JPH04351931A - Optical fiber distribution type temperature sensor - Google Patents

Abstract

PURPOSE:To obtain an optical fiber temperature distribution sensor which has correction function inside a device and accurately seizes temperature measurement positions in succession in the longitudinal direction of connected optical fiber. CONSTITUTION:An optical fiber distribution type temperature sensor is to measure the temperature at each section of optical fiber by using Raman backward scattering light. A correction optical fiber 11 of known length is previously connected thereto and the portion at a preset length from a known position is maintained at a constant temperature by a constant temperature equipment 12 and housed in a device 8. Sensor optical fiber 1 placed on a measured object is connected to the terminal of the correction optical fiber 11, and an adjusting means 14 is provided to operate sampling timing so that the temperature of the portion maintained at a constant temperature in temperature distribution information found by Raman scattering light for the correction optical fiber 11 can be closet to the true temperature of the constant temperature equipment 12. The connection point of the detector is accurately matched to the rising point of measurement data with the temperature distribution of the sensor optical fiber.

Description

[Detailed description of the invention]

0001

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a distributed temperature sensor that uses the optical fiber itself as a sensor to measure temperature distribution along the longitudinal direction of the optical fiber.

0002

[Prior Art] OTD is a sensor that uses an optical fiber to measure continuous temperature distribution along its length.
An optical fiber type distributed temperature sensor based on the R method is known.

The optical fiber distributed temperature sensor utilizes the fact that the intensity of scattered light in an optical fiber changes with temperature, and as shown in FIG. 4, a light pulse is transmitted from a light source 3 to a sensor optical fiber 1. Of the scattered light incident on the optical fiber and generated within the optical fiber, the Raman backscattered light that returns to the input side is separated by a demultiplexer 4, received by a light receiver 5, and detected as an electrical signal. Since this Raman scattered light is extremely weak,
A trigger signal 9 of a specific period is sent from the averaging processing device 6 to the light source 3.
, a repeated optical pulse is input into the optical fiber 1, the backscattered optical signal that returns is received each time, and the O/E converted electrical signal 10 is sent to the averaging processing device 6, where it is A/E converted.
After D conversion, averaging processing is performed to increase the S/N ratio and enable highly accurate measurement. Further, this high S/N ratio scattered light intensity signal is converted into temperature by the data processing device 7.

It should be noted that the time difference between the time when a light pulse enters the optical fiber and the time when the scattered light reaches the input end is 2.
Since it is expressed as L/C (L: distance from the input end of the optical fiber to the position where the scattered light occurs, C: the speed of light in the optical fiber), if the above time difference is detected, the position where the backscattered light occurs can be determined. is located.

[0005] In this way, the temperature and its position can be detected simultaneously, and the temperature distribution can be determined.

[0006]

[Problems to be Solved by the Invention] However, conventional distributed temperature sensors have the following problems.

(1) The backscattered light signal from the photoreceiver 5 is transferred to the averaging processing device 6, where this analog signal is sampled, converted to a digital signal, and averaged. If the sampling start timing is different, the position of the light distribution will shift. For this reason, it is difficult to make the sampling start timing the same for all the different detection devices 8, and when measuring temperature distribution by connecting the optical fiber 1, the timing from the optical fiber connection point to the temperature change point for each device is difficult. The locations will be different and it is difficult to orient the exact location.

(2) Optical fiber 1 connected to detection device 8
The temperature distribution obtained by
In order to check whether the optical fiber 1 is satisfied (distance resolution), it is necessary to test the optical fiber 1 on-site by placing it under constant temperature conditions after it is installed, which is difficult to perform in a complicated installation system. .

(3) When abnormal temperature distribution is detected,
It is not possible to determine whether the problem is with the device itself or with the installed optical fiber.

An object of the present invention is to solve the above-mentioned drawbacks of the prior art, and to provide an optical fiber type temperature control device that has a calibration function inside the device and can accurately determine continuous temperature measurement positions in the longitudinal direction of connected optical fibers. An object of the present invention is to provide a distributed sensor.

[0011]

[Means for Solving the Problems] The optical fiber type distributed temperature sensor of the present invention is an optical fiber type distributed type temperature sensor that detects Raman scattered light generated within an optical fiber using an OTDR method and measures the temperature of each part of the optical fiber. In the temperature sensor, a calibration optical fiber of a known length is connected in advance, and a portion of a predetermined length from a known position is maintained at a constant temperature in a thermostat and stored in the device, and the calibration optical fiber terminal is Connect the sensor optical fiber installed on the measurement target, and sample the calibration optical fiber so that the temperature of the part maintained at the above constant temperature in the temperature distribution information obtained from Raman scattered light is the closest value to the true temperature. This configuration includes an adjusting means for changing the timing of.

The calibration optical fiber has a length corresponding to the distance obtained by half the product of the sampling time interval for sampling the electrical signal after O/E conversion of the received Raman scattered light and the speed of light in the optical fiber. Preferably, the portion is heated or cooled from a known position to a constant temperature.

The adjustment means for changing the sampling timing includes a delay circuit that adjusts the delay time for sending the O/E conversion signal of the received Raman scattered light to the sampling circuit, and a delay time of the trigger signal that drives the laser pulse. A delay circuit can be used.

[0014]

[Operation] A calibration optical fiber of a known length housed in the apparatus is maintained at a constant temperature at a predetermined length from a known position in a thermostat. The temperature measured by this calibration optical fiber is closest to the true temperature when the sampling point is within the area maintained at the constant temperature (see the dashed line in Figure 2); (See the solid line in FIG. 2). Therefore, by comparing the true temperature and the temperature measurement value on the calibration optical fiber, and using the adjustment means,
By adjusting the sampling timing so that both values are the closest, the sampling position along the optical fiber can be accurately determined. That is, the connection point of the sensor optical fiber is set as the reference point zero, and the measurement position (sampling position) in the longitudinal direction can be determined from this sensor optical fiber connection point, which greatly improves the positioning accuracy.

Specifically, the length of the portion of the calibration optical fiber maintained at a constant temperature is determined by the O/R of the received Raman scattered light.
The distance obtained by 1/2 of the product of the sampling time interval for sampling the electrical signal after E-conversion and the speed of light in the optical fiber, that is, the length equivalent to the round trip propagation distance in the optical fiber corresponding to the sampling time interval. The performance of the distance resolution can be easily confirmed by comparing the temperature measured by the calibration optical fiber with a length equivalent to the distance resolution and the temperature of the incubator.

[0016]

DESCRIPTION OF THE PREFERRED EMBODIMENTS An embodiment of the present invention will be described below in detail with reference to the accompanying drawings.

FIG. 1 shows an optical fiber type distributed temperature sensor according to a positional embodiment of the present invention.

The optical fiber type distributed temperature sensor is composed of a detection device 8 and a sensor optical fiber 1. A light pulse emitted from the light source 3 passes through a calibration optical fiber 11 in the detection device 8 and enters the sensor optical fiber 1 . In the calibration fiber 11 and the sensor optical fiber 1, Raman scattered light is generated in response to the incident light pulse, and the backscattered light component that returns to the input side is separated by the optical demultiplexer 4.
After being detected by the light receiver 5, it is converted into an electrical signal 10. This O/
The E-converted electrical signal 10 passes through a delay circuit 14 and is sent to the averaging processing device 6. The averaging processing device 6 provides the light source 3 with a trigger signal 9 for emitting light pulses at a specific period, and also inputs the trigger signal 9 at a predetermined timing via a delay circuit 14. The above-mentioned O/E converted electric signal 10 is sampled, and after converting it into a digital value, it is sequentially stored in the memory in the averaging processing device 6, and the signals input in the next cycle are sequentially stored in the memory. Add and average the values. In this way, a predetermined repeated averaging is performed to obtain a scattered light distribution with a good signal-to-noise ratio, which is converted into temperature by the data processing device 7 and displayed.

In the optical fiber type distributed temperature sensor constructed in this manner, the calibration fiber 11 in the detection device 8 is connected to the sampling distance (corresponding to the sampling time interval) of the averaging device 6 in the thermostat 12. The round trip distance of light beam propagation in the optical fiber, d=ts×c×1/2 (
d: sampling distance, ts: sampling time interval, c: speed of light in the optical fiber), and is installed from a known position. In this embodiment, the calibration fiber 11 is heated to a constant temperature from a known position by the incubator 12, but it can also be cooled to a constant temperature from a known position.

The temperature measured by the optical fiber 11 in the incubator 12 varies depending on whether the sampling point 18 falls within the heating section 16 or not, as shown by the dashed and solid lines in FIG. That is, as shown in the temperature distribution indicated by the broken line in FIG. If the temperature is outside this range, the temperature distribution will be relaxed as shown by the solid line in FIG. This means that the true temperature inside the thermostat 12 and the optical fiber 1
By comparing the temperature measurement values in step 1 and adjusting the sampling timings so that the two values are the closest, the sampling start timings can all be adjusted to be the same even if there are multiple different detection devices 8. This means that accurate location can be determined.

[0021] Therefore, a thermometer 13 is provided in the thermostat 12 and the true temperature inside the thermostat 12 is inputted to the data processing device 7, while the true temperature and the measured temperature determined from the Raman scattered light are the closest values. Adjustment means is provided to change the sampling timing. In the case of this embodiment, the sampling timing adjustment means is a delay circuit 14 that delays the O/E conversion signal 10 after receiving light and then sends it to the sampling circuit of the averaging processing device 6.
The sending delay time is controlled by the signal 15 from the data processing device 7, and the sampling timing is adjusted so that the true temperature and the measured temperature determined from the Raman scattered light are the closest values. With this timing adjustment, the sampling position along the optical fiber 11 can be accurately determined, and the longitudinal position can be determined by setting the connection point of the sensor optical fiber 1 connected to the detection device 8 as the reference point "0". Can be accurately grasped.

FIG. 3 shows an example of temperature distribution measurement according to this embodiment. By finding the sampling timing at which the measured temperature in the calibration zone 17 corresponding to the heating zone 16 is closest to the true temperature, the sampling points are adjusted to the calibration zone. 17 is shown in the center. “0” of the sensor optical fiber 1 based on the sampling point at the center of this calibration section 17
By determining the points, the temperature and position in the longitudinal direction of the sensor optical fiber 1 can be determined by determining the temperature distribution area 19 in the device before this "0" point, and defining the sensor optical fiber temperature distribution region 20 after the "0" point. It is possible to accurately determine the relationship between

In the above embodiment, as a timing adjustment means for controlling the sampling start timing,
Although the delay circuit 14 is provided in the line of the O/E conversion signal 10 from the optical receiver 5, the delay circuit 14 in FIG.
It is also possible to adjust the sampling start timing by controlling the delay time of the trigger signal 9 that drives the laser pulse.

[0024]

[Effects of the Invention] As described above, according to the present invention, the following excellent effects can be obtained.

(1) The temperature distribution obtained by connecting the sensor optical fiber to the device allows the detection device connection point to accurately match the starting point of the measurement data, greatly improving the locating accuracy of the temperature measurement position. can.

(2) By comparing the temperature measured by a calibration optical fiber placed in a thermostat within the device with the temperature of the thermostat, temperature calibration and temperature accuracy confirmation within the device can be easily performed.

(3) The performance of the distance resolution can be easily confirmed by comparing the temperature measured by a calibration optical fiber with a length equivalent to the distance resolution placed in the incubator in the device and the temperature of the incubator. At the same time, it is also possible to detect abnormalities in light source driving such as pulse width expansion.

(4) By monitoring the measured values of a calibration optical fiber placed in a thermostat within the apparatus, abnormalities in the apparatus and abnormalities in the sensor optical fiber can be detected separately.

(5) It does not require new equipment or major modifications, and is highly economical.

[Brief explanation of drawings]

FIG. 1 is a configuration diagram of an optical fiber type temperature distribution sensor according to an embodiment of the present invention.

[Figure 2] Explanatory diagram showing the relationship between sampling points and measurement results when measuring a temperature distribution with a temperature rise section

[Figure 3]
Characteristic diagram showing an example of the results of measuring temperature distribution with the optical fiber type temperature distribution sensor of the present invention

[Figure 4] Configuration diagram showing a conventional optical fiber type temperature distribution sensor

[Explanation of symbols]

1 Optical fiber for sensor 2 Connector connection part 3. Light source 4 Optical demultiplexer 5 Photo receiver 6 Averaging processing device 7 Data processing device 8 Detection device 9 Trigger signal 10 O/E conversion electrical signal 11 Optical fiber for calibration 12　Thermostat 13 Thermometer 14 Delay circuit 15 Signal 16 Heating section 17 Calibration interval 18 Sampling point 19 Temperature distribution inside the device 20 Optical fiber temperature distribution for sensor

Claims (4)

[Claims] Claim 1: In an optical fiber distributed temperature sensor that detects Raman scattered light generated within an optical fiber using an OTDR method and measures the temperature of each part of the optical fiber, a calibration optical fiber of a known length is connected in advance. Then, a part of a predetermined length from a known position is maintained at a constant temperature in a thermostat and stored in the device, and the sensor optical fiber installed on the measurement target is connected to this calibration optical fiber terminal. An optical fiber characterized in that an adjustment means is provided for adjusting sampling timing so that the temperature of the portion maintained at the constant temperature in the temperature distribution information obtained from Raman scattered light for the optical fiber becomes the closest value to the true temperature. Type distributed temperature sensor. 2. The calibration optical fiber has a speed of 1/ of the product of the sampling time interval for sampling the electrical signal after O/E conversion of the received Raman scattered light and the speed of light in the optical fiber.
2. The optical fiber type temperature distribution type temperature sensor according to claim 1, wherein a length corresponding to the distance obtained by step 2 is heated or cooled from a known position to a constant temperature. 3. The optical system according to claim 1, wherein the adjusting means for changing the sampling timing is a delay circuit that adjusts a delay time for sending an O/E conversion signal of the received Raman scattered light to a sampling circuit. Fiber type distributed temperature sensor. 4. A first method characterized in that the adjusting means for changing the sampling timing is a delay circuit that adjusts a delay time of a trigger signal that drives a laser pulse.
Optical fiber distributed temperature sensor as described in .