The present invention relates to an ultrasonic flowmeter that measures a propagation time of ultrasonic waves by use of a pair of transmittable/receivable ultrasonic transducers, thereby measuring a flow volume of a measurement target fluid.
Under an ultrasonic wave propagation time measurement method used in a related-art ultrasonic flowmeter, a pair of transmittable/receivable ultrasonic transducers are placed opposite each other. One of the ultrasonic transducers is driven by means of a burst signal, thereby transmitting ultrasonic waves. The other ultrasonic transducer receives the ultrasonic waves, to thus measure a propagation time of the ultrasonic waves (see; for instance, Patent Document 1).
As shown in
The measurement method is now described by reference to
In
Specifically, since the receiving start time point R0 cannot be detected with high accuracy, the starting time point T0 of the drive waveform W1 and the receiving start time point R0 can be indirectly measured by utilization of the end point R1 of the mth wave.
In order to attain further improvements in accuracy, a reflected wave is actually received to thereby enhance measurement accuracy. The principle of improvement of measurement accuracy is described hereunder.
Receive delay time measurement means provided in the propagation time measurement block 5 measures a time Tp elapsed from when a transmission-side ultrasonic transducer transmits ultrasonic waves by means of a driving waveform W1 until when a receiving-side ultrasonic transducer receives a first received waveform W2. Next, the measurement means measures a time Tp2 elapsed from when the receiving-side ultrasonic transducer and the transmission-side ultrasonic transducer each reflect the ultrasonic waves once until when the receiving-side ultrasonic transducer receives a second receive waveform W4. In other words, the ultrasonic waves reflected by the receiving-side ultrasonic transducer arrives as a waveform W3 at the transmission-side ultrasonic transducer. The ultrasonic waveform further undergoes reflection on the transmission-side ultrasonic transducer, thereupon arriving as a receive waveform W4 at the receiving-side ultrasonic transducer. If the arrival of the ultrasonic waveform is taken as a second receipt of the waveform, a true propagation time Tp0 unsusceptible to a shape of a received waveform, or the like, can be determined by the following equation (Eq. 1). Thus, it is possible to prevent deterioration of measurement accuracy due to an error in true propagation time, which would otherwise be caused when a receive waveform is changed by variations in characteristic of the ultrasonic transducer, a temperature change, or a waveform reflected by the measurement flow path.
Tp0=(Tp2−Tp)/2  (Eq. 1)
PTL1: JP-A-2005-172556
However, in the related-art configuration, measurement is continually performed each time until reflected waveforms are generated. Hence, there are problems; namely, an increase in current consumption, the impossibility of performance of accurate measurement because of a shape of a receive waveform being distorted by reflection, and complication of measurement software.
The present invention solves the problems of the related art and aims at providing an ultrasonic flowmeter that exhibits improved measurement accuracy and accomplishes lower current consumption by measuring for each propagation time a correction value for a difference between a true propagation time and a measured propagation time.
In order to solve the aforementioned problems of the conventional apparatus, an ultrasonic flowmeter according to the present invention includes, a measurement flow path through which a measurement target fluid flows; a pair of ultrasonic transducers that are placed in the measurement flow path and that can transmit and receive an ultrasonic signal; a propagation time measurement block for measuring a propagation time elapsed before the ultrasonic signal transmitted from one of the pair of ultrasonic transducers arrives at the other ultrasonic transducer after propagating through a measurement target fluid; a propagation time correction block for correcting the propagation time measured by the propagation time measurement block, to thus calculate a corrected propagation time; and a control block for calculating a flow volume of the measurement target fluid from the corrected propagation time, wherein the propagation time correction block has correction value calculation means for calculating a correction value used for correcting the propagation time measured by the propagation time measurement block from a true propagation time previously measured under predetermined conditions.
Even when a receive waveform is changed by variations in ultrasonic transducer, a temperature change, or the like, a correction value for each of propagation times is calculated from a previously-measured true propagation time. Therefore, an accurate propagation time can be measured at all times.
The ultrasonic flowmeter of the present invention can calculate an accurate propagation time of ultrasonic waves at all times without being affected by variations in ultrasonic transducer, a temperature change, or waves reflected from an interior of a flow path. Accordingly, an ultrasonic flowmeter with extremely high precision involving lower current consumption can be implemented.
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A first invention includes a measurement flow path through which a measurement target fluid flows; a pair of ultrasonic transducers that are placed in the measurement flow path and that can transmit and receive an ultrasonic signal; a propagation time measurement block for measuring a propagation time elapsed before the ultrasonic signal transmitted from one of the pair of ultrasonic transducers arrives at the other ultrasonic transducer after propagating through a measurement target fluid; a propagation time correction block for correcting the propagation time measured by the propagation time measurement block, to thus calculate a corrected propagation time; and a control block for calculating a flow volume of the measurement target fluid from the corrected propagation time, wherein the propagation time correction block has correction value calculation means for calculating a correction value used for correcting the propagation time measured by the propagation time measurement block from a true propagation time previously measured under predetermined conditions, whereby the flow volume can be calculated from the true propagation time, and measurement accuracy of an ultrasonic flowmeter can be enhanced.
A second invention includes a measurement flow path through which a measurement target fluid flows; a pair of ultrasonic transducers that are placed in the measurement flow path and that can transmit and receive an ultrasonic signal; a propagation time measurement block for measuring a propagation time elapsed before the ultrasonic signal transmitted from one of the pair of ultrasonic transducers arrives at the other ultrasonic transducer after propagating through a measurement target fluid; a propagation time correction block for correcting the propagation time measured by the propagation time measurement block, to thus calculate a corrected propagation time; and a control block for calculating a flow volume of the measurement target fluid from the corrected propagation time, wherein the propagation time correction block has correction value calculation means for calculating for each propagation time a correction value used for correcting the propagation time measured by the propagation time measurement block from a true propagation time previously measured under predetermined conditions, storage means for storing a correction value calculated by the correction value calculation means, and correction value selection means for selecting from correction values stored in the storage means a correction value suitable for the propagation time measured by the propagation time measurement block, whereby the flow volume can be calculated from the true propagation time and measurement accuracy of an ultrasonic flow meter can be enhanced.
In a third invention based on the first or second invention, the measurement fluid target is a gas; and the correction value calculation means is configured so as to calculate a relationship at an arbitrary temperature between a propagation time and a correction value from a true propagation time that has been measured by changing a temperature while a kind of gas is kept constant as a predetermined condition. As a result, a correction value at each propagation time acquired when the kind of gas is fixed can be calculated, so that a correction can be made for each temperature. Even when a change has occurred in temperature, the measurement accuracy of the ultrasonic flowmeter can be enhanced.
In a fourth invention based particularly on the first or second invention, the measurement fluid target is a gas; and the correction value calculation means is configured so as to calculate a relationship for an arbitrary kind of gas between a propagation time and a correction value from a true propagation time that has been measured by changing a kind of gas while a temperature is kept constant as a predetermined condition. As a result, a correction value for each propagation time achieved when the temperature is fixed can be calculated, so that a correction can be made for each kind of gas. Even when a change has occurred in temperature, the measurement accuracy of the ultrasonic flowmeter can be enhanced.
In a fifth invention based particularly on any one of the first through fourth inventions, the correction value calculation means calculates a correction value when the flow volume of the measurement target fluid is zero. The correction value is calculated at timing when there is no flow volume, whereby current consumption can be diminished.
Embodiments of the present invention are hereunder described by reference to the drawings. The present invention, however, shall not be limited to the embodiments.
As shown in
Working and operation of the above-configured ultrasonic flowmeter are now described.
First, the correction value calculation means 9 that calculates an appropriate correction value according to a kind of gas that is a measurement target fluid is configured so as to be able to calculate for each propagation time a correction value taking into account variations in characteristics of the ultrasonic transducers, a delay between transmission of ultrasonic waves from the transmission-side ultrasonic transducer and commencement of measurement of a propagation time, a delay between arrival of ultrasonic waves at the receiving-side ultrasonic transducer and detection of the ultrasonic waves performed by a receipt detection circuit, and a difference between the measured propagation time and a true propagation time resultant from combination of a received wave with a reflected wave. The correction value calculation means 9 calculates a correction value from a propagation time acquired through actual measurement of a flow rate and makes a correction to the propagation time measured by the propagation time measurement block 5, thereby calculating a true propagation time.
Incidentally, it is also possible for the correction value calculation means 9 to obtain beforehand a computing equation that enables calculation of a correction value from a relationship between a true propagation time measured under the method using (Eq. 1) described in connection with the related art and a propagation time Tp0 shown in
As above, the present embodiment is equipped with the propagation time correction block 11 that makes a correction to a propagation time by means of the correction value calculation means 9 calculating a correction value from the propagation time measured by the propagation time measurement block 5. It is thereby possible to make corrections to variations in characteristics of the ultrasonic transducers, a delay between transmission of ultrasonic waves from the transmission-side ultrasonic transducer and commencement of measurement of a propagation time, a delay between arrival of ultrasonic waves at the receiving-side ultrasonic transducer and detection of the ultrasonic waves performed by a receipt detection circuit, and influence resultant from combination of a received wave with a reflected wave.
In
Working and operation of the above-configured ultrasonic flowmeter are hereunder described.
First, the correction value calculation means 9 that calculates an appropriate correction value according to a kind of gas calculates for each propagation time a correction value taking into account variations in characteristics of the ultrasonic transducers, a delay between transmission of ultrasonic waves from the transmission-side ultrasonic transducer and commencement of measurement of a propagation time, a delay between arrival of ultrasonic waves at the receiving-side ultrasonic transducer and detection of the ultrasonic waves performed by a receipt detection circuit, and a difference between the measured propagation time and a true propagation time resultant from combination of a received wave with a reflected wave; and then stores the thus-calculated correction value into the storage means 14. The correction value selection means 10 selects a suitable correction value in accordance with a propagation time measured when a flow volume measurement has been actually performed and makes a correction to the propagation time, thereby calculating a true propagation time.
Meanwhile, the correction value calculation means 9 can also be arranged so as to calculate a correction value from a relationship between a true propagation time measured by the method using (Eq. 1) described in connection with the related art and the propagation time Tp0 shown in
As above, in the present embodiment, the propagation time correction block 12 has the correction value calculation means 9 for calculating a correction value to be made on a propagation time and the correction value selection means 10 for selecting a correction value conforming to the propagation time measured by the propagation time measurement block 5. It is thereby possible to make corrections to variations in characteristics of the ultrasonic transducers, a delay between transmission of ultrasonic waves from the transmission-side ultrasonic transducer and commencement of measurement of a propagation time, a delay between arrival of ultrasonic waves at the receiving-side ultrasonic transducer and detection of the ultrasonic waves performed by a receipt detection circuit, and influence, such as that resulting from combination of a received wave with a reflected wave.
The correction value calculation means 9 is also set so as to calculate a correction value when there is no flow, so that measurement accuracy can be enhanced with low power consumption.
If the correction value calculation means 9 is configured so as to calculate a relationship between a temperature and a correction value by means of fixing a kind of gas and changing a temperature at two or more points, a correction will be made at each temperature. Therefore, even when a temperature change occurs, the measurement accuracy of the ultrasonic flowmeter can be enhanced.
If the correction value calculation means 9 is configured so as to calculate a relationship between a kind of gas and a correction value by fixing a temperature and changing a kind of gas, the measurement accuracy of the ultrasonic flowmeter can be enhanced even when a change occurs in the kind of gas.
This invention is intended to contain, as a range to be protected, various changes and applications performed by those skilled in the art based on the description of the specification and well known techniques without departing from the gist and range of this invention. Further, the constituent elements of the aforesaid embodiments may be arbitrarily combined within a range not departing from this invention.
This invention is based on Japanese Patent Application (Japanese Patent Application No. 2010-001686) filed on Jan. 7, 2010, the content of which is incorporated herein by reference.
As above, since the ultrasonic flowmeter of the preset invention makes a correction at each propagation time, there is obviated a necessity to take into account characteristics of the ultrasonic transducers and influence of a reflected wave. Since an accurate propagation time of ultrasonic waves can be measured at all times, an extremely highly accurate ultrasonic flowmeter can be implemented. Therefore, the present invention can be applied to use applications, like a flow measurement standard, a gas meter, and a water meter.
1 MEASUREMENT FLOW PATH
2, 7 ULTRASONIC TRANSDUCER
5 PROPAGATION TIME MEASUREMENT BLOCK
9 CORRECTION VALUE CALCULATION MEANS
10 CORRECTION VALUE SELECTION MEANS
11 PROPAGATION TIME CORRECTION BLOCK
12 PROPAGATION TIME CORRECTION BLOCK
14 STORAGE MEANS
Number | Date | Country | Kind |
---|---|---|---|
2010-001686 | Jan 2010 | JP | national |
Filing Document | Filing Date | Country | Kind | 371c Date |
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PCT/JP2011/000028 | 1/6/2011 | WO | 00 | 6/29/2012 |