JPH1144584A - Optical fiber type temperature distribution measuring device - Google Patents

Abstract

(57) [Problem] To provide an optical fiber type temperature distribution measuring device with high measurement accuracy of temperature and position and short measurement time. A plurality of light sources for pulse light causing Raman scattering are used to increase the pulse light intensity, to convert Stokes light and anti-Stokes light into electric signals at the same time, and to perform digital conversion at the same time.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

TECHNICAL FIELD The present invention relates to a temperature distribution measuring device,
In particular, the present invention relates to an optical fiber type temperature distribution measuring device using Raman scattered light.

[0002]

2. Description of the Related Art An optical fiber type temperature distribution measuring apparatus utilizes Raman scattered light generated when monochromatic pulsed light having high light intensity is incident on an optical fiber. That is, when monochromatic light of wavelength λ0 is incident on the optical fiber from the light source, if the light intensity of the incident light is sufficiently strong, anti-Stokes light λas is on the shorter wavelength side than incident light λ0, and Stokes light λs is on the longer wavelength side than incident light λ0. Occurs.

[0003] The light intensity of the anti-Stokes light λas is fa
Assuming that the light intensity of s and Stokes light λs is fs, these ratios R = fa / fas are purely functions of temperature, and the temperature T can be measured by measuring R.

FIG. 2 is a configuration diagram of a conventional optical fiber type temperature distribution measuring device. It comprises a sensor device 12, a sensor optical fiber 11, a temperature distribution calculation device 9, and a display device 10. The sensor device 12 includes a trigger 1, a light source 2, an optical demultiplexer 3, light receivers 4, 5, AD converters 6, 7, and a data processor 8.

[0005] An electric signal from the trigger 1 is applied to the light source 2 having a wavelength λ0 to generate pulsed light having a pulse width Tw and a pulse period Tp. This pulse light is incident on the optical fiber for sensor 11 through the optical demultiplexer 3.

The sensor optical fiber 11 is usually a multimode optical fiber in which the core is doped with germanium so that Raman scattering easily occurs and the relative refractive index difference is about 1 to 2%.
When the optical pulse light passes through the sensor optical fiber 11, Raman scattering occurs at the place where the light pulse light passes.

Although Raman scattering occurs in a spherical wave shape, backscattered light returning to the input end of the optical fiber is used for measurement. That is, attention is paid to the anti-Stokes light λas and the Stokes light λs in the backscattered light.

The Stokes light λs and the anti-Stokes light λas are separately separated by the optical demultiplexer 3 into respective wavelengths. Then, the light is converted into an electric signal by the light receivers 4 and 5, and is further converted into a digital signal by the AD converters 6 and 7. However, the Stokes light λs and the anti-Stokes light λa
For s, these conversions are not performed simultaneously. That is, first, the Stokes light λs is converted into an electric signal by the light receiver 4, converted into a digital signal by the AD converter 6, and sent to the data processor 8. Then, the anti-Stokes light λa
s is converted into an electric signal by the light receiver 7, converted into a digital signal by the AD converter 7, and sent to the data processor 8.

The data processor 8 performs processing such as temporarily storing converted signals from the A / D converters 6 and 7 which are sequentially sent, and after all the data are prepared, the scattered light intensity fs of the Stokes light λs and the anti-Stokes Scattered light intensity fa of light λas
Calculate the ratio R of s and convert it to temperature. Here, since the anti-Stokes light λas and the Stokes light λs are a function of the longitudinal direction of the sensor optical fiber 11, that is, the position, the ratio R of the scattered light intensity fs of the Stokes light λs to the scattered light intensity fas of the anti-Stokes light λas is also obtained. It is a function of position.

If the time difference between the time when the pulse light from the light source 2 enters the optical fiber for sensor 11 and the time when the Stokes light λs and the anti-Stokes light λas return to the incident end is t seconds, The corresponding position on the optical fiber 11 is represented by Cf · t /
2. Note that the pulse light, Stokes light λs, and anti-Stokes light λas travel at the same speed in the sensor optical fiber 11.

The data processor 8 calculates the temperature and, at the same time, calculates the corresponding position in the sensor optical fiber 11 according to the above equation.

The calculated result is calculated for display by the temperature distribution calculating device 9 and is displayed by the display device 10.

This optical fiber type temperature distribution measuring device measures various longitudinal temperature distributions, for example, monitoring the temperature of many points in concrete, detecting an abnormal temperature of a power cable, and identifying a fire occurrence position in a building. Can be.

[0014]

In the above prior art, there is a problem that the measurement accuracy of the temperature and the position is low because the light intensity of the light source 2 for generating the incident pulse is weak. In the conventional measuring device, the temperature resolution is ± 1 ° C and the position resolution is 1
m. Furthermore, since the digital conversion of the Stokes light and the anti-Stokes light is not performed simultaneously, there is a problem that the measurement time is long.

Accordingly, the present invention has been made in order to solve the above-mentioned problems of the prior art, and to provide an optical fiber type temperature distribution measuring device which has high accuracy in measuring temperature and position and has a short measuring time. It is in.

[0016]

According to the present invention, in order to realize the above-mentioned object, pulsed light is incident on an optical fiber to cause Raman scattering, and light of Stokes light and anti-Stokes light in the Raman scattered light is used. An optical fiber type temperature distribution measurement for measuring a temperature from an intensity ratio and obtaining a measurement position from a time difference between a time when the pulsed light is incident on the optical fiber and a time when the Stokes light and the anti-Stokes light return to an incident end. Provided is an optical fiber type temperature distribution measuring device, wherein a plurality of light sources for generating pulsed light are installed in the device.

According to the present invention, in order to realize the above object, the Stokes light and the anti-Stokes light are simultaneously converted into electric signals by separate light receivers, and the electric signals are simultaneously converted into digital signals by separate AD converters. An optical fiber type temperature distribution measuring device is provided.

[0018]

FIG. 1 is a block diagram showing an embodiment of an optical fiber type temperature distribution measuring apparatus according to the present invention. The apparatus comprises a sensor device 12, a sensor optical fiber 11, and a temperature distribution calculating device 9. , And a display device 10. The sensor device 12 includes a trigger 1, light sources 2a and 2b, an optical demultiplexer 3, light receivers 4 and 5, AD converters 6 and 7, and a data processor 8.
It is composed of

The oscillation wavelengths of the light sources 2a and 2b are both λ0
Thus, pulse light is generated simultaneously by one trigger 1. These pulsed lights enter the optical fiber for sensor 11 through the optical demultiplexer 3.

The difference from the prior art is that the light intensity of the pulse light incident on the sensor optical fiber 11 is sufficiently increased. As a result, the light intensity of the backscattered light from the sensor optical fiber 11, that is, the Stokes light λs and the anti-Stokes light λas can be increased.

The Stokes light λs and the anti-Stokes light λas whose light intensities have been increased are separately separated by the optical demultiplexer 3 into respective wavelengths. The light is converted into an electric signal by the light receivers 4 and 5, and is further converted into a digital signal by the AD converters 6 and 7.

Another difference from the prior art is that the Stokes light λs and the anti-Stokes light λas are
, And simultaneously converts the signals into electric signals, and simultaneously performs digital conversion in the AD converters 6 and 7, and transmits the digital converted signals to the data processor 8.

In the data processor 8, the A / D converters 6, which are sent simultaneously for the Stokes light and the anti-Stokes light,
The memory and the electric circuit etc. necessary for receiving the digital conversion signal simultaneously from 7 and calculating the temperature immediately are added. That is, the ratio R = fa / fas of the scattered light intensity fs of the Stokes light λs and the scattered light intensity fas of the anti-Stokes light λas can be immediately calculated and converted into temperature.

Here, since the light intensity of the pulse light incident on the sensor optical fiber 11 is increased, the light intensity of the Stokes light λs and the anti-Stokes light λas is also increased, and as a result, the temperature calculated by using their ratios The accuracy of is improved.

In this embodiment, both the light pulses generated by the light sources 2a and 2b have a half width of 6 ns and a peak output of 10 W
When two of these are input to the sensor optical fiber 11, the light intensity of the incident pulse becomes approximately 20 W, and the scattered light intensity fs of the Stokes light λs and the scattered light intensity fas of the anti-Stokes light λas are also approximately 2 W. Doubled,
The resolution of the temperature measured using the ratio R is ± 0.
The temperature improved to 7 ° C.

The time when the Stokes light λs and the anti-Stokes light λas return to the incident end after the pulse light is incident on the optical fiber for sensor 11 from the light sources 2a and 2b is t.
In the case of seconds, the corresponding position in the sensor optical fiber 11 is Cf · t / 2, where Cf is the speed at which the pulse advances. Note that the pulse light, the Stokes light λs, and the anti-Stokes light λas travel at the same speed through the sensor optical fiber 11. These principles are the same as those of the prior art, but the SN ratio with respect to the noise level is improved by increasing the light intensity of the anti-Stokes light λas and the Stokes light λs, and the position resolution is also improved to 0.7 m.

The measurement time is determined by the optical fiber 11 for the sensor.
In this embodiment, when the sampling interval is set to 1 m with a 2 km sensor optical fiber, although it depends on the number of points measured in the longitudinal direction, that is, the sampling interval.
0 seconds could be reduced to 20 seconds. This means that if the same measurement time is allowed, the measurement accuracy with respect to temperature can be further improved.

The use of such a new optical fiber type temperature distribution measuring apparatus makes it possible to measure an instantaneous / partial temperature rise such as a temperature distribution of a power cable.

[0029]

According to the present invention, a plurality of light sources for pulsed light that cause Raman scattering are used to increase the pulsed light intensity, to simultaneously convert Stokes light and anti-Stokes light into electric signals, and to perform digital conversion at the same time. And an optical fiber type temperature distribution measuring device with high measurement accuracy of position and reduced measurement time can be provided.

[Brief description of the drawings]

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

FIG. 2 is a configuration diagram of a conventional optical fiber type temperature distribution measuring device.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Trigger 2, 2a, 2b Light source 3 Optical demultiplexer 4, 5 Light receiver 6, 7 AD converter 8 Data processor 9 Temperature distribution calculating device 10 Display device

Claims (2)

[Claims] 1. A pulsed light is incident on an optical fiber to cause Raman scattering, a temperature is measured from a ratio of light intensity of Stokes light and anti-Stokes light in the Raman scattered light, and the pulsed light is converted to the light. In an optical fiber type temperature distribution measuring device for obtaining a measurement position from a time difference between the time when the light enters the fiber and the time when the Stokes light and the anti-Stokes light return to the incident end, a plurality of light sources that generate pulsed light are installed. Characteristic optical fiber type temperature distribution measuring device. 2. The light according to claim 1, wherein the Stokes light and the anti-Stokes light are simultaneously converted into electric signals by separate light receivers, and the electric signals are simultaneously converted into digital signals by separate AD converters. Fiber type temperature distribution measuring device.