EP0886763A1 - Mesure du temps de parcours d'un signal - Google Patents

Mesure du temps de parcours d'un signal

Info

Publication number
EP0886763A1
EP0886763A1 EP95934963A EP95934963A EP0886763A1 EP 0886763 A1 EP0886763 A1 EP 0886763A1 EP 95934963 A EP95934963 A EP 95934963A EP 95934963 A EP95934963 A EP 95934963A EP 0886763 A1 EP0886763 A1 EP 0886763A1
Authority
EP
European Patent Office
Prior art keywords
signal
flight
time
measuring
attribute
Prior art date
Legal status (The legal status is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the status listed.)
Withdrawn
Application number
EP95934963A
Other languages
German (de)
English (en)
Other versions
EP0886763A4 (fr
Inventor
William Freund
Winsor Letton
James Mcclellan
Boacang Jai
Anni Wey
Wen Chang
Current Assignee (The listed assignees may be inaccurate. Google has not performed a legal analysis and makes no representation or warranty as to the accuracy of the list.)
Daniel Industries Inc
Original Assignee
Daniel Industries Inc
Priority date (The priority date is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the date listed.)
Filing date
Publication date
Application filed by Daniel Industries Inc filed Critical Daniel Industries Inc
Publication of EP0886763A1 publication Critical patent/EP0886763A1/fr
Publication of EP0886763A4 publication Critical patent/EP0886763A4/xx
Withdrawn legal-status Critical Current

Links

Classifications

    • G—PHYSICS
    • G01—MEASURING; TESTING
    • G01F—MEASURING VOLUME, VOLUME FLOW, MASS FLOW OR LIQUID LEVEL; METERING BY VOLUME
    • G01F1/00—Measuring the volume flow or mass flow of fluid or fluent solid material wherein the fluid passes through a meter in a continuous flow
    • G01F1/66—Measuring the volume flow or mass flow of fluid or fluent solid material wherein the fluid passes through a meter in a continuous flow by measuring frequency, phase shift or propagation time of electromagnetic or other waves, e.g. using ultrasonic flowmeters
    • G01F1/667—Arrangements of transducers for ultrasonic flowmeters; Circuits for operating ultrasonic flowmeters

Definitions

  • the present invention relates to a method and apparatus for measuring the time of flight of a signal between two points or the time of flight of a reflected signal to return to the original point. Also, the present invention relates to a method for measuring the time difference between reception of the same signal at two different locations. Both analog and digital techniques are applicable to the present invention.
  • the method and apparatus of the present invention is applicable with ultrasonic flow meters and, generally, any detector which uses the time a signal takes to go from one point to another to make a measurement. All measurements applicable for use with the present invention are referred to as time of flight measurements . BACKGROUND OF THE INVENTION
  • the measurement of the time of flight of a sonic or ultrasonic signal has different complications than the measurement of the time of flight of a radar signal.
  • the time of flight can be readily measured by viewing the envelope of the returning energy.
  • the measurement when the time resolution is short with respect to the period of the signal is more difficult.
  • Such prior devices and methods which can be used with or are associated with the present invention include, for example, United States Patent No. 2,724,269 to Kalmus entitled "Apparatus for Measuring Flow," U.S. Patent No. 4,646,575 to O ⁇ air and Nolan entitled "Ultrasonic Flow Meter" and U.S. Patent No.
  • a feature of the present invention to provide an method and apparatus for measuring accurately the time of flight of a signal where the period of the signal is long compared to the required time resolution.
  • a feature of the present invention is to provide an method and apparatus for enhancing the ability to select a specific part of the associated waveform for determining the time of flight of the signal.
  • Yet still another feature of the present invention is to provide an method and apparatus for measuring the time of flight of a signal which method and apparatus is adaptive to signal changes caused by external influences.
  • the apparatus for measuring the time of flight of a signal between two points comprises a transmitter for emitting a signal, a receiver for receiving the signal from the transmitter, means for detecting the onset of the received signal, means for determining a point of measurement within the received signal, and means for measuring the elapsed time from transmission of the signal to the point of measurement.
  • the present invention provides a method for determining the time of flight of a signal comprising the steps of receiving a transmitted signal, operating on the received signal for generating a pre-conditioned signal, operating on the pre-conditioned signal to remove irregularities therefrom for generating a conditioned signal, and operating on the conditioned signal to find the onset of the signal and thus the time of flight thereof.
  • the onset of the signal is represented by or defined as the critical point.
  • the step of operating on the received signal for generating a pre-conditioned signal can be applying any function to the received signal which enhances the ability to detect the received signal.
  • the received signal can be squared.
  • numerous and sundry methods for operating on the received signal may be known to those skilled in the art. For example, the absolute value of the received signal may be taken, a full wave rectification of the received signal may be used, and a half wave rectification of the received signal may be used for enhancing the ability to detect the received signal.
  • the step of operating on the pre-conditioned signal to remove irregularities can be accomplished in numerous ways by those skilled in the art of signal analysis.
  • a preferred embodiment of the present invention is to average the pre-conditioned signal using a moving window thus forming a conditioned signal.
  • Various window functions can be used.
  • various window lengths can be used.
  • the window function moves along the pre ⁇ conditioned signal averaging groups of points. In the presently preferred embodiment, 21 points have been used. It has been found that a rectangular window function provides exceedingly good results.
  • Other conditioning techniques are readily known in the art and may be adopted for use with the present invention.
  • the step of determining the critical point is important with respect to practicing the present invention.
  • the critical point discriminates between where the received signal is present, and where it is not present or, worse, occupied by noise. Determining the critical point is preferably accomplished by using some discrimination function, f(n,n -l).
  • f(n,n -l) some discrimination function
  • an energy ratio is used to determine the critical point which identifies the beginning or onset of the received signal. The energy ratio is provided by the following equation:
  • ER n is the energy ratio at location n
  • E n is representative of the energy at location n
  • £ compost_ is representative of the energy at location n - 1 such that / is the time lag, i.e., the number of time units prior to sample n.
  • the discrimination function may be accomplished by taking the derivative of the conditioned signal.
  • a method for measuring the time of flight of a signal comprising the steps of identifying a critical point associated with the beginning of the received signal, ascertaining a marker point related to an intrinsic characteristic of the received signal and having a temporal relationship with the critical point, and using the marker point for determining the time-of-flight of the signal.
  • an intrinsic characteristic may be a peak, a positive zero crossing or a negative zero crossing.
  • a signal attribute is defined as a particular intrinsic characteristic of the signal.
  • An example of a signal attribute is the second zero crossing after the critical point.
  • a method for measuring the time of flight of a signal comprising identifying a critical point associated with the beginning of the received signal.
  • the identification of the critical point is accomplished by evaluating the energy ratio of the received signal, and setting the critical point on the positive slope and at approximately one-fourth of the maximum of the energy ratio.
  • Marker points on the received signal are determined.
  • the marker points are determined by ascertaining two or more points related to a signal attribute which attribute is an intrinsic characteristic of the received signal.
  • the signal attribute has a temporal relationship with the critical point.
  • the signal attribute selected is a zero crossing, and the marker points on the received signal are proximate to and bracket the zero crossing.
  • the location of the attribute is determined by interpolating between the marker points to determine the point of measurement of the zero crossing.
  • the location of the attribute represents the time-of-flight ofthe signal.
  • the present invention provides a method for measuring the time-of-flight of a signal that finds a set of potential measurement points and applies a function to determine the best point in the set upon which to make the measurement.
  • the method provides for measuring the time-of-flight of a signal by identifying at least one critical point associated with the beginning of the received signal. Then, a plurality of marker points are found related to a sequence of a signal attribute.
  • the signal attribute is an intrinsic characteristic of the signal and has a temporal relationship with the critical point.
  • a plurality of target functions are calculated at each signal attribute.
  • a criteria function is determined for each incidence of the signal attribute based upon the target functions.
  • a desired incidence of the signal attribute is located based on the criteria function.
  • the time-of-flight of the signal is determined.
  • FIG. 1 is a flow diagram illustrating an overview of multiple embodiments of the method of the present invention.
  • FIG. 2 is a block diagram illustrating the time of flight measurement of the present invention.
  • FIG. 3 is an overview illustration of an apparatus employing the present invention.
  • FIG. 4 is a perspective cross-section of a pipe illustrating one embodiment of the orientation of transducers which could be used in association with the present invention.
  • FIG. 5 is an illustration of a received signal or waveform which has been digitized in association with practicing one embodiment of the present invention.
  • FIG. 6 is an illustration of one embodiment of a pre ⁇ conditioned signal associated with the received signal illustrated in FIG. 5.
  • FIG. 7 is an illustration of one embodiment of a conditioned signal associated with the pre-conditioned signal illustrated in FIG. 6 and the received signal illustrated in FIG. 5.
  • FIG. 8 is an illustration of the discriminated signal and the critical point associated with the received signal practicing one embodiment of the present invention.
  • FIG. 9 is an illustration of a location determined to be the marker point of the received signal proximate to the signal characteristic.
  • FIG. 10 is a blow-up view of another typical received signal, including its associated energy ratio, critical point and marker points.
  • FIG. 11 is a diagram illustrating electronics associated with the apparatus of the present invention.
  • FIG. 12 is a flow diagram illustrating one embodiment of the method of the present invention.
  • FIG. 13 is a flow diagram illustrating another embodiment of the method of the present invention.
  • FIG. 14 is a flow diagram illustrating yet another embodiment of the method of the present invention.
  • FIG. 1 is a flow diagram illustrating an overview of several embodiments of the method of the present invention.
  • the received signal is operated on for generating a pre-conditioned signal as illustrated in FIG. 6.
  • the pre ⁇ conditioned signal is operated on for generating a conditioned signal.
  • An illustration of the conditioned signal as practiced by the present invention is illustrated in FIG. 7.
  • a discrimination function is apphed based upon the ratio of the energy of the received signal with a time shifted version of itself, i.e., the energy ratio.
  • the energy ratio provides an exceptional, although not exclusive, technique for determining the critical point.
  • the critical point provides an indication of initial rise or the onset of the received signal.
  • the critical point is applied to the received signal for determining a point of measurement. Thereafter, the time of flight can be determined.
  • FIG. 1 illustrates numerous embodiments of the present invention.
  • the specific steps are operating on the received signal for generating a pre-conditioned signal, operating on the pre-conditioned signal for generating a conditioned signal, operating on the conditioned signal for generating a discriminated signal, determining the critical point, applying the critical point to the received signal for determining a point of measurement, and determining the time of flight.
  • the specific steps can be implemented using various procedures or techniques.
  • the step of operating on the received signal for generating a pre-conditioned signal can include squaring the signal, taking the absolute value of the signal, applying a full wave rectification of the signal, applying a half wave rectification of the signal, or some other method which would provide for the type of operation described which would generate the pre-conditioned signal.
  • the operation on the pre-conditioned signal for generating a conditioned signal provides that an average is taken by applying a moving window function.
  • the moving window function is rectangular.
  • other window functions are readily applicable in practicing the present invention, for example, a Hanning window, a Kaiser window, a cosine window or a Bartlett window are also applicable when using the present invention.
  • the operation on the conditioned signal for generating a discriminated signal preferably provides that an energy ratio is evaluated with respect to the conditioned signal.
  • This determination of the critical point includes using a positive slope, using a negative slope, using a maximum value or the like.
  • the application of the critical point to the received signal for determining a point of measurement includes selecting the critical point, determining the marker points, and evaluating an appropriate signal attribute. Thereafter, the time of flight can be determined.
  • FIG. 2 is a block diagram illustrating the time of flight measurement of the present invention.
  • a signal is received and digitized to form a received signal that can be electronically manipulated.
  • the received signal can be enhanced.
  • the need for enhancement of the signal, or not, is situation specific. Enhancement is possible by techniques known to those skilled in the art.
  • the received signal can be enhanced by filtering out high or low frequency noise.
  • the received signal can be enhanced by stacking. With respect to the present invention, stacking is defined as the repeated summation of several signals so as to diminish the random noise and emphasize the real signal.
  • the energy associated with the received signal is calculate to form a pre-conditioned signal.
  • the pre-conditioned signal is then averaged to form a conditioned signal.
  • the averaging is accomplished by using a moving window function.
  • a discrimination function is then used.
  • the discrimination function determines the ratio of the energy of the received signal with a time shifted version of itself.
  • the critical point is located with respect to the received signal.
  • the received signal is detected by determining the location of the critical point on the leading edge of the energy ratio. In a preferred embodiment, the value of the critical point is 25% of the maximum of the energy ratio.
  • a marker point is located on the received signal.
  • the marker point is a sampled point on the received signal proximate to an attribute of the signal, and in known temporal relationship to the critical point.
  • the signal is checked or validated. A check is performed to determine that a valid analysis has been achieved.
  • the check can, for example, use one or more of the following: identify points on the received signal before the marker points, identify points on the received signal after the marker points, check the signal for the expected period and amplitude, check that the difference between each marker point and the critical point is within an allowed range. Thereafter, the transit time can be readily calculated.
  • FIG. 3 is a general illustration of a representative apparatus for employing the present invention.
  • FIG. 4 is a perspective cross-section of a pipe illustrating one embodiment of the orientation of transducers which could be used in practicing the present invention.
  • the pipe 102 is adapted for receiving the transducers 104, 106.
  • the transducers 104, 106 are displaced on opposite sides of the pipe 102 by a distance L between each transducer.
  • the transducers 104, 106 are longitudinally displaced by a distance of X.
  • the pipe 102 has notches 112, 114 for receiving the transducers 104, 106, respectively.
  • FIG. 5 is an illustration of a received signal or waveform which has been digitized in association with practicing one embodiment of the present invention.
  • the signal is transmitted from a transducer, for example, the transducer illustrated in FIG. 4.
  • the signal takes some period of time to travel a distance, L, from transmission to reception.
  • the signal is received by a transducer, for example, the transducer illustrated in FIG. 4.
  • the received signal is digitized.
  • FIG. 6 is an illustration of one embodiment of a pre ⁇ conditioned signal associated with the received signal illustrated in FIG. 5.
  • a preferred way, as practiced by the present invention is to take the square of the received signal, yielding a representation of the energy. Numerous and sundry methods for operating on the received signal to achieve an effective pre-conditioned signal may be known to those skilled in the art as previously discussed.
  • the curve of FIG. 6 illustrates the pre ⁇ conditioned signal or function of the received signal illustrated in FIG. 5 which has been squared.
  • FIG. 7 is an illustration of one embodiment of a conditioned signal associated with the pre-conditioned signal illustrated in FIG. 6 and the received signal illustrated in FIG. 5.
  • a preferred way of determining the conditioned signal or function, as practiced by the present invention, is to average the pre-conditioned signal using a moving window.
  • the window function moves along the pre ⁇ conditioned signal averaging groups of points. In the presently preferred embodiment, 21 points have been used for each window frame. It has been found that a rectangular window function provides exceedingly good results. It can be appreciated that other window types can be used such as those known in the art as Hamming, Kaiser, Hanning and Bartlett windows. Further, a different number of points can be adopted for use with the present invention.
  • the curve of FIG. 7 illustrates the conditioned signal formed from the pre-conditioned signal by averaging using a moving window.
  • FIG. 8 is an illustration of the energy ratio and the critical point associated with the received signal practicing one embodiment of the present invention.
  • the critical point is determined by operating on the conditioned signal with a discrimination function such as f(n,n -l).
  • the determination of the critical point from the energy ratio is used to identify the beginning or onset of the signal.
  • the energy ratio is provided by the following equation:
  • ER n is the energy ratio at the location n
  • E n is representative of the energy at location n
  • E n _ ⁇ is representative of the energy at location n -l such that / is the time lag, i.e., the time units prior to sample n.
  • L is 15 time units.
  • An example of the energy ratio curve is illustrated in FIG. 8.
  • the energy ratio is a steep, spiked curve occuring approximately at the same time as the onset of the received signal (See FIG. 9).
  • FIG. 8 illustrates the critical point marked "X" on the energy ratio curve at approximately 25% of the maximum of the energy ratio.
  • FIG. 9 is an illustration of the location determined to be the marker point of the received signal proximate to the signal attribute.
  • the signal attribute is an intrinsic characteristic of the received signal.
  • the marker points are actual points of the received signal proximate to the received signal attribute, which attribute is a zero crossing after the critical point.
  • the marker points can be, for example, the points of the signal adjacent to the attribute. Choosing sample points immediately adjacent to the attribute as the marker points is a presently preferred embodiment of the invention. It is preferred to calculate the time of flight of the signal using the signal attribute, however, the time of flight of the signal can be calculated based upon the marker points' representation.
  • the preferred embodiment of the measurement of the time of flight of the signal practicing the present invention uses an approximation of the signal attribute.
  • the preferred approximation of the signal attribute is the approximation of a zero crossing.
  • the approximation can be made by determining two sample points which are adjacent to and bracket the signal attribute. These particular sample points are the marker points for the signal.
  • the attribute can be determined by interpolating between the marker points.
  • the time of flight of the signal is calculated based upon the location ofthe signal attribute.
  • FIG. 10 is a blow-up view of another typical received signal, including its associated energy ratio, critical point and marker points.
  • the received signal is illustrated as a thin sohd line.
  • the energy ratio associated with the received signal is illustrated as a thick solid line.
  • the value of one-fourth of the energy ratio is illustrated on the increasing slope of the energy ratio curve.
  • various other signal location points such as the marker points, can be readily determined from this technique. It is considered that finding all of these other signal locations, as associated with the general method of the present invention, are adapted for use, and included in, the present invention.
  • the present invention provides that one or more points on the received signal are to be used as the marker points with generally known interpolation techniques for determining the point of measurement for making the time measurement.
  • the present invention provides a method for measuring the time-of-flight of a signal that finds a set of potential measurement points and applies a function to determine the best point in the set upon which to make the measurement.
  • This method uses a target functions based upon the signal attribute to be evaluated.
  • Such signal attributes include, for example, the zero crossings.
  • the target functions can be used as components of a criteria function to identify preferred parts of the received signal to use as measurement points.
  • the presently preferred method comprises using a weighted sum of the target functions for each point evaluated.
  • the step of applying the critical point to the received signal for determining the points to use in making the time measurement can be accomplished in various ways.
  • Standards can be set to determine which point is to be selected as the measurement point. For example, the point that generates the largest positive value from the criteria function is the best for use as the measurement point.
  • a preferred embodiment uses the steps of identifying a plurality of points of the signal with common attributes, for example, the zero crossings or the peaks. Thereafter, for each point identified, one or more characteristics are measured, for example, the peak amplitude following a point, or the span (difference in time between each point and the critical point). Based upon the signal characteristic to be evaluated, a target function is built based upon the defined target values or the preferred spot.
  • a criteria function is built using the target functions as elements.
  • the criteria function is used to locate the point of measurement (the desired incidence of the signal attribute).
  • a weighted sum of the target functions for each point is calculated to provide the values of the criteria function.
  • criteria are set to evaluate which point "wins" and is used as the measurement point. For example, the largest positive value generated from the criteria function is the presently preferred choice.
  • the present invention determines a point of measurement as follows:
  • the three target functions are target span #1 (FSl), target amplitude (FA), and target span #2 (FS2).
  • FSl target span #1
  • FA target amplitude
  • FS2 target span #2
  • Pi is the position ofthe ith zero-crossing point.
  • Ai ( ⁇ i*100)/Max., with ai being the amplitude following the ith zero-crossing point and Max. being the maximum amplitude of the signal.
  • TSI is the target span away from the energy function
  • TA is the target amplitude.
  • TS2 is the target span away from the energy ratio, Pf.
  • SA 51 is the sensitivity of target span #1 function.
  • SA is the sensitivity of target amplitude function.
  • a criteria function, FU " ), is calculated for each zero-crossing point.
  • WS1 is the waiting factor of FSl.
  • WA is the waiting factor of FA.
  • WS2 is the waiting factor of FS2.
  • FIG. 11 is a block diagram illustrating the apparatus 200 of the present invention.
  • the apparatus 200 of the present invention comprises a clock 202, a counter 204, a transmitter 206, a first transducer 208, a memory 210, a controller 212, an analog-to-digital converter 214, a receiver 216 and a second transducer 218.
  • the clock 202 is used for timing.
  • the transmitter 206 is fired.
  • the apparatus 200 starts digitizing.
  • the A/D converter 214 is activated.
  • the counter 204 starts counting.
  • the A/D converter 214 places a magnitude from the receiver 216 into the next location in the memory 210.
  • the memory 210 develops a curve as illustrated in FIG. 5.
  • the data accumulated in the memory 210 is processed as previously discussed to determine the time measurement.
  • the apparatus 200 illustrated in FIG. 11 indicates there are dual transducers 208, 218, it can be appreciated that a single transducer may be readily adapted for practicing the present invention.
  • a single transceiver device may be used to measure a reflected signal.

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  • Physics & Mathematics (AREA)
  • Electromagnetism (AREA)
  • Fluid Mechanics (AREA)
  • General Physics & Mathematics (AREA)
  • Measurement Of Unknown Time Intervals (AREA)

Abstract

Appareil de mesure du temps de parcours d'un signal. L'appareil de mesure du temps de parcours d'un signal comporte un émetteur (206) émettant un signal, un récepteur (216) recevant le signal de l'émetteur (206) et un dispositif de détection de l'apparition du signal lorsqu'il arrive au niveau du récepteur (216), de sorte que l'intervalle de temps s'écoulant entre l'émission par l'émetteur (206) et le moment où le récepteur (216) reçoit initialement le signal peut être déterminé. Dans un autre mode de réalisation, l'invention concerne un procédé de détermination du temps de parcours d'un signal, consistant à recevoir un signal émis, à travailler ce signal reçu pour obtenir un signal préconditionné, à éliminer les irrégularités de ce dernier pour obtenir un signal conditionné, à travailler ce signal conditionné pour former un signal discriminé, et à déterminer le point critique du signal discriminé.
EP95934963A 1995-09-05 1995-09-05 Mesure du temps de parcours d'un signal Withdrawn EP0886763A1 (fr)

Applications Claiming Priority (1)

Application Number Priority Date Filing Date Title
PCT/US1995/011118 WO1997009591A1 (fr) 1995-09-05 1995-09-05 Mesure du temps de parcours d'un signal

Publications (2)

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EP0886763A1 true EP0886763A1 (fr) 1998-12-30
EP0886763A4 EP0886763A4 (fr) 1998-12-30

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EP95934963A Withdrawn EP0886763A1 (fr) 1995-09-05 1995-09-05 Mesure du temps de parcours d'un signal

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EP (1) EP0886763A1 (fr)
AU (1) AU3716095A (fr)
WO (1) WO1997009591A1 (fr)

Family Cites Families (7)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US4103551A (en) * 1977-01-31 1978-08-01 Panametrics, Inc. Ultrasonic measuring system for differing flow conditions
US4480485A (en) * 1982-10-01 1984-11-06 Panametrics, Inc. Acoustic flowmeter with envelope midpoint tracking
US4515021A (en) * 1983-07-29 1985-05-07 Panametrics, Inc. Intervalometer time measurement apparatus and method
US5040415A (en) * 1990-06-15 1991-08-20 Rockwell International Corporation Nonintrusive flow sensing system
US5228347A (en) * 1991-10-18 1993-07-20 Ore International, Inc. Method and apparatus for measuring flow by using phase advance
US5329821A (en) * 1992-05-08 1994-07-19 Nusonics, Inc. Autoranging sonic flowmeter
AU7358194A (en) * 1993-07-06 1995-02-06 Daniel Industries, Inc. Method and apparatus for measuring the time of flight of a signal

Non-Patent Citations (2)

* Cited by examiner, † Cited by third party
Title
No further relevant documents disclosed *
See also references of WO9709591A1 *

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Publication number Publication date
EP0886763A4 (fr) 1998-12-30
WO1997009591A1 (fr) 1997-03-13
AU3716095A (en) 1997-03-27

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