JP2009008692A - Flow measuring apparatus - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a flow measuring apparatus capable of maintaining flow-quantity accuracy even when the type of gas is changed. <P>SOLUTION: The flow measuring apparatus includes transmitters/receivers 5 and 6 for transmitting and receiving ultrasonic waves to and from a fluid; a measuring circuit 8 for measuring the propagation delay time of transmission from the upstream side to the downstream side of a flow or transmission from the downstream side to the upstream side; a flow computation means 9 for computing the quantity of flow on the basis of ultrasonic-wave propagation delay time; a fluid determination means 10 for determining the type of fluid in a channel from the transmitters/receivers; and a circuit constant correction means 11 for changing a constant of the measuring circuit 18 on the basis of a value of the fluid determination means 10. An optimal measuring circuit is thereby selected according to the components of gases to convert ultrasonic waves into appropriate signals and highly accurately maintain flow-quantity accuracy. <P>COPYRIGHT: (C)2009,JPO&INPIT

Description

  The present invention relates to a flow rate measuring device that measures the flow rate of a fluid such as a gas.

As shown in FIG. 8, the conventional flow measuring device of this type measures the signal propagation time by the propagation time difference detecting means 3 at the time of measuring the flow rate from the receiving means 2 connected by the flow velocity detecting means 1, and the propagation time storage means 4 When the measurement by the receiving means is longer than the stored value, it is detected that a different medium is mixed and a warning is displayed.
Japanese Patent Laid-Open No. 10-318811

  However, in the above-described conventional flow rate measuring device, it can be detected that a different medium is mixed, but the flow rate cannot be accurately measured in the mixed state, and it is a problem to maintain the flow rate accuracy in a state where the gas component changes. It was.

  In order to solve the above problems, the present invention provides a transceiver for transmitting and receiving ultrasonic waves in a fluid, a measurement circuit for measuring a propagation time of transmission from upstream to downstream of a flow or transmission from downstream to upstream, and ultrasonic waves Flow rate calculating means for calculating a flow rate according to propagation time, fluid determining means for determining the type of fluid in the flow path from the transmitter / receiver, and circuit constant correcting means for changing the constant of the measurement circuit according to the value of the fluid determining means A repetitive unit that transmits the ultrasonic wave again after receiving the ultrasonic wave, and a repetitive flow rate calculating unit that calculates a flow rate from the accumulated time of the repetitive transmission / reception. The setting of the means is changed.

  Since the repetition means for transmitting again through the delay means after reception of the ultrasonic wave and the repetition flow rate calculation means for calculating the flow rate from the accumulated time of this repeated transmission and reception, the setting of the delay means is changed by the fluid discrimination means. It is possible to improve the flow rate accuracy by preventing the reflection of ultrasonic waves that differ depending on the species.

  The present invention relates to a transmitter / receiver for transmitting / receiving ultrasonic waves in a fluid, a measurement circuit for measuring a propagation time of transmission from upstream to downstream of a flow or transmission from downstream to upstream, and a flow rate for calculating a flow rate by the ultrasonic propagation time. A delay means after receiving the ultrasonic wave, comprising: a computing means; a fluid discrimination means for determining the type of fluid in the flow path from the transceiver; and a circuit constant correction means for changing the constant of the measurement circuit according to the value of the fluid discrimination means. And a repetitive flow rate calculating means for calculating the flow rate from the accumulated transmission / reception time, and the setting of the delay means is changed by the fluid discriminating means.

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

(Embodiment 1)
Embodiment 1 of the present invention will be described. In FIG. 1, transmitters / receivers 5 and 6 for transmitting / receiving ultrasonic waves in a fluid are provided upstream and downstream of a flow path 7, respectively, and the propagation time of transmission from upstream to downstream or transmission from downstream to upstream is measured. As a result of the measurement circuit 8, the ultrasonic propagation time is obtained, and the flow rate calculation means 9 calculates the flow rate. Further, there is a fluid discriminating means 10 for judging the type of fluid in the flow path from the signal magnitudes and propagation times of the transceivers 5 and 6, and a circuit constant for changing the constant of the measuring circuit 8 according to the value of the fluid discriminating means 10. And correction means 11.

  Next, the operation will be described. An ultrasonic drive signal is transmitted from the transmission means 13 of the measurement circuit 8 by the signal of the start 12, and ultrasonic waves are transmitted from the transceivers 5 to 6 through the switching means 14, that is, along the flow, and propagate through the flow path 7. The ultrasonic wave reaches the transmitter / receiver 6 after being accelerated by the flow velocity. The signal in the transmitter / receiver 6 is amplified by the amplifying means 15 and further sent to the comparing means 16 to detect reception of ultrasonic waves. The ultrasonic transmission time from the transceivers 5 to 6 is measured by the time measuring means 17 and stored as the forward propagation time. Next, the switching means 14 is switched to transmit ultrasonic waves against the flow from the transmitter / receiver 6 to 5, and the transmission time from the transmitter / receiver 6 to 5 is stored as the backward propagation time in the same manner as described above. The flow rate calculation means 9 calculates the flow rate from the time difference between the time and the forward propagation time, and the flow rate coefficient calculated in advance according to the cross-sectional area of the flow path 7 and the flow state. In the actual calculation, the flow rate is calculated based on the reciprocal difference of the propagation time so that the influence of the sound speed is theoretically eliminated.

  Next, the case where the type of fluid flowing through the flow path 7 is changed will be described. The components of natural gas and LP gas as fuel supplied to the home are not always constant, and vary considerably depending on the season and place of supply. When the fluid component changes, the signal of the transceiver 6 also changes. For example, when hydrogen gas is mixed in propane gas, which is the main component of LP gas, the ultrasonic reception voltage is reduced and the propagation time is also reduced. The fluid discriminating means 10 detects the received voltage and the propagation time, discriminates the type of gas from the values, and the circuit constant of the measuring circuit 8 is corrected, for example, by the circuit constant correcting means 11 to correct the amplification degree and the transmission voltage, thereby maintaining the flow rate accuracy. Acts like

(Embodiment 2)
FIG. 2 shows the second embodiment, and the fluid is discriminated based on the value of 17 of the time measuring means, that is, the propagation time of the ultrasonic wave. The flow rate coefficient used in the flow rate calculation unit 9 is corrected by the coefficient correction unit 18 in accordance with the type of fluid determined by the fluid determination unit 10, and the flow rate is accurately calculated. If the type of fluid changes, the state of the flow changes, and the flow velocity distribution in the flow path 7 changes, which affects the flow coefficient and causes a flow rate error. Since the value of the flow coefficient depends on the Reynolds number of the fluid, the Reynolds number may be estimated by the fluid discrimination means. If the type of gas mixed, such as the propane gas and hydrogen gas described above, is clear, the relationship between the propagation time and the Reynolds number may be obtained in advance by experiments and stored in a microcomputer or the like. Since the propagation time changes as the fluid temperature changes, the temperature is detected by the temperature detection means 19 when the fluid temperature changes, and the type of fluid is determined based on the propagation time converted to, for example, 20 ° C. Since the Reynolds number also changes depending on the temperature, it can be corrected simultaneously.

(Embodiment 3)
FIG. 3 shows the third embodiment, in which the type of fluid is determined by the magnitude of the received signal level. When hydrogen gas is mixed into the propane gas shown in the first embodiment, propane gas is used. When the hydrogen gas is mixed, the reception level becomes smaller as in the fluid B than in the fluid A. It can be estimated how much hydrogen gas is mixed by the magnitude of the reception level.

(Embodiment 4)
FIG. 4 shows the fourth embodiment, in which the amplification factor of the received signal is increased by the preamplifier 19 by the circuit constant corrector 11. As described in the fourth embodiment, when the hydrogen gas is mixed, the reception level becomes small, so that the lack of ultrasonic reception sensitivity is corrected. If the reception level is high, the pre-amplification means 19 is not necessary, so it may be set to sleep. As another means for adjusting the reception sensitivity, the circuit constant correction means 11 switches the comparator comparison signal of the comparison means 16 to correct the circuit. As shown in FIG. 3, when the fluid is expected to have a large received signal, the fluid is operated at the comparison level C, and when the fluid is expected to be small, the fluid is operated at the comparison level D.

(Embodiment 5)
FIG. 5 shows a fifth embodiment, in which the transmission means 13 is controlled by the circuit constant correction means 11. As described in the fourth embodiment, when it is expected that the fluid has low reception sensitivity, for example, the wave number of burst transmission is increased or the transmission voltage is set high to obtain an appropriate ultrasonic signal. .

(Embodiment 6)
FIG. 6 shows a sixth embodiment, which is an embodiment in the sing-around method in which an ultrasonic wave is received and then transmitted again, and the flow rate is calculated from the total time of repeating this transmission and reception a plurality of times. In the third embodiment, when hydrogen gas is mixed, the received voltage is reduced, so that the ratio of noise to the received signal is increased and the S / N is reduced, so that the variation in measurement time is increased. Therefore, in the sixth embodiment, the flow rate accuracy is maintained by discriminating the type of fluid due to the decrease in the received voltage and increasing the number of repetitions by the repetition means 20.

(Embodiment 7)
FIG. 7 shows the seventh embodiment, in which the delay time from reception to transmission is changed by the delay means 21 in accordance with the kind of fluid in the above-described sing-around method. In the sing-around method, since ultrasonic waves are repeatedly transmitted, the ultrasonic waves are reflected between the transmitter / receivers 5 and 6 and become noise, so that accurate ultrasonic detection cannot be performed. Therefore, a delay time is provided between reception and transmission of the next ultrasonic wave to reduce the influence of reflection. The optimum delay time varies depending on the properties of the fluid. Therefore, a delay time is set in advance according to the type of fluid, and a delay time corresponding to the determined type of fluid is set. If the delay time is obtained by dividing a delay element of 1 microsecond or less a plurality of times, the delay time can be set by changing the setting value of the counter.

  In the present embodiment, the mixed gas of propane gas and hydrogen gas is described as the type of gas. However, in the natural gas, a flammable fluid such as methane gas and propane gas or hydrogen gas, or a mixed fluid of flammable fluid and air. It can also be applied to.

  Further, the mixing ratio and fluid properties can be set from the outside via a communication means by a non-volatile memory or the like in addition to being stored by a microcomputer.

1 is a block diagram of a flow rate measuring device according to Embodiment 1 of the present invention. Block diagram of a flow rate measuring apparatus according to Embodiment 2 of the present invention Received signal diagram of flow rate measuring apparatus according to embodiment 3 of the present invention Block diagram of a flow rate measuring device according to a fourth embodiment of the present invention Block diagram of a flow rate measuring device according to a fifth embodiment of the present invention Block diagram of a flow rate measuring device according to a sixth embodiment of the present invention Block diagram of a flow rate measuring device according to a seventh embodiment of the present invention Block diagram of a conventional flow measurement device

Explanation of symbols

5, 6 Transceiver 8 Measuring circuit 9 Flow rate calculating means 10 Fluid discriminating means 11 Circuit constant correcting means 13 Transmitting means 16 Comparing means 18 Coefficient correcting means 19 Preamplifying means 20 Repeating means 21 Delay means

Claims (1)

A transmitter / receiver for transmitting / receiving ultrasonic waves in the fluid, a measurement circuit for measuring a propagation time of transmission from upstream to downstream of the flow or transmission from downstream to upstream, and a flow rate calculation means for calculating a flow rate by the ultrasonic propagation time; A flow rate measuring device comprising: a fluid discriminating unit that determines the type of fluid in the flow path from the transceiver; and a circuit constant correcting unit that changes a constant of the measuring circuit according to a value of the fluid discriminating unit. A flowmeter side that includes a repeating unit that transmits again through the delay unit after receiving the sound wave, and a repeated flow rate calculating unit that calculates a flow rate from the accumulated time of the repeated transmission and reception, and the setting of the delay unit is changed by the fluid discrimination unit apparatus.

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