CN201837485U - Fiber bragg grating detection system for temperature and depth of seawater - Google Patents

Abstract

A fiber grating seawater temperature depth detection system, including a data processing device connected by a transmission optical cable and an underwater optical fiber sensor chain; the data processing device includes an optical fiber coupler connected to a light source, and a wavelength detection module connected to the optical fiber coupler, And the wavelength detection module is connected with the data processing module; the optical fiber sensor chain is composed of two or more temperature and depth sensing probes with the same structure connected in series through transmission optical cables and optical fiber connectors. The fiber optic sensor chain usually includes 4 to 8 temperature and depth sensing probes with a distance of 2 to 10 meters. The utility model is simple in structure, safe and reliable, easy to use, easy to expand the measurement depth and the number of layers, the detection signal is an optical signal, avoiding the technical problems of watertightness and pressure resistance of traditional electrical signal detection equipment, the measurement signal is stable, and the effect is obvious. The temperature and depth sensing probe is small in size and light in weight, and is connected through a connector, which is convenient for transportation, installation, commissioning, and maintenance.

Description

Fiber Bragg Grating Seawater Temperature Depth Detection System

technical field

The utility model relates to the fields of fiber grating sensing and marine environment monitoring, in particular to a fiber grating seawater temperature and depth detection system.

Background technique

Traditional seawater temperature and depth detection, especially profile detection systems, are mainly based on ship-borne CTD profile measurement, disposable CTD and combined temperature and salt sensor chain measurement methods. The ship-borne launch method requires the survey ship to drive to the designated location, and the CTD sensor is hoisted into the water by a marine winch at a constant speed to complete the profile measurement. This method requires a survey ship, which requires a high cost, limited data volume, and the sensor is watertight. Disposable The cost of CTD is high and the risk is relatively high; the combined temperature and salt sensor chain uses CTD sensors to be set at intervals along the main cable and a data recorder is arranged at the bottom to realize the detection of different depth profiles and the recording of detection data. In this way, the main cable and the suspended multiple The group CTD is connected through a branch watertight cable interface formed by a special mold, the cost is high, and the sensor detection signals are all electrical signals, which makes it difficult for underwater pressure resistance and watertight treatment. More importantly, due to the harsh working environment of marine measurement equipment, the damage rate of underwater optical fiber sensor chains is high. The cost of traditional CTD detection equipment is almost all on CTD sensors. To increase the number of underwater measurement layers, CTD sensors must be added. Quantity, system cost will increase multiple times, the price of each CTD sensor is around tens of thousands, if it is damaged, the loss will be heavy.

Fiber Bragg Grating is a kind of fiber passive device formed by the permanent periodic perturbation of the refractive index of the fiber core, which can partially or completely reflect the light of a specific wavelength in the incident light. The central wavelength of reflected light has a linear relationship with the physical quantities of strain, temperature, and pressure. According to these characteristics, fiber gratings can be made into various sensors for strain, temperature, pressure, and acceleration. Due to the advantages of small size, no electromagnetic interference, and easy formation of sensor networks, fiber grating sensors have been widely used in many fields such as industry, agriculture, and military affairs.

Contents of the invention

The purpose of the utility model is to propose a fiber grating seawater temperature and depth detection system to make up for the shortcomings of the existing ship-borne CTD profile measurement, discarding measurement and combined temperature-salt chain measurement system.

A fiber grating seawater temperature depth detection system is characterized in that the system includes a data processing device on the water surface connected by a transmission optical cable and an optical fiber sensor chain located under water; the data processing device includes an optical fiber coupling connected to a light source device, and a wavelength detection module connected to the optical fiber coupler, and the wavelength detection module is connected to the data processing module; the optical fiber sensor chain is two or more temperature and depth sensing probes with the same structure through transmission optical cables and optical fiber connectors It is formed in series up and down, and a temperature and depth sensing probe at the top is connected to the fiber coupler in the data processing device through a fiber optic connector and a transmission cable.

The above-mentioned temperature and depth sensing probe includes a pressure-guiding cylinder with a pre-pressure adjustment tube connected to the bottom between the upper and lower end covers; the pressure-guiding cylinder is provided with a longitudinal through hole and a side opening leading to the The pressure guide hole of the elastic pressure tube; the lower part of the pre-pressure adjustment tube is provided with an adjustment cover and is located in the inner cavity of the lower end cover of the barrel-shaped structure; A cylinder, an adjustment cover and a lower end cover, and a temperature fiber grating is arranged in the above-mentioned through hole, and a depth fiber grating is arranged between the elastic pressure tube and the adjustment cover.

In order to maintain a good sealing effect when the temperature and depth sensing probe passes through the transmission optical cable, rubber columns for sealing are filled at the positions where the upper end cover, adjustment cover and lower end cover pass through the transmission optical cable.

The above-mentioned elastic pressure tube is a tubular structure with a closed lower end and is fixedly connected to the lower end surface of the pressure guiding cylinder.

The above-mentioned adjusting cover can move up and down in the pre-pressure adjusting tube.

Considering the actual needs of measuring the number of layers and detecting different depth profiles during marine environment monitoring, the above optical fiber sensor chain usually includes 4 to 8 temperature and depth sensing probes, and the distance between each temperature and depth sensing probes is 2 to 10 meters within range.

The temperature fiber grating in the above-mentioned temperature depth sensing probe is an arc-shaped structure with both ends glued and fixed, and the middle is bent without stress.

The temperature fiber Bragg grating and the depth fiber Bragg grating in the above temperature and depth sensing probe are all Bragg fiber gratings.

The transmission optical cable between the above-mentioned optical fiber coupler and the temperature depth sensing probe is an armored optical cable.

The transmission optical cables between the above-mentioned temperature and depth sensing probes are armored optical cables.

The process of using the utility model to detect the depth of seawater temperature is as follows: the broadband light emitted by the light source enters the transmission optical cable through the optical fiber coupler, and is transmitted to a series of temperature and depth sensing probes packaged with optical fiber gratings through the optical fiber cable. Light signals of specific wavelengths are reflected back, and these light signals contain pressure and temperature information of the environment where the sensor is located. The reflected optical signal enters the other channel arm of the fiber coupler through the transmission cable, and then the wavelength change is demodulated by the wavelength detection module, and the pressure and temperature values are calculated by the data processing module containing related software.

It can be seen that all temperature and depth sensing probes share a set of water data processing devices. If you need to increase the number of underwater measurement layers, you only need to add underwater temperature and depth sensing probes. Its cost is very low, and the number of probes needs to be increased. The increase in the system cost is very small, unlike the traditional CTD detection system, the cost is mainly in the CTD sensor. To increase the number of underwater measurement layers, the number of CTD sensors must be increased, and the cost will increase rapidly; the data processing device is the core of the monitoring system. It will not be easily damaged when installed on the water surface, and the cost of the temperature and depth sensing probe is low. Even if it is damaged, the loss is very small, which effectively overcomes the defects of the traditional CTD chain profile detection. The optical fiber sensor chain under the water surface is an all-optical device, and the detection signal is an optical signal, which avoids technical problems such as watertightness and pressure resistance caused by the electrical signal of the traditional detection system; the probe is small in size and light in weight, and the connection method is completed through a connector. It is very convenient to transport, install, debug and maintain.

The utility model is simple in structure, safe and reliable, easy to use, easy to expand the measurement depth and the number of layers, and the measurement signal is stable, and the effect is obvious. The utility model utilizes the advantage that the optical fiber grating sensing probe is an all-optical device, and is easy to form a sensor network for section detection, and realizes the temperature and depth detection of seawater in a vertical section of the ocean. The optical fiber grating sensing probe works safely and reliably underwater, and the detection signal is an optical signal, which avoids technical problems such as watertightness and pressure resistance of traditional electrical signal detection equipment; the utility model adopts the principle of optical fiber grating wavelength division multiplexing, which is easy to expand It is only necessary to increase the number of sensing probes to measure the number of layers; important equipment is on the water, which is convenient for protection and maintenance, and the cost of underwater sensing probes is low, even if it is damaged, the loss is small.

Description of drawings

Fig. 1 is a schematic diagram of the overall structure of the utility model.

Fig. 2 is a structural schematic diagram of the temperature and depth sensing probe of the present invention.

Fig. 3 is a schematic diagram of an exploded structure of the temperature and depth sensing probe of the present invention.

Among them, 1. Data processing device, 2. Optical fiber sensor chain, 3. Wavelength detection module, 4. Data processing module, 5. Light source, 6. Optical fiber coupler, 7. Transmission optical cable, 8. Optical fiber connector, 9, Temperature Depth sensing probe, 10. Upper end cover, 11. Rubber column, 12. Pressure guide cylinder, 13. Temperature fiber grating, 14. Pressure guide hole, 15. Elastic pressure tube, 16. Pre-pressure adjustment tube, 17. Depth Fiber grating, 18. Adjusting cover, 19. Lower end cover, 20. Through hole.

Detailed ways

As shown in Figure 1, the utility model comprises the data processing device 1 that is positioned on the water surface and the optical fiber sensor chain 2 that is positioned at underwater that are connected by transmission optical cable 7; 6, and the wavelength detection module 3 connected with the optical fiber coupler 6, and the wavelength detection module 3 is connected with the data processing module 4; the optical fiber sensor chain 2 is that more than two temperature and depth sensing probes 9 with the same structure pass through The transmission optical cable 7 and the optical fiber connector 8 are connected in series up and down, and a temperature and depth sensing probe 9 at the top is connected to the optical fiber coupler 6 in the data processing device 1 through the optical fiber connector 8 and the transmission optical cable 7 .

As shown in Figures 2 and 3, the above-mentioned temperature depth sensing probe 9 includes a pressure guide column 12 connected with a pre-pressure adjustment tube 16 at the bottom between the upper and lower end covers 10 and 19; the pressure guide column 12 is provided with a longitudinal There is a through hole 20 on the side and a pressure guide hole 14 leading to the elastic pressure tube 15 located in the pre-pressure adjusting tube 16; the lower part of the pre-pressure adjusting tube 16 is provided with an adjusting cover 18 and is located in a barrel-shaped structure. The inner cavity of the lower end cover 19; and the transmission optical cable 7 passes through the upper end cover 10, the pressure guiding cylinder 12, the adjustment cover 18 and the lower end cover 19 from top to bottom in sequence, and a temperature fiber grating 13 is provided in the above-mentioned through hole 20 , A depth fiber grating 17 is provided between the elastic pressure tube 15 and the adjustment cover 18 .

As shown in Figures 2 and 3, in order to maintain a good sealing effect when the temperature and depth sensing probe 9 passes through the transmission cable 7, it is useful to fill the position where the above-mentioned upper end cover 10, adjustment cover 18 and lower end cover 19 pass through the transmission cable 7 For the sealed rubber column 11.

As shown in FIGS. 2 and 3 , the elastic pressure tube 15 is a tubular structure with a closed lower end and can be fixedly connected to the lower end surface of the pressure guiding column 12 by means of welding or the like.

As shown in FIG. 2 , the adjustment cover 18 can move up and down in the pre-pressure adjustment tube 16 .

Considering the actual needs of measuring the number of layers and detecting different depth profiles when monitoring the marine environment, the above-mentioned optical fiber sensor chain 2 usually includes 4 to 8 temperature and depth sensing probes 9, and the distance between the temperature and depth sensing probes 9 is 2 ~10 meters range.

As shown in FIGS. 2 and 3 , the temperature fiber grating 13 inside the temperature and depth sensing probe 9 is an arc-shaped structure with both ends glued and fixed, and the middle is bent without stress.

The temperature fiber Bragg grating 13 and the depth fiber Bragg grating 17 in the above temperature and depth sensing probe 9 are all Bragg fiber gratings.

The transmission optical cable 7 between the fiber optic coupler 6 and the temperature and depth sensing probe 9, and the transmission optical cable between the temperature and depth sensing probe 9 are armored optical cables.

The data processing device 1 on the water surface is the main body of the entire detection system, including the wavelength detection module 3, the data processing module 4, the light source 5 and the optical fiber coupler 6, where most of the cost of the system is concentrated. The optical fiber sensor chain 2 under the water surface is a measurement chain, and each temperature depth sensing probe 9 is small in size, light in weight, and low in cost. Therefore, to increase the number of measurement layers, it is only necessary to increase the number of temperature depth sensing probes 9. The cost increase is small.

Example 1

The structures of the data processing device 1 and the optical fiber sensor chain 2 are shown in FIG. 1 , and the structures of the temperature and depth sensing probe 9 are shown in FIGS. 2 and 3 .

The light source 5 in the data processing device 1 can be an optical fiber broadband light source based on light absorption and re-excitation of an erbium-doped optical fiber. Its spectral width ranges from 1520 to 1580 nm. Inductive system coupling and other advantages.

The wavelength detection module 3 in the data processing device 1 can adopt the WaveCaptureTMFBGA wavelength detection module of BaySpec Company, which has the advantages of ultra-fast response time, no moving parts, low power consumption, wide dynamic range, and low cost.

The transmission optical cable 7 between the optical fiber coupler 6 in the data processing device 1 and the underwater temperature and depth sensing probe 9, and the transmission optical cable 7 between the temperature and depth sensing probe 9 all adopt a diameter of 3.5 mm and a thickness of 0.4 mm. The stainless steel armored optical cable has the characteristics of compression resistance, tensile resistance and corrosion resistance. It can be used in seawater for a long time and can effectively protect the optical fiber inside.

As shown in Figures 2 and 3, the transmission optical cable 7 in the above-mentioned temperature and depth sensing probe 9 has a temperature fiber grating 13 and a depth fiber grating 17, both of which are Bragg fiber gratings, to perform temperature-sensitive detection and pressure-sensitive detection respectively , and then the pressure can be converted into depth; the upper and lower ends of the temperature and depth sensing probe 9 are reserved with connecting optical fibers for easy connection with other sensing probes.

Among them, the two ends of the temperature fiber grating 13 can be fixed in the through hole 20 of the pressure guide cylinder 12 by epoxy glue, and the middle of the temperature fiber grating 13 is kept in a free bending state, that is, it is an arc-shaped structure without force, and is only sensitive to temperature. , its upper end is sealed and fixed in the upper end cover 10 through the rubber column 11, and a section of outgoing optical fiber is left outside the upper end cover 10 to facilitate connection with other temperature and depth sensing probes 9; the side of the pressure guiding cylinder 12 is provided with a pressure guiding hole 14 It leads to the elastic pressure tube 15 welded on the lower end surface of the pressure guide cylinder 12; the upper end of the depth fiber grating 17 can also be fixed on the elastic pressure tube 15 by epoxy glue, and the lower end is fixed on the adjustment cover 18 through the rubber column 11. Adjust the position of the 18 in the pre-pressure adjustment tube 16 (such as adjusting the upper and lower positions by threads), add a pre-tension to the depth fiber grating 17, thereby improving the sensitivity of detection; the lower end of the depth fiber grating 17 passes through the 18 through adjustment The lower end cover 19 is fixed by a rubber column 11, and a section of outgoing optical fiber is left outside to facilitate connection with other temperature and depth sensing probes 9. Since the two ends of the temperature fiber grating 13 are fixed, and the middle is free and unstressed, the variation of the reflected wavelength is only related to the external temperature, so the temperature can be measured by demodulating the variation of the reflected wavelength of the grating; the depth fiber grating 17 It can be fixed at the bottom of the elastic pressure tube 15. It is sensitive to both pressure and temperature, but because it is in the same environment as the temperature fiber Bragg grating 13, the wavelength change caused by temperature is easily removed, and then detected The amount of change in grating reflection wavelength caused by pressure changes, and converted into depth.

The wide-spectrum light emitted by the light source 5 passes through the optical fiber coupler 6 through the optical fiber 7, and then enters the underwater sensor chain 2 composed of the optical fiber connector 8 and the temperature and depth sensing probe 9 in series from top to bottom through the optical fiber 7 (wherein the optical fiber connector 8 can adopt the existing equipment); the reflected optical signal of each fiber grating specific wavelength that contains the depth and temperature information of the surrounding environment of each sensing probe enters another channel of the optical fiber coupler 6 through the transmission optical fiber 7 , and enter the wavelength detection module 3, the wavelength variation of the sensing fiber grating in each temperature depth sensing probe 9 is demodulated by the wavelength detection module 3, and then the optical fiber sensor is calculated and demodulated by the relevant software through the data processing module 4 Surrounding pressure, temperature information, and save and transmit (wherein relevant software can adopt the software commonly used in this field).

The fiber Bragg grating temperature and depth detection system encodes the changes in the Bragg reflection wavelengths caused by the changes in the measured values of the fiber gratings in the temperature and depth sensing probes 9. Generally, the reflection wavelength bandwidth of a single fiber grating is about 0.3nm. Therefore, within the available wavelength range of the broadband light source, assign a unique wavelength range to each sensing grating of the temperature depth sensing probe 9, and utilize the broadband light source to irradiate all the fiber gratings in the fiber sensor chain 2, Make the reflection peaks of each grating change within their respective wavelength intervals, and finally use the wavelength detection module 3 to detect the composite spectrum of all gratings, and find out the wavelength shift value of each grating according to the pre-defined intervals, so as to realize multiple Bura Multiplexing of grid rasters.

Claims (10)

1. A fiber grating seawater temperature depth detection system is characterized in that the system comprises a data processing device (1) on the water surface connected by a transmission cable (7) and an optical fiber sensor chain (2) under water; The data processing device (1) comprises a fiber coupler (6) connected to the light source (5), and a wavelength detection module (3) connected to the fiber coupler (6), and the wavelength detection module (3) is connected to the data The processing module (4) is connected; the optical fiber sensor chain (2) is formed by connecting two or more temperature and depth sensing probes (9) with the same structure through the transmission optical cable (7) and the optical fiber connector (8), and A temperature and depth sensing probe (9) at the top is connected with an optical fiber coupler (6) in the data processing device (1) through an optical fiber connector (8) and a transmission optical cable (7). 2. The temperature and depth detection system according to claim 1, characterized in that the above-mentioned temperature and depth sensing probe (9) includes a pre-pressure adjustment tube (16) connected to the bottom between the upper and lower end covers (10, 19) The pressure guide cylinder (12); the pressure guide cylinder (12) is provided with a longitudinal through hole (20) and a guide leading to the elastic pressure tube (15) in the pre-pressure adjustment tube (16) is opened on the side. pressure hole (14); the lower part of the pre-pressure adjustment tube (16) is provided with an adjustment cover (18) and is located in the inner cavity of the lower end cover (19) of the barrel-shaped structure; and the transmission optical cable (7) from the top And pass through the upper end cover (10), the pressure guiding cylinder (12), the adjustment cover (18) and the lower end cover (19) in turn, and a temperature fiber grating (13) is arranged in the above-mentioned through hole (20). A depth fiber grating (17) is arranged between the elastic pressure tube (15) and the adjustment cover (18). 3. The optical fiber grating seawater temperature depth detection system as claimed in claim 2, is characterized in that above-mentioned upper end cover (10), adjustment cover (18) and lower end cover (19) pass through the position of transmission optical cable (7) and are filled with for Sealed rubber post (11). 4. The temperature and depth detection system according to claim 2, characterized in that the elastic pressure tube (15) is a tubular structure with a closed lower end and is fixedly connected to the lower end surface of the pressure guiding cylinder (12). 5. The temperature and depth detection system according to claim 2, characterized in that the adjustment cover (18) moves up and down in the pre-pressure adjustment tube (16). 6. The temperature and depth detection system according to claim 1, characterized in that the above-mentioned optical fiber sensor chain (2) includes 4 to 8 temperature and depth sensing probes (9), and between each temperature and depth sensing probes (9) The distance is in the range of 2 to 10 meters. 7. The optical fiber grating seawater temperature depth detection system as claimed in claim 2, characterized in that the temperature optical fiber grating (13) in the above-mentioned temperature depth sensing probe (9) is glued and fixed at both ends, bent in the middle and is not stressed arc structure. 8. The temperature and depth detection system according to claim 2, characterized in that the temperature fiber Bragg grating (13) and the depth fiber Bragg grating (17) in the temperature and depth sensing probe (9) are all Bragg fiber gratings. 9. The optical fiber grating seawater temperature depth detection system as claimed in claim 1, characterized in that the transmission optical cable (7) between the above-mentioned optical fiber coupler (6) and the temperature depth sensing probe (9) is an armored optical cable. 10. The optical fiber grating seawater temperature and depth detection system according to claim 1, characterized in that the transmission optical cable (7) between the above-mentioned temperature and depth sensing probes (9) is an armored optical cable.

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