WO1996008700A1 - Procede pour mesurer les vibrations d'un objet soumis a essai - Google Patents

Procede pour mesurer les vibrations d'un objet soumis a essai Download PDF

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Publication number
WO1996008700A1
WO1996008700A1 PCT/SE1995/001018 SE9501018W WO9608700A1 WO 1996008700 A1 WO1996008700 A1 WO 1996008700A1 SE 9501018 W SE9501018 W SE 9501018W WO 9608700 A1 WO9608700 A1 WO 9608700A1
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WO
WIPO (PCT)
Prior art keywords
ultrasonic
test object
signal
frequency
measuring
Prior art date
Application number
PCT/SE1995/001018
Other languages
English (en)
Inventor
Hans Wilhelm Persson
Original Assignee
Hans Wilhelm Persson
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 Hans Wilhelm Persson filed Critical Hans Wilhelm Persson
Priority to AU35366/95A priority Critical patent/AU3536695A/en
Publication of WO1996008700A1 publication Critical patent/WO1996008700A1/fr

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Classifications

    • G—PHYSICS
    • G01—MEASURING; TESTING
    • G01H—MEASUREMENT OF MECHANICAL VIBRATIONS OR ULTRASONIC, SONIC OR INFRASONIC WAVES
    • G01H9/00—Measuring mechanical vibrations or ultrasonic, sonic or infrasonic waves by using radiation-sensitive means, e.g. optical means

Definitions

  • This invention relates to a method for measuring the vibrations of a test object, wherein an ultrasonic mea ⁇ suring signal having a frequency that is much higher than the vibration frequency of the test object is transmitted from an ultrasonic transmitter towards the vibrating test object, the ultrasonic signal reflected from the test object is detected by an ultrasonic receiver and is fre ⁇ quency-demodulated, and the frequency-demodulated signal is frequency-analysed with a view to determining the vibration frequency and/or the maximum vibration velocity of the test object.
  • This prior-art measuring method is advantageous by being contact-free, which is an absolute necessity when measuring the vibrations of light-weight objects.
  • This method further enables a high measuring accuracy, pro ⁇ vided that the vibration frequency of the test object is much lower than the frequency of the measuring signal.
  • a high ultrasonic frequency enables narrow ultra ⁇ sonic beams and, hence, small and well-defined measuring points on the test object.
  • the object of the present invention is, therefore, to make the above method for vibration measurement bet ⁇ ter suited for use by ensuring reproducible measurement results.
  • this object is achieved by a method which is characterised in that, before the vibration measurement, the absence of signals interfering with the ultrasonic signal reflected from the test object is ensured by transmitting from the ultrasonic transmit- ter an ultrasonic burst signal having the same frequency as the ultrasonic measuring signal and by substantially eliminating, through an alteration of the direction and/ or distance of the ultrasonic transmitter and/or the ultrasonic receiver in relation to the test object, any signals received by the ultrasonic receiver outside a predetermined time interval for the reception of the ultrasonic burst signal reflected against the test object.
  • the invention is thus based on the insight that the poor reproducibility of the measurement results, which may vary, say, something like ⁇ 30%, is among other things due to repeated reflections of the ultrasound between the ultrasonic transmitter and the ultrasonic receiver or reflections against objects located essen- tially somewhere between the transmitter/receiver and the test object.
  • the absence of inter ⁇ fering signals can be ensured before each measurement of the vibrations of the test object. This is of special importance when the conditions round the test object may change between successive measurements.
  • the measurement results are especially adversely affected when the ultrasonic measuring signal can bounce back and forth between the ultrasonic transmitter and the ultrasonic receiver. According to the invention, this is conveniently prevented by so directing the ultrasonic transmitter and the ultrasonic receiver that the direc ⁇ tion of the ultrasonic receiver does not coincide with the direction of the mirror reflection of the ultrasonic measuring signal in the test object.
  • Fig. 1 is a block diagram showing the arrangement of the equipment used for performing a vibration measurement according to the invention
  • Fig. 2 shows the frequency spectrum of an output signal from the equipment in Fig. 1
  • Figs 3 and 4 show a reflected measuring signal in, respectively, the presence and the absence of an inter ⁇ fering signal.
  • Fig. 1 illustrates the principle for the measurement method according to the invention.
  • a signal generator 1 operates an ultrasonic transmitter 2, which transmits ultrasound in the direction of a vibrating measuring point, for instance on the vibrating surface of a test object 3.
  • the transmitted ultrasonic signal is frequency-modulated as a result of the Doppler effect.
  • an ultrasonic receiver 4 the reflected ultrasonic signal is detected and converted to an electric signal.
  • the signal is demodu- lated in a detector 6 in the form of an FM demodulator.
  • the demodulated signal from the FM demodulator 6 is proportional to the vibration velocity of the measuring point.
  • the signal is also dependent on a few other parameters related to the ultrasonic signal.
  • the transmitted ultrasonic signal u c may be rendered as follows
  • V 1 is the peak value of the vibration velocity
  • u Cl KU c sin[2 ⁇ (f c +2f c V 1 cos( ⁇ 1 t)cos( ⁇ )/c)t] (5)
  • the FM demodulation results in a signal v x ⁇ corre ⁇ sponding to ⁇ f in the expression given above, i.e.
  • the output signal from the measuring system is a function of the transmitted ultrasonic fre ⁇ quency f c , the ultrasonic velocity c, the angle of inci- dence ⁇ of the ultrasound, the maximum vibration velocity V : of the measuring point, and the vibration frequency f .
  • the signal can be analysed with the aid of a frequency analyser, providing information on the vibration fre ⁇ quency f 1 and an amplitude V x ⁇ (see Fig. 2) .
  • V x ⁇ can be rendered as follows
  • V x ⁇ 2f c V 1 cos( ⁇ )/c (7)
  • V. V 1 ⁇ c/2f c cos( ⁇ ) (8)
  • the instantaneous vibration velocity Vi at the mea ⁇ suring point being now known as regards both amplitude and frequency, also the position x x and the acceleration a 1 of the measuring point can be calculated, since
  • a high ultrasonic frequency is required to achieve good measuring accuracy as regards the frequency and the amplitude. This is so because the equation (3) presup ⁇ poses that the vibration frequency is much lower than the ultrasonic frequency.
  • the presence of interfering signals can be estab ⁇ lished by setting the signal generator 1 in burst mode in accordance with the invention, i.e. having the signal generator transmit the ultrasonic measuring signal during a short period which, at the most, is of the same order as the propagation time of the measuring signal from the ultrasonic transmitter to the ultrasonic receiver via the test object, and which preferably is but about a third of this propagation time, and analysing the signal received by the ultrasonic receiver.
  • Fig. 3 shows, as a func ⁇ tion of time, an ultrasonic measuring signal reflected against a vibrating test object and received by the ultrasonic receiver 4.
  • the signal is shown before demo ⁇ dulation.
  • a signal portion A represents the transmitted ultrasonic burst signal, as reflected once against the vibrating test object, whereas a signal portion B repre ⁇ sents the same measuring signal reflected twice against the vibrating test object after bouncing back from the ultrasonic transmitter.
  • the presence of such interfering signals as the signal portion B represents normally results in an error in the amplitude v x ⁇ of the output signal from the detector 6.
  • the duration t 2 -t x of the burst period is about a third of the propagation time t ! -t 0 of the ultra ⁇ sonic signal from the transmitter 2 to the test object 3 and back to the receiver 4. If the burst period were to be prolonged, it might become difficult to discern the presence of interfering signals.
  • the presence of reflections from objects located essentially somewhere between the transmitter/receiver and the test object may result in interfering signals which, like the signal portion B, come after the signal portion A in time or come before the signal portion A in time. There may also occur such interfering signals as result in the signal portion A having a duration exceed- ing a predeterminable time interval.
  • the sig ⁇ nal generator having a measuring mode in which a conti ⁇ nuous ultrasonic signal is transmitted from the ultra ⁇ sonic transmitter 2, and a burst mode in which an ultra ⁇ sonic burst signal having the same frequency as the ultrasonic measuring signal is transmitted from the ultrasonic transmitter 2 towards the test object 3. It is detected whether the ultrasonic receiver 4 receives signals outside the predetermined time interval (for instance the interval t ! -t 2 in Fig. 3) for the reception of the ultrasonic burst signal reflected against the test object 3.
  • this or these interfering signals are eliminated by altering the direction and/or distance of the ultrasonic transmitter 2 and/or the ultrasonic receiver 4 in relation to the test object 3.
  • This proce ⁇ dure is repeated until the signal received by the ultra ⁇ sonic receiver 4 essentially presents only the signal portion A according to Fig. 4 and this signal portion A further falls within the predetermined time interval for the reception of the ultrasonic burst signal reflected once against the test object.
  • the absence of interfering signals may have to be checked more or less often. In order to guarantee correct measurement results at all times, the absence of interfering signals can be ensured before each measurement of the vibrations of the test object.
  • a particularly common interfering signal has proved to be the signal represented by the signal portion B in Fig. 3, i.e. an ultrasonic measuring signal bouncing several times between the ultrasonic transmitter 2 and the ultrasonic receiver 4. This signal may, for instance, be easily disposed of by not directing the ultrasonic transmitter 2 and the ultrasonic receiver 4 at the same angle to the normal to the surface of the test object 3 at the measuring point.
  • the ultrasonic transmitter 2 and the ultrasonic receiver 4 can be offset in relation to each other in the plane of the test object 3 at the measuring point.
  • the direction of the ultrasonic receiver 4 should not coincide with the direc- tion of the mirror reflection of the ultrasonic measuring signal in the test object 3.
  • Other signals interfering with the signal received by the ultrasonic receiver 4 can be disposed of by chang- ing the spacings of the test object 3 and, respectively, the ultrasonic transmitter 2 and the ultrasonic receiver 4.
  • the amplitude of any interfering sig ⁇ nals can be reduced by increasing these spacings.
  • the frequency of the ultrasonic measuring sig- nal is of importance to the presence of interfering sig ⁇ nals.
  • a high frequency of the ultrasonic measuring signal is advantageous already for the reason that it enables well-defined measuring points and the measurement of fairly high vibration frequencies.

Abstract

Dans un procédé pour mesurer les vibrations d'un objet soumis à essai, un signal de mesure ultrasonore présentant une fréquence bien supérieure à la fréquence de vibration de l'objet soumis à essai (3) est émis par un émetteur ultrasonore (2) en direction de l'objet vibrant soumis à essai. Le signal ultrasonore réfléchi par l'objet soumis à essai est détecté par un récepteur ultrasonore (4) et est démodulé en fréquence, puis le signal démodulé en fréquence est analysé en fréquence en vue de déterminer la fréquence de vibration et/ou la vitesse de vibration maximale de l'objet soumis à essai. Avant cette mesure de vibration, l'émission par l'émetteur ultrosonore (2) d'un signal de salve ultrasonore ayant la même fréquence que le signal de mesure ultrasonore permet de s'assurer de l'absence de signaux brouillant le signal ultrasonore réfléchi par l'objet soumis à essai. Tous les signaux reçus par le récepteur ultrasonore (4) en dehors d'un intervalle de temps prédéterminé pour la réception du signal de salve ultrasonore réfléchi par l'objet soumis à essai (3) sont pratiquement éliminés par modification de la direction et/ou de la distance de l'émetteur ultrasonore et/ou du récepteur ultrasonore par rapport à l'objet soumis à essai.
PCT/SE1995/001018 1994-09-12 1995-09-11 Procede pour mesurer les vibrations d'un objet soumis a essai WO1996008700A1 (fr)

Priority Applications (1)

Application Number Priority Date Filing Date Title
AU35366/95A AU3536695A (en) 1994-09-12 1995-09-11 Method for measuring the vibrations of a test object

Applications Claiming Priority (2)

Application Number Priority Date Filing Date Title
SE9403028A SE502506C2 (sv) 1994-09-12 1994-09-12 Sätt att mäta vibrationer hos ett mätobjekt
SE9403028-5 1994-09-12

Publications (1)

Publication Number Publication Date
WO1996008700A1 true WO1996008700A1 (fr) 1996-03-21

Family

ID=20395194

Family Applications (1)

Application Number Title Priority Date Filing Date
PCT/SE1995/001018 WO1996008700A1 (fr) 1994-09-12 1995-09-11 Procede pour mesurer les vibrations d'un objet soumis a essai

Country Status (3)

Country Link
AU (1) AU3536695A (fr)
SE (1) SE502506C2 (fr)
WO (1) WO1996008700A1 (fr)

Cited By (3)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
GB2463257A (en) * 2008-09-04 2010-03-10 Elio Poggiagliolmi Stabilized platform for an ultrasonic Doppler vibrometer for sensing motion of a surface
CN109143245A (zh) * 2018-09-18 2019-01-04 国网江苏省电力有限公司盐城供电分公司 一种基于超声波的非接触式振动信号测量系统及其测量方法
US10240972B2 (en) 2015-08-05 2019-03-26 Lovejoy Controls Corporation Doppler ultrasonic velocity probe

Citations (3)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US2733597A (en) * 1956-02-07 Apparatus for measuring vibrations
GB1535745A (en) * 1974-12-23 1978-12-13 Hewlett Packard Yokogawa Moving target detector
DE3404032A1 (de) * 1984-02-06 1985-08-08 Robert Bosch Gmbh, 7000 Stuttgart Ultraschall-sensor zur bewegungserkennung

Patent Citations (3)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US2733597A (en) * 1956-02-07 Apparatus for measuring vibrations
GB1535745A (en) * 1974-12-23 1978-12-13 Hewlett Packard Yokogawa Moving target detector
DE3404032A1 (de) * 1984-02-06 1985-08-08 Robert Bosch Gmbh, 7000 Stuttgart Ultraschall-sensor zur bewegungserkennung

Cited By (7)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
GB2463257A (en) * 2008-09-04 2010-03-10 Elio Poggiagliolmi Stabilized platform for an ultrasonic Doppler vibrometer for sensing motion of a surface
WO2010026386A2 (fr) * 2008-09-04 2010-03-11 Elio Poggiagliolmi Appareil pour détecter le mouvement d'une surface
WO2010026386A3 (fr) * 2008-09-04 2011-04-21 Elio Poggiagliolmi Appareil pour détecter le mouvement d'une surface
US8842494B2 (en) 2008-09-04 2014-09-23 Entec Integrated Technologies Apparatus for sensing motion of a surface
US9081113B2 (en) 2008-09-04 2015-07-14 Entec Integrated Technologies Limited Apparatus for sensing motion of a surface
US10240972B2 (en) 2015-08-05 2019-03-26 Lovejoy Controls Corporation Doppler ultrasonic velocity probe
CN109143245A (zh) * 2018-09-18 2019-01-04 国网江苏省电力有限公司盐城供电分公司 一种基于超声波的非接触式振动信号测量系统及其测量方法

Also Published As

Publication number Publication date
AU3536695A (en) 1996-03-29
SE9403028D0 (sv) 1994-09-12
SE9403028L (sv) 1995-10-30
SE502506C2 (sv) 1995-10-30

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