JPH06174561A - Optical fiber sensor - Google Patents

Abstract

(57) [Summary] [PROBLEMS] An object of the present invention is to provide an optical fiber sensor suitable for measuring a fluid layer having no temperature difference across an interface or an interface position of a fluidized bed. In the optical fiber sensor 10 of the present invention, an optical fiber 12 for measuring a temperature distribution is surrounded by a tubular metal tubular heater 14, and a current is supplied to both ends of the tubular heater 14. The power source 16 of is connected. The tubular heater 14 is uniformly heated by the current from the power supply 16, and the optical fiber 12 measures the temperature distribution along the tubular heater 14.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an optical fiber sensor using an optical fiber for measuring a temperature distribution, and more particularly to continuously measuring a fluid layer or an interface position of a fluidized bed, a velocity distribution in a fluid and the like. To an optical fiber sensor suitable for.

[0002]

2. Description of the Related Art Conventionally, it has been generally difficult to measure the interface between a fluid layer composed of a gas phase or a liquid phase and a fluidized bed in which particles are dispersed in a fluid. For example, there was no measuring device for continuously measuring the riverbed position by fluidized sand in a river. Further, it has been more difficult to measure the interface position between two different fluid layers. For example, it has been difficult to measure the interface position between the gas phase and liquid phase of liquefied natural gas or the like.

On the other hand, in recent years, an optical fiber temperature distribution measuring device for measuring a temperature distribution using an optical fiber as a temperature sensor has attracted attention. The optical fiber temperature distribution measuring device measures the temperature of the optical fiber itself by injecting excitation light such as laser pulse light into the optical fiber sensor and measuring the temperature dependence of Raman scattered light (inelastically scattered light) generated thereby. Is. Instead of using many temperature sensors, an optical fiber is provided to measure the temperature distribution. When there is a temperature difference at the fluid layer or the interface of the fluidized bed, the interface position can be determined from the temperature distribution measured by the optical fiber temperature distribution measuring device.

[0004]

However, in general, there are many cases where the temperature difference between the two different fluid layers at the boundary is not significant, and even if the conventional optical fiber temperature distribution measuring device is used, Such an interface position could not be measured. An object of the present invention is to provide an optical fiber sensor suitable for measuring an interface position of a fluid layer or a fluidized bed having no temperature difference across the interface.

[0005]

The above object is to provide an optical fiber for measuring a temperature distribution, a tubular tubular heater enclosing the optical fiber, and a power supply for supplying a current to the tubular heater for heating. Is achieved by a fiber optic sensor having It should be noted that the tubular heater includes not only one having a circular cross section but also one having another cross section such as an ellipse, a quadrangle, or a triangle. Further, the tubular heater does not need to be completely closed, and may be partially opened as long as the optical fiber is wrapped. Furthermore, a corrugated fold may be formed on the surface of the tubular heater.

Another object of the present invention is to provide an optical fiber sensor having a rod-shaped heating / cooling means in the shape of a rod for heating or cooling, and an optical fiber wound around the rod-like heating / cooling means for measuring temperature distribution. Is also achieved. In addition,
The rod-shaped heating / cooling means includes not only a section having a circular section but also another section having an elliptical section, a square section, a triangular section, or the like.

[0007]

According to the present invention, the object to be measured is uniformly heated by the tubular heater, and the temperature distribution of the tubular heater is measured by the optical fiber. The temperature of the tubular heater depends on the heating state of the tubular heater and the thermal state of the measurement target. This thermal state depends on the flow velocity and thermal conductivity of the fluidized bed or fluidized bed, and changes at the interface of the fluidized bed or fluidized bed as a boundary. Therefore, by measuring the temperature distribution of the tubular heater, , The position of the fluid bed or the interface of the fluid bed can be measured. It is also possible to detect the difference in the flow velocity of the fluid bed or the fluidized bed.

According to the present invention, the rod-shaped heating / cooling means uniformly cools or heats the object to be measured, and the optical fiber measures the temperature distribution of the rod-shaped heating / cooling means. Therefore, it is possible to measure an object to be measured that cannot be heated, an object to which an electric current such as a flammable material cannot flow, or the like.

[0009]

DESCRIPTION OF THE PREFERRED EMBODIMENTS An optical fiber temperature distribution measuring device using an optical fiber sensor according to an embodiment of the present invention will be described with reference to FIGS. As shown in FIG. 1, in the optical fiber sensor 10 of this embodiment, an optical fiber 12 for measuring a temperature distribution is surrounded by a tubular metal tubular heater 14, and both ends of the tubular heater 14 are provided. A power supply 16 for supplying a current is connected. The tubular heater 14 is uniformly heated by the current from the power supply 16, and the optical fiber 12 measures the temperature distribution along the tubular heater 14. The tubular heater 14 is covered with an insulator for electric liquid insulation.

Thus, the optical fiber sensor 1 of this embodiment
At 0, since the tubular heater 14 functions as both a protective tube for the optical fiber 12 and a heater, not only the intended purpose can be achieved with an extremely simple structure, but also a uniform amount of heat is generated in the longitudinal direction. Easily obtained. Further, it is ideal that the tubular heater 14 and the optical fiber 12 are in thermal contact with each other, and it can be considered that the tubular heater 14 itself also serves as a temperature sensor. have.

An optical fiber temperature distribution measuring device using the optical fiber sensor of this embodiment is shown in FIG. The optical fiber temperature distribution measuring device 20 makes excitation light incident on the optical fiber sensor 10 and measures the temperature at each position from the inelastically scattered light scattered at each position of the optical fiber sensor 10.

In FIG. 2, the optical fiber sensor 10 is wound around an insulating pipe 18 made of vinyl chloride to improve the measurement resolution in the measurement length direction. Both ends of the optical fiber sensor 10 are connected to the optical fiber connectors 22a and 22b of the optical fiber temperature distribution measuring device 20. In the optical fiber temperature distribution measuring device 20, an optical directional coupler 26 is connected to a laser light source 24 which emits pulsed excitation light. An optical fiber switch 28 for switching the optical fiber to be connected is connected to the optical directional coupler 26. The optical fiber switch 28 has two reference coils 30 each having an optical fiber wound in a coil shape.
a and 30b are connected. Reference coil 30
The a and 30b are housed in the constant temperature layer 32 and maintained at a predetermined constant temperature, and are used as the base points for measuring the position of the optical fiber sensor 10. The reference coils 30a and 30b are connected to both ends of the optical fiber sensor 10 via optical fiber connectors 22a and 22b, respectively.

A photodetector 34 is connected to the optical directional coupler 26. Optical fiber 12 of optical fiber sensor 10
The Raman scattered light scattered by is branched by the optical directional coupler 26, and the Stokes light and the anti-Stokes light are detected by the photodetector 34. An amplifier 36 is connected to the photodetector 34 and amplifies the photodetection signal of the photodetector 34. An A / D converter 38 is connected to the amplifier 36 and A / D converts the photodetection signal amplified by the amplifier 36.

The digital photodetection signal A / D converted by the A / D converter 38 is input to the calculator 40. The arithmetic unit 40 averages the input photodetection signals,
The temperature distribution at each position of the optical fiber sensor 10 is calculated based on the light intensity of the inelastically scattered light and the delay time. The temperature distribution of the optical fiber sensor 10 calculated by the calculation unit 40 is displayed by the personal computer 42 provided outside the optical fiber temperature distribution measuring device 20.

A measurement experiment of an optical fiber temperature distribution measuring device was conducted using the experimental device shown in FIG. In the experimental apparatus shown in FIG. 3, a container having a bottom filled with sand was prepared, and tap water was poured over the sand. The optical fiber sensor 10 was coiled around a plastic tube 18 having an outer diameter of 50 mmφ and a total length of 350 mm to form a probe 50 for measurement. Stand the probe 50 for this measurement in the sand,
/ 3 is buried in the sand, about 1/3 of the center is immersed in water,
About 1/3 of the upper part was exposed to the atmosphere.

The tubular heater 14 of the optical fiber sensor 10
Has an outer diameter of 1.2 mmφ and an inner diameter of 0.8 mmφ and is made of stainless steel SUS304. The optical fiber sensor 10 is coiled around a plastic tube 18 at a pitch of about 3.5 mm. A power source 16 is connected to both ends of the tubular heater 14 made of metal, and a current is not passed, a current of 0.5 A is passed, and a current of 1.0 A is passed. The temperature of each phase inside was measured. The measurement results are shown in Table 1 below.

[0017]

[Table 1] As shown in the measurement results in Table 1, in the state where no current is passed through the tubular heater 14, 23.4 ° C. in the atmosphere and 24.
The temperature was 0 ° C. and 24.3 ° C. in the soil, but when a current of 0.5 A was applied and heated, the temperature increased by 1.5 ° C. in the atmosphere, 0.4 ° C. in water, and 0. 7 ℃ rise, in the atmosphere,
The temperature increased in the order of soil and water. When the current value was increased to 1.0 A, this tendency became more prominent, the temperature rose 10.1 ° C in the atmosphere and 3.7 ° C in the soil, but only 0.8 ° C in water. It was The interface position of each phase could be accurately measured from such a difference in temperature rise.

As a result of consideration of the mechanism causing such a difference in temperature rise, the following has been found. When the tubular heater 14 made of metal is energized, Joule heat is generated. Since the amount of Joule heat generated is substantially uniform over the entire length of the tubular heater 14, the temperature of the tubular heater 14 is determined by the condition of heat transfer to the surroundings. In the atmosphere, heat is mainly taken by the convection phenomenon of air, and in water, the heat is taken mainly by the convection phenomenon of water. Since water generally has a heat transfer coefficient much larger than that of air, the temperature of the tubular heater 14 hardly rises in water and becomes almost equal to the water temperature, while the temperature of the tubular heater 14 greatly rises in the air.
On the other hand, in the soil, since the metal heater 14 is in contact with the mixture of water and sand particles, heat transfer due to convection of water is very small, and heat is mainly taken away by heat conduction. For this reason, the heat transfer coefficient becomes smaller than that in water, and the tubular heater 14 in soil is
Temperature rises more.

An application example of the optical fiber temperature distribution measuring device using the optical fiber sensor of this embodiment will be described with reference to FIGS. 4 and 5. In this application example, the fluctuation of the water level of the river is measured, and the scour of the river bottom and the immersion of the river water in the bank are detected. As shown in FIG. 4, a measurement probe 5 in which an optical fiber sensor 10 is wound around a plastic tube 18 in a coil shape.
At least two 0s are prepared, one probe 50A is buried in the soil at the river bottom, and the other probe 50B is buried deep in the bank.

An example of measurement by the probes 50A and 50B is shown in FIG. While energizing the optical fiber sensor 10,
The water level of the river can be measured by the probe 50A from the difference between the temperature in the atmosphere (40 ° C.) and the temperature in the water (20 ° C.). When the water level changes, it can be immediately detected by the probe 50A. The position of the river bottom can be measured by the probe 50A from the difference between the temperature in water (20 ° C.) and the temperature in soil (25 ° C.) while the optical fiber sensor 10 is energized. When the riverbed is scourd, it can be easily detected by the temperature drop near the riverbed.

When the river water is not immersed in the bank, the temperature in the bank is relatively high (50% by the probe 50B).
However, if the river water is immersed in the bank, the temperature will drop and the immersion of the river water in the bank can be easily detected. As an application example of the optical fiber temperature distribution measuring device using the optical fiber sensor of the present embodiment, various application examples other than the above-mentioned ones are conceivable.

That is, not only the position detection of the interface between the gas phase, the liquid phase and the solid phase of various substances, but also the position detection of the boundary where physical properties and phenomena affecting the heat transfer coefficient change and their distribution are It can also be detected. For example, it is also possible to measure the distribution of the density and the flow velocity in a substance whose heat transfer coefficient changes due to the change of the density and the flow velocity. Specifically, the optical fiber sensor of this embodiment is placed in the air. Similar to the existing hot-wire anemometer, the heat transfer coefficient on the surface of the tubular heater of the optical fiber sensor changes depending on the wind speed. The wind velocity distribution can be measured by measuring the temperature distribution due to the change in the thermal conductivity coefficient with the optical fiber. Since the optical fiber sensor need only be stretched in the air, the wind velocity distribution in a wide range can be easily measured. For example, it is possible to easily measure the wind speed distribution of an abnormal wind that is known to occur around a high-rise building.

When there is already a temperature distribution in the space to be measured, as in the case of measuring the flow velocity distribution generated by the air conditioner in the room, the above method can be used to accurately obtain the flow velocity distribution. Disappear. This is because the temperature of cold air or warm air that is blown out generally does not match room temperature and the temperature distribution is present at the same time. In such a case, two optical fiber sensors are provided in parallel in the air at appropriate intervals so that one optical fiber sensor is energized and the other optical fiber sensor is not energized. Since the temperature distribution itself can be measured by the non-energized optical fiber sensor, the wind speed distribution can be measured by the difference in the temperature distribution by the energized optical fiber sensor. By doing so, both the temperature distribution and the wind speed distribution can be simultaneously measured over a wide range.

If it is considered that there is little time-dependent fluctuation of the measurement target, only one optical fiber sensor is placed in the air, and the temperature distributions when energized and de-energized are respectively measured, and the measured temperature is measured. By comparing the distributions, both the temperature distribution and the wind speed distribution can be measured over a wide range. An optical fiber sensor according to another embodiment of the present invention is shown in FIG. All the optical fiber sensors shown in FIG.
An optical fiber for measuring the temperature distribution is wound around the rod-shaped heating / cooling means.

The optical fiber sensor 60 shown in FIG.
An optical fiber 64 for measuring a temperature distribution is wound around a rod-shaped heating / cooling member 62 through which a heating / cooling fluid for heating / cooling flows. The rod-shaped heating / cooling member 62 has a hollow tubular shape, and the rod-shaped heating / cooling member 62 is uniformly heated or discharged by allowing the heating / cooling liquid to flow in from one end and flow out from the other end. Cooled down
The optical fiber 64 measures the temperature distribution along the rod-shaped heating / cooling member 62.

An optical fiber sensor 70 shown in FIG. 6 (b).
An optical fiber 74 for measuring a temperature distribution is wound around a rod-shaped heating / cooling member 72 through which a heating / cooling fluid for heating / cooling flows. The rod-shaped heating / cooling member 72 is a double pipe, and the heating / cooling liquid is introduced from an inflow port 72a provided at one end and is made to flow out from an outflow port 72b provided at the same end. The rod-shaped heating / cooling member 72 is uniformly heated or cooled, and the optical fiber 74
Measures the temperature distribution along the rod-shaped heating / cooling member 72.

An optical fiber sensor 80 shown in FIG. 6 (c).
The optical fiber 84 for measuring the temperature distribution is wound around the rod-shaped heating / cooling member 82 which is heated or cooled by passing an electric current. By supplying an electric current from the power supply 86 to the rod-shaped heating / cooling member 82, the rod-shaped heating / cooling member 8
2 is uniformly heated or cooled, and the optical fiber 84 measures the temperature distribution along the rod-shaped heating / cooling member 82.

According to this embodiment, not only the heating but also the cooling can be performed, so that it is possible to measure the interface which is impossible in the above-mentioned embodiments. For example, when an interface between water and ice is to be detected, the ice around the optical fiber sensor is melted by heating, which makes it difficult to detect the interface with water. In such a case, for example, if a low temperature fluid such as liquid nitrogen is used for cooling, a temperature difference occurs between ice and water, and the interface between ice and water can be detected.

Further, in the case of the optical fiber sensor shown in FIGS. 6 (a) and 6 (b), since heating or cooling is possible without energization, it is possible to measure safely even in a flammable atmosphere. For example, when monitoring the liquid level of liquefied natural gas,
There is a risk of ignition, so it is not possible to pass an electric current,
In the case of the optical fiber sensor shown in FIGS. 6 (a) and 6 (b), it suffices to flow the heating / cooling fluid, so that the measurement can be performed safely.

[0030]

As described above, according to the present invention, the object to be measured is uniformly heated by the tubular heater, and the temperature distribution of the tubular heater is measured by the optical fiber. The temperature of the tubular heater depends on the heating state of the tubular heater and the thermal state of the measurement target. This thermal state depends on the flow velocity and thermal conductivity of the fluidized bed or fluidized bed, and changes at the interface of the fluidized bed or fluidized bed as a boundary. Therefore, by measuring the temperature distribution of the tubular heater, , The position of the fluid bed or the interface of the fluid bed can be measured. It is also possible to detect the difference in the flow velocity of the fluid bed or the fluidized bed.

According to the present invention, the rod-shaped heating / cooling means uniformly cools or heats the object to be measured, and the optical fiber measures the temperature distribution of the rod-shaped heating / cooling means. Therefore, it is possible to measure an object to be measured that cannot be heated, an object to which an electric current such as a flammable material cannot flow, or the like.

[Brief description of drawings]

FIG. 1 is a diagram showing an optical fiber sensor according to an embodiment of the present invention.

FIG. 2 is a diagram showing an optical fiber temperature distribution measuring device using an optical fiber sensor according to an embodiment of the present invention.

FIG. 3 is a diagram for explaining a measurement experiment using the optical fiber temperature distribution measuring device of FIG.

FIG. 4 is a diagram showing an arrangement of optical fiber sensors of an application example using the optical fiber temperature distribution measuring device of FIG.

5 is a diagram showing a measurement example of an application example using the optical fiber temperature distribution measuring device of FIG.

FIG. 6 is a diagram showing an optical fiber sensor according to another embodiment of the present invention.

[Explanation of symbols]

 10 ... Optical fiber sensor 12 ... Optical fiber 14 ... Tubular heater 16 ... Power supply 18 ... Insulation pipe 20 ... Optical fiber temperature distribution measuring device 22a, 22b ... Optical fiber connector 24 ... Laser light source 26 ... Optical directional coupler 28 ... Optical Fiber switch 30a, 30b ... Reference coil 32 ... Constant temperature layer 34 ... Photodetector 36 ... Amplifier 38 ... A / D converter 40 ... Arithmetic unit 42 ... Personal computer 50, 50A, 50B ... Probe 60 ... Optical fiber sensor 62 ... Rod shape Heating / cooling member 64 ... Optical fiber 70 ... Optical fiber sensor 72, 72a, 72b ... Rod heating / cooling member 74 ... Optical fiber 80 ... Optical fiber sensor 82 ... Rod heating / cooling member 84 ... Optical fiber 86 ... Power supply

Claims (2)

[Claims] 1. An optical fiber sensor comprising an optical fiber for measuring a temperature distribution, a tubular tubular heater enclosing the optical fiber, and a power supply supplying an electric current to the tubular heater for heating. 2. An optical fiber sensor having a rod-shaped heating / cooling means for heating or cooling, and an optical fiber wound around the rod-shaped heating / cooling means for measuring a temperature distribution.