RU2126538C1 - Split method of ultrasonic inspection - Google Patents

Abstract

FIELD: nondestructive testing by ultrasonic methods. SUBSTANCE: invention can be used in various branches of mechanical engineering to test materials and articles, predominantly large-sized and with great damping of sound. Method consists in excitation of ultrasonic vibrations in article by train of radio pulse quasi-harmonics, in reception of echoes, in optimal filtering and collection of them in storage circuit. Parameters of inspected article are found by result of collection of pulses. Carrier frequency of each radio pulse is selected different from carrier frequencies of other radio pulses within limits of joint bandwidth of emitting and receiving electroacoustic converters. EFFECT: enhanced sensitivity of ultrasonic inspection. 2 dwg

Description

 The invention relates to the field of non-destructive testing by ultrasonic methods and can be used in various industries for the control of materials and products, mainly large and with a large attenuation of ultrasound.

 A known method of ultrasonic testing of products [Ultrasound. Little Encyclopedia. Chap. Ed. I.P. Golyamin. -M .: Soviet Encyclopedia, 1979, p. 105], which consists in the fact that a short acoustic pulse is excited in a product, echo signals reflected from the product are received, they are converted into an electrical signal by which the parameters of the controlled product are determined.

 The disadvantage of this method is the low sensitivity of the control, determined by the maximum value of the amplitude of the probe signal, which in turn is associated with structural and other limitations.

 The known method [Aksenov V.P. The use of radar methods of optimal detection in ultrasonic echo control./ Defectoscopy, N 2, 1982, p.67-74.] Ultrasonic inspection of products, which consists in the fact that in the controlled product excite complex-modulated probe signal, receive echoes reflected from the product -signals, convert them into a sequence of electrical complex-modulated pulses, each of the pulses is optimally filtered, and the parameters of the controlled product are determined by the result of optimal filtering.

 The disadvantage of the above method is the low sensitivity and reliability of the control, due to the fact that with the increase in attenuation of ultrasound, a strong dependence of the attenuation coefficient on frequency is simultaneously manifested. The latter leads to a distortion of the shape of the echo signals and, as a consequence, to a violation of the optimality of filtering, a significant distortion of the waveform at the output of the optimal filter, a decrease in the sensitivity and reliability of the control.

 A known method of ultrasonic testing, adopted as a prototype, described in [Non-destructive testing. In 5 kn. Book 5 Introscopy and automation of non-destructive testing: A practical guide / V.V. Sukhorukov, E.I. Weinberg, R. - I.Yu. Kazhis, A.A. Abakumov; Ed. V.V.Sukhorukova. - M .: Higher. Shk. , 1993, p. 112-113. ], which consists in the fact that ultrasonic vibrations are excited in the product by a periodic sequence of pulses, receive echoes reflected from the product, convert them into a sequence of electrical pulses and accumulate, and the parameters of the controlled product are determined by the result of the accumulation of pulses.

 The disadvantage of this method is the low sensitivity of the control, limited by a potentially small number of accumulated pulses, the number of which is determined by structural, technological or other considerations.

 The technical task of the proposed method is to increase the sensitivity of the control.

 This task is achieved by the fact that in the known method of ultrasonic control, which consists in the fact that ultrasonic vibrations are excited by a probing signal in the product, echo signals are received and accumulated in the drive, and the parameters of the product being monitored are determined by the result of the accumulation of pulses, the probe sequence is used the set of radio pulses is quasiharmonic, and the carrier frequency of each radio pulse differs from the carrier frequency of other radio pulses and is selected within the total TVOC transmittance emitting and receiving electroacoustic transducers, and each radar pulse received signal to optimally accumulation (suboptimally) filtered.

The invention is illustrated by drawings, where:
- in FIG. 1 shows a structural diagram of a device that implements the proposed method;
- figure 2.a shows a probing signal;
- Fig.2.b shows the total amplitude-frequency characteristic of the electro-acoustic transducers (curve 1) and the amplitude-frequency spectra of radio pulses - quasiharmonics that make up the signal;
- figure 2.c shows a signal after optimal filtering;
- on fig.2g - 2.g shows the relative position in time of the radio pulses - quasiharmonics that make up the signal in the process of accumulation;
- figure 2.z shows the pulse at the output of the drive.

 The split method of ultrasonic control of the thickness of the products consists in the fact that in the controlled product a probing signal, which is a set of quasiharmonics, excites ultrasonic vibrations, receives echo signals of quasiharmonics, each received quasiharmonics of the signal is filtered optimally (quasi-optimum), after which all quasiharmonics are in phase drive, and the frequency of each quasi-harmonic is selected within the total bandwidth of the emitting and receiving electro-acoustic transducers. The combination of the optimal filtration of each quasiharmonics with the in-phase accumulation of optimally filtered quasiharmonics makes it possible to achieve the maximum sensitivity possible at a given time, bringing it closer to the theoretically possible limit. Split, from English "split", which means "divided, split." Split is an established technical term applied to the designation of a device or mechanism distributed in space, and also applied to the designation of a process divided in time into functionally completed phases aimed at achieving a common goal.

 A device that implements the inventive method consists of electro-acoustically connected synchronizer 1, generator 2 of probe pulses, power amplifier 3, emitting electro-acoustic transducer 4, receiving electro-acoustic transducer 5, controlled band-pass (or optimal) filter 6, drive 7, the second input of which is combined with the second input of the controlled band-pass optimal filter 6 and is connected to the second output of the synchronizer and indicator 8. As indicator 8 can be used Call of the cathode-ray oscilloscope. The number 9 indicates the controlled product.

 A device for implementing the method (see figure 1) works as follows.

на фиг.2.а. Взаимное положение во времени некоторых из последовательностей квазигармоник показано на фиг.2.г. - фиг.2.ж. Фазы несущей квазигармоники после оптимальной фильтрации выбираются при излучении таким образом, чтобы синфазное их суммирование происходило в момент максимума огибающей каждой квазигармоники на выходе фильтра. Суммирование квазигармоник реализует процесс гармонического синтеза эхо-сигнала, по виду приближающегося к виду δ-функции (см.фиг2.з). Принимая во внимание, что амплитуда сигнала на выходе оптимального фильтра пропорциональна энергии входного сигнала, в результате описанного выше процесса обработки эхо-сигнала амплитуда сигнала на выходе накопителя оказывается пропорциональной суммарной энергии радиоимпульсов.The probe 2 generator 2 started by the synchronizer 1 generates a probe signal of duration T _{to the} input of the power amplifier 3 whose shape is shown in Fig.2.a, which is a set of radio pulses of duration T _g each, of a well-defined frequency F _i , different from the frequency of two radio pulses. Figure 2b shows the relative position of the spectra of each quasi-harmonic (curves 1) within the total passband of the emitting and receiving electro-acoustic transducers (curve 2). The power amplifier 3 excites the emitting electro-acoustic transducer 4. The ultrasonic echo signals received from the product 9 after the reverse electro-acoustic conversion by the receiving transducer 5 are fed to the input of a controlled optimal filter 6. The filter 6 is organized in such a way that its frequency response when receiving an echo signal is consistent with the frequency response of the quasiharmonics currently being received. The shape of the radio pulses at the output of the controlled optimal filter 6 is shown in FIG. The operation of the drive 7, controlled by the pulses of the synchronizer 1, cyclically resumes at the time points marked

Fig.2.a. The relative position in time of some of the sequences of quasiharmonics is shown in Fig. - Fig.2.zh. The phases of the carrier quasiharmonics after optimal filtering are selected during emission in such a way that their in-phase summation occurs at the instant of maximum envelope of each quasiharmonic at the filter output. Summing quasiharmonics implements the process of harmonic synthesis of an echo signal, which is similar in appearance to the form of a δ-function (see Fig. 2.z). Taking into account that the amplitude of the signal at the output of the optimal filter is proportional to the energy of the input signal, as a result of the processing of the echo signal described above, the amplitude of the signal at the output of the storage ring is proportional to the total energy of the radio pulses.

Из условия однозначности контроля определим потребное количество N гармоник:

При максимально допустимом времени контроля Т = 1 сек длительность Т_к квазигармоники составит

а полоса амплитудно-частотного спектра каждой квазигармоники всего 200 Гц. Реализация предлагаемого способа позволяет получить выигрыш по чувствительности в сравнении с прототипом

что при заданных выше числовых значениях составит величину более 30 дБ.We give an example of calculating the parameters of the sounding signal, based on the given parameters of the electro-acoustic path. So, as initial parameters we accept:
C is the ultrasound speed (2000 m / s);
L is the required control depth (up to 100 mm);
T - the maximum time allotted for product inspection at one point (not more than 1 second);
ΔL - radiation resolution (not worse than 1 mm);
Define the necessary frequency band:

From the condition of uniqueness of control, we determine the required number of N harmonics:

At the maximum permissible control time T = 1 sec, the duration of T _to quasi-harmonic is

and the band of the amplitude-frequency spectrum of each quasi-harmonic is only 200 Hz. The implementation of the proposed method allows to obtain a gain in sensitivity in comparison with the prototype

that at the numerical values set above will be more than 30 dB.

Claims (1)

 The split method of ultrasonic control, which consists in the fact that ultrasonic vibrations are excited by a probing signal in the product, receive echo signals and accumulate them in the drive, and the parameters of the controlled product are determined by the result of accumulation, characterized in that the echo signals are optimal before accumulation (quasi-optimal ) are filtered, and a set of sequentially emitted radio pulses — quasiharmonics — is used as the probe signal, and the carrier frequency of each radio pulse is selected different from the carrier pilots at other radio pulses within the total bandwidth of the emitting and receiving electroacoustic transducers.

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