CN111189615A - Optical fiber dynamic fatigue test equipment and test signal processing method - Google Patents
Optical fiber dynamic fatigue test equipment and test signal processing method Download PDFInfo
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- CN111189615A CN111189615A CN201910740958.7A CN201910740958A CN111189615A CN 111189615 A CN111189615 A CN 111189615A CN 201910740958 A CN201910740958 A CN 201910740958A CN 111189615 A CN111189615 A CN 111189615A
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- G—PHYSICS
- G01—MEASURING; TESTING
- G01M—TESTING STATIC OR DYNAMIC BALANCE OF MACHINES OR STRUCTURES; TESTING OF STRUCTURES OR APPARATUS, NOT OTHERWISE PROVIDED FOR
- G01M11/00—Testing of optical apparatus; Testing structures by optical methods not otherwise provided for
- G01M11/30—Testing of optical devices, constituted by fibre optics or optical waveguides
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- G—PHYSICS
- G01—MEASURING; TESTING
- G01N—INVESTIGATING OR ANALYSING MATERIALS BY DETERMINING THEIR CHEMICAL OR PHYSICAL PROPERTIES
- G01N3/00—Investigating strength properties of solid materials by application of mechanical stress
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- G—PHYSICS
- G01—MEASURING; TESTING
- G01N—INVESTIGATING OR ANALYSING MATERIALS BY DETERMINING THEIR CHEMICAL OR PHYSICAL PROPERTIES
- G01N3/00—Investigating strength properties of solid materials by application of mechanical stress
- G01N3/20—Investigating strength properties of solid materials by application of mechanical stress by applying steady bending forces
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Abstract
The invention discloses an optical fiber dynamic fatigue testing device and a testing signal processing method, wherein the testing device comprises a pressure tank, an acoustic emission sensor, a signal conversion circuit, a digital signal processing device and a stepping motor displacement table, wherein the acoustic emission sensor converts a vibration signal into a voltage signal; the signal conversion circuit performs analog-to-digital conversion on the voltage signal output by the acoustic emission sensor and outputs the converted digital quantity; the digital signal processing equipment receives the digital quantity, converts a time domain signal corresponding to the digital quantity into a frequency domain for analysis, outputs a driving pulse signal by the digital signal processing equipment and controls the stepping motor to rotate. The optical fiber dynamic fatigue testing equipment and the testing signal processing method improve the anti-interference capability of the testing system and improve the accuracy of the calculation of the breaking stress of the optical fiber.
Description
Technical Field
The invention belongs to the technical field of optical fiber fracture detection, and particularly relates to an optical fiber dynamic fatigue testing device and a testing signal processing method.
Background
The optical fiber is the main transmission medium of modern high-speed communication systems, and the performance of the optical fiber is directly related to the quality of communication. One important property of an optical fiber is the service life, which is characterized by a dynamic fatigue parameter. The dynamic fatigue means that stress is applied to the optical fiber through a clamping plate with a constant displacement rate, the breaking stress and time when the optical fiber breaks are measured, and dynamic Weber parameters and dynamic fatigue factors are obtained, so that the service life of the optical fiber is predicted. In the above testing process, it is necessary to accurately detect the signal when the optical fiber is broken in time and extract useful information therefrom, so that a device is needed to monitor the process of breaking the optical fiber and collect and analyze the signal when the optical fiber is broken.
In actual test, the splint displacement rate required by corresponding international standards reaches 1um/s at the lowest, 1000um/s at the highest and has a precision requirement of +/-10 percent, and an audio signal is a very weak ultrasonic signal when an optical fiber is broken, so that the design and implementation of the optical fiber dynamic fatigue test system have certain technical difficulty.
Disclosure of Invention
The invention aims to solve the technical problem of providing the optical fiber dynamic fatigue testing equipment and the testing signal processing method, so that the accuracy of calculating the breaking stress of the optical fiber is improved.
The technical scheme adopted by the invention for solving the technical problems is as follows: firstly, providing an optical fiber dynamic fatigue testing device, which comprises a pressure tank, an acoustic emission sensor, a signal conversion circuit, a digital signal processing device and a stepping motor displacement table, wherein the acoustic emission sensor converts a vibration signal into a voltage signal; the signal conversion circuit performs analog-to-digital conversion on the voltage signal output by the acoustic emission sensor and outputs the converted digital quantity; the digital signal processing equipment receives the digital quantity, converts a time domain signal corresponding to the digital quantity into a frequency domain for analysis, outputs a driving pulse signal by the digital signal processing equipment and controls the stepping motor to rotate.
According to the technical scheme, the stepping motor displacement table is connected with the pressure groove and is controlled to generate displacement through pulse signals.
According to the technical scheme, the optical fiber bending device further comprises a movable pressing groove which is arranged above the pressing groove and is matched with the pressing groove to adjust the bending radius of the optical fiber.
According to the technical scheme, the acoustic emission sensor is a medium-low frequency acoustic emission sensor.
According to the technical scheme, the pressure groove is a metal pressure groove, and the movable pressure groove is a metal movable pressure groove.
The invention also provides a processing method of the optical fiber dynamic fatigue test signal, which comprises the following steps that firstly, the acoustic emission sensor converts the vibration signal into a voltage signal; secondly, the signal conversion circuit performs analog-to-digital conversion on the voltage signal output by the acoustic emission sensor and outputs the converted digital quantity; and step three, the digital signal processing equipment receives the digital quantity, converts a time domain signal corresponding to the digital quantity into a frequency domain for analysis, and outputs a driving pulse signal by the digital signal processing equipment to control the stepping motor to rotate.
According to the technical scheme, the third step specifically comprises the steps of carrying out independent process control and timing on frequency domain processing of the control pulse signal and the digital signal, carrying out Fast Fourier Transform (FFT) on the signal, and controlling the time consumption of the FFT; and performing frequency domain analysis on the result after the fast Fourier transform, and calculating the fracture stress when the optical fiber is fractured only by responding to the amplitude-frequency signal which accords with the frequency domain characteristics of the optical fiber fracture.
According to the technical scheme, the independent process control and timing of the frequency domain processing of the control pulse signal and the digital signal specifically comprises the steps that the digital signal processing equipment internally controls the generation of the pulse signal (marked as process A) and the frequency domain processing of the digital signal (marked as process B) through two independent processes, when the optical fiber is broken, the interval of the control pulse sent out by the process A is T1, and the process B judges that the time consumed by one optical fiber breakage event is T2 after the signal processing is finished.
According to the technical scheme, the Fast Fourier Transform (FFT) is carried out on the signal, and the time consumption of the FFT is controlled specifically, under the condition that the number of sampling points and the sampling frequency are fixed, the digital signal processing equipment adopts a multistage assembly line to enable the T2 to be a certain value.
According to the technical scheme, the step of calculating the breaking stress when the optical fiber is broken specifically comprises the steps of calculating the breaking stress at the moment of breaking the optical fiber according to the distance between the pressure groove and the movable pressure groove, controlling the distance between the pressure groove and the movable pressure groove by using a stepping motor displacement table, calculating the number N (N is T2/T1, and an integer part) of pulses generated in a T2 time interval, converting the displacement of the metal pressure groove from the breaking generation to the system judgment of the breaking event generation, and deducting the displacement to obtain the distance between the metal pressure grooves at the moment of breaking the optical fiber. The stepping motor displacement platform is connected with the pressure groove, displacement is generated through pulse signal control, and the movable pressure groove is matched with the pressure groove to adjust the bending radius of the optical fiber.
The invention has the following beneficial effects: (1) the anti-interference capability of the system is improved, in the scheme of detecting the optical fiber breakage signal generally, threshold judgment is carried out on the amplitude of the voltage signal output by the acoustic emission sensor, and when the amplitude exceeds a certain threshold value, the system considers that the optical fiber breakage signal is detected. In practice, this approach is disturbed by ambient noise and vibrations: even if the fiber is not broken, the system can be falsely triggered when vibration or noise from the surrounding environment is coupled to the acoustic emission sensor for some reason and the intensity exceeds a set threshold. After the frequency domain analysis is carried out on the fracture signal, the system has the capability of narrow-band filtering, and the system can be triggered only by the signal of which the vibration accords with the frequency domain characteristics of the optical fiber fracture.
(2) The calculation time of FFT is accurate through a multistage assembly line structure in the digital signal processing equipment, and the accuracy of fracture stress calculation is improved.
(3) And the data analysis approach is increased. The fiber breakage is the result of the comprehensive action of the factors of the stress on the fiber, the strength of the fiber quartz fiber, the strength of the fiber coating material and the hydrolysis degree of the fiber quartz material, and the breakage condition caused by different conditions can be better distinguished by carrying out frequency spectrum analysis on the breakage audio frequency.
Drawings
The invention will be further described with reference to the accompanying drawings and examples, in which:
fig. 1 is a block diagram of a fiber dynamic fatigue testing apparatus according to an embodiment of the present invention.
FIG. 2 is a diagram illustrating the relationship between the FFT time consumption and the number of driving pulses.
Fig. 3 is an illustration of the main functional blocks within the digital signal processing apparatus.
Fig. 4 shows the results of a frequency domain analysis of the fiber break signal.
Detailed Description
In order to make the objects, technical solutions and advantages of the present invention more apparent, the present invention is described in further detail below with reference to the accompanying drawings and embodiments. It should be understood that the specific embodiments described herein are merely illustrative of the invention and are not intended to limit the invention.
The first embodiment is as follows: fig. 1 is a block diagram of the apparatus according to the embodiment of the present invention, in which a section of bent optical fiber 2 is held in a fixed metal pressure groove 1, and an acoustic emission sensor 3 is tightly mounted on the metal pressure groove 1. The digital signal processing equipment 4 sends out driving pulse, drives the stepping motor displacement table 6 through the lead 5, so that the stepping motor displacement table 6 generates uniform displacement, the distance between the movable metal pressure groove 7 and the fixed metal pressure groove 1 which are arranged on the stepping motor displacement table is smaller and smaller, and the stress generated by the local part of the extruded and bent optical fiber is larger. Under the comprehensive action of the stress on the optical fiber, the strength of the optical fiber quartz fiber, the strength of the optical fiber coating layer material and the hydrolysis degree of the optical fiber quartz material, when the distance between the metal press grooves reaches a certain position, the stress born by the section of the optical fiber reaches the limit, and the optical fiber is broken. And outputting a pulse signal by using digital signal processing equipment to control the stepping motor, and performing frequency domain analysis on the ultrasonic signal released in the optical fiber breaking process in the same digital signal processing equipment.
When the optical fiber is broken, a high-frequency vibration signal is synchronously generated along with the rapid release of stress, and the signal is detected by the acoustic emission sensor 3 through the conduction action of the metal pressure groove.
Inside the acoustic emission sensor 3, the vibration signal is converted into a voltage signal due to the piezoelectric effect of the piezoelectric ceramics. The input of the signal conversion circuit 8 is connected to the output end of the acoustic emission collection sensor 3 through a section of cable 9, and the circuit outputs a group of digital quantity which is in direct proportion to the voltage amplitude value through collecting the output voltage signal of the acoustic emission sensor.
Example two: in the embodiment, the optical fiber dynamic fatigue test signal processing method comprises the following steps that an acoustic emission sensor converts a vibration signal into a voltage signal, a signal conversion circuit performs analog-to-digital conversion on the voltage signal output by the acoustic emission sensor and outputs the converted digital quantity; the digital signal processing equipment receives the digital quantity, converts a time domain signal corresponding to the digital quantity into a frequency domain for analysis, outputs a driving pulse signal by the digital signal processing equipment and controls the stepping motor to rotate. The stepping motor displacement platform is connected with the pressure tank and is controlled to generate displacement through a pulse signal.
And carrying out independent process control and timing on the frequency domain processing of the control pulse signal and the digital signal: the processing device internally controls the generation of the pulse signal (denoted as process a) and the frequency domain processing of the digital signal (denoted as process B) by two separate processes. When the optical fiber is broken, the interval of the control pulse sent out by the process A is T1, and the time consumed for judging that the signal is processed and is a fiber breakage event is T2 by the process B.
The method comprises the steps of carrying out Fast Fourier Transform (FFT) on a signal, accurately controlling the time consumption of the FFT, and enabling T2 to be a certain value through a technical means of adopting a multistage pipeline in the digital signal processing equipment under the condition that the number of sampling points and the sampling frequency are fixed.
And performing frequency domain analysis on the result after the FFT, and only responding to the amplitude-frequency signal which accords with the fiber fracture frequency domain characteristics. In the test site, there are various environmental noises, most of which are low-frequency noises of the operation of the equipment. The frequency of the audio signal at the break in the fiber was found to peak around the 20Khz attachment. Therefore, narrow-band filtering processing can be carried out aiming at the frequency spectrum range, and the anti-interference capability of the system is improved.
Calculating the breaking stress when the optical fiber breaks: the breaking stress at the moment of fiber breakage can be calculated from the spacing between the metal indents. The distance between the metal pressure grooves is controlled by a stepper motor displacement table, and the control principle of the stepper motor can be known, the number N (N is T2/T1, and an integer part) of pulses generated in a T2 time interval is calculated, namely the displacement of the metal pressure grooves from the occurrence of the fracture to the occurrence of the fracture event determined by the system can be converted, and the distance between the metal pressure grooves at the moment of the optical fiber fracture can be obtained by deducting the displacement.
Example three: the digital signal processing device 4 is connected with the signal conversion circuit 8 through a digital IO port 10, and the digital signal processor performs fast Fourier transform on the digital quantity and calculates a corresponding frequency domain spectrum. A typical sampling rate is 100Ksps, and an FFT calculation is performed for 1 second of acquired data, i.e., 100000 data points. By configuring the digital signal processing device, in this embodiment, a clock, a multiplier, and a memory resource inside an FPGA (field programmable gate array) are selected, so that the time of each FFT calculation can be accurately controlled to 500 milliseconds, and the error is less than 10 nanoseconds. The 500 millisecond value is fully considered: for convenience of calculation, T2 is preferably an integer multiple of 1 second or 1/2 or 1/5 of 1 second, so that an integer displacement distance can be obtained by directly multiplying the displacement rate of the displacement table by T2 without calculating N ═ T2/T1. When T2 is too long, the displacement table is not necessarily strictly uniform due to the fit margin between the mechanical pieces, and the longer T2, the more likely this error is to accumulate; when T2 is small, it puts high demands on the performance of the FPGA, increasing the hardware cost. Therefore, after the integration, T2 is controlled to be 500 msec.
Fig. 2 is a diagram illustrating the relationship between the total time consumption T2 from the generation of the fragmentation signal (time domain) to the completion of FFT computation (frequency domain) by the digital signal processing apparatus, the pulse interval T1, and the number of pulses N.
Fig. 3 is a block diagram of main functional blocks inside the digital signal processing apparatus 4. The data buffer 41 receives the digital quantity 45 transmitted through the digital IO port, and completes FFT computation in the multiplier module 42, and the computation result is output through the interface 46. The pulse synchronization delay module 43 calculates the delay time of the pulse synchronization according to the time consumed by the multiplier to complete the calculation, and generates a corresponding driving pulse 47 to be output through the pulse generation module 44.
The effect after completion of the FFT is the spectrum diagram illustrated in fig. 4.
As can be seen from FIG. 4, the amplitude of the generated break signal for this fiber section under test conditions was about 20mv, and the maximum amplitude signal frequency was 21.756 kHz.
The step pitch of each step of the selected stepper motor displacement table is 0.1 um. The following data discussion is presented in terms of the rate and pulse interval T1 of the stepper motor stage, and the FFT elapsed time T2 for the actual test:
in standard testing, testing at three different rates, 10um/s, 100um/s, 1000um/s, respectively, is required. Because the step distance of the stepper motor displacement table is small, T1 is much smaller than T2 at all three speeds. The drive pulse frequency scaled by the displacement rate is: 100Hz, 1000Hz, 10000 Hz. Since T1 has been accurately controlled to 500 milliseconds, N50, N500, and N5000 are calculated from the three rates. The shifts that need to be subtracted are 5um, 50um and 500 um. In this embodiment, the Nd value of the extracted qualified optical fiber is 22, which is consistent with the previous test result.
It will be understood that modifications and variations can be made by persons skilled in the art in light of the above teachings and all such modifications and variations are intended to be included within the scope of the invention as defined in the appended claims.
Claims (10)
1. An optical fiber dynamic fatigue testing device is characterized by comprising a pressure tank, an acoustic emission sensor, a signal conversion circuit, a digital signal processing device and a stepping motor displacement table, wherein the acoustic emission sensor converts a vibration signal into a voltage signal; the signal conversion circuit performs analog-to-digital conversion on the voltage signal output by the acoustic emission sensor and outputs the converted digital quantity; the digital signal processing equipment receives the digital quantity, converts a time domain signal corresponding to the digital quantity into a frequency domain for analysis, outputs a driving pulse signal by the digital signal processing equipment and controls the stepping motor to rotate.
2. The optical fiber dynamic fatigue testing apparatus of claim 1, wherein the stepping motor displacement stage is connected to the pressure tank and is controlled to generate displacement by a pulse signal.
3. The optical fiber dynamic fatigue testing apparatus of claim 1 or 2, further comprising a movable pressure groove disposed above the pressure groove, and cooperating with the pressure groove to adjust the bending radius of the optical fiber.
4. The fiber optic dynamic fatigue test apparatus of claim 1 or 2, wherein the acoustic emission sensor is a medium and low frequency acoustic emission sensor.
5. The optical fiber dynamic fatigue testing apparatus of claim 3, wherein the indent is a metal indent and the movable indent is a metal movable indent.
6. An optical fiber dynamic fatigue test signal processing method based on any one of claims 1 to 5, characterized in that the method comprises the steps of, firstly, converting a vibration signal into a voltage signal by an acoustic emission sensor; secondly, the signal conversion circuit performs analog-to-digital conversion on the voltage signal output by the acoustic emission sensor and outputs the converted digital quantity; and step three, the digital signal processing equipment receives the digital quantity, converts a time domain signal corresponding to the digital quantity into a frequency domain for analysis, and outputs a driving pulse signal by the digital signal processing equipment to control the stepping motor to rotate.
7. The method for processing the optical fiber dynamic fatigue test signal according to claim 6, wherein the third step specifically comprises performing independent process control and timing on the frequency domain processing of the control pulse signal and the digital signal, performing fast Fourier transform on the signal, and controlling the time consumption of FFT; and performing frequency domain analysis on the result after the fast Fourier transform, and calculating the fracture stress when the optical fiber is fractured only by responding to the amplitude-frequency signal which accords with the frequency domain characteristics of the optical fiber fracture.
8. The method as claimed in claim 7, wherein the independent process control and timing of the frequency domain processing of the control pulse signal and the digital signal specifically includes that the digital signal processing device internally controls the generation of the pulse signal and the frequency domain processing of the digital signal through two independent processes, when the optical fiber is broken, the interval of the control pulse sent by process a is T1, and the time consumed for process B to complete the signal processing and determine as one optical fiber breakage event is T2.
9. The method according to claim 7, wherein the performing fast fourier transform on the signal and controlling the time consumption of FFT specifically includes that the digital signal processing apparatus adopts a multistage pipeline to make T2 a certain value under the condition that the number of sampling points and the sampling frequency are fixed.
10. The method of claim 7, wherein the calculating the breaking stress at the time of the optical fiber breaking specifically includes calculating the breaking stress at the time of the optical fiber breaking from the distance between the time slot and the movable slot, controlling the distance between the slot and the movable slot by a stepper motor displacement table, calculating the number N of pulses generated in the time interval T2, where N is T2/T1, taking an integer part, converting the integer part into the displacement of the metal slot between the breaking event and the breaking event, and subtracting the displacement to obtain the distance between the metal slots at the time of the optical fiber breaking.
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Cited By (1)
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| CN111721643A (en) * | 2020-07-03 | 2020-09-29 | 浙商检测集团有限公司 | Low-temperature flexible detector for waterproof coiled material |
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Application publication date: 20200522 |