SU913235A1 - Device for measuring ultrasound absorption coefficient - Google Patents

Description

one

The device relates to non-destructive materials research methods and can be used in determining the absorption coefficient of ultrasound in gases and liquids.

Known digital ultrasonic interferometer of constant length, designed to measure the speed and absorption of ultrasound in liquids, containing an electro-acoustic path consisting of a series-connected frequency generator, a measuring chamber of constant length with radiating and receiving electroacoustic transducers, an amplifier, a level determination unit 0.707 and a setting unit, also frequency - voltage, detector and digital voltmeter connected in series to indicate the coefficient of the absorption unit and measuring the ultrasonic velocity (13.

A disadvantage of this device is the low accuracy of measurements, due to the accuracy of the conversion time2

This is the voltage and non-linearity of the detector * torus.

The closest to the invention in technical essence and the achieved result is a device for measuring the absorption coefficient of ultrasound, containing a series-connected and ring-closed ultrasonic oscillation generator, a radiating transducer, an electro-acoustic chamber, a receiving transducer, an amplifier, a threshold element and the first tuner, serially connected mixer , the first input of which is connected to the output of the generator of ultrasonic vibrations, and the measuring unit, will follow flax connected the second tuner and a local oscillator whose output is connected to a second input of the mixer (2].

A disadvantage of the known device is the low measurement accuracy, since the measurement process is divided into several intervals, in each of the cat

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There is an error of discreteness equal to the unit of the lower order.

The chain of the invention is to improve the measurement accuracy.

The assigned circuit is achieved by the fact that the 5 second tuner configured as a series-connected frequency demodulator having an input connected to the output of the mixer, the low pass filter ^- and subtractor block 10 torogo Ko output represents the output of the second tuner, and the detector connected between the output of the frequency demodulator and the second input of the subtracting unit. 15

FIG. 1 is a block diagram of the device; in fig. 2 - voltage diagrams explaining the operation of the circuit.

A device for measuring the absorption coefficient of ultrasound, contains 20 series-connected and ring-closed ultrasonic oscillator 1, a radiating transducer 2, an electro-acoustic chamber 3, a receiving transducer 4, an amplifier 5, a threshold 25 element 6 and the first tuning unit 7 connected in series by a mixer 8, the first input coupled to an output of the generator 1 of the ultrasonic vibration and the measurement block 9, po- _W d consequently connected the second adjustment unit 10 and a local oscillator 11 whose output is cos dinene with the second input of the mixer 8, in addition, the second tuner is made in the form of serially connected frequency demodulator 12, the input of which is connected to the output of the mixer 8, low-frequency filter 13 and subtractive unit 14, the output of which is the output of the second tuning unit ₄ θ 10 and a detector 15 connected between the output of the frequency demodulator 12 and the second input of the subtracting unit 14.

The first block 7 settings can be ₍ performed, for example, in the form of serially connected counting trigger 16 and integrator 17.

The device works as follows.

The frequency of the oscillator 1 ultrasonic vibrations under the influence of the signal from the first block 7 settings is changed in one direction or another. Ultrasonic waves emitted by transducer 2 propagate in the medium under study in chamber 3 and are repeatedly reflected from transducers 2 and 4. At the frequency at which a whole number of half-waves are located in the medium under study, the column of the medium resonates. At this frequency £ _{0, the} output voltage 18 (Fig. 2) of the converter 4 and the amplifier 5 is maximum and decreases with detuning in any direction. The threshold element 6 remembers the amplitude of the maximum voltage, compares it on a certain scale with the current amplitude and gives out a pulse every time the current amplitude becomes equal to 0.707 from the maximum value. The pulses from the output of the threshold element 6 are fed to the counting input of the trigger 16 in the first block 7 settings and periodically transfer it from "O" to "1" and back. The voltages from the output of the trigger 16, having the form of a meander, are converted by a integrator 17 into a triangular pulse forms, the constant component of which is equal to the average value of the output voltage of the trigger 16, and the period is proportional to the band of the resonance curve of the camera 3, measured at the level of 0.707. As a result of the triangular impulse sequence cos input generator 1, the latter generates a frequency-modulated oscillation, is equal to the average frequency £ _0, and the frequency deviation is equal to half of said strip.

Frequency-modulated oscillations from the output of the generator 1 are also fed to one of the inputs of the mixer 8, which is included in the auto-frequency closed loop (AFC) of the local oscillator 11. After starting the measurement of the absorption coefficient due to the AFC, the local oscillator 11 produces a signal whose frequency approaches the average frequency ίο of the oscillator 1 , and at the end of the adjustment process, its frequency becomes equal to ~ d £ where $ 0 · is the oscillator frequency, the local oscillator frequency, is the oscillator frequency deviation 1.

The mixer 8 selects the signal 19 of the difference frequency. The average value of the difference frequency, corresponding to the absorption coefficient, is measured by block 9 for a sufficient time, so that the fraction of the error due to the discreteness of the measurement becomes very small. The above adjustment of the local oscillator is provided by the second block 10 settings, which works as follows. The signal of the difference frequency from the output of the mixer is converted by the frequency demodulator into a low-frequency signal. This signal 19 represents the end

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the process of adjusting the heterodyne triangle-connected in series and closed

oscillations, the amplitude of which is proportional to the frequency deviation of the generator 1, and the constant component corresponds to the difference between the average value of the frequency of the generator 1 and the current frequency of the local oscillator 11. The variable component is filtered by filter 13, and at the first input of the block 14 there is only a constant component This is the demodulated signal 19. The variable component is also detected by the detector 15 and in the form of a constant level 20 is fed to the second input of the subtracting unit 14. The AFC system reduces the difference between for these voltages to the level of static regulation error and thus ensures the correspondence between the constant component of the difference frequency at the input of the measuring unit 9 and the frequency deviation of the generator 1.

The proposed implementation of the second tuner allows, in the process of measuring the absorption coefficient of up-25 ka, to use as an informative parameter not the generator frequency deviation, but its average value, which can be measured with a very high degree of accuracy. . .. go

Claims (1)

Claim Device for measuring the absorption coefficient of ultrasound, containing in the ring generator of ultrasonic vibrations, a radiating transducer, an electro-acoustic chamber, a receiving transducer, an amplifier, a threshold element and the first tuner, a serially connected mixer, the first input of which is connected to the output of the ultrasonic oscillator, and a measuring unit, sequentially connected the second tuner and the local oscillator, the output of which is connected to the second input of the mixer, characterized in that, in order to improve the measurement accuracy, the second setting unit is designed as ovatelno connected frequency demodulator having an input connected to the output of the mixer, the low pass filter and subtractor unit whose output represents the output of the second tuner, and a detector connected between the output of the frequency demodulator and a second input of the subtractor unit.