Distributed optical fiber sensor with controllable temperature fluctuation
There is no limit to creativity, and the instrument is invented. Today we introduce a national invention patent, a distributed optical fiber sensor and temperature measurement system and method with temperature fluctuation controllable. The patent was filed by Weihai Beiyang Electric Group Co., Ltd. and was authorized to be announced on March 1, 2017.
The invention relates to the technical field of optical fiber temperature measurement, in particular to a distributed optical fiber sensor and a temperature measuring system capable of improving the correction precision of the middle section of the sensing fiber and maintaining the temperature fluctuation of the two ends of the sensing fiber. And methods.
Background of the invention
As we all know, distributed optical fiber temperature sensor is a fiber optic sensing system developed in recent years for real-time measurement of spatial temperature field. The system uses Raman scattering effect and OTDR technology to realize distributed measurement of the temperature field of sensitive fiber. Compared with traditional electric temperature sensors, fiber optic temperature sensors have the advantages of high sensitivity, immunity to electromagnetic interference, light weight and long life, so they can be widely used in power cables , subway tunnels, coal mine roadways, oil storage tanks and large buildings. Temperature monitoring and fire alarms.
Although the research on Raman-type distributed optical fiber temperature sensor is relatively mature, there are still some imperfect problems. At present, the development direction of distributed optical fiber temperature sensor is long distance and high precision, and high precision is high temperature fluctuation and high space. The resolution and spatial resolution are determined by the laser pulse width and can be solved by a narrow pulse laser. Long-distance and high-temperature fluctuations are achieved, and finally a high signal-to-noise ratio is pursued. At present, the temperature fluctuation of a common distributed optical fiber temperature sensor is The increase in the measured distance increases, that is, the temperature fluctuation at the nominal distance of the system is the nominal temperature fluctuation of the system.
In 2011, the Italian Soto team announced its latest development "High-Performance"
Raman-ba sed Distributed Fiber-Optic Sensing Under a Loop Scheme Using Anti-Stokes Light Only, a single-channel anti-Stokes Raman fiber-optic sensing system with a double-ended correction scheme, although the study is better for loss, etc. The correction effect, but the temperature fluctuation still exists in the middle better than the two ends.
Summary of the invention
The invention aims at the shortcomings and shortcomings in the prior art, and proposes that in the optical fiber temperature measuring system, the correction precision of the middle section of the optical fiber can be effectively sensed, and the temperature fluctuation degree of the fluctuation index of the two ends of the sensing fiber is controlled. Distributed fiber optic sensor and temperature measurement system and method.
Figure is a block diagram of the distributed optical fiber sensor in the present invention
The invention can be achieved by the following measures: a distributed optical fiber temperature sensor with controllable temperature fluctuation, including pulse fiber laser, wavelength division multiplexer, 1*2 optical switch, sensing fiber, photoelectric receiving module and data acquisition card The characteristic is that the light emitted by the pulsed fiber laser enters the 1*2 optical switch through the multiplex end of the wavelength division multiplexer, and the two output ends of the 1*2 optical switch are respectively connected with the two ends of the sensing fiber, and the photoelectric receiving module and The back signal output end of the wavelength division multiplexer is connected, the control signal output end of the data acquisition card is connected with the pulse fiber laser, and the other control signal output end of the data acquisition card is connected with the 1*2 optical switch, and the photoelectric The signal output end of the receiving module is connected to the data collecting end of the data acquisition card.
In the data acquisition card of the invention, an optical switch channel control circuit, a pulse fiber laser control circuit, a back Raman scattering signal acquisition and accumulation circuit and an accumulated data upload circuit are provided for controlling the output optical signal of the pulsed fiber laser. At the same time, the working state of the 1*2 optical switch is controlled, and the self-accumulation operation of the back Raman scattered optical signal for the forward or reverse transmitted light is realized according to the selection of different channels of the 1*2 optical switch, the present invention The optical switch channel control circuit of the data acquisition card realizes the control signal required by the optical switch by using the FPGA to form an inverter or a digital circuit of serial-to-parallel conversion, realizes a logic sequence composed of 0 and 1, and controls the channel of the optical switch Selectively, the pulse fiber laser control circuit is divided by the frequency converter PLL of the FPGA to realize the periodic signal of the fixed frequency and the duty cycle, and the back Raman scattering signal acquisition circuit is composed of the first stage operational amplifier, the ADC adjustment differential circuit and the ADC, and accumulates. The circuit is composed of a direction determining circuit, a ping-pong accumulating circuit, etc., and the accumulating uploading circuit is implemented by a protocol conversion circuit and a USB2.0 hardware environment.
A distributed optical fiber temperature measuring system with temperature fluctuation controllable, comprising an industrial computer and a fiber Raman temperature sensor connected to the industrial computer, wherein the fiber Raman temperature sensor is the above fiber Raman temperature sensor, The data acquisition card in the fiber Raman temperature sensor is connected to the industrial computer via the USB bus.
A method for measuring temperature by using the above-mentioned temperature fluctuation controllable distributed optical fiber temperature measuring system, comprising the following steps: Step 1: The optical signal output by the pulse laser enters the 1*2 optical switch through the wavelength division multiplexer com end, the steps The 2:1*2 optical switch is controlled by the channel selection signal outputted by the optical switch channel control circuit of the data acquisition card, that is, the effective high and low level sequence, such as: 101 is one channel, 110 is another channel, and the control is divided by wave division. The optical signal entering the com terminal of the multiplexer enters the sensing fiber from a certain channel, and the channel is recorded as the first channel. The optical signal entering the sensing fiber is recorded as forward transmission light, and the forward transmission light is in sensing. Backward Raman scattered light is generated in the optical fiber, and the back Raman scattered light is split into Stokes light and anti-Stokes light by a wavelength division multiplexer, and respectively connected to the wavelength division multiplexer. The photoelectric receiving module respectively receives the Stokes light and the anti-Stokes optical signal, respectively converts them into corresponding electrical signals and sends them to the back Raman scattering signal acquisition and accumulation circuit in the data acquisition card.
Step 3: The 1*2 optical switch is controlled by the effective high-low sequence of the channel selection signal output of the data acquisition card, such as: 101 is a certain channel, 110 is another channel, and the control is performed by a wavelength division multiplexer com terminal. The incoming optical signal enters the sensing fiber from another channel, and the channel is the second channel. The optical signal entering the sensing fiber is recorded as reverse transmission light, and the reverse transmission light generates back Raman in the sensing fiber. The scattered light and the back Raman scattered light are separated into Stokes light and anti-Stokes light by a wavelength division multiplexer, and respectively received by two sets of photoelectric receiving modules connected to the wavelength division multiplexer. The X-ray and anti-Stokes optical signals are respectively converted into corresponding electrical signals and sent to the back Raman scattering signal acquisition and accumulation circuit in the data acquisition card. Step 4: Count Step 2 and Step 3 and compare with the set number of times. If it is less than the set number of times, repeat steps 2 and 3 until the set number of accumulations is reached, the back Raman scattering in the data acquisition card. The signal acquisition and accumulation circuit respectively accumulates the back signal generated by the received forward transmission light and the back signal generated by the reverse transmission light, and sends the accumulated result to the accumulation data upload circuit. Step 5: The accumulated data uploading circuit uploads the received data to the industrial computer. Step 6: The industrial computer processes the data uploaded by the data acquisition card to obtain the temperature measurement result.
The invention has the beneficial effects of providing a distributed optical fiber temperature sensor with controlled temperature fluctuation with certain correction function, using double-end measurement and Raman scattering based on anti-Stokes demodulation Stokes curve The principle realizes the correction operation of the middle section of the fiber, while retaining the fluctuation index of the two ends of the fiber, and adjusting the operating range of the middle section by software, so that the system has controllable temperature fluctuation.
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