JP2009174987A - Distributed optical fiber temperature sensor - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a distributed optical fiber temperature sensor aiming to making a measuring apparatus main body compact. <P>SOLUTION: The distributed optical fiber temperature sensor includes: a measuring optical fiber 2 disposed along a temperature-measurement place; the measuring apparatus main body 3 which makes light incident to the measuring optical fiber 2, detects backscattered light, and measures a temperature distribution along the measuring optical fiber 2; a reference temperature fiber part 11 formed in the measuring optical fiber 2; and a reference temperature sensor 12 being disposed at the reference temperature fiber part 11 and detecting a temperature of an area close to the reference temperature fiber part 11, and compensates a temperature distribution of the whole of the measuring optical fiber 2, by compensating the temperature of the reference temperature fiber part 11 which is obtained by the measuring apparatus main body 3, by using a detection temperature from the reference temperature sensor 12. In above configuration, the reference temperature fiber part 11 is disposed at the measuring optical fiber 2 which is positioned apart from the measuring apparatus main body 3. <P>COPYRIGHT: (C)2009,JPO&INPIT

Description

  The present invention relates to a distributed optical fiber temperature sensor that detects Raman scattered light generated in an optical fiber and measures temperature.

  There are optical sensors that measure temperature, strain, pressure, and the like using an optical fiber, and in particular, there are distributed optical fiber temperature sensors that use Raman scattered light generated in the optical fiber.

  FIG. 5 is a circuit diagram showing a conventional distributed optical fiber temperature sensor.

  As shown in FIG. 5, a conventional distributed optical fiber temperature sensor 51 is configured by connecting a measurement optical fiber 52 disposed along a temperature measurement location to a measurement apparatus main body 53.

  When a pulsed optical signal is incident on the measurement optical fiber 52 from the light source 54 of the measurement apparatus main body 53, weak Raman scattered light is generated at each location of the measurement optical fiber 52. Raman scattered light is generated in the wavelength band on both sides of the incident light wavelength. The Raman scattered light on the long wavelength side is Stokes light, and the Raman scattered light on the short wavelength side is anti-Stokes light.

  The intensity ratio between Stokes light and anti-Stokes light generated in the measurement optical fiber 52 depends on the temperature of the measurement optical fiber 52. Therefore, the temperature of the measurement optical fiber 52 changes depending on the temperature of the object to be measured, and the intensity ratio between the detected Stokes light and anti-Stokes light changes. By obtaining this light intensity ratio, the temperature of the object to be measured can be measured.

  In the distributed optical fiber temperature sensor 51, the back-scattered Stokes light and anti-Stokes light are demultiplexed by the wavelength filter module 55 and received by the photodetectors 56 and 57, respectively. The received light is converted into an electric signal by the photodetectors 56 and 57, the electric signal is amplified by the amplifier 58, and the amplified electric signal is converted into a digital signal by the AD converter 59 and then sent to the signal processing circuit 60. Entered. A temperature distribution is obtained by the signal processing control circuit 60 from the inputted electric signal.

  When the reception power of anti-Stokes light is Pa and the reception power of Stokes light is Ps, the measured temperature is calculated based on the ratio Pa / Ps. However, these received powers Pa and Ps are obtained after the wavelengths of the Stokes light and the anti-Stokes light fluctuate due to the change in the multiplication factor of the photodetectors 56 and 57 and the wavelength fluctuation of the light source 54 and pass through the wavelength filter module 55. It changes when the light quantity fluctuates. Therefore, the ratio Pa / Ps also changes, and the temperature distribution calculated based on the ratio Pa / Ps also changes.

Therefore, in the distributed optical fiber temperature sensor 51, the reference temperature fiber portion 61 is formed in the measurement optical fiber 52, and the reference temperature sensor 62 is prepared. The ratio Pa / Ps in the reference temperature fiber portion 61 and the reference temperature are prepared. The correlation with the temperature T ₀ detected by the sensor 62 is taken. Thereby, the ratio Pa / Ps at the temperature T ₀ is determined, and the correct temperature can be calculated.

  The prior art document information related to the invention of this application includes the following.

JP 2000-121452 A JP-A-7-12655

  However, in the conventional distributed optical fiber temperature sensor 51, the reference temperature fiber portion 61 is formed by winding a part of the measurement optical fiber 52, but the length of the reference temperature fiber portion 61 is due to Raman backscattered light. Considering the distance responsiveness (distance resolution), it is necessary to make the length more than the distance responsiveness, preferably about 5 times the distance responsiveness (about 30 to 50 m), and the reference temperature fiber part 61 becomes large. End up. Therefore, the measuring device main body 53 that houses the reference temperature fiber portion 61 also becomes large.

  Furthermore, a case for housing the reference temperature fiber portion 61 is required, and the internal structure of the measuring apparatus main body becomes complicated.

  SUMMARY OF THE INVENTION Accordingly, an object of the present invention is to provide a distributed optical fiber temperature sensor that solves the above-described problems and is intended to reduce the size of the measuring device body.

  The present invention was devised to achieve the above-described object, and includes a measurement optical fiber disposed along a temperature measurement location, light incident on the measurement optical fiber, and detection of backscattered light. A measuring device main body for measuring a temperature distribution along the measuring optical fiber, a reference temperature fiber portion formed in the measuring optical fiber, and the reference temperature fiber portion provided in the reference temperature fiber portion. A reference temperature sensor for detecting a temperature in the vicinity of the temperature of the reference optical fiber section obtained by correcting the temperature of the reference temperature fiber portion obtained by the measurement apparatus main body with the detected temperature from the reference temperature sensor, Is a distributed optical fiber temperature sensor for correcting the reference temperature fiber portion, wherein the reference temperature fiber portion is disposed in the measurement optical fiber at a position away from the measurement apparatus main body. Iba is a temperature sensor.

  Further, the present invention is a distributed optical fiber temperature sensor in which the reference temperature fiber portion is disposed in the vicinity of the measurement apparatus main body.

  Alternatively, the present invention is the distributed optical fiber temperature sensor in which the reference temperature fiber portion is installed near the center in the longitudinal direction of the measurement optical fiber.

  Further, according to the present invention, a temperature data transmitter is provided in a reference temperature sensor for detecting an ambient temperature of the reference temperature fiber portion, and the temperature data from the temperature data transmitter is received and input to the measurement apparatus main body. This is a distributed optical fiber temperature sensor provided in the measuring apparatus main body.

  In the present invention, the temperature data transmitter and the reference temperature sensor are driven by a photoelectric converter, and the photoelectric converter is connected to the measuring device main body that supplies light for power generation via a power supply fiber. This is a distributed optical fiber temperature sensor.

  The present invention is a distributed optical fiber temperature sensor in which a plurality of the reference temperature fiber portions are formed in the measurement optical fiber.

  According to the present invention, the measuring device main body can be miniaturized.

  Preferred embodiments of the present invention will be described below with reference to the accompanying drawings.

  The distributed optical fiber temperature sensor according to the present embodiment is used for, for example, power line temperature monitoring, temperature management of gas ducts in factories and buildings, and road temperature measurement for examining road surface freezing.

  FIG. 1 is a schematic view of a distributed optical fiber temperature sensor showing a preferred first embodiment of the present invention, and FIG. 2 is a circuit diagram thereof.

  As shown in FIGS. 1 and 2, the distributed optical fiber temperature sensor 1 according to the first embodiment includes a measurement optical fiber 2 disposed along a temperature measurement location, and the measurement optical fiber 2. A measuring device main body 3 for detecting the backscattered light and measuring the temperature distribution along the measuring optical fiber 2, and a reference temperature unit 4 arranged in the vicinity of the measuring device main body 3. Prepare mainly.

  As the measurement optical fiber 2, a general communication multimode fiber having a core doped with Ge or a single mode fiber may be used.

  The measurement apparatus main body 3 includes a light source 5 that makes light incident on the measurement optical fiber 2, a wavelength filter module 6 that demultiplexes Raman scattered light from backscattered light generated by the measurement optical fiber 2, and the wavelength filter module 6. A light detector 7 that detects the Raman scattered light demultiplexed in step S4 and converts it into an electrical signal and outputs a light reception signal, and a signal processing control circuit 8 that processes the light reception signal from the light detector 7 are mainly used. Prepare.

  The light source 5 is composed of, for example, a semiconductor laser (LD). The light source 5 is connected to an LD driver 5 a that drives the light source 5, and the LD driver 9 is connected to a signal processing control circuit 8 that controls the LD driver 9.

  The photodetector 7 includes a Stokes light receiving photodetector 7a that detects Stokes light (ST light) out of Raman scattered light, and an anti-Stokes light receiving photodetector 7b that detects anti-Stokes light (AS light). Consists of. The Stokes light receiving photodetector 7a and the anti-Stokes light receiving photodetector 7b are made of, for example, an APD (Avalanche Photo Diode).

  The light source 5, the Stokes light receiving photodetector 7 a, and the anti-Stokes light receiving photodetector 7 b are connected to the measurement optical fiber 2 via the wavelength filter module 6.

  The wavelength filter module 6 includes a long-wavelength side band-pass filter that transmits Stokes light among the Raman scattered light of the backscattered light generated in the measurement optical fiber 2, and a short-wavelength side band-pass filter that transmits anti-Stokes light. Prepare.

  The wavelength filter module 6 outputs the light from the light source 5 to the measurement optical fiber 2 and also receives the Stokes light of the backscattered light from the measurement optical fiber 2 that has passed through the long wavelength side bandpass filter. The anti-Stokes light that has been output to the optical detector 7a and passed through the short wavelength band-pass filter is output to the anti-Stokes light receiving photodetector 7b.

  The long wavelength side band pass filter and the short wavelength side band pass filter are configured not to pass light in the wavelength band of the semiconductor laser used for the light source 5 in order to avoid mixing of the Rayleigh scattered light component.

  The Stokes light receiving photodetector 7a is connected to an amplifier 9a that amplifies the received light signal output from the Stokes light receiving photodetector 7a. Connected to the amplifier 9a is an AD (analog / digital) converter 10a for converting the received light signal amplified by the amplifier 9a into a digital signal.

  Similarly, the anti-Stokes light receiving photodetector 7b is connected to an amplifier 9b that amplifies the received light signal output from the anti-Stokes light receiving photodetector 7a. The amplifier 9b is connected to an AD converter 10b that converts the light reception signal amplified by the amplifier 9b into a digital signal.

  Each AD converter 10a, 10b is connected to a signal processing control circuit 8. The signal processing circuit 8 includes a signal processing control unit 8a including a field programmable gate array (FPGA), and a temperature distribution calculation unit 8b including a CPU (central processing unit) connected to the signal processing control unit 8a.

  The signal processing control unit 8a measures the received light signals from the Stokes light receiving light detector 7a and the anti-Stokes light receiving light detector 7b a plurality of times, and averages them. And a control circuit (not shown) for controlling the LD driver 5a to drive the light source 5, and a synchronization circuit (not shown) for synchronizing the averaging circuit and the control circuit.

  The reference temperature unit 4 includes a reference temperature fiber unit 11 formed in the measurement optical fiber 2 and a reference temperature sensor 12 that detects a temperature in the vicinity of the reference temperature fiber unit 11 and is movably disposed. The reference temperature unit 4 is a unit in which the reference temperature fiber unit 11 and the reference temperature sensor 12 are accommodated in a closed space such as a container or a box.

  The reference temperature fiber portion 11 is formed by winding a part of the measurement optical fiber 2 in a loop shape. As the reference temperature sensor 12, a known temperature sensor such as a platinum resistor, a thermistor, or a thermocouple may be used. The reference temperature sensor 12 is installed in the vicinity of the reference temperature fiber unit 11.

  The reference temperature sensor 12 and the temperature distribution calculation unit 8b of the measuring apparatus body 3 are connected by a cable 13. The cable 13 supplies power for operating the reference temperature sensor 12 from the temperature distribution calculation unit 8b side, and propagates temperature data detected by the reference temperature sensor 12 to the temperature distribution calculation unit 8b.

  Next, the operation of the distributed optical fiber temperature sensor 1 will be described.

  First, the light source 5 is driven by the LD driver 5a to emit a pulsed optical signal. The optical signal emitted from the light source 5 passes through the wavelength filter module 6 and propagates through the measurement optical fiber 2. When this optical signal propagates through the measurement optical fiber 2, backscattered light is generated at each location of the measurement optical fiber 2. The generated backscattered light propagates through the measurement optical fiber 2 in the direction opposite to the traveling direction of the optical signal and enters the wavelength filter module 6.

  Stokes light of Raman scattered light out of backscattered light incident on the wavelength filter module 6 passes through the long wavelength band pass filter, is detected by the Stokes light receiving photodetector 7a, and is converted into an electric signal. The received light signal output from the Stokes light receiving photodetector 7a is amplified by the amplifier 9a, converted into a digital signal by the AD converter 10a, and output to the signal processing control unit 8a of the signal processing control circuit 8.

  Similarly, of the backscattered light incident on the wavelength filter module 6, the Raman scattered light anti-Stokes light passes through the short wavelength band-pass filter and is detected by the anti-Stokes light receiving photodetector 7 b and converted into an electrical signal. Is done. The light reception signal output by the anti-Stokes light receiving photodetector 7b is amplified by the amplifier 9b, converted into a digital signal by the AD converter 10b, and output to the signal processing control unit 8a.

  The signal processing control unit 8a measures each of the received light signals a plurality of times, averages them, and outputs an average output of each received light signal to the temperature distribution calculation unit 8b. The signal processing control unit 8a measures the time from when the light signal is emitted from the light source 5 until the Raman scattered light returns, and the distance from the measuring device body 3 corresponding to each received light signal is determined from that time. It is obtained and output to the temperature distribution calculation unit 8b together with the average output of each received light signal.

  The temperature distribution calculation unit 8b that receives the average output of each light reception signal and the distance data corresponding to each light reception signal obtains a temporary temperature distribution based on each average output from the signal processing control unit 8a. That is, assuming that the average output of the light reception signal of anti-Stokes light is Pa and the average output of the light reception signal of Stokes light is Ps, the intensity ratio Pa / Ps is obtained, and the temporary ratio is calculated from the intensity ratio Pa / Ps and the corresponding distance data. Obtain the temperature distribution of.

  Further, the temperature distribution calculation unit 8b obtains the temperature (intensity ratio Pa / Ps) of the reference temperature fiber unit 11 from the Raman scattered light (Stokes light and anti-Stokes light) from the reference temperature fiber unit 11 of the reference temperature unit 4. The temperature of the reference temperature fiber part 11 is correlated with the temperature in the vicinity of the reference temperature fiber part 11 detected by the reference temperature sensor 12. When the above-described provisional temperature distribution is corrected so that the temperature of the reference temperature fiber portion 11 and the temperature detected by the reference temperature sensor 12 coincide with each other, a temperature distribution along the measurement optical fiber 2 is obtained.

  The operation of the first embodiment will be described.

  In the distributed optical fiber temperature sensor 1 according to the first embodiment, the measuring device main body 3 and the reference temperature unit 4 are formed separately, and the measuring optical fiber 2 at a position away from the measuring device main body 3 has a reference temperature. Part 4 is formed.

  Thereby, the reference temperature unit 4 that has been stored in the measurement apparatus main body 3 can be taken out of the measurement apparatus main body 3, and the measurement apparatus main body 3 can be downsized. Therefore, the installation area when the measurement apparatus main body 3 is installed can be reduced.

  In the distributed optical fiber temperature sensor 1, since the reference temperature unit 4 is movably disposed, the reference temperature unit 4 is brought into contact with an object to be measured, and the temperature is measured by the reference temperature sensor 12 and the reference temperature fiber unit 11. The reference temperature unit 4 can be used as a highly accurate spot temperature sensor.

  When the reference temperature unit 4 is used as a spot temperature sensor, the temperature of the reference temperature unit 4 is the same as the temperature of the object to be measured. At this time, since the temperature of the reference temperature sensor 12 is equal to the temperature of the reference temperature fiber unit 11, even when the reference temperature unit 4 is used as a spot temperature sensor, the reference temperature unit 4 is corrected by the temperature distribution calculation unit 8b. It can be used as a reference when performing.

  Further, in the distributed optical fiber temperature sensor 1, since the reference temperature unit 4 is installed in the vicinity of the measuring apparatus body 3, the temperature in the vicinity of the measuring apparatus body 3 can be obtained. The reference temperature unit 4 can be used as a checker whether or not the temperature is within the range.

  Next, a second embodiment will be described.

  As shown in FIG. 3, the distributed optical fiber temperature sensor 31 according to the second embodiment has basically the same configuration as the distributed optical fiber temperature sensor 1 of FIG. 33, and the measuring device main body 32 and the reference temperature unit 33 are connected by a power supply fiber 34.

  The reference temperature unit 33 is installed near the center in the longitudinal direction of the measurement optical fiber 2. The reference temperature unit 33 includes a temperature data transmitter 35 that transmits temperature data detected by the reference temperature sensor 12, and a photoelectric converter (photogenerator) that drives the temperature data transmitter 35 and the reference temperature sensor 12. Is provided.

  The measuring device main body 32 is supplied with light to the receiver 36 that receives the temperature data transmitted from the temperature data transmitter 35 of the reference temperature unit 33 and inputs the temperature data to the measuring device main body 32, and the photoelectric converter of the reference temperature unit 33. A power generation light source is provided. The photoelectric converter of the reference temperature unit 33 and the power generation light source of the measuring device main body 32 are connected by a power supply fiber 34.

  In the distributed optical fiber temperature sensor 31, the temperature data detected by the reference temperature sensor 12 is transmitted from the transmitter 35, and the temperature data transmitted from the transmitter 35 is received by the receiver 36 of the measuring apparatus main body 32. The temperature data received at 36 is input to the temperature distribution calculation unit 8b.

  For example, the reference temperature unit 33 may be arranged at a position several km away from the measuring device main body 32. Therefore, the reference temperature sensor 12 and the temperature distribution calculation unit 8b are simply connected by an electric wire, and the reference temperature sensor 12 is connected. When the temperature data detected in (1) is transmitted using an electric wire, the temperature data signal transmitted from the reference temperature sensor 12 is attenuated by the resistance of the electric wire, and the temperature data may not be received on the measuring device main body 32 side.

  In the distributed optical fiber temperature sensor 31, the temperature data detected by the reference temperature sensor 12 is transmitted by the transmitter 35, and the temperature data is received by the receiver 36 and input to the temperature distribution calculation unit 8b. The temperature data signal from the temperature sensor 12 can be reliably input to the temperature distribution calculation unit 8b without being attenuated.

  The distributed optical fiber temperature sensor 31 supplies light from the light source for power generation provided in the measurement apparatus main body 32 to the photoelectric converter of the reference temperature unit 33 through the power supply fiber 34, and the supplied light is supplied. It converts into electric power with a photoelectric converter, the reference temperature sensor 12 and the transmitter 35 are driven with the electric power, and electric power can be supplied with light.

  Further, in the distributed optical fiber temperature sensor 31, the reference temperature unit 33 is installed near the center in the longitudinal direction of the measurement optical fiber 2. Since the measurement error of the distributed optical fiber temperature sensor 31 increases as the distance from the reference temperature portion 33 increases, the reference temperature portion 33 is disposed near the center of the measurement optical fiber 2 in the longitudinal direction. Measurement errors at the far end and near end can be reduced.

  In the embodiment described above, one reference temperature unit is arranged. However, the present invention is not limited to this, and a plurality of reference temperature units may be arranged. When arranging a plurality of reference temperature sections, it is preferable to arrange the reference temperature sections 42 in series with the measurement optical fiber 2 as shown in FIG. At this time, the interval between the reference temperature units 42 may be an arbitrary interval.

  In addition, when receiving a signal from the reference temperature unit 42 far from the measuring device main body 43 (temperature data detected by the reference temperature sensor 12), the signal may not be received because the wiring is long and the signal is attenuated. In that case, a transmitter is provided in the reference temperature unit 42 and a receiver is provided in the measuring device main body 43, the temperature data detected by the reference temperature sensor 12 is transmitted by the transmitter, and the temperature data is received by the receiver. The temperature distribution calculation unit 8b of the measurement apparatus main body 43 may be input.

  By disposing a plurality of reference temperature units 42, the accuracy is improved with the installed reference temperature unit 42 as the center, so that the temperature distribution can be accurately measured over the entire length of the measurement optical fiber 2.

  In the above embodiment, power for operating the reference temperature sensor (and transmitter) is supplied from the measurement apparatus main body. However, when there is a power source near the reference temperature unit, power may be supplied from there. .

1 is a schematic view of a distributed optical fiber temperature sensor showing a preferred embodiment of the present invention. FIG. 2 is a circuit diagram of the distributed optical fiber temperature sensor of FIG. 1. It is the schematic of the distributed optical fiber temperature sensor which shows 2nd Embodiment. It is the schematic of the distributed optical fiber temperature sensor which shows one modification of this invention. It is a circuit diagram of a conventional distributed optical fiber temperature sensor.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Distribution type optical fiber temperature sensor 2 Optical fiber for measurement 3 Measuring device main body 4 Reference temperature part 11 Reference temperature fiber part 12 Reference temperature sensor

Claims (6)

A measurement optical fiber disposed along a temperature measurement location, and a measurement for measuring the temperature distribution along the measurement optical fiber by making light incident on the measurement optical fiber and detecting backscattered light The measurement apparatus comprises: an apparatus main body; a reference temperature fiber portion formed in the measurement optical fiber; and a reference temperature sensor that detects a temperature in the vicinity of the reference temperature fiber portion provided in the reference temperature fiber portion. A distributed optical fiber temperature sensor that corrects the temperature distribution of the entire measurement optical fiber by correcting the temperature of the reference temperature fiber portion obtained by the main body with the detected temperature from the reference temperature sensor,
The distributed optical fiber temperature sensor, wherein the reference temperature fiber portion is disposed in the measurement optical fiber at a position away from the measurement apparatus main body.   The distributed optical fiber temperature sensor according to claim 1, wherein the reference temperature fiber portion is disposed in the vicinity of the measurement apparatus main body.   The distributed optical fiber temperature sensor according to claim 1, wherein the reference temperature fiber portion is installed in the vicinity of the center in the longitudinal direction of the measurement optical fiber.   A temperature data transmitter is provided in a reference temperature sensor that detects the ambient temperature of the reference temperature fiber portion, and a receiver that receives temperature data from the temperature data transmitter and inputs the temperature data to the measurement device body is the measurement device body. The distributed optical fiber temperature sensor according to any one of claims 1 to 3, wherein the distributed optical fiber temperature sensor is provided.   5. The temperature data transmitter and the reference temperature sensor are driven by a photoelectric converter, and the photoelectric converter is connected to the measurement apparatus main body for supplying light for power generation via a power supply fiber. Distributed optical fiber temperature sensor.   The distributed optical fiber temperature sensor according to claim 1, wherein a plurality of the reference temperature fiber portions are formed in the measurement optical fiber.

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