CN115950482A - A time-division multiplexing optical fiber sensing system for temperature and vibration measurement - Google Patents

Abstract

The invention discloses a time division multiplexing temperature and vibration measurement optical fiber sensing system, which comprises a light source, an optical switch, a first coupler, a second coupler and a third coupler, wherein the light source emits continuous light to enter the optical switch, the optical switch is controlled by an upper computer and can be selectively input into the wavelength division multiplexer or the 1X 2 coupler II, and when the input into the 1X 2 coupler II is selected, temperature detection is carried out; when the input wavelength division multiplexer is selected, the continuous light is filtered by the wavelength division multiplexer and amplified by the erbium-doped optical fiber, and the continuous light suitable for vibration detection is obtained; the filtered light is circularly amplified under the action of the isolator; the amplified continuous light enters a modulator and an amplifier through a coupler to be modulated and amplified, enters a detection optical fiber through a circulator, returned back scattering light respectively enters a wavelength division multiplexer and an interferometer according to different detection modes, data acquisition is carried out by an acquisition card after photoelectric conversion, and finally data processing is carried out in an upper computer. The invention adopts a time division multiplexing method, has high measurement speed on double parameters and can realize real-time detection.

Description

A time-division multiplexing optical fiber sensing system for temperature and vibration measurement

technical field

The invention relates to the field of sensing technology, in particular to a time-division multiplexing optical fiber sensing system for temperature and vibration measurement.

Background technique

As a distributed optical fiber vibration sensor, phase-sensitive optical time domain reflectometer (Phase-sensitive Optical Time Domain Reflectometer, Φ-OTDR) has the advantages of long monitoring distance, high positioning accuracy and simultaneous monitoring of multi-point vibration. It is a major facility safety early warning Research hotspots and development trends in the monitoring field. The principle is to detect the influence of the vibration signal on the optical phase and intensity by collecting and processing the backscattering curve, and realize the positioning and restoration of the vibration signal.

Raman Optical Time-Domain Reflectometry (ROTDR) is based on the wide operating temperature range of optical fibers and can be used for distributed high and low temperature detection. The principle is that the incident pulsed light generates backward Raman scattered light, and its light intensity changes with the temperature of the fiber. The detected backward Raman scattered light is demodulated, and the photodetector completes the photoelectric conversion. The signal is amplified by the signal amplification circuit, collected by the data acquisition card and transmitted to the computer, and the temperature along the optical fiber can be obtained through data processing. In engineering, it is applied to scenarios such as gangue hill fire warning, cable temperature detection, belt conveyor fire warning, and tunnel fire warning.

However, the requirements of the two systems on light sources and optical fibers limit the multiplexing of the two systems. Due to the low intensity of Raman light, ROTDR is suitable for a wide-spectrum light source that can provide higher power, and multi-mode fiber is often used to enhance the intensity of scattered light; the intensity of Rayleigh scattered light in the Φ-OTDR system is relatively higher. A narrow linewidth light source is used, and in order to reduce the number of oscillation modes, a single-mode fiber is generally used. It is difficult for existing multiplexing schemes to meet the requirements of two systems at the same time, and the multiplexing effect is not good.

Among the existing multiplexing technologies of two systems, CN201810775655, a leaky bag location detection device and method for a distributed optical fiber bag filter, uses multi-core optical fiber measurement to achieve single optical cable detection, and does not really integrate These two methods are used in combination with the same light source and optical fiber;

An optical fiber sensing device integrating temperature, strain and vibration CN20211105755 uses a parallel narrow-band filter-cascade amplification method to drive the system to achieve temperature and vibration integrated sensing and measurement, but this method uses three light sources, And the structure is complex, which increases the cost.

CN201810584400 is an optical fiber sensing device integrating temperature, strain and vibration. In the existing dual-parameter detection scheme, a single light source and a single optical fiber can be used to simultaneously perform distributed acoustic and temperature detection systems, which only use Φ-OTDR. In each long period, the wavelength of the pulsed light is changed stepwise at intervals, and the temperature signal is obtained by analyzing the reflected signals with different wavelengths in a long period. Although this method is simple to set up the optical channel, but the measurement speed is slow.

Contents of the invention

A time-division multiplexing temperature and vibration measurement optical fiber sensing system proposed by the present invention can solve at least one of the above technical problems, and is used for long-distance distributed temperature and vibration dual-parameter detection of large structures such as oil and gas pipelines and cables.

To achieve the above object, the present invention adopts the following technical solutions:

A time-division multiplexing optical fiber sensor system for temperature and vibration measurement, including a light source that emits continuous light into an optical switch, the optical switch is controlled by a host computer, and can choose to input a wavelength division multiplexer or a 1*2 coupler. When the wavelength division multiplexer is used, the continuous light is filtered by the wavelength division multiplexer and amplified by the erbium-doped fiber, and the wavelength of the emitted light is continuous light suitable for vibration detection; Circular amplification is performed in a closed loop composed of multiplexer, erbium-doped fiber, and optical isolator; the amplified continuous light enters 1*2 coupler 1 through 1*2 coupler 1, and then enters the modulator for continuous light The modulated light enters the optical amplifier for amplification. The light at this time is the processed detection light. The detection light enters the detection fiber through the circulator, and the backscattered light enters the wavelength division multiplexer through the circulator for filtering, and will carry the vibration signal The light is separated and then enters the interferometer. The two signals from the interferometer are photoelectrically converted by photodiode 1 and photodiode 2 respectively. The electrical signal is collected by the acquisition card and finally processed in the host computer.

Further, it also includes that when the optical switch selects to directly input the 1*2 coupler 2, the continuous light enters the modulator from the 1*2 coupler 2 for continuous light modulation, enters the optical amplifier for amplification, and the light at this time is processed The detection light enters the detection fiber through the circulator, and the backscattered light enters the wavelength division multiplexer through the circulator for filtering, and the two Raman lights are separated, and the separated Raman light passes through the avalanche photodiode It performs photoelectric conversion with the avalanche photodiode, the electrical signal is collected by the acquisition card, and finally the data is processed in the host computer.

It can be known from the above technical solution that the present invention discloses a time-division multiplexed temperature and vibration measurement optical fiber sensor system, which includes a light source that emits continuous light and enters an optical switch. 1*2 coupler 2, when the input 1*2 coupler 2 is selected, temperature detection is performed; when the input wavelength division multiplexer is selected, the continuous light is filtered by the wavelength division multiplexer and amplified by the erbium-doped fiber, and comes out The continuous light suitable for vibration detection; the filtered light will be cyclically amplified under the action of the isolator; the amplified continuous light enters the modulator and amplifier through the coupler for modulation and amplification, and enters the detection fiber through the circulator According to different detection modes, the returned backscattered light enters the wavelength division multiplexer and the interferometer respectively. After photoelectric conversion, the data is collected by the acquisition card, and finally the data is processed in the host computer. The invention adopts the method of time-division multiplexing, has fast measurement speed of double parameters, and can realize real-time detection.

In general, the time-division multiplexed temperature and vibration measurement optical fiber sensor system of the present invention, the vibration and temperature detection of the present invention respectively use the light of the wavelength band that is more sensitive to the changes of these two parameters, and the detection accuracy is high. The optical path structure of the present invention is relatively simple, uses a single light source and single-mode optical fiber, and has low cost. The invention adopts the method of time-division multiplexing, has fast measurement speed of double parameters, and can realize real-time detection.

Description of drawings

Fig. 1 is the overall structural representation of the embodiment of the present invention;

Fig. 2 is the schematic diagram of the vibration detection module of the embodiment of the present invention

Fig. 3 is the schematic diagram of the temperature detection module of the embodiment of the present invention

1. Light source 2, optical switch 3, wavelength division multiplexer (WDM) 4, erbium-doped fiber 5, optical isolator 6, 1*2 coupler one 7, 1*2 coupler two 8, modulator 9, optical Amplifier 10, circulator 11, measuring fiber 12, wavelength division multiplexer (WDM) 13, avalanche photodiode 1 (APD) 14, avalanche photodiode 2 (APD) 15, interferometer 16, photodiode 1 (PD) 17 , photodiode two (PD) 18, acquisition card 19, upper computer.

Detailed ways

In order to make the purpose, technical solutions and advantages of the embodiments of the present invention clearer, the technical solutions in the embodiments of the present invention will be clearly and completely described below in conjunction with the drawings in the embodiments of the present invention. Obviously, the described embodiments It is a part of embodiments of the present invention, but not all embodiments.

As shown in Figure 1, the time-division multiplexing temperature and vibration measurement optical fiber sensing system described in this embodiment is specifically a system in which Φ-OTDR and ROTDR are combined to perform dual-parameter detection. For temperature detection) and semiconductor laser wavelength conversion (for vibration detection) combined to achieve distributed temperature and vibration measurement using only a single light source and single-mode fiber. The overall structure is shown in Figure 1.

The light source 1 emits continuous light and enters the optical switch 2. The optical switch 2 is controlled by the host computer 19, and the input wavelength division multiplexer (WDM) 3 or 1*2 coupler 7 can be selected. When the input wavelength division multiplexer (WDM) At 3 o'clock, the continuous light is filtered by the wavelength division multiplexer (WDM) 3 and amplified by the erbium-doped optical fiber 4, and the emitted light wavelength is continuous light suitable for vibration detection. The filtered light will be cyclically amplified in a closed-loop circuit composed of a wavelength division multiplexer (WDM) 3, an erbium-doped fiber 4, and an optical isolator 5 under the action of a 5-isolator. The amplified continuous light enters the 1*2 coupler 27 through the 1*2 coupler-6, then enters the modulator 8 to modulate the continuous light, and enters the optical amplifier 9 to amplify. The light at this time is processed Detect light. The detection light enters the detection optical fiber through the circulator 10, and the backscattered light enters the wavelength division multiplexer (WDM) 12 through the circulator 10 for filtering, and the light carrying the vibration signal is separated, and then enters the interferometer 15, and the interferometer 15 The output two signals are photoelectrically converted by photodiode (PD) one 16 and photodiode (PD) two 17 respectively, and the electrical signal is collected by the acquisition card 18, and finally processed in the upper computer 19.

When the optical switch 2 chooses to directly input the 1*2 coupler 7, the continuous light enters the modulator 8 from the 1*2 coupler 7 to modulate the continuous light, and enters the optical amplifier 9 for amplification, and the light at this time is processed detection light. The detection light enters the detection fiber through the circulator 10, and the backscattered light enters the wavelength division multiplexer (WDM) 12 through the circulator 10 for filtering, and the two Raman lights are separated, and the separated Raman light is passed through the avalanche photoelectric The first diode (APD) 13 and the second avalanche photodiode (APD) 14 perform photoelectric conversion, the electrical signal is collected by the acquisition card 18, and finally the data is processed in the upper computer 19.

In the temperature measurement system, the wavelength used is lower than the general cut-off wavelength of single-mode fiber 1260nm. At this time, there are multiple oscillation modes in the fiber, and the intensity of scattered light will also increase. This method takes advantage of the operating characteristics of single-mode fiber and meets the requirements of both measurement systems.

The continuous light emitted by the light source is controlled by an optical switch and can enter two systems respectively. If the optical switch controls and enters the wavelength division multiplexer (WDM) 3, the system can realize the function of Φ-OTDR, which is called mode 1, as shown in the figure 2. If the optical switch control directly enters the 1*2 coupler 72, the system can realize the function of ROTDR, which is called mode 2, as shown in Figure 3.

Working process of the present invention is specifically as follows:

The light source emits continuous laser light, which enters the optical switch. The optical switch is connected with the host computer, and the selection of the optical switch is controlled by the host computer. Since the temperature change is a slow process compared with the disturbance change, in terms of duration, Φ-OTDR takes longer than ROTDR, and the wavelength of mode 1 can be 10ms, and the wavelength of mode 2 can be 1ms.

The specific instructions are as follows:

Mode one:

1. The continuous light emitted by the light source passes through the 1*2 optical switch. When the optical switch is connected to the channel leading to 3, it enters the filtering and amplifying part. Through the wave selection of the wavelength division multiplexer, the amplification of the erbium-doped fiber and the resonant cavity, the continuous light with a wavelength suitable for detection by the Φ-OTDR system is obtained. , output to the optical modulator through the coupler 6.

2. The continuous light is modulated into a rectangular pulse by the optical modulator, amplified by the optical amplifier, and enters the measuring fiber through the circulator.

3. The backscattered light enters the wavelength division multiplexer through the circulator to separate the Rayleigh scattered light. The Rayleigh scattered light generates two interference signals through the interferometer, and the interference signals enter the acquisition card through the photoelectric conversion of the PD.

4. For the processing method of this part of data, firstly, the data of each pulse cycle is separated through array reconstruction, and the disturbance point is located by difference. After the disturbance point position is determined, the data of this point can be extracted and processed by demodulation algorithm. Get the phase signal at the disturbance.

Mode two:

1. When the optical switch 2 is connected to the 1*2 coupler 27, the continuous light is modulated into a rectangular pulse by the optical modulator, amplified by the optical amplifier, and enters the measuring fiber through the circulator.

2. The backscattered light of the optical fiber enters the wavelength division multiplexer through the circulator, separates the Stokes light (Stokes) and the anti-Stokes light (Anti-Stokes), and performs photoelectric conversion through two APDs. The signal goes to the capture card.

3. Among Raman scattered light, anti-Stokes light is sensitive to temperature changes, while Stokes light has little relationship with temperature. Therefore, the temperature change on the optical fiber link is obtained by using the Strokes/Anti-Strokes ratio method.

The light source of the embodiment of the present invention can be replaced by a laser of any wavelength that can produce Raman spectra; the working wavelength of the wavelength division multiplexer of the resonator can use any other available light that can detect Rayleigh scattered light; the semiconductor laser changes The wavelength method can use the method of changing the operating temperature or input current of the semiconductor laser to achieve the same purpose; the interferometer can use a balanced interferometer (such as Sagnac interferometer) or an unbalanced interferometer (MZ interferometer); in the Φ-OTDR system , you can use heterodyne detection or coherent detection, or directly detect a single signal without using an interferometer; in the ROTDR system, because anti-Stokes light is sensitive to temperature changes, and Stokes light is sensitive to temperature Insensitive, so it is possible to collect only anti-Stokes light and use single-channel signal detection.

To sum up, the time-division multiplexing optical fiber sensing system for temperature and vibration measurement of the present invention, the vibration and temperature detection of the present invention use light in the wavelength bands that are more sensitive to the changes of these two parameters, and the detection accuracy is high. The optical path structure of the present invention is relatively simple, uses a single light source and single-mode optical fiber, and has low cost. The invention adopts the method of time-division multiplexing, has fast measurement speed of double parameters, and can realize real-time detection.

The above embodiments are only used to illustrate the technical solutions of the present invention, rather than to limit them; although the present invention has been described in detail with reference to the foregoing embodiments, those of ordinary skill in the art should understand that: it can still be described in the foregoing embodiments Modifications are made to the recorded technical solutions, or equivalent replacements are made to some of the technical features; and these modifications or replacements do not make the essence of the corresponding technical solutions deviate from the spirit and scope of the technical solutions of the embodiments of the present invention.

Claims (4)

1. A time-division multiplexed temperature, vibration measurement optical fiber sensor system, comprising a light source (1) that sends continuous light into an optical switch (2), is characterized in that, The optical switch (2) is controlled by the host computer (19), and the input wavelength division multiplexer (3) or 1*2 coupler two (7) can be selected. When the input wavelength division multiplexer (3) is selected, the continuous optical After being filtered by the wavelength division multiplexer (3) and amplified by the erbium-doped fiber (4), the light wavelength that comes out is continuous light suitable for vibration detection; Circular amplification is performed in the closed-loop circuit composed of the multiplexer (3), the erbium-doped optical fiber (4), and the optical isolator (5); the amplified continuous light enters the 1*2 coupler (6) through the 1*2 Coupler two (7), then enter the modulator (8) for continuous light modulation, enter the optical amplifier (9) for amplification, the light at this time is the detection light that has been processed, and the detection light passes through the circulator (10) Entering the detection optical fiber, the backscattered light enters the wavelength division multiplexer (12) through the circulator (10) for filtering, and the light carrying the vibration signal is separated, and then enters the interferometer (15), and the interferometer (15) comes out two The signals of the two channels are photoelectrically converted by photodiode 1 (16) and photodiode 2 (17), and the electrical signals are collected by the acquisition card (18), and finally processed in the host computer (19). 2. The temperature of time division multiplexing according to claim 1, optical fiber sensing system for vibration measurement, is characterized in that: also comprise when optical switch (2) selects direct input 1*2 coupler two (7), at this moment The wavelength of the light is used for temperature detection. The continuous light enters the modulator (8) from the 1*2 coupler (7) to modulate the continuous light, and then enters the optical amplifier (9) for amplification. The light at this time is the processed detection light The detection light enters the detection optical fiber through the circulator (10), and the backscattered light enters the wavelength division multiplexer (12) through the circulator (10) for filtering, and the two-way Raman light is separated, and the separated Raman The light is photoelectrically converted by the avalanche photodiode 1 (13) and the avalanche photodiode (14), the electrical signal is collected by the acquisition card (18), and finally the data is processed in the host computer (19). 3. the temperature of time-division multiplexing according to claim 2, vibration measurement optical fiber sensor system, it is characterized in that: used wavelength is lower than the general cut-off wavelength 1260nm of single-mode fiber, at this moment there is a plurality of oscillation modes in the fiber, scattering The intensity of the light will also increase. 4. The time-division multiplexing temperature and vibration measurement optical fiber sensor system according to claim 2, characterized in that: the interferometer (15) uses a balanced interferometer.

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