JPH02201233A - Distribution type optical fiber temperature sensor and its method of temperature measurement - Google Patents

Abstract

PURPOSE:To enable measurement of an absolute temperature distribution of a fiber to be measured by providing a thermostatic device to keep a part of the fiber to be measured at a fixed temperature. CONSTITUTION:A thermostatic device such as Peltier element 8 provided in a fiber 4 to be measured keeps a part of the fiber 4 to be measured provided with the device at a known fixed temperature and serves as a reference temperature part 10 with respect to a change in temperature in a range other than the part. Then, a variation of intensity of an anti-Stokes light pertaining to a variation of temperature for a reference temperature is stored into a computer 7 at a desired point. The reference temperature is preferably a room temperature level of about 20-30 deg.. Thus, the intensity of the anti-Stokes light is compared with the reference temperature part 10 thereby enabling measuring of an absolute temperature distribution of the fiber 4 to be measured.

Description

[Detailed description of the invention]

[Industrial Application Field] The present invention relates to a distributed optical fiber temperature sensor and a temperature measurement method, and in particular to a distributed optical fiber temperature sensor that measures the absolute temperature distribution from the intensity of anti-Stokes light among the Raman scattered light of a fiber to be measured. The present invention relates to a fiber temperature sensor and a temperature measurement method. [Prior art] Raman scattered light generated when a high peak power pulsed laser beam is input into an optical fiber is detected by the 0TDR method,
Distributed optical fiber temperature sensors that continuously measure temperature at arbitrary positions along an optical fiber are known. Also,
A distributed optical fiber temperature sensor using Raman scattered light is
Broadly speaking, it can be divided into the following two methods. (1) A method of detecting only anti-Stokes light and measuring temperature distribution from its intensity. (2) A method of detecting the intensity ratio of anti-Stokes light and Stokes light and measuring temperature distribution. The present invention aims to solve the following problems of the measurement method (1) above. [Problem to be solved by the invention] The basic configuration of the conventional distributed optical fiber temperature sensor is
Pulsed laser light from a semiconductor laser 12 as a light source shown in the figure passes through an optical directional coupler 13 such as an acousto-optic device, and is guided to a fiber 14 to be measured. From the fiber to be measured 14, Raman scattered light is generated according to the amount of incident light. , in the signal processing device 16, tooo. The processed signal, which is subjected to the same level of averaging processing, is displayed as data by the computer 17. In this example, detector 15. Signal processing device 16, computer 1
7 together constitute a measuring device. The pulse oscillator 11 drives the semiconductor laser 12 and oscillates a trigger signal for the signal processing device 16 . A problem with this system is that only the anti-Stokes light is used as the detection light, so the temperature change in the fiber 14 to be measured can only be known relatively. That is, when the surrounding temperature changes, the measured value changes, and there is a problem that absolute temperature measurement cannot be performed.

[Means to solve the problem]

The present invention has been made to solve the above-mentioned problems, and includes a light source that injects a pulsed laser beam into a fiber to be measured, and an optical directional coupling that converts the optical path of Raman scattered light from the fiber to be measured to a measuring device. In a distributed optical fiber temperature sensor consisting of a measuring device that measures the temperature distribution of the fiber to be measured from the intensity distribution of the Raman scattered light with respect to the distance, 1. A constant temperature sensor that maintains a part of the fiber to be measured at a constant temperature; A distributed optical fiber temperature sensor is characterized in that it is equipped with a device, and a part of the fiber to be measured is provided with a constant temperature device that keeps the temperature constant. The Raman scattered light from the is guided to the measurement device by an optical directional coupler, and the part where the constant temperature device is installed is set as a reference temperature part, and the anti-Stokes light intensity in the reference temperature part and the anti-Stokes intensity in other parts are calculated. The present invention provides a temperature measurement method characterized by measuring the absolute temperature distribution of the fiber under test by comparing the The constant temperature device maintains the part of the fiber under test where the constant temperature device is installed at a known constant temperature, and serves as a reference temperature section for temperature changes in other ranges.Therefore, the reaction regarding the amount of temperature change with respect to the reference temperature is By storing the amount of change in the Stokes light intensity in a computer at an arbitrary point, the absolute temperature at an arbitrary point on the fiber to be measured can be measured. [Example] An example of the present invention is shown in Fig. 1. It is shown in Fig. 2. Pulsed laser light from a semiconductor laser 2 as a light source passes through an optical directional coupler 3 such as an acousto-optic device, and is connected to a fiber under test 4.
guided by. From the fiber to be measured 4, Raman scattered light is generated according to the amount of incident light. , signal processing device 6
In this step, the processed signal, which is averaged approximately 10,000 times, is displayed as data by the computer 7. In this example, the detector 5, signal processing device 6, and computer 7 are collectively used as a measuring device. The pulse oscillator 1 is a driver for the semiconductor laser 2 and a signal processing device 6
The reference temperature section 1O, which oscillates the trigger signal of Although it varies depending on the resolution, if the resolution is higher than the resolution, that is, the resolution is about ±10 m, it is sufficient to wrap the wire around 20 ra or more. Actually, the shorter the distance, the better, so in this example, it may be 20 m. Further, the computer 7 controls the temperature through the temperature controller 9 so that the temperature of this part is always constant. FIG. 2 shows an example of processing the measurement data. Usually, the signal waveform of the Raman scattered light intensity relative to the distance from the fiber under test is an attenuation curve expressed by an exponential function of e. but,
In the present invention, the amount of change in the anti-Stokes light intensity with respect to the amount of temperature change with respect to the reference temperature is stored in the combinator at an arbitrary point, and only the absolute temperature change is extracted and displayed. Therefore, as shown in FIG. 2, the portions where there is no temperature change do not form an attenuation curve with respect to distance, but form a flat straight line, and only the portions where the temperature has changed can be displayed. In addition, the constant temperature device that creates the reference temperature section may be kept at a higher or lower temperature than room temperature, and in addition to the Peltier element, a constant temperature chamber with a built-in heating wire can be used, and the reference temperature can be Room temperature levels of about 20°C to 30°C are preferred. [Effects of the Invention] The present invention has an excellent effect in that the absolute temperature distribution of the fiber to be measured can be measured by comparing the anti-Stokes light intensity with a reference temperature section.

[Brief explanation of the drawing]

1 and 2 show embodiments of the present invention, FIG. 1 is a block diagram of a distributed optical fiber temperature sensor, and FIG. 2 is a graph showing an example of displaying data processed by a computer. , FIG. 3 is a block diagram of a conventional distributed optical fiber temperature sensor. 4...Fiber under test 7...Computer 8
...Peltier element Figure 1 Figure 2

Claims (2)

[Claims] (1) A light source that injects a pulsed laser beam into the fiber under test, an optical directional coupler that converts the optical path of the Raman scattered light from the fiber under test to the measuring device, and a measured object based on the intensity distribution of the Raman scattered light with respect to distance. 1. A distributed optical fiber temperature sensor comprising a measuring device for measuring the temperature distribution of a fiber, the distributed optical fiber temperature sensor comprising a constant temperature device that maintains a part of the fiber to be measured at a constant temperature. (2) A pulsed laser beam oscillated from a light source is input into the fiber to be measured, which is equipped with a constant temperature device that keeps the temperature constant, and the Raman scattered light from the fiber to be measured is measured by an optical directional coupler. The absolute temperature of the fiber to be measured is determined by guiding the light to the device, setting the part where the constant temperature device is installed as a reference temperature part, and comparing the anti-Stokes light intensity in the reference temperature part with the anti-Stokes light intensity in other parts. A temperature measurement method characterized by measuring distribution.