ULTRASONIC TYPE FLOWMETER APPARATUS AND METHOD OF USING THE SAME
1. Field of the Invention The present invention relates to an ultrasonic type flowmeter apparatus and a method of using the same. Particularly, the present invention relates to an ultrasonic type flowmeter apparatus preferably used in a cardiac surgery for measuring a flow rate of a blood flowing through an auxiliary heart, in which a part of the ultrasonic type flowmeter apparatus is disposed in order to avoid undesired infection. 2. Related Art Statements The ultrasonic type flowmeter apparatus comprises a conduit having, for instance a crank shape, and a pair of piezo-electric transducer elements each serving as an ultrasonic signal transmission and reception element are provided at both ends of a straight portion of the conduit. To this end, the conduit must include fitting portions, and furthermore the conduit has to comprise an inlet portion and an outlet portion. It is difficult to make the conduit by a single molding of synthetic resin. Therefore, usually a plurality of parts of the conduit are formed separately, and then these parts are assembled or composed by fusing or cementing to form the final conduit. According to the above assembling operation, beads and debris might be produced within the straight portion of the conduit through which an ultrasonic beam propagates during the measurement. Moreover, centerlines of the fused parts might not be coincided with each other, and therefore a liquid could not flow through the conduit smoothly and an undesired turbulence might be generated. Furthermore, a length and an inner diameter of the straight portion might include error and a precision of securing the ultrasonic signal transmission and reception elements might be lowered. Therefore, flow characteristics of respective conduits are sometimes different from one another. In order to compensate the differences in the flow characteristics of respective crank-shaped conduits or inner reflection type conduits, it has been known to derive calibration data from measured values obtained in electrical measuring circuits by flowing a standard liquid such as water at known rates through the respective conduits. Then, the thus obtained calibration data is stored in memories installed in respective electrical measuring circuits. A pair of a conduit and a measuring circuit having a memory storing calibration data obtained for the relevant conduit is shipped from a factory. In the Patent Publication 1, there is disclosed a blood flowmeter apparatus for monitoring a blood flow rate during the cardiac surgery. In this field, the conduit can be used only once, and the used conduit has to be disposed together with an auxiliary artificial heart after the cardiac surgery in order to avoid infection. However, the electrical measuring circuit is more expensive than the conduit, and therefore it is desired to use the measuring circuit repeatedly. In the Patent publications 2 and 3, there are proposed disposable type conduits for use in blood flowmeter apparatuses in which the measuring circuit is used repeatedly. In the ultrasonic type flowmeter apparatuses using the disposable conduits, it is desired to derive calibration data by flowing standard liquid such as water through a conduit at known flow rates. Even if the thus derived calibration data is stored in the electrical measuring circuit, it is rather difficult to correlate the calibration data with plural conduits, when the electrical measuring circuit is repeatedly used. In the Patent Publication 3, there is described that since a variation of inner diameters of conduits is not larger than 1%, it is unnecessary to derive the calibration data before the actual measurement. However, in practice, a fluctuation of flow characteristics of respective conduits due to errors in processing the conduits could not be ignored as described above. In the known ultrasonic type flowmeter apparatuses described in the Patent Publications 2 and 3, piezo-electric elements serving as the ultrasonic signal transmission and reception elements are repeatedly used. That is to say, after the measurement, these elements are removed from a used conduit and before conducting a new measurement; the removed elements are secured to a new conduit. Conditions of securing the piezo-electric elements to the conduit might affect largely the measurement precision, but a degree of the affection of the securing condition to the measurement could not be known. Therefore, it has been impossible to assure the accurate measurement when the piezo-electric elements are repeatedly used. The present invention has for its object to provide a novel and useful ultrasonic type flow sensor which can remove the above mentioned drawbacks of the known flowmeter apparatuses and can attain a high measurement precision by deriving calibration data before measurement, storing the thus derived calibration data in a memory installed in a disposable conduit, and reading the thus stored calibration data into a repeatedly used electrical measuring circuit upon the actual measurement. According to the invention, an ultrasonic type flowmeter apparatus includes a disposable unit and a non-disposable unit, characterized in that said disposable unit comprises a conduit having a straight pipe portion through which a liquid whose flow rate is to be measured is flown, an inlet pipe portion arranged at an upstream position for introducing the liquid into the straight pipe portion, and an outlet pipe portion arranged at a downstream position for drawing the liquid from the straight pipe portion, said straight pipe portion, inlet pipe portion and outlet pipe portion being coupled with one another; a pair of ultrasonic signal transmission and reception elements arranged at the upstream position and a downstream position, respectively of said straight pipe portion; and a memory portion for storing calibration data specific to the relevant conduit, said calibration data being obtained from a standard electrical measuring circuit by flowing a standard liquid through the conduit at known flow rates; and that said non-disposable unit comprises an electrical measuring circuit portion for reading the calibration data out of said memory portion upon an actual measurement, driving said pair of the ultrasonic signal transmission and reception elements to emit ultrasonic beams alternately, receiving ultrasonic signal generated from the ultrasonic signal transmission and reception elements which receive the ultrasonic beams, calculating flow rates by processing the ultrasonic signals and correcting the flow rates in accordance with the calibration data. According to another aspect of the invention, a method of using an ultrasonic type flowmeter apparatus as defined above, wherein said method includes a step of deriving the calibration data specific to the relevant conduit by flowing the standard liquid through the conduit at known flow rates; a step of storing the calibration data into said memory portion; a step of reading the calibration data stored in the memory portion into the electrical measuring circuit portion upon the actual measurement; a step of driving said pair of the ultrasonic signal transmission and reception elements to emit ultrasonic beams alternately; a step of receiving ultrasonic signal generated from the ultrasonic signal transmission and reception elements which receive the ultrasonic beams; and a step of processing the ultrasonic signals together with the calibration data to derive corrected flow rates of the liquid. In the ultrasonic type flowmeter apparatus according to the invention, the calibration data is stored in the memory portion fixed to the disposable conduit, upon the actual measurement the calibration data stored in the memory portion is read into the electrical measuring circuit portion which is non-disposable, and the ultrasonic signals generated from the ultrasonic signal transmission and reception elements are processed in the electrical measuring circuit portion in accordance with the calibration data. In this manner, it is possible to derive the flow rate accurately corrected by the calibration data. Moreover, the rather expensive electrical measuring circuit portion can be used repeatedly, and therefore a running cost of the whole system can be reduced. In the drawings, a reference numeral 1 denotes a conduit, 1 Now embodiments of the ultrasonic flow sensor according to the invention will be explained in detail with reference to the attached drawings. The conduit 1 made of a synthetic resin such as polypropylene and Teflon (registered trade mark) comprises a straight pipe portion 1 The straight pipe portion 1 The conduit 1 is consisting of members, i.e. a straight pipe member 1 The above mentioned three members 1 The inlet and outlet pipe members 1 Lead wires 8 Upon securing the piezo-electric elements 2 Since the O-rings 5 are inserted between the locking members 6 and the pushing members 4, the piezo-electric elements 2 In general, flow characteristics of the conduits of the ultrasonic type flowmeter apparatus differ from respective conduits. Also in the ultrasonic type flowmeter apparatus according to the invention, flow characteristics of respective conduits are affected by various factors such as deviations of axial lines of the combined pipe portions 1 In the present embodiment, respective conduits are used together with a standard measuring circuit to measure a flow rate while flowing a liquid under known flow rate. Then, the measured flow rate is compared with the actual flow rate to derive calibration data. The calibration data thus derived is stored in the memory chip 10 via the signal wires 9 In actual measurement, the calibration data stored in the memory chip 10 is read out and is supplied to the measuring circuit, and actually measured value is calibrated in accordance with the calibration data to derive a correct flow rate. In this manner, any conduits can be used for any measuring circuits. To this end, each of the measuring circuits has the same characteristic as the standard measuring circuit used for deriving the calibration data. Therefore, any conduits each having specific calibration data stored in the memory chip can be used for any measuring circuits having the same specifications or model numbers. In this manner, according to the invention, the rather expensive measuring circuit can be used repeatedly without being disposed. In order to derive the calibration data, a standard flowmeter 21 and pump 24 are connected to the conduit 1 via tubes 22 and 23 as shown in In an actual measuring of flow rate of blood, a sterilized conduit 1 having the calibration data stored therein is held on a holder 31 made of synthetic resin as illustrated in A longer portion of each of the walls 31 The conduit 1 is set on the holder 31 as depicted in As illustrated in Before measuring the flow rate, the calibration data stored in the memory chip 10 installed in the conduit 1 is read into the calculation and control circuit portion of the electrical measuring circuit portion 32. The calculation and control circuit portion produces a calibration equation or calibration table from the calibration data read out of the memory chip 10. Since the calibration data stored in the memory chip 10 is derived at discrete flow rates, additional calibration data for flow rates situating between the discrete flow rates is derived by the interpolation method. It should be noted that the calibrating operation may be conducted not only by preparing a calibrating equation, but also by correcting output signals obtained from the conduit 1 in accordance with the calibration data. Next, the inlet and outlet pipe portions 1 During the operation, the auxiliary artificial heart pump 35 makes a blood flow passing through the inlet pipe portion 1 The ultrasonic beam B emitted from the piezo-electric element 2 A propagation speed of the ultrasonic beam B emitted from the piezo-electric element 2 After the measurement, the plugs 11 In the embodiment so far explained, the members 1 Furthermore, a means for securing the piezo-electric elements 2 In the above embodiment, the signal wires 9 Furthermore, a wireless IC tag may be used instead of the memory chip 10. Alternatively, the memory chip 10 may be replaced by a label having a bar code representing calibration data. Then, the bar code is read by a bar code reader to derive the calibration data. In the above explained embodiment, the flowing speed of the blood is first calibrated in accordance with the calibration data read out of the memory chip 10, and then the flow rate is calculated from the thus calibrated flow speed. According to the invention, the calibration may be performed in various ways. For instance, a flow rate calculated from a measured flow speed may be corrected in accordance with calibration data. It should be noted that in the present invention, the calibration for the flow rate includes a case in which a flow speed is calibrated. In the embodiment mentioned above, the conduit 1 is formed as the crank-type conduit, but according to the invention a pair of piezo-electric elements may be secured to the straight pipe portion such that the ultrasonic beams propagate within the straight pipe portion in inclined directions with respect to a center axial line. In the above embodiment, the flow rate of blood is measured, but the ultrasonic type flowmeter apparatus according to the invention may be equally applied to any other liquid such as liquid containing medicines and biological molecular substances. Also in such cases, the conduit must be disposed after being used once. The ultrasonic type flowmeter apparatus according to the invention is preferably used for measuring a flow rate under such circumstance that the conduit should be disposed after being used once, but it is apparent that the conduit of the ultrasonic type flowmeter apparatus according to the invention may be used repeatedly. A disposable conduit 1 includes piezo-electric elements 2 1. An ultrasonic type flowmeter apparatus comprising:
a disposable unit; and a non-disposable unit, wherein said disposable unit comprises:
a conduit having a straight pipe portion through which a liquid whose flow rate is to be measured is flown, an inlet pipe portion arranged at an upstream position for introducing the liquid into the straight pipe portion, and an outlet pipe portion arranged at a downstream position for drawing the liquid from the straight pipe portion, said straight pipe portion, inlet pipe portion and outlet pipe portion being coupled with one another; a pair of ultrasonic signal transmission and reception elements arranged at the upstream position and a downstream position, respectively of said straight pipe portion; and a memory portion for storing calibration data specific to the relevant conduit, said calibration data being obtained from a standard electrical measuring circuit by flowing a standard liquid through the conduit at known flow rates; and wherein said non-disposable unit comprises: an electrical measuring circuit portion for reading the calibration data out of said memory portion upon an actual measurement, driving said pair of the ultrasonic signal transmission and reception elements to emit ultrasonic beams alternately, receiving ultrasonic signal generated from the ultrasonic signal transmission and reception elements which receive the ultrasonic beams, calculating flow rates by processing the ultrasonic signals, and correcting the flow rates in accordance with the calibration data. 2. The ultrasonic type flowmeter apparatus according to 3. The ultrasonic type flowmeter apparatus according to 4. The ultrasonic type flowmeter apparatus according to 5. The ultrasonic type flowmeter apparatus according to 6. The ultrasonic type flowmeter apparatus according to 7. The ultrasonic type flowmeter apparatus according to 8. A method of using the ultrasonic type flowmeter apparatus according to deriving the calibration data specific to the relevant conduit by flowing the standard liquid through the conduit at known flow rates; storing the calibration data into said memory portion; reading the calibration data stored in the memory portion into the electrical measuring circuit portion upon the actual measurement; driving said pair of the ultrasonic signal transmission and reception elements to emit ultrasonic beams alternately; receiving ultrasonic signal generated from the ultrasonic signal transmission and reception elements which receive the ultrasonic beams; and processing the ultrasonic signals together with the calibration data to derive corrected flow rates of the liquid. 9. The method according to 10. The ultrasonic type flowmeter apparatus according 11. The ultrasonic type flowmeter apparatus according 12. The ultrasonic type flowmeter apparatus according to 13. The ultrasonic type flowmeter apparatus according to 14. The ultrasonic type flowmeter apparatus according to 15. The ultrasonic type flowmeter apparatus according to 16. The ultrasonic type flowmeter apparatus according to 17. The ultrasonic type flowmeter apparatus according to BACKGROUND OF THE INVENTION
PRIOR ART PUBLICATIONS
SUMMARY OF THE INVENTION
Problems to be Solved by the Invention
BRIEF DESCRIPTION OF THE DRAWINGS
DESCRIPTION OF THE PREFERRED EMBODIMENTS
Embodiment 1