JP2016017952A - Ultrasonic flowmeter - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an ultrasonic flowmeter capable of measuring the flow rate with high accuracy by suppressing influence due to pulsation.SOLUTION: An ultrasonic flowmeter which has a pair of facing ultrasonic vibrators 11, 12 with a constant distance on the upstream side and the downstream side of a flow channel 10 where gas flows in the ultrasonic flowmeter, repeatedly performs transmission and reception of ultrasonic signals plural times between the facing ultrasonic vibrators 11, 12, and measures the propagation time of the ultrasonic wave between the ultrasonic vibrator 11 on the upstream side and the ultrasonic vibrator 12 on the downstream side to calculate the flow rate value on the basis of the propagation time difference comprises at least: a frequency discrimination circuit 19 discriminating the frequency component of the propagation time from the propagation time; and a timing generation circuit 20 which decides the timing of the driving pulse signal of transmission of the ultrasonic vibrator 11 on the upstream side and the ultrasonic vibrator 12 on the downstream side in accordance with output of the frequency discrimination circuit.SELECTED DRAWING: Figure 1

Description

  Embodiments of the present invention relate to an ultrasonic flowmeter capable of measuring flow rate with high accuracy while suppressing the influence of pulsation.

  As a conventional ultrasonic flow meter, a pair of ultrasonic transducers are installed facing each other at a certain distance on the upstream side and downstream side of a flow path through which gas such as city gas flows, and an ultrasonic signal is transmitted between them. Repeatedly transmit and receive multiple times to obtain the flow velocity from the difference between the accumulated time of the ultrasonic signal propagation time from the upstream side to the downstream side and the accumulated time of the ultrasonic signal propagation time from the downstream side to the upstream side. In some cases, the flow rate is multiplied by the cross-sectional area of the flow path to calculate the instantaneous flow rate of the fluid, and the instantaneous flow rate value is integrated to obtain the integrated flow rate value.

  In such an ultrasonic flow meter, for example, when a gas engine heat pump is installed in a neighbor connected to the same gas pipe, when the gas heat pump is used, a repeated operation of pressure fluctuation occurs in the supply gas pressure. As a result, a pulsation of several Hz to 20 Hz is generated in the gas flowing in the gas pipe. This pulsation is transmitted to the gas flowing in the flow path of the ultrasonic flowmeter, is measured as an instantaneous flow rate, and there is a problem that erroneous measurement is performed on the gas flow rate actually used.

  To solve this problem, there is a pulsation when the difference between the instantaneous flow rate Q (i) measured by the ultrasonic flow rate detection means and the instantaneous flow rate Q (i-1) measured last time is taken and the difference is greater than or equal to a predetermined value. In the case where there is pulsation, there is a technique for calculating a flow rate by a stable flow rate calculation means through a filter process.

JP 2000-298042 A

  However, in the above-described prior art, since the presence or absence of pulsation is determined only by the difference in instantaneous flow rate, when the repetition cycle of pulsation coincides with the measurement sampling cycle of instantaneous flow rate, the same portion of the pulsation waveform is sampled every time. There is a possibility that a difference in instantaneous flow rate due to pulsation cannot be detected, and as a result, there is a possibility that it may be determined that there is no pulsation despite occurrence of pulsation.

  An object of an embodiment of the present invention is to provide an ultrasonic flowmeter capable of measuring the flow rate with high accuracy while suppressing the influence of pulsation.

  In order to achieve the above-described object, the ultrasonic flowmeter according to the embodiment of the present invention has a pair of ultrasonic transducers facing each other with a certain distance between the upstream side and the downstream side of the flow path through which the gas flows. In the meantime, transmission and reception of ultrasonic signals are repeated several times between each other, the propagation time of the ultrasonic wave between the ultrasonic transducer on the upstream side and the ultrasonic transducer on the downstream side is measured, and the difference in propagation time In the ultrasonic flowmeter that calculates the flow value based on the frequency, a frequency discrimination circuit that discriminates at least a frequency component of the propagation time from the propagation time, and the upstream ultrasonic transducer according to the output of the frequency discrimination circuit And a timing generation circuit for determining the timing of the drive pulse signal transmitted from the downstream ultrasonic transducer.

The block diagram containing sectional drawing of the ultrasonic flowmeter which concerns on one Embodiment of this invention. FIG. 2 is a diagram for explaining the operation of the propagation time measuring circuit of FIG. 1, wherein (a) is the propagation of ultrasonic waves from the upstream ultrasonic transducer to the downstream ultrasonic transducer when the gas is flowing at a substantially constant flow rate. Time (b) shows the ultrasonic wave from the upstream ultrasonic transducer to the downstream ultrasonic transducer when a pulsation of period τ and amplitude D is superimposed on the gas flowing at a constant flow shown in (a). Propagation time. It is a figure explaining the measuring method using the ultrasonic flowmeter concerning one embodiment of the present invention, and (a) is a method of performing transmission and reception with a period of 1/2 of τ, and obtaining propagation time with a transmission time measuring circuit, (B) is an example of the spectrum of the frequency component of the pulsation extracted from (a).

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

(Constitution)
FIG. 1 is a block diagram including a cross-sectional view of an ultrasonic flowmeter according to an embodiment of the present invention.
As shown in FIG. 1, the ultrasonic flowmeter 1 includes a pair of super flow meters installed facing each other at a certain distance (L) on the upstream side and the downstream side of a gas flow path 10 through which a gas such as city gas flows. The ultrasonic transducers 11 and 12, the transmission circuit 13 that generates a drive pulse signal that is applied to the ultrasonic transducers 11 and 12 to output ultrasonic waves, and the transmission / reception switching that switches between transmission and reception of the ultrasonic transducers 11 and 12. A circuit 14, a reception circuit 15 that amplifies reception signals output from the ultrasonic transducers 11 and 12, a comparator circuit 16 that converts an analog signal from the reception circuit 15 into a digital signal, and an output signal of the comparator circuit 16 and transmission The propagation time measurement circuit 17 that measures the propagation time of the ultrasonic wave between the ultrasonic transducers 11 and 12 from the signal, and the gas flow rate is multiplied by the propagation time obtained by the propagation time measurement circuit 17 and the cross-sectional area of the flow path 10. Calculation The flow rate measuring circuit 18, the frequency discriminating circuit 19 for discriminating the frequency component of the propagation time from the propagation time obtained by the propagation time measuring circuit 17, and the output of the frequency discriminating circuit 19 for the timing of the drive pulse signal generated by the transmitting circuit 13. A timing generation circuit 20 that generates the clock signal, and an oscillation circuit 21 that generates a clock signal used in the propagation time measurement circuit 17 and the timing generation circuit 20.

(Function)
In FIG. 1, the signal generated by the timing generation circuit 20 is amplified by the transmission circuit 13 and applied as a drive pulse to the ultrasonic transducer 11 or 12 through the transmission / reception switching circuit 14. Thereby, the ultrasonic transducer 11 or 12 outputs an ultrasonic wave corresponding to the signal level of the pulse toward the other ultrasonic transducer 12 or 11. The ultrasonic waves are received by the other ultrasonic vibrators 11 and 12 with a propagation time corresponding to the distance L between the sound velocity V and the ultrasonic vibrators 11 and 12 and the flow velocity of the fluid. The received ultrasonic wave is converted into an electrical signal and output.

  A reception signal from the ultrasonic transducer 11 or 12 is input to the reception circuit 15 through the transmission / reception switching circuit 14 and is amplified by an amplifier having a certain gain built in the reception circuit 15. Thereafter, the signal is converted into a digital signal by the comparator 16, and the propagation time required until the reception signal arrives from the output of the transmission signal is calculated by the propagation time measurement circuit 17. Specifically, the transmission and reception operations of the ultrasonic transducers 11 and 12 are switched by the transmission / reception switching circuit 14, the propagation time Td from the upstream ultrasonic transducer 11 to the ultrasonic transducer 12, and the ultrasonic vibration The propagation time Tu from the child 12 to the ultrasonic transducer 11 is repeatedly obtained several times, and the fluid flow velocity is obtained from the difference of the accumulated propagation times.

(Measurement method of propagation time of gas with superimposed pulsation)
FIG. 2A shows the propagation time of the ultrasonic wave from the upstream ultrasonic transducer 11 to the downstream ultrasonic transducer 12 when the gas is flowing at a substantially constant flow rate. The propagation time Td is It is almost constant. FIG. 2B shows the flow from the upstream ultrasonic transducer 11 to the downstream ultrasonic transducer 12 when a pulsation of period τ and amplitude D is superimposed on the gas flowing at a constant flow shown in FIG. Ultrasonic propagation time. When measuring the gas flow rate in FIG. 2 (b), if transmission / reception is performed with the period of the mark ● shown in the figure equivalent to the pulsation period τ, the propagation time differs from the propagation time Td depending on the gas flow rate used. The maximum value Th is measured every time, resulting in erroneous measurement. Similarly, the above-described erroneous measurement is also performed in the measurement of the propagation time of the ultrasonic wave from the ultrasonic transducer 12 to the ultrasonic vibration 11.

Hereinafter, a method for accurately measuring the propagation time of a gas with superimposed pulsation will be described.
First, the frequency of the pulsation is specified by transmitting / receiving ultrasonic waves at a frequency about twice the maximum frequency of the pulsation that can occur (sampling theorem). For example, as shown by ◇ in FIG. 3A, transmission / reception is performed at a period of ½ of τ shown in FIG. 2B, and the propagation time measurement circuit 17 obtains the propagation time. The obtained propagation time is stored in a memory circuit (not shown) by the frequency discriminating circuit 19, and fast Fourier transform (hereinafter referred to as "FFT") is performed using a plurality of stored data to extract the frequency component of pulsation. To do. An example of the extracted frequency component spectrum is shown in FIG. FIG. 3B shows that the pulsation frequency in FIG. 3A is 10 Hz.

  In the present embodiment, the pulsation frequency of FIG. 3A is specified from FIG. 3B, and the transmission / reception cycle is determined based on the specified frequency. For example, when the maximum frequency at which pulsation can occur is 20 Hz, transmission / reception is repeatedly performed at twice the frequency of 40 Hz, the propagation time is measured, and the frequency of the pulsation actually occurring is identified by extraction by FFT.

  When the specified pulsation frequency is 10 Hz as shown in FIG. 3B, if measurement is continued at a repetition period of 40 Hz, the power consumed by the measurement is large and the consumption of the battery mounted on the ultrasonic gas meter increases. The expected battery life will be accelerated. Therefore, in order to reduce power consumption and extend battery life, it is necessary to repeat transmission / reception of ultrasonic waves at a frequency commensurate with the pulsation frequency.

  When the above pulsation frequency is 10 Hz, the timing generation circuit 20 creates the ultrasonic wave transmission / reception at the double frequency 20 Hz from the sampling theorem, and the drive pulse is transmitted to the ultrasonic transducer 11 via the transmission circuit 13. 12 is applied. By averaging a plurality of measured propagation time values obtained by transmission / reception at 20 Hz, the propagation time Td can be obtained without using the maximum value Th that fluctuates due to pulsation as the propagation time. Thereby, it is possible to detect the fluctuation period of the pulsation and reduce the power consumption.

(When pulsation frequency changes or pulsation disappears)
When the frequency of pulsation changes or the pulsation disappears during measurement of propagation time by specifying the frequency of pulsation by the above method and determining the frequency of transmission and reception based on it, the propagation time of the same frequency is If the measurement is continued, the propagation time is erroneously measured.

  In order to prevent this erroneous measurement, the difference between the measured propagation time and the previous value is obtained, and when the difference value changes to a predetermined set value (for example, ± 5%) or more, the maximum frequency of the pulsation described above is obtained. Ultrasound is transmitted / received at about twice the frequency, and after specifying the frequency of pulsation by FFT, transmission / reception is performed at twice the specified frequency (sampling theorem). If the frequency cannot be specified, the difference determination circuit determines that there is no pulsation, and changes the transmission / reception frequency at a low frequency such as 1 Hz. Thereby, it is possible to prevent erroneous measurement and suppress power consumption.

(effect)
According to this embodiment, the frequency of pulsation is detected by FFT, ultrasonic waves are repeatedly transmitted and received at a period corresponding to the pulsation frequency, and the propagation time is averaged, thereby suppressing the influence of pulsation and high accuracy. Can measure the flow rate.

[Other embodiments]
(1) In the above embodiment, when the maximum frequency at which pulsation can occur is 20 Hz, transmission / reception is repeatedly measured at a double frequency of 40 Hz. However, the propagation time is not accurately doubled, but doubled. If it is above, you may measure propagation time at 50 Hz or 100 Hz.

(2) In the above embodiment, the frequency component of pulsation is extracted by performing fast Fourier transform (FFT). However, not only the fast Fourier transform (FFT) but also the frequency component of pulsation can be extracted by other methods. good.

(3) In the above-described embodiment, the difference between the measured propagation time and the previous value is obtained, and when the difference value changes to a predetermined set value or more, the difference is greater than about twice the maximum pulsation frequency described above. The sound wave was transmitted and received, and the frequency of the pulsation was specified by FFT, but the difference in flow rate changed to a predetermined set value or more, for example, when the flow rate changed by ± 5% or more, not the difference in propagation time. In some cases, the above processing can also be performed.

(4) Although several embodiments of the present invention have been described above, these embodiments are presented as examples and are not intended to limit the scope of the invention. These embodiments can be implemented in various other forms, and various omissions, replacements, and changes can be made without departing from the spirit of the invention. These embodiments and their modifications are included in the scope and gist of the invention, and are also included in the invention described in the claims and the equivalents thereof.

DESCRIPTION OF SYMBOLS 1 ... Ultrasonic flowmeter 10 ... Flow path 11 ... Upstream ultrasonic transducer | vibrator 12 ... Downstream ultrasonic transducer | vibrator 13 ... Transmission circuit 14 ... Transmission / reception switching circuit 15 ... Reception circuit 16 ... Comparator circuit 17 ... Propagation time measurement circuit 18 ... Flow measurement circuit 19 ... Frequency discrimination circuit 20 ... Timing generation circuit 21 ... Oscillation circuit

Claims (5)

A pair of ultrasonic transducers are placed facing each other at a certain distance upstream and downstream of the flow path through which gas flows in the ultrasonic flow meter, and ultrasonic signals are repeatedly transmitted between them several times between them. In the ultrasonic flow meter that performs reception and measures the propagation time of the ultrasonic wave between the ultrasonic transducer on the upstream side and the ultrasonic transducer on the downstream side, and calculates the flow value based on the propagation time difference, at least,
A frequency discriminating circuit for discriminating a frequency component of the propagation time from the propagation time;
A timing generation circuit that determines the timing of the drive pulse signal for transmission of the upstream ultrasonic transducer and the downstream ultrasonic transducer according to the output of the frequency discrimination circuit;
An ultrasonic flowmeter comprising:   The ultrasonic flowmeter according to claim 1, wherein the frequency discrimination circuit extracts a frequency component of pulsation by performing high-speed Fourier transform using a plurality of data relating to the propagation time.   The timing generation circuit sets the timing of drive pulse signals transmitted from the upstream ultrasonic transducer and the downstream ultrasonic transducer so that the frequency is twice or more the frequency component of the extracted pulsation. The ultrasonic flowmeter according to claim 2, wherein the ultrasonic flowmeter is determined.   When the measured value of the propagation time exceeds a predetermined value compared with the previous measured value, the frequency discriminating circuit discriminates the frequency component of the propagating time from the propagation time, and the timing generation circuit performs the frequency discrimination The timing of the drive pulse signal of transmission of the said upstream ultrasonic transducer | vibrator and the said downstream ultrasonic transducer | vibrator is determined according to the output of a circuit, The any one of Claims 1-3 characterized by the above-mentioned. Ultrasonic flow meter.   Furthermore, a flow rate measurement circuit that calculates the gas flow rate by multiplying the propagation time and the cross-sectional area of the flow path is provided, and the measured value of the gas flow rate calculated by the flow rate measurement circuit is a predetermined value compared to the previous measurement value. The frequency discriminating circuit discriminates the frequency component of the propagating time from the propagation time, and the timing generation circuit determines the upstream ultrasonic transducer and the downstream side according to the output of the frequency discriminating circuit. The ultrasonic flowmeter according to any one of claims 1 to 3, wherein the timing of the drive pulse signal transmitted from the ultrasonic transducer is determined.