SU446824A1 - Digital device for measuring the speed of propagation of ultrasonic vibrations - Google Patents

Description

The invention relates to the field of ultrasonic measuring technology.

Devices for measuring the velocity of propagation are known. ultrasonic combi nation containing an electroacoustic sensor with a buffer rod and a test object, connected to an amplifier connected to an oscilloscope, and a generator of radio pulses, and a clock extraction circuit containing an electric meter.

However, these devices have a comparatively low accuracy in measuring the attenuation of acoustic oscillations near the points of phase transitions in ferroelectric crystals due to the distortion of the envelope shape of the reflected pulses. These distortions cause temporal shifts of the pulses at the output of the formation circuit and, accordingly, changes in the repetition rate in the ring circuit.

2

In order to improve the accuracy of measuring the propagation speed of ultrasonic vibrations, the proposed device contains a short video pulse generator connected to a frequency meter and a sync pulse extraction circuit, and an additional circuit for extracting two pulses from a sequence of pointed pulses, coupled with a short video pulse generator, a sync pulse extraction circuit and a radio pulse generator and consisting of the first trigger connected via the coincidence circuit to the second trigger, with the output of the second The first trigger is connected to the input of the first trigger, and the input of the coincidence circuit is connected to a high-frequency generator.

Figure 1 shows the block diagram of the proposed device; 2 shows graphs explaining the operation of the device.

The device contains a generator

I pointed video pulses, frequency meter 2, clock extraction circuit 3, 4 coincidence circuit, first trigger 5, second trigger b, generator 7 radio pulses, sensor 8, buffer rod 9, object under study 10, amplifier II, oscilloscope 12, sequence extraction circuit 13 from two pulses.

The device works as follows.

In the initial state, the triggers 5 and 6 are in the zero position and the circuit is in the closed state. The generator I produces short pulses (Fig. 2a), the frequency of which is controlled by the frequency meter 2. These pulses go to circuit 3 and circuit 13. Circuit 3 produces short pulses of low frequency (Fig.26), synchronous in frequency with the pulses of the generator I.

The output pulse of the synchronization circuit trigger 5 switches to state I (Fig. 2b), opening circuit 4. Another pulse from generator I through circuit 4 triggers trigger b to state I Figure 2d) This trigger is turned on in counting mode, therefore after When it arrives at its., the input of the second impulse trigger b returns to its original state, and after the front edge of the output impulse of this trigger, the trigger is reset: to the initial zero state, as a result of which the circuit is closed. Thus, with the arrival of each sync pulse at the output of the coincidence circuit, two pulses are selected from the sequence received from generator 1, and the distance between these pulses is equal to the period of the pulse generator t and t (fig.2d).

Each of the two pulses triggers a generator 7, which produces two radio pulses (Figure 2e), the distance between which is equal to the distance between the trigger pulses. The generator 7 is made according to the shock excitation scheme, therefore the initial phases of the radio pulses are the same. Received radio pulses are fed to an electroacoustic transducer of sensor 8. Acoustic pulses of sensor 8 through a buffer rod 9 are fed to the object under study 10. Repeatedly reflected pulses are extracted on an electro-acoustic transducer of the sensor as a series of damped radio pulses. Number of such

The pulses depend on the magnitude of the acoustic loss in the sample and vary depending on the substance under study and its phase state.

When two radio pulses arrive, the distance between which is equal to twice the transit time of acoustic pulses in the sample, the sequences of multiply reflected pulses formed by the first and second pulses are superimposed, so that the first reflected pulse of the second series coincides with the second reflected pulse of the first series and so on. d. The conditional position of the superimposed series of pulses is shown in Figures 2g, 3, and.

The considered alignment is performed by adjusting the frequency of the oscillator -I, as a result of which the distance between the radio pulses changes until the complete alignment of the reflected pulses of the first and second series in phase. The combination is monitored by an oscilloscope 12 connected to sensor 8 through amplifier II.

The speed of propagation of ultrasonic pulses will be equal to:

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 21-T

V

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where I is the thickness of the sample,

 Thus, when examining samples in which the shape of the envelope of the reflected pulses is distorted, these distortions are the same and, when combined, overlap. With an exact overlap, when it is reached, the maximum amplitude of the combined pulse, no additional distortion occurs.

SUBJECT OF INVENTION

A digital device for measuring the speed of propagation of ultrasonic vibrations, containing an electroacoustic sensor with a buffer rod and a test object, connected to an amplifier connected to an oscilloscope and a radio pulse generator, and a sync pulse extraction circuit containing an electric meter, characterized in that contains a generator of short video pulses, connected with frequency

and a clock extraction circuit, and an additional two pulse extraction circuit from a sequence of pointed pulses, connected to a short video pulse generator, a clock extraction circuit, and a radio pulse generator, and consisting of a first trigger connected via a coincidence circuit to the second trigger, the second trigger output being connected to 5 to the input of the first trigger, and the input of the coincidence circuit is connected to: a high-frequency generator.

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