Measuring and testing – Volume or rate of flow – By measuring vibrations or acoustic energy
Patent
1989-02-03
1990-04-10
Ruehl, Charles A.
Measuring and testing
Volume or rate of flow
By measuring vibrations or acoustic energy
7386118, G01F 166
Patent
active
049149598
DESCRIPTION:
BRIEF SUMMARY
BACKGROUND OF THE INVENTION
1. Field of the Invention
This invention relates to a ultrasonically operating transducer device for the measurement of the flow velocity of a fluid in a pipe, comprising two transducers mounted on either side of the pipe and directed obliquely in relation to the direction of the flow, which transducers alternately transmit and receive sonic pulses to and from each other.
2. Discussion of the Related Art
The invention is especially developed in connection with the need for measuring the gas flow in a so-called flare in connection with facilities for exploration and production of hydro carbons, but it is not limited to such a utilization.
There is a need to be able to cover, with one transducer arrangement, a relatively wide range of flow velocities in an accurate manner, while there is also a need for safety, particularly when measuring in hazardous areas.
The transducer devices known today, of the kind mentioned initially, have the disadvantage that the measurable range of velocity is relatively limited. Also, the accuracy of measurement is not always completely satisfactory. In the case of measuring in hazardous areas (for example, where there is a danger of explosion) it is necessary to transmit signals for evaluation to a safety zone. This transmission of signals will often disturb the measurements, because the signals are exposed to electromagnetic influences from the environment during the required transmission through cables.
SUMMARY OF THE INVENTION
According to the present invention, two transducers are arranged with their center axes deviating from the imaginary connecting line between the transducers in a direction against the mentioned direction of flow of the fluid, the flow velocity of which is to be measured. A wider range of measurement is thus achieved because the divergent orientation of the transducers compensates for the deviation of the ultrasonic beam between the transducers, which will affect the sonic pulses in the fluid flow.
According to the invention, in connection with intended utilization of the new transducer device for measuring the velocity of a gas flow in a pipe leading to a flare, it has been found that the imaginary connecting line can advantageously form an angle of approximately 55.degree. in relation to the flow direction, and that the deviation for the respective transducers will be approximately 7.degree.-10.degree..
With such a deviation of orientation of the two transducers, which deviation of orientation is independent of the diameter of the pipe, a potential measurement range of 0 to approximately 100 meters/second can be covered with only one transducer device according to the invention.
Further, according to the invention, it has been found that in a range of low flow velocities, preferably from 0 to 7 meters/second, a CW-signal (continuous wave signal) can be utilized in combination with a CHIRP-signal (a signal with rectangular pulse whose momentary frequency increases linearly throughout the duration of the pulse), while for medium and higher flow-velocities preferably, over 7 meters/second and up to over 100 meters/second, a CHIRP-signal with correlative detection is used.
By using two signal systems in this way a broad measurement range is achieved in a very advantageous manner. For high and medium rates of flow velocity, a CHIRP-signal with correlation 2 detection is used in order to overcome high levels of noise, while a CW-phase measurement in combination with the CHIRP-measurement is used for the lower velocity. The CHIRP-signals are sent upstream and downstream in order to roughly determine the flow-velocity value, followed by CW-bursts which increase resolution. The omission of the CW-measurement for flow-velocities over 7 meters/second enables a doubling of the bandwidth for the CHIRP-measurements.
According to the invention it can be advantageous to use, as respective transducers, a transducer which is designed as a cup-shaped metal body whose base as membrane is assigned an electrode on its inside and which is seal
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Lynnorth, L. C., "Clamp on Ultrasonic Flowmeters", Instrumentation Technology, vol. 22, No. 9, pp. 37-44, Sep. 1975.
Derwent's Abstract, 87-219534/31 SU 1,273,740 published 30-Nov.-1986; "Ultrasonic Single-Channel Method of Flow Measurement-by Vectorial Summation of Signal Envelopes Which Monitor the Flow".
Derwent's Abstract, 84-106438/17 SU 1,030,656 published 23-Jul.-1983; "Liquid Media Ultrasonic Flowmeter-Uses Two Electroacoustic Propagation Speed Measurements in Pipe and Liquid".
"Theoretical Analysis of the Basic Parameters of Ultrasonic Flowmeters" by N. I. Brazhnikov (Translated from Izmeritel'naya Teknika), No. 8, pp. 57-62, Aug., 1966.
"High-Rangeability Ultrasonic Gas Flowmeter for Monitoring Flare Gas" by K. S. Mylvaganam, Reprinted from IEEE Transactions on Ultrasonics, Ferroelectronics and Frequency Control, vol. 36, No. 2, 1989.
Hammer Erling
Mylvaganam Kanagasaba
Den Norske Stats Oljeselskap A.S.
Ruehl Charles A.
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