MA Yong-hui， LIU Kang， YANG Da-zhi
（College of Mechanical Engineering,Sichuan University  of Science and Engineering, Zigong 643000, China)

Abstract:  A set  of system about  acoustic  emission  collection   is developed，analysis  and  processing based on LabVIEW software and the PCI-6251 data acquisition  card. The system not only can collect,
store and playback  acoustic emission signal through the real operation but also can realize the acoustic emission
frequency  spectrum analysis and wavelet denoising  processing by using powerful  modules and interface functions of LabVIEW.
Key words: labview； signal acquisition； signal analysis and processing
The introduction

Acoustic emission detection methods can be checked for CNG cylinders, by analysis and rational number, and when the hair is short of, avoid the matter produce.
Because of the sound radiation signals of mining set analyse and handle it as a heavy
Points, the using virtual instrument LabVIEW and high speed data collection card can very good implementation of acoustic radiation signals, mining, analyse and handle,
And when do the appraisal for the state of steel bottle provided in accordance with the according to, the possibility of reduce accident happening.
 
1 acoustic emission detection
Sofar shoot inspection measurement is a kind of dynamic state with no damage inspection measurement method, it can be used in the materials department within defects remaining in the lead up the sound of anti should change
Within the materials department of stuck in line inspection, measurement and the defects of the state to do the judgment and evaluation. For CNG cylinders, cylinder itself or within the department
The lack of adding pressure, such as raw fruit production become trapped in the form or have defects expansion exhibition, in the process of produce should be force should be changed to will to elastic wave form release
Come out, this play wave is the number of acoustic radiation signals, these letters are come from the defects of steel bottle, of this some letter number into the line set analyse and handle
But the real is to review of state of the cylinder.
 
2 system overall design
Signal pick set is use the sensor and other equipment since the move from single element to be tested by integrating the information of the routine, it is hard and soft parts system or product. After a whole set of mining system including the sensor, signal conditioning circuit, data acquisition and analysis software, etc. Hard by a system of main sensor, signal in advance in electric road management, data mining set card unit and calculation. Its principle 
 

Needle of acoustic radiation signals provided, its frequency rate is main to set in 100 ~ 400 kHz, center frequency in 100 ~ 200 kHz, the selection of sensor system for domestic Beijing PengXiang PXR15 resonant sensor technology co., LTD., it adopts Japan Fuji PZT sensor, in the spirit acuity, consistency, temperature stability, good performance, it can sex refers to the heart of the labeled rate 150 kHz, with 100 ~ 400 kHz, wide 65 dB sensitivity, which is very applicable to the acoustic emission signal.
In actual measure, mining sets to the letter, to the letter, the mining of set card transport into one set to beg, the sensor has a high resistance capacitance and resistance resistance, the output of 10 points and the weak acoustic radiation signals, if after a long cable to lose to send will result in low signal-to-noise ratio. Sensor when receive the signal with the pick up charge to noise are sounds that some noise to signal a set of analysis, because of the need to use for these letters, electric road into a line filter wave, eliminate useless signals. According to the system, in order to improve the signal-to-noise ratio, to do the one letter at a part number into the line filter, because of this the one channel signal conditioning circuit is shown in figure 2.

After signal adjustment principle, can be in connected to the card number according to the mining set into the line, data mining hard set card is a system of nuclear heart, its performance for data acquisition speed and precision can be directly impact. The system selected by letter, the collection card is NI company the number of PCI - 6251 according to the set of CARDS, NI PCI - 6251 - M series is a high speed can work more DAQ card board, under the high sample rate can maintain high precision. It can reach in multipass way acquisition to 1 MS/s, with 16 road model is proposed to lose, 16 points and distinguishing rate, 2 road model is proposed to lose out, a new speed rate is 2.8 MS/s, high speed can be up to eight road
10 MHz, by in steel gas bottle of sound radiation frequency rate is main to set between 100 ~ 400 kHz, because of this the number according to the card can be set to reach to the mining effect.
Software computing machine and the signal collect set hard finish form into a whole piece of signal collection, analysis and display system. Labview is a layer of software on high sex can open hair process sequence should use platforms, it since the body belt drive traverse sequence can be hard for a system of each parameter line number into a phase locked, and according to set up a good reference for the signal acquisition.

3 the software system
Test instrument device by letter, set, letter, analysis, and put back to show three points set, the software in the system including signal analysis and decommissioning
Replays showed. Its main function is to transport into the computer the signal of interest in store, so after 3, believe they can use, another is mention in the letter, using LabVIEW for routine sequence into lines by close surface analysis, and show come out, go out from the faith, interest rates and to useful information.
 
3.1 signal acquisition and storage
Data mining set in the whole system of a heavy to ground, directly decide the letter number analysis must indeed, master in the step to the acquisition of the equipment is set and the number in a set, including word choice, sample frequency rate and recovery rate of each sample number on the sample frequency rate is too high or too low will letter for mining production living a set number of negative impact, for guarding against this produce some negative surface impact, is their root according to kratos, principle of the minimum sample frequency rate must is twice the signal frequency rate, verified by a large amount of real test, the sample frequency rate as set a place for lost into the letter, the high frequency rate of 7 ~ 10 times, in the cases, can be in is still the original wave shape, to manage to waveform. , in the letter, mining set is collected each set are through several data according to the analysis after the show will once again into the line set, this sample will lead to time delay which affects the data acquisition cycle later. So this system with multiple line cheng letter type identifying number set and analyse, namely by using labview column mode of the state machine into a line set, the state machine by a while and case system group, the state variable in moving through a jump turn to implementation of the register, while system implementation to the letter number of consecutive sets, while real case system is not under the state into the row with cao cao, case structure. The points and the shape of a form of a team should, within the department process sequence for the into line, make a list of names deposit in the state, through tuning word in the name of the state in line with the queue state jump, adjustable after use the names of the Element used to Dequeue VI deleted from the queue, root according to the need for a new state name will be added to the queue. Such a loop system can be not to break into the line number according to the mining rate will be adopted to the letter into the column, another loop system does not break from the team take message to read several columns according to the lines, 2 system implemented the interoperability of the letter, and each other.
 


Figure 3 queue state machine diagram
In figure 3, on the surface of a loop to process sequence control refers to the order, will need to state name column in addition to the team, in the face of the cycle for each state in the case of need to execution of the task of the process sequence and enum to solid is now even with the next state, beginning at the beginning of the as in the case of programming required number according to the transmission interface, the whole binding in a cluster, and proceeded to the bundle phase refers to make to identifying data exchange with the change.
In the Case of needles for the state to create a task, data mining, data display and processing status. By creating a task to realize the signal entered, then through a number according to the mining, the set number identifying the letter read again after the data display and signal processing is completed and the relevant place. Used as stated in the number of square law of acoustic radiation signals into line set, including channel for 2-channel, each channel sampling number is 1, 000, because the sound of steel gas bottle with frequency rate of main set in the 100 ~ 400 kHz, shown below.
 

 
plot((0:nfft/2-1)/nfft*fs,Y(1:nfft/2)); xlabel(‘ f/Hz’); ylabel(‘  P/W’);
prompt
Choose a file name and location
*.tdms open(read-only)

Figure 4 number set to the letter
From diagram can sound to some observers to two way shape into the acoustic radiation signals, this letter, the identities of operator and acoustic radiation signals, sudden onset signals. A path through the mining set often encounter to the letter, mining sets of high speed in the letter, the hard disk read take rate and made into a letter for this lost lost, mining set for when the real high speed signal line and into the store, this system with double slow saved, that construct two slow to save space, a for loop delay, one as moving slow, when the loop delay save saved to a half, the number of according to be kao bei to turn move slow, when the loop delay deposit is full,
The new number according to the old number according to the overlying cover, such as the loop into the bank deposit reserve, for the warranty card
The plot ((0, NFFT / 2-1)/fs NFFT * and Y (1: NFFT / 2)); Xlabel (' frequency f/Hz); Ylabel (' power spectrum P/W);
Prompt
Choose a file name and location
*. TDMS open (read - only)
Data can be saved, the good enough to move slow save big small than the loop delay save a empty one and a half between big, loop delay deposit in the area of big is small to less for sweep rate of 2 times, ten times the effect of the most beautiful. This system under the vc state to save storage process sequence into the line of code, and born into a DLL, then through labview
Call Library Function Node mold piece of tuning in to real double slow save saved can work now, must be in the process sequence should also adjust with number according to the mining collection letter repository nidaq32. Lib and nidex32 lib.
Signal collected set of data quantity is big, because of the mining data into line with TDMS lattice type deposit, line number and the letter into the description of sexual addition, there are advantages in number according to the check and management, by to the number according to the reservoir storage type
Is a binary system, because this rate is very quick, very high speed of commingled production sets
According to.
Signals to TDMS lattice type line into the store, due to the signal back into place when the need to make letter on TDMS article a fuck number into the line of code, from reading data.
3.2 signal analysis and processing
Signal analysis and handle is not a lack of step, its main purpose is from the measured to find out like letter number provided is used
Letter, LabVIEW software for signal analysis and provide the decommissioning is strong, in the letter size package, such as wavelet analysis, time-frequency analysis, time sequence
Column analysis, etc., greatly convenient for testers programming operation.
Frequency spectrum analysis is a kind of traditional square method of photoacoustic signal, the original reason
Y = abs (FFT (x, NFFT));
The plot ((0, NFFT / 2-1)/fs NFFT * and Y (1: NFFT / 2)); Xlabel (' frequency f/Hz); Ylabel (' power spectrum P/W);
Is use fu made leaf variable number in the letter within the range of frequency domain to analyse,
And research in the letter, of various kinds of identities, find out is used,
It is several words in the letter number, often use, heavy to party a,
LabVIEW provide the abundant in the frequency spectrum analysis of the process sequence, with needle on no conditions for signal in frequency domain analysis. Lab - VIEW at work can be very strong, but is still have some
Work can make now, no method to compensate is not enough, which provide the strong outside big department process sequence interface for full use of its optimal potential he become soft, such as MATLAB interface, this system use MATLAB interface into the line number to code the letter into the power spectrum analysis, the program is shown in figure 5.
MATLAB programming as shown below:
 


Power spectrum is shown in figure 6.
 

 

Figure 6 power spectrum analysis

In figure 6 can send shot to look to clear out the sound signal in the frequency rate provided within the scope of the amplitude.
By in each kind of deposit in the environment question, mining sets of mixed noise in the signal is interfered with more letter, those letters, save in the letter, analysis provide a kind of kind of difficult, lead to can not allowed it to find out the letter really is provided.
The wavelet analysis in, there is a kind of effective noise cancellation method, its main to the original
Principle is to choose a wavelet, the signal line into N layers of wavelet analysis, then to point solution to the number of layers is choosing a threshold, the fine line section is the number into the soft threshold in the sciences, noise reduction, after the department number through wavelet heavy build restore after the original signal. Wavelet base selection should be the full foot from small things, tight branch, to say, are the sexual several identities, due to the choice with Symlers wavelet into line to its points, points obtained feet root according to the frequency rate of big is small determine 7, article in the MATLAB interface under a letter from a sound in the road, the wavelet analysis, the results are shown in figure 7.