SU1753295A1 - Vibration measuring method - Google Patents

Abstract

The invention relates to a measurement technique and can be used to measure mechanical vibration parameters using acoustic waves. The purpose of the invention is to improve the accuracy by taking into account the nonlinearity that occurs when the frequency modulation of an acoustic wave during reflection. When implementing the method of a vibrating object, a reflected wave is received, a frequency shift is differentiated by time, according to characteristic time intervals, measured between extreme values of a differentiated signal, taking into account the derived working relationships, judging the amplitude of mechanical vibrations, 1 sig.

Description

The invention relates to a measurement technique and can be used to measure mechanical vibration parameters using acoustic waves.

There is a method for measuring the motion parameters using radiated and reflected acoustic waves, which determines the velocity of an object in terms of the Doppler frequency shift. Here, it is considered that the Doppler frequency shift Af is proportional to the velocity v of the movement of the object:

Af 2f0v / c,

Yelvano yns.

to the woman about the dog (D

Comparing formulas (2) and (1), it can be seen that when calculating the velocity v by formula (1), one encounters a measurement error. This is a disadvantage of the method. In addition, in the definition method, to determine v, the frequency fo must be additionally measured, since it is included in the working expression (1).

The closest to the present invention is a method for measuring the amplitude x0 of mechanical vibrations of an object from the Doppler shift of the frequency of the acoustic incident and reflected waves. If the vibration of the object is harmonic, then the vibration velocity changes according to the law.

VI

SP

with you

SP

where fo is the frequency of the emitted wave;

c is the phase velocity of wave propagation in the medium.

However, the exact formula for calculating the Doppler frequency shift, which in our case is derived from the well-known formula for H 0, is as follows:

"J i-hr

f

v NC x0cos (tt) t),

(3)

where (o is the cyclic frequency of the object,

t - time

However, in this method, the law of dependence of L f on v is considered linear, i.e. as a calculation formula for determining

x0 takes formula (1), and encounters a systematic measurement error,

The disadvantage is that it is necessary to additionally measure the reference frequency f0, which is included in the calculation formula (1).

The aim of the invention is to improve accuracy by taking into account non-linearities.

The essence of the invention is that when differentiating the Doppler frequency shift in time, measuring characteristic time intervals and determining x0 by the formula (4), it is possible to improve the accuracy by taking into account the nonlinearities of the main dependence of the Doppler effect (2).

The drawing shows the characteristic course of the informative signal obtained by time differentiation of the Doppler frequency shift (2) when measuring the vibration velocity according to the law (3).

The method is carried out as follows.

An acoustic wave is propagated in the direction of the vibrating object (so that the wave vector is collinear to the velocity vector). Accept the wave reflected from the object. The informative signal is obtained by time differentiation of the Doppler frequency shift. Conditionally take the second extremum from any pair of nearby neighboring extremes of the informative signal for the first. The time interval Ati between the first and nth extremes (n is an even number, n 2: 2) and the time interval A t between the first and (n + 1) th extremums of the last signal are measured, and the amplitude of oscillations is determined by the formula

Ho

with At

HACS (LP (Ati / At - 1) / 2)

Where A ctgV n (A ti / At -1) / 2);

c is the phase velocity of wave propagation in the medium.

We present the derivation of formula (4).

Let the vibration velocity of an object vary according to the law (3). Substituting v from (3) into expression (2), we obtain the dependence of the Doppler frequency shift A f on time t. The obtained A f is differentiated in time t and we obtain the dependence of the informative signal on time t. To find the condition of the extremum of the informative signal, we once again differentiate the previous time dependence. Equate to the result of this

expression is zero and we get a relation relating the desired amplitude of mechanical vibrations x0 to the phase of the maximum of the informative signal (l) max. Considering

relations connecting the maximum phase of the informative signal (ftrtjmax with characteristic time intervals Au and At; we express from the previous relation and we obtain the calculation formula of method (4).

The method provides for the possibility of carrying out calculations over large intervals of time (in the sense that information can be obtained not only by one, but also by any number of informatics periods; a hich signal), which also increases the accuracy of measurements.

For the implementation of the method, UT was used in the 1 MHz range.

Using a generator, electric

the signal of which was amplified by a power amplifier, and a connected piezoelectric transducer was irradiated with an ultrasonic wave by a vibrating object. The reflected signal, perceived by the receiving piezoelectric element, was transformed by it again into an electrical signal. This signal was amplified and fed to the mixer. On the same mixer received a signal from the reference frequency. From the mixer output, the frequency of the resulting electrical signal, equal to the Doppler frequency shift A f, was measured using a digital frequency meter connected to a computing unit built on the basis of Electronics-60,

The operations of differentiation and change of characteristic time intervals Ati and At were carried out programmatically.

The developed method allows measuring vibration velocities in a wide range of up to several hundred m / s.

To determine x0, it is not necessary to additionally measure the reference frequency f0, as can be seen from the working formula (4).

In the proposed method, non-linearities are taken into account (systematic errors of the prototype are excluded), since the working formula (4) is derived from (2) with all non-linearities taken into account (without approximate assumptions), which increases the accuracy by an average of 3.2

times.

The dynamic measurement range is expanded, as in the proposed method the ratios are exact, while in the prototype because of the assumed linearity assumption

limit the dynamic range of measurements so that systematic errors do not increase.

Claims (1)

Compared to other known technical solutions, for example, by measuring using piezoelectric sensors, the proposed method has the advantages associated with the possibility of measuring the meter from the object, as well as the ability to measure a high level of vibrations, in which contact piezoelectric transducers are usually destroyed. The method of measuring vibrations, which consists in directing an acoustic wave to a controlled object, registering the reflected acoustic wave converted into an electrical signal, detecting it, and judging by the parameters of the detected electrical signal, that, in order to improve accuracy by taking into account the nonlinearity arising in the frequency module 0 reflection of the acoustic wave, differentiate the detected electric signal by time, determine the time interval Ati between any of the extremes of the received signal, which is taken as the first, and the nth extremum of this signal, counting n 2k, where k 1,2 , 3 ..., measure the time interval At between the First and (n + 1) th extremums, and the amplitude of the object oscillations is determined by the formula: x0 With At jzncos LP (Ati / At - 1) 751 BUT four-, rfleA (Ati / At- 1) c is the phase velocity of wave propagation in the medium. 20