulse of the received wave pulse group received by the receiving means. And amplifying means for amplifying the signal at an amplification factor corresponding to the frequency of the received wave pulse group based on the reception frequency-conversion voltage characteristic of the ultrasonic transducer on the reception side. According to the ultrasonic flowmeter of the fourth aspect, the amplification factor of the amplifying means is adjusted in accordance with the frequency of one specific pulse of the received wave pulse group, so that the vibration of the ultrasonic transducer on the reception side is reduced. There is no need to wait for the elapsed time to reach the anti-resonance frequency, and the transmission wave frequency can be quickly controlled.

The ultrasonic flowmeter according to claim 5 is provided with a pair of ultrasonic transducers on the upper side in the flow direction and the lower side in the flow direction in the flow path through which the fluid flows, and ultrasonic waves are predetermined between the pair of ultrasonic transducers. A transmission wave pulse group emitted from an ultrasonic transducer on a transmission side in an ultrasonic flowmeter that controls the frequency of a clock of a transmission wave pulse group so as to obtain a predetermined lock wave number and obtains a flow velocity and a flow rate based on the frequency And a reception-side ultrasonic wave for a specific pulse time of the received wave pulse group when the count value of the lock wave number counter reaches a predetermined arbitrary count value. Receiving means for receiving the received wave conversion signal from the transducer, and one specific pulse of the received wave pulse group received by the receiving means. Amplifying means for amplifying the received wave converted signal at an amplification factor corresponding to the frequency of the received wave pulse group based on the received frequency-converted voltage characteristic of the ultrasonic transducer on the receiving side, and the amplified by the amplifying means A binarizing means for binarizing a received wave conversion signal for one specific pulse of the received wave pulse group at a clock cycle of the transmitted wave pulse group, and binarization binarized by the binarizing means A phase-locked loop that controls the frequency of the clock of the transmission wave pulse group so that the phases of the post-reception wave conversion signal are compared with the phase of the clock of the transmission wave pulse group so that both phases coincide with each other. To do. According to the ultrasonic flowmeter of claim 5, the phase of the binarized received wave conversion signal is compared with the phase of the clock of the transmission wave pulse group using a phase-locked loop so that both phases coincide with each other. By controlling the wave frequency, the transmission wave frequency can be controlled easily and quickly, and low power consumption can be expected.

The ultrasonic flowmeter according to claim 6 is the ultrasonic flowmeter according to any one of claims 1 to 5, wherein one specific pulse of the received wave pulse group is a head pulse of the received wave pulse group. It is characterized by. According to the ultrasonic flowmeter of the sixth aspect, since one specific pulse of the reception wave pulse group is the head pulse of the reception wave pulse group, the transmission wave frequency can be controlled in the shortest time.

By using only one specific pulse of the received wave pulse group received by the ultrasonic transducer on the receiving side and comparing the phase with the clock of the transmitted wave pulse group, the transmission wave frequency can be controlled quickly.

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

FIG. 1 is a circuit block diagram showing a configuration of an ultrasonic flowmeter 1 according to Embodiment 1 of the present invention. The ultrasonic flowmeter 1 according to the first embodiment includes a flow path 3, an ultrasonic transducer (a forward ultrasonic transducer) 2 a installed on the upper side in the flow direction in the flow path 3, and a flow in the flow path 3. An ultrasonic transducer (reverse ultrasonic transducer) 2b installed on the lower side of the direction, a transmitting means 4, a receiving means 5 comprising an amplifying means 6 and a binarizing means 7, and a forward VCO (Voltage Controlled Oscillator) 8 , A forward PLL (Phase-Locked loop) composed of a forward LPF (low pass filter) 9 and a forward PD (Phase Detector) 10, and a reverse PLL composed of a reverse VCO 11, a reverse LPF 12 and a reverse PD 13; Control unit 18 comprising forward counter 14, reverse counter 15, lock wave number counter 16 and transmission control unit 17, phase comparison output width measuring means 19, and forward measurement And a reverse direction measurement and a switch SW1 for switching the, SW2, SW3, SW4, SW5 and SW6 Prefecture.

The forward ultrasonic transducer 2a and the reverse ultrasonic transducer 2b are ultrasonic transducers configured using piezoelectric elements, diaphragms, electrodes, and the like, and have a low Q value representing mechanical resonance sharpness. The transmission / reception switching between the forward ultrasonic transducer 2a and the reverse ultrasonic transducer 2b is performed by switches SW1, SW2, SW3, SW4, SW5 and SW6 constituted by analog switches or the like.

In the flow path 3, the forward ultrasonic transducer 2a and the reverse ultrasonic transducer 2b are arranged so as to face each other in the flow direction, and the shape and the cross-sectional area of the axial cross section are the same in the flow direction. When the measurement fluid is a gas, the axial cross-sectional shape of the flow path 3 may be any shape that forms a space closed by a wall portion. For example, any one of a circular shape, an elliptical shape, a square shape, a rectangular shape, etc. is adopted. May be.

The transmission means 4 includes a drive voltage circuit for generating a drive pulse for causing the forward ultrasonic transducer 2a and the reverse ultrasonic transducer 2b to emit a transmission wave pulse group.

The receiving means 5 includes an amplifying means 6 including a voltage detection circuit for detecting a reception wave conversion voltage (reception wave conversion signal) of the forward ultrasonic transducer 2a and the reverse ultrasonic transducer 2b, and a reception wave pulse group. And binarizing means 7 for binarizing a specific pulse at a cycle of a transmission wave clock (clock of a transmission wave pulse group).

The forward direction VCO 8 is a voltage control oscillator that outputs a forward direction clock CLK _j having a forward direction transmission wave frequency f _j corresponding to an input voltage signal, and has an input terminal connected to an output terminal of the forward direction LPF 9 and outputs The terminal is connected to one input terminal of the forward direction PD 10. Forward VCO8 receives the voltage signal from the forward LPF 9, if there is a phase shift between the received wave converted signal and the forward clock CLK _j, forward such that the phase shift becomes zero clock CLK _j the transmission wave frequency f _j and changes, carried forward ultrasound transducer 2a, a lock wavenumber N become so that the phase adjustment wavenumber predetermined between backward ultrasonic transducer 2b.

The forward LPF 9 is a filter that receives a phase comparison output signal (see FIG. 4 (e)), averages the phase comparison output signal (see FIG. 4 (e)), and outputs the averaged output signal. The output terminal is connected to the input terminal of the forward VCO 8.

The forward direction PD 10 compares the phases of two input signals and outputs a signal proportional to the phase difference. One input terminal is directed to one contact terminal of the switch SW3 and the other input terminal is forwarded. The output terminal of the direction VCO 8 is connected, and the output terminal is connected to the input terminal of the forward direction LPF 9. The forward direction PD 10 compares the phase of the forward direction clock CLK _j (see FIG. 4A) and the binarized received wave converted signal (see FIG. 4D) and is proportional to the phase difference. A comparison output signal (see FIG. 4E) is output.

The reverse direction VCO 11 is a voltage control oscillator that outputs a reverse direction clock CLK _g having a reverse direction transmission wave frequency f _g corresponding to an input voltage signal, and has an input terminal connected to an output terminal of the reverse direction LPF 12 and outputs The terminal is connected to one input terminal of the reverse direction PD 13. Reverse VCO11 receives the voltage signal from the reverse direction LPF 12, if there is a phase shift between the received wave converted signal and the reverse clock CLK _g, backward so that the phase shift becomes zero clock CLK _g change the transmission wave frequency f _g, backward ultrasonic transducer 2b, and phase adjustment so that the wave number between the forward ultrasound transducer 2a is predetermined lock wavenumber N performed.

The reverse LPF 12 is a filter that receives the phase comparison output signal (see FIG. 4E), averages the phase comparison output signal (see FIG. 4E), and outputs the average. The output terminal is connected to the input terminal of the reverse direction VCO 11.

The reverse direction PD 13 compares the phases of two input signals and outputs a signal proportional to the phase difference. One input terminal is one contact terminal of the switch SW3 and the other input terminal is reversed. The output terminal of the direction VCO 11 is connected, and the output terminal is connected to the input terminal of the reverse direction LPF 12. The reverse direction PD 13 compares the phases of the reverse direction clock CLK _g (see FIG. 4A) and the binarized received wave converted signal (see FIG. 4D) and is proportional to the phase difference. A comparison output signal (see FIG. 4E) is output.

The forward counter 14 is connected to the output terminal of the forward VCO 8 and serves to count the forward clock CLK _j (see FIG. 4A).

The reverse counter 15 is connected to the output terminal of the reverse VCO 11 and serves to count the reverse clock CLK _g (see FIG. 4A).

The lock wave number counter 16 has an input terminal connected to the switching terminal of the switch SW6 and an output terminal connected to the control terminal of the receiving means 5, and in order to input only one specific pulse of the received wave pulse group, Each time the direction clock CLK _j or the backward clock CLK _g (see FIG. 4A) is counted by the number of lock waves N, the mask cancellation signal (see FIG. 4C) of the received wave pulse group is turned on for a certain period. To.

The transmission control unit 17 has one input terminal connected to the output terminal of the forward direction VCO 8, the other input terminal connected to the output terminal of the reverse direction VCO 11, and the output terminal connected to the transmission means 4. Controls the output of drive pulses.

The phase comparison output width measuring means 19 is a means for measuring the width of the phase comparison output signal (see FIG. 4E), the input terminal is connected to the switching terminal of the switch SW4, and the output terminal is the switching terminal of the switch SW5. It is connected to the. The phase comparison output width measuring means 19 inputs the phase comparison output signal (see FIG. 4E) output from the forward direction PD 10 via the switch SW4, measures the phase comparison output width, and determines the phase comparison output width. Large, medium, and small are output to the forward LPF 9 via the switch SW5.

The switch SW1 has a switching terminal connected to the transmission means 4, one contact terminal connected to the forward ultrasonic transducer 2a, and the other contact terminal connected to the reverse ultrasonic transducer 2b. The switch SW1 connects the transmission means 4 to the forward transducer 2a during forward measurement, and connects the transmission means 4 to the reverse transducer 2b during reverse measurement.

The switch SW2 has a switching terminal connected to the amplifying means 6 of the receiving means 5, one contact terminal connected to the forward ultrasonic transducer 2a, and the other contact terminal connected to the reverse ultrasonic transducer 2b. The switch SW2 connects the receiving means 5 to the backward transducer 2b during forward measurement, and connects the receiving means 5 to the forward transducer 2a during backward measurement.

The switch SW3 has a switching terminal connected to the binarizing means 7 of the receiving means 5, one contact terminal connected to the other input terminal of the forward direction PD10, and the other contact terminal connected to the other input terminal of the reverse direction PD13. Has been. The switch SW3 connects the binarizing means 7 to the forward direction PD10 when measuring the forward direction, and connects the binarizing means 7 to the reverse direction PD13 when measuring the reverse direction.

The switch SW4 has a switching terminal connected to the input terminal of the phase comparison output width measuring means 19, one contact terminal connected to the output terminal of the forward direction PD10, and the other contact terminal connected to the output terminal of the reverse direction PD13. The switch SW4 connects the forward direction PD10 to the phase comparison output width measurement unit 19 during forward direction measurement, and connects the reverse direction PD13 to the phase comparison output width measurement unit 19 during backward measurement.

The switch SW5 has a switching terminal connected to the output terminal of the phase comparison output width measuring means 19, one contact terminal connected to the control terminal of the forward LPF 9, and the other contact terminal connected to the control terminal of the reverse LPF 12. The switch SW5 connects the phase comparison output width measurement means 19 to the forward LPF 9 during forward measurement, and connects the phase comparison output width measurement means 19 to the reverse LPF 12 during reverse measurement.

The switch SW6 has a switching terminal connected to the input terminal of the lock wave number counter 16, one contact terminal connected to the output terminal of the forward direction VCO 8, and the other contact terminal connected to the output terminal of the reverse direction VCO 11. The switch SW6 connects the forward direction VCO 8 to the lock wave number counter 16 during forward direction measurement, and connects the reverse direction VCO 11 to the lock wave number counter 16 during reverse direction measurement.

FIG. 3 is a diagram showing the forward LPF 9 and the backward LPF 12 in more detail. The forward LPF 9 and the reverse LPF 12 are selectively connected in parallel with an LPF 111 having a small time constant, an LPF 112 having a medium time constant, and an LPF 113 having a large time constant sandwiched between the switch SW11 and the switch SW12. ing. The switch SW11 and the switch SW12 selectively connect any one of the LPF 111, the LPF 112, and the LPF 113 according to the phase comparison output width from the phase comparison output width measuring unit 19 according to the large, medium, and small. A high-speed PLL is required in order to perform phase synchronization by several phase comparisons and at high speed. Therefore, if the phase comparison output width is large, an LPF 111 with a small time constant is connected, and if the phase comparison output width is medium, an LPF 112 with a medium time constant is connected, and if the phase comparison output width is small, the time is The LPF 113 having a large constant is connected to advance the phase synchronization time. As a result, the number of times and the time that the circuit operates are shortened, so that the current saving of the ultrasonic flowmeter can be expected.

FIG. 4 is a timing chart when the phase comparison is performed between the transmission wave pulse group (clock) and the first pulse p ₁ of the reception wave pulse group in the ultrasonic flowmeter 1 according to the first embodiment.

FIG. 5 is an enlarged view for explaining the first pulse p _{1 to} the fifth pulse p ₅ of the received wave pulse group in the ultrasonic flowmeter 1 according to the first embodiment.

FIG. 6 shows the relationship between the reception wave frequency f ₁ of the first pulse p ₁ of the reception wave pulse group, the reception wave frequency f ₂ of the second pulse p ₂ , and the third pulse p ₃ with respect to the transmission wave frequency fin of the transmission wave pulse group. is a diagram illustrating the following capability of the received wave frequency f _3. The phase comparison output width measuring means 19 detects the output widths of the phase comparison output signals (see FIG. 4E) in the forward direction PD10 and the reverse direction PD13, that is, the phase difference between the transmission wave frequency fin and the reception wave frequency fout. Then, a transmission wave frequency fin is obtained such that the detected phase difference becomes zero. Therefore, the followability of the reception wave frequency fout with respect to the transmission wave frequency fin is known in advance as shown in FIG. Specifically, the resonance frequency f0 of the ultrasonic transducer depends on the amount of deviation from f0 based on the relationship between the transmission wave frequency fin, which is a forced vibration frequency input to the ultrasonic transducer, and the pulse response due to the natural vibration of the ultrasonic transducer. Therefore, the deviation of the reception frequency at the time of reception increases, and the deviation decreases as the deviation from the resonance frequency f0 decreases. This shift in the reception frequency is largely related to the pulse response due to the natural vibration of the ultrasonic transducer and the damping characteristic due to the damper effect coming from the structure and vibration mode. When transmitting and receiving ultrasonic waves from an ultrasonic transducer, the influence of the frequency (in this case: fin) due to forced vibration from the outside is that the leading rising pulse at the beginning of reception has vibration mode characteristics unique to the ultrasonic transducer. Therefore, the frequency value does not coincide with the forced vibration frequency (fin), and the influence of the natural vibration frequency becomes large. As the received pulse moves backward to the first pulse p ₁ , second pulse p ₂ , and third pulse p ₃ , forced vibration gradually appears due to the influence of the ultrasonic transducer natural vibration. However, in this case, the more the influence of forced vibration shifts backward, the closer the reception frequency accuracy is to the ideal value, but using the fact that the reception characteristics are reproducible as shown in FIG. Phase synchronization is performed only with the leading rising pulse at the beginning of reception. The reception wave frequency f ₁ , reception wave frequency f ₂ , and reception wave frequency f ₃ change linearly with respect to the transmission wave frequency fin, but between the forward ultrasonic transducer 2a and the reverse ultrasonic transducer 2b. Since it takes time to mechanically rise the vibration, it is not the transmission wave frequency fin itself indicated by the ideal line.

FIG. 7 is a diagram showing the reception peak output voltage Vpp (fa is an anti-resonance frequency) of the forward ultrasonic transducer 2a and the reverse ultrasonic transducer 2b with respect to the transmission wave frequency fin. As can be seen from this figure, the reception peak output voltage Vpp has a characteristic that peaks at the anti-resonance frequency fa, and therefore the transmission wave frequency fin.
The reception peak output voltage Vpp is amplified by the amplifying means 6 in accordance with the deviation from the anti-resonance frequency fa. In this way, the phase can be matched using any one pulse of the received wave pulse group without waiting for the elapsed time required for the mechanical vibration to rise due to the ultrasonic wave of the ultrasonic transducer on the receiving side. be able to.

Next, the operation of the ultrasonic flowmeter 1 according to the first embodiment configured as described above will be described.

In the ultrasonic flowmeter 1 according to the first embodiment, the forward direction measurement is first performed, and then the backward direction measurement is performed.

(1) Forward measurement

First, all the switches SW1, SW2, SW3, SW4, SW5 and SW6 are switched to the forward direction measurement side.

Next, in the control unit 18, the transmission control unit 17 applies a drive pulse group for emitting a transmission wave pulse group to the forward ultrasonic transducer 2 a by the transmission unit 4. Further, the control unit 18 causes the transmission wave pulse group to be emitted, and at the same time, causes the forward counter 14 to start counting the forward clock CLK _j from the forward VCO 8. As described above, the control unit 18 sets the firing timing of the drive pulse group (for example, synchronization of application of the drive pulse group and the forward clock CLK _j ) in order to cause the forward counter 14 to perform forward measurement. I am trying. Further, the control unit 18 inputs the forward clock CLK _j from the forward VCO 8 to the lock wave number counter 16 via the switch SW6 and starts counting.

When the transmission wave pulse group emitted from the forward ultrasonic transducer 2a propagates through the medium and reaches the reverse ultrasonic transducer 2b as the reception wave pulse group, the reception wave pulse group is mechanically transmitted by the reverse ultrasonic transducer 2b. -Electrically converted and input to the receiving means 5 via the switch SW2 as a received wave converted signal (see FIG. 4B). However, before the count value of the lock wave number counter 16 reaches the lock wave number N, the mask release signal (see FIG. 4C) from the lock wave number counter 16 is off, and the received wave conversion signal (FIG. 4). (B) is masked by the receiving means 5.

When the count value of the lock wave number counter 16 reaches the lock wave number N, the reception means 5 turns on the mask cancellation signal (see FIG. 4C) for a certain period of the forward clock CLK _j , and the received wave converted signal by a first pulse _{p 1} in (see FIG. 4 (b)) is input.

Therefore, amplifier means 6 amplifies only the first pulse p ₁ of the received wave converted signal (see Figure 4 (b)). As shown in FIG. 7, the amplification factor of the amplification means 6 at this time is set so as to increase as the reception peak output voltage Vpp with respect to the transmission wave frequency fin is lower. In other words, the reception peak output voltage Vpp is amplified so as to be leveled.

Subsequently, the binarizing means 7 binarizes the first pulse p ₁ of the received wave converted signal (see FIG. 4B) amplified by the amplifying means 6 at the period of the forward clock CLK _j. And then output as a received wave converted signal (see FIG. 4D).

The forward PD 10 receives the binarized received wave converted signal (see FIG. 4D) of the first pulse p ₁ input from the receiving means 5 via the switch SW3, and the forward clock CLK from the forward VCO 8. Phase comparison with _j is performed, and a phase comparison output signal (see FIG. 4E) corresponding to the phase difference is output.

The phase comparison output width measuring means 19 inputs the phase comparison output signal (see FIG. 4E) output from the forward direction PD 10 via the switch SW4, measures the phase comparison output width, and calculates the phase comparison output width. Are output to the forward LPF 9 via the switch SW5.

The forward LPF 9 receives the large, medium, and small phase comparison output widths from the phase comparison output width measuring means 19 via the switch SW5, so that the forward PLL according to the large, medium, and small phase comparison output widths. Change the loop characteristics. Specifically, as illustrated in FIG. 3, if the phase comparison output width is small, the switches SW11 and SW12 are switched so that the LPF 113 having a large time constant is connected. If the phase comparison output width is medium, the time constant is The switches SW11 and SW12 are switched so that the middle LPF 112 is connected. If the phase comparison output width is large, the switches SW11 and SW12 are switched so that the LPF 111 having a small time constant is connected.

The forward direction VCO 8 receives the voltage signal from the forward direction LPF 9, and there is a phase shift between the received wave converted signal after binarization in the forward direction PD 10 (see FIG. 4D) and the forward direction clock CLK _j. If, locks the phase shift changes the forward transmission wave frequency f _j of the forward clock CLK _j to be zero, the forward ultrasound transducer 2a, the wave number between the inverted ultrasonic transducer 2b predetermined Phase adjustment is performed so that the wave number is N. In other words, the forward direction VCO 8 uses the forward direction transmission wave frequency f _j necessary for phase adjustment of the phase shift compared with the received wave converted signal after binarization (see FIG. 4D) by the forward direction PD 10. The forward clock CLK _j adjusted in the above is output.

(2) Reverse direction measurement

When the forward direction measurement is completed, all the switches SW1, SW2, SW3, SW4, SW5 and SW6 are switched to the reverse direction measurement side.

Next, in the control unit 18, the transmission control unit 17 applies a drive pulse group for emitting the transmission wave pulse group to the backward ultrasonic transducer 2 b by the transmission unit 4. Further, the control unit 18 causes the transmission wave pulse group to be emitted, and at the same time, causes the backward counter 15 to start counting the backward clock CLK _g from the backward VCO 11. Thus, the control unit 18, in order to perform the reverse direction measurement in the opposite direction counter 15, the drive pulse group of firing timing (e.g., to synchronize the application of the drive pulse group and a reverse clock CLK _g) I am trying. Further, the control unit 18, the reverse clock CLK _g from reverse VCO11 to lock wavenumber counter 16 starts counting entered via the switch SW6.

When the transmitted wave pulse group emitted from the backward ultrasonic transducer 2b propagates through the medium and reaches the forward ultrasonic transducer 2a as the received wave pulse group, the received wave pulse group is mechanically transmitted by the forward ultrasonic transducer 2a. It is electrically converted and input to the receiving means 5 via the switch SW2 as a received wave conversion signal (see FIG. 4B). However, before the count value of the lock wave number counter 16 reaches the lock wave number N, the mask release signal (see FIG. 4C) from the lock wave number counter 16 is off, and the received wave conversion signal (FIG. 4). (B) is masked by the receiving means 5.

When the count value of the lock wavenumber counter 16 becomes locked wavenumber N, the receiving unit 5, a mask release signal by a certain period of time the reverse clock CLK _g (see FIG. 4 (c)) is turned on, the reception wave converted signal by a first pulse _{p 1} in (see FIG. 4 (b)) is input.

Therefore, amplifier means 6 amplifies only the first pulse p ₁ of the received wave converted signal (see Figure 4 (b)). As shown in FIG. 7, the amplification factor of the amplification means 6 at this time is set so as to increase as the reception peak output voltage Vpp with respect to the transmission wave frequency fin is lower. In other words, the reception peak output voltage Vpp is amplified so as to be leveled.

Subsequently, the binarizing means 7 binarizes the first pulse p ₁ of the received wave converted signal (see FIG. 4B) amplified by the amplifying means 6 at the cycle of the backward clock CLK _g. And then output as a received wave converted signal (see FIG. 4D).

The reverse direction PD ₁₃ receives the binarized received wave converted signal (see FIG. 4D) of the first pulse p ₁ input from the receiving means 5 via the switch SW 3 and the reverse direction clock CLK from the reverse direction VCO 11. A phase comparison output signal (see FIG. 4E) corresponding to the phase difference is output by comparing the phase with _g .

The phase comparison output width measuring means 19 inputs the phase comparison output signal (see FIG. 4E) output from the reverse direction PD 13 via the switch SW4, measures the phase comparison output width, and determines the phase comparison output width. Large, medium and small are output to the reverse LPF 12 via the switch SW5.

When the reverse direction LPF 12 receives a large, medium, or small phase comparison output width from the phase comparison output width measuring means 19 via the switch SW5, the reverse direction PLL outputs the reverse PLL according to the large, medium, or small phase comparison output width. Change the loop characteristics. Specifically, as illustrated in FIG. 3, if the phase comparison output width is small, the switches SW11 and SW12 are switched so that the LPF 113 having a large time constant is connected. If the phase comparison output width is medium, the time constant is The switches SW11 and SW12 are switched so that the middle LPF 112 is connected. If the phase comparison output width is large, the switches SW11 and SW12 are switched so that the LPF 111 having a small time constant is connected.

The reverse direction VCO 11 receives the voltage signal from the reverse direction LPF 12, and there is a phase shift between the received wave converted signal (see FIG. 4D) after binarization in the reverse direction PD 13 and the reverse direction clock CLK _g. If, locks the phase shift changes the reverse transmission wave frequency f _g of the reverse clock CLK _g to be zero, reverse ultrasonic transducer 2b, the wave number between the forward ultrasound transducer 2a predetermined Phase adjustment is performed so that the wave number is N. In other words, the reverse direction VCO 11 has the reverse direction transmission wave frequency f _g necessary for adjusting the phase of the phase shift compared with the received wave converted signal after binarization (see FIG. 4D) by the reverse direction PD 13. outputs a reverse clock CLK _g adjusted to.

Thereafter, the control unit 18 counts the count value of the forward counter 14 counted by the forward measurement, that is, the forward transmission wave frequency f _j, and the inverse counted by the backward measurement for a certain time, for example, 1 second. The count value of the direction counter 15, that is, the reverse direction transmission wave frequency _fg is obtained. Then, the control unit 18 calculates the flow velocity V based on the above-described formula (4), multiplies the flow velocity V by the cross-sectional area S of the flow path 3, and responds to the temperature / pressure, the measurement fluid, and the obtained flow velocity V. The flow rate Q is obtained by multiplying the correction coefficient H.

Incidentally, in the description of the first embodiment, the received wave converted signal (see FIG. 4 (b)) the first pulse p by the _first mask release signal (see FIG. 4 (c) refer) turned on to binarization after receiving the The wave conversion signal (see FIG. 4D) is generated, but the count value for turning on the mask release signal is changed by the lock wave number counter 16, and the mask release signal (see FIG. 4C) is turned on. By changing the time to perform the binarized reception wave conversion signal (FIG. 4 (FIG. 4 (b)), from any pulse after the second pulse p ₂ (see FIG. 5) of the reception wave conversion signal (see FIG. 4 (b)). d) See) may be generated. This is because, assuming a sudden flow rate change or temperature change, the count value of the lock wave number counter 16 is (N-1) or (N-2), and the received wave may reach the reception-side ultrasonic transducer. Because there is. In this case, since the pulse at the time when the vibration of the ultrasonic transducer on the receiving side approaches the anti-resonance frequency fa, a more stable received wave conversion signal after binarization can be obtained, but only that amount has elapsed. Since time is required, it cannot be denied that it takes time to control the transmission wave frequency.

In the first embodiment, the forward direction measurement is first performed and then the backward direction measurement is performed. However, the measurement order may be reversed.

Further, in the first embodiment, the explanation has been made so that the rectangular-wave drive pulse group is applied to the ultrasonic transducer on the transmission side, but it may be driven by a sine wave, step drive, or burst drive. . It is also conceivable that the time to a predetermined reception point (eg, zero cross point) is obtained and used together with the forward clock CLK _j or the backward clock CLK _g for measuring the propagation time.

As mentioned above, although the Example of this invention was described, this is only an illustration, this invention is not limited to this, Based on the knowledge of those skilled in the art, unless it deviates from the meaning of a claim Various changes are possible.

1 is a block diagram of an ultrasonic flow meter according to Embodiment 1 of the present invention. The figure explaining the measurement principle of the flow velocity in the ultrasonic flowmeter of this invention. The internal block diagram of LPF in FIG. 4 is a timing chart for explaining phase comparison in the ultrasonic flowmeter according to the first embodiment. The enlarged view of the received wave conversion signal in FIG. The figure explaining the followable | trackability of the received wave frequency for every received wave pulse. The graph which shows the reception peak output voltage with respect to a transmission wave frequency. The timing chart explaining the phase comparison in the conventional ultrasonic flowmeter.

Explanation of symbols

1 Ultrasonic Flowmeter 2a Forward Ultrasonic Transducer (Ultrasonic Transducer)
2b Reversed Ultrasonic Transducer (Ultrasonic Transducer)
3 Flow path 4 Transmitting means 5 Receiving means 6 Amplifying means 7 Binarizing means 8 Forward VCO
9 Forward LPF
10 Forward PD
11 Reverse VCO
12 Reverse LPF
13 Reverse direction PD
14 Forward counter 15 Reverse counter 16 Lock wave number counter 17 Transmission control unit 18 Control unit 19 Phase comparison output width measuring means 111 to 113 LPF
SW1, SW2, SW3, SW4, SW5, SW6, SW11, S12 switch

Claims (6)

A pair of ultrasonic transducers is provided on the upper side and the lower side in the flow direction in the flow path through which the fluid flows, and the transmission wave pulse is set so that the ultrasonic wave has a predetermined lock wave number between the pair of ultrasonic transducers. In an ultrasonic flowmeter that controls the frequency of a group clock and obtains the flow velocity and flow rate based on the frequency,
Based on the emission timing of the transmission wave pulse group from the transmission-side ultrasonic transducer, the reception-side ultrasonic transducer controls the frequency of the transmission wave pulse group clock using only one specific pulse of the reception wave pulse group. An ultrasonic flowmeter characterized by: Binarizing means for binarizing a specific pulse of the received wave pulse group in one cycle of the clock of the transmitted wave pulse group, and specifying the received wave pulse group binarized by the binarizing means 2. The ultrasonic flow rate according to claim 1, further comprising: a phase-locked loop that controls a frequency of the clock of the transmission wave pulse group by performing phase comparison between one pulse of the transmission wave and the clock of the transmission wave pulse group. Total. After the lock wave number counter that counts the clock of the transmission wave pulse group and the mask release time for taking out one specific pulse of the reception wave pulse group, the lock wave number counter counts to an arbitrary count value that is predetermined, The ultrasonic flowmeter according to claim 1, further comprising a receiving unit configured to make one cycle of the clock of the transmission wave pulse group. The received wave converted signal for one specific pulse of the received wave pulse group received by the receiving means is responsive to the frequency of the received wave pulse group based on the received frequency-converted voltage characteristics of the ultrasonic transducer on the receiving side. 4. The ultrasonic flowmeter according to claim 1, further comprising an amplifying unit that amplifies at an amplification factor. A pair of ultrasonic transducers is provided on the upper side and the lower side in the flow direction in the flow path through which the fluid flows, and the transmission wave pulse is set so that the ultrasonic wave has a predetermined lock wave number between the pair of ultrasonic transducers. In an ultrasonic flowmeter that controls the frequency of a group clock and obtains the flow velocity and flow rate based on the frequency,
A lock wave number counter that counts a clock of a transmission wave pulse group emitted from an ultrasonic transducer on the transmission side;
When the count value of the lock wave number counter reaches a predetermined arbitrary count value, the received wave conversion signal from the ultrasonic transducer on the receiving side is received for a time corresponding to one specific pulse of the received wave pulse group. Receiving means;
A received wave converted signal for one specific pulse of the received wave pulse group received by the receiving means is converted to a frequency of the received wave pulse group based on a received frequency-converted voltage characteristic of the ultrasonic transducer on the receiving side. Amplifying means for amplifying at a corresponding amplification rate;
Binarization means for binarizing a received wave converted signal for one specific pulse of the received wave pulse group amplified by the amplifying means at a clock cycle of the transmitted wave pulse group;
The phase of the received wave conversion signal after binarization binarized by the binarization means is compared with the phase of the clock of the transmission wave pulse group so that both phases coincide with each other. An ultrasonic flowmeter comprising a phase-locked loop for controlling a frequency. 6. The ultrasonic flowmeter according to claim 1, wherein one specific pulse of the received wave pulse group is a head pulse of the received wave pulse group.

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