GB2156075A - Ultrasonic flow discontinuity identification - Google Patents

Abstract

A method of and apparatus for obtaining discontinuity and mass flow information comprises a Doppler-based system in which ultrasonic pulses reflected from discontinuities are converted into frequency spectra whereby the discontinuities may be identified by comparison with spectra from known discontinuities, and their concentration determined, and when combined with Doppler-obtained velocity information, the mass flow measured. The transducer 12 emits ultrasound energy at an angle other than 90 DEG to the flow so that Doppler information may be obtained from the reflected signal. <IMAGE>

Description

SPECIFICATION Ultrasonic sensing Field of the Invention This invention relates to a method of and apparatus for obtaining discontinuity and mass flow information.

Background of the Invention In many processes involving fluid flows, e.g., secondary oil recovery or the use of blood pumps in certain medical treatments, it is important to keep the process going continuously or as nearly continuously as possible.

At the same time, however, it is equally important that the process be shut down if the flow contains any discontinuities which would adversely affect the process, the associated equipment or in the medical cases, the patient.

There are two principal problems, however, in deciding whether or not to shut down such a system. First, the flow may contain many different types of discontinuities, and only one type may be harmful. Thus, it is necessary to be able to accurately identify the various discontinuities, and in particular to positively detect the presence of one or more specific types. Secondly, in some instances, the particular discontinuity may not be harmful unless it exists in the flow in a concentration above a certain limit. Thus, it is desirable to be able to measure mass flow as well.

Summary of the Invention We have discovered that discontinuities can be identified and the mass flow determined by using a Doppler-based system of simple electronics to obtain a frequency-shifted signal from the discontinuities and then comparing the spectrum from the signal, or an approximation thereof, with known spectra, thereby providing information about the discontinuities. This information may be used in connection with the velocity information to obtain a mass flow measurement.

In the preferred embodiment, the system uses an ultrasonic transducer positioned to direct a series of broadbanded pulses into a flow at an angle. Any pulses reflected from discontinuities are detected by the transducer.

The frequency-shifted, detected pulse is converted to frequency spectrum or is combined with a reference signal to produce an approximation thereof, either of which is then compared with the spectra of known discontinuities to identify the detected discontinuity. A count of discontinuities or the magnitude of the spectrum gives the concentration information, which when combined with the velocity information also obtained from the return pulse, gives a mass flow measurement.

Description of the Preferred Embodiment Drawings We turn now to a description of the structure and operation of the preferred embodiment, after first briefly describing the drawings.

Figure 1 is a cross-sectional view of the transducer and conduit arrangement of the preferred embodiment: Figure 2 is a block diagram of the circuit elements of the invention; Figure 3 is a plot of a frequency spectrum for a discontinuity; and Figure 4 is a plot of a frequency spectrum for another discontinuity.

Structure Referring to Fig. 1, a Doppler system is shown at 1 0. The system 10 comprises an ultrasonic transducer 1 2 which is mounted in a pipe extension 14 connected to a main flowcarrying conduit 16. The extension 14 is disposed at an angle of about 45 to the main conduit 16, although other angles may be used. The transducer is generally the same type as that of Abts U.S. Patent Application Serial No. 187,615, filed September 15, 1980, assigned to the same assignee as this application and hereby incorported by reference. The only change is that the crystal is the broadbanded one of Abts U.S. Patent Application Serial No. 360,773, filed March 22, 1982, also incorporated herein by reference.

The electronic pulse-generating and detection circuit 20 for the preferred embodiment is shown in Fig. 2. The output of a signal generator 22 is connected to the transducer 1 2 through a transmit gate 24. The transducer 1 2 is connected through an amplifier 26 to a demodulator 28, which is also connected to the signal generator 22 through a range gate 32. The output of the demodulator 28 is connected to a bandpass filter 30 and then to a sample and hold circuit 34. The range gate 32 may also be located between the filter and the sample and hold circuit 34 or between the amplifier and the demodulator.

Operation In operation the signal generator 22 periodically, as determined by the timing of the transmit gate 24, sends a triggering signal to the transducer 1 2. The transducer 1 2 then generates a focused ultrasonic pulse, which is directed into the flow, as shown in Fig. 1. The basic frequency of the ultrasonic pulse is determind by a number of factors, including crystal type, and the frequency is between 1 MHz and 1 50MHz. The overall pulse, however, is preferably broad banded having frequency components covering a large frequency range.

When struck by the pulse, any discontinuity in the flow will reflect at least a portion of the pulse back to the transducer 12, which de tects it. The timing of the signal generator 22 and the transmit gate 24 assures that the transducer will not be receiving another triggering signal from the signal generator 22 during the time period when a reflected signal might be detected. As is usual for a Doppler type of system, the reflected pulse has a frequency shift, which depends in part upon the speed of the discontinuity. This shift, however, is also related to discontinuity type, as different types of discontinuities (e.g., different types of solid particles), affect different frequency components of the striking pulse.

This detected, frequency-shifted pulse is then sent to the amplifier 26 and on to the demodulator 28, which multiplies the detected pulse with a reference signal. The reference signal from the range gate is derived from the triggering signal. This is accomplished by gating the triggering pulse with a time-delayed range pulse of much shorter duration. The time delay itself is simply chosen so as to select a relevant range in which the detected pulse is recognized and processed by the system. This delay approximately equals the time it takes for the ultrasonic pulse to travel to and from most detected discontinuities so that the detected pulse and the reference pulse arrive at the demodulator 28 at the same time. Thus, this delay effectively determines the distance at which the system detects discontinuities.

The combined output from the demodulator 28 is then sent to the bandpass filter 30, which is the actual output signal of the system 1 0. The sample and hold circuit 34 merely allows a number of reflected pulses to combine to produce a single such output.

The output from the filter 30 is an approximation of the frequency spectrum which would be obtained from the pulse reflected from the discontinuity. This is largely because of narrow width of the range gate pulse. Due to the Doppler effect, this output, however, is somewhat compressed and frequency-shifted downward so that it is usually in the 1 to 10 KHz range. (The actual frequency spectra of the returning pulses would not be compressed and would be in the frequency range of the transmitted pulse, i.e., 1 MHz to 1 50 MHz.) A pair of such outputs are shown in Figs. 3 and 4. There, the two plots show that the system outputs for two different discontinuities are clearly distinguishable. Thus, the particular discontinuity may be identified by a comparison between this actual output spectrum and those of known discontinuities.

Alternatively, the frequency spectrum can be obtained by performing a fast Fourier transform directly on the detected pulse, as set forth in Abts U.S. Patent Application Serial No. 151,834, filed May 21, 1980, hereby incorporated by reference. There, however, the electronics used are much more complex, and it is necessary to first do a high speed analog-to-digital conversion which is avoided by the method and apparatus of the preferred embodiment.

The amount of discontinuities in the flow may be determined in either of two ways. If there are relatively few discontinuities, the number of pulses reflected from them may be counted for a given unit of time. If, on the other hand, there are too many to count individually, the average concentration is determined from the amplitude of the system's output signal, i.e., the higher the concentration, the greater the amplitude of the spectrum. With this information, mass flow may then be measured.

The frequency shift of the returning signal is related to the flow velocity as determined by the following equation: fdC v = 2fcosy where f is the frequency of the transmitted pulse, fd is the frequency of the reflected pulse, c is the speed of sound in the fluid and y is the angle at which the transmitted pulse is sent into the flow. This velocity measurement, combined with the amount of discontinuity information referred to above, gives a mass flow value.

It is also possible to use a continuous Doppler system rather than a pulsed one, as in the preferred embodiment, by employing a separate receiving transducer.

Other variations will occur to those skilled in the art.

Claims (11)

1. A method of identifying discontinuities in a flow comprising: transmitting ultrasonic energy across a flow at an angle other than 90 , detecting the portion of the ultrasonic energy reflected from a discontinuity in the flow, converting the dtected energy into a frequency spectrum, and comparing the frequency spectrum of the detected energy with the spectra of known discontinuities.

2. The method of claim 1 wherein converting the detected energy includes using the detected energy to produce a compressed and lower frequency output signal which approximates the frequency spectrum of the detected energy.

3. The method of claim 1 wherein transmitting and detecting are performed by a single transducer.

4. The method of claim 1 further comprising determining the amount of discontinuities by counting the number of energy reflections from such discontinuities.

5. The method of claim 1 further comprising determining the amount of discontinuities by measuring the magnitude of the frequency spectrum of the detected energy.

6. The method of claims 4 or 5 further comprising determining mass flow by computing the velocity of the detected discontinuities from the detected energy and combining the velocity with the amount of discontinuities in the flow.

7. The method of claim 1 wherein said ultrasonic energy is in the form of a series of high frequency pulses.

8. The method of claim 1 wherein said ultrasonic energy is in the form of a continuous wave.

9. The method of claim 1 wherein said converting comprises performing a high speed analog-to-digital conversion on the detected energy and performing a fast Fourier transform on the resulting digital signal.

1 0. An apparatus for identifying discontinuities in a flow comprising: a transducer, said transducer arranged to direct ultrasonic energy across a flow at an angle other than 90; means for detecting ultrasonic energy reflected from discontinuities in the flow; means for converting the detected energy into a frequency spectrum, and means for comparing the frequency spectrum of the detected energy with the spectra of known discontinuities.

11. The appartus of claim 10 wherein said means for detecting comprises said transducer.

1 2. The apparatus of claim 10 wherein said means for converting comprises a Dop pler detection circuit.

1 3. The apparatus of claim 1 2 wherein said circuit produces a compressed and lower frequency output signal which approximates the frequency spectrum of the detected energy.

1 4. The apparatus of claim 10 further comprising means for determining the amount of discontinuities in the flow.

1 5. The apparatus of claim 14 further comprising means for determining flow velocity and means for using the determined flow velocity and the amount of discontinuities to determine mass flow.

1 6. A method of identifying discontinuities in a flow substantially as hereinbefore described with reference to the accompanying drawings.

1 7. Apparatus for identifying discontinuities in a flow substantially as hereinbefore described with reference to and as shown in the accompanying drawings.