WO2008018813A1

WO2008018813A1 - Method for increasing interference protection of ultrasonic testing and a device for carrying out said method

Info

Publication number: WO2008018813A1
Application number: PCT/RU2006/000675
Authority: WO
Inventors: Andrei Vasilievich Kirikov; Alexandr Nikolaevich Zabrodin; Alexei Mikhailovich Kashin; Konstantin Nikolaevich Makarenkov
Original assignee: Otkrytoe Aktsionernoe Obschestvo 'nordinkraft'
Priority date: 2006-12-15
Filing date: 2006-12-15
Publication date: 2008-02-14
Also published as: DE112006003795T8; JP2010513867A; DE112006003795T5; JP5497448B2

Abstract

The inventive method is directed at increasing the interference protection of ultrasonic testing and consists in dividing a signal received by an ultrasound converter into several time zones, in separating the signal from the components thereof situated in waiting zones of signal reflected from defects, in individually processing signals received from different time zones by emitting signals from zones of action of sounding pulses and base echo waiting areas to broadband amplifiers, in filtering reflected from defect signals, which are coming from the signal waiting zones, in determining a maximum signal amplitude of a signal in the waiting zones of signals reflected from a defect, in comparing said amplitude value with a maximum permissible value and in concluding about the presence / absence of a defect according to said comparison results. The certainty of determination of the presence / absence of defects is evaluated by comparing, in the waiting zones of the signals which are reflected from a defect, the amplitudes of frequency components intrinsic to the spectrum of sounding pulses or to the spectrum of received useful signals with the amplitude of the frequency components which are not intrinsic to the spectrum of sounding pulses or to the spectrum of received useful signals. Synchronised interferences are removed from the received signals by means of main and auxiliary received-signal accumulation cycles and the thus synchronised interference-free received signal is obtained by subtracting sum signals which are obtained by means of the main and auxiliary accumulation cycles. A device for carrying out said method is also disclosed.

Description

METHOD FOR IMPROVING INTERFERENCE PROTECTION OF ULTRASONIC CONTROL AND DEVICE FOR ITS IMPLEMENTATION

FIELD OF THE INVENTION

The invention relates to the field of non-destructive testing and can be used in ultrasonic testing systems, mainly installations for automated ultrasonic testing of sheet and long products and pipes.

State of the art

In the process of ultrasonic testing, the transducer of an ultrasonic flaw detector emits pulses of high-frequency elastic vibrations into the product. The radiation of the probe pulses occurs mainly along the normal to the surface of the controlled products hundreds or even thousands of times per second. Accordingly, the receiving transducer (often receiving and emitting using the same transducer) hundreds or thousands of times per second receives responses from the product or, as they are also called, “realizations”.

Each implementation contains signals reflected from rolled surfaces and from defects, as well as pulses due to interference, which in most cases is acoustic or electromagnetic in nature (see the book by J. Krautkremer and G. Krautkremer “Ultrasonic material control. Help”, Moscow , ed. "Metallurgy", 1991).

In the absence of interference, each implementation contains information that allows you to judge the thickness of the controlled product at the location of the ultrasonic transducer, the presence or absence of discontinuities, etc. Interference can distort the information received, cause the wrong decision to be made about the physical and consumer properties of the controlled product,

Various methods are used to reduce the level of interference, for example, a previously known defective place is preliminarily sounded and the spectrum code of the received signal is recorded in the memory unit, and the control results are judged by comparing this code with the echo spectrum code of the monitored area of the product (SU 1341571).

In addition, in the method according to patent RU 2123401, pulse normalization of the magnetic state of the material being monitored, as well as coherent, is used to reduce the level of interference during the control by an electromagnetic-acoustic converter or incoherent accumulation of implementations. Useful signals that are “tied” to the probe pulse and therefore have relatively slowly varying amplitudes and phases from realization to realization, are effectively added up and, as a result, quickly “resolved”. In turn, the interference, arrival time, the amplitude and phase of which are for the most part random, is not so efficiently added up in the drive and, as a result, it “accumulates” much more slowly. Therefore, coherent (as, by the way, incoherent) accumulation in most cases can effectively increase the ratio of useful syral / pomexa.

Methods SU 1341571, SU 932391, GB 1034724, and in particular the method RU 2123401, do not allow to deal with specific ultrasonic monitoring specific interference, which is partially or fully synchronized with probing pulses and, therefore, with useful signals (often whose spectra coincide with spectra of useful signals). Such interference is very dangerous, since it can cause false alarms and accumulate in the drive, thereby reducing the “good signal / sweep” ratio. An example of a source of synchronous interference is a computer controlling a computer complex, which is part of any modern multichannel system of automated ultrasonic monitoring. In many cases, synchronous interference is also fluctuations in the product that are not attenuated due to previous probing pulses or spurious vibrations of scale particles or air bubbles that fall into the working area of the ultrasonic transducer.

For random, but quite powerful and long-term interference, there is also the possibility of “passing” through the drive, which reduces the efficiency of the method according to patent RU 2123401. This is also facilitated by the following circumstance.

Basically, the registration of signals from pulsed ultrasonic flaw detectors involves the use of broadband filters, which is due to the need for selection of defects located fairly close to natural reflectors, which, as a rule, form powerful "bottom" signals.

A broadband filter provides reception of signals without “falling over” their fronts, which favorably affects the resolution. However, the noise immunity of such a filter in some practical cases may be unsatisfactory.

When trying to match the filter response with the spectrum of received signals, the shape of the latter is significantly distorted. The signal fronts “collapse”, and this adversely affects the possibility of detecting defects, especially when controlling sheet metal of relatively small thickness.

In the absence of interference, broadband reception provides significant advantages, which are as follows:

- signals at the output of a broadband receiver have a significantly (sometimes several times) shorter "dead zone";

- the ability to identify defects located in close proximity to natural reflectors;

- a wider range of rolled thicknesses that can be controlled.

Another advantage of a broadband receiver is its ability to provide significantly higher accuracy in determining the distance between the "bottom" pulses. This is extremely important, for example, when performing ultrasonic thickness measurement.

However, all these advantages of broadband reception appear only in the absence of interference.

In the presence of interference, for example, industrial pulsed electromagnetic disturbances, broadband reception leads to false positives of flaw detection equipment. These false positives lead to unreasonable rejection and in most cases are completely unacceptable to the manufacturer of metal products.

This is especially true for cases of the use of high-performance multichannel systems of automated ultrasonic testing, standing directly in the technological stream of rolled metal production. An important property of such systems, in contrast to manual flaw detectors, is the need to carry out monitoring on a “one-pass” basis. It is very difficult, and often impossible, to return to the controlled area.

On the other hand, the optimization of the reception channel bandwidth is always a compromise and in some cases does not bring the desired result. As a rule, such systems have neither the required noise immunity nor satisfactory resolution. SUMMARY OF THE INVENTION

The present invention eliminates this contradiction.

The present invention is based on the task of creating an ultrasonic monitoring method with increased noise immunity, which allows monitoring with high resolution time and, as a result, with a maximum reduction in the dead zones of control and maintaining the accuracy of thickness measurement while ensuring high reliability of the control results. In addition, the objective of the invention is to develop a device that implements such a method.

This problem is solved by the fact that in the method of increasing the noise immunity of ultrasonic testing, including broadband reception using ultrasonic transducers, registration and processing of ultrasonic signals, according to the invention, the received signal is divided into several time zones, its components located in the waiting areas are separated from the main signal signals reflected from defects, signals from different time zones are subjected to independent processing by supplying signals from n the action of the probe pulse and the expectation of bottom signals on broadband amplifiers, the signals from the waiting areas of signals reflected from defects are filtered to ensure the maximum signal to noise ratio at the output of the corresponding device, the maximum signal amplitude in the waiting areas of signals reflected from the defect is determined, the value of this amplitude is compared with the maximum permissible value and the presence / absence of a defect is judged by the results of this comparison. In this case, the reliability of determining the presence / absence of defects is evaluated by comparing in the waiting areas of signals reflected from defects, the amplitude of the frequency components characteristic of the spectrum of the probe pulses or the spectrum of the received useful signals, with the amplitude of the frequency components not typical of the spectrum of the probe pulses or the spectrum of the received useful signals. To clean the received signals from synchronized interference with them (i.e., from the regular component), the main and auxiliary cycles of accumulation (coherent or incoherent) of the received signals are carried out, and the received signal cleared of synchronized interference is obtained by subtracting the total signals obtained as a result of the main and auxiliary accumulation cycles. A device that allows the implementation of the above method includes blocks for receiving ultrasonic oscillation signals, processing and recording them, while this device contains four switching devices, band-pass and notch filters, six peak detectors, a signal delay device, two blocks for measuring signal level ratios, two threshold devices, an addition device and a signal subtraction device. The received signals through the first two switching devices are fed to the inputs of the first two peak detectors, as well as through the amplifier and the third switching device to the inputs of the bandpass and notch filters. The input of the bandpass filter is connected to the input of the signal delay device and to the input of the third peak detector, and the output of the notch filter is connected to the input of the fourth peak detector. The outputs of the third and fourth peak detectors are connected to the inputs of the second block for measuring signal level ratios. The output of the third peak detector is connected to the input of the first signal level measuring unit, the second input of which is connected to the output of the first peak detector. The outputs of both signal ratio meters through threshold devices are connected to the inputs of the addition device, the output of the latter is connected to the control input of the fourth switching device, the signal input of which is connected to the output of the signal delay device. The output of the switching device is connected to the inputs of the first and second drives, the outputs of which are connected to the inputs of the subtracting device. The output of the subtractor is connected to the input of the sixth peak detector, and the output of the first drive is connected to the input of the fifth peak detector, the amplitude values of the signals processed and cleared of noise are taken from the outputs of the peak detectors.

Brief Description of the Drawings

The invention is further explained in the description of specific examples of its implementation and the accompanying drawings, in which: FIG. 1 shows a signal in the absence of interference using a receiver with matched filtering; FIG. 2 is a view of a received signal in the absence of interference using a broadband receiver; FIG. 3 is a view of a received signal with a rolled thickness four times reduced using a receiver with matched filtering; FIG. 4 is a view of a received signal at a rental thickness reduced by four times, using a broadband receiver; FIG. 5 is a view of a received signal in the presence of interference using a broadband receiver; FIG. 6 - signal spectrum in the absence of interference; FIG. 7 - signal spectrum in the presence of interference; FIG. 8 is a structural diagram of the proposed device; FIG. 9 is a generalized transfer characteristic of a band-pass filter; FIG. 10 is an example of an amplitude-frequency response of a real band-pass filter; FIG. 11 is a view of a signal cleared of interference; FIG. 12 is a spectrum of a signal filtered and processed by the device shown in FIG. 8.

DETAILED DESCRIPTION OF THE INVENTION

In FIG. Figures 1 and 2 show a signal typical of sheet and long products using a receiver with matched filtering (Fig. 1) and using a broadband receiver (Fig. 2). Position 1 indicates the probe pulse, positions 2 and 3 indicate the first and second "bottom" pulses, respectively, and position 4 indicates signals from defects. The signals at the output of the broadband receiver have a significantly (sometimes several times) shorter "dead zone". In FIG. 2, the probe pulse 1 is much shorter than that of FIG. 1. Because of this, one of the pulses 4, visible in FIG. 2 is practically indistinguishable in FIG. 1 (the first after the probe pulse). The type of signal shown in FIG. 1, it is not possible to establish the presence or absence of some signals reflected from defects, which, nevertheless, are clearly defined in the signal, the form of which is shown in FIG. one.

Broadband reception provides a wider range of rolled thicknesses that can be controlled. For example, when the thickness is reduced by four times, monitoring using a matched receiver is not possible: pulses 2 and 3 in FIG. 3 almost merge. At the same time, for a broadband receiver (Fig. 4), monitoring will be possible, since the gap between pulses 2 and 3 will be sufficient to register pulses reflected from defects in it.

The signal received by the broadband receiver is divided into several time zones: A, B, C and D (Fig. 2). Signals from different time zones are subjected independent processing by supplying signals from the areas of operation of the probe pulse and waiting for bottom signals to broadband amplifiers, the signals from the waiting areas of signals reflected from defects are filtered to ensure the maximum signal to noise ratio at the output of the corresponding device, the maximum signal amplitude in the waiting areas of signals is determined reflected from the defect, the value of this amplitude is compared with the maximum permissible value, and the presence / absence of EKTA.

For example, if in the spectrum of signals received in zones B and D the frequency components prevail that are not characteristic of the useful signal, they conclude that the conclusion about the detection of a defect (discontinuity) is unreliable. It is very likely that exceeding the allowable threshold occurred as a result of interference.

Additionally, the signal is cleaned in the waiting areas of pulses reflected from defects, from the noise synchronized with the useful signal, which at the rental can be caused, for example, by undamped oscillations or by the presence of spurious waves excited by piezoelectric or electromagnetic acoustic transducers. For this signal purification, the main and auxiliary cycles of accumulation of the received signals are carried out, and the received signal cleared of synchronized interference is obtained by subtracting the total signals obtained as a result of the main and auxiliary accumulation cycles. The process of accumulation of signals is the memorization of several successive implementations of the signals of the corresponding time zones (zones B and D), and then the mutual time-by-time addition of the signals of the same zones of waiting for defects belonging to different cycles of radiation-reception, followed by normalization of the results of the auxiliary accumulation cycle relative to the results of accumulation of the main cycle .

In general, to assess product quality, it is necessary to know at least the following parameters: amplitudes of bottom signals 2, 3 (Fig. 5, signals in zones C and E, respectively) and signal amplitudes in zones B and D.

In FIG. 8 shows a block diagram of a device that allows the above actions to be performed on signals. This device contains a broadband amplifier 6; switching devices 7, 8, 9 and 10; peak detectors-meters 11, 12, 13, 14, 15 and 16 maximum amplitude values; band-pass filter 17, which optimally selects the spectrum of the useful signal; notch filter 18, suppressing the useful signal; blocks 19 and 20 performing the operation measuring the ratio of the signal amplitude from the output of block 13 to the amplitudes of the signals from the outputs of block 11 and block 14, respectively; threshold devices 23 and 24; device 25 addition (logical circuit "And"); signal delay device 26; drives 27 and 28 with the number of accumulations, respectively, Nl and N2, while Nl is much less than N2; a subtracting device 29 that subtracts the signal transmitted through the drive 28 from the signal transmitted by the drive 27.

In addition, the diagram indicates: point 5 of the input signal input; point 21 measuring the amplitude of the first "bottom" signal; point 22 measuring the amplitude of the second "bottom" signal; point 30 measuring the amplitude of the useful signal at the output of the first drive 27 for zone B (or D); point 31 measuring the amplitude of the useful signal from zone B (or D), cleared of synchronized interference.

The informative input signal 5 shown in FIG. 5 (36 indicates the impulse from interference) is supplied to the inputs of the switches 7 and 8 and then to the peak detectors 11 and 12, which measure the amplitude values of the first two “bottom” signals 21 and 22. In the future, these signals can be used to implement a mirror-shadow and multiple mirror shadow methods for detecting discontinuities. In addition, the amplitude value of the first “bottom” impulse characterizes, under certain conditions, the amount of energy introduced into the control object (OK). With respect to this value, it is convenient to measure the amplitudes of all other received signals. At the same time, the input signal 5 is fed to the input of the broadband amplifier 6, which is designed to compensate for the decrease in the amplitude of the signals received from zones B and D, which is inevitable with a coordinated (or optimal) filtering. The mixture of the useful signal and interference passes through the band-pass and notch filters 17, 18, to the inputs of which it passes through the switch 9. The signal spectra in the absence of interference and when exposed are presented, respectively, in FIG. 6 and 7, where 33 denotes the spectrum of the useful signal, and 34 denotes the interference spectrum.

The frequency response (AFC) of the bandpass filter 17 is shown in FIG. 9 and 10. The parameter characterizing the attenuation of the frequency components of the signal lying outside the passband of the filter is denoted by _A.sub.d , and the parameter characterizing the unevenness of the amplitude-frequency characteristics (AFC) in the passband of the filter is denoted by _Ap .

At the output of the bandpass filter 17, the useful signal already dominates (Figs. 11 and 12), and at the output of the notch filter 18, there is interference. The useful signal is sent to a delay device 26, and further, through the switch 10, to the drives 27 and

28. Here, its additional processing is carried out in order to increase the signal-to-noise ratio (using drive 27) and separating synchronized interference from the signal (using drives 27 and 28 and subtractor 29).

The spectrum of the received signal processed by the device of FIG. 8 is shown in FIG. 12, where 33 denotes the spectrum of the wanted signal in zones B and D after processing; 34 - interference spectrum after processing; position 35 is the amplitude-frequency response of the bandpass filter.

The switch 10 is used to block inaccurate data, preventing their flow to the drives 27 and 28.

A sign of data inaccuracy and the possible prevalence of interference in the signal delayed in the device 26 is the excess of the interference amplitude of certain levels measured relative to the amplitude values of the first bottom signal 21 and the signal (mainly useful) generated at the output of the peak detector-meter 13.

Thus, devices 10, 17, 18, 19, 20, 24, 25, 26 serve solely to control the reliability of the data. In conditions where the probability of the presence of interference at the output of the bandpass filter 17 can be neglected, the above blocks can be excluded.

The amplitude values of the fully processed signal 30 and the same signal after clearing the synchronized interference 31 appear at the outputs of the peak detectors 15 and 16, respectively.

In order to reduce the dead zone as much as possible due to the masking effect of the “bottom” pulses, signals from the “bottom” pulse action zones can also be supplied to the amplifier and the third switching device, where they are then processed similar to that which is performed on the signals from the standby zones defects.

The device in accordance with the present invention allows to implement protection against interference of the measured useful signals by spectrally processing them in the waiting areas of signals from defects, as well as to suppress signals synchronized with the useful interference signal, which can limit the sensitivity of the control or cause false alarms. In addition, the device eliminates the dead zones of control due to the presence of "bottom" signals, by applying the procedure for removing synchronized interference to “bottom” signals, which can mask signals from defects lying close to the surface.

This device to increase the noise immunity of ultrasonic testing can be implemented using well-known electronic devices and components, as well as computer hardware.

Claims

CLAIM

1. A method of increasing the noise immunity of ultrasonic testing, including broadband reception of ultrasonic signals using ultrasonic transducers, recording and processing received signals, characterized in that the signal received by the ultrasonic transducer is divided into several time zones, its components located in the signal waiting areas are separated reflected from defects, the signals from different time zones are subjected to independent processing by supplying signals from the zones of the zones a dimming pulse and waiting for bottom signals to broadband amplifiers, signals from the waiting areas of signals reflected from defects are filtered to ensure the maximum signal / noise ratio at the output of the corresponding device, the maximum signal amplitude in the waiting areas of signals reflected from the defect is determined, the value of this amplitude compare with the maximum permissible value and the results of this comparison judge the presence / absence of a defect, and the reliability of determining the presence / absence of defect CTs are estimated by comparing in the waiting areas of signals reflected from defects, the amplitudes of the frequency components characteristic of the spectrum of the probe pulses or the spectrum of the received useful signals, with the amplitude of the frequency components not typical of the spectrum of the probe pulses or the spectrum of the received useful signals, while additionally for cleaning received useful signals from synchronized interference with it carry out the main and auxiliary cycles of accumulation of received signals, and cleared of synchronization For a given interference, the received signal is obtained by subtracting the total normalized signals obtained as a result of the main and auxiliary accumulation cycles.

2. A device for increasing the noise immunity of ultrasonic testing, including blocks for receiving ultrasonic vibrations, processing and recording signals, characterized in that it contains four switching devices, band-pass and notch filters, six peak detectors, a signal delay device, two blocks for measuring signal level ratios, two threshold devices, an addition device and a device for subtracting signals, while the received signals through the first two switching devices arrive at the inputs of the first two peak detectors, and also through an amplifier and a third switching device to the inputs of the bandpass and notch filters, while the input of the bandpass filter is connected to the input of the signal delay device and to the input of the third peak detector, and the output of the notch filter is connected to the input of the fourth peak detector, , the outputs of the third and fourth peak detectors are connected to the inputs of the second unit for measuring the signal level relations, in addition, the output of the third peak detector is connected to the input of the first unit of measurement ur the signal, the second input of which is connected to the output of the first peak detector, the outputs of both signal ratio meters through threshold devices are connected to the inputs of the addition device, the output of the latter is connected to the control input of the fourth switching device, the signal input of which is connected to the output of the signal delay device, the output of the switching device connected to the inputs of the first and second drives, the outputs of which are connected to the inputs of the subtracting device, the output of the subtracting device is connected to the input of the sixth peak detector, and the output of the first drive is connected to the input of the fifth peak detector, the amplitude values of the processed and cleared from interference signals are taken from the outputs of the data of the peak detectors.