JPH0230655B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION Field of the Invention The present invention relates to optical fiber temperature measuring devices, and more particularly to devices for measuring temperature using optical fibers.

Prior Art A method of supplying a laser beam to a sensor fiber placed at a measurement target location, mixing the laser beam with reflected light from the sensor fiber to generate interference light, and detecting the amount of interference fringe movement of the interference light. The principle of optical fiber temperature measurement for measuring the temperature at a location to be measured is well known.

That is, the phase and speed of light passing through the optical fiber change as the temperature of the optical fiber changes.
This is primarily because the refractive index of the optical fiber core changes with temperature. Therefore, the phase of light propagated through an optical fiber of a predetermined length changes depending on the temperature. Interference fringes are generated by mixing the light that has propagated through the optical fiber and the reference light that has not propagated, and the interference fringes move as the temperature changes. The amount of movement of the interference fringes can be detected by two photoelectric conversion detectors, and the temperature of the location to be measured where the optical fiber is placed can be measured from the amount of movement.

OBJECTS OF THE INVENTION An object of the present invention is to provide an optical fiber temperature measuring device that is compact, has excellent operability, and has high measurement accuracy.

Structure of the Invention In order to achieve the above object, the present invention includes a sensor fiber of a predetermined length, the open end of which is coated with a reflective film and placed in a part to be measured; A supply optical cable, the other end of the sensor fiber, and one end of the supply optical cable are fixed to face each other, and the measurement laser beam is supplied to the sensor fiber through a semi-transparent mirror provided inside, and the measurement an interferometer unit that mixes the laser beam for use with the reflected light from the sensor fiber using the semi-transparent mirror to generate interference light;
two detection optical cables each having one end connected to the interferometer section with an interval approximately equal to an interference fringe phase angle of the interference light to receive the interference light and transmitting the interference light; and the laser light source. The other end of the supply optical cable is connected to supply the laser light output from the laser light source to the supply optical cable, and the other end of the detection optical cable is connected, and the interference light transmitted from the detection cable is connected. A light source with two detectors that electrically convert
A detection unit is characterized in that it generates interference light near the sensor fiber.

Embodiments Hereinafter, preferred embodiments of the present invention will be described based on the drawings.

FIG. 1 shows a schematic configuration of an optical fiber temperature measuring device according to the present invention, and FIG. 2 shows a block configuration of the device shown in FIG.

As is clear from FIG. 2, the device of this embodiment has the following features:
A sensor unit 10 disposed at a location to be measured, an interferometer unit 12 that supplies a measurement laser beam 102 to the sensor unit 10 and generates interference light 106, and an interferometer unit 12.
A light source/detection unit 14 supplies the laser light 100 to the interferometer unit 12 and electrically detects the interference light 106 from the interferometer unit 12; 106, and a calculation/display unit 18 that calculates and displays the temperature of the measured location based on the interference light 106 detected by the light source/detection unit 14.

The sensor section 10 has a sensor fiber 20 such as a single mode optical fiber or a constant polarization optical fiber,
The sensor fiber 20 is placed at the location to be measured. The sensor fiber 20 has a predetermined length, and its open end is coated with a reflective film 22, so that the measuring laser beam 102 supplied to the sensor fiber 20
passes through the sensor fiber 20 at a phase velocity corresponding to the temperature of the object to be measured, is reflected by the reflective film 22, and passes through the sensor fiber 20 again in the opposite direction at the same phase velocity as reflected light 104.

Further, the interferometer section 12 includes a sensor fiber 2.
0 is fixed, and the interferometer section 12 supplies a predetermined measurement laser beam 102 to the sensor fiber 20, and also mixes the measurement laser beam 102 and the reflected light 104 from the sensor fiber 20 to produce interference light. 10
6. That is,
The interferometer section 12 includes a collimating lens 24 such as a laser condensing lens or a self-occurring lens, a condensing collimating lens 26, a condensing lens 28, and a semi-transparent mirror 3.
0 and reflecting mirrors 32 and 34. A part of the laser beam 100 supplied to the collimating lens 24 passes through the semi-transparent mirror 30 as a measuring laser beam 102 and travels straight, passes through the condensing collimating lens 26 and is supplied to the sensor fiber 20. Ru. Reflected light 104 from sensor fiber 20
passes through the condensing and collimating lens 26, and a part of it is reflected by the semi-transparent mirror 30. Further, a part of the laser beam 100 supplied to the collimating lens 24 is transmitted to the semi-transparent mirror 3 as a measurement laser beam 102.
0 and are each reflected by the reflecting mirror 32, and a part of it is transmitted through the semi-transparent mirror 30. Therefore, the measurement laser beam 102 and the reflected light 10 from the sensor fiber 20
4 are mixed at the position of the semi-transparent mirror 30, and as a result, interference light 106 is generated. As shown in FIG. 3, the interference light 106 has a cross-sectional shape in the bright area 10.
It consists of interference fringes such as 6a and dark area 106b, and from the amount of movement of these interference fringes, it is possible to measure the temperature change with respect to the reference temperature, that is, the temperature of the measured location. In this way, the interference light 106 generated by the semi-transparent mirror 30 is reflected by the reflecting mirror 34, passes through the condensing lens 28, and part of it passes through the optical cable 46,
48.

Furthermore, the light source/detection unit 14 has a laser light source 36 such as a gas laser such as He-Ne or a semiconductor laser, and the laser light 100 from the laser light source 36 is passed through a condensing lens 38 such as a laser condensing lens or a self-occurring lens. and is supplied to the interferometer section 12. Further, the light source/detection section 14 has two detectors 40 and 42 that electrically detect the amount of interference fringe movement of the interference light 106 generated in the interferometer section 12, and these detectors 40 and 42 are configured using photodiodes or It consists of phototransistors, photomultiplier tubes, etc.

Further, the cable section 16 has a supply optical cable 44 for supplying the laser light 100 from the laser light source 36 to the interferometer section 12, and this supply optical cable 44 includes a single mode optical fiber, a polarization constant optical fiber, etc. is used. The cable section 16 also includes detection optical cables 46 and 48 for supplying the interference light 106 from the interferometer section 12 to the detectors 40 and 42, and these detection optical cables 46 and 48 include multimode optical fibers, A single mode optical fiber or a constant polarization optical fiber is used. And these detection optical cables 4
The interference light 106 is incident on the end faces 6 and 48. For example, as shown in FIG. 3, one ends of the detection optical cables 46 and 48 are respectively arranged at an intermediate position of the bright part 106a and at a boundary position between the bright part 106a and the dark part 106b. Therefore, out of the interference light 106 generated in the interferometer section 12, only the interference light 106 at a predetermined position is detected by the detection optical cable 4.
6, 48 and supplied to detectors 40, 42.

For example, assume that the electrical output voltages x and y of the detectors 40 and 42 are arranged as follows: x=cosθ (1) y=sinθ (2). θ is the phase of the interference fringe.

When the above equation (2) is divided by the equation (1), it is expressed as y/x=sin θ/cos θ=tan θ, and θ=tan ⁻¹ The phase angle θ of the interference fringe can be determined from y/x.

Further, the calculation/display unit 18 is configured as follows in order to calculate the above-mentioned phase angle θ and the temperature of the measured location based on the phase angle θ, and to display this. That is, the brightness detection signal 108 of the interference light 106 detected by each detector 40, 42,
110 is the data processing device 5 via the amplifier 50.
2. The data processing device 52 is composed of an A/D converter, a microcomputer, etc., and calculates the phase angle θ described above, and further calculates the temperature of the measured point from the result of the calculation. Then, the calculated temperature of the measured location is displayed on the display 54 in digital or analog form.

The optical cables 44 to 48 in the cable section 16 described above are bundled as shown in FIG. 1 to reduce the size of the device.

The embodiment of the present invention has the above-mentioned configuration, and its operation will be schematically explained below.

Laser light 100 generated by the laser light source 36
After passing through the condensing lens 38 , the light is transmitted through the supply optical cable 44 and supplied to the interferometer section 12 . The laser beam 100 supplied to the interferometer section 12 passes through the collimating lens 24, and a part of it passes through the semi-transparent mirror 30 as the measurement laser beam 102.
The light passes through a condensing collimating lens 26 and is supplied to the sensor fiber 20. Then, the measurement laser beam 102 is reflected by the reflective film 22 of the sensor fiber 20, and the sensor fiber 2 is reflected as reflected light 104.
0 in the opposite direction, condensing and collimating lens 2
6 and a part of it is reflected by the semi-transparent mirror 30. Also, the laser beam 10 supplied to the interferometer section 12
0 passes through the collimating lens 24, a portion of which is reflected by the semi-transparent mirror 30 and the reflecting mirror 32 as the measurement laser beam 102, and further, a portion thereof passes through the semi-transparent mirror 30. Therefore, the measurement laser beam 1
02 and the reflected light 104 from the sensor fiber 20 are mixed at the position of the semi-transparent mirror 30, and the interference light 10
6 is generated. The interference light 106 is reflected by the reflecting mirror 34 and passes through the condenser lens 28. As shown in FIG. 3, a part of this interference light 106 is transmitted to, for example, detection optical cables 46 and 48 disposed at positions separated from each other by a phase angle θ=π/2 of interference fringes.
is input from each end of each of these optical cables 4.
6, 48 to the detectors 40, 42.

Interference light 106 supplied to each detector 40, 42
are output as bright/dark detection signals 108, 110 corresponding to the bright portion 106a and dark portion 106b of the interference light 106 at the arrangement position of each optical cable 44, 46, and are supplied to the data processing device 52 via the amplifier 50. The data processing device 52 calculates the phase angle θ based on the light/dark detection signals 108 and 110, and further calculates the temperature of the measurement point based on the calculation result. Then, the calculated temperature of the measured location is displayed on the display 54 in digital or analog form.

As described above, in this embodiment, since the device is composed of five blocks for each function,
The device can be made smaller.

Furthermore, in this embodiment, since the interferometer section 12 does not include any electrical parts, the device is further miniaturized, and as a result, it can be easily placed even in a narrow measurement area, and the interferometer section 12 is Since it is disposed adjacent to the sensor section 10, the influence of temperature fluctuations on areas other than the sensor section is minimized. In addition, it is possible to easily perform operations such as moving the sensor unit 10.
Furthermore, the interferometer section 12 is not affected by electric fields or magnetic fields, and measurement errors based on these do not occur.

Furthermore, in this embodiment, each of the optical cables 44 to 48 of the cable section 16 is used only for transmitting the laser beam 100 or the interference light 106, and is not directly connected to the sensor fiber 20, so that each of the optical cables 44 to 48 has a high temperature. , even when influenced by mechanical stress, etc., measurement errors based on these do not occur.

Effects of the Invention As explained above, according to the present invention, since the device is configured to include a sensor fiber, an interferometer section, a measurement optical cable, and a detection optical cable for each function, it is possible to downsize the device. can. Miniaturization also increases mechanical stability, which is especially essential for high-sensitivity temperature measurements such as the present device.

Further, according to the present invention, the interferometer section has a structure that has the functions of supplying a laser beam for measurement and generating interference light, and does not include any electrical parts, so that the device can be further miniaturized, and as a result, The sensor fiber can be easily placed in a narrow measurement area, the sensor fiber can be easily moved, and it is not affected by electric or magnetic fields, so measurement errors due to these do not occur.

Furthermore, according to the present invention, the supply optical cable and the detection optical cable are used only for transmitting laser light and interference light, respectively, and do not directly transmit reflected light from the sensor fiber. Even if the optical cable is affected by external factors such as temperature and mechanical stress, no measurement errors occur.

[Brief explanation of drawings]

Fig. 1 is a block diagram showing a preferred embodiment of the optical fiber temperature measuring device according to the present invention, Fig. 2 is a detailed block diagram of the device shown in Fig. 1, and Fig. 3 is the arrangement of the optical fiber cable for measurement. It is an explanatory view showing a position. 10...sensor section, 12...interferometer section, 14...
...Light source/detection section, 16...Cable section, 18...
Calculation/display unit, 20...Sensor fiber, 36...
...Laser light source, 40, 42...Detector, 44...
Measurement optical cable, 46, 48...Detection optical cable, 100...Laser light, 102...Measurement laser light, 104...Reflected light, 106...Interference light.

Claims (1)

[Scope of Claims] 1. A sensor fiber of a predetermined length, the open end of which is coated with a reflective film and placed in a measurement target part; and a supply optical cable that supplies measurement laser light output from a laser light source to the sensor fiber. , the other end of the sensor fiber and one end of the supply optical cable are fixed to face each other, and the measurement laser beam is supplied to the sensor fiber through a semi-transparent mirror provided inside, and the measurement laser beam and the sensor fiber are connected to each other. an interferometer unit that mixes reflected light from the semi-transparent mirror to generate interference light; two detection optical cables connected to the part and transmitting the interference light, and the other end of the supply optical cable having a built-in laser light source connected to the supply optical cable supplying the laser light output from the laser light source to the supply optical cable. and a light source/detection unit having two detectors to which the other end of the detection optical cable is connected and which electrically converts the interference light transmitted from the detection cable, and generates interference light near the sensor fiber. An optical fiber temperature measuring device characterized by: