JPH02206737A - Distribution type optical fiber temperature sensor and temperature measuring method - Google Patents

Abstract

PURPOSE:To miniaturize an entire system and to perform continuous operation by providing a calibration part for measuring the absolute temperature distribution from the temperature of an optical fiber in a part of the optical fiber to be measured and arranging a temperature sensor in the calibration part. CONSTITUTION:Laser pulses oscillated from a laser pulse emitting part 7 are made incident on the optical fiber to be measured 1 through an acoustic optical switch 4. The optical fiber for calibration 2 which is a part of the fiber 1 is incorporated in a heat insulating material 20 which is difficult to accept the variation of external temperature and the temperature sensor 3 is provided to the optical fiber 2. The Raman scattered light generated in the fiber 1 is introduced to a measuring device by a switch 4. In the measuring device, anti-Stokes light in the Raman scattered light is detected by a photoelectric conversion part 5, amplified by an amplifier 6 and transmitted to an AD converter 9. The signal digitized by the converter 9 is averaging-processed in a signal processing part 10 after performing stored measurement about ten thousand times. In such a case, the temperature of the calibration part is measured by the sensor 3 and transmitted to the processing part 10 by switching a switch 8, thereby measuring the absolute temperature distribution.

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 particularly relates to an absolute temperature distribution based on the intensity of anti-Stokes light among Raman scattered light of an optical fiber to be measured. The present invention relates to a distributed optical fiber temperature sensor and a temperature measurement method for measuring temperature.

[Prior Art] FIG. 2 is a block diagram of a conventional distributed optical fiber temperature sensor. A laser pulse emitted from a laser pulse emitting unit 16 consisting of a semiconductor laser and its driving circuit, etc. is transmitted to an acousto-optic optical switch 14 of an undriven optical directional coupler.
The light is input to the optical fiber 11 to be measured. The Raman scattered light generated in the optical fiber 11 to be measured is guided to the measuring device by the driven acousto-optic switch. The following processing is performed in the measuring device. Anti-Stokes light in the Raman scattered light is detected by a photoelectric converter 15 such as a photomultiplier or a photodiode, amplified by an amplifier 17, and transmitted to an AD converter 18. The signal digitized by the AD converter 18 is stored in the signal processing section 19 and subjected to averaging processing after being measured approximately 10,000 times.

In this case, a part of the optical fiber 11 to be measured is used as the optical fiber 13 for calibration, and the optical fiber 13 for calibration is kept at a known temperature T in a constant temperature oven. Conventionally, only relative temperature distribution could be measured by measuring only the anti-Stone light, so this constant temperature area was used as the reference temperature area for measuring absolute temperature distribution.
The absolute temperature distribution was measured by comparing the anti-Stokes light intensity in the reference temperature part and the anti-Stokes light intensity in other parts.

[Problem to be solved by the invention] Conventional distributed optical fiber temperature sensors suffer from drift (variations in measured values from true values) due to fluctuations in the driving of the light emitting part such as a semiconductor laser or the measuring device. In addition, since a constant temperature bath was provided to measure the absolute temperature distribution, there were problems as shown below.

■When drift occurs, the temperature distribution of the optical fiber being measured fluctuates from its true value.

■A temperature controller was required to keep the constant temperature bath at a constant temperature.

■Even if a temperature controller was installed, it was not easy to maintain a constant temperature at all times, and small temperature fluctuations were unavoidable.

■The constant temperature chamber itself, including the temperature controller, has a large volume (
This led to an increase in the size of the entire system.

■Depending on the temperature chamber, it may be necessary to make adjustments such as replacing the built-in refrigerant, such as ice water, and continuous operation may not be possible.

[Means for Solving the Problems] The present invention has been made to solve the above-mentioned problems, and includes a light emitting section that injects a laser pulse into an optical fiber to be measured, and a light emitting section that measures Raman scattered light from the optical fiber to be measured. In a distributed optical fiber temperature sensor consisting of an optical directional coupler that converts the optical path to the device, and a measurement device that measures the temperature distribution of the optical fiber to be measured from the intensity distribution of the Raman scattered light with respect to the distance, one of the optical fibers to be measured is Distributed optical fiber temperature sensor, characterized in that a calibration part for measuring absolute temperature distribution from the temperature is provided in the part, and a temperature sensor is arranged in the calibration part, and an optical fiber to be measured in which a part thereof is provided with a temperature sensor. A laser pulse oscillated from a light emitting part is input to the optical fiber to be measured, and the Raman scattered light from the optical fiber to be measured is guided to a measuring device by an optical directional coupler.
The part where the temperature sensor is provided is used as a calibration part, and the absolute temperature distribution of the optical fiber to be measured is measured by comparing the anti-Stokes light intensity of the calibration part and the anti-Stokes light intensity of other parts. The present invention provides a method for measuring temperature.

[Operation] The present invention measures absolute temperature distribution based on the basic principle as shown below.

Now, the drift of this distributed fiber optic temperature sensor (
(variation of the measured value from the true value). If the cause of the drift occurs in the acousto-optic switch, photoelectric conversion section 9, laser pulse emitting section, amplifier, AD converter, and signal processing section other than the optical fiber under test, the influence will not be affected. Measurement optical fibers and calibration optical fibers are also received in the same way. For example, the influence of a ΔP change in the light emission power is similarly exerted on the optical fiber to be measured and the optical fiber for calibration as ΔT. That is, the measurement result R(
Q) is R(Q)=t, (Q)+ΔT (Q is distance, t
(Q) is the true value). On the other hand, since the temperature T and distance are known in the calibration section, ΔT can be canceled by performing the following process.

K=R(L) −T (=ΔT) R(Q)−=t(Q) Therefore, by measuring the temperature of the calibration section at any temperature, it becomes possible to measure the absolute temperature distribution.

[Embodiment] FIG. 1 shows a block diagram of an embodiment of the present invention. A laser pulse emitted from a laser pulse emitting unit 7 consisting of a semiconductor laser, its driving circuit, etc. is incident on the optical fiber 1 to be measured through the acousto-optic optical switch 4 of the undriven optical directional coupler. A part of the optical fiber 1 to be measured is used as a calibration optical fiber, and the calibration optical fiber 2 is housed in a heat insulating material 20 so as to be hardly affected by temperature fluctuations in the outside world, and a temperature sensor 3 is provided. Raman scattered light generated in the optical fiber 1 to be measured is guided to a measuring device by a driven acousto-optic switch. The following processing is performed in the measuring device. Anti-Stokes light in the Raman scattered light is detected by a photoelectric converter 5 such as a photomultiplier or a photodiode, amplified by an amplifier 6, and transmitted to an AD converter 9. The signal digitized by the AD converter 9 is stored in the signal processing unit 10 and subjected to measurement diameter averaging processing approximately 10,000 times. At that time, the temperature of the calibration section is measured by the temperature sensor 3, and the measurement signal is switched by the switch 8 and transmitted to the AD converter 9 and the signal processing section 10 to measure the absolute temperature distribution. 2
0, the temperature of the calibration optical fiber 2 changes from moment to moment, so it is necessary to capture the signal from the temperature sensor 3 in real time. Time division multiplexing is performed in the gap between the scattered optical signal and the signal.

Further, if an interface is added between the AD converter 9 and the signal is input to the signal processing unit IO in parallel, the switch 8 is not necessary. However, since this is generally more expensive than using switch 8, it is preferable to use switch 8. The heat insulating material 20 is not necessary if the entire optical fiber 2 for calibration has a uniform temperature, but it is preferable to use it generally because it is difficult to receive temperature changes in the outside world. A hot body, a high-precision semiconductor temperature sensor, or a thermocouple with sufficient cold junction compensation is used.

[Effects of the Invention] The present invention has the excellent effect that by measuring the temperature of the calibration section at an arbitrary temperature, it is possible to measure the absolute temperature distribution of the optical fiber to be measured. Furthermore, since the conventional constant temperature bath is not required, the entire system can be downsized, and continuous operation is possible without interrupting measurement due to adjustment of the constant temperature bath.

[Brief explanation of the drawing]

FIG. 1 is a block diagram of a distributed optical fiber temperature sensor according to the present invention, and FIG. 2 is a block diagram of a conventional example. 1: Optical fiber for measurement 2: Optical fiber for calibration 3: Temperature sensor 8: Switch

Claims (2)

[Claims] (1) A light emitting 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 an optical directional coupler that converts the optical path of the Raman scattered light from the optical fiber to be measured, and the measured target from the intensity distribution of the Raman scattered light with respect to distance. In a distributed optical fiber temperature sensor comprising a measuring device for measuring temperature distribution of an optical fiber, a part of the optical fiber to be measured is provided with a calibration section for measuring the absolute temperature distribution from the temperature thereof,
A distributed optical fiber temperature sensor characterized in that a temperature sensor is disposed in the calibration section. (2) A laser pulse oscillated from a light emitting part is input into the optical fiber to be measured, which has a temperature sensor installed in a part thereof, and the Raman scattered light from the optical fiber to be measured is guided to the measuring device by an optical directional coupler. , the part where the temperature sensor is provided is used as a calibration part, and the absolute temperature distribution of the optical fiber to be measured is measured by comparing the anti-Stokes light intensity of the calibration part and the anti-Stokes light intensity of other parts. temperature measurement method.