1, the preface
Acoustic emission technology in recent years is very good in the domestic promotion, but because of its stronger, professional users of various parameters of acoustic emission instrument is not very understanding, so when the choose and buy is some blind.
The author for many years engaged in acoustic emission instrument development and acoustic emission field testing, in the process of acoustic emission instrument sales also made more in-depth understanding of user requirements. Now from technical point of view to talk about the choose and buy of acoustic emission instrument, is only for your reference. (this article only discusses the choose and buy of digital acoustic emission instrument)
2, the composition of acoustic emission instrument
Acoustic emission instrument system generally by acoustic emission sensor, preamplifier, acoustic emission acquisition card (or ae card), software system and the necessary cable accessories and host, etc. The core part is the acoustic emission acquisition card, so attention should be paid to the choose and buy the appropriate acquisition card. Ae CARDS usually have 2 channel/card, 4 / card, 8 channel/card three, generally single card integrated channel is more conducive to maximize the number of channels per unit volume, often for field engineering test. Multiple CARDS work in parallel can be composed of 2 n, 4 n, 8 n multi-channel instrument, after determine the number of channels can be sure need to purchase the number of ae card.
3, acoustic emission acquisition card choices
Due to the PCI bus has a plug and play, easy to upgrade expansion, high data transfer rate, so at present most of the acoustic emission signal acquisition part of the instrument adopt PCI bus structure. This article only discusses the acoustic emission of PCI bus CARDS.
Acoustic emission is the primary indicator of the acquisition card sampling rate, sampling precision and frequency range, and single cartoon channel number. The sampling precision of ae card is commonly 10, 12, 16 and 18, per channel sampling rate for 3 m, 5 m, 10 m, 20 m and 40 m. Decided to acquisition card the two indicators of core components is modulus conversion chip (namely A/D converter, ADC), in order to ensure the integrity of the waveform signal, ADC sampling rate generally need to 5 ~ 10 times the frequency of the signal frequency. Commonly used 16 mn steel such as pressure vessel in the acoustic emission signal frequency is 100 KHZ to 600 KHZ, commonly ADC to the sampling frequency in MHZ 3 ~ 6 MHZ is advisable. And materials such as glass fiber, the composite material in the acoustic emission signal frequency, sometimes up to 2 MHZ and 5 MHZ, and in the related literature at home and abroad, to study the frequency of the acoustic emission signal also hasten the situation of higher year by year, so laboratory study using acoustic emission card sampling rate is often required in more than 10 m, can guarantee to gather more and more complete acoustic emission signal.
Acoustic emission acquisition card is different from general data collection card, due to the acoustic emission signal data traffic is bigger, can only use FIFO (first in first out) data transmission structure. In addition, there are some ae card signal amplifying, filtering, parameter extraction and other auxiliary functions. Combined with acoustic emission technology more professional, the limited market capacity the ae card price will be much higher than general collection card. Although some synchronization acquisition card also can undertake acoustic emission signal acquisition, but there is no hardware clock card, triggering mechanism is imperfect, often is used in the request is not too high a simple test.
As a result, the acoustic emission instrument of choice to determine the sampling rate, sampling precision of ae card and frequency range can meet the requirements of their own use, best can have certain allowance, facilitate replacement of different sensors to different materials in the future of the acoustic emission detection. After all cheaper than the price of the acoustic emission sensor card dozens of times on even one hundred times, replace the sensor than ae card replacement is much more easy and economy.
4, selection of acoustic emission software system
Acoustic emission software in addition to the most basic of collection, storage, display and playback and analysis function, other packages on-demand best, just work. Completely unnecessary for 4 channel acoustic emission system equipped with spherical positioning software. While considering the problem of data format, had better choose open software data format, easy to use third-party mathematical software for further analysis and validation.
5, selection of acoustic emission sensor and preamplifier
Acoustic emission sensor generally according to the material in the frequency of the acoustic emission signal to determine, such as the resonance frequency of the acoustic emission signal in the known material, so you can choose the corresponding frequency of the sensor. When the frequency of the signal has not yet been determined in material, can use broadband sensor test in the first place, through the test and then select the corresponding sensor signal frequency. If you want to detect the signal spectrum, then had better choose broadband sensor. Preamplifier, generally can choose the products of a wide band, to increase the flexibility of the sensor selection.
Conformity of avoid by all means the choice of sensor, it is best to use broadband sensor first do a test to select appropriate sensors. The author has in hohai university participated in the concrete structure of the acoustic emission test, laboratory staff before 60 KHZ was used for the sensor, then think again with broadband sensor test, the results found that the acoustic emission signal waveform in addition to the 60 KHZ to 90 KHZ with a rush, between 1.1 MHz to 1.4 MHz and a more obvious peaks. Spectrum analysis results also confirmed a large proportion of more than 1 MHZ signal in frequency component. While many in the literature with 60 KHZ sensor is recommended for acoustic emission testing of concrete.
6, selection of cable accessories
Cable accessories in the acoustic emission system is one of the most overlooked part, is also the most vulnerable parts. Should pay attention to when choosing signal cable joint is best integrate whole injection, so as to avoid the long-term use of loose causes lead to poor contact.
In short, choose the acoustic emission instrument before must be aware of their needs, and the concrete scheme of using acoustic emission technology to realize. Then follow the ae card > > acoustic emission sensor and preamplifier system software > attachment and the order of the host to select them one by one. Finally I hope you can choose to share of the acoustic emission instrument.
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