JP2000249582A - Ultrasonic flowmeter - Google Patents

Abstract

PROBLEM TO BE SOLVED: To improve measurement accuracy by eliminating the biasing of a measurement error. SOLUTION: An ultrasonic flowmeter is provided with a transmitter 1 for transmitting an ultrasonic signal, a drive circuit 9 for driving the transmitter 1, a receiver 2 for receiving an ultrasonic signal that is transmitted from the transmitter 1 and is propagated through fluid, a reception detection circuit 10 for receiving the output of the receiver 2 and detecting the ultrasonic signal, a timer 11 for measuring the propagation time of the ultrasonic signal, an operation part 12 for obtaining a flow rate from the output of the timer 11 by an operation, and a drive frequency modification part 13 for modifying the drive frequency of the drive circuit 9. As a result, the drive frequency modification part changes the drive frequency of the transmitter with time for transmission, thus preventing influence being given to a reception signal by reverberation and reflection waves for dispersing and averaging and hence eliminating the biasing of a measurement error.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an ultrasonic flow meter.

[0002]

2. Description of the Related Art Conventionally, as shown in FIG. 11, this type of ultrasonic flowmeter is arranged such that a transmitter 1 for transmitting ultrasonic waves disposed in a fluid, a receiver 2 for receiving ultrasonic waves, and a transmitter 1 for transmitting ultrasonic waves. , A reception detection circuit 4 that determines reception from an output signal of a receiver 2 that receives an ultrasonic wave transmitted through the fluid to be measured, and outputs the result to the transmission circuit 1, and outputs a measurement start signal to the transmission circuit 3. And a counter 6 for measuring the number of repetitions from transmission of ultrasonic waves to reception and return, and measurement of the time from the start of transmission of the first ultrasonic wave until the number of repetitions reaches a predetermined number. A timer 7 and a calculation unit 8 for calculating the flow rate from the value of the timer 7 were provided.

Next, the operation will be described. First, the control unit 5 outputs a measurement start signal to the transmission circuit 3. The transmission circuit 3 that has received the measurement start signal drives the transmitter 1, and the transmitter 1 transmits an ultrasonic wave. The receiver 2 receives the ultrasonic wave transmitted through the fluid to be measured, and outputs a reception signal to the reception detection circuit 4. The reception detection circuit 4 makes a reception determination, confirms reception of the ultrasonic wave, and outputs it to the transmission circuit 3. The transmission circuit 3 receiving the output of the reception detection circuit 4 drives the ultrasonic transducer 1 again. Counter 6
Counts the number of times from transmission of this ultrasonic wave to reception, and stops the timer 7 when this number reaches the set value of the counter 6 (N times). The timer 7 measures the time from the start of the measurement, and the value t1 of the timer 7 at this time is N which is the propagation time of the ultrasonic wave.
Double. Based on this value, the calculation unit 8 obtains the flow rate by the following calculation.

The propagation distance of the ultrasonic wave is L, the sectional area of the fluid to be measured is S, the sound velocity of the fluid to be measured at rest is C, the flow velocity of the fluid to be measured is V, and the propagation time from upstream to downstream is t.
(1) An equation for calculating the flow rate Q when the counter 7 is set is shown in (Equation 1).

Q = S [{L / (t / N)} − C] (Equation 1)

[0006]

However, in the above-mentioned conventional ultrasonic flowmeter, the transmission of the ultrasonic waves is performed at regular intervals, and the receiver 2 receives the ultrasonic waves reflected on the ultrasonic wave propagation path and the previous ultrasonic waves. A measurement error has occurred because a signal that overlaps with the reverberation of the ultrasonic wave transmitted during the period is received.

Further, the degree of this phenomenon varies depending on the propagation time, and the propagation time varies depending on the temperature and gas components, so that it is impossible to perform correction, and there has been a problem that this measurement error is reduced.

A method of adding a delay circuit for delaying the time until transmission and reducing the measurement error by temporally changing the delay amount has been considered. However, the delay time required for the operation is reduced. Since it could not be determined accurately, the measurement accuracy could not be significantly improved.

[0009]

According to the present invention, in order to solve the above-mentioned problems, a driving frequency changing section changes a driving frequency of a driving circuit with time.

[0010] According to the above invention, the drive frequency changing unit changes the drive frequency of the ultrasonic transducer temporally, so that reverberation,
The influence of the reflected wave on the received signal is not constant, and dispersion averaging improves the measurement accuracy without biasing the measurement error.

[0011]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS An ultrasonic flowmeter according to a first aspect of the present invention includes a transmitter for transmitting an ultrasonic signal, a driving circuit for driving the transmitter, and transmitting a fluid transmitted from the transmitter. A receiver that receives the output ultrasonic signal, a reception detection circuit that receives the output of the receiver and detects the ultrasonic signal, a timer that measures the propagation time of the ultrasonic signal, and calculates a flow rate from the output of the timer. And a drive frequency changing unit that changes the drive frequency of the drive circuit.

[0012] Since the drive frequency change unit changes the drive frequency of the transmitter over time and performs transmission, the effects of reverberation and reflected waves on the received signal are dispersion-averaged, thereby eliminating the bias of measurement errors. it can.

An ultrasonic flowmeter according to a second aspect of the present invention comprises:
A transmitter that transmits an ultrasonic signal, a driving circuit that drives the transmitter, a receiver that receives an ultrasonic signal transmitted from the transmitter and propagates a fluid, and an ultrasonic signal that receives an output of the receiver A feedback circuit that receives the output of the reception detection circuit, outputs the signal to the transmitter, and transmits the ultrasonic wave again, a counter that measures the number of feedbacks of the feedback circuit, and the transmitter. A timer for measuring the time from the start of ultrasonic transmission until the counter reaches a preset end frequency, a calculation unit for calculating the flow rate from the output signal of the timer by calculation, and a drive frequency for changing the drive frequency of the drive circuit A change unit.

Since the propagation of the ultrasonic wave is continuously performed a plurality of times and the total time is measured by the timer, the propagation time is 1
At the same time as the measurement resolution per time is improved, the drive frequency changing unit changes the drive frequency of the drive circuit for each feedback operation, so that a standing wave generated by repeated transmission on the ultrasonic wave propagation path does not occur, and reverberation does not occur. Since the influence of the reflected wave on the received signal is dispersion-averaged, it is possible to eliminate the bias of the measurement error.

In the ultrasonic flowmeter according to the third aspect of the present invention, since the number of times of feedback is an integral multiple of the number of patterns whose frequency is changed by the driving frequency changing unit, the error generated at each driving frequency is always calculated uniformly. Therefore, a stable measurement result can be obtained without changing the calculation result when the number of feedbacks is changed.

In the ultrasonic flowmeter according to the fourth aspect of the present invention, since the driving frequency changing unit changes the driving frequency while the driving circuit is driving the transmitter, the ultrasonic flowmeter is compared with the case where the transmitter is driven at a single frequency. There is no significant change in transmission / reception sensitivity, and there is no need to perform correction by changing the frequency. This simplifies the circuit configuration and does not cause an error caused by the correction.

In the ultrasonic flowmeter according to a fifth aspect of the present invention, the frequency changed by the drive frequency changing unit changes to the same frequency as the ultrasonic transmission / reception sensitivity between the transmitter and the receiver. Does not need to be corrected by the transmission output or the reception sensitivity, the circuit configuration is simplified, and no error occurs due to the correction.

In the ultrasonic flowmeter according to the sixth aspect of the present invention, since the frequency is changed irregularly, the regularity of the transmission signal can be completely eliminated.

[0019]

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

(Embodiment 1) FIG. 1 is a block diagram showing an ultrasonic flowmeter according to Embodiment 1 of the present invention, and FIG. 2 is a diagram showing a change in driving frequency of a transmitter of the ultrasonic flowmeter.

In FIG. 1, 1 is a transmitter for transmitting an ultrasonic signal, 2 is a receiver for receiving an ultrasonic signal transmitted from the transmitter 1 and having propagated a fluid, 9 is a driving circuit for driving the transmitter 1, 10 Is a reception detection circuit that receives the output of the receiver 2 and detects an ultrasonic signal, 11 is a timer that measures the propagation time of the ultrasonic signal, 12 is a calculation unit that calculates the flow rate from the output of the timer 11, and 13 is a drive circuit. Reference numeral 14 denotes a drive frequency change unit for changing the drive frequency, and reference numeral 14 denotes a control unit for outputting signals to the drive frequency change unit, the drive circuit 9 and the timer.

Next, the operation and operation will be described. First, the control unit 14 outputs a signal for determining the driving frequency to the driving frequency changing unit 13 and determines the frequency for driving the transmitter 1. Next, the control section 14 outputs a transmission start signal to the drive circuit 9 and at the same time, starts the time measurement of the timer 11.
When receiving the transmission start signal, the drive circuit 9 drives the transmitter 1 at the drive frequency determined by the drive frequency changing unit to transmit the ultrasonic waves. The transmitted ultrasonic wave propagates through the fluid, is received by the receiver 2 and is converted into an electric signal, and the reception detection circuit 1
Output to 0. The reception detection circuit 10 determines the reception timing of the reception signal and stops the timer 11.

The calculation unit 12 calculates the flow rate from the propagation time measured by the timer 11 by calculation. The same operation is repeatedly performed, but the control unit 14 changes the signal output to the drive frequency change unit 13 to change the drive frequency of the drive circuit 9 each time. FIG. 2 shows the variation of the driving frequency, the horizontal axis shows the number of measurements, and the vertical axis shows the driving frequency. As described above, since the drive frequency changing unit 13 changes the drive frequency of the transmitter 1 with time and performs transmission, the influence of reverberation and reflected waves on the received signal is dispersion-averaged, so that the bias of the measurement error can be eliminated. it can.

Although the driving frequency is changed irregularly in this example, it may be changed in a fixed pattern. In addition, the ultrasonic wave is transmitted only in one direction and the flow rate is calculated.
In the method of transmitting ultrasonic waves in both directions and calculating the flow rate from the reciprocal difference thereof, the method of changing the drive frequency is also effective.

(Embodiment 2) FIG. 3 is a block diagram showing an ultrasonic flowmeter according to Embodiment 2 of the present invention, and FIG. 4 is a diagram showing transmission / reception timing and transmission frequency of the ultrasonic flowmeter.

The second embodiment differs from the first embodiment in that the output of the reception detection circuit is fed back to the drive circuit 15 as a feedback signal and the number of times of feedback is measured by the counter 16. Drive frequency change unit 13
Is that the drive frequency of the drive circuit 15 is changed.

The components having the same reference numerals as those in the first embodiment have the same structure, and a description thereof will be omitted.

The operation and operation will be described. First, the control unit 14 outputs a transmission start signal to the drive circuit 15 and simultaneously starts the time measurement of the timer 11. Upon receiving the transmission start signal, the drive circuit 15 drives the transmitter 1 at a drive frequency determined by the initial value of the drive frequency changing unit to transmit an ultrasonic wave. The transmitted ultrasonic wave propagates through the fluid, is received by the receiver 2, is converted into an electric signal, and is output to the reception detection circuit 10. The reception detection circuit 10 determines the reception timing of the reception signal and outputs the reception detection signal to the drive circuit 15. The driving frequency changing unit 13 receives the output of the counter 16 and outputs a signal to the driving circuit to change the driving frequency. When receiving the reception detection signal, the drive circuit 15 drives the transmitter 1 again at the drive frequency determined by the drive frequency changing unit 13. FIG. 2 shows changes in the counter value and the drive frequency. The end feedback count is set in the counter 16 in advance, and when the count is reached, the output of the feedback signal to the drive circuit 15 is stopped, and at the same time, the timer 11 is stopped to end the time measurement. The calculation unit 12 determines the flow rate by calculation in consideration of the number of times of end feedback from the time measured by the timer 11. Since the driving frequency changing unit 13 changes the driving frequency of the transmitter 1 in accordance with the number of times of feedback and performs transmission, the effects of the reverberation of the ultrasonic wave propagation path and the reflected wave on the received signal are dispersion-averaged. The bias of the measurement error can be eliminated.

Further, the number of end feedback times is set to the number of frequency change patterns (for example, the driving frequency to be changed is 90 KHz, 10 KHz).
By setting the number of patterns to be an integer multiple of 0 KHz and 110 KHz, the errors occurring at the respective frequencies are uniformly used for the calculation, so that the errors are averaged and dispersed, so that the measurement errors are not biased.

(Embodiment 3) FIG. 5 is a block diagram showing an ultrasonic flowmeter according to a third embodiment of the present invention, FIG. 6 is a diagram showing driving waveforms of the ultrasonic flowmeter, and FIG. FIG. 6 is a diagram showing signal sensitivity between the transmitter and the receiver of FIG. The third embodiment is different from the first embodiment in that the driving frequency of the driving circuit 9 is not changed for each measurement, but the output of the driving circuit is changed to the driving frequency changing unit 1.
3 is that the frequency is changed during driving.

The components having the same reference numerals as in the first embodiment have the same structure, and the description is omitted.

The operation and operation will be described. The driving circuit 9 also inputs a signal for driving the transmitter 1 to the driving frequency changing unit 13 and changes the driving frequency for driving the transmitter 1 each time.

FIG. 6 shows how the drive frequency changes. As shown in FIG. 6, the drive frequency changes for each drive cycle. FIG. 7 shows the change range of the driving frequency and the sensitivity between the transmitter and the receiver. Since the drive frequency is set to be changed uniformly between f1 and f2 shown in FIG. 7, the difference between each measurement is smaller than the difference when driven at the single frequencies fa and fb. There is no significant change in the sensitivity, and there is no need to perform sensitivity correction by changing the frequency. This simplifies the circuit configuration and does not cause an error caused by the correction.

(Embodiment 4) FIG. 8 is a block diagram of an ultrasonic flowmeter according to a fourth embodiment of the present invention, and FIG. 9 is a diagram showing the driving frequency of the ultrasonic flowmeter and the sensitivity between the transmitter and the receiver.

The second embodiment is different from the first embodiment in that the driving frequency changing unit 13 includes a frequency setting unit A17, a frequency setting unit B18, a frequency setting unit C19, and a frequency setting unit D2.
0, and a frequency selection circuit 21 that selects the output of the frequency setting unit A17-D20 and outputs it to the driving circuit 9, and all of the driving frequencies set by the frequency setting unit A17-D20 are set between the transmitter and the receiver. That is, the sensitivities are almost equal.

The components having the same reference numerals as in the first embodiment have the same structure, and the description will be omitted.

FIG. 9 shows the relationship between the sensitivity between the transceiver and the drive frequency. As described above, the frequencies set by the frequency setting units A17 to D20 correspond to f1 to f4, and the sensitivity between the transmitter and the receiver does not change even when the drive frequency is changed. Alternatively, there is no need to make corrections based on the reception sensitivity, and the circuit configuration is simplified, and at the same time, no error occurs due to the corrections.

Here, the sensitivity of the frequency setting unit is set in advance assuming that the sensitivity between the transmitter and the receiver is known. However, the drive frequency is changed to perform transmission and reception, and the sensitivity between the transmitter and the receiver is checked. Almost the same driving frequency can be selected. In this case, if a rewritable unit such as a memory is used as the frequency setting unit, the optimum frequency can be written each time, so that the configuration of the present invention can be easily realized.

(Embodiment 5) FIG. 10 is a block diagram showing an ultrasonic flowmeter according to Embodiment 5 of the present invention.

The fifth embodiment differs from the first embodiment in that the input of the frequency changing unit is a random number table 21.

The components having the same reference numerals as in the first embodiment have the same structure, and a description thereof will be omitted.

Next, the operation and operation will be described. The random number table 21 receives the output of the control unit 14 and outputs an irregular frequency signal to the frequency change unit. Since the frequency is completely irregularly changed in this manner, the regularity of the transmission signal can be completely eliminated. Therefore, the errors are averaged and dispersed, so that the measurement errors are not biased.

[0043]

As is apparent from the above description, the following effects can be obtained according to the ultrasonic flowmeter of the present invention.

In the ultrasonic flowmeter according to the first aspect, since the drive frequency changing unit changes the drive frequency of the transmitter with time and performs transmission, the influence of reverberation and reflected waves on the received signal is dispersion-averaged. The bias of the measurement error is eliminated, and a high-accuracy ultrasonic flowmeter can be realized.

In the ultrasonic flowmeter according to the second aspect of the present invention, the ultrasonic wave is continuously transmitted a plurality of times and the total time is measured by a timer. Since the driving frequency changing unit changes the driving frequency of the driving circuit for each feedback operation, a standing wave generated by repeated transmission in the ultrasonic wave propagation path does not occur,
Since the effects of reverberation and reflected waves on the received signal are dispersion-averaged, measurement errors are not biased and a high-accuracy ultrasonic flowmeter can be realized.

Further, in the ultrasonic flowmeter according to the third aspect, since the number of times of feedback is an integral multiple of the number of patterns for which the driving frequency changing section changes the frequency, errors generated at each driving frequency can always be calculated uniformly. Since it is used, the calculation result does not fluctuate when the number of times of feedback is changed, a stable measurement result is obtained, and a high-accuracy ultrasonic flowmeter can be realized.

In the ultrasonic flowmeter according to the fourth aspect, since the driving frequency changing unit changes the driving frequency while the driving circuit is driving the transmitter, the ultrasonic flow meter is compared with a case where the transmitter is driven at a single frequency. There is no significant change in transmission / reception sensitivity, and there is no need to perform correction by changing the frequency. This simplifies the circuit configuration, and realizes a high-accuracy ultrasonic flowmeter with no error caused by correction.

Further, in the ultrasonic flowmeter according to the fifth aspect, the frequency changed by the drive frequency changing unit is changed to the same frequency as the ultrasonic transmission / reception sensitivity between the transmitter and the receiver. It is not necessary to correct the sensitivity by the transmission output or the reception sensitivity, and the circuit configuration is simplified, and at the same time, a high-accuracy ultrasonic flowmeter without errors caused by the correction can be realized.

In the ultrasonic flowmeter according to the sixth aspect, since the frequency is changed irregularly, the regularity of the transmission signal can be completely eliminated.

[Brief description of the drawings]

FIG. 1 is a block diagram of an ultrasonic flow meter according to a first embodiment of the present invention.

FIG. 2 is a diagram showing a change in driving frequency in a transmitter of the ultrasonic flowmeter.

FIG. 3 is a block diagram of an ultrasonic flowmeter according to a second embodiment of the present invention.

FIG. 4 is a diagram showing transmission and reception timings and transmission frequencies of the ultrasonic flowmeter.

FIG. 5 is a block diagram of an ultrasonic flow meter according to a third embodiment of the present invention.

FIG. 6 is a diagram showing a driving waveform of the ultrasonic flowmeter.

FIG. 7 is a signal sensitivity characteristic diagram between a transmitter and a receiver of the ultrasonic flowmeter.

FIG. 8 is a block diagram of an ultrasonic flowmeter according to a fourth embodiment of the present invention.

FIG. 9 is a diagram showing sensitivity characteristics between a driving frequency and a transmitter / receiver of the ultrasonic flowmeter.

FIG. 10 is a block diagram of an ultrasonic flowmeter according to a fifth embodiment of the present invention.

FIG. 11 is a block diagram of a conventional ultrasonic flowmeter.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Transmitter 2 Receiver 9 Drive circuit 10 Reception detection circuit 11 Timer 12 Operation part 13 Drive frequency change part 14 Control part 15 Drive circuit 16 Counter

 ────────────────────────────────────────────────── ─── Continued on the front page (72) Inventor Akihisa Adachi 1006 Kadoma Kadoma, Osaka Prefecture F-term (reference) 2F035 DA14 DA22 in Matsushita Electric Industrial Co., Ltd.

Claims (6)

[Claims] A transmitter for transmitting an ultrasonic signal; a driving circuit for driving the transmitter; a receiver for receiving an ultrasonic signal transmitted from the transmitter and propagating a fluid; and an output of the receiver. A reception detection circuit for detecting the ultrasonic signal, a timer for measuring the propagation time of the ultrasonic signal, an arithmetic unit for calculating the flow rate from the output of the timer, and a driving frequency of the driving circuit in time. An ultrasonic flowmeter having a drive frequency changing unit for changing. 2. A transmitter for transmitting an ultrasonic signal, a driving circuit for driving the transmitter, a receiver for receiving an ultrasonic signal transmitted from the transmitter and propagating a fluid, and an output of the receiver. A reception detection circuit that receives and detects an ultrasonic signal, a feedback circuit that receives the output of the reception detection circuit, outputs the output to the transmitter, and performs transmission of the ultrasonic wave again, and a counter that measures the number of feedbacks of the feedback circuit. A timer for measuring the time from the start of ultrasonic transmission by the transmitter to the end of the counter reaching a preset number of times, and a calculation unit for calculating the flow rate from the output of the timer, and An ultrasonic flowmeter having a drive frequency changing unit for changing a drive frequency, wherein the drive frequency of the drive circuit is changed for each feedback operation. 3. The ultrasonic flowmeter according to claim 2, wherein the feedback frequency is an integral multiple of the number of patterns for which the drive frequency changing section changes the frequency. 4. The ultrasonic flowmeter according to claim 1, wherein the driving frequency changing unit changes the driving frequency while the driving circuit drives the transmitter. 5. The ultrasonic flowmeter according to claim 1, wherein the frequency changed by the drive frequency changing unit is changed to a frequency at which the ultrasonic transmission / reception sensitivity between the transmitter and the receiver is substantially the same. 6. The ultrasonic flowmeter according to claim 1, wherein the frequency is changed irregularly.