SU1552013A2 - Device for determining frequency dependence of damping of acoustic vibrations - Google Patents

Abstract

The invention relates to acoustic measurements and can be used to evaluate the properties of materials from the non-uniformity of their amplitude-frequency response when probing them with acoustic vibrations. The purpose of the invention is to improve the measurement accuracy by measuring the relative frequency deviations of the path gain regardless of the absolute voltage levels of the fixed and variable frequencies, the conversion factors of the elements of the electrical conversion paths and the level of acoustic noise. The medium is probed with fixed and variable frequency acoustic packets. The reception signal is amplified, detected and fed to the recorder, where the probing variable frequency is also observed. Circuits for automatic level control of packets and transformations in the channels from the first 7 and second 22 acoustic transducers eliminate the instability of the probing signals and reduce the effect of acoustic interference. 1 il.

Description

The invention relates to acoustic measurements, can be used to record the frequency characteristics of acoustic paths and assess the geometric and physicomechanical properties of materials and media from the unevenness of their amplitude-frequency characteristics when sounding them by acoustic vibrations and is an improvement of the invention according to the author. St. No. 1016692.

The aim of the invention is to improve the accuracy of measuring the frequency deviations of the transmission coefficient of the acoustic path by measuring the relative frequency deviations of

t

path transmission efficiency regardless of the absolute voltages of fixed and variable frequencies, conversion factors of electrical transducer links and the level of acoustic noise.

The drawing shows a block diagram of a device for determining the frequency dependence of the attenuation of acoustic oscillations.

The device contains a series-connected fixed-frequency generator 1, an adjustable voltage amplifier 2, an automatic switch 3, to the second input of which a frequency generator 4 is connected, an acoustic vibrator 5, an acoustic path 6 under study, an acoustic transducer 7, an amplifier 8 made by a wideband amplitude detector 9, a switching frequency amplifier 10 and a synchronous detector 11, the output of which is connected via a low-pass filter 12 to. control input of adjustable voltage amplifier 2.

The device contains an adjustable attenuator 13, an amplifier 14, an amplitude detector 15, a switching frequency amplifier 16, a synchronous detector 17, the output of which is connected to the first input of the recorder 18, the second input of which is connected to the variable frequency generator 4. The output of the amplitude detector 15 is connected through the low-pass filter 19 to the first input of the differential amplifier 20, the second input of which is connected to the reference voltage source 21, and the output to the control input of the adjustable attenuator 13. The control inputs of the synchronous detectors 11 and 17, and

0

five

0

five

0

five

0

five

0

five

also the automatic switch 3 is connected to the output of the frequency divider 22, the input of which is connected to the output of the generator 1 of a fixed frequency. The second acoustic transducer 23 is connected to the input of an adjustable attenuator 13.

The device works as follows.

The output voltage of the generator 1 of the fixed frequency U4 Um4 / 1 + + U, / cos / (x) 0t is reduced by the adjustable amplifier 2 voltage to the level of the output voltage of the generator 4 of the variable frequency Ux Um2 / 1 + Cr / cos / COt + Cf /. The coefficient jp takes into account the relative changes in the amplitude Um, under the action of the control voltage of the amplifier 2. And the coefficient relative frequency changes to the amplitudes Umz. The fixed frequency C00 of the oscillator 1 is the reference, and the variable CO of the probe, varying in the range of the studied: frequencies of the acoustic

The path 6. The output voltage of the voltage amplifier 2 and the output voltage of the generator 4 are fed to the inputs of an automatic switch 3 controlled by the voltage of the generator 1 through a frequency divider 22. The switching frequency of switch 3 is selected from the condition Q "OE. Packages of electric voltages of a fixed frequency C00 and variable frequency Cx) are alternately converted into acoustic oscillations of the radiator 5, passing through the acoustic path under study 6. Packages of acoustic oscillations of a fixed cos (C00t +

+), (i + p. (t-Ј,) + (& :) and

variable tot + U) K, LU, rii (1 + fr) x (l + jf5) cos (tt |) + frequencies pass the acoustic path 6. The coefficient knots takes into account the relative frequency changes of the conversion coefficient K (electrical oscillations into an acoustic signal, and the parameter c, is the time delay in the process of converting electrical oscillations into acoustic oscillations. With the aid of a receiving acoustic transducer 7, acoustic oscillations are converted into electrical oscillations

and, -K, (1 + p2 Kgi „, ((t-V) +

, | r (1st) (1 +) (1 + y, zhg (n

+ f4) tWcos a (t-ЈI-Јi) (2)

15520136

variable component tends to zero and equality is established

where {- acoustic transmission coefficient

Ček tract 6; K 2 is the coefficient of the inverse transformation of acoustic oscillations into electrical ones; 6 - relative frequency deviations of the transmission coefficient of the acoustic path 6; 4 coefficient taking into account

relative frequency variations of the acousto-electric conversion coefficient;

2 time delay of acousto-electric conversion. Packs of electrical voltages U and U are alternately amplified by a wideband amplifier 8 and detected by an amplitude detector 9. When the voltage packet is not equal, the output voltage component of the switching frequency Q is formed at the output of the detector 9 with amplitude

Ut

thirty

K0 KoKlK (1 +

+ fcHi + fJ (i + y4Ki + f5 i + e D, n2 (ni,) (t), (3)

where KQ is the amplification factor of the amplifier 35 at the reference frequency C00;

V5 is the coefficient taking into account the non-uniformity of the amplitude-frequency characteristic 40 ki (AFC) of the amplifier 8; U (t) is a random voltage that takes into account acoustic disturbances in the probed path 6.-45

AC voltage AND is amplified by switching frequency amplifier 10 and rectified by synchronous detector 11. Interference U (t) is suppressed by a filter 12 from a large 50 constant time, the rectified voltage is fed to the control input of the regulated voltage amplifier about R automatic adjustment of the coefficient (equalize the amplitudes of the voltage packets of the reference and fixed frequencies at the output of the amplitude detector 9. At the same time

um, (1 + y,) it2 (1 +) (1 + y3) (c- + p (n-fc) (i + 6), (O

from where

I (1 + PO + X1 + dCHN1 + H1 +

Umz

+ Ј)

and

(five)

mi

The acoustic oscillations a and aa, which excite the subsequent path 6, are also converted into electrical oscillations t proportional to radiation. acoustic oscillations, and removed from the second electrode of converter 5, at the output of which we have

, (1 + y,) K2UM | cos Q, (t-C.-ti)

+ (6)

(1 + y2) (1+) Ka +

+ Y) lWcos GO (t-fc, -c2) + (f. (7)

Packages of electrical voltage U, - and U are attenuated by attenuator 13 and amplified by wideband amplifier 14. The initial attenuation of the adjustable attenuator 13 is chosen to be approximately equal to the attenuation of acoustic oscillations in path 6 at the reference frequency G50. Due to this, the gain of the wideband amplifier 14 is chosen to be approximately equal to the gain of the amplifier 8 and the blocks of the electrical paths 14-17 and 8-11 are identical. Frequency distortions in the amplifiers 8 and 14 are the same, the voltage bursts detected by the amplitude detector 15 are

, (1 + y,) K2K3K0 Um ((t- (8)

, K2K3 () (1 +) (1 +) (1 + + (t-t) -Ј1) +, (9)

where K3 t is the attenuator transfer ratio 13.

The constant component of the detected voltage is extracted by a low-pass filter 19.

Ua + Ui 1r.

uio22 ° 1 H-1

+ gr (1 + 1Г5) (1 + У4 (1 + у5) igo2 +

+ (1 + U,) itG. (S)

The voltages U, 0 and U0 of the source 21 of the reference voltage are compared using a differential amplifier 20, and the difference voltage U ,, К „(io-U ta) is used to adjust the gain ratio of the attenuator 2U,

K0K, (T + U,) (

TO

Variable voltage component Q of the output of the amplitude detector 16

and ynUfi

and 2

U,

mi

(1 + Ы (1 + 11Н1 + 1) () And | 1 1 1л1и

(T + uG) (1 + g7) o) (T + y7Tig + (1 + y,) and No.;

Thanks to the automatic regulation of the transfer ratio deli {

bodies 2 and the steady-state value of the coefficient 30, receive

(1 + B) -1

U

about

(14)

“„ - -tt; ty7r and

e

2 + 6 "

(15)

estimate the frequency dependence of the attenuation of acoustic oscillations.

From the expression (16) it follows that the measurement result is not affected by the inadequacy of the output voltage of the tunable frequency generator (y), the frequency variations of the electrical and acoustic frequency (jf}) and acoustic acoustics 6 ) f4) and non-uniformity of the frequency response of the wideband amplifier (jfg) Compared to the prototype, the effect of inconsistency in the levels of the packets of detected voltages u and tg is excluded, as well as the instability of the gains of the wideband waist amplifier and sensitivity

amplified by an amplifier 15 frequency-D5 amplitude detectors and their frequency distortions on the measurement result. This is achieved by introducing into the circuit of the device of an additional circuit of automatic adjustment of the path 6 the relative frequency variations of the acoustic transmission coefficient are small (). With this in mind, the expression (15) can be represented as

40

U

about

(sixteen)

Variable component

and,

You are switching and rectifying with a synchronous detector 17. The rectified voltage is applied to one input of the register 18, to the other input of which the output voltage JQ of the variable frequency generator 4 is applied. As a result, the relative frequency deviations of the 6 transmission coefficient H of the acoustic

nor (blocks 13, 19, 20, 21).

At the same time, the influence of the instability of the transmission coefficient of the inserted attenuator 13 (coefficient Ke) and the instability of the coefficient as a function of the frequency of the transmission probe of the differential transmission is excluded.

oscillations.

Based on the recorded relative frequency deviations of the acoustic path transmission coefficient

the amplifier 20 (the ratio K). Connecting an adjustable voltage amplifier through appropriate electrical units (7-11) allows

torus 13. As a result of the automatic adjustment of the attenuator transfer ratio 13, the compared voltages at the inputs of the differential amplifier 20 are equalized. As a result, equality is established.

one

  - K.KTsPP + U. + P (1 + y5 Umi + 0 + f,) Um, U0. (eleven)

In this case, the attenuation coefficient of the attenuator 13 becomes equal to

  (n

I

(12) + Ug) (II,) (1 +) (1-) it20

-d + fl,) um,

(13)

In view of the steady-state value of the attenuator transfer ratio 13,

i

U

about

(14)

nor (blocks 13, 19, 20, 21).

In this case, the influence of the instability of the transmission coefficient of the introduced attenuator 13 (coefficient Ke) and the instability of the coefficient 20 (coefficient K) is excluded. Connecting an adjustable voltage amplifier 2 through appropriate electrical units (7-11) allows

Using a low-pass filter 12, with a large time constant, the effect of acoustic noise in the path under study 6 is reduced, and the frequency dependence of the attenuation of acoustic oscillations is recorded using excitatory electrical oscillations in which there are no acoustic interferences.

Claims (1)

Invention Formula A device for determining the frequency dependence of the attenuation of acoustic oscillations according to ed. No. 1016692, characterized in that, in order to increase accuracy, it provides c but with an adjustable attenuator connected between the output of the second receiving acoustic transducer and the amplifier input, a differential amplifier, a reference voltage source and the first low-pass filter, whose input is connected to the input of the second switching amplifier, and the second low-pass filter, connected to the inputs, connected between the output of the first synchronous detector and the control input of an adjustable voltage amplifier, and the output of the differential amplifier is connected to the control one adjustable attenuator.