WO1981000456A1 - Procede et dispositif de mesure de distance - Google Patents

Procede et dispositif de mesure de distance Download PDF

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Publication number
WO1981000456A1
WO1981000456A1 PCT/AU1980/000040 AU8000040W WO8100456A1 WO 1981000456 A1 WO1981000456 A1 WO 1981000456A1 AU 8000040 W AU8000040 W AU 8000040W WO 8100456 A1 WO8100456 A1 WO 8100456A1
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WO
WIPO (PCT)
Prior art keywords
signal
samples
memory
received signal
transmitted
Prior art date
Application number
PCT/AU1980/000040
Other languages
English (en)
Inventor
Jones P Leigh
I Chatwin
Original Assignee
Dorian Ind Pty Ltd
Jones P Leigh
I Chatwin
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 Dorian Ind Pty Ltd, Jones P Leigh, I Chatwin filed Critical Dorian Ind Pty Ltd
Priority to AU61296/80A priority Critical patent/AU6129680A/en
Publication of WO1981000456A1 publication Critical patent/WO1981000456A1/fr

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Classifications

    • G—PHYSICS
    • G01—MEASURING; TESTING
    • G01S—RADIO DIRECTION-FINDING; RADIO NAVIGATION; DETERMINING DISTANCE OR VELOCITY BY USE OF RADIO WAVES; LOCATING OR PRESENCE-DETECTING BY USE OF THE REFLECTION OR RERADIATION OF RADIO WAVES; ANALOGOUS ARRANGEMENTS USING OTHER WAVES
    • G01S15/00—Systems using the reflection or reradiation of acoustic waves, e.g. sonar systems
    • G01S15/02—Systems using the reflection or reradiation of acoustic waves, e.g. sonar systems using reflection of acoustic waves
    • G01S15/06—Systems determining the position data of a target
    • G01S15/08—Systems for measuring distance only
    • G01S15/10—Systems for measuring distance only using transmission of interrupted, pulse-modulated waves
    • G01S15/102—Systems for measuring distance only using transmission of interrupted, pulse-modulated waves using transmission of pulses having some particular characteristics
    • G01S15/104—Systems for measuring distance only using transmission of interrupted, pulse-modulated waves using transmission of pulses having some particular characteristics wherein the transmitted pulses use a frequency- or phase-modulated carrier wave

Definitions

  • the present invention relates to a method and device for measuring the distance between two or more locations.
  • bursts of acoustical energy derived from a shot blast may be reflected from a geological formation and then examined by a cross-correlation technique.
  • the present invention attempts to provide a method and apparatus for measuring the distance between two or more locations and which will in one embodiment do so in noisy environments.
  • the invention provides a process for measuring the distance between two or more locations which process comprises first transmitting from a first location an amount of acoustical energy in the form of a transmitted signal in a manner such that at least part of said energy impinges on an object located at a second location to provide an amount of reflected acoustical energy; secondly receiving at least a part of the said reflected energy at a receiving station in the form of a received signal; thirdly subjecting
  • OMP said received signal to an analytical procedure such that any component thereof derived from the said transmitted signal may be identified; fourthly measur ⁇ ing the interval of time elapsing between the time of the transmission of the said transmitted signal and the time of the receipt of the said received signal; and fifthly calculating from said interval of time the distance between said first location and said second location, said process being characterized in that the said transmitted signal comprises a tone burst and being characterized further in that the said analytical procedure comprises a cross-correlation procedure.
  • the tone burst is a frequency modulated tone burst.
  • frequency modulated tone burst a signal having a finite period of duration, the instantaneous frequency of said signal being a continuous function of time during the said period of duration.
  • a frequency modulated tone burst may be a signal which commences at a first frequency and which during its period of duration changes its frequency continuously to terminate at a second frequency. Said second frequency may be the same as or different from the said first frequency.
  • Such a tone burst would contain 25 cycles.
  • Such tone bursts are often referred to as "glide tones" or - '
  • the cross-correlation procedure referred to above is a procedure whereby a real time comparison may be made between the transmitted signal and a received signal. Such comparisons may conveniently be performed by logic means whereby certain characteristics of the transmitted signal and received signal may be compared. Thus for example the signals may be examined with reference to a multiplicity of characteristics such as signal amplitude and signal polarity, or alternatively they may be examined with reference to a single, charac ⁇ teristic such as signal polarity. Typically, the . cross-correlation procedure may be achieved by multip ⁇ lication of the signal magnitudes of n paired, period ⁇ ically sampled values of the transmitted and received signals and integrated over the period of duration of the frequency modulated tone burst.
  • the transmitted and received signals may be examined for like polarity of the n paired values and the result summed.
  • x(t) reference (or transmitted) signal.
  • y(t) echo signal to be correlated - always finite.
  • t time.
  • the transmitted signal may have a frequ ⁇ ency in a range from audible frequencies, say from about 100 cycles per second to frequencies which are in the mid-acoustic range, typically up to about 1,00Q,000 cycles per second but the use of frequencies ranging above one megacycle per second although less preferred, is not excluded.
  • the frequency of the transmitted signal be in a range from 1 to 100 kilohertz and an especially preferred range of frequencies for the transmitted signal is from 5 to 40 kilohertz.
  • the transmitted signal comprises a multiplicity of cycles and the number of cycles therein may be varied dependent to some extend on the use to which the transmitted signal is to be put. Whilst signals comprising a large number of cycles are useful it is preferred for many purposes that the number of cycles be comparatively small, say less than 100, and more preferably that the number of cycles be in the range from 10 to 20. It is also desirable that the transmitted signal be transmittable directionally to the second location and it is also preferred that the transmitted signal be focusable
  • a suitable transmitted signal useful in the process of the invention is a signal derived from an electronic circuit comprising a gated phase locked loop and transmitted by moveable shaped transmitting means for example a transmitting means which is essentially parabolic in configuration which produces sound waves which may be focussed, directed and transmitted into an area to be explored or examined by the sound waves, the area being scanned by the sound waves-by moving the transmitting means.
  • the process of the invention may be performed conveniently with the aid of a device comprising electronic components.
  • the invention provides a device comprising in combination means for transmitting from a first location an amount of acoustical energy in the form of a transmitted signal comprising a tone burst as in a manner such that at least a part of said energy impinges on an object located at a second location to provide an amount of reflected acoustical energy; means for receiving at least a part of said reflected energy at a receiving station in the form of a received signal; means for subjecting said received signal to a cross- correlation procedure in a manner such that a component thereof derived from the said transmitted signal may be identified; means for measuring the interval of time elapsing between the time of the transmission of the said transmitted signal and the time of the receipt of the said received signal; and means for calculating
  • the means for transmitting the transmitted acous ⁇ tical signal may, if desired, comprise a plurality of transmitters, but for most practical purposes it has been found that one transmitter is adequate for perfor ⁇ ming the process of the invention.
  • the transmitter may be fabricated from components which in combination form a phase locked loop which is capable of transmitting a frequency modulated tone burst.
  • a voltage controlled oscillator which runs continuously and in combination with components comprising power amplifier means, variable inductor means, transducer means, phase comparator means-, loop filter means, and buffer means forms a phase locked loop which causes the transducer means to oscillate at a variable frequency set by the variable inductor means and maintained by sensed voltage and current inputs to the phase comparator means.
  • Such an arrangement of components reduces, and usually prevents, excessive phase locked loop oscillator pull-in time and is typi ⁇ cal of transmitting means according to the invention which is capable of providing a transmitted signal comprising a frequency modulated tone burst which displays a so-called chirp characteristic.
  • the use of a correctly tuned phase locked loop is advantageous in that it ensures that the transducer means functions at or very near resonance and therefore tends to maxi ⁇ mize the transmitted acoustic energy derivable from a given input of electrical power.
  • the use of a trans- mitted signal in the form of a chirp tone or a glide tone is advantageous in that it provides a signal having unique characteristics which may be recognized and which facilitate the cross-correlation of the transmitted signal with the receiving signal.
  • the means for receiving a received signal is suitably a conventional means used to receive acoust- - ical energy and to convert it to a suitable electrical form of energy.
  • the received signal may be received by one or more geophones or alternat- ively by transducing means.
  • the receiving means may be physically located adjacent to the transmitting means though the two means may be at a spaced distance if desired.
  • transduc- ing means comprising concentric receiving and transmi ⁇ tting means and shaped reflecting means located within parabolic reflecting means in a cassegrainian or planar reflector arrangement.
  • the means for subjecting the received signal to a cross-correlation procedure comprises components which in combination are capable of making comparisons between the transmitted signal and the received signal.
  • the said means is a digital receiver comprising two complementary counter and memory means driven by a two phase-nonoverlapping clock means and ancilliary control logic means capable of
  • a signal from the transmitting means is converted to digital form by an analog to digital converter and fed as an input to a first n-word reference memory means and a signal - herein ⁇ after for convenience referred to as an echo signal - from the receiving means is also converted by the converter and then fed as an input to a second n-word echo memory means.
  • pulses are fed to a first and second counter means so as to increment both the modulo-n reference memory counter means and the echo memory counter means.
  • Samples of the transmitted signal in the reference memory means are compared with samples of the echo signal in ' the echo memory means in a correlating counter means and are thereafter converted to a visible or other usable form.
  • the comparison and cross-correlation of the transmitted and echo signals may be performed in a continuous or intermittent manner.
  • the means for measuring the lapse of time between the time of transmission of the transmitted signal and the time of receipt of the received signal is suitably a conventional means and may be for example a range time based oscilloscope display.
  • the means for caculating the distance between the first location and the second location is not narrowly critical and may be a conventional calculating means for example a suitably calibrated interval timer.
  • the device of the invention may be used in a process for measuring distances, as hereinbefore described, in a range of media.
  • the device may be used in seismic prospecting for the examination of geological structures of appropriate physical paramet ⁇ ers within the earth, or on the surface of the earth.
  • the device may also be used for determining the dist ⁇ ance between objects in a fluid medium such as an aqueous medium like sea water or fresh water, or in a non-aqueous medium such as a deposit of oil.
  • the fluid medium may be gaseous such as a deposit of gas, for example natural gas.
  • the device is partic ⁇ ularly useful for determining distances in the atmos ⁇ phere surrounding the earth, especially within the lower confines of that atmosphere wherein the concent ⁇ ration of air is sufficient to permit the transmission of acoustic energy therein.
  • the device may be used to determine the distance of an object, or objects, from a transmitting location. Whilst such an object may be stationary, for example it may be a building, an outcrop of rocks, or a tree; such an object may alter ⁇ natively be in a state of movement such as a moving vehicle, a crowd of people, a glacier, a lava flow or a moving particulate mass.
  • the device is of particular utility in operations commonly encountered in the general area of mining and quarrying.
  • acoustic noise constitute sound waves which exhibit a continuous frequency.spectrum composed of incoherent wave trains of different frequencies in which no frequency, phase or phase relationship is characteristic.
  • the means used hitherto to segregate the component comprising the transmitting signal from the noise component in the received signal have been insufficiently sophisticated to achieve a suitable degree of segregation unless the proportion of the noise component in the received signal was comparativ ⁇ ely small.
  • the cross-correlation techniques referred to herein and which we believe to be novel in this application are capable of segregating the noise component and the transmitted component to an extent which has not previously been possible in practical commercial terms. These techniques have been shown to be substantially immune to electronic component drift, and to be capable of segregating even a weak transmit- ted component from the noise component.
  • an alternative receiver employing a commutative filter technique may be used to advantage because of its simplicity and cost benefits.
  • Fig. 1 is a block schematic diagram showing a sequential connection of components to form a transmit ⁇ ting means used in a device of the invention and which is capable of converting electrical energy to acousti ⁇ cal energy which is transmitted as a frequency modul ⁇ ated tone burst as hereinbefore described;
  • Fig. 2 is a block schematic diagram showing a sequential connection of components to form a means for subjecting a received signal and a transmitted signal to a cross-correlation procedure as hereinbefore described;
  • Fig. 3 is a block diagram of an alternative trans ⁇ mitting and receiving device for use in low noise
  • Fig. 4 is a diagram outlining a mechanical arrang ⁇ ement of a sonic transmitting and receiving device in the preferred cassegrainian form.
  • FIG. 1 a voltage controlled oscillator (VCO) 1, an amplifier 2, a variable inductor 3, a transducer 4, phase comparator 5 and a buffer 6 form a phase locked loop.
  • VCO voltage controlled oscillator
  • the inductor 3 and transducer 4 form a resonant circuit and the phase comparator senses the phase of the current and voltage of this resonant circuit on.lines 5a (from current transformer 8) and 5b respectively so that when the phases are equal the circuit is at resonance the phase comparator supplies a voltage to the VCO via resisr tor R and switch Sib to VCO 1 so that the VCO supplies the desired frequency to maintain the circuit at or near resonance.
  • the inductor 3 includes a second winding 3a which is supplied with a signal which almost saturates the inductor 3 to alter the resonant frequency of the resonant circuit comprised of the inductor 3 and transducer 4 after swit- ches Sla and Sib are closed. Accordingly when the swit ⁇ ches are closed the transmitter omits an acoustic signal at the resonant frequency which is modulated by a freque ⁇ ncy modulating signal applied to the second winding 3a to alter the resonant frequency of the circuit so that the omitted frequency of the acoustic signal changes grad ⁇ ually to produce a chirp characteristic.
  • the switches Slb and Sla are opened to end the tone burst and the voltage which was applied to the VCO remains across capacitor C so that when the switches are again closed to produce another tone burst the desired voltage is applied to the VCO from capacitor C to ensure that the VCO applies the desired resonant frequency to the inductor and the transducer 4.
  • the switches Sib and Sla are open when the device receives a received signal including noise and an echo of the transmitted signal. Accordingly the circuit of figure 1 is able to produce a frequency modulated tone burst which will have no resemblance to the random noise generated in the environment in which the device of figures 1 and 2 is used.
  • Figure 2 is a logic diagram of a receiver.
  • the digital receiver which comprises two complementary counter and memory locations, is driven by a two phase non-overlapping clock and ancilliary control logic to make real-time comparisons between the transmitted and received signals.
  • comparisons of polarity only are made but the system may be expanded to compare signal amplitude as well as polarity if desired.
  • a signal representative of current wave form in the line 5a (figure 1) is applied to line 11 to be written into memory 100.
  • the signal representative of the current wave form of course corresponds to the emitted tone burst from transmitter 5.
  • the signal is converted to a digital signal by an A-D convertor (not shown) .
  • a two phase clock (the phases of which are shown in figure 2A) is represented by references ⁇ i and ⁇ 2 .
  • the count of phase ⁇ i is applied to OR gates 50 and 80 on line 12 and is then counted in counter 20 and 30.
  • the counters reach n counts (for example 256) the counters 20 and 30 produce a signal R ⁇ and En which in turn is applied to AND gates 60 and 70.
  • Mode control element 100 applies a signal Tx to gate 60 so that as soon as an output En from counter 30 and a pulse from the second phase ⁇ 2 arrive at gate 60 a write signal RWE is applied to memory 10 and a wave form sample on line 11 is written into the first memory location in memory 10.
  • n for example 256 storage locations in the memory have been filled.
  • the counter 20 will have an even n (256) counts more than counter 30 so that both counters will apply a signal Rn and En respectively to the AND gate 90 at the same time this produces an output at gate 90 which switches mode control 100 to produce an output Rx to gate 70 whilst disabling output Tx from gate 60.
  • the pulse which was emitted from transducer 4 is refl ⁇ ected from the desired object and is received by the
  • OM transducer 4 (which acts as a receiver) together with noise and this signal is converted by an A-D convertor (not shown) and is applied to line 14 as a sample of the received signal which contains both the desired echo and also noise.
  • OMPI means or otherwise to maintain the output Rx and to prevent the output Tx from being applied to gate 60. Accordingly further received samples on the line 14 will be written into memory 40 over the first n samples previously stored in the memory.
  • this sample is compared with the first sample in memory 10 whilst the memory 40 is awaiting the second write signal EWE to write the second sample into memory 40.
  • the first sample in memory 40 is applied on line 15 to EXCLUSIVE OR gate 120 whilst the first sample stored in memory 10 is applied to the gate 120 on line 16. If there is correlation between the two samplesi.e. if the samples are both high or both low an output will appear from gate 120 on line 19. " If the two samples are unlike one another no output will result from gate 120.
  • each of the n samples in each memory have been compared.
  • the gate 120 will produce an output as noted above and these outputs will be counted by correlator counter 130 and produces a total after each n samples have been correlated by receiving a signal from AND gate 110 when a pulse from phase ⁇ i and signal Rn (which occurs after each n counts in counter 20) to result in the total in counter 130 being passed to the output latch 140.upon receipt of the signal from gate 110. If there is good correla ⁇ tion between the samples in each memory the count in counter 130 will be relatively high. If the memory 40 contains mostly noise the count of course will be low.
  • EXCLUSIVE OR gate 120 produces the multi- pland x(t) y(t- ⁇ ) if there is correlation and the correlator counter 130 performs the addition over time.
  • the transducer 4 may be the transducer to be described with reference to figure 4 or it may simply be a transmitter such as a speaker and a separate receiver such as a micro ⁇ phone with associated amplifier etc. may be used to receive the echo and noise and apply the same as an electrical signal to line 14 (figure 2) .
  • Figure 3 shows an embodiment which may be used in a lessnoisy environment.
  • a phase comparator 51, resistor R,, capacitor C, buffer 61, VCO 62 and amplifier 21 form a phase locked loop which functions in the same manner as that described with reference to figure 1 by comparing the phase of the voltage and current on lines Sib and Sla respectively to provide an output from phase comparator 51 to VCO sufficient to result in the VCO 62 to produce an output n times the resonant frequency of inductor 31 and transducer 41.
  • the output of VCO 62 is divided by divider 71 by a factor of n to result in the resonant frequency being applied to the inductor 31 and transducer 41.
  • the transducer 41 may be a speaker and the inductance of inductor 31 remains constant to result in a tone burst of constant frequency being emitted from the transducer 41.
  • the VCO 62 is also coupled to a commutative filter 4 to sequentially switch the filter 74through n steps of n condensers C, to C . Accordingly the stepping frequency of the commutative filter 74 is controlled by the VCO 62 and is stepped at a rate n times greater than the frequency of the output tone burst from transducer 41 so that for one cycle of the output from transducer 41 the commutative filter 74 will be stepped over n times i.e. one complete cycles of the steps in the filter 74. Accordingly when the echo is received by a micro ⁇ phone 70 or any suitable transducer and amplified by amplifier 72 the signal is then filtered in narrow band filter 73 which allows only frequencies very close to the constant transmitted frequency of the tone burst to pass therethrough.
  • each full cycle of n steps will occupy a time interval exactly equal to the time interval occupied by one cycle of the transmi ⁇ tted signal, and hence also one cycle of the received signal.
  • any noise which happens to pass through filter 73 will not have a frequency synchronised with the stepping rate of the switch in commutative filter 74 and accordingly the noise will result in a mean charge on each of the capicators tending to zero.
  • the signal is synchronised with the stepping rate of the switch as will be the case when an echo is received each of the capacitors C-, to C will receive substantially the same charge during each switching cycle because the switching cycle as noted above occupies one cycle of the transmitted tone burst.
  • the commutative switch together with the resistor R, and capacitors C- C ⁇ -.-C of which there is one capacitor for each switch position, in combination form a band pass filter network the selectivity of which is optimised for the transmitted tone burst period and the signal input to which is restricted to frequencies at or near the transmitted tone burst frequency due to the action of the preceding but less selective, band pass filter 3.
  • the capacitors will individually accumulate a mean charge determined by the phase relationship of the signal and the output will be a series of n voltage steps having a similar waveform to the transmitted signal.
  • This output is applied to a squaring device 75 which squares the output so that the signal represent ⁇ ative of the echo will have a far greater magnitude than any noise which may remain in the system and this squared signal is filtered at 76 and displayed on an A scan as a peak.
  • the A scan commences its sweep or produces a peak when the tone burst was transmitted from the transducer 41 and the time for the transmitted signal to reach an object and return to the microphone 70 will be given by the time base scale on the A scan between the two peaks or at the location of the peak of the scan commenced when the tone burst was transmitted.
  • Figure 4 shows the preferred form of the transducer used in the embodiment of figures 1 to 3.
  • the transducer comprises a support element 108 which supports a base element 101 of the transducer.
  • the base element 101 is coupled to radiating element
  • a piezoelectric receiving element 110 is located at the end of the radiating element 102.
  • the support element 108 also supports a parabolic reflector 105 and planar reflector 113.
  • the planar reflector 113 is coupled to the parabolic reflector 105 by supporting rods 107 which extend from the periphery of the reflector to the planar reflector.
  • the energy is reflected from planar reflector 113 to the parabolic reflector 105 and then towards an object as shown by the line 111.
  • the planar reflector is so located relative to the parabolic reflector so that the acoustic energy produced from radiating element 102 appears to emanate from the focal point of the parabolic reflector 105 so as to produce generally parallel tone burst from reflector 105. Accordingly the acoustic energy can be directed at an object with great accuracy.
  • the echo or reflected tone burst 112 is reflected from the parabolic reflector 105 onto the planar refle- ctor 116 and then to the receiving element 110.
  • planar reflector is within the focal distance of the parabolic reflector 105 which results in a very compact transducer.

Abstract

Un dispositif de mesure de distance permet, dans un mode de realisation, d'identifier un echo d'un signal acoustique transmis dans un environnement brayant et, dans un second mode de realisation, est adapte davantage aux environnements moins bruyants. Le dispositif comprend un circuit de boucles fermees de phase (5, 6, 1, 2) qui envoient une frequence resonnante a un transducteur (4) qui resulte dans la transmission d'un train de signaux comptant pour une unite de tonalite de frequence modulee. Un signal recu subit une correlation croisee en stockant des echantillons du signal transmis dans une premiere adresse de memoire (10) et des echantillons du signal recu dans une seconde adresse de memoire (40). Les echantillons sont compares par une porte OU EXCLUSIF (120) pour determiner s'il y a correlation entre le signal recu et le signal transmis. Le nombre de correlations est compte dans un compteur (130) et le nombre est affiche sous forme de crete ou d'exploration A. Plus la crete est grande plus la correlation est grande. Par consequent, lorsqu'une grande crete est affichee, c'est une indication de la reception de l'echo et le temps ecoule entre la transmission et la reception peut etre lu a partir de la base de temps de l'exploration A et de la distance calculee. Dans un second mode de realisation un filtre (74) est synchronise avec un train de signaux comptant pour une unite de tonalite a transmission constante de sorte qu'un echo recu charge des condensateurs C1...Cn de la meme maniere pendant chaque cycle de l'echo recu indiquant la reception de l'echo. Le signal recu est ensuite applique a une exploration A de la meme maniere que celle decrite ci-dessus de sorte que de grandes cretes seront une indication de la reception de l'echo et le temps ecoule entre la transmission et la reception peut etre utilise pour calculer la distance entre l'objet et le point de reception.
PCT/AU1980/000040 1979-07-30 1980-07-30 Procede et dispositif de mesure de distance WO1981000456A1 (fr)

Priority Applications (1)

Application Number Priority Date Filing Date Title
AU61296/80A AU6129680A (en) 1979-07-30 1980-07-30 Method and device for measuring distances

Applications Claiming Priority (2)

Application Number Priority Date Filing Date Title
AU9774/79 1979-07-30
AU977479 1979-07-30

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WO1981000456A1 true WO1981000456A1 (fr) 1981-02-19

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Cited By (5)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
EP0286623A2 (fr) * 1987-04-09 1988-10-12 Alexander Dipl.-Ing. Dr. Metchev Arrangement de circuit pour l'acquisition de signaux chirp-modulés en particulier pour l'acquisition de signaux ultrasonique chirp-modulés
WO1993006503A1 (fr) * 1991-09-17 1993-04-01 British Nuclear Fuels Plc Dispositifs de mesure ultrasonore de distance
WO1996009559A1 (fr) * 1994-09-23 1996-03-28 Mayser Gmbh & Co. Procede de detection d'obstacles par ultrasons
EP0969292A2 (fr) * 1998-06-30 2000-01-05 Subacoustech Limited Télémètres, altimètres et aéronefs
WO2006129060A2 (fr) * 2005-06-01 2006-12-07 Tecteon Plc Detecteur d'echos a retard

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FR2353901A1 (fr) * 1976-06-01 1977-12-30 Standard Oil Co Procede et dispositif de calcul de correlation
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FR2414734A1 (fr) * 1978-01-13 1979-08-10 Schlumberger Prospection Dispositif et procede pour determiner la vitesse d'ondes acoustiques dans des formations terrestres
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US3217289A (en) * 1961-08-18 1965-11-09 Phillips Petroleum Co Signal analysis
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Cited By (12)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
EP0286623A2 (fr) * 1987-04-09 1988-10-12 Alexander Dipl.-Ing. Dr. Metchev Arrangement de circuit pour l'acquisition de signaux chirp-modulés en particulier pour l'acquisition de signaux ultrasonique chirp-modulés
EP0286623A3 (fr) * 1987-04-09 1990-11-28 Alexander Dipl.-Ing. Dr. Metchev Arrangement de circuit pour l'acquisition de signaux chirp-modulés en particulier pour l'acquisition de signaux ultrasonique chirp-modulés
WO1993006503A1 (fr) * 1991-09-17 1993-04-01 British Nuclear Fuels Plc Dispositifs de mesure ultrasonore de distance
AU646976B2 (en) * 1991-09-17 1994-03-10 British Nuclear Fuels Plc Ultrasonic ranging devices
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