JPH0321837A - Distributed optical fiber temperature sensor and temperature measuring method - Google Patents

Abstract

PURPOSE:To easily reduce a drift error by providing a calibration part which measures an absolute temperature distribution from the temperature of an optical fiber to be measured at part of the optical fiber to be measured and comparing the intensity ratio of the regular and an anti-Stokes' light beam at the part with that at another part. CONSTITUTION:The calibration part consists of a light source part 1, a directional coupler 2, an optical fiber 3 for calibration, and a temperature sensor 4 and a measuring instrument consists of a spectroscope 7, photoelectric converters 8 and 9, amplifiers 10 and 11, and a signal processing part 12. The optical fiber 6 to be measured is connected by a connector 5 to the fiber 3 in series. Then laser pulses from the light source part 1 are made incident on the fiber 6 by the coupler 2 and the sensor 4 measures the temperature at the same time. Back ward scattered light generated with the laser pulses enters the measuring instrument again through the coupler 2 and is separated into the regular and anti-Stokes' light beams, which are converted into electric signals. The processing part 12 calculates the regular and anti-Stokes' signal ratio after S/N ratio improvement averaging, performs temperature conver sion processing, and adjusts an entire-area offset so that the calibration part temperature becomes as high as the measured temperature of the sensor 4. Consequently, the drift error is easily reduced.

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 temperature measurement method based on the intensity ratio of Stokes light and anti-Stokes light contained in Raman scattered light of an optical fiber to be measured. The present invention relates to a distributed optical fiber temperature sensor that measures absolute temperature distribution and a temperature measurement method.

[Prior Art] A block diagram of a conventional distributed optical fiber temperature sensor is shown in FIG.

Laser pulses oscillated from a light source unit l3 such as an LD are sent to an optical directional coupler l such as an optical fiber coupler or an acousto-optic element.
4 and enters the optical fiber 15 to be measured. A part of the Raman scattered light from the optical fiber 15 returns and is guided to the measuring device by the optical directional coupler 14.

The measurement device performs the following processing. Stokes light and anti-Stokes light contained in the Raman scattered light are separated by a spectrometer 16 such as an optical filter, and each is separated by a photoelectric converter 17.
Detected at 18. Furthermore, an amplifier 19. After being amplified in step 20, the signal processing unit 2l performs processing such as averaging processing or calculating temperature distribution from the intensity ratio of Stokes light and anti-Stokes light. It has long been known that the intensity ratio of Stokes light and anti-Stokes light is a function only of absolute temperature. Manipulating the Stokes light intensity. , the anti-Stokes light intensity is calculated. , ν. When is the incident light wavelength, ν7 is the Raman shift, C is the speed of light in the optical fiber, k is Boltzmann's constant, and h is Blank's constant, then F. The ratio of I8 and I8 is expressed as... (1). In the above equation, if we take the natural logarithm of both sides as 8=(ν0+ν.)'/(νo-vR)4, then hcy true in(I./I.) =1nA- --...
(ikT, and the left side is a function only of absolute temperature T.

Therefore, absolute temperature can be measured by determining the intensity ratio of anti-Stokes light and Stokes light. Conventionally, output electric signals va. Take the ratio of V*, and this is 1. /I. The temperature was detected by substituting it into equation (2) as being equal to .

[Problems to be Solved by the Invention] In the prior art, the detection system is composed of two types of independent detectors (photoelectric converters) for Stokes light and anti-Stokes light, and an amplifier, each of which has a different drift. arise. As a result, the output electric signal ratio V
．． '/v1 is no longer equal to the true intensity ratio of the anti-Stokes light and the Stokes light, causing an error in the measurement results. [Operation] The present invention compensates for drift by the following method.

The output signal (true value) of the detection system in the ideal state is V @ %
6 I a / I s = Va /Vm = gd (va
'/Vm')・・・・・(3) Substitute into equation (2) and get tlc'L'* 1 incd +ln(va'/vm') =1nA+k
TT (4) (5) That is, εd uniformly affects the entire measurement area as a so-called offset error that does not depend on distance or temperature.

Therefore, a part of the optical fiber to be measured is used as a calibration part, and the fiber temperature of this part is measured with a temperature sensor and referenced to compensate for the offset of the entire measurement area.

[Embodiment] FIG. 1 is a block diagram of an embodiment, in which a laser pulse from a light source section 1 is inputted into an optical fiber 6 to be measured through a directional coupler 2. In FIG. Reference numerals 3 and 4 indicate a calibration section consisting of a calibration optical fiber 3 and a temperature sensor 4, and the temperature of 4 degrees in this section is simultaneously measured by the temperature sensor 4 such as a platinum thermometer, a semiconductor transducer, a thermistor, or the like. This optical fiber 3 for calibration is connected in series with an optical fiber 6 to be measured which is actually used for measurement through a connecting portion 5 such as an FC connector.

The length of the calibration optical fiber 3 has a distance resolution of 1 to 1 lom.
The length should be 2.5 times or more, and the length should be smaller than 2.5 times.
The measurement accuracy is insufficient.

The backscattered light generated by the incident laser pulse is
The light passes through the optical directional coupler 2 again and is guided to the measuring device. The measuring device includes a spectrometer 7, photoelectric converters 8 and 9, an amplifier 10,
11. Consists of a signal processing unit l2, which separates Stokes light and anti-Stokes light and converts them into electrical signals.
In the signal processing unit 12, after averaging to improve the S/N ratio, a process is performed in which the ratio of the Stokes signal and the anti-Stokes signal is calculated and converted into temperature. At this time, the offset values of all regions are adjusted so that the temperature of the calibration section becomes equal to the temperature measured by the temperature sensor 4.

[Effects of the Invention] The present invention has the excellent effect of reducing drift errors by simple means without increasing the accuracy and stability of the measuring device itself.

[Brief explanation of the drawing]

FIG. 1 is a block diagram showing an embodiment of the present invention, and FIG.
The figure is a block diagram showing a conventional example. 3. 4. 6. 12. ・Optical fiber for calibration・Temperature sensor・Optical fiber to be measured・Signal processing section

Claims (2)

[Claims] (1) A light source unit that injects a laser pulse into the optical fiber to be measured, an optical directional coupler that converts the optical path of the Raman scattered light from the optical fiber to be measured, and a light directional coupler that converts the Stokes light contained in the Raman scattered light. A distributed optical fiber temperature sensor comprising a measuring device that measures the temperature distribution of an optical fiber to be measured from the intensity ratio of Stokes light, wherein a calibration part is provided in a part of the optical fiber to be measured to measure the absolute temperature distribution from the temperature, A distributed optical fiber temperature sensor characterized in that a temperature sensor is disposed in the calibration section. (2) Injecting a laser pulse oscillated from a light source into an optical fiber to be measured, a part of which is provided with a temperature sensor, and guiding the Raman scattered light from the optical fiber to be measured to a measuring device by an optical directional coupler; In the temperature measurement method in which the temperature distribution of the optical fiber to be measured is measured from the intensity ratio of Stokes light and anti-Stokes light contained in the Raman scattered light using the measurement device, a portion where the temperature sensor is provided is used as a calibration section, and the calibration is performed. A temperature measurement method characterized by measuring the absolute temperature distribution of an optical fiber to be measured by comparing the intensity ratio of Stokes light and anti-Stokes light in one part with the intensity ratio of Stokes light and anti-Stokes light in another part. .