CN103033284A - Distributed fiber temperature detection system noise reduction method based on fast fourier transform algorithm (FFT) - Google Patents
Distributed fiber temperature detection system noise reduction method based on fast fourier transform algorithm (FFT) Download PDFInfo
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- CN103033284A CN103033284A CN201110294759.1A CN201110294759A CN103033284A CN 103033284 A CN103033284 A CN 103033284A CN 201110294759 A CN201110294759 A CN 201110294759A CN 103033284 A CN103033284 A CN 103033284A
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Abstract
The invention discloses a distributed fiber temperature detection system noise reduction method based on a fast fourier transform algorithm (FFT). The method comprises filtering collected signals though the FFT, namely conducting FFT switching firstly, then filtering signals outside a system frequency band, conducting FFT reverse switching to obtain filtered pure signals. The method adopts the FFT switching, removes noise outside the system frequency band, effectively reduces noise, improves signal-to-noise ratio of the system and accordingly improves temperature measurement accuracy.
Description
Technical field
The present invention relates to the technical field of temperature-measuring system of distributed fibers, relate in particular to a kind of temperature-measuring system of distributed fibers noise-reduction method based on FFT.
Background technology
It is on-the-spot that temperature-measuring system of distributed fibers (hereinafter referred to as the DTS system) is widely used in various fire hazard monitorings, scenes such as the power cable tunnel of vcehicular tunnel, subway tunnel, electric power power plant, petrochemical complex storage tank.The DTS system is a kind of temperature measurement system that develops based on OTDR and Raman scattering principle, and its temperature sensor is optical fiber (usually being made into optical cable).The DTS system utilizes the Ramam effect of optical fiber, and namely the backward Raman scattering light that transmits in the optical fiber has been modulated in the temperature field of optical fiber paving location (space), just can demodulate the real time temperature information in temperature field after opto-electronic conversion and signal processing.DTS system composition generally comprises high power pulse laser light source, optical fibre wavelength-division multiplex coupling mechanism, sensing optic cable, photodetector, signal amplification module, data acquisition module and system host (PC or industrial computer).Because DTS is distributed, namely optical cable is laid on the scene that needs monitoring continuously, and apart from growing (normally several kilometers), compares and other temp measuring systems, and DTS has obvious advantage.
At present the DTS system satisfy fully the temperature measurement accuracy requirements such as highway, tunnel lower the application requirements in fire hazard monitoring place; But for the power cable load monitoring of picture electric power power plant etc. temperature accuracy is required higher application scenario, the DTS system of at present domestic manufacturer's development still can not satisfy application requirements.Therefore how to improve the temperature measurement accuracy of DTS system, namely how to reduce system noise, become the emphasis that domestic colleges and universities institutes and producer are studied energetically.
The DTS system comes principle to come the demodulation temperature information according to Raman scattering, because Raman diffused light is very faint, so the electric signal that produces after the opto-electronic conversion (generally adopting APD as photoelectric commutator) is also very faint, and signal almost all is submerged in the noise.The ASE noise that the dark current noise that produces except APD in these noises and light source produce, the white noise that also has APD and Circuits System to produce.APD dark current noise and ASE noise can be removed with the AC coupling of circuit, and be the multi collect signal to the traditional method of the elimination of white noise, then average again after these signals being added up, theoretical analysis adopts averaging method can effectively reduce noise (noise is eliminated mutually).But white noise is broadband noise, that is to say that its bandwidth is very wide, by cumulative and averaging method, can eliminate a part, but the impact of white noise still clearly, system signal noise ratio or undesirable, so its noise of Demodulation Systems temperature signal out is also larger, namely temperature measurement accuracy is not high enough.In addition, adopt cumulative rear average method, Measuring Time increases along with the increase of accumulative frequency.
FFT conversion (Fast Fourier Transform (FFT)) is a kind of very important algorithm of digital processing field, generally is used for the frequency spectrum of analytic signal, in actual applications, can be used for signal is carried out filtering, for example, is used for the signal of the some frequency ranges of filtering.
Summary of the invention
In order to solve problems of the prior art, the invention provides a kind of temperature-measuring system of distributed fibers noise-reduction method based on FFT, the method adopts the FFT conversion, remove the noise outside the system bandwidth, effectively reduce noise, improve system signal noise ratio, thereby improve temperature measurement accuracy.
In order to achieve the above object, the present invention adopts a kind of temperature-measuring system of distributed fibers noise-reduction method based on FFT, and described a kind of temperature-measuring system of distributed fibers based on FFT comprises narrow-pulse laser light source, optical fibre wavelength-division multiplex coupling mechanism, sensing optic cable, APD (photodetector), small-signal amplification module, data acquisition module and system host (PC or industrial computer).
According to theoretical analysis, the noise of DTS system has mainly comprised the white noise that APD dark current noise, light source ASE noise and circuit system produce.APD dark current noise, light source ASE noise are the low-frequency noises close to direct current, can adopt ac-coupled circuit effectively to reduce; And white noise is the very wide noise of bandwidth, and experiment shows that the high fdrequency component (mainly being white noise) of DTS system signal has higher energy to exist; On the other hand, DTS system its bandwidth of effective temperature signal is also wider, has signal distributions, experiment to show from the low frequency to the HFS always, and the energy of temperature signal mainly concentrates on tens Hz in tens MHz scopes.Therefore, the signal that collects is carried out filtering by FFT, namely carry out first the FFT conversion, then the outer target signal filter of band system band, carry out again the FFT inverse transformation, just can obtain cleaner signal after the filtering, thus the raising system signal noise ratio.
A kind of temperature-measuring system of distributed fibers noise-reduction method based on FFT comprises the steps:
Step 1, one section valid data of system acquisition when synchronizing signal produces namely obtain the data (such as temperature signal etc.) of each position on the optical cable (such as each rice);
Step 2 is done the FFT conversion to the data that step 1 collects, the frequency domain information of picked up signal (comprising noise);
Step 3, frequency domain information to signal is further analyzed, spectrum value close to the component of signal of direct current (such as frequency less than 10Hz) and high frequency (such as frequency greater than 50MHz) component of signal is set to 0, and the spectrum value of the signal of other band components remains unchanged;
This step is namely carried out filtering to the out-of-band noise filtering of temperature signal to signal;
Step 4 is carried out the FFT inverse transformation to the spectrum component of filtered signal, the time-domain signal of reconstruct after the acquisition filtering;
Signal filtering this moment the outer noise of signal band, signal to noise ratio (S/N ratio) has obtained larger raising;
Step 5 is done traditional accumulation process to filtered time-domain signal, and namely repeating step one is to step 4, and each result's (being the result of step 4) who processes is added up, until accumulative frequency reaches the number of times of default.Usually accumulative frequency is up to tens thousand of times (namely repeating step one is tens thousand of inferior to step 4).
Step 6 is done average treatment to the accumulation result that step 5 obtains, and namely accumulation result is divided by accumulative frequency.
Step 7 is sent into computing machine to the data after processing through filtering and through progressive mean and is carried out temperature demodulation computing, obtains the temperature information of each position at system sensing optical cable place.
Adopt the beneficial effect of method of the present invention to be: system noise reduces greatly, has increased substantially system signal noise ratio, thereby so that the temperature measurement accuracy of system be greatly improved.
Description of drawings
Fig. 1 is system architecture schematic diagram of the present invention.
The implementation formula
Further specify the specific embodiment of the present invention below in conjunction with accompanying drawing.
The present invention adopts a kind of temperature-measuring system of distributed fibers noise-reduction method based on FFT, and described a kind of temperature-measuring system of distributed fibers based on FFT comprises narrow-pulse laser light source 1, optical fibre wavelength-division multiplex coupling mechanism 2, sensing optic cable 3, APD (photodetector) 4, small-signal amplification module 5, data acquisition module 6 and system host 7 (PC or industrial computer).
System's various piece function is as follows:
Described narrow-pulse laser light source 1, its function are to produce narrow-pulse laser, and narrow-pulse laser enters sensing optic cable 3 by optical fibre wavelength-division multiplex coupling mechanism 2, and transmits forward along sensing optic cable, simultaneously at the rear Raman diffused light to transmission of the inner generation of optical cable; Raman diffused light is got back to optical fibre wavelength-division multiplex coupling mechanism 2 backward along optical cable transmission, goes forward side by side into photodetector 4, produces opto-electronic conversion.
Described optical fibre wavelength-division multiplex coupling mechanism 2, its function is: so that narrow-pulse laser can from narrow-pulse laser light source 1 by optical fibre wavelength-division multiplex coupling mechanism 2, can only enter into sensing optic cable 3, but can not enter into photodetector 4; So that Raman diffused light can from sensing optic cable 3 by optical fibre wavelength-division multiplex coupling mechanism 2, can only enter into photodetector 4, but can not enter into many narrow-pulse lasers light source 1.
Described sensing optic cable 3, its function are the temperature variation of detecting optical cable environment of living in.When optical cable environment temperature of living in changed, its inner Raman scattering light intensity also changed, and according to this variation, just can demodulate the temperature information of optical cable environment of living in.
Described APD (photodetector) 4, its function is that light signal is transformed into electric signal; The normal light signal is the faint light signal of power, and the electric signal that is transformed into also is ultra-weak electronic signal.
Described small-signal amplification module 5, its function are that the ultra-weak electronic signal that photodetector produces is amplified and filtering.
Described data acquisition module 6, its function are to finish the conversion of electric signal analog to digital (being data acquisition), and do accumulation process, then the data transmission of handling well are arrived system host 7.
Described system host 7 (PC or industrial computer), its function is to finish the demodulation of temperature information, the processing such as the demonstration of temperature curve.
Further, described narrow-pulse laser light source 1 and data acquisition module 6 come collaborative work according to synchronizing signal, and the effect of synchronizing signal is so that data acquisition module is able to gather useful signal in the correct moment.Synchronizing signal is pulse signal, has certain repetition frequency, and for example repetition frequency is 2kHz; Synchronizing signal can be produced or be produced by data acquisition module by light source.When synchronizing signal produced, light source produced pulse laser, at this moment data collecting module collected to one piece of data be that effectively data length is relevant with the optical cable product degree that system configures, data of each meter optical cable correspondence for example.
A kind of temperature-measuring system of distributed fibers noise-reduction method based on FFT comprises the steps:
Step 1, one section valid data of system acquisition when synchronizing signal produces namely obtain the data (such as temperature signal etc.) of each position on the optical cable (such as each rice).Further, data length is relevant with the cable length that system configures, for example the corresponding data of each meter optical cable.
Step 2 is done the FFT conversion to the data that step 1 collects, the frequency domain information of picked up signal (comprising noise).
Step 3, frequency domain information to signal is further analyzed, spectrum value close to the component of signal of direct current (such as frequency less than 10Hz) and high frequency (such as frequency greater than 50MHz) component of signal is set to 0, and the spectrum value of the signal of other band components remains unchanged.This step is namely carried out filtering to the out-of-band noise filtering of temperature signal to signal.
Step 4 is carried out the FFT inverse transformation to the spectrum component of filtered signal, the time-domain signal of reconstruct after the acquisition filtering.Signal filtering this moment the outer noise of signal band, signal to noise ratio (S/N ratio) has obtained larger raising.
Step 5 is done traditional accumulation process to filtered time-domain signal, and namely repeating step one is to step 4, and each result's (being the result of step 4) who processes is added up, until accumulative frequency reaches the number of times of default.Usually accumulative frequency is up to tens thousand of times (namely repeating step one is tens thousand of inferior to step 4).
Step 6 is done average treatment to the accumulation result that step 5 obtains, and namely accumulation result is divided by accumulative frequency.
Step 7 is sent into computing machine to the data after processing through filtering and through progressive mean and is carried out temperature demodulation computing, obtains the temperature information of each position at system sensing optical cable place.
Above demonstration and description be ultimate principle of the present invention, principal character and advantage of the present invention; the technician of the industry should understand the restriction that the present invention is not subjected to said method; that describes in said method and the instructions just says principle of the present invention; the present invention also has various changes and modifications without departing from the spirit and scope of the present invention, and these changes and improvements all fall in the protection domain that is defined by appending claims of the present invention and equivalent thereof.
Claims (1)
1. temperature-measuring system of distributed fibers noise-reduction method based on FFT is characterized in that: may further comprise the steps:
Step 1, one section valid data of system acquisition when synchronizing signal produces namely obtain the data of each position on the optical cable;
Step 2 is done the FFT conversion to the data that step 1 collects, the frequency domain information of picked up signal;
Step 3 is further analyzed the frequency domain information of signal, and setting to 0 close to the component of signal of direct current and the spectrum value of high frequency component signal, the spectrum value of the signal of other band components remains unchanged;
Step 4 is carried out the FFT inverse transformation to the spectrum component of signal after the filtering, the time-domain signal of reconstruct after the acquisition filtering;
Step 5 is done traditional accumulation process to filtered time-domain signal, and namely repeating step one is to step 4, and each result's (being the result of step 4) who processes is added up, until accumulative frequency reaches the number of times of default.
Step 6 is done average treatment to the accumulation result that step 5 obtains, and namely accumulation result is divided by accumulative frequency.
Step 7 is sent into computing machine to the data after processing through filtering and through progressive mean and is carried out temperature demodulation computing, obtains the temperature information of each position at system sensing optical cable place.
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Cited By (3)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| CN106500870A (en) * | 2016-11-29 | 2017-03-15 | 武汉理工光科股份有限公司 | Distributed fiber optic temperature detector and the method that spatial resolution is improved using frequency modulating technology |
| CN109341892A (en) * | 2018-08-20 | 2019-02-15 | 苏州光格设备有限公司 | Data acquisition circuit and data processing method for distributed optical fiber temperature measurement |
| CN111157143A (en) * | 2020-01-10 | 2020-05-15 | 河北华仁通电电气科技有限公司 | Distributed optical fiber temperature measurement and noise reduction device and noise reduction method thereof |
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- 2011-09-30 CN CN201110294759.1A patent/CN103033284A/en active Pending
Cited By (3)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| CN106500870A (en) * | 2016-11-29 | 2017-03-15 | 武汉理工光科股份有限公司 | Distributed fiber optic temperature detector and the method that spatial resolution is improved using frequency modulating technology |
| CN109341892A (en) * | 2018-08-20 | 2019-02-15 | 苏州光格设备有限公司 | Data acquisition circuit and data processing method for distributed optical fiber temperature measurement |
| CN111157143A (en) * | 2020-01-10 | 2020-05-15 | 河北华仁通电电气科技有限公司 | Distributed optical fiber temperature measurement and noise reduction device and noise reduction method thereof |
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Application publication date: 20130410 |