JP4910867B2 - Optical fiber temperature sensor device - Google Patents

Description

  The present invention relates to an optical fiber temperature sensor device that detects Raman scattered light scattered from an optical fiber and measures temperature, and in particular, information obtained from detected Raman scattered light is used to control the output of a light source and the device itself. The present invention relates to an optical fiber type temperature sensor device used for detecting an abnormality of the optical fiber.

  As shown in FIG. 3, in the conventional optical fiber temperature sensor device 31, a pulse signal is generated by the signal processing control circuit 33 of the sensor body 32, and this pulse signal is converted into a pulsed optical signal (LD) by an LD (semiconductor laser) module 34. The input light is converted into an input wavelength λ 0), and the pulsed light signal is incident on the optical filter unit 36 through the in-device optical fiber 35 a and transmitted through the reference temperature optical fiber 37 through the measurement optical fiber 35 b. Then, backscattered light is generated from each point of the measurement optical fiber 35b.

  The backscattered light includes Rayleigh scattered light having a transmission wavelength λ0, Stokes light (St light) having a wavelength λSt, which is two components of Raman scattered light, and anti-Stokes light (As light) having a wavelength λAs (see FIG. 4). ).

Then, the St filter light and the As light are separated from the backscattered light by the optical filter unit 36, and these lights are respectively received by the light receivers 38 to be converted into electric signals and input to the signal processing control circuit 33.
The signal processing control circuit 33 processes this electrical signal, obtains the intensity ratio of St light and As light, and obtains the temperature of the measurement location from this intensity ratio. The obtained temperature is transmitted as data from the signal processing control circuit 33 to the personal computer 39 and displayed on the personal computer 39.

  In this optical fiber type temperature sensor device 31, a reference temperature optical fiber 37 is accommodated in a fiber storage box 40, and a temperature sensor 41 is provided on the reference temperature optical fiber 37. The temperature sensor 41 is connected to the signal processing control circuit 33.

  Since the intensity ratio between the St light and the As light depends on the temperature, the temperature distribution around the measurement optical fiber 35b can be measured by measuring the intensity ratio with the optical fiber type temperature sensor device 31.

  By the way, for example, since the output of the LD provided in the LD module 34 varies depending on the ambient temperature, it is desirable to keep the power of the LD constant during the measurement.

As a method of making the LD power constant,
(I) When the LD module 34 includes a monitor PD (photodiode) that detects light emitted to the side opposite to the emission direction of the LD, a signal processing control circuit is based on the output of the monitor PD. (Ii) A method of controlling the LD power constant by providing a Peltier element having a temperature adjusting function in the LD module 34 and controlling the LD temperature constant. Yes, it can be applied to the optical fiber temperature sensor 31.

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

Japanese Patent No. 2577199

  However, when the above (i) and (ii) are applied to the conventional optical fiber temperature sensor device 31, a monitor PD is required for the LD module 34 in the case (i), and a Peltier element in the case (ii) Therefore, each method has a problem that the cost of the entire optical fiber temperature sensor device 31 is increased.

  Further, since the LD module 34 includes the monitor PD and the Peltier element, there is a problem that the entire configuration of the optical fiber temperature sensor device 31 becomes complicated.

  Furthermore, since the signal processing control circuit 33 processes the St light and As light signals, the signal from the monitor PD or the Peltier element, the signal processing control circuit 33 also has a problem that the configuration is complicated.

  A monitor PD is also required when detecting an abnormality of the LD, and the same problem as described above occurs.

  SUMMARY OF THE INVENTION An object of the present invention is to provide an optical fiber temperature sensor device that can be realized almost by a conventional device configuration, is inexpensive, and has a simple configuration.

The present invention has been devised to achieve the above object, and the invention of claim 1 is characterized in that an optical fiber is provided from the sensor body to a temperature measurement point, light is incident on the optical fiber from a light source, An optical fiber type temperature sensor device that detects Stokes light and anti-Stokes light scattered from an optical fiber and measures the temperature at the measurement location, and a reference temperature optical fiber having a known temperature provided between the light source and the optical fiber; And control means for monitoring the Stokes light intensity and the anti-Stokes light intensity scattered from the reference temperature optical fiber, and controlling the output of the light source , wherein the control means has the reference temperature light at any two temperatures in advance. A reference calculation value of the Stokes light intensity and anti-Stokes light intensity scattered from the fiber is obtained, and a reference value indicating the relationship between the reference calculation value and temperature is obtained. An equation is obtained and stored in a storage device, and then the Stokes light intensity and anti-Stokes light intensity scattered from the reference temperature optical fiber at another temperature are obtained, and the approximation at the other temperature is obtained. An optical fiber temperature sensor device that obtains a calculated value by an equation and controls a bias current applied to the light source so that the calculated value is equal to a stored calculated value by the approximate equation .

According to the second aspect of the present invention, an optical fiber is provided from the sensor body to a temperature measurement location, light is incident on the optical fiber from the light source, and the Stokes light and the anti-Stokes light scattered from the optical fiber are detected to perform the measurement. In a fiber optic temperature sensor device for measuring the temperature of a location, a reference temperature optical fiber having a known temperature provided between the light source and the optical fiber, and Stokes light intensity and anti-Stokes light intensity scattered from the reference temperature optical fiber Control means for controlling the output of the light source, and the control means obtains reference calculation values of Stokes light intensity and anti-Stokes light intensity scattered from the reference temperature optical fiber at a number of temperatures in advance. This is stored in a storage device, and the stored reference calculation value and the Stokes scattered from the reference temperature optical fiber are stored. As is the calculated value of the light intensity and anti-Stokes light intensity equal, an optical fiber temperature sensor device for controlling the bias current applied to the light source.

In the invention of claim 3, the control means monitors the Stokes light intensity and the anti-Stokes light intensity scattered from the reference temperature optical fiber or the optical fiber, and based on the monitored Stokes light intensity and anti-Stokes light intensity. Or an optical fiber temperature according to claim 1 or 2 , wherein the reference temperature optical fiber or the reflected light intensity reflected from the optical fiber is monitored, and an abnormality of the device is detected based on the monitored reflected light intensity. It is a sensor device.

In the invention of claim 4, the control means monitors the Stokes light intensity and the anti-Stokes light intensity scattered from the reference temperature optical fiber, and based on the monitored Stokes light intensity and the anti-Stokes light intensity, The optical fiber temperature sensor device according to claim 1 or 2, which detects an abnormality.

  According to the present invention, it is possible to realize almost the conventional apparatus configuration, and the excellent effect is obtained that the configuration is simple and inexpensive.

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

  FIG. 1 is a configuration diagram of an optical fiber type temperature sensor device showing a preferred embodiment of the present invention.

  As shown in FIG. 1, an optical fiber temperature sensor device 1 having an APC (Automatic Power Control) control function and / or an abnormality detection function according to this embodiment includes a sensor body 2 and a measurement optical fiber for temperature measurement. 3b and a display / control personal computer 4 as an external arithmetic processing means for controlling the control means in the sensor body 2 to be described later and displaying the temperature of the measurement location.

  The sensor body 2 is an LD module 5 serving as a light source that emits a pulsed light signal having a wavelength λ0 and light that transmits the pulsed light signal and separates St light having a wavelength λSt and As light having a wavelength λAs from backscattered light. The filter unit 6 mainly includes a light receiver 7 that receives St light and As light and converts them into electrical signals, and a signal processing control circuit 8 that serves as control means.

  The LD module 5 includes an LD 9 and a driver 10 that drives the LD 9. As the optical filter unit 6, for example, a filter in which only a filter that transmits only St light and a filter that transmits only As light are arranged so as to face each other at a predetermined angle. The light receiver 7 includes an APD (avalanche photodiode) 11 and a preamplifier 12 that amplifies the output of the APD 11. An AD (analog / digital) converter 13 is connected between each light receiver 7 and the signal processing control circuit 8.

  In the optical fiber temperature sensor device 1, the LD module 5 and the optical filter unit 6 are connected by the in-device optical fiber 3a, and the optical fiber type temperature sensor device 1 is separated from the measuring optical fiber 3b between the optical filter unit 6 and the measuring optical fiber 3b. These optical fibers were connected to a reference temperature optical fiber 14 having a known temperature. Of course, the extra length of the measurement optical fiber 3b may be the reference temperature optical fiber 14.

  The signal processing control circuit 8 monitors the St light intensity and the As light intensity scattered from the reference temperature optical fiber 14, controls the output of the LD based on the St light intensity and the As light intensity, and performs an optical fiber temperature. It has a function of detecting an abnormality in the sensor device 1 itself. The signal processing control circuit may have only the function of controlling the output of the LD or only the abnormality detection function of the optical fiber type temperature sensor device 1 itself.

  More specifically, the signal processing control circuit 8 obtains, for example, values of St light intensity and As light intensity scattered from the reference temperature optical fiber 14 (for example, four arithmetic operations that are addition / subtraction / multiplication / division) and uses the calculated values. The bias current applied to the LD 9 is controlled. Thereby, the signal processing control circuit 8 controls the output of the LD 9 to be constant even if there is a temperature change in the optical fiber temperature sensor device 1.

  The signal processing control circuit 8 includes, for example, an MCU (Micro Controller Unit) as a storage device and an FPGA (Field Programmable Gate Array) as an arithmetic processing device. Various data relating to temperature measurement (such as four arithmetic operation values for addition, subtraction, multiplication and division described later) may be stored in the MCU, for example.

  The signal processing control circuit 8 has substantially the same function as the signal processing control circuit 33 of the conventional optical fiber temperature sensor device 31 of FIG. Detailed operation of the signal processing control circuit 8 will be described later.

  The reference temperature optical fiber 14 is stored in a fiber storage box 15. The sensor body 2 includes temperature detection means 16 that detects the temperature of the reference temperature optical fiber 14. The temperature detection means 16 is connected to the signal processing control circuit 8. As the temperature detection means 16, a thermocouple or a temperature measurement IC may be used.

Next, the operation of the optical fiber temperature sensor device 1 will be described.
(APC control)
A pulse signal is generated by the signal processing control circuit 8, and this pulse signal is converted into a pulse optical signal (output wavelength λ 0) by the LD module 5, and the pulse optical signal passes through the optical filter unit 6 to the reference temperature optical fiber 14. Incident. Then, backscattered light is generated from the reference temperature optical fiber 14.

  The light filter unit 6 separates the St light having the wavelength λs and the As light having the wavelength λAs from the backscattered light, and each of these lights is received by the light receiver 7 to be converted into an electric signal and input to the signal processing control circuit 8.

  When the temperature in the optical fiber temperature sensor device 1 changes, the temperature of the reference temperature optical fiber 14 changes and the St light intensity and the As light intensity change.

(1) When using an approximate expression First, prior to the temperature measurement at the measurement location, the signal processing control circuit 8, as shown in FIG. 2, arbitrarily selects any two temperatures of the reference temperature optical fiber 14 (measurement points to be measured in advance). (Stage temperature or known temperature) Ta and Tb, St light intensity and As light intensity scattered from the reference temperature optical fiber 14 are measured, and processed to obtain data, and the data is obtained as a reference calculation value to the MCU. Store it. Any two temperatures are measured by the temperature detection means 16 provided in the sensor body 2.

  The signal processing control circuit 8 obtains an approximate expression from the above data with respect to the relationship between the temperatures Ta and Tb and the calculated values Da and Db of the St light intensity and the As light intensity, and obtains a graph X of the approximate expression. The approximate expression graph X is stored in the arithmetic processing unit or the storage device by the signal processing control circuit 8.

  The graph X of the stored approximate expression is, for example, the relationship between (ST0 + AS0) obtained by the approximate expression from the St light intensity ST0 and the As light intensity AS0 (ST0 + AS0) at ambient temperatures of 25 ° C., 30 ° C., etc. and the temperature. It is a graph which shows.

  From the graph X of this approximate expression, the calculated values of the St light intensity and the As light intensity scattered from the reference temperature optical fiber 14 at another temperature other than the actually obtained temperature can be obtained. (Procedure 1) The approximate expression graph X can also be obtained from (ST0 + AS0) at one ambient temperature. This is because a graph showing the relationship between (ST0 + AS0) and temperature can be roughly estimated by a conventional technique except that the graph changes greatly with the wavelength of the LD9.

  Next, APC control and abnormality detection of the optical fiber temperature sensor device 1 are performed according to the following procedure.

  When the data up to the procedure 1 is collected, the signal processing control circuit 8 detects another temperature detected by the temperature detecting means 16 (temperature at the time when it is desired to detect an abnormality of the APC control or the optical fiber temperature sensor device 1) (T1 and In this case, the calculated values (denoted as D1) of the St light intensity and the As light intensity scattered from the reference temperature optical fiber 14 are obtained.

  The signal processing control circuit 8 obtains the calculated value Dk1 of the St light intensity and the As light intensity by the approximate expression at the temperature T1 from the approximate expression, compares the calculated value Dk1 by the approximate expression and D1, and compares Dk1 and D1. Are controlled so that the bias current of the driver 10 or the LD 9 is constant, and the output of the LD 9 is controlled to be constant.

  Here, the reason why the APC control is performed by the signal processing control circuit 8 using the approximate expression is that the number of times of measurement in advance can be reduced. If there are arbitrary two temperatures Ta and Tb, and St light intensity and As light intensity calculated values Da and Db scattered from the reference temperature optical fiber 14 at these temperatures, an approximate expression is obtained as described in FIG. be able to.

  At the same time, the signal control circuit 8 generates a warning signal and transmits it to the personal computer 4, for example, when the variation amount of (ST0 + AS0) exceeds the set value. As a result, the optical fiber temperature sensor device 1 detects an abnormality of the LD module 5 as an example of detecting whether the LD 9, that is, the LD module 5 is operating normally, that is, an abnormality of the optical fiber temperature sensor device 1. it can.

  The reference temperature optical fiber 14 is accommodated in the sensor body 2, and the LD 9 is similarly accommodated in the sensor body 2. The change in the temperature of the reference temperature optical fiber 14 means that the temperature of the apparatus main body 2 changes, and the temperature of the LD 9 also changes in the same manner as the reference temperature optical fiber 14. Therefore, in order to make the power of the LD 9 constant with respect to the temperature change of the LD 9, it is necessary to control the bias current of the LD 9 by the signal processing control circuit 8 as described above.

(2) When a large number of prediction data are used Further, the signal processing control means 8 measures the St light intensity and the As light intensity scattered from the reference temperature optical fiber 14 at a large number of temperatures in advance without using an approximate expression, Data may be acquired and stored in the MCU as a reference calculation value.

  The stored data is, for example, a graph showing the relationship between (ST0 + AS0) and temperature obtained from the sum (ST0 + AS0) of each St light intensity ST0 and As light intensity AS0 at an ambient temperature of −30 to + 70 ° C.

  For measurement at a large number of temperatures, for example, it is sufficient to obtain reference calculation values of St light intensity and As light intensity scattered from the reference temperature optical fiber 14 every 1 ° C. and store them in a storage device. . This is because the temperature detection means 16 has a measurement accuracy of about 1 ° C.

  In this case, the signal processing control circuit 8 compares with the data (ST1 + AS1 etc.) acquired during the temperature measurement at the measurement location based on the data obtained in advance, and the driver 10 or the LD 9 becomes equal to the data obtained in advance. The bias current is controlled, and the output of the LD 9 is controlled to be constant.

The method using a large number of prediction data requires more pre-measurements than the method using the approximate expression described above, but can perform APC control and abnormality detection of the optical fiber temperature sensor device 1 with high accuracy. There is an advantage that the measurement error is small. This is because the graph showing the relationship between temperature and the calculated values of St light intensity and As light intensity is generally a curve.
(Temperature measurement)
While performing the APC control described above every predetermined time, the temperature of the measurement location is measured. The predetermined time here may be determined arbitrarily.

  The signal processing control circuit 8 obtains the intensity ratio of St light and As light from each point of the measurement optical fiber 3b at each sampling time interval in the same manner as in the APC control, and the temperature at the measurement location is determined from this intensity ratio. Ask. The sampling time interval varies depending on the number of additions. The obtained temperature is displayed on the personal computer 4.

  However, since the St light and As light are very weak, the temperature measurement is repeated, and the obtained data is added to the previous data, and the temperature is calculated using the addition result to obtain the temperature result at each point.

  As described above, the optical fiber temperature type sensor device 1 applies the APC control to the LD 9 by using the St light and As light signals scattered from the reference temperature optical fiber 14 whose temperature is known and enters the signal processing control circuit 8. Yes.

  As a result, the optical fiber temperature sensor device 1 can detect whether the LD 9, that is, the LD module 5 is operating normally, even if the LD module 5 does not include a monitor PD or a Peltier element. The temperature at the measurement location can be measured with high accuracy by keeping it constant.

  Since the optical fiber type temperature sensor device 1 does not require the monitor PD in the LD module 5, the LD 9 which is less expensive than the conventional one, that is, the LD module 5, can be used, and the cost of the entire optical fiber type temperature sensor device is reduced.

  Further, since the LD module 5 has a simpler configuration than the conventional LD module 34 of FIG. 3, the overall configuration of the optical fiber temperature sensor device is also simplified.

  Further, the signal processing control circuit 8 has a simple configuration as compared with the prior art because it only needs to process a total of two signals of St light and As light as temperature calculation processing.

  In the above embodiment, the sum is used as the four arithmetic operation values of the intensity of the St light and the As light, but a difference, a product, and a quotient may be used.

  When using the difference, the signal processing control circuit 8 measures in advance the difference (ST0-AS0) between the reference intensity ST0 of the St light scattered from the reference temperature optical fiber 14 and the reference intensity AS0 of the As light and stores it in the MCU. The bias current applied to the LD 9 is controlled so as to be equal to the difference (ST0-AS0) in the predetermined temperature of the reference temperature optical fiber 14 previously set.

  When the product is used, the signal processing control circuit 8 measures in advance the product (ST0 × AS0) of the reference intensity ST0 of the St light scattered from the reference temperature optical fiber 14 and the reference intensity AS0 of the As light (ST0 × AS0). The bias current applied to the LD 9 is controlled so as to be equal to the product (ST0 × AS0) of the stored reference temperature optical fiber 14 at a predetermined temperature.

  Further, when divisor is used, the signal processing control circuit 8 measures in advance the quotient (ST0 ÷ AS0) of the reference intensity ST0 of the St light scattered from the reference temperature optical fiber 14 and the reference intensity AS0 of the As light. The bias current applied to the LD 9 is controlled so as to be equal to the quotient (ST0 ÷ AS0) at a predetermined temperature of the reference temperature optical fiber 14 stored in the MCU.

  In these cases, the same effects as described above can be obtained.

  Further, as the four arithmetic operation values of the intensity of St light and As light, a combination of two or more of sum, difference, product and quotient may be used. For example, (ST0 × AS0) × (ST0 ÷ AS0) may be used.

  In the above embodiment, the signal processing control circuit 8 detects the abnormality of the LD module 5 as an example of detecting the abnormality of the optical fiber temperature sensor device 1. However, the signal processing control circuit 8 It is also possible to detect disconnection of the optical fiber 3a and the measurement optical fiber 3b.

  In this case, if there is a broken portion in the in-device optical fiber 3a or the measurement optical fiber 3b, reflected light (the same wavelength as the incident light) is generated by Fresnel reflection at the broken portion. By monitoring the reflected light intensity with the signal processing control circuit 8, the calculated value described above becomes abnormal, so that the disconnection and the disconnection location of the in-device optical fiber 3a and the measurement optical fiber 3b can be detected.

  In the above embodiment, the optical fiber temperature sensor device 1 includes the reference temperature optical fiber 14, and the signal processing control circuit 8 monitors the Stokes light intensity and the anti-Stokes light intensity scattered from the reference temperature optical fiber 14, and As described above, the control of the output and the abnormality of the device 1 are detected.

  As another embodiment of the present invention, the reference temperature optical fiber 14 is omitted from the optical fiber temperature sensor device 1, and the signal processing control circuit 8 is configured to reduce the Stokes light intensity scattered from the measurement optical fiber 3 b for temperature measurement and the anti-Stokes light intensity. The Stokes light intensity may be monitored to control the output of the light source or detect an abnormality in the apparatus. The operation of the apparatus in another embodiment is the same as the operation of the optical fiber temperature sensor apparatus 1 described above, except that the reference temperature optical fiber 14 is replaced with a measurement optical fiber 3b for temperature measurement. Also in this case, the same effect as the optical fiber temperature sensor device 1 can be obtained.

It is a block diagram of the optical fiber type temperature sensor apparatus which shows suitable embodiment of this invention. It is a figure explaining operation | movement in the case of using an approximate expression in the optical fiber type temperature sensor apparatus shown in FIG. It is a block diagram of the conventional optical fiber type temperature sensor apparatus. It is a figure which shows the intensity spectrum of the backscattered light of an optical fiber.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Optical fiber type temperature sensor apparatus 2 Sensor main body 3a Optical fiber in apparatus 3b Optical fiber for measurement 5 LD module (light source)
8 Signal processing control circuit (control means)
14 Reference temperature optical fiber

Claims (4)

Light that provides an optical fiber from the sensor body to the temperature measurement location, makes light from the light source incident on the optical fiber, detects Stokes light and anti-Stokes light scattered from the optical fiber, and measures the temperature at the measurement location In the fiber-type temperature sensor device, the reference temperature optical fiber provided between the light source and the optical fiber is monitored, the Stokes light intensity and the anti-Stokes light intensity scattered from the reference temperature optical fiber are monitored, and the light source of the light source is monitored. Control means for controlling the output, and the control means obtains reference calculation values of Stokes light intensity and anti-Stokes light intensity scattered from the reference temperature optical fiber at two arbitrary temperatures in advance, and the reference calculation value An approximate expression indicating the relationship between the temperature and the temperature is obtained and stored in a storage device. The calculated values of Stokes light intensity and anti-Stokes light intensity scattered from the temperature optical fiber are calculated, the calculated value by the approximate expression at the other temperature is determined, and the calculated value and the stored calculated value of the approximate expression are An optical fiber type temperature sensor device which controls a bias current applied to the light source so as to be equal . Light that provides an optical fiber from the sensor body to the temperature measurement location, makes light from the light source incident on the optical fiber, detects Stokes light and anti-Stokes light scattered from the optical fiber, and measures the temperature at the measurement location In the fiber-type temperature sensor device, the reference temperature optical fiber provided between the light source and the optical fiber is monitored, the Stokes light intensity and the anti-Stokes light intensity scattered from the reference temperature optical fiber are monitored, and the light source of the light source is monitored. A control means for controlling the output, and the control means obtains reference calculation values of Stokes light intensity and anti-Stokes light intensity scattered from the reference temperature optical fiber at a number of temperatures in advance and stores them in a storage device. The stored reference calculation value and the Stokes light intensity and anti-scatter scattered from the reference temperature optical fiber As calculated value of Kusu light intensity and is equal, the optical fiber temperature sensor and wherein the controlling the bias current applied to the light source. The control means monitors the Stokes light intensity and anti-Stokes light intensity scattered from the reference temperature optical fiber or the optical fiber, or based on the monitored Stokes light intensity and anti-Stokes light intensity, or the reference temperature light The optical fiber temperature sensor device according to claim 1 or 2 , wherein the intensity of the reflected light reflected from the fiber or the optical fiber is monitored, and an abnormality of the device is detected based on the monitored reflected light intensity . The control means monitors the Stokes light intensity and anti-Stokes light intensity scattered from the reference temperature optical fiber, based on the monitored Stokes light intensity and anti-Stokes light intensity, according to claim 1 for detecting the abnormality of the light source Or the optical fiber type temperature sensor apparatus of 2.

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