Background
At the present stage, development of a reliable, safe and efficient smart grid has risen to the national energy strategy. In the process, the sensor is the first link for realizing automatic detection and automatic control and is the core basic equipment of the intelligent power grid. The temperature is an important operating parameter of the power equipment, and obtaining the operating condition of the power equipment by monitoring the temperature information of the power equipment is a research hotspot of power system fault prediction and diagnosis. The traditional electric sensor is very easy to be interfered by external environment, and the optical fiber temperature sensor can meet the requirement of realizing passive and long-distance monitoring under the strong electromagnetic interference environment. Therefore, the optical fiber temperature sensor is developed rapidly, and various optical fiber temperature measurement schemes are researched and developed at home and abroad and are put into field application.
The mature optical temperature sensors in the market at present mainly comprise a fluorescent type, a fiber grating type, a 2Raman/Brillouin scattering type, a distributed type and the like, but have the problems of narrow temperature measurement range (about 100 ℃), short transmission distance (generally less than 20m), complex demodulation principle, high price and the like. The most applied of them are distributed optical fiber temperature sensors and fiber grating temperature sensors.
Since the first successful development of a silica glass optical fiber with a transmission loss of 20dB in the us in 1970, the optical fiber technology has been successfully applied to the fields of optical fiber sensors and the like, and many applications have been made abroad in the development of optical fiber temperature sensors, and various optical fiber temperature sensors have been developed by many universities and research units in China. Fiber optic sensors that have been or are being developed fall into two categories: one is that the optical fiber has a certain sensitive function to make the optical fiber function of temperature measurement; another type is that the optical fiber only functions to transmit light waves.
The optical fiber temperature sensor is used as a novel temperature sensor, breaks through the traditional electric sensing, has the advantages of high measurement precision, electromagnetic interference resistance, safety, explosion resistance, insulation, fire resistance and the like, and is widely applied to many special occasions. Therefore, research and development on optical fiber temperature sensors have been one of the hot spots and difficulties in the optical fiber sensing field, especially in power systems, power generation, power transmission and power distribution systems are usually accompanied by severe electromagnetic and temperature environments, so that optical fiber sensors made of insulating materials play an important role in parameter measurement and monitoring of power systems, and a series of requirements of passive and remote control can be met. Many research institutions at home and abroad are dedicated to developing practical optical fiber sensors for power application, and some of the optical fiber sensors are successfully tried out. The LUXTRON company has successfully developed an optical fiber temperature sensor for monitoring hot spots of large transformer windings, the measurement accuracy of the system is +/-2 ℃ within minus 30-200 ℃, and the temperature detection and temperature field measurement of the transformer in the processes of research and development, service life estimation and dynamic load management are realized by using the sensor.
Disclosure of Invention
The utility model provides a multi-channel polarization interference type optical fiber temperature sensing device, which realizes temperature monitoring of a plurality of optical paths, has a simpler structure and reduces the cost.
In order to achieve the above object, an embodiment of the present invention employs a multichannel polarization interference type optical fiber temperature sensing device, which includes a broadband light source, a tunable filter, an optical fiber coupler, a polarizer, a first photoelectric detection module, a second photoelectric detection module, a divider, an a/D conversion module, a computer, and a polarization maintaining coupler group; the output port of the broadband light source is connected with the first port of the tunable filter; the first port of the optical fiber coupler is connected with the second port of the tunable filter; the second port of the optical fiber coupler is connected with the input port of the first photoelectric detection module; the third port of the optical fiber coupler is connected with the input port of the second photoelectric detection module; the fourth port of the optical fiber coupler is connected with the first port of the polarizer; the second port of the polarizer is connected with the polarization-maintaining coupler group through the polarization-maintaining optical fiber; the output port of the first photoelectric detection module and the output port of the second photoelectric detection module are respectively connected with the input port of the divider, the output port of the divider is connected with the input port of the A/D conversion module, and the output port of the A/D conversion module is connected with the input port of the computer.
Preferably, the polarization maintaining coupler groups are N groups, each group of polarization maintaining coupler groups includes a polarization maintaining coupler and a sensing head, a first port of the sensing head is connected with a second port of the polarization maintaining coupler, and a first port of the polarization maintaining coupler in a first polarization maintaining coupler group is connected with a polarization maintaining optical fiber; starting from the second polarization maintaining coupler group, the first port of the polarization maintaining coupler positioned at the rear and the third port of the polarization maintaining coupler positioned at the front are connected in the two adjacent polarization maintaining coupler groups.
Preferably, the sensing head comprises a polarization maintaining optical fiber, a sensing optical fiber, glass and a filtering reflection film, wherein a first port of the polarization maintaining optical fiber is connected with a second port of the polarization maintaining coupler, a second port of the polarization maintaining optical fiber is connected with a first port of the sensing optical fiber, a second port of the sensing optical fiber is connected with a first port of the glass, and a second port of the glass is plated with the filtering reflection film.
Preferably, the stress principal axis of the second port of the polarization maintaining optical fiber and the stress principal axis of the first port of the sensing optical fiber are welded at an angle of 45 degrees.
Preferably, the polarization maintaining coupler adopts a splitting ratio of 10: 90.
Preferably, the first and second photodetecting modules have the same structure, and the first photodetecting module employs a PIN photodiode.
Preferably, the conversion chip in the a/D conversion module is a model ADC0832CCN chip manufactured by texas instruments, usa.
Compared with the prior art, the embodiment of the utility model has the following beneficial effects: the sensor device uses an interference light path channel, realizes temperature monitoring of a plurality of light paths, has simpler structure and lower cost, and is not easy to be interfered by external electromagnetic waves. In the traditional multi-channel optical fiber temperature sensor, one polarizer and one sensing head can only monitor one optical path, and a plurality of groups of multi-channels and devices are needed. The existing device is inefficient and expensive. If the light path is increased, it is not suitable for practical use. The temperature monitoring device comprises a broadband light source, a tunable filter, an optical fiber coupler, a polarizer, a first photoelectric detection module, a second photoelectric detection module, a divider, an A/D conversion module, a computer and a polarization-maintaining coupler group. The utility model only uses one light source and one polarizer, and adopts a plurality of polarization-maintaining couplers to branch the light path, thereby not only realizing the temperature monitoring of a plurality of light paths, but also having simple structure, reducing the use of devices to the maximum extent, having lower cost and being more efficient.
Detailed Description
The utility model will be further explained with reference to the drawings.
As shown in fig. 1, a multichannel polarization interference type optical fiber temperature sensing device according to an embodiment of the present invention includes a broadband light source 1, a tunable filter 2, an optical fiber coupler 3, a polarizer 4, a first photoelectric detection module 5, a second photoelectric detection module 6, a divider 7, an a/D conversion module 8, a computer 9, and a polarization maintaining coupler group. An output port of the broadband light source 1 is connected with a first port 2a of the tunable filter 2, a first port 3a of the optical fiber coupler 3 is connected with a second port 2b of the tunable filter 2, a second port 3b of the optical fiber coupler 3 is connected with an input port of the first photoelectric detection module 5, a third port 3c of the optical fiber coupler 3 is connected with an input port of the second photoelectric detection module 6, a fourth port 3d of the optical fiber coupler 3 is connected with a first port 4a of the polarizer 4, and a second port 4b of the polarizer 4 is connected with the polarization maintaining coupler group through the polarization maintaining optical fiber 13. The output port of the first photoelectric detection module 5 and the output port of the second photoelectric detection module 6 are respectively connected with the input port of the divider 7, the output port of the divider 7 is connected with the input port of the A/D conversion module 8, and the output port of the A/D conversion module 8 is connected with the input port of the computer 9. The signal data output by the a/D conversion module 8 is transmitted to the computer 9 and recorded in the computer 9.
As a preferred example, the polarization maintaining coupler groups are N groups, each group of polarization maintaining coupler groups includes a polarization maintaining coupler 10 and a sensing head 11, a first port 11a of the sensing head 11 is connected with a second port 10b of the polarization maintaining coupler 10, and a first port 10a of the polarization maintaining coupler 10 in a first polarization maintaining coupler group is connected with a polarization maintaining fiber 13; from the second polarization maintaining coupler group, the first port 10a of the polarization maintaining coupler 10 located at the rear and the third port 10c of the polarization maintaining coupler 10 located at the front are connected to each other in the adjacent two polarization maintaining coupler groups. And N is an integer in the value range of 1-100. The multi-group polarization maintaining coupler group is arranged, one path of light source is divided into multiple paths to reach the sensing head, so that one broadband light source and one interference light path can monitor multiple light paths, the number of devices is greatly reduced, the cost is reduced, and the effect is improved.
Preferably, the sensing head 11 includes a polarization maintaining fiber 13, a sensing fiber 14, a glass 15 and a filtering reflection film 16, wherein a first port of the polarization maintaining fiber 13 is connected with a second port 10b of the polarization maintaining coupler 10, a second port of the polarization maintaining fiber 13 is connected with a first port of the sensing fiber 14, a second port of the sensing fiber 14 is connected with a first port of the glass 15, and a second port of the glass 15 is coated with the filtering reflection film 16. The sensing head 11 with the structure can monitor the temperature of a plurality of channels for light sources with different wavelengths, and realize wavelength division multiplexing.
Preferably, the second port of the polarization maintaining fiber 13 and the first port of the sensing fiber 15 are welded together with a stress principal axis at an angle of 45 °. By using the temperature birefringence effect of the polarization maintaining fiber, two optical paths of a fast axis and a slow axis can be excited, and the optical paths reach the reflecting film and then are reflected back to generate interference at the position.
As a preferred example, the polarization maintaining coupler 10 adopts a splitting ratio of 10: 90. The splitting ratio is determined according to the number of the sensor heads (how many channels are measured for temperature). The polarization maintaining coupler 10 adopts a splitting ratio of 10:90, and can realize temperature monitoring of 10 groups of channels.
As a preferred example, the first and second photodetecting modules 5 and 6 have the same structure, and the first photodetecting module 5 employs a PIN photodiode. As shown in fig. 3, the PIN photodiode operation mode selects the photovoltaic mode: the high-voltage linear low-noise amplifier has zero bias, no 'dark current', linearity and low noise, a first-stage reverse amplification uses LF356, a PIN photodiode long PIN (+) is connected with GND, a short PIN (-) is connected with a reverse input end of the LF356, the reverse input end is connected with an output end of the LF356 through a 180K omega resistor, a non-inverting input end of the LF356 is connected with GDN through a 180K omega resistor, a second-stage voltage is followed by OP27, the output end of the LF356 is connected with a non-inverting input end of OP27, and the reverse input end of OP27 is connected with an output end of OP 27.
Preferably, the conversion chip in the a/D conversion module is ADC0832CCN manufactured by texas instruments, usa.
The components in the above embodiments are all existing components. The optical fiber sensing is adopted, the loss is extremely low, and the interference of external electromagnetic waves is not easy to happen, so that the temperature can be accurately monitored. The polarization maintaining coupler is adopted for light splitting, and a broadband light source and an interference light path are used for monitoring a plurality of light paths. The device of this embodiment adopts polarization maintaining fiber as the sensor, based on polarization interference technique, realizes the monitoring to multichannel temperature, but each field such as the monitoring of wide application power equipment temperature, industrial temperature measurement.
In the above embodiment, after entering the optical fiber coupler 3 through the tunable filter 2, the light emitted from the broadband light source 1 is divided into two equal parts, wherein one part of the light passes through the polarizer 4 and becomes linearly polarized light, and enters the polarization maintaining optical fiber, the polarization main axis of the polarization maintaining optical fiber is in the same direction as the light transmission axis of the polarizer, and the polarized light is transmitted along the polarization main axis. The polarization maintaining fiber is used for polarized light transmission and can realize remote measurement, the other end of the polarization maintaining fiber is connected with the first polarization maintaining coupler 10, light splitting is carried out on the light in a ratio of 10:90, one branch is welded with the sensing head 11, the other branch enters the next polarization maintaining coupler 10 to be split again, and the rest is repeated, so that the temperature monitoring of multiple paths is realized. The concrete structure of the connecting point makes the stress principal axis (slow axis) of one port polarization-maintaining fiber 13 of the polarization-maintaining coupler 10 and the sensing fiber 14 form an angle of 45 degrees. The sensing head is a small section of polarization maintaining optical fiber, the length of the polarization maintaining optical fiber is only a few millimeters, and the other end of the sensing optical fiber is connected with glass plated with a filtering reflection film. Thus, when light transmitted along the main axis of the polarization-maintaining optical fiber enters the sensing head, two polarization modes are excited in the sensing head, and light waves with specific wavelengths are totally reflected at the other end of the sensing head, so that the temperature sensitive to the optical fiber can be determined by measuring the intensity of output interference light, and the measurement range and sensitivity can be adjusted by changing the length of the polarization-maintaining optical fiber and the wavelength of the light.
Specifically, in the temperature monitoring device according to the above embodiment, the broadband light source 1 emits the optical signal, the first optical path enters the optical fiber coupler 3 through the first port 3a of the optical fiber coupler 3, and the first optical path is divided into three parts, namely, a first optical sub-path, a second optical sub-path, and a third optical sub-path. The first sub-optical path is led out through a second port 3b of the optical fiber coupler 3 and then led into the first photoelectric detection module 5, and the change of the power of the light source is monitored in real time; then comes out of the first photo-detection module 5 into a divider 7 and then into a digital-to-analog converter 8, and after the conversion is completed, enters a PC to process the signal 9.
The second sub-optical path is output through a third port 3c of the optical fiber coupler 3, enters a second photoelectric detection module 6, converts an electric signal into an optical signal, amplifies the signal, monitors the power of a light source in real time, converts the optical signal into an analog electric signal through a PIN photodiode, amplifies the analog electric signal, enters a divider 7, converts the analog electric signal into a digital signal through an A/D conversion module 8, and transmits the digital signal into a raspberry pie; and then enters the computer 9 to process the signals.
The third sub-optical path is led out through the fourth port 3d of the optical fiber coupler 3, then enters the polarizer 4 from the first port 4a of the polarizer 4, then the second port output by the polarizer 4 is welded with the polarization maintaining optical fiber, the polarization maintaining optical fiber is then connected with the first port 10a of the polarization maintaining coupler 10, then enters the polarization maintaining coupler 10 for 10:90 light splitting, the third sub-optical path is divided into two sub-optical paths again, the first sub-optical path is connected with the sensing head 11 for temperature monitoring, the second sub-optical path is connected with the polarization maintaining coupler 10 of the next polarization maintaining coupler group for light splitting again, and the similar connection mode is analogized in the following.
The sensing head 11 is a section of polarization maintaining fiber, the transmission polarization maintaining fiber is welded with the stress main shaft of the sensing fiber 14 at an included angle of 45 degrees, and the other port of the sensing fiber 14 is connected with the glass 15 plated with the filtering reflection film 16, so that the reflection of the incident light with the specific wavelength is realized. Based on the temperature birefringence effect of the polarization maintaining fiber, the light excites two polarization eigenmodes in the sensing head, and the temperature of the fiber sensing head is determined by measuring the intensity change of the interference light. The change of the optical signal enters the photoelectric detection module, and the optical signal is converted into an electric signal to carry out signal processing, so that the temperature monitoring function of a plurality of optical paths is realized.
The first photoelectric detection module 5 receives optical signals by using a PIN type photodiode, the utility model belongs to precision application, and the photodiode selects a working mode as a photovoltaic mode: zero bias, no "dark current", linearity, low noise. The PIN photodiode outputs weak analog electrical signals, and analog voltage signals with proper size are output through primary reverse amplification.
The A/D conversion module uses a GPIO pin of a raspberry pi to simulate a corresponding clock signal to drive the A/D conversion chip. The clock signal required to be simulated is in microsecond level, so that the driver is written by using C language, and the control of the GPIO pin can be realized by loading the WiringPi library. The conversion chip in the A/D conversion module is an ADC0832CCN chip manufactured by Texas instruments and Inc. in America.
The utility model realizes the monitoring of the temperature of multiple channels by effectively connecting the existing components, greatly reduces the cost and improves the effect.
Although the preferred embodiments of the present invention have been described in detail, the present invention is not limited to the details of the embodiments, and various equivalent modifications can be made within the technical spirit of the present invention, and the scope of the present invention is also within the scope of the present invention.