RU2621890C1 - Method for reducing dead zone under product control by ultrasonic echo-pulse method - Google Patents

Abstract

FIELD: physics.

SUBSTANCE: method for reducing the dead zone in the product control by the ultrasonic pulse-echo method is that a transducer is mounted on the controlled product through the acoustic delay line, an ultrasonic pulse is input to the controlled product, and the pulse is compensated, reflected from the product interface and the acoustic delay line, by the pulse analogous by shape and amplitude. Before the control, the transducer is mounted on the adjustment sample through the acoustic delay line, the ultrasonic vibrations are excited, the pulse is fixed, reflected from the adjustment sample interface and the acoustic delay line, and this pulse is used for compensation. Herewith the thickness of the adjustment sample is chosen such that the acoustic delay in the adjustment sample is greater than or equal to the acoustic delay in the controlled product layer. The delay line is a waveguide, and the pulse is used as a compensating pulse doubly reflected from the acoustic delay line interface and the controlled product.

EFFECT: improving the accuracy.

5 cl, 4 dwg

Description

The invention relates to non-destructive testing and can be used with ultrasonic flaw detection and thickness measurement.

There is a method of reducing the dead zone when monitoring products using an ultrasonic echo-pulse method (ed. Certificate of the USSR No. 125935), in which a piezoelectric element (transducer) is installed on the controlled product through an acoustic delay line, for example through a liquid layer, an ultrasonic pulse is introduced into the controlled product and compensate for the impulse reflected from the interface of the product and the acoustic delay line with a similar in shape and amplitude impulse obtained by reflecting the main oscillations of the piezoelectric element from the additional th special reflector.

In this case, the pulse reflected from the boundary “controlled product - liquid layer” is compensated by subtracting two acoustic pulses arriving at the piezoelectric element, which can significantly reduce the “dead zone” within which defect detection is impossible.

The disadvantage of this method is the low accuracy of the compensation of the pulse reflected from the boundary "line of acoustic delay - controlled product". Indeed, when using a pulse reflected from a reflector and excited by the back of a piezoelectric element located in a liquid as a compensating signal, it should be taken into account that the reflector itself will distort the shape of the pulse, since in addition to the pulse reflected from the “reflector – liquid” interface, an additional signal caused by repeated re-reflection of the initial pulse in the reflector. In addition, during the control process, both the amplitude and the acoustic delay of the pulse reflected from the boundary “liquid - controlled product” can change. Since the compensating impulse is supplied directly to the piezoelectric element, to compensate for these changes, it is necessary to mechanically change the distance between the piezoelectric element and the reflector, as well as the size of the reflector itself.

Thus, in the method under consideration, the compensation of the pulse reflected from the boundary “controlled product is the acoustic delay line” is performed by subtracting the acoustic pulses supplied to the piezoelectric element, with the compensation pulse being adjusted mechanically, which makes this variant of the considered method not applicable for practical control.

The objective of the invention is to increase the accuracy of the compensation of the impulse reflected from the boundary "line of acoustic delay - controlled product", as well as expanding the scope of the method.

The technical result consists in the fact that the compensation of the pulse reflected from the boundary of the "controlled product is the line of acoustic delay", a similar in shape and amplitude of the pulse is carried out electronically.

The technical result is achieved by the fact that in the method of reducing the dead zone when monitoring products with an ultrasonic echo-pulse method, namely, that a transducer is installed on the controlled product through an acoustic delay line, an ultrasonic pulse is introduced into the controlled product and the pulse reflected from the “controlled” border is compensated the product is an acoustic delay line ”, similar in shape and amplitude to a pulse, according to the invention, before the product is checked, Tel via line acoustic delay adjustment sample excite ultrasonic vibrations fixed pulse reflected from the boundary of the adjustment sample section, and the acoustic delay line, and use this pulse to compensate.

The method works as follows. The transducer 1 (see Fig. 1) through the acoustic delay line 2, made, for example, in the form of a liquid layer, is installed on the tuning sample 3, the thickness of which is selected so that the condition

T _r ≥T _s

where T _about - the acoustic delay of the signal in the tuning sample;

T _with - the acoustic delay of the signal in the controlled layer of the product.

Ultrasonic vibrations are excited, a pulse is received reflected from the boundary “acoustic delay line - tuning sample”, the pulse amplitude is normalized and stored, for example, by digital signal processing on a PC. Install the same transducer 1 through the same line of acoustic delay 2 to the controlled product 4 (Fig. 2), excite ultrasonic vibrations, receive a signal, normalize the amplitude of the pulse reflected from the boundary “acoustic delay line - controlled product”, and subtract from the received signal previously stored pulse. Since the main and compensating pulses from the interface are received by the same converter, their mutual compensation can be performed quite accurately, while the pulse from defect 5 can be distinguished.

Conditions _of T ≥T _with bottom ensures that no sample pulse in the control zone product.

For the convenience of normalizing the first arrivals of pulses reflected from the boundary and controlling the completeness of compensation, it is preferable to choose the length of the acoustic delay line from the condition:

2T _l > T _imp ,

where T _l is the acoustic delay of the signal in the line of acoustic delay;

T _imp - pulse duration.

In some cases, with the stability of the waveform at the surface of the controlled object, the fulfillment of this condition is not mandatory.

In the case when the acoustic delay line is made in the form of a waveguide, i.e. in the form of a medium bounded in the transverse direction, an impulse reflected from the “waveguide –controlled product” interface will be formed both due to rays normally incident on the “waveguide –controlled product” interface and due to rays incident on the interface at some angle. Since the reflection coefficient in the general case depends both on the angle of incidence of the wave and on the ratio of the wave resistances of the boundary media, the momentum reflected from the interface “waveguide - controlled product” may differ from the momentum reflected on the interface “waveguide - tuning sample ".

In the proposed method according to claim 2, the technical result is achieved in that in the method of reducing the dead zone according to claim 1, a waveguide is taken as the acoustic delay line, and the tuning sample is made of a material whose acoustic properties are close to the acoustic properties of the material of the controlled product.

The method works similarly to the method of claim 1.

In the case when the surface of the controlled product or the acoustic properties of the material of the product are not homogeneous enough, during the control process the signal reflected from the surface of the product can change its shape. In this case, the compensation by the pulse received from the training sample will not be complete.

The technical result of the method according to claim 3 is achieved by the fact that in the method of reducing the dead zone according to claim 1, the controlled product itself is taken as a tuning sample, and a pulse reflected twice from the boundary of the acoustic delay line and the controlled product is used as a compensating pulse. the length of the delay line is selected from the condition:

T _l ≥T _s

The method works as follows. On the controlled product 4 through the line of acoustic delay 2 install the Converter 1 (Fig. 3). Signal U _{1 is} recorded and stored, consisting of a pulse reflected directly from the product boundary, as well as a pulse reflected from defect 5, if any (or a bottom pulse during thickness measurement), and re-reflection pulses.

Where

F _(t) is a function that defines the shape of the pulse;

R ₂ is the reflection coefficient of the signal at the boundary between the acoustic delay line and the product;

R _d - the reflection coefficient of the signal from the defect (from the opposite surface of the product);

D is the coefficient of signal transmission through the boundary of the acoustic delay line and the product;

t _2l - acoustic signal delay at twice the thickness of the acoustic delay line;

t _d - acoustic signal delay on the way from the surface of the product to the defect and vice versa.

The signal U ₁ after reflection from the surface propagates in the direction of the transducer and is reflected from the outer surface of the acoustic delay line on which it is mounted. A signal U ₂ is recorded that is repeatedly reflected from the surface of the article and the defect.

where R ₁ is the reflection coefficient of the signal from the outer surface of the acoustic delay line.

It was assumed that the pulses arriving at the transducer after repeated reflections from the defect and boundaries (3 or more) have a smaller amplitude and were not taken into account in these ratios. In addition, attenuation of the signal due to absorption in the material of the product and as a result of the divergence of the beam of ultrasonic waves can lead to the appearance in the formulas of coefficients proportional to the propagation time of the pulses.

The first signal is multiplied by a coefficient R ₁ R ₂ , delayed by a time t _2l and subtracted from the second signal. The resulting signal U _p will be equal to

Thus, only pulses reflected from the defect once and twice are present in the resulting signal. Since the pulse twice reflected from the defect arrives later than the pulse reflected from the defect once and has a lower amplitude, it is not an obstacle in detecting the defect.

The proposed method of reducing the dead zone can also be used for flaw detection (thickness measurement) of the inner layer of a two-layer structure. In the method according to claim 4, the transducer is installed directly on the controlled product, and the external layer of the structure is used as the acoustic delay line.

The method works similarly to the method according to claim 3, and it is assumed that the first layer of the controlled product has no defects.

When considering methods of reducing the dead zone, in which the pulse twice reflected from the boundary “acoustic delay line –controlled product” was used as a compensating one, it was assumed that when the pulse was reflected from the boundary “acoustic delay line – transducer”, the pulse shape did not change. However, when a pulse falls from the acoustic delay line to the transducer, in addition to direct reflection from the interface between the two media, an acoustic delay arrives to the acoustic delay line many times reflected in the transducer itself, which leads to distortion of the initial pulse, and therefore to incomplete compensation of the pulse reflected from the boundary acoustic delay line is a controlled product. "

The accuracy of compensation for a pulse reflected from the boundary “acoustic delay line - controlled product” can be improved by eliminating the effect of distortion of the pulse when it is reflected from the boundary “acoustic delay line - transducer”.

In the method according to claim 5, the technical result is achieved by the fact that between the transducer and the acoustic delay line an additional acoustic delay line is established, the length of which is selected from the condition

T ₂ > 2T _l + 2T _s ,

where T ₂ is the acoustic delay of the signal in the additional line of acoustic delay.

The method works as follows. The Converter 1 through an additional 6 and the main 2 acoustic delay lines are installed on the controlled product 4 (Fig. 4). An ultrasonic pulse is introduced into the additional acoustic delay line. The pulse reflected from the boundary “the main line of acoustic delay - controlled product”, at the border of the main and additional delay lines partially passes towards the transducer, partially reflected towards the controlled product. The pulse passed in the direction of the Converter, forms a signal U ₁ . The impulse transmitted towards the controlled product is reflected from it and, having passed through the main and additional acoustic delay lines, it is received by the converter, forming a signal U ₂ . Further signal conversion is carried out as described above, isolating the signal from defect 5. Since the signal is not distorted at the boundary of the main and additional delay lines, the compensation of the pulse reflected from the boundary “main line of acoustic delay - controlled product” can be performed quite accurately.

The condition T ₂ > 2T _l + 2T _s guarantees the absence of superposition of the reflection pulses in the additional acoustic delay line to the signal pulse from the defect.

The present invention can be used for echo-pulse defectoscopy and thickness measurement and can significantly expand the scope of the method by improving the accuracy of the compensation of the pulse reflected from the boundary “acoustic delay line - controlled product”, and reducing the dead zone.

Claims (11)

1. A method of reducing the dead zone when monitoring products with an ultrasonic echo-pulse method, which consists in installing a transducer through the acoustic delay line on the controlled product, introducing an ultrasonic pulse into the controlled product and compensating for the pulse reflected from the interface between the product and the acoustic delay line, a pulse similar in shape and amplitude, characterized in that before the control is installed, the transducer is installed through the acoustic delay line on the tuning pattern C, excite ultrasonic vibrations, record and store the pulse reflected from the interface between the training sample and the acoustic delay line, and use this pulse to compensate, while the thickness of the training sample is selected from the condition T _r ≥T _s , where T _about - the acoustic delay of the signal in the tuning sample; T _with - the acoustic delay of the signal in the controlled layer of the product. 2. The method according to p. 1, characterized in that the waveguide is taken as the acoustic delay line, and the tuning sample is made of a material whose acoustic properties are close to the acoustic properties of the material of the controlled product. 3. The method according to p. 1, characterized in that as a compensating pulse use a pulse that is twice reflected from the boundary of the acoustic delay line and the controlled product used as a training sample. 4. The method according to p. 3, characterized in that when controlling the inner layer of the two-layer structure, the transducer is installed directly on the controlled product, and the external layer of the structure is used as the acoustic delay line. 5. The method according to p. 3, characterized in that between the transducer and the acoustic delay line establish an additional line of acoustic delay, which must satisfy the condition T ₂ > 2T _l + 2T _s , where T ₂ is the acoustic delay of the signal in the additional line of acoustic delay; T _l - the acoustic delay of the signal in the main line of the acoustic delay; T _with - the acoustic delay of the signal in the controlled product.

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