Measuring and testing – Volume or rate of flow – By measuring vibrations or acoustic energy
Patent
1997-09-15
1999-11-23
Oen, William
Measuring and testing
Volume or rate of flow
By measuring vibrations or acoustic energy
G01F 166
Patent
active
059879971
DESCRIPTION:
BRIEF SUMMARY
According to a first theory, the invention concerns an ultrasound method of measuring the flow of flowing media using a measuring tube and at least two pairs of ultrasound transducers attached to the measuring tube forming a measuring path, in which the amount of flowing medium is determined from the velocity of the medium along at least two measuring paths. The term medium here includes both liquids and gases.
According to a second theory, the invention also concerns a device for using the ultrasound method of measuring the flow of flowing media with a measuring tube, at least two pairs of ultrasound transducers arranged on the measuring tube forming a measuring path, a transducer determining the velocities of the medium along the measuring path from the signals of the pair of ultrasound transducers and an adder that finds the amount of flowing medium from the velocity of the medium along the measuring paths.
The known methods and devices for measuring the average velocity and the amount of flow of a flowing medium by ultrasound use a large number of measuring paths, which form the supporting points of a digital integration method that is as optimal as possible Here, the integration method is normally determined by the dimension or geometry of the measuring path and the measuring tube. There are various traditional optimal integration methods by Chebichev, Gauss or Taylor, which are given for example in unexamined patent applications CH-A-610 038, DE-A-30 38 213 and EP-A-0 125 845. The methods and devices known from these unexamined patent applications are dependent on the viscosity of the medium and hence on the Reynolds' number for their precision. For example, please refer to the article "A New Integration Technique for Flowmeters with Chordal Paths" in Flow Measurement and Instrumentation, vol. 1, No. 4, July 1990, Pages 216 to 224.
The methods and devices known from said unexamined patent applications for ultrasound flow measurement have insufficient precision due to their dependence on the viscosity of the medium, since the viscosity can change sharply during measurement, particularly as a result of temperature changes. However, high precision is generlly required particularly when measuring quantities of flowing gases, petroleum products and chemical products, for example second important problem with the known methods and devices is disturbances in the velocity profile caused by integration effects, which also has a negative influence on precision.
The products specified have extraordinarily high requirements for measurement precision. For example, for petroleum, in the range of a flow quantity from 50% to 100% of the nominal flow quantity, the maximum error is .+-.0.15%, and in the range of a flow quantity 10% to 100% of the nominal flow quantity, the maximum error is .+-.0.25%. In the past, this precision could only be guaranteed with turbine meters.
When measuring the quantity of a medium flowing in a measuring tube, it is advantageous not to disturb the flow of the medium. At the same time, the point is to obtain the high measurement precision required using a relatively inexpensive device, which also has a long life it is also advantageous if such a device can be calibrated with water after production and can then be recalibrated with other liquids or even gases during operation by the users, in order to guarantee the precision required.
The task of the invention is therefore to eliminate the problems mentioned and to provide a method and a device with which such high precision can be guaranteed. Another task of the invention consists of making it possible with the method and device in the invention to sharply reduce the influence of the viscosity of the medium. The task of the invention is also to provide a method and a device that reduce the influence of changes in the flow profile and that offer the possibility of self-calibration during operation. Finally, it is also the task of this invention to provide a method and a device that make possible constant determination of viscosity of the m
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Roskam Abram Klaas
Smychliaev Vladimir
van Bekkum Jan Aart
Krohne A.G.
Oen William
Thompson Jewel V.
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