JP4650574B2 - Ultrasonic flow meter - Google Patents

Description

  The present invention relates to an ultrasonic flowmeter.

  Conventionally, as shown in FIG. 11, this type of ultrasonic flowmeter is arranged in a fluid to transmit a transmitter 1 that transmits ultrasonic waves, a receiver 2 that receives ultrasonic waves, and a transmission circuit that drives the transmitter 1. 3, a reception detection circuit 4 that determines reception from the output signal of the receiver 2 that receives the ultrasonic wave propagated through the fluid to be measured, and outputs it to the transmission circuit 1, and a control unit 5 that outputs a measurement start signal to the transmission circuit 3 A counter 6 for measuring the number of repetitions from transmission of ultrasonic waves to reception and return, a timer 7 for measuring the time from the start of transmission of the first ultrasonic wave until the number of repetitions reaches a predetermined number, and a timer And a calculation unit 8 for obtaining a flow rate from the value of 7.

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

  The ultrasonic propagation distance is L, the cross-sectional area through which the fluid to be measured flows 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, the propagation time from upstream to downstream is t1, and the counter 7 (Formula 1) shows a calculation formula for obtaining the flow rate Q when the set value is.

  Q = S [{L / (t / N)}-C] (Formula 1)

  However, in the above-described conventional ultrasonic flowmeter, ultrasonic waves are transmitted at regular intervals, and the receiver 2 receives the ultrasonic waves reflected by the ultrasonic wave propagation path and the reverberation of ultrasonic waves transmitted in the previous period. A measurement error has occurred because the overlapping data is received.

  In addition, the degree of this phenomenon varies depending on the propagation time, and the propagation time varies depending on the temperature and gas components. Therefore, correction cannot be performed, and there is a problem of reducing this measurement error.

  In addition, a method of reducing the measurement error by adding a delay circuit that delays the time until transmission and changing the delay amount with time was also considered, but the delay time required for the calculation is accurately obtained. Therefore, the measurement accuracy could not be improved greatly.

  In order to solve the above-described problems, the present invention is such that the drive frequency changing unit changes the drive frequency of the drive circuit in terms of time.

According to the above invention, since the drive frequency changing unit temporally changes the drive frequency of the ultrasonic transducer, the influence of the reverberation and reflected waves on the received signal is not constant, and the measurement error is biased because dispersion averaging is performed. Measurement accuracy is improved.

  According to the ultrasonic flow meter of the present invention, since the ultrasonic flow meter performs transmission by changing the drive frequency of the transmitter in time, the influence of reverberation and reflected waves on the received signal is distributed average Therefore, there is no bias in measurement error, and a highly accurate ultrasonic flowmeter can be realized.

  An ultrasonic flowmeter according to the present invention includes a transmitter that transmits an ultrasonic signal, a drive circuit that drives the transmitter, a receiver that receives an ultrasonic signal transmitted from the transmitter and propagated through a fluid, A reception detection circuit that receives an output of the receiver and detects an ultrasonic signal, a timer that measures a propagation time of the ultrasonic signal, a calculation unit that calculates a flow rate from the output of the timer, and driving of the drive circuit A drive frequency changing unit for changing the frequency.

  Since the drive frequency changing unit performs transmission by changing the drive frequency of the transmitter in time, the influence of reverberation and reflected waves on the received signal is distributed and averaged, so that it is possible to eliminate measurement error bias.

  In addition, the ultrasonic flowmeter according to the present invention has a transmission / reception sensitivity compared to the case where the transmitter is driven at a single frequency because the drive frequency changing unit changes the drive frequency while the drive circuit is driving the transmitter. There is no significant change, and it is not necessary to perform correction by changing the frequency, the circuit configuration is simplified, and errors caused by the correction do not occur.

  In addition, the ultrasonic flowmeter according to the present invention changes the frequency changed by the drive frequency changing unit to the same frequency as the ultrasonic transmission / reception sensitivity between the transmitter and the receiver. Alternatively, it is not necessary to make corrections according to reception sensitivity, the circuit configuration is simplified, and errors caused by correction do not occur.

  Moreover, since the ultrasonic flowmeter according to the present invention changes the frequency irregularly, the regularity of the transmission signal can be completely eliminated.

  Hereinafter, embodiments of the present invention will be described with reference to the drawings.

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

  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 propagated through a fluid, 9 is a drive circuit for driving the transmitter 1, and 10 is a receiver. 2 is a reception detection circuit that detects an ultrasonic signal in response to the output of 2, 11 is a timer that measures the propagation time of the ultrasonic signal, 12 is a calculation unit that calculates a flow rate from the output of the timer 11, and 13 is a drive circuit 9. A drive frequency changing unit 14 for changing the frequency, and a control unit 14 for outputting signals to the drive frequency changing unit, the drive circuit 9, and the timer.

Next, the operation and action will be described. First, the control unit 14 outputs a signal for determining the driving frequency to the driving frequency changing unit 13 to determine the frequency for driving the transmitter 1. Next, the control unit 14 outputs a transmission start signal to the drive circuit 9 and starts the time measurement of the timer 11 at the same time. When the drive circuit 9 receives the transmission start signal, the drive circuit 9 drives the transmitter 1 with the drive frequency determined by the drive frequency changing unit to transmit ultrasonic waves. The transmitted ultrasonic wave propagates through the fluid, is received by the receiver 2, is converted into an electrical signal, and is output to the reception detection circuit 10. 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. Although the same operation is repeated, the control unit 14 changes the signal output to the drive frequency changing unit 13 to change the drive frequency of the drive circuit 9 each time. FIG. 2 shows the variation of the drive frequency, the horizontal axis indicates the number of measurements, and the vertical axis indicates the drive frequency. As described above, since the drive frequency changing unit 13 performs transmission by changing the drive frequency of the transmitter 1 in time, the influence of reverberation and reflected waves on the received signal is distributed and averaged. it can.

  In this example, the drive frequency is irregularly changed, but may be changed in a certain pattern. Further, although the flow rate is obtained by transmitting ultrasonic waves only in one direction, the method of changing the drive frequency is also effective in the method of obtaining the flow rate from the reciprocal difference by transmitting ultrasonic waves in both directions.

(Reference example)
FIG. 3 is a block diagram showing an ultrasonic flowmeter as a reference example related to the present invention, and FIG. 4 is a view showing transmission / reception timing and transmission frequency of the ultrasonic flowmeter.

  In this reference example, the difference from the first embodiment is 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, and the drive frequency is changed by the output of the counter 16. The point is that the unit 13 changes the drive frequency of the drive circuit 15.

  In addition, the thing of the same code | symbol as Embodiment 1 has the same structure, and abbreviate | omits description.

  The operation and action will be described. First, the control unit 14 outputs a transmission start signal to the drive circuit 15 and simultaneously starts time measurement of the timer 11. When receiving the transmission start signal, the driving circuit 15 drives the transmitter 1 with a driving frequency determined by the initial value of the driving frequency changing unit to transmit ultrasonic waves. The transmitted ultrasonic wave propagates through the fluid, is received by the receiver 2, is converted into an electrical 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 so as to change the driving frequency. When receiving the reception detection signal, the driving circuit 15 drives the transmitter 1 again at a driving frequency determined by the driving frequency changing unit 13. FIG. 2 shows changes in the counter value and the driving frequency. The counter 16 has an end feedback count set in advance. When the counter 16 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 and the time measurement is ended. The calculation unit 12 calculates the flow rate by calculation in consideration of the number of end feedbacks from the time measured by the timer 11. As described above, since the drive frequency changing unit 13 changes the drive frequency of the transmitter 1 according to the number of feedbacks and performs transmission, the influence of the reverberation of the ultrasonic propagation path and the reflected wave on the received signal is distributed and averaged. Measurement bias can be eliminated.

  Also, by making the number of end feedbacks an integer multiple of the number of frequency change patterns (for example, if the drive frequency to be changed is 90 KHz, 100 KHz, or 110 KHz, the number of patterns will be 3), the error occurring at each frequency is calculated uniformly. Since the error is averaged and dispersed for use in measurement, the measurement error is not biased.

(Embodiment 2)
FIG. 5 is a block diagram showing the ultrasonic flowmeter according to the second embodiment of the present invention, FIG. 6 is a diagram showing a driving waveform of the ultrasonic flowmeter, and FIG. 7 is a signal sensitivity between the transceivers of the ultrasonic flowmeter. FIG. The second embodiment is different from the first embodiment in that the drive frequency of the drive circuit 9 is not changed for each measurement, but the drive circuit output is input to the drive frequency changing unit 13 to change the frequency during driving. It is a point.

  In addition, the thing of the same code | symbol as Embodiment 1 has the same structure, and abbreviate | omits description.

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

  FIG. 6 shows how the drive frequency changes. As shown in FIG. 6, the driving frequency changes for each driving cycle. FIG. 7 shows the change range of the drive frequency and the sensitivity between the handset and the handset. Since the drive frequency is set to be uniformly changed between f1 and f2 shown in FIG. 7, the difference in each measurement is smaller than the difference in the case of driving with the single frequencies fa and fb. There is no significant change in sensitivity, and it is not necessary to perform sensitivity correction by changing the frequency, the circuit configuration is simplified, and at the same time, errors caused by the correction do not occur.

(Embodiment 3)
FIG. 8 is a block diagram of the ultrasonic flowmeter according to the third embodiment of the present invention, and FIG. 9 is a diagram showing the drive frequency of the ultrasonic flowmeter and the sensitivity between the transmitter and the receiver.

  The third embodiment is different from the first embodiment in that the drive frequency changing unit 13 outputs the frequency setting unit A17, the frequency setting unit B18, the frequency setting unit C19, the frequency setting unit D20, and the frequency setting unit A17-D20. Is selected and output to the drive circuit 9, and all of the drive frequencies set by the frequency setting units A17-D20 are frequencies with substantially the same sensitivity between the transmitter and the receiver.

  In addition, the thing of the same code | symbol as Embodiment 1 has the same structure, and abbreviate | omits description.

  FIG. 9 shows the relationship between the sensitivity between the transceiver and the drive frequency. In this way, the frequencies set by the frequency setting units A17-D20 correspond to f1-f4, respectively, and even if the drive frequency is changed, the sensitivity between the transmitters and receivers does not change. Alternatively, it is not necessary to make corrections according to reception sensitivity, the circuit configuration is simplified, and errors caused by correction do not occur.

  Here, the frequency of the frequency setting unit has been set in advance assuming that the sensitivity between the transmitter and receiver is known. However, the sensitivity between the transmitter and receiver is checked by changing the drive frequency to check the sensitivity between the transmitter and receiver. A frequency can also be selected. In this case, if the frequency setting unit uses a rewritable device such as a memory, the optimum frequency can be written each time, so that the configuration of the present invention can be easily realized.

(Embodiment 4)
FIG. 10 is a block diagram showing an ultrasonic flowmeter according to the fourth embodiment of the present invention.

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

  In addition, the thing of the same code | symbol as Embodiment 1 has the same structure, and abbreviate | omits description.

  Next, the operation and action 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 changing unit. Since the frequency is changed irregularly in this way, the regularity of the transmission signal can be completely eliminated. For this reason, the error is averaged and dispersed, so that the measurement error is not biased.

Block diagram of ultrasonic flowmeter in embodiment 1 of the present invention The figure showing the change of the drive frequency in the transmitter of the same ultrasonic flowmeter Block diagram of an ultrasonic flowmeter as a reference example related to the present invention Diagram showing transmission / reception timing and transmission frequency of the ultrasonic flowmeter Block diagram of ultrasonic flowmeter in embodiment 2 of the present invention Diagram showing the drive waveform of the ultrasonic flowmeter Signal sensitivity characteristic diagram between transmitter and receiver of the ultrasonic flowmeter Block diagram of ultrasonic flowmeter in embodiment 3 of the present invention Sensitivity characteristics between the frequency of the ultrasonic flowmeter and the transmitter / receiver Block diagram of ultrasonic flowmeter in embodiment 4 of the present invention Block diagram of conventional ultrasonic flowmeter

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

Claims (4)

A transmitter for transmitting ultrasonic signals;
A drive circuit for driving the transmitter;
A receiver for receiving an ultrasonic signal transmitted from the transmitter and propagated through the fluid;
A reception detection circuit that receives an output of the receiver and detects an ultrasonic signal;
A timer for measuring the propagation time of the ultrasonic signal;
A calculation unit for calculating the flow rate from the output of the timer;
A drive frequency changing unit for temporally changing the drive frequency of the drive circuit;
And a control unit for controlling the timer and the driving frequency changing unit and the drive circuit,
The ultrasonic flowmeter that outputs a transmission start signal to the drive circuit after the control unit outputs a signal to the drive frequency changing unit and changes the drive frequency with time each time time measurement is started. The ultrasonic flowmeter according to claim 1, wherein the driving frequency is changed in a constant pattern. 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. The ultrasonic flowmeter according to claim 1, wherein the driving frequency is irregularly changed.

Images