JPH04174331A - Optical fiber sensor - Google Patents

Abstract

PURPOSE:To detect highly accurately actual temperature of a part to be measured by forming a winding part of an optic fiber in concentric and plane shape. CONSTITUTION:A winding part 11 is formed by winding one optic fiber having no coating in concentric shape and in plane shape, this winding part 11 is fixed on a thin-film shaped base member 12 which has an improved thermal conductivity, and the upper part is coated with a coating member 13. An inner diameter of this winding part 11 is prescribed by a bending limit angle of an optical fiber to be used and the outer diameter is determined by the length of the optical fiber to be wound. Also, the length of the optical fiber to be wound should exceed a unit resolution distance of a measurement system. Further, an edge part of the optic fiber to be wound is coated with a vinyl sheath 14 and is optically connected to an optic fiber cord for connection by fusion. Then, the member 12 is fitted to a surface to be measured, for example an outer surface of a reaction furnace or a surface of a power-distribution panel, and heat on these surfaces is transmitted to the optic fiber so that it is desirable that a material with a small thermal capacity and an improved thermal conductivity such as aluminum foil should be used.

Description

DETAILED DESCRIPTION OF THE INVENTION (Industrial Application Field) The present invention relates to an optical fiber sensor suitable for a temperature distribution measurement system using an optical fiber.

(Prior Art) In chemical plants, substations, power plants, etc., there is a strong demand for the development of a centralized monitoring system that monitors the surface temperature distribution of transformers and distribution boards, or the temperature distribution of reactors, etc.

In this centralized monitoring system, it is necessary to be able to accurately detect the temperature of each part whose temperature is to be measured and to be able to specify each part to be measured. As a temperature distribution measurement system that satisfies these requirements, a temperature distribution measurement system that utilizes the temperature sensitivity of an optical fiber is known, and is disclosed in, for example, Japanese Patent Laid-Open No. 61-270632.

In this known temperature distribution measurement system, one optical fiber is used as a temperature detection sensor, one optical fiber is linearly arranged in the area where the temperature is to be measured, and a pulsed laser beam is emitted from the input end of the optical fiber. The backscattered light generated at each part of the optical fiber is received, and the temperature and measurement position of each part are detected from the intensity and arrival time of the backscattered light.

(Problem to be solved by the invention) A temperature distribution measurement system that utilizes the temperature sensitivity of an optical fiber uses a single optical fiber to intensively detect temperature changes in multiple parts of an area to be monitored. It has extremely high utility value as a monitoring device.

However, since the optical fiber temperature distribution measurement system is limited by the distance resolution of the measurement system including the processing circuit, the detected temperature is the average temperature per unit resolution distance of the measurement system. For this reason, in conventional temperature distribution measurement systems, only one optical fiber is arranged linearly within the measurement area as a sensor, so the temperature of each detected area is calculated as the average temperature per unit resolution distance. There was a drawback that the measured temperature was detected to be lower or higher than the actual temperature. In other words, when using a temperature measurement system with a distance resolution of 7.5 m, for example, even if a minute length of the optical fiber, for example a 1 m long part, is exposed to high temperature, the averaged temperature will be measured, which will be lower than the actual temperature. Low temperatures were also detected.

On the other hand, it is also conceivable that the optical fiber is wound and the wound portion is housed in a metal case to form one sensor. In this case, the temperature of the optical fiber rises to the temperature of the part to be measured through the metal case, or cools down to the temperature of the part to be measured, and since the metal case has a large heat capacity, the optical fiber itself is heated to the temperature of the part to be measured. It takes a long time for this to occur, and as a result, the responsiveness to temperature changes becomes extremely poor.

SUMMARY OF THE INVENTION Accordingly, an object of the present invention is to eliminate the above-mentioned drawbacks and provide an optical fiber sensor that can detect the actual temperature of a part to be measured with high precision and has improved responsiveness to temperature changes.

(Means for Solving the Problems) The optical fiber sensor for temperature measurement according to the present invention includes an optical fiber sensor for temperature measurement that generates backscattered light with an intensity depending on the temperature, and includes an input end, an output end, and a winding. The present invention is characterized in that it comprises an optical fiber having a section and a thin film-like base member that supports the optical fiber, and the winding section of the optical fiber is formed concentrically and planarly.

(For I) In the present invention, an optical fiber having a length longer than the distance resolution of the measurement system is concentrically wound in a planar manner so that the winding diameter gradually increases to form a winding portion. The optical fiber sensor is constructed by fixing the rotating portion to a thin film-like base member made of resin, ceramic, metal, or the like. Among these, a base member in the form of a thin metal film, such as aluminum, copper, or stainless steel, which has good thermal conductivity, is preferable. Then, the input end and output end of this optical fiber sensor are optically coupled to a connecting optical fiber, a plurality of optical fiber sensors are connected in series to form a temperature measurement sensor, and this temperature measurement sensor is connected to a measurement system. Therefore, since the optical fiber sensor according to the present invention is a flat sensor with a small area, it can be easily mounted on the wall surface of a reactor, transformer, etc. Since the heat on the surface of the object to be measured is transmitted to the entire optical fiber winding section through the base member, the entire optical fiber winding section whose length is longer than the distance resolution quickly reaches the temperature of the measurement object. Therefore, by tightly winding the optical fiber, the area of the optical fiber sensor can be made extremely small, so that the temperature of a minute area can be measured with high precision. Moreover, in the present invention, since the winding portion of the optical fiber is fixed on the thin film base member, the temperature inside the winding portion quickly reaches the temperature of the part to be measured.
Responsiveness to temperature changes can be further improved.

In addition, the measurement system calculates and outputs the average temperature per unit resolution distance, or in the case of the optical fiber sensor according to the present invention, since the entire optical fiber winding over a length longer than the unit resolution distance has the same temperature, it is possible to average the temperature. However, it is still possible to measure the actual temperature. Note that it is desirable that the length of the optical fiber to be wound is at least twice the unit resolution distance of the measurement system.

(Example) FIG. 1 is a diagram showing an example of a temperature distribution measurement system according to the present invention. For example, a light source 1 composed of a semiconductor laser emits pulsed light. This pulsed light is projected onto an optical fiber within an optical fiber cord 3 through a condensing optical system (not shown) and an optical coupler 2. The optical coupler 2 can be a half mirror or an optical fiber coupler. The optical fiber cord 3 uses an optical fiber coat in which a graded index multimode optical fiber is coated with Kevlar fiber and Hynyl resin. Optical fiber cord 3-a for connecting optical fiber sensors 4-a to 4-d to optical fiber coat 3
~3-c, respectively, are connected in series. This optical fiber sensor functions as a temperature detection sensor, and is formed by concentrically winding a single optical fiber over a predetermined length, as will be described later. Therefore, between each optical fiber sensor -a~4-
d each has an input end and an output end, and by fusing those ends with the optical fibers in the optical fiber cord 3 or via optical connectors, the necessary number of fibers are connected in series at desired intervals. I can do two things.

Then, each of the optical fiber sensors 4-a to 4-d is attached to each part where the temperature is to be measured. For example, when centrally monitoring temperature distribution at a substation, it is fixed to the wall surface of a transformer, distribution board, etc. using adhesive, double-sided tape, or the like. A light pulse projected from the input end 3a of the optical fiber cord 3 propagates through the optical fiber cord 3 and the optical fiber sensors connected therebetween, and reaches each of the optical fiber sensors 4-a to 4-d.

Rayleigh scattering and Raman scattering occur in each optical fiber sensor, and light including Rayleigh scattered light and Raman scattered light propagates toward the incident side as backscattered light. Of this backscattered light, the intensity of the Raman scattered light varies depending on the temperature of the optical fiber, so the temperature at each optical fiber sensor is sequentially detected by detecting the intensity of the Raman scattered light and its arrival time. I can do it. Incidentally, as the projection pulsed light, either pulsed light having a Raman threshold value or more and pulsed light having a Raman threshold value or less can be used. The backscattered light generated by each optical fiber sensor 4-a to 4-d is transmitted through an optical fiber cord 3-4 that connects each fiber sensor.
It propagates toward the incidence side through each of the optical fibers that constitute the optical fiber sensor and the Raman scattered light, and enters the interference filter 5 through the optical coupler 2. The light is incident on the photodetector 6. This photodetector 6 is composed of an avalanche photodiode capable of responding at high frequencies. The output signal from the photodetector 6 is sent to the A/D converter 7.
The signal is converted into a digital signal and supplied to the arithmetic processing unit 8. The arithmetic processing unit 8 selects each optical fiber sensor 4-a to 4- based on the time required from the projection of the light pulse until the backscattered light enters the photodetector 6 and the intensity of the Raman scattered light.
The temperatures of d are sequentially calculated and output. The temperature of each optical fiber sensor is displayed on the monitor 9, and the supervisor can monitor the temperature distribution of each measurement area based on the temperature information displayed on the monitor.

FIGS. 2a and 2b are a diagrammatic plan view and a sectional view showing the structure of an example of an optical fiber sensor according to the present invention. In this example, a single uncoated optical fiber is wound concentrically and planarly to form a winding portion 11, and this winding portion is fixed onto a thin film-like base member 12 with good thermal conductivity. Then, this is covered with a covering member 13. The inner diameter of this ring-shaped winding portion 11 is determined by the bending limit angle of the optical fiber used, and the outer diameter is determined by the length of the optical fiber to be wound. The length of the optical fiber to be wound should be longer than the unit resolution distance of the measurement system. That is, if the distance resolution of the measurement system is 7.5 m, the winding should be 7.5 m or more.

The end of the optical fiber to be wound is covered with a vinyl sheath 14 and optically coupled to an optical fiber cord for connection by fusion or by using a coupler. The thin film base member 12 is attached to the surface of the part to be measured, such as the outer surface of the reactor or the surface of the distribution panel, and it also functions to transfer the heat from these surfaces to the optical fiber, so it is made of a thermally conductive material with a small heat capacity. It is preferable to use a metal foil such as aluminum foil.

In particular, since metal foil has mechanical strength and flexibility, even if the wall surface to which it is mounted is uneven, it can be deformed and mounted to follow the surface shape. When the base member 12 is fixed to the surface whose temperature is to be measured with adhesive or tape, the heat from the wall is transmitted to the optical fiber through the base member 12, and the temperature of the entire optical fiber in the winding portion 11 is raised to the temperature of the wall surface. .

Next, the fiber winding length of the optical fiber sensor will be explained. When measuring temperature, the measurement system including the processing unit calculates and outputs the average temperature in the area for each unit resolution distance. That is, the unit resolution distance is 7.5
In the case of a measurement system of m, the average temperature of the optical fiber of that length is sequentially output every 7.5 m. Therefore, in order to accurately measure the actual temperature of the part to be measured, it is preferable to wind the wire over a length that is at least twice the unit resolution distance. That is, by winding it twice or more,
This is because the average temperature of the area of unit resolution distance included in the optical fiber sensor is always measured.

FIG. 3 is a sectional view showing the configuration of a modified example of the optical fiber sensor. In this example, the optical fiber is tightly wound in two layers, and a heat-resistant adhesive 15 is applied between the base member 12 and the covering member 13.
The base member 12, the optical fiber, and the covering member are integrally fixed by interposing the base member 12, the optical fiber, and the covering member. In this case, since there is a risk that the optical fiber may expand or contract due to thermal expansion, it is preferable to apply adhesive partially to fix the optical fiber so that it can expand or contract even if thermal expansion occurs.

Alternatively, it is also suitable to fix with an elastic heat-resistant adhesive such as silicone rubber or fluororubber.

In this way, the winding portion of the optical fiber only needs to be wound in a plane, and therefore, it is not only possible to wind the optical fiber in a single layer, but also to wind it in multiple layers.

FIGS. 4a and 4b are cross-sectional views showing the structure of another modification of the optical fiber sensor. In FIG. 4a, a plate-shaped permanent magnet 16 is fixed onto the coating member 13 via an adhesive, and in FIG. Cover and fix the member 13.

If the permanent magnet 16 is fixed integrally, if the wall portion I7 whose temperature is to be measured is a magnetic material, the optical fiber sensor can be detachably attached to the wall surface by magnetic force. Since fiber optic sensors are completely unaffected by magnetic fields, a significant advantage can be achieved by attaching the sensor using magnets.

Furthermore, FIG. 5 is a plan view showing the configuration of a modified example of the optical fiber sensor according to the present invention. In this example, one optical fiber 20 is folded back at a predetermined position between its input end and output end, and the input side portion and the output side portion of the optical fiber are maintained in a parallel relationship based on the folding point. and the wound portion is fixed onto the thin film base member. With this configuration, the incident end 20a and the outgoing end 20b can be arranged adjacent to each other, making it easier to connect the sensors. Moreover, since the optical fibers do not overlap, the sensor can be made thinner.

The present invention is not limited to the embodiments described above, and various modifications and changes are possible. For example, in the embodiments described above, the optical fiber is wound in one or two layers, or it can be wound in multiple layers as long as it is wound in a plane.

Further, in the above-mentioned embodiment, an example in which the optical fiber sensor is applied to a temperature measurement system has been described, but it can also be used as a detection sensor for a fire detection system using an optical fiber.

(Effects of the Invention) The effects of the present invention explained above are summarized as follows.

(11) Since the temperature sensor is constructed by concentrically and planarly winding an optical fiber that generates backscattered light with an intensity corresponding to the temperature, it is possible to construct a small, planar optical fiber sensor. It is possible to accurately detect the surface temperature of walls, etc.

(The actual temperature of the measured part can be accurately measured because the temperature of the entire optical fiber winding portion having a length longer than the unit resolution distance of the measurement system or the measured part is measured.)

(3) Since a large number of optical fiber sensors can be connected in series via the connecting optical fiber cord, temperatures at a large number of desired measurement positions can be measured almost simultaneously.

(4) Since the winding part is supported by a thin film base member with a small heat capacity, temperature changes in the part to be measured can be detected more quickly than when the winding part is housed in a metal case with a large heat capacity. I can do it.

(5) If the winding portion is supported by a flexible metal foil, the sensor can be deformed and mounted according to the shape of the part to be measured even if the part to be measured has unevenness.

[Brief Description of the Drawings] Fig. 1 is a diagram showing the configuration of an example of a temperature measurement system using an optical fiber sensor according to the present invention, and Fig. 2 a and b show a configuration of an example of the optical fiber sensor according to the present invention. A plan view and a sectional view, FIGS. 3 and 4 a and 4 b are sectional views showing a modified example of the optical fiber sensor, and FIG. 5 is a plan view showing the configuration of a modified example of the optical fiber sensor. 3... Optical fiber cords 4-a to 4-d... Optical fiber sensor 11... Winding portion 12... Thin film pace member 13...
- Covering member 15... Permanent magnet Fig. 2 Fig. 3 Fig. 4 Fig. 4 ZOa i (, lb

Claims (1)

[Claims] 1. An optical fiber sensor for temperature measurement that generates backscattered light with an intensity depending on the temperature, which comprises an optical fiber having an input end, an output end, and a winding part, and a winding of this optical fiber. What is claimed is: 1. An optical fiber sensor comprising: a thin film-like base member supporting a winding portion; and the winding portion of the optical fiber is formed concentrically and planarly. 2. The optical fiber sensor according to claim 1, wherein the base member is a metal foil, and the winding portion is fixed onto the metal foil with an elastic adhesive.