JP2007064988A - Flowmeter - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To realize a flowmeter which can calculate exact and stable flow rate value, in the flowmeter measuring the fluid flow rate. <P>SOLUTION: A pair of ultrasonic wave transmitter and receiver 8, 9 is set facing each other on the upstream side and the downstream side in a flow path 7 where the fluid flows. The flowmeter comprises a time-measuring means 16 which measures the ultrasonic wave propagation time between a pair of the ultrasonic transmitter and receiver, a flow rate calculation means 17 which calculates the flow rate of the fluid from the ultrasonic wave propagation time, an offset value storing means 18 which stores the offset value by using the flow rate calculation. By using this constitution, since the offset value will always be stored, calculation can be made by using the offset value, low flow rate can be measured accurately and stably. <P>COPYRIGHT: (C)2007,JPO&INPIT

Description

  The present invention relates to a flow rate measuring device that measures a flow rate of a fluid.

A conventional flow measuring device of this type will be described with reference to FIG. In the figure, a pair of ultrasonic transceivers 2 and 3 are provided on the upstream side and the downstream side in the flow path 1 through which the fluid flows, and ultrasonic waves are transmitted from the upstream side to the downstream side or from the downstream side to the upstream side, and received. To do. The flow rate of the fluid was calculated from the propagation time difference of the ultrasonic wave at this time, and the flow rate was calculated by multiplying the cross-sectional area of the flow path 1 to obtain a flow rate measuring device (see, for example, Patent Document 1). In the figure, an arrow 4 indicates the direction in which the fluid flows, a broken line 5 indicates the ultrasonic wave propagation path, and an alternate long and short dash line indicates the direction in which the fluid flows.
Japanese Patent Laid-Open No. 9-318411

  However, the conventional flow measuring device has the following problems. That is, since the ultrasonic transmitters / receivers 2 and 3 for transmitting and receiving ultrasonic waves are provided in the flow path, they are greatly affected by the physical conditions of the fluid, that is, the pressure, temperature, type, etc. of the fluid. There was a problem that the low flow rate could not be measured accurately and stably.

  In order to solve the above problems, the present invention provides a pair of ultrasonic transmitters and receivers facing the upstream side and the downstream side of the flow path through which the fluid flows, and sets the ultrasonic propagation time between the pair of ultrasonic transmitters and receivers. The time measurement means for measuring, the flow rate calculation means for calculating the flow rate of the fluid from the ultrasonic propagation time, and the offset value storage means for storing the offset value used for the flow rate calculation are provided.

  With this configuration, since the offset value is always stored, the calculation can be performed using the offset value, so that the low flow rate can be measured stably and accurately.

  Since the flow rate measuring device of the present invention stores the offset value, it is possible to calculate a stable and accurate flow rate value.

  The present invention provides a pair of ultrasonic transceivers facing each other on the upstream side and the downstream side of the flow path through which the fluid flows, and measures time measurement means for measuring the ultrasonic propagation time between the pair of ultrasonic transceivers; The flow rate calculation means for calculating the flow rate of the fluid from the ultrasonic propagation time and the offset value storage means for storing the offset value used for the flow rate calculation are provided.

  With this configuration, since the offset value is always stored, the calculation can be performed using the offset value, so that the low flow rate can be measured stably and accurately.

  In addition, the offset value is a value obtained by multiplying the period of the ultrasonic signal received by each of the pair of ultrasonic transceivers by a predetermined value.

  For this reason, the fluctuation | variation of an offset value can be confirmed from a received signal, and a flow volume can be measured stably.

  In addition, the time between the zero cross point and the zero cross point of the received ultrasonic signal is set as the period of the received ultrasonic signal.

  For this reason, the period of the received signal can be easily measured, the offset value can be confirmed, and the flow rate can be stably measured.

  Moreover, it was set as the structure provided with the environmental change detection means which detects the environmental change of a fluid.

  For this reason, the environmental change of the fluid can be detected, the offset value can be updated according to the environmental change of the fluid, and the flow rate can be stably measured over a long period of time.

  The environment change detecting means is constituted by temperature detecting means. Therefore, the offset value can be updated when a temperature change occurs in the fluid, and the flow rate can be stably measured even if the temperature changes.

  In addition, temperature detection means for detecting the temperature of the fluid from the ultrasonic propagation time between the pair of ultrasonic transceivers is provided. For this reason, the temperature of the fluid can be detected with a simple configuration.

  In addition, a pair of ultrasonic transmitters / receivers are provided opposite to the upstream side and the downstream side of the flow path through which the fluid flows, time measuring means for measuring the ultrasonic propagation time between the pair of ultrasonic transmitters / receivers, The flow rate calculation means for calculating the flow rate of the fluid from the propagation time and the offset value storage means for storing the offset value used for the flow rate calculation are provided, and the offset value is obtained by a predetermined method when no fluid is flowing. It became the composition which becomes. Therefore, a stable and accurate flow rate measuring device can be realized with a simple configuration.

  Hereinafter, embodiments of the present invention will be described with reference to the drawings. Note that the present invention is not limited to the present embodiment.

(Embodiment 1)
FIG. 1 is a block diagram showing a flow rate measuring apparatus according to Embodiment 1 of the present invention. In FIG. 1, ultrasonic transceivers 8 and 9 are provided on the upstream side and the downstream side of the flow path 7. An arrow 10 in the flow path 7 indicates the flow direction of the fluid (one-dot chain line 11), and intersects the ultrasonic wave propagation path 12 (broken line) at an angle θ. For example, a transmission signal is transmitted from the transmission unit 13 to the upstream ultrasonic transmitter / receiver 8 via the switching unit 14, and the ultrasonic wave is transmitted into the flow path 7 and received by the downstream ultrasonic transmitter / receiver 9. .

  The received ultrasonic signal is transmitted to the receiving unit 15 via the switching unit 14. At this time, time from transmission to reception is measured in the time measuring means 16. Next, a transmission signal is transmitted from the transmission unit 13 to the ultrasonic transmitter / receiver 9 on the downstream side via the switching unit 14, and the ultrasonic wave is transmitted into the flow path 7 and received by the ultrasonic transmitter / receiver 8 on the upstream side. The The received ultrasonic signal is transmitted to the receiving unit 15 via the switching unit 14. At this time, time from transmission to reception is measured in the time measuring means 16.

In order to increase the time resolution, when the receiving unit 15 receives the ultrasonic signal, it passes through the time measuring means 16 and transmits the signal to the transmitting unit 13, and repeatedly transmits and receives as many as 2 to 256 times. (Thing-around measurement method). In this case, the time measuring means 16 measures the number of repetitions and the total time. Assuming that the distance between the ultrasonic transceivers 8 and 9 is L, the flow velocity of the fluid is V, and the sound velocity of the ultrasonic wave propagating in the fluid is C, the ultrasonic transceiver 9 on the downstream side from the ultrasonic transceiver 8 on the upstream side. ultrasonic wave propagation time to the _{T up -> down} and downstream from the ultrasonic transceiver 9 of the upstream side of the ultrasonic transducer 8 ultrasonic wave propagation time T _{dow
n-> up} is shown as follows.

T _{up-> down} = L / [C + V cos (θ)]
_{Tdown-> up} = L / [C-Vcos (θ)]
Than this,
C + V cos (θ) = L / T _{up-> down}
C-Vcos (θ) = L / T _{down-> up}
Therefore,
2 × C = L [(1 / T _{up-> down} ) + (1 / T _{down-> up} )]
From this, the sound speed of the ultrasonic wave is added to the above two formulas,
C = (L / 2) × [(1 / T _{up-> down} ) + (1 / T _{down-> up} )]
It becomes.

The fluid flow velocity V is calculated by subtracting the above two formulas.
2 × V cos (θ) = L [(1 / T _{up-> down} )-(1 / T _{down-> up} )]
It becomes. From this, the flow velocity V of the fluid is
V = [L / 2 × cos (θ)] × [(1 / T _{up −−> down} ) − (1 / T _{down −−> up} )] is calculated.

Here, since the ultrasonic transmitter / receiver distance L and the crossing angle θ are constants determined in advance, the ultrasonic propagation times T _{up-> down} and T _{down-> up} are measured by the time measuring means 16. By doing so, the flow velocity V of the fluid is obtained. Further, the flow rate Qcal of the fluid is calculated by multiplying the predetermined cross-sectional area of the flow path 7. The above calculation processing is performed by the flow rate calculation means 17.

  FIG. 2 shows signals transmitted and received by the ultrasonic transceivers 8 and 9. A rectangular wave 19 indicates a transmission signal applied to the ultrasonic transmitter / receiver 8 or 9. A sinusoidal signal 20 indicates a reception signal received and amplified by the ultrasonic transmitter / receiver 8 or 9. In general, the reception point for time measurement often uses the next zero cross point 22 that exceeds a certain threshold (broken line 21). In this case, the rising time Tst of the rectangular wave of the transmission signal is the transmission start time, and the zero cross point 22 is the reception time Tar. Therefore, the propagation time Tpr of the measured ultrasonic wave is the time between the time Tar and the time Tst. That is, Tpr = Tar−Tst.

  However, as is apparent from the received signal 20 in FIG. 2, the time when the transmitted ultrasonic wave is received by the ultrasonic transmitter / receiver 8 or 9 is Tre, which is the head of the received signal 20. The time delay Td between the time Tre and the time Tar can be considered as the time delay Td until the reception unit 15 receives the ultrasonic wave after the ultrasonic wave arrives at the reception-side ultrasonic transmitter / receiver 8 or 9.

This time delay Td greatly depends on the individual characteristics of the ultrasonic transceiver 8 or 9. Therefore, in the ultrasonic propagation time T up- _{> down} from the upstream ultrasonic transmitter / receiver 8 to the downstream ultrasonic transmitter / receiver 9, the downstream ultrasonic wave which is the ultrasonic transmitter / receiver on the receiving side is included. Td9 determined by the characteristics of the transceiver 9 is included. Further, in the ultrasonic propagation time _{Tdown-> up} from the downstream ultrasonic transmitter / receiver 9 to the upstream ultrasonic transmitter / receiver 8, the upstream ultrasonic transmission / reception which is the ultrasonic transmitter / receiver on the reception side is included. Td8 determined by the characteristics of the device 8 is included.

In this way, the inherent times Td8 and Td9 determined by the characteristics of the ultrasonic transmitter / receiver are stored in advance in the offset value storage unit 18 as offset values, and the ultrasonic propagation measured respectively during the flow rate calculation described above. Time T _{up-> down} and By subtracting the respective offset values Td8 and Td9 from Tdown- _{> up} , a more accurate ultrasonic propagation time can be obtained, and a more accurate flow rate value is calculated. In the case of the present embodiment, the upstream and downstream offset values are 2.5 times the period of the received waveform received by each of the ultrasonic transceivers 8 and 9. Thus, by subtracting the offset value of the ultrasonic transceiver on the receiving side from the measured ultrasonic propagation time, the flow value can be calculated with high accuracy, and a highly accurate flow measuring device can be realized.

  What has been described above can be expressed by the following formula.

That is, the formula V = [L / 2 × cos (θ)] × [(1 / T _{up-> down} )-(1 / T _{down-> up} )]
T up- _{> down} = Tud + Td9 = Tud × [1+ (Td9 / Tud)]
Tdown- _{> up} = Tdu + Td8 = Tdu × [1+ (Td8 / Tdu)]
It is.

  Here, the time during which the ultrasonic wave propagates in the fluid from the upstream side to the downstream side or from the downstream side to the upstream side is defined as Tud and Tdu, respectively. In normal cases, the times Tud and Tdu during which ultrasonic waves propagate in the fluid are approximately 100 to 300 μsec, and the times Td8 and Td9 are sufficiently small, approximately 1 to 5 μsec, which is several times the period of the ultrasonic waves. . Therefore, the above equation can be approximated as follows.

1 / T up- _{> down} = 1 / {Tud × [1+ (Td9 / Tud)]}
≒ (1 / Tud) x [1- (Td9 / Tud)]
1 / T down- _{> up} = 1 / {Tdu × [1+ (Td8 / Tdu)]}
≒ (1 / Tdu) x [1- (Td8 / Tdu)]
When these are used, the flow velocity V of the fluid is as follows.

V = [L / 2 × cos (θ)] × [(1 / Tud) × {1+ (Td9 / Tud)}
− (1 / Tdu) × {1+ (Td8 / Tdu)}]
For example, when the flow of fluid is stopped here, the propagation time Tud from the upstream side to the downstream side of the ultrasonic wave and the propagation time Tdu from the downstream side to the upstream side are the distance L between the ultrasonic transceivers and the sound velocity C Therefore, Tud = L / C and Tdu = L / C, which are completely equal. Assuming that time is T0, the apparent flow velocity Vz at that time is
Vz = [L / 2 × cos (θ)] × [(1 / T0) × {1+ (Td9 / T0)}
− (1 / T0) × {1+ (Td8 / T0)}]
= [L / 2 × cos (θ)] × [(Td9−Td8) / T0 ^ 2]
It becomes.

  Here, L and θ are constants fixed by the flow path, and can be considered as constant values. The time T0 is also a value determined when the ultrasonic sound velocity C is determined, and can be considered as a fixed value. This indicates that the Vz value is determined when the offset values Td8 and Td9 of the ultrasonic transceiver are determined.

  Thus, when there is a difference between the values Td9 and Td8 unique to the ultrasonic transmitter / receiver, the flow velocity Vz as described above appears even if the fluid flow is zero. When this flow velocity Vz is multiplied by the cross-sectional area of the flow path, an offset flow rate Qz as an apparent flow rate is obtained. This value Qz may be stored in advance as an offset value, and the flow rate value Qcal calculated above may be corrected.

  As described above, by storing the offset value, an accurate flow rate value can be calculated.

(Embodiment 2)
A method for obtaining the period of the received signal, which is an offset value of the ultrasonic transceiver, will be described with reference to FIG. FIG. 3 shows a received signal 20 received by the ultrasonic transmitter / receiver 8 or 9 on the upstream side or the downstream side shown in FIG. In the normal case, the time Tar of the next zero cross point 22 that exceeds the threshold value (broken line 21) is the reception time. However, when the offset value is to be measured, the second zero cross point 23 that exceeds the threshold value is received. The time Tar ′ is measured, and the difference Tar′−Tar is calculated as one period of the received signal. Alternatively, the threshold value (broken line 21) may be increased and the zero cross point Tar ′ may be measured as a new threshold value (not shown).

  Further, the amplification factor of the received signal is decreased, the threshold value (broken line 21) is left as it is, the amplitude of the received signal 20 is decreased as a whole, and the next zero cross point exceeding the threshold value (broken line 21) is measured. And the time Tar ′ can be measured.

  As described above, the accurate flow rate value can always be calculated by measuring the period of the received signal every time measurement is performed and setting the 2.5 times as the offset value.

(Embodiment 3)
The third embodiment will be described with reference to FIG. The difference from the first embodiment is that an environmental change detection means 24 such as a fluid temperature detection means, a fluid type detection means or a fluid pressure detection means is provided. For this reason, only when it is considered that the temperature, type, or pressure of the fluid has changed due to the environment change detection means 24 and the offset value has changed, the upstream and downstream ultrasonic transceivers 8 shown in the second embodiment. , 9 is measured, and the offset value can be updated efficiently by measuring the period of the received signal as an offset value.

  Therefore, it is not always necessary to measure the offset value every time the flow rate is calculated, the offset value can be updated efficiently, and the measurement time can be shortened. Of these environmental change factors, the largest fluctuation in the offset value was the temperature of the fluid. Therefore, it is most effective to configure the environment change detecting means 24 by at least the temperature detecting means.

(Embodiment 4)
In the third embodiment, although the fluid temperature detection means is provided, a method for detecting the fluid temperature from the propagation velocity of the ultrasonic wave propagating in the fluid will be described. In this case, it is not necessary to detect the temperature as the environment change detecting means 24, the temperature of the fluid can be detected as long as the propagation time of the ultrasonic wave can be measured, and the configuration of the flow rate measuring device is simplified.

In the first embodiment, it has been shown that the ultrasonic wave propagation velocity and the sound velocity C are calculated by the following equations. That is,
C = (L / 2) × [(1 / T _{up-> down} ) + (1 / T _{down-> up} )]
It is.

In this way, the ultrasonic wave propagation speed C can be detected by measuring the ultrasonic wave propagation times T _{up-> down} and T _{down-> up} . For example, when the fluid is air, the sound velocity Cair in the air is represented by the sound velocity Cair = 341.45 + 0.607 × Tair [m / sec], where the temperature of the air is Tair [° C.]. Therefore, if the sound velocity Cair can be measured, the air temperature Tair can be calculated. In addition, when the fluid is water, if the water temperature is Twater, the underwater sound velocity Cwater = 1500 + 25 × Twater [m / sec] is indicated, so if the sound velocity Cwater can be measured, the water temperature Twater can be calculated.

  In this way, the temperature of the fluid can be detected without providing temperature detecting means as environmental change detecting means, and the configuration of the flow rate measuring device is simplified. In addition, since the temperature of the fluid can be measured by the time measuring means in the same manner as when the flow velocity V is measured, the configuration becomes very simple.

(Embodiment 5)
A fifth embodiment will be described with reference to FIGS. 1 and 5. FIG. 5 shows the relationship between the offset value based on the reception period measured from the reception signals of the ultrasonic transceivers 8 and 9, the difference between Td8 and Td9, and the offset flow rate Qz as the apparent flow rate on the vertical axis. Show. As seen in the figure, this relationship shows a relationship approximated by a linear function s,
Qz = A × (Td8−Td9) + B
It is expressed by Here, A and B are predetermined constants.

  For example, the flow path shown in FIG. 1 provided with an ultrasonic transmitter / receiver having such offset values, Td8 and Td9, is prepared, the upstream and downstream are closed, and the flow rate value is calculated in the absence of flow. A constant B is newly obtained so that the calculated flow rate value Qz becomes zero, and the two constants A and B are updated (A is unchanged). In this way, the constants A and B are stored as offset values. Thus, by determining the constants A and B, it is possible to realize a flow rate measuring apparatus that calculates a stable and accurate flow rate value.

From the above description, according to the flow rate measuring apparatus in the embodiment of the present invention, the following effects can be obtained.
(1) Since the offset value is stored, a stable and accurate flow rate value can be calculated.
(2) Since the offset value can be measured from the received signal, the flow value can always be calculated stably and accurately.
(3) Since the environment change detecting means is provided, the offset value may be measured only when the environment change is detected, and the offset value can be updated efficiently.
(4) Since the temperature of the fluid can be detected from the propagation time of the ultrasonic wave, a flow measuring device with a simple configuration can be realized.
(5) Since the offset value is updated in a state where there is no flow rate in advance, a stable and accurate flow rate measuring device can be realized.

The block diagram of the flow measuring device of Embodiment 1, 5 of this invention Ultrasonic wave transmission / reception waveform diagram of the first embodiment Ultrasonic wave transmission / reception waveform diagram of embodiment 2 of the present invention Block diagram of a flow rate measuring apparatus according to Embodiment 3 of the present invention Ultrasonic characteristic chart in Embodiment 5 of the present invention Block diagram of a conventional flow measurement device

Explanation of symbols

7 Flow path 8 Upstream ultrasonic transmitter / receiver 9 Downstream ultrasonic transmitter / receiver 13 Transmitting means 14 Switching means 15 Receiving means 16 Time measuring means 17 Flow rate calculating means 18 Offset value storage means 19 Transmitting waveform 20 Received waveform 21 Threshold 24 Environmental change detection means

Claims (2)

A pair of ultrasonic transmitters / receivers are provided oppositely on the upstream side and downstream side of the flow path of fluid, time measuring means for measuring ultrasonic propagation time between the pair of ultrasonic transmitters / receivers, and ultrasonic propagation time A flow rate measurement device comprising: a flow rate calculation unit that calculates a flow rate of fluid from the flow rate; and an offset value storage unit that stores an offset flow rate value used for flow rate calculation. A pair of ultrasonic transmitters / receivers are provided oppositely on the upstream side and downstream side of the flow path of fluid, time measuring means for measuring ultrasonic propagation time between the pair of ultrasonic transmitters / receivers, and ultrasonic propagation time A flow rate measuring device comprising: a flow rate calculation means for calculating a flow rate of fluid from the flow rate; and an offset value storage means for storing an offset value used for the flow rate calculation, and obtaining an offset flow rate value in a state where no fluid is flowing.

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